U.S. GOVERNMENT PUBLISHING OFFICE

30–322PDF WASHINGTON : 2018

USING TECHNOLOGY 

TO ADDRESS CLIMATE CHANGE 

HEARING 

BEFORE THE

COMMITTEE ON SCIENCE, SPACE, AND 

TECHNOLOGY 

HOUSE OF REPRESENTATIVES 

ONE HUNDRED FIFTEENTH CONGRESS 

SECOND SESSION 

MAY 16, 2018 

Serial No. 115–59 

Printed for the use of the Committee on Science, Space, and Technology 

( 

Available via the World Wide Web: http://science.house.gov 
(II) 

COMMITTEE ON SCIENCE, SPACE, AND TECHNOLOGY 

HON. LAMAR S. SMITH, Texas, Chair 

FRANK D. LUCAS, Oklahoma 

DANA ROHRABACHER, California 

MO BROOKS, Alabama 

RANDY HULTGREN, Illinois 

BILL POSEY, Florida 

THOMAS MASSIE, Kentucky 

RANDY K. WEBER, Texas 

STEPHEN KNIGHT, California 

BRIAN BABIN, Texas 

BARBARA COMSTOCK, Virginia 

BARRY LOUDERMILK, Georgia 

RALPH LEE ABRAHAM, Louisiana 

GARY PALMER, Alabama 

DANIEL WEBSTER, Florida 

ANDY BIGGS, Arizona 

ROGER W. MARSHALL, Kansas 

NEAL P. DUNN, Florida 

CLAY HIGGINS, Louisiana 

RALPH NORMAN, South Carolina 

DEBBIE LESKO, Arizona 

EDDIE BERNICE JOHNSON, Texas 

ZOE LOFGREN, California 

DANIEL LIPINSKI, Illinois 

SUZANNE BONAMICI, Oregon 

AMI BERA, California 

ELIZABETH H. ESTY, Connecticut 

MARC A. VEASEY, Texas 

DONALD S. BEYER, JR., Virginia 

JACKY ROSEN, Nevada 

CONOR LAMB, Pennsylvania 

JERRY MCNERNEY, California 

ED PERLMUTTER, Colorado 

PAUL TONKO, New York 

BILL FOSTER, Illinois 

MARK TAKANO, California 

COLLEEN HANABUSA, Hawaii 

CHARLIE CRIST, Florida 
(III) 

C O N T E N T S 

May 16, 2018 

Page 

Witness List ............................................................................................................. 2 

Hearing Charter ...................................................................................................... 3 

Opening Statements 

Statement by Representative Lamar S. Smith, Chairman, Committee on 

Science, Space, and Technology, U.S. House of Representatives ..................... 4 

Written Statement ............................................................................................ 16 

Statement by Representative Eddie Bernice Johnson, Ranking Member, Committee on Science, Space, and Technology, U.S. House of Representatives .... 9 

Written Statement ............................................................................................ 11 

Statement by Representative Andy Biggs, Committee on Science, Space, and 

Technology, U.S. House of Representatives ....................................................... 12 

Written Statement ............................................................................................ 13 

Statement by Representative Suzanne Bonamici, Committee on Science, 

Space, and Technology, U.S. House of Representatives .................................... 15 

Written Statement ............................................................................................ 17 

Witnesses: 

Mr. Oren Cass, Senior Fellow, Manhattan Institute 

Oral Statement ................................................................................................. 20 

Written Statement ............................................................................................ 22 

Mr. Ted Nordhaus, Executive Director, The Breakthrough Institute 

Oral Statement ................................................................................................. 48 

Written Statement ............................................................................................ 50 

Dr. Phil Duffy, President and Executive Director, Woods Hole Research Center 

Oral Statement ................................................................................................. 62 

Written Statement ............................................................................................ 64 

Discussion ................................................................................................................. 71 

Appendix I: Answers to Post-Hearing Questions 

Dr. Phil Duffy, President and Executive Director, Woods Hole Research Center .......................................................................................................................... 98 

Appendix II: Additional Material For The Record 

Statement submitted by Dr. Judith Curry, President, Climate Forecast Applications Network; Professor Emerita, Georgia Institute of Technology ............ 104 

Slide submitted by Representative Lamar S. Smith, Chairman, Committee 

on Science, Space, and Technology, U.S. House of Representatives ................ 119 

Article submitted by Representative Eddie Bernice Johnson, Ranking Member, Committee on Science, Space, and Technology, U.S. House of Representatives ........................................................................................................... 120 

Study submitted by Representative Conor Lamb, Committee on Science, 

Space, and Technology, U.S. House of Representatives .................................... 122 

(1) 

USING TECHNOLOGY 

TO ADDRESS CLIMATE CHANGE 

WEDNESDAY, MAY 16, 2018 

HOUSE OF REPRESENTATIVES, 

COMMITTEE ON SCIENCE, SPACE, AND TECHNOLOGY, 

Washington, D.C. 

The Committee met, pursuant to call, at 10:10 a.m., in Room 

2318 of the Rayburn House Office Building, Hon. Lamar Smith 

[Chairman of the Committee] presiding. 
2 

Q:ongrcss of the tinitcd ;6mtcs 

}10USC of 'RcprcscntatiU£S 

COMMITIEE ON SCIENCE, SPACE, AND TECHNOLOGY 

2321 RAYBURN HousE OFFICE Bu!LD!N(3 

WASHINGTON, DC 20515-6301 

(202) 225-6371 

www sdence.house.9ov 

Full Committee 

EDDIE 

Using Technology to Address Climate Change 

Wednesday, May 16,2018 

!O:OOa.m. 

2318 Rayburn House Office Building 

Witnesses 

Mr. Oren Cass, Senior Fellow, Manhattan Institute 

Mr. Ted Nordhaus, Executive Director, The Breakthrough Institute 

Dr. Phil Duffy, President and Executive Director, Woods Hole Research 

Center 

Dr. Judith Curry, President, Climate Forecast Applications Network; 

Professor Emerita, Georgia Institute of Technology 
3 

U.S. HOUSE OF REPRESENTATIVES 

COMMITTEE ON SCIENCE, SPACE, AND TECHNOLOGY 

HEARING CHARTER 

Wednesday, May 16,2018 

TO: Members, Committee on Science, Space and Technology 

FROM: Majority Staff, Committee on Science, Space, and Technology 

SUBJECT: Full committee hearing: "Using Technology to Address Climate Change" 

The Committee on Science, Space, and Technology will hold a hearing titled Using 

Technology to Address Climate Change on Wednesday, May 16, 2018, at 10:00 a.m. in Room 

2318 of the Rayburn House Office Building. 

Hearing Purpose: 

The purpose of the hearing is to examine climate change response policy. This hearing· 

will emphasize the need for policy plarming to account for technological developments designed 

to adapt to future conditions. 

Witness List: 

• Mr. Oren Cass, Senior Fellow, Manhattan Institute 

Mr. Ted Nordhaus, Executive Director, The Breakthrough Institute 

Dr. Phil Duffy, President and Executive Director, Woods Hole Research Center 

Dr. Judith Curry, President, Climate Forecast Applications Network; Professor Emerita, 

Georgia Institute of Technology 

Staff Contact 

For questions related to the hearing, please contact Majority Staff at 202-225-6371. 
4 

Chairman SMITH. The Committee on Science, Space, and Technology will come to order, 

Without objection, the Chair is authorized to declare recesses of 

the Committee at any time. 

Welcome to today’s hearing titled ‘‘Using Technology to Address 

Climate Change.’’ I’ll recognize myself for five minutes for an opening statement and then the Ranking Member. 

Today we will consider the use of technology to address climate 

change. We must take into account Americans’ ability to develop 

innovations that will solve or mitigate challenges associated with 

climate change. 

The climate is always changing, but what remains uncertain is 

the extent to which humans contribute to that change. What is certain is that human ingenuity will play a significant role in resolving future environmental issues. 

Before we impose energy taxes or costly and ineffective government regulations, we should acknowledge the uncertainties that 

surround climate change research. Natural climate variability contributes to this uncertainty. Solar cycles, volcanic activity, El Nin ̃ o/ 

La Nin ̃ a temperature fluctuations, and long-term oceanic circulation patterns are all naturally occurring events that have a major 

impact on the climate. Other unknowns such as the future of energy production and consumption also create uncertainty about future predictions. 

Advanced nuclear reactors could change the landscape of both 

the developed world as well as developing economies. 

Here’s an example of an alarmist prediction not allowing for 

technological advances. A recent study found that the Intergovernmental Panel on Climate Change’s worst-case scenario, which 

claimed further increasing emissions and temperatures, was based 

on outdated assumptions of coal usage. These assumptions didn’t 

anticipate the American shale gas revolution and further undercut 

the reliability of the IPCC’s findings. 

In the field of climate science, there is legitimate concern that 

scientists are biased in favor of reaching predetermined conclusions. This inevitably leads to alarmist findings that are wrongfully 

reported as facts. Anyone who then questions the certainty of these 

findings is wrongly labeled a denier. 

We will hear today about how the U.S. Government Accountability Office found that annual costs from worsening extreme 

weather events could increase as much as $112 billion annually by 

the year 2100. The GAO relied on studies that used outdated heat 

mortality rate statistics before the use of air conditioning became 

prevalent. This is a simple adaptation that would have changed the 

study’s results dramatically. 

Predicting economic and environmental conditions hundreds of 

years from now while ignoring humans’ capacity to innovate and 

adapt is irresponsible. It is also intentionally misleading—the ultimate fake news. For instance, claiming that extreme weather will 

become more costly and deadly in the future as a result of climate 

change disregards inevitable advances in building materials and 

construction design. Instead of relying on big government to solve 

climate change problems, we should look to technological innova-
5 

tions that increase resilience and decrease vulnerability to inevitable climate change. 

For decades, climate policy has focused solely on emissions reduction. Overreaching and costly regulations like the Obama Clean 

Power Plan do little to reduce emissions. Climate mitigating technologies are much more likely to benefit the environment. Similarly, non-binding international agreements with arbitrary temperature goals like the Paris Climate Agreement do not offer any 

realistic solutions and come at a high price to the taxpayer. Even 

if fully implemented by all 195 countries, which isn’t and won’t 

happen, it would only reduce global temperature by 0.3 degrees 

Fahrenheit over the next century. 

Technology, though, provides the solution. Carbon emissions in 

the United States have decreased significantly over the last ten 

years thanks to fracking technology that has boosted access to affordable and clean burning natural gas. 

Throughout our history, technology has always led the way. All 

major breakthroughs in transportation, medicine, communication, 

and space exploration have occurred because of scientific discoveries. Why wouldn’t technology apply to climate change too? 

Recognizing this, Microsoft founder Bill Gates and other high- tech giants recently put up $1 billion to find technology-related solutions. Together they launched Breakthrough Energy Ventures in 

2016 to fund research into emerging energy and climate technologies. This is exactly the kind of innovative initiative we should 

encourage and support. 

To solve climate change challenges, we first need to acknowledge 

the uncertainties that exist. Then we can have confidence that innovations and technology will enable us to mitigate any adverse 

consequences of climate change. 

[The prepared statement of Mr. Smith follows:] 
6 

COM~AITTEE ON 

SCIENCE, SPACE, & TECHNOLOGY Lamar Smith, Chairman 

For Immediate Release 

May 16.2018 

Media Contacts: Thea McDonald, Brandon VerVelde 

(202) 225-6371 

Statement by Chairman Smith (R-Texas) 

Using Technology To Address Climate Change 

Chairman Smith: Today we will consider using technology to address climate change. 

We must ensure that our strategies take into account Americans' ability to develop 

innovations that will solve or mitigate challenges associated with climate change. 

The climate is always changing, but what remains uncertain is the extent to which 

humans contribute to that change. What is certain is that human ingenuity will play a 

significant role in resolving future environmental issues. 

Before we impose energy taxes or costly and ineffective government regulations. we 

should acknowledge the uncertainties that surround climate change research. 

Natural climate variability contributes to this uncertainty. Solar cycles. volcanic activity, 

El Nino/La Nina temperature fluctuations and long term oceanic circulation patterns 

are all naturally occurring events that have a major impact on the climate. 

Other unknowns such as the future of energy production and consumption also create 

uncertainty about future predictions. 

Advanced nuclear reactors could change the landscape of both the developed world 

as well as developing economies. 

Here's an example of an alarmist prediction not allowing for technological advances. A 

recent study found that the Intergovernmental Panel on Climate Change's [IPCC) worst 

case scenario. which claimed further increasing emissions and temperatures. was 

based on outdated assumptions of coal usage. 

These assumptions didn't anticipate the American shale gas revolution and further 

undercut the reliability of the IPCC's findings. 

In the field of climate science, there is legitimate concern that scientists are biased in 

favor of reaching predetermined conclusions. 

This inevitably leads to alarmist findings that are wrongfully reported as facts. Anyone 

who then questions the certainty of these findings is wrongly labeled a "denier." 
7 

We will hear today about how the U.S. Government Accountability Office (GAO) found 

that annual costs from worsening extreme weather events could increase as much as 

$112 billion annually by the year 2100. 

The GAO relied on studies that used outdated heat mortality rate statistics before the 

use of air conditioning became prevalent. This is a simple adaptation that would have 

changed the study's results dramatically. 

Predicting economic and environmental conditions hundreds of years from now while 

ignoring humans' capacity to innovate and adapt is irresponsible. It is also intentionally 

misleading-the ultimate "fake" news. 

For instance, claiming that extreme weather will become more costly and deadly in the 

future as a result of climate change disregards inevitable advances in building materials 

and construction design. 

Instead of relying on big government to solve climate change problems, we should look 

to technological innovations that increase resilience and decrease vulnerability to 

inevitable climate change. 

For decades, climate policy has focused solely on emissions reduction. Overreaching 

and costly regulations like the Obama Clean Power Plan do little to reduce emissions. 

Climate mitigating technologies are much more likely to benefit the environment. 

Similarly, non-binding international agreements with arbitrary temperature goals like the 

Paris Climate Agreement do not offer any realistic solutions and come at a high price to 

the taxpayer. Even if fully implemented by all 19 5 countries, which won't happen, it 

would only reduce global temperature by 0.3 degrees Fahrenheit over the next century 

(according to Dr. Bjorn Lomborg). 

Technology is what provides the solution. Carbon emissions in the U.S. have decreased 

significantly over the last 1 0 years thanks to tracking technology that has boosted 

access to affordable and clean burning natural gas. 

Throughout our history, technology has always led the way. All major breakthroughs in 

transportation, medicine, communication and space exploration have occurred 

because of scientific discoveries. Why wouldn't technology apply to climate change 

too? 

Recognizing this, Microsoft founder Bill Gates and other high-tech giants recently put up 

$1 billion to find technology-related solutions. Together they launched Breakthrough 

Energy Ventures in 2016 to fund research into emerging energy and climate 

technologies. This is exactly the kind of innovative initiative we should encourage and 

support. 
8 

To solve climate change challenges, we first need to acknowledge the uncertainties 

that exist. Then we can have confidence that innovations and technology will enable 

us to mitigate any adverse consequences of climate change. 

### 
9 

Chairman SMITH. That concludes my opening statement, and the 

gentlewoman from Texas, the Ranking Member, Ms. Johnson, is 

recognized for hers. 

Ms. JOHNSON. Thank you very much, Mr. Chairman. 

Let me start by expressing my disappointment that 16 months 

into this Administration, the Science Committee has yet to receive 

testimony from THE EPA Administrator, Scott Pruitt. Mr. Pruitt 

has appeared in front of multiple other committees multiple times. 

Yet, our repeated inquiries as to when we can expect Mr. Pruitt to 

appear in front of our committee have been met with unfulfilled assurances that a plan is in motion. By not inviting Mr. Pruitt to testify, we are—you are not only preventing this Committee from carrying out its oversight responsibilities, but you are preventing the 

American public from holding him accountable for his actions. It 

really is not too late. I ask you to commit today to holding a full 

Committee hearing before the August recess with Administrator 

Pruitt so that members on this Committee can do their jobs and 

get answers for the American people. 

Today’s hearing should be an opportunity to have a comprehensive discussion about the necessary climate adaptation and mitigation strategies our country needs to address climate change. Instead, today’s hearing is a continuation of the Majority’s seemingly 

unending attempts to call into question climate science and promote delay instead of action. 

We will hear familiar stories from two of our witnesses who are 

making repeat appearances, one of whom who has testified numerous times in the past, espousing the same views on climate that we 

have heard before. 

Climate is a complex and critically important issue. We cannot 

do good oversight if we only hear from those whom we have already heard. 

Despite the title of this hearing, none of the witnesses invited by 

the Majority are themselves developers of technologies used in climate adaptation. Instead, the hearing seems to be focused on setting up a false policy choice between mitigation and adaptation 

strategies. In reality, adaptation and mitigation are not either/or 

solutions, and there is strong evidence to suggest that both adaptation and mitigation strategies are necessary. 

The Risky Business Project, the Intergovernmental Panel on Climate Change, and the 2017 National Climate Assessment all recognize that near-term and long-term benefits from mitigation and 

long-term benefits from adaptation are mutually achievable. 

Let me state this very clearly: the reality of climate change is inescapable. Our planet is warming, and human activity is a major 

driver of that warming. The visible impacts of climate change are 

everywhere, and while the Trump Administration has already set 

us on a backward trajectory when it comes to dealing with the 

causes of climate change, we must not permit a similar retreat 

when dealing with responses to climate change. 

And let me just say before I yield the floor, I’d like to note that 

after six years with the Committee, Pamitha is leaving us to work 

for the Union of Concerned Scientists. He started on the Committee as an intern and was promoted over the years to press, then 

professional staff. So we thank him for all of his hard work and 
10 

dedication, and we wish him well in his new position, and you can 

tell the scientists that we do support them. 

Thank you, Mr. Chairman. 

[The prepared statement of Ms. Johnson follows:] 
11 

Thank you. 

OPENING STATEMENT 

Ranking Member Eddie Bernice Johnson 

House Committee on Science, Space, and Technology 

"Using Technology to Address Climate Change" 

May 16, 2018 

Let me start, Mr. Chairman, by expressing my disappointment that 16 months into this 

Administration, the Science Committee has yet to receive testimony from EPA Administrator 

Scott Pruitt. Mr. Pruitt has appeared in front of multiple other committees multiple times. Yet, 

our repeated inquiries as to when we can expect Mr. Pruitt to appear in front of our committee 

have been met with unfulfilled assurances that plans are in motion. By not inviting Mr. Pruitt to 

testify you are not only preventing this Committee from carrying out its oversight 

responsibilities, but you are preventing the American public from holding Mr. Pruitt accountable 

for his actions. Mr. Chairman, it is not too late. I ask you to commit today to holding a full 

committee hearing before the August recess with Administrator Pruitt so that members on this 

Committee can do their jobs and get answers for the American people. 

Today's hearing should be an opportunity to have a comprehensive discussion about the 

necessary climate adaptation and mitigation strategies our country needs to address climate 

change. Instead, today's hearing is a continuation of the Majority's seemingly unending attempts 

to call into question climate science and promote delay instead of action. We will hear familiar 

stories from two witnesses who are making repeat appearances, one of whom who has testified 

numerous times in the past, espousing the same views on climate for that we have heard before. 

Climate is a complex and critically important issue. We cannot do good oversight if we only hear 

from those whom we have already heard. 

Despite the title of this hearing, none of the witnesses invited by the Majority arc themselves 

developers of technologies used in climate adaptation. Instead, the hearing seems to be focused 

on setting up a false policy choice between mitigation and adaptation strategies. In reality, 

adaptation and mitigation are not either/or solutions, and there is strong evidence to suggest that 

both adaptation and mitigation strategies are necessary. The Risky Business Project, the 

Intergovernmental Panel on Climate Change, and the 2017 National Climate Assessment, all 

recognize that near-term and long-term benefits from mitigation, and long-tetm benefits from 

adaptation, are mutually achievable. 

Let me state this clearly: the reality of climate change is inescapable. Our planet is warming, and 

human activity is a major driver of that warming. The visible impacts of climate change are 

everywhere, and while the Trump Administration has already set us on a backwards trajectory 

when it comes to dealing with the causes of climate change, we must not permit a similar retreat 

when dealing with responses to climate change. 
12 

Chairman SMITH. Thank you, Ms. Johnson. 

The gentleman from Arizona, Mr. Biggs, the Chairman of the Environment Subcommittee, is recognized for his opening statement. 

Mr. BIGGS. Thank you, Chairman Smith, for holding this important hearing to discuss climate change policy. 

It is crucial that U.S. policy focuses on American technological 

innovation to address future environmental conditions. 

Let me be very blunt: I firmly believe we must eliminate all costly, unjustifiable regulations and international agreements related 

to climate change from our policy agenda. President Obama’s Clean 

Power Plan and the Paris Climate Agreement were estimated to 

cost billions annually, despite having a negligible projected impact 

on the environment. The Trump administration is rightfully putting an end to these egregiously pointless measures. Instead we 

should advance policies that encourage the development of technology to help mitigate and adapt to future environmental hazards, 

whether climate-related or otherwise. 

To take just one example, hydraulic fracturing drove the shale 

gas revolution, which lowered U.S. carbon emissions in addition to 

boosting the national economy. No climate regulation can claim a 

similarly beneficial impact. Far from it. 

The benefits or downsides of any new technology, such as 

fracking, cannot always be predicted when first developed. However, one thing we can count on is that humans will continue to 

innovate and find solutions to address pressing problems. Our capacity for ingenuity is something that cannot and should not be 

discounted. This ability to adapt through technology must be recognized by policymakers and scientists alike. For example, claiming 

with certainty that islands will be uninhabitable in 20 years because rising seas will eliminate access to drinking water, as one recent study has predicted, is grossly irresponsible. Not only is it an 

exaggerated and unrealistic prediction, it completely ignores the 

potential for innovations in land use and advancements in technology like water desalinization. Ignoring innovation effectively stifles further discoveries and technological advancements. 

Assuming the status quo will remain in terms of technology and 

climate response ignores American ingenuity, which has driven economic progress and environmental improvements around the 

world. It would be foolish to craft policy in such a narrow-minded, 

stasis-reliant manner. 

I look forward to testimony from our witnesses today that will 

identify the folly of climate alarmism and emphasize the need for 

a robust debate on the future of climate policy. 

Chairman Smith, I thank you for holding this hearing, and I 

thank all of our witnesses for being here today, and I yield back 

the balance of my time. 

[The prepared statement of Mr. Biggs follows:] 
13 

COMMITTEE ON 

SCIENCE, SPACE, & TECHNOLOGY Lamar Sm~th, Chairman 

For Immediate Release 

May 16,2018 

Media Contacts: Thea McDonald, Brandon VerVelde 

(202) 225-6371 

Statement by Rep. Andy Biggs (R-Ariz.) 

Using Technology to Address Climate Change 

Chairman Biggs: Thank you Chairman Smith for holding this important hearing to discuss 

climate change policy. It is crucial that U.S. policy focuses on American technological 

innovation to address future environmental conditions. 

Let me be very blunt: I firmly believe we must eliminate all costly, unjustifiable 

regulations and international agreements related to climate change from our policy 

agenda. President Obama's Clean Power Plan and the Paris Climate Agreement were 

estimated to cost billions annually, despite having a negligible projected impact on the 

environment. The Trump administration is rightfully putting an end to these egregiously 

pointless measures. 

Instead we should advance policies that encourage the development of technology to 

help mitigate and adapt to future environmental hazards, whether climate-related or 

otherwise. To take just one example, hydraulic fracturing drove the shale gas revolution, 

which lowered U.S. carbon emissions in addition to boosting the national economy. No 

climate regulation can claim a similarly beneficial impact-far from it. 

The benefits-or downsides-of any new technology, such as tracking, cannot always 

be predicted when it is first developed. However, one thing we can count on is that 

humans will continue to innovate and find solutions to address pressing problems. Our 

capacity for ingenuity is something that cannot and should not be discounted. 

This ability to adapt through technology must be recognized by policymakers and 

scientists alike. For example, claiming with certainty that islands will be uninhabitable in 

20 years because rising seas will eliminate access to drinking water, as one recent study 

has predicted, is grossly irresponsible. 

Not only is it an exaggerated and unrealistic prediction, it completely ignores the 

potential for innovations in land use and advancements in technology like water 

desalinization. Ignoring innovation effectively stifles further discoveries and 

technological advancements. 

Assuming the status quo will remain in terms of technology and climate response 

ignores American ingenuity, which has driven economic progress and environmental 

improvements around the world. It would be foolish to craft policy in such a narrowminded manner. 
14 

I look forward to testimony from our witnesses today that will identify the folly of climate 

alarmism and emphasize the need for a robust debate on the future of climate policy. I 

thank you all for being here today and yield back the balance of my time. 

### 
15 

Chairman SMITH. Thank you, Mr. Biggs. 

And the gentlewoman from Oregon, Ms. Bonamici, the Ranking 

Member of the Environment Subcommittee, is recognized for her 

statement. 

Ms. BONAMICI. Thank you very much, Mr. Chairman and Ranking Member Johnson, and thank you to our witnesses for being 

here today. 

Climate change is an important issue to our constituents and to 

our country. Today we should be having a robust conversation 

about climate adaptation and mitigation technologies and policies. 

We should not be using valuable time trying to discredit established scientific facts. The Science Committee should not be a 

forum where the human role in climate change is still debated. 

What would be best for our constituents would be working in a bipartisan manner to determine the best course of action to help 

them deal with the reality of a quickly changing climate. 

The consequences of climate change are well known, and our understanding about how to address the causes of climate change continues to improve. We can no longer sit back and debate the merits 

of taking action. The time is now. 

It’s critical that we support scientific research about climate, and 

that we build on rather than break down decades worth of progress 

on this issue. Several of today’s witnesses will try to present a false 

choice between climate adaptation and mitigation, but we know 

that these strategies go hand in hand. 

In my home State of Oregon, devastating wildfires tore through 

the region last summer, endangering lives, harming local tourism, 

and resulting in significant losses for the timber industry. Although 

it is not possible to say that climate change causes a particular extreme weather event, we need to know more about how climate 

change increases the frequency and severity of these events. 

Mitigation can provide near-term relief and help make sure communities are prepared to keep their families safe, but adaptation 

is necessary to address the larger issue of increasing frequency of 

severe weather events. 

Coastal communities in Northwest Oregon are facing the consequences of ocean acidification, rising sea temperatures and levels, 

hypoxia, and other environmental stressors. Local shellfish growers 

and commercial fisheries are seeing the direct effects of climate 

change in their industries. Both mitigation and adaptation strategies can help people in the district I represent and across the country who are directly affected by droughts, rising sea levels, flooding, 

and severe weather. 

The challenges of course are not unique to Oregon. In Alaska, for 

example, more than 30 towns and cities may need to relocate, costing hundreds of millions of dollars, because the permafrost is thawing and destabilizing the infrastructure. 

These issues deserve attention. We should be directing more resources to the full range of potential solutions that are available, 

rather than continuing to debate whether humans contribute to climate change, which the rest of the world considers settled. 

I am especially pleased that Dr. Phil Duffy from the Woods Hole 

Research Center is here to provide a scientific perspective on climate change and discuss the need for more federal research on 
16 

global change. I also look forward to discussing the need for prompt 

action on climate adaptation and mitigation, rather than encouraging inaction with claims of uncertainty. 

I hope the day comes soon when this Committee can talk about 

and work on bipartisan solutions to address the important issue of 

climate change. 

And Mr. Chairman, as I yield back, I want to join Ranking Member Johnson in thanking Pamitha for his six years of dedication 

and good work to this Committee on Science, Space, and Technology, and I yield back. 

Thank you, Mr. Chairman. 

[The prepared statement of Ms. Bonamici follows:] 
17 

OPENING STATEMENT 

Ranking Member Suzanne Bonamici (D-OR) 

of the Subcommittee on Environment 

House Committee on Science, Space, and Technology 

"Using Technology to Address Climate Change" 

May 16,2018 

Thank you Mr. Chairman and Ranking Member Johnson, and thank you to our witnesses for 

being here today. 

Climate change is an important issue to our constituents and our country. Today we should 

be having a robust conversation about climate adaptation and mitigation technologies and 

policies; we should not be using valuable time trying to discredit established scientific facts. 

The Science Committee should not be a forum where the human role in climate change is 

still debated. What would be best for our constituents would be working in a bipartisan 

manner to determine the best course of action to help them deal with the reality of a quickly 

changing climate. 

The consequences of climate change are well known, and our understanding about how to 

address the causes of climate change continues to improve. We can no longer sit back and 

debate the merits of taking action. The time is now. It is critical that we support scientific 

research about climate, and that we build on rather than break down decades worth of 

progress on this issue. Several oftoday's witnesses will try to present a false choice between 

climate adaptation and mitigation, but we know that these strategies go hand in hand. 

In my home state of Oregon, devastating wildfires tore through the region last summer 

endangering lives, harming local tourism, and resulting in significant losses for the timber 

industry. Although it is not possible to say that climate change causes a particular extreme 

weather event, we need to know more about how climate change increases the frequency and 

severity of those events. Mitigation can provide near-term relief and help make sure 

communities are prepared to keep families safe, but adaptation is necessary to address the 

larger issue of increasing frequency of severe weather events. 

Coastal communities in Northwest Oregon have faced the consequences of ocean 

acidification, rising sea temperatures and levels, hypoxia, and other environmental stressors. 

Local shellfish growers and commercial fisheries are seeing the direct effects of climate 

change in their industries. Both mitigation and adaptation strategies can help people in the 

district I represent and across the country who are directly affected by droughts, rising sea 

levels, flooding, and severe weather. 

The challenges arc not unique to Oregon. In Alaska, for example, more than 30 towns and 

cities may need to relocate, costing hundreds of millions of dollars, because the permafrost is 

thawing and destabilizing the infrastructure. 
18 

These issues deserve attention. We should be directing more resources to the full range of 

potential solutions that are available, rather than continuing to debate whether humans 

contribute to climate change, which the rest of the world considers settled. 

I am especially pleased that Dr. Phil Duffy from the Woods Hole Research Center is here to 

provide a scientific perspective on climate change and discuss the need for more federal 

research on global change. I also look forward to discussing the need for prompt action on 

climate adaptation and mitigation, rather than encouraging inaction with claims of 

uncertainty. I hope the day comes soon when this Committee can talk about and work on 

bipartisan solutions to address the causes of climate change. 

Thank you Mr. Chairman, I yield back. 
19 

Chairman SMITH. Thank you, Ms. Bonamici. 

And before I introduce our witnesses today, let me say that we 

are actually missing one individual, and she is not able to be with 

us. Her flight was canceled, not because of extreme weather, no, 

and this is Judith Curry, and we wish she had been able to come, 

but without objection, her written testimony will be made part of 

the record, and hopefully she’ll be able to testify at another time. 

[The prepared statement of Ms. Curry appears in Appendix II] 

Chairman SMITH. Our first witness today is Mr. Oren Cass, a 

Senior Fellow at the Manhattan Institute, where he focuses on energy, environment, and anti-poverty policy. Mr. Cass was the Domestic Policy Director for Mitt Romney’s presidential campaign in 

2012. In this role, he helped shape campaign policy and communication on a variety of issues ranging from healthcare to energy 

to trade. Prior to joining the Manhattan Institute, Mr. Cass was a 

Management Consultant for Bain and Company, where he advised 

global companies on implementing growth strategies and performance improvement programs. Mr. Cass holds a bachelor of arts in 

political economy from Williams College and a juris doctor from 

Harvard University, where he was an Editor and the Vice President of the Harvard Law Review. 

Our next witness is Mr. Ted Nordhaus, Founder and Executive 

Director of the Breakthrough Institute. He is a recognized author, 

researcher and political strategist in climate and energy policy. Mr. 

Nordhaus is the co-author of Breakthrough, the widely distributed 

book that was reviewed as ‘‘a vital strain of realism’’ by Time magazine. His opinion and editorial writings have been published in 

the Harvard Law and Policy Review, Wall Street Journal, New 

York Times, Scientific American, and other nationally distributed 

media. Over the years, Mr. Nordhaus has received the Green Book 

Award and Times’ Heroes of the Environment Award. He holds a 

bachelor of arts in history from the University of California-Berkley. 

Dr. Phil Duffy, our third witness, is President and Executive Director of Woods Hole Research Center. Prior to joining WHRC, Dr. 

Duffy served as a Senior Adviser in the White House National 

Science and Technology Council and as a Senior Policy Analyst in 

the White House Office of Science and Technology Policy. Before 

this, Dr. Duffy was the Chief Scientist for Climate Central, Inc. He 

has held senior research positions with Lawrence Livermore National Laboratory and visiting positions at the Carnegie Institute 

for Science and the Woods Institute for the Environment at Stanford University. Dr. Duffy was the recipient of the United Nations 

Association Global Citizen Award. He holds a bachelor’s degree 

from Harvard University and a Ph.D. in applied physics from Stanford University. 

We welcome you all. We appreciate your presence and your effort 

to get here. It wasn’t easy for everybody. And Mr. Cass, if you’ll 

begin? 
20 

TESTIMONY OF MR. OREN CASS, 

SENIOR FELLOW, 

MANHATTAN INSTITUTE 

Mr. CASS. Thank you very much. Good morning, Chairman 

Smith, Ranking Member Johnson, and Members of the Committee, 

and thank you again for inviting me to participate in today’s hearing. My name is Oren Cass. I’m a Senior Fellow at the Manhattan 

Institute for Policy Research, where my work addresses environmental policy including climate change economics. 

My primary message to the Committee is this: The assumptions 

that we make about how human society will adapt to climate 

change are central to our understanding of the challenges the phenomenon presents and the costs that it will impose. Analyses that 

do not properly account for adaptation describe an alternative universe that does not exist. The estimates they produce are not plausible forecasts of future costs and should not be credited by policymakers. 

Let me pause here to clarify that this issue does not concern climate science, and also to clarify that I would agree with the opening remarks that mitigation as well as adaptation is an important 

part of addressing climate change, and both of those points are addressed in my written testimony as well. 

I believe policymakers should use mainstream climate science as 

the starting point for their work but we depart the world of climate 

science for that of climate economics when we turn to the question 

of how those changes will affect human society via their influence 

on public health or infrastructure or the economy. 

The common failure to consider adaptation has profound consequences for how people conceptualize climate change, leading to 

what I call climate catastrophism. If the entire brunt of a century 

of climate change were to land on civilization tomorrow, the result 

might well be catastrophic, but if those changes occur gradually, as 

they are expected to, if they emerge in a world far wealthier and 

more technologically advanced than today’s, as we expect it to be, 

and if policymakers ensure that people have the information and 

incentives to plan well, something over which we have control, then 

climate change will impose real costs but ones that we should have 

confidence in our ability to manage. 

I’d like to briefly show what happens when we do this wrong and 

do not take account of adaptation properly. These are results of 

some recent studies that I describe the details of in my written testimony and which I’d be happy to answer questions about in more 

detail as well. 

The first is from a study published in 2015 in Nature that looks 

at the relationship between year-to-year variations in temperature 

and year-to-year variations in economic growth across countries, 

and what they found was that there’s a relationship. Some temperatures are better than others for growth, and they extrapolated 

that relationship out through the end of the century, essentially assuming that by the end of the century, countries will react every 

year to significantly warmer temperatures as if they came from out 

of nowhere. 
21 

What you’re seeing here is the GDP per capita estimates produced by the study. You see essentially that China and India never 

grow wealthy because they become too warm. The United States 

does continue to grow, but by the end of the century has essentially 

flatlined, and if we begin to move higher up the chart, we reach 

Mongolia, which achieves per capita income roughly four times that 

of the United States, thanks to the warmer temperatures it would 

experience, or if we move even higher, we eventually reach all the 

way to Iceland at per capita incomes of $1.5 million, again because 

warmer temperatures would imply higher growth rates in perpetuity. 

Now, these are obviously in some cases the outlying or extreme 

examples from the study but I think that that’s the point, that if 

you don’t consider the fact that these relationships will not simply 

hold unchanged, you end up with absurd results. 

I’d like to look next at a study—excuse me, sorry, if we can skip 

to the next slide. Next slide. Thank you. 

[Slide] 

I’d like to look next at the GAO assessment of climate costs published last fall, which looked at two syntheses of costs to the 

United States. On the left is one published by the EPA, and on the 

right, one published by Rhodium. The Rhodium study finds most 

of its costs from extreme-heat deaths, literally it being so hot that 

tens of thousands of people die. The EPA study finds even higher 

costs from declines in air quality. And if we flip to the next slide, 

this is the EPA finding, that for both ozone and particulate matter, 

which have declined substantially in just the last 15 years, a very 

small uptick would essentially be the largest and in fact majority 

of all costs of climate change in the United States. This assumes 

that despite all progress to date, there is no further progress and 

we reduce pollution no more throughout the rest of the century. 

[Slide] 

And finally, if we flip to the last slide—this is my favorite—EPA 

looks at heat-related deaths and produces a chart that at first 

glance seems reasonable. Baseline in 2000, you see very small red 

dots, not a lot of deaths. By 2100, it’s hotter and you see more 

deaths. But if you click ahead one click, notice what this implies, 

that the deaths in the North in 2100 will be dramatically higher 

than in the South in 2000, and if you flip ahead one more time, 

this is again the data on the EPA website showing that if we assume cities don’t adjust in any way, deaths in places like Pittsburgh, Detroit, and New York will be 50 to 75 times the rate we 

see in Phoenix, Houston, and New Orleans today. This is obviously 

not what is going to happen. It’s not a responsible way to connect 

economic analyses, and we should not be using it as the basis for 

policymaking. 

Thank you very much. 

[The prepared statement of Mr. Cass follows:] 
22 

Testimony of Oren M. Cass before the 

House Committee on Science, Space, and Technology 

May16,2018 

Summary of Major Points 

• Assumptions about how human society will adapt to climate change are central to 

our understanding of the challenges that the phenomenon presents and the costs 

that it will impose. 

• This issue does not concern climate science but rather climate economics, which 

attempts to address the question of how the changes to our physical environment 

anticipated by climate science will affect human society via their influence on public 

health or infrastructure or the economy. 

• In recent years, prominent studies that purport to forecast the cost of climate change 

have begun to rely on statistical analyses of the effects of temperature variation. 

These correlation-based, temperature-impact studies-" temperature studies"-start 

with present-day relationships between temperatures and outcomes such as 

mortality or economic growth. They extrapolate from those relationships a 

proportionally larger response to long-term projected climate warming and assign 

dollar values to the very large impacts that appear to emerge. 

• The fallacies underlying this framework are (a) that the same responses detected for 

small, random variations in historical temperatures will manifest themselves 

proportionally in large, gradual, permanent future changes, and (b) that society will 

not change or adapt in any way to mitigate the effects. 

• The GAO's 2017 report, "Climate Change: Information on Potential Economic 

Effects Could Help Guide Federal Efforts to Reduce Fiscal Exposure," derives the 

vast majority of its costs from such studies, accepting absurd forecasts like one 

created by EPA that finds Pittsburgh's extreme-heat mortality rising to 75 times the 

level experienced in Phoenix or Houston today. 

• Another emerging line of research seeks to link rising temperatures directly to 

changing rates of economic growth, again leading to bizarre predictions like Iceland 

and Mongolia becoming the world's leading economies while India's economy 

begins rapidly contracting. The Federal Reserve Bank of Richmond has recently 

published a working paper that uses a similar methodology. 

• Analyses that do not properly account for adaptation describe an alternative 

universe that does not exist; the estimates they produce are not plausible forecasts of 

future costs and should not be credited by policymakers. 

• Instead, policymakers should focus on understanding what adaptation is likely to be 

necessary, in what circumstances it will be difficult, and how better public policy 

can create the information and incentives to facilitate its occurrence. 
23 

Testimony of Oren M. Cass 

before the House Committee 

on Science, Space, and Technology 

Mayl6, 2018 

Good morning Chairman Smith, Ranking Member Johnson, and Members of the 

Committee. Thank you for inviting me to participate in today's hearing. 

My name is Oren Cass. I am a senior fellow at the Manhattan Institute for Policy 

Research where my work addresses environmental policy including the economics of 

climate change. This testimony focuses on the role that adaptation may play in the 

human response to climate change and the importance of accounting for such 

adaptation when conducting economic analyses of climate costs and when formulating 

climate policy. I addressed this topic recently in a Manhattan Institute report titled 

"Overheated: How Flawed Analyses Overestimate the Costs of Climate Change."1 

My primary message to the committee is this: The assumptions that we make about 

how human society will adapt to climate change are central to our understanding of 

the challenges that the phenomenon presents and the costs that it will impose. 

Relative to most problems that we encounter in public policy, climate change is a 

gradual process; its most dangerous effects will appear on decades- and even centurieslong timescales. Yet analysts frequently analyze these effects as if they will happen now, 

without accounting for how our economy, society, and technology are likely to evolve 

independent of climate change and- especially-in response to climate change. 

Analyses that do not properly account for adaptation describe an alternative universe 

that does not exist; the estimates they produce are not plausible forecasts of future 

costs and should not be credited by policymakers. 

Let me pause here to clarify that this issue does not concern climate science. I believe 

that mainstream climate science, particularly as summarized by the UN's 

Intergovernmental Panel on Climate Change, provides the best available assessment of 

the changes to our physical environment that a given level of greenhouse-gas emissions 

will cause and that policymakers should use it as the starting point for their own work. 

But we depart the world of climate science for that of climate economics when we turn 

to the question of how those changes will affect human society via their influence on 

public health or infrastructure or the economy. 

1 See Oren Cass, "Overheated: How Flawed Analyses Overestimate the Costs of Climate Change," Manhattan 

Institute for Policy Research, March 2018, https://www.manhattan-institute.org/htmlioverheated-how-flawcdanalvses-overestimate-costs-climate-change-1 0986.html; see also Oren Cass, "The Problem with Climate 

Catastrophizing,'' Foreign Affairs, March 21, 2017, https:/iwww.foreignaffairs.comiarticles/2017-03-21iproblemclimate-catastrophizing. 

2 
24 

The common failure to consider adaptation has profound consequences for how people 

conceptualize climate change, leading to what I call climate catastrophism. If the entire 

brunt of a century of climate change were to land on civilization tomorrow- if a 

substantial share of agricultural output suddenly vanished, if sea levels were suddenly 

several feet higher, if regions accustomed to temperate summers suddenly experienced 

outdoor temperatures to which they were unaccustomed, if hundreds of millions of 

people were suddenly displaced- the result might well be catastrophic. But if those 

changes occur gradually (as they are expected to), if they emerge in a world far 

wealthier and more technologically advanced than today's (as we expect it to be), and if 

policymakers ensure that people have the information and incentives to plan well 

(something over which we have control), then climate change will impose real costs but 

ones that we should have confidence in our ability to manage. 

*** 

The no-adaptation fallacy reaches its most concrete and absurd results in formal 

economic analyses of climate costs, and it is here that I want to focus your attention 

today. In recent years, prominent studies that purport to forecast the cost of climate 

change have begun to rely on statistical analyses of the effects of temperature variation. 

These correlation-based, temperature-impact studies- hereinafter referred to as 

temperature studies-start with present-day relationships between temperatures and 

outcomes such as mortality or economic growth. They extrapolate from those 

relationships a proportionally larger response to long-term projected climate warming 

and assign dollar values to the very large impacts that appear to emerge. 2 

A critical assumption underlying such an extrapolation is ceteris paribus, or "other 

things constant." The effect of small, random fluctuations in today's temperatures will 

only hold for large, gradual, permanent changes in future temperatures if no 

confounding factors exist and nothing in the world changes. For most economic studies, 

that construct is a valuable one. The whole point, typically, is to isolate the specific 

effect of one variable on another in the present. In estimating how additional years of 

education boost income, for instance, one need not worry that the labor market might 

look different eighty years hence. 

In the climate context, however, this framework is wholly inappropriate. Given decades 

to respond to a gradual shift in temperatures, "other things" most certainly will not be 

"constant." Studies typically acknowledge that they assume no adaptation, but 

announcing a bad assumption does not make it a good one. They will sometimes argue 

that adaptation is unlikely to occur, by showing that it has not occurred in the past. But 

2 Most temperature studies, including those discussed here, acknowledge their failure to account for adaptation or 

caveat that their conclusions will not hold if adaptation occurs. Nevertheless, their no-adaptation findings are 

reported as credible estimates of future climate costs. 

3 
25 

a failure to adapt to small, temporary changes says nothing about whether a society 

would adapt to large, permanent ones. 

An adaptation may represent a cost-effective response to a large change in underlying 

climate but offer very little return on investment if implemented in response to a small 

change, or in response to unpredictable fluctuations. The failure to install an air 

conditioner for a year with one extra gooF day, for instance, does not mean that air 

conditioners will not be installed in the face of 40 extra gooF days annually. Adhering to 

a standard workday when the average temperature shifts from 82°F to 83°F does not 

rule out adjusting the workday, should the average reach gsoF. 

Even where adaptations are immediately cost-effective, they may nevertheless be 

gradual. Social norms, economic configurations, and technologies emerge over time. 

Even if temperature fluctuations are enormous .in magnitude, adaptations will be 

impossible where their implementation period is longer than that for which the 

condition lasts. People living in a location where the temperature swings annually by 

10°F around an 80°F average may wish that it could sometimes have the permanent 

characteristics of a 70°F location and sometimes have those of a gooF location, but that's 

not plausible; it will instead adapt to the behaviors optimal for an 80°F average with 

high variability. But if the underlying average shifts from 80°F to gooF, a very different 

range of adaptations becomes likely. 

The conceptual flaws of temperature studies are laid bare in the implausible outputs 

that they yield. Yet those outputs are accepted unc:ritically by the newsmedia and even 

the federal government, as reflected in last year's GAO report on climate costs-an 

assessment that relied overwhelmingly on such studies. 

At the request of Senators Maria Cantwell (D., Washington) and Susan Collins (R., 

Maine), the GAO worked from December 2015 to September 2017 to review "the 

potential economic effects of climate change impacts and resulting risks to the federal 

government." Its report, "Climate Change: Information on Potential Economic Effects 

Could Help Guide Federal Efforts to Reduce Fiscal Exposure" (hereinafter: GAO),' 

summarized two other studies that drew on and synthesized a further range of studies 

to provide national-scale estimates of the economic costs of projected climate change for 

the United States (see Figure 1). 

In both of these synthesis studies, the largest costs and vast majority of total costs derive 

from temperature studies that assert correlations between higher temperatures and 

more extreme-heat deaths, more air-pollution deaths, and fewer hours worked. The two 

synthesis studies GAO relied on are: 

3 U.S. Govemment Accountability Office. "Climate Change: lnfonnation on Potential Economic Effects Could Help 

Guide Federal Efforts to Reduce Fiscal Exposure,"' Sept. 2017, https:i/www.gao.gov/asscts/690/687466.pdf. 

4 
26 

• "Climate Change in the United States: Benefits of Global Action," published in 

June 2015 by the U.S. Environmental Protection Agency (EPA).4 This study 

estimates that by 2100, climate change annually will cost the U.S. $1.3 trillion-

$1.5 trillion more than if aggressive action were taken to mitigate warming. At 

least 89% of this sum comes from temperature studies. 

• "American Climate Prospectus: Economic Risks in the United States," 

published in October 2014 by the Rhodium Group (Rhodium),s a research 

Consultancy. This study estimates that by 2100, climate change will cost the U.S. 

$228 billion-$945 billion per year. At least 71% of this sum is based on the 

estimates from temperature studies. 

FIGURE 1: Sources of Climate-Change Cost Estimates in the GAO Report 

Note: Midpoints shown where analyses provide both high and low estimates. Rhodiwn reports estimates in 2011$, updated here to 2014$, 

using the U.S, Bureau of Economic Analysis GDP deflator. The GAO overview of Rhodium reports duplicative totals for ''lost l!fettme labor 

supply" and ''storm losses," excluded here. EPA provides no 2100 estimate for power~systems savings; the 2050 value is used here. The 

EPA estimate tmderstates sea~ level impact by comparing it with a mitigation case in which sea levels still rise. 

A review of the studies that account for the majority of costs provides a helpful view 

into how such studies are conducted and why they should be ignored. The following 

pages discuss, in turn, two studies used by EPA to produce its estimates of air-pollution 

and extreme-temperature mortality, and then two studies used by Rhodium to produce 

its estimate of extreme-temperature mortality. 

"U.S. Environmental Protection Agency, "Climate Change in the United States: Benefits of Global Action," June 

2015. https://www.epa.gov/sitesiproduction/files/2015·06/documents/cirareport.pdf. EPA includes $10 billion-$34 

billion in energy-system costs reported for 2050; it provided no estimate for 2100. 

5 Robert Kopp et al., "American Climate Prospectus: Economic Risks in the United States," Rhodium Group, Oct. 

2014, https:/ igspp.berkeley.edu/assets/uploads/research/pd!l American Climate Prospectus. pdf. Rhodium provides 

alternative measures for heat-related mortality and coastal impacts. The totals here use the methodologies that 

produced the highest cost estimates. Rhodium figures, as reported by GAO, use constant 2011 dollars. Figures here 

are updated to 2014 dollars. 

5 
27 

The very fact that researchers are identifying small changes in air-quality and direct 

deaths from heat as the primary costs of climate change should indicate that something 

has gone wrong in how we are evaluating the issue. 

The EPA Assessment of Climate Costs 

The majority of all climate-related costs identified by EPA for the United States by the 

year 2100 derive from small changes in air quality; that study is discussed first. The 

second largest cost, from extreme-temperature deaths, is discussed second. 

Pollution-Related Mortality: Fernando Garda-Menendez et al., "U.S. Air Quality and 

Health Benefits from Avoided Climate Change Under Greenhouse Gas Mitigation," 

Environmental Science & Technology 49 (June 2015): 7580-88. (Garcia-Menendez) 

Higher temperatures can interact with other environmental processes to change the 

atmospheric concentration of pollutants, even if pollutant emission rates do not change. 

For instance, ground-level ozone ("smog") gets worse on hot days. EPA tried to 

quantify these air-quality effects based on Garcia-Menendez. That study combined 

existing air-quality and climate-change models to forecast changes in atmospheric 

concentrations of ground-level ozone and particulate matter by 2100 if emissions 

remained constant but temperatures increased. It found that while concentrations 

would increase in some places and decrease in others, the average U.S. resident would 

be exposed to slightly increased levels of pollution: an increase of 3.2 parts per billion 

for ozone and 1.5Jlg m-3 (micrograms per cubic meter) for particulate matter (or, 

respectively, 2.6 parts per billion and 1.2Jlg m-3 greater than an alternative scenario in 

which climate change is aggressively fought). 

Garcia-Menendez applied existing EPA formulas to these pollution increases to estimate 

that unchecked global warming would cost 57,000 lives per year in 2100, relative to an 

alternative scenario with aggressive action against global warming.6 EPA assigned a 

value of $930 billion per year to those lives. The number of deaths seems alarming but 

appears much less consequential when placed in the context of present-day experience. 

Here's why. The paper estimated that unchecked climate change would increase ozone 

levels by 2.6 parts per billion and particulate-matter levels by 1.2 pg m-3, over the 

alternative scenario.? But those concentrations have fallen since 2000, from 82 and 13.4, 

respectively. In 2009 alone, particulate matter fell by an amount almost equal to the 

increase that climate change would cause over the century. In most of the years from 

6 Garcia-Menende=, Table 2. 

' While Garcia-fvfenendez reports the effect of climate change on population-weighted concentrations, the 

underlying EPA data presented here on nationwide levels between 2000 and 2015 are not population-weighted. 

6 
28 

2000 to 2015, ozone levels fluctuated by more than the climate-induced effect over a 

century.8 Put another way, the forecasted effect of climate change on air pollution is to 

return atmospheric quality from 2015 to 2011levels (see Figure 2). 

Garcia-Menendez also implicitly assumes that recent decades' extraordinary pollution 

reductions will cease for the rest of the century and that no new technologies will 

reduce human exposure to pollution or its danger to health. In fact, ozone and 

particulate-matter levels for most of the country are already below thresholds that EPA 

deems safe, and those levels will almost certainly be far lower by century's end. In the 

context of a century of economic, social, technological, and environmental change, the 

identified impact of climate change on air pollution is barely noise. Yet it represents the 

majority of costs of all climate effects that EPA reports-$930 billion of $1,391 billion.9 

FIGURE 2: Air-Pollution Concentrations in 2000, 2015, and 2100 

Source: Garcia-Aienende::. "Particulate Matter (PM2.5) Trends,' US Env1ronmcntal Protectwn Agency. ''Ozone Trends:· US 

Environmental Protection Agem::y. 

Temperature-Related Mortality: David Mills et al., "Climate Change Impacts on 

Extreme Temperature Mortality in Select Metropolitan Areas in the United States," 

Climatic Change 131, no. 1 (July 2015): 83-95. (Mills) 

The EPA estimate of costs due to additional heat deaths in 2100 relies on Mills. That 

study examined the effect on mortality rates from days of "extreme" heat (or cold) in 33 

cities, defined, respectively, as days with a low temperature in the warmest 1% of the 

city's lows, or a high temperature in the coldest 1% of the city's highs. In Pittsburgh, for 

example, 99% of daily low temperatures were less than 2l.TC (71.1 °F); a day with a 

8 ··Particulate Matter (PM2.5) Trends," U.S. Environmental Protection Agency; "Ozone Trends," U.S. 

Environmental Protection Agency. 

9 EPA, pp. 78-79; see also GAO, p. 22. 

7 
29 

warmer minimum temperature 

would count as "extremely hot." 10 

For each city, the researchers 

measured the change in mortality 

on days with temperature 

extremes during 1989-2000. 

Using climate models, the 

researchers then estimated for the 

years 2000 and 2100 a distribution 

of daily temperatures for each city. 

In 2000, the climate model's 

simulation of Pittsburgh had fewer 

than five extremely hot days;11 for 

2100, it had approximately 70,12 

each of which Mills assumed 

would have the elevated mortality 

level associated with extremely hot 

days in the past. Overall, Mills 

estimated that extreme-heat deaths 

in the 33 cities studied would rise 

FIGURE 3: Heat-Related Mortality in 

Select Southern Cities (2000) and 

Northern Cities (2100) 

Source: The 2000 and 2!00 city estimates come from the same EPA 

extrapolation of Mills. See EPA, Extreme T~mperature, Figure 1. 

from fewer than 600 in 200013 to more than 7,500 in 2100,14 even if their populations 

remained constant. 

EPA employed the Mills methodology but used a different climate model to forecast the 

increase in extremely hot days, applied the work to additional cities, and accounted for 

population growth over the century.15 In the EPA model, Pittsburgh's annual death rate 

from extreme temperatures increases 30-fold, from 0.4 per 100,000 people in 2000 to 12.8 

in 2100.16 Across all cities, excess fatalities by 2100 would exceed 12,000. 

The Mills estimates of heat deaths provide a quintessential illustration of the flaw in an 

assumption of no adaptation. The study uses historical data to predict the response to 

temperature variation 100 years later, which presumes that society's reaction to a given 

variation will be the same at both points in time. That assumption is a poor one. 

10 Mills. Online Resource 1. 

11 Mills, Online Resource 2. 

"Mills, Online Resource 5. 

13 Mills. Online Resource 3. 

14 Mills, Table 2. 

15 E-mail correspondence with David Mills, Jan. 17,2018. See EPA, ''Extreme Temperature," n. 29, for discussion 

of EPA's extension of the Mills model to additional cities. 

16 EPA, "Extreme Temperature," Figure l. 

8 
30 

If global warming makes heat currently regarded as extreme more frequent and less 

surprising, then temperate cities will almost certainly make adaptations to function 

better in heat, much as people moving to cities in warmer climates have already done. 

But Mills assumes, implausibly, that an anomalous temperature in 2000 does the same 

harm as an equal, but by then less anomalous, temperature in 2100. 

The implausibility of the no-adaptation assumption is most obvious in the single-city 

mortality estimates it produces. EPA uses the model in Mills to estimate 12,000 annual 

heat deaths nationally in 2100. Much of the estimate stems from temperature increases 

in northern cities such as Pittsburgh, Detroit, and New York, with forecasted heatrelated mortality rates of 12.8, 9.2, and 8.9 per 100,000. Yet southern cities such as 

Phoenix, Houston, and New Orleans, which were already hotter in 2000 than northern 

cities are predicted to be in 2100, had mortality rates in 2000 of only 0.2 per 100,000 (see 

Figure 3). 

Mills explained that its main findings" explicitly exclude consideration of the possibility 

of there being an adaptive response over time to extreme temperatures." Still, Mills did 

provide an alternative analysis in which every city increases its extreme-heat threshold 

to that of present-day Dallas. With this alternative assumption, extreme-heat deaths fell 

by almost two-thirdsY EPA did not use this result. 

The Rhodium Assessment of Climate Costs 

In sharp contrast to EPA, Rhodium did not incorporate any cost estimate for air pollution 

into its analysis; temperature-related mortality thus plays a much larger role. Rhodium 

used two different studies to develop its cost estimate for temperature-related 

mortality. The first, which applied a historical mortality rate to future warming, pointed 

toward a very high cost estimate. The second focused specifically on adaptation and 

found that Americans have become well-adapted to extreme heat thanks to airconditioning. But Rhodium concluded anyway that climate change will cause tens of 

thousands of American deaths each year by century's end, leaving its discussion of 

future adaptation to a separate chapter that did not inform its top-line cost estimate. 

Temperature-Related Mortality: Olivier Deschenes and Michael Greenstone, 

"Climate Change, Mortality, and Adaptation: Evidence from Annual Fluctuations in 

Weather in the US," Applied Economics 3, no. 4 (Oct. 2011): 152-85. (DeschenesGreenstone) 

Deschenes-Greenstone underlies the Rhodium estimate of heat deaths due to warming. 

This study used an approach different from that of Mills; it grouped temperatures into 

10-degree-Fahrenheit buckets (70°-80°F, 80°-90°F, >90°F, etc.), counted the days with 

"Mills. Table 2. 

9 
31 

average temperatures at each level in each U.S. county in each year during 1968-2002, 

and compared these counts with total mortality rates in each county and year. The 

researchers found that an additional very cold (<30°F) or very hot (>90°F) day was 

associated with 0.5-1.0 additional deaths per 100,000 people.18 

Like Mills, Desclu?nes-Greenstone used climate models to estimate the temperature 

distribution at the end of the century. Their analysis found that climate change would 

reduce cold-related deaths somewhat but increase heat-related deaths much more. The 

average county saw one >90°F day each year during 1968-2002 but would see 44 such 

days each year during 2070-99.19 If the danger of experiencing a daily temperature 

within a given bucket did not change, the result of climate change would be 123,000 

more heat-related deaths and 59,000 fewer cold-related deaths each year, for a net 

impact of 63,000 additional deaths by 2100 (totals do not sum due to rounding).2o 

Unlike Mills, Desclu?nes-Greenstone focuses on an absolute threshold of >90°F for an 

extremely hot day, valid for all locations and times. Whereas Mills assumes that the 

ability to cope with high temperatures is location-specific and does not change with 

climate, Desc/u?nes-Greenstone assumes that certain temperatures are more costly 

everywhere and always. 

This approach has the virtue of allowing the researchers to consider more carefully the 

effects of climate adaptation because it can compare the future effects of global 

warming- for example, higher temperatures in northern cities- with conditions that 

exist today, such as temperatures in southern cities, and thereby assess whether cities in 

already-hot climates have already made adaptations. Technological advances may 

further improve adaptation to hot weather, but if a study can at least show that presentday adaptations do not improve hot cities' resilience, it can better justify high estimates 

of global warming's harms. 

Deschenes-Greenstone conducted several useful analyses to test for adaptation and found 

that absolute extreme heat worsened mortality in both hotter and colder climates. Yet 

their conclusion was undermined by a subsequent paper- which is also cited by 

Rhodium, and of which Deschenes and Greenstone themselves are coauthors. 

Temperature-Related Mortality: Alan Barreca et al., "Adapting to Climate Change: 

The Remarkable Decline in the US Temperature-Mortality Relationship over the 

Twentieth Century," Journal of Political Economy 124, no. 1 (Feb. 2016): 105-59. 

(Barreca) 

"Deschenes-Greenstone, Figure 2. 

19 Deschi!nes-Greenstone, Table 1. 

Deschenes-Greenstone, Table 5. 

10 
32 

Rhodium also cites Barreca21 for its calculation of extreme-temperature deaths. But rather 

than focus on projecting deaths from extreme temperature in the future, Barreca 

demonstrates the extraordinary reduction in such deaths in the past. Barreca found that 

the lethality of temperatures above 90°F fell by 80% from the first to the second half of 

the 20th century, thanks primarily to the adoption of residential air-conditioning. This 

trend continued even within the second half of the 20th century, with the mortality 

effect falling by half from the 1960-79 period to the 1980-2004 period. 22 

The researchers concluded that air-conditioning "has positioned the United States to be 

well adapted to the high-temperature-related mortality impacts of climate change." 

Applying the Deschenes-Greenstone estimate of 42.3 additional >90°F days by 2100, they 

estimated that climate change could cause roughly 60,000 additional deaths in 2100 at 

the 1960 level of air-conditioner adoption. But at the 2004level of air-conditioner 

adoption, "the null hypothesis that additional80°F-89°F and >90°F days would have no 

impact on mortality cannot be rejected." Or, to put this in plain English: additional 

extremely hot days could mean zero additional heat deaths. 

Eliminating the extreme-heat estimate from Deschenes-Greenstone, or even reducing it to 

the statistically insignificant estimate provided in Barreca, raises another possibility: 

climate change could reduce extreme-temperature mortality. Deschenes-Greenstone 

estimated nearly 60,000 cold-related deaths avoided (specifically, a 2.8% reduction in 

the mortality rate), offset by twice as large an increase in heat-related deaths (a 5.8% 

increase in the mortality rate).23 Yet with Barreca's lower estimate of heat-related costs 

(only a 1.5% increase in the mortality rate by the 1990-2004 period),24 the cold-related 

benefits would dominate. Climate change would reduce mortality by roughly 28,000 

lives annually (see Figure 4). 

" The version of Barreca cited here is the paper published in its final form after the release of Rhodium. Rhodium 

cites a substantively comparable version of the paper released in Jan. 2013 as an NBER working paper. 

2

::: Barreca, Figure 3. 

23 Deschi!nes-Greenstone presents its final mortality estimates for both increased heat-related deaths and decreased 

cold-related deaths in Table 5 (co Is. la-Ic). The net effect, an increase of 63,000 deaths, translates to a 3.0% 

increase in the mortality rate (col. 4). 

'" The suggestion to translate the Barreca estimate into terms comparable with the Deschiines-Greenstone estimate, 

as well as the technique for doing so. comes from one of the study's authors (e-mail correspondence with Olivier 

Deschenes, Dec. 20-22, 2017). The Barreca point estimate of 0.0021 for 1990-2004 is divided by six (to account 

for its two-month exposure window) and multiplied by 100 to give the percentage change in mortality per >90°F 

day, and then multiplied by 42.3 additional days to give a mortality increase equivalent to those discussed in 

Deschenes-Greenstone. The Rhodium authors use a similar process to convert the Barreca analysis into terms 

comparable with Deschi!nes-Greenstone; see Solomon Hsiang eta!., "Estimating Economic Damage from Climate 

Change in the United States," Science 356, no. 6345 (June 30, 2017): 1362-69, Supplemental Material, B.3. Given 

the differences in the Deschenes-Greenstone and Barreca methodologies and data sets, combining their outputs 

provides only a rough estimate. The approach is used here to illustrate the large effect of accounting just for alreadyexhibited adaptation; a full reanalysis would be required to produce a new point estimate. 

11 
33 

Rhodium acknowledges Barreca's finding but declines to employ it, instead combining 

the Deschenes-Greenstone and Barreca analyses in a way that projects a substantial 

increase in mortality, while deferring discussion of adaptation to a separate chapter and 

excluding it from the main cost estimates25 If Rhodium had used the extremetemperature mortality decrease that Barreca's adaptation finding implies, rather than 

forecasting a mortality increase, its total climate-cost estimate would fall by more than 

90%.26 

The Mongolian Century 

Temperature studies have progressed even beyond the framework described above, in 

which temperature is linkt>d to public health; the next frontier establishc'S an abstract 

link from temperature directly to economic growth, finding that warmer temperatures 

slow growth and so climate change could cause the global economy to stalL 

63; the discussion of adaptation on p. 166 estimates that the effect would remain negative but reduces 

by approximately hal f. 

Rhodium uses a value-per-life of$7.9 million to yield a midpoint cost estimate of$298 billion (seep. 108), 

implying roughly 37.000 total excess fatalities. If that were instead 28.000 fewer fatalities, the benefit would be 

$222 billion. This would change the total estimated cost in Rhodium from $557 billion to $36 billion ($586 billion to 

$38 billion in 2014$). 

12 
34 

Marshall Burke, Solomon Hsiang, 

and Edward Miguel, "Global 

Non-Linear Effect of Temperature 

on Economic Production," Nature 

527 (Nov. 2015): 235-39. (Burke) 

Burke compares year-to-year 

variations in a country's average 

temperature with variations in 

those same years in economic 

growth, controlling for associated 

changes in precipitation. It found 

that in countries with average 

temperatures below 13°C (55°F, 

about the average temperature of 

Baltimore, Milan, Beijing, or 

Wellington), growth was better in 

warm years; countries with higher 

average temperatures saw better 

growth in cool years. 

Burke theorizes that these shortterm fluctuations evinced a 

universal effect of temperature on 

growth: every country would see 

its maximum growth (determined 

by non-meteorological factors) at a 

13°C average temperature-a 

dynamic that will not change as the 

climate warms. To extrapolate from 

this relationship to a possible effect 

of climate change, Burke constructs 

a model in which every country's 

baseline temperature is its average 

during 1980-2010 and its baseline 

rate of economic growth is that 

forecasted by the Shared 

Socioeconomic Pathway (SSP, a 

widely used set of national GDP 

predictions that assumes a stable 

climate). The difference between 

the baseline temperature and 

temperature forecasted in some 

FIGURE 5: Projected GOP per Capita 

Following Climate Change 

Source: Burke; replication data available at https://web.stanford.edu/ 

-mburke/chmate/data htm!, ·'ProJected per capita GDP w1th chmate 

change (based on SSP5 and RCP8.5), 2010-2099." 

13 
35 

future year by a climate model provides the variation used to predict how growth in 

that year will vary from the SSP forecast. 

Let's say that a country's gradual warming raises its temperature from, for example, 

l5°C during 1980-2010, to 19°C in 2100. The model attempts to predict the effect on 

economic growth of a 15oc country experiencing a sudden 19°C year. But the economic 

performance of other countries with a present-day 19°C average is ignored. The shift in 

the country's own long-run average is ignored. 

Burke builds a modified set of SSP growth forecasts that accounts for the effect of 

warmer temperatures on every country in every year, and concludes that global 

warming will reduce per-capita gross world product (GWP) by 23% by 2100.27 

Projecting each location's response to a century-long temperature change on the basis of 

how locations reacted to small variations from their own averages in the past produces 

extremely dubious, if not preposterous, results. Burke's model takes normal economic 

growth in cold or hot countries as a sign not of economic specialization to a local 

climate but of often stupendous underlying growth potential that the local climate 

suppresses. 

Burke forecasts that Mongolia, whose per-capita income of $861 made it the 118th 

wealthiest country in 2010, will leap to seventh in 2100, with a per-capita income of 

$390,000-more than four times America's projected per-capita income of $90,000. 

Iceland achieves a per-capita income of $1.5 million, more than twice that of any other 

country besides Finland ($860,000), with annual economic growth above 5% and 

accelerating (see Figure 5). Canada's economy becomes the world's second-largest 

(behind only the U.S.), nearly seven times larger than China's. 

Conversely, Burke expects India to be the world's poorest country in 2100, with percapita income no higher than in 2030 and declining at almost 4% per year. It expects 

Israel, the country that made the desert bloom (and found itself with a water surplus 

during the intense drought that some consider a catalyst for Syria's civil war), to have a 

per-capita income in 2100 similar to its 2010 level and declining at more than 2% per 

year. 28 

Perhaps we should accept that a 23% loss in global per-capita income is plausible, 

however dramatic. But the model's country-specific outputs are irreconcilable with any 

plausible understanding of the determinants of economic growth and the potential 

For comparison, this estimate is an order of magnitude larger than the cost of 1%-4% of GDP estimated by the 

Obama administration in its "Social Cost of Carbon" analysis; see Figure IB in "Technical Support Document: 

Social Cost of Carbon for Regulatory Impact Analysis-Under Executive Order 12866," Interagency Working 

Group on Social Cost of Carbon, Feb. 2010. 

28 The authors provide country-specific model results at https:ilweb.stanford.edui-mburkeiclimateidata.html; see 

"Projected per capita GDP with climate change." 

14 
36 

course of economic development in the coming century. It might seem unfair to hold 

the study accountable for its least reasonable-seeming implications. Sure, the result~ for 

Iceland and Mongolia are wrong, but how much can that matter if they contribute little 

to the ultimate result? That is the wrong way to analyze the issue. Either one believes 

the premise that gradual shifts in temperature will drive economic growth on the basis 

of the curve that Burke derives, or one does not. If a statistical model makes easily 

falsifiable predictions, it is a bad model. 

To believe Burke, one must believe that a gradual rise in average temperature from oo 

(32°F) to soc (41°F) will turn Iceland and Mongolia into the leading economies of the 

21st century. The more plausible conclusion is that responses to large, gradual 

temperature changes are qualitatively unlike responses to small temperature 

fluctuations and that the entire enterprise in Burke, as in other adaptation-ignoring 

temperature studies, is flawed. 

Burke attempts to defend its assumption of no adaptation by showing that countries 

responded similarly to short-term temperature fluctuations before and after 1990, 

suggesting that no adaptation has occurred to date. It also finds that rich and poor 

countries responded similarly, suggesting that future wealth will not insulate countries 

from the effects of warming. But such findings say nothing about whether relationships 

identified for fractional-degree variations can be extrapolated to multiple degrees of 

warming, or how countries will respond to not just yearly fluctuations but changes in 

their own underlying baselines. 

Analyses like Burke will likely proliferate as researchers employ the same statistical 

techniques to generate large estimates of climate costs in a variety of contexts. For 

instance, earlier this year the Federal Reserve Bank of Richmond published a working 

paper that applied a similar methodology across U.S. states and found that climate 

change "could reduce U.S. economic growth by up to one-third over the next 

century." 29 

Such a finding is particularly bemusing because, as the authors acknowledge, the effect 

is largest in southern states-ones that have shown strong economic growth in recent 

years. Reporting on the findings, the Wall Street Journal observed, "their projections 

partly reflect the emergence of the southern U.S. as a major contributor to national 

economic growth. As overall temperatures rise, they'll hit that already warm zone 

hard." 30 Americans are moving in large numbers to the nation's warmest states, and 

"Riccardo Colacito et al., ''Temperature and Growth: A Panel Analysis of the United States," Federal Resen·e 

Bank of Richmond, Working Paper 18-09 (Mar. 2018), https://www.richmondfed.orgl-

/media/richmondfedorg/publ icationslresearchlworking papers/20 18/pdf/wp 18-09 .pdf. 

30 :VIichael S. Derby, "Climate Change May Deeply Wound Long-Term U.S. Growth, Richmond Fed Paper Finds," 

Wall Street Journal, May 2, 2018, https:ilblogs.wsj.comieconomics/2018105'02/climate-change-may-decply-woundlon g-term-u-s- growth-richmond~ fed-paper~ ti nds/. 

15 
37 

such states have exhibited especially robust economic performance, and somehow this 

compounds rather than refutes the concern that warm temperatures will lead 

unavoidably to economic stagnation. 

*** 

The flaws in these temperature studies do not mean that researchers should abandon 

estimates of the future costs of human-caused climate change. There is every reason for 

policymakers to continue to carefully consider legitimate cost estimates. So, too, 

researchers should continue to study the concrete effects of absolute changes in 

temperature and the nature of associated adaptation, as these findings help to identify 

which climate-related threats are the most severe and which adaptations may require 

changes in public policy. 

For example, continued research on sea-level changes and their implications for coastal 

development will be invaluable to responsible public policy in the decades to come. In 

Deschenes-Greenstone, the authors also study the effects of extreme temperatures on 

energy consumption and show that it (and the associated cost) rises significantly. Just 

because adaptation is desirable and likely to occur docs not make it free. 

Policymakers should work to ensure that society has the best possible information 

about likely effects of climate change and the right incentives to take that information 

into account. Specifically: 

• Continue to invest in climate science. If decision-makers from urban planners to 

farmers to coastal property owners are to make intelligent investments that build 

resilience and adapt to changes in climate, they will need the best possible forecasts 

of what those changes are likely to be. 

• Focus research directly on adaptation. Rather than accept the convenience of 

modeling a future without adaptation, emphasize the need for better understanding 

of adaptation pathways: Where will it occur naturally? Where will it occur but at a 

cost or only with better policy? In what situations might adaptation be insufficient 

and what contingency planning is required? Understanding the answers to those 

questions will highlight the costs that are most concerning and point toward the 

policy responses that might be most effective. 

• Ensure that decision-makers have the right incentives to account for climate change 

and its costs. If government insulates people from the costs of climate change, they 

will not have sufficient incentive to prepare for the costs or avoid them. Insurance 

products must accurately reflect risk; the price of water must reflect its supply and 

demand; urban planners must understand their own cities will be responsible for 

upgrading infrastructure that they build unwisely. 

16 
38 

Finally, the prospect of adaptation to climate change does not mean that mitigation is 

unimportant. Ultimately, greenhouse-gas emissions must decline if atmospheric 

concentrations are to stabilize. Low-cost, low-carbon energy technologies therefore 

remain vital and Congress should continue to fund research and development in this 

area. Congress should also review its use of subsidies, which today serves primarily to 

prop up wind and solar industries that have had decades to become competitive. 

Subsidies should be time-limited for a given technology, to keep innovation focused on 

solutions with the potential to out-compete fossil fuels in the market- especially in the 

developing world. 

Thank you again for the opportunity to appear before the Committee. I hope my 

testimony will be helpful to you as you assess economic analyses of, and consider 

appropriate federal responses to, climate change. 

17 
39 

Biography for Oren M. Cass 

Oren Cassis a senior fellow at the Manhattan Institute, where he focuses on energy, the 

environment, and antipoverty policy. He has written about climate change for 

publications including the Wall Street journal and Foreign Affairs, testified before House 

and Senate committees, briefed EPA and White House officials, spoken on campuses 

including MIT and the University of Texas, and appeared on national and international 

media including NPR and the BBC. An archive of his published work is available at 

http: I I www .orencass.com. 

In 2011-12, Cass was the domestic policy director for Mitt Romney's presidential 

campaign, where he shaped campaign policy and communication on issues from health 

care to energy to trade. Prior to joining the Manhattan Institute, Cass was a 

management consultant for Bain & Company in the firm's Boston and New Delhi 

offices, where he advised global companies across a range of industries on 

implementing growth strategies and performance-improvement programs. 

Cass holds a B.A. in political economy from Williams College and a J.D. from Harvard 

University, where he was an editor and the vice president of volume 125 of the Han•ard 

Law Review. 

18 
40 

[Slides] 
41 

Ml 
42 

Mongolia 

$100,000 Ml 
43 

Projected GOP per Capita Following Climate Change, 2010-2100 

Ml 
44 

Nature study of climate effect on growth 

Iceland and Finland become world's richest countries 

Canada's economy becomes seven times larger than China's 

India becomes the world's poorest country, shrinking at 4% per year 

Why might this not be true? 

Assumes "other things constant" when other things are not constant 

Assumes the response to small, random changes will be 

proportionally comparable to the response to large, gradual changes 

From Cas.t testimony before the House Committee on Science, Space, & Technology, Figure 5 

Ml 
45 
46 

assessment of climate effect on air quality 

Sp<ICC, & 
47 
48 

Chairman SMITH. Thank you, Mr. Cass, very much. 

Mr. Nordhaus. 

TESTIMONY OF MR. TED NORDHAUS, 

EXECUTIVE DIRECTOR, 

THE BREAKTHROUGH INSTITUTE 

Mr. NORDHAUS. Thank you for having me. It’s an honor to testify 

today. My name is Ted Nordhaus, and I am the Founder and Executive Director of the Breakthrough Institute. We’re an environment 

think tank located in Oakland, California. My think tank counts 

among its senior fellows a number of prominent climate scientists, 

technologists and social scientists, and my testimony today will 

draw upon this work to present a synthesis reflecting our assessment of the nature of climate risk, the uncertainties associated 

with action and inaction, and pragmatic steps that we might take 

today to address those risks. 

To begin, let me offer a few observations about climate science 

and climate risk. First, there is a well-established scientific consensus regarding atmospheric anthropogenic climate change: global 

temperatures are rising, and that rise has been caused in significant part by greenhouse gas emissions resulting from the combustion of fossil fuels. 

Second, and to the best of my knowledge, none of the witnesses 

called today for either the Majority or the Minority contest these 

well-established facts. 

Third, there are a range of uncertainties beyond this consensus 

about the sensitivity of the climate, the likelihood of specific climate impacts, the capacity for adaptation, and the costs of mitigation that provide ample justification for either far-reaching and immediate action or no action whatsoever. 

So how then should policymakers respond? Let me first address 

climate mitigation. Efforts to cap price and regulate greenhouse 

gas emissions have not much affected the trajectory of emissions 

anywhere to date. Under the best of circumstances, they have modestly tipped the scales toward lower carbon fuels and technologies. 

For this reason, the success of efforts to substantially drive 

decarbonization to levels that diverge from business-as-usual trajectories will depend primarily upon the availability of low-carbon 

technologies that are cheap and scalable. 

Presently, there are important short-term steps that federal policymakers can take to assure that America sees continuing declines 

in emissions. Most importantly among these are measures to keep 

America’s existing fleet of nuclear reactors online. We should also 

abandon misguided efforts to bail out the coal industry. 

Reducing atmospheric concentrations of greenhouse gases to levels sufficient to much alter the trajectory of climate change, however, will require a concerted and collaborative effort between the 

public and private sectors to develop a range of low-cost, low-carbon technologies for the 70 percent of emissions in the United 

States that emanate from outside of the power sector in the industrial, transportation, and agricultural sectors. These include advanced nuclear energy, carbon capture, advanced renewable and 

geothermal energy, and long-term energy store capabilities. 
49 

Even in the best case, however, decarbonization efforts alone are 

unlikely to limit global temperatures to 2 degrees Celsius. For this 

reason, climate adaptation will play a large role in determining 

how well human societies weather a change in climate. Infrastructure, sea walls and flood channels, modern housing and transportation networks, water and sewage systems and similar are what 

makes us resilient to extreme climate events. As such, there are 

few things more impactful that this Congress could do than to substantially increase national investment in infrastructure so too recommitting ourselves to ensuring a comprehensive federal response 

to all natural disasters for all of America’s citizens. 

So to summarize, climate change is real, its origins are primarily 

anthropogenic, and it presents risks that are difficult to quantify 

but could be catastrophic. For this reason, reasonable measures to 

mitigate and adapt to climate change are prudent, but climate policy debates have too often overemphasized mitigation at the expense of adaptation focused on decarbonization at the expense of 

other mitigation pathways, attempting to make dirty energy expensive rather than clean energy cheap, and focused heavily upon renewable-energy technologies to the exclusion of the broad sweep of 

low-carbon technologies that will likely be necessary to deeply 

decarbonize the global economy. 

So let me close finally with a call for moderation and humility 

on both sides of the aisle in place of bombast, alarmism, and denial 

in the face of irresolvable uncertainties that the issue presents 

America and the world will be better served by turning down the 

rhetoric and focusing on pragmatic measures to mitigate climate 

risk and adapt to risks that we won’t be able to avoid. 

Thank you very much for considering my testimony. 

[The prepared statement of Mr. Nordhaus follows:] 
50 

Written Testimony of 

Ted Nordhaus 

Founder and Executive Director, The Breakthrough Institute 

To the U.S. House of Representatives 

Committee on Science, Space, and Technology 

Hearing Entitled: 

U5ing Technology to Address Climate Change 

May 16,2018 
51 

It is an honor to testify before this committee. My name is Ted Nordhaus. I am the founder and executive 

director of the Breakthrough Institute. an environmental think tank located in Oakland. California. I have 

spent a fair portion of my career working with environmental NGOs and have researched and written 

about the issue of anthropogenic climate change for most of the last two decades. My think tank counts 

among its senior fellows prominent climate scientists, technologists and social scientists whose work has 

been widely cited in the relevant scholarly literatures, the IPCC. and other leading assessments of the 

risks associated with anthropogenic climate change. My testimony today will draw upon this work to 

present a synthesis that broadly reflects our assessment of the nature of climate risk, the uncertainties 

associated with both action and inaction. and the pragmatic steps that we might take today to address 

those risks. All of the perspectives I offer today will be broadly consistent with the assessment reports of 

the Intergovernmental Panel on Climate Change. 

Climate Science, Risk, and Uncertainty 

Let me begin with a few observations about climate science and climate risk: 

• First, there is a well established scientific consensus regarding anthropogenic climate change. 

That consensus is as follows- global temperatures, as measured at the surface level and the upper 

atmosphere have risen since the industrial revolution, that increa~e has been caused in significant 

part by anthropogenic forcings, notably the emissions of carbon dioxide from the burning of fossil 

fuels, and these anthropogenic greenhouse gas emissions are responsible for a significant share of 

anthropogenic forcing.'·' We also know that current C02 concentrations in the atmosphere are 

higher than the Earth has experienced for at least several hundred thousand years. with most of 

the increase occurring since the early 1950's. 

• Second, to the best of my knowledge. none of the witnesses called today. by either the majority or 

the minority, contest these well established facts. 

• Third, while the basic relationship between rising atmospheric concentrations of greenhot1se 

gases and global temperatures is well established. much else that might inform societal responses 

to climate change is not. including the extent of climate impacts that will result from rising global 

average temperatures, the costs to human societies of those impacts, and the cost of avoiding 

those impacts, where they can be avoided. To wit: 

The IPCC estimates a wide range of temperature outcomes associated with a doubling of 

atmospheric greenhouse gas concentrations from pre-industrial levels. In the most recent 

IPCC estimate, published in 2014, the estimated range of climate sensitivity was 1.5 to 

1 World Meteorological Organization. WJJO Statement on the State of' the Global Oimate in 201- (20 !8), p. 4. 

https:.'. librarv .\vmo.int/opac/doc num.php?explnum id-=:4453 2 Intergovernmental Panel on Climate Change. Climate Change 20/.1: Synthesis Report, Contribution ()/'Working 

Groups I, II and Ill to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (2015). 

http: /ar5-svr.ipccch ipcc ipccir~sourc~s-pdfiPCC SynthesisReportpdf 
52 

4.5 degrees celsius 3 In the prior assessment, the range was 2 to 4.5 C.' In the next 

assessment, scheduled for 2022. that estimate will probably shift again. 

The estimated relationship between global temperature increases and climate impacts at 

the local and regional scales at which they actually affect human societies is also 

uncertain. While it is likely that many climate related phenomena will intensiry, there is 

significant uncertainty as to by how much and over what timescales. This is true of most 

of the impacts that we worry most about, such as sea level rise, the intensity of 

land falling hurricanes, the duration of droughts. or incidence of floods. 

2 

We have limited foreknowledge as to how well human societies will adapt to climate 

impacts. This is due in part to uncertainties about the timescales and extent of climate 

impacts but arguably more so to uncertainties regarding the adaptability of human sociaL 

economic, and technological systems and the efficacy of the social and political 

institutions upon which they depend. Even a cursory review of the differential human and 

economic impacts associated with natural disasters of similar magnitude around the world 

should establish that the primary factor that mediates the relationship between natural 

disasters of various sorts and human impacts associated with those events are societal 

affluence, infrastructure, technology. and institutions. 

We have little certainty about the cost of climate mitigation. There have been many 

attempts to estimate the costs and benefits of mitigating climate change. But all are highly 

dependent upon assumed rates of technological change that are ultimately unknowable. 

Assume that technological change, with or without a helping hand from government, will 

be rapid, and the cost of deeply cutting greenhouse gas emissions will be very modest. 

Assume slower rates of technological change and costs will be prohibitive.' 

• Fourth. given all of the uncertainties delineated above, one can find ample justification within the 

consensus climate science to advocate either far reaching and immediate action to mitigate 

climate change or no action whatsoever. Neither position is inconsistent with what we know with 

certainty about climate risk. as established by the IPCC and other similar assessments. 

For all of these reasons, all discussions of climate change and what we ought to do about it revolve, 

unavoidably. around how we should orient ourselves toward uncertainty and risk. The dilemma that 

climate change ultimately presents us with is that we know that there is some significant possibility of 

catastrophic impacts AND that efforts to assess the appropriate response to those risks are confounded by 

cascading uncertainty and complexity in both the climate system and human social and technological 

3 Ibid., p. 43. 4 Intergovernmental Panel on Climate Change. Oimate Change 2007: Synthesis Report. Contribution ofirorking 

Groups I, If and lllto the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (2008), p. 

38. https:/iwww.ipcc.ch/pd['asscssmcnt~report/ar4/syr!ar4 svr full report pdf 

' See Edmonds, Jae, eta!. "Technology and the economics of climate change policy." Pew Center on Global 

Climate Change (2000). https: /ww\\.c2es.org.site.assetsiuploads/2000'09 technolog; economics.pdf 
53 

systems. In my remaining remarks, I will offer some thoughts about how then we might best navigate 

those uncertainties in order to take wise action in the coming years and decades to both prepare for and 

mitigate climate variability and change. 

Climate Mitigation and Uncertainty 

Given high present day uncertainty, in which the consequences of inaction are potentially catastrophic and 

the costs of mitigation are potentially large, how should policy makers respond" Faced with many 

competing national and global priorities, what level of resources should we invest today to mitigate 

impacts that will unfold over the course of decades and centuries and whose consequences are highly 

uncertain and may not be knowable within the timeframes in which policy-makers have to act'' 

Let me first dispense with a common objection to asking the question in this way. Many suggest that we 

are already facing the consequences of anthropogenic climate change, in the form of increasingly severe 

climate related natural disasters. 1 will not attempt to parse for you the evidence for and against this claim. 

Rather I will simply observe two things that can be found in the consensus view of both the IPCC and the 

US National Climate Assessment. 

• First, insofar as various studies have suggested that a climate signal can be found in recent 

disasters, the signal is relatively modest in the context of both known variability and projected 

future changes.6

·

7 To take a prominent recent example, one recent study estimated that rainfall 

associated with Hurricane Harvey was 15% greater than would otherwise have been the case due 

to anthropogenic climate change. To put that finding in context, Hurricane Harvey produced an 

extreme rainfall event that resulted in approximately 40" of rainfall in some locations. The 15% 

increase associated with global wam1ing according to this analysis would mean that Hurricane 

Harvey produced 40" of rainfall in these locations over three days rather than 34" I will let this 

committee draw its own conclusions as to whether 40" of rainfall rather than 34" of rainfall 

during this period materially contributed to the human and economic costs associated with this 

event. Suffice to say that the 34" of rainfall that the authors recognize was due to natural climate 

variability was an extreme event, outside of the observed climatic record for the region and would 

have brought extraordinary impacts without regard to additional anthropogenic forcings. 8 

• Second, even assuming that climate change is here today, intensifying natural disasters in some 

meaningful fashion. measures to mitigate emissions undertaken today will not appreciably 

influence the trajectory of either global temperatures or climate impacts for many decades to 

6 For example. this study suggests that warming will increase the area scorched by wildfires in Southern California: Jin, Yufang. 

et al.. "Identification oft\\0 distinct fire regimes in Southern California: implications for economic impact and future change,'' 

Environmental Research Letters 10, no. 9 (2015): 094005. bttp··'ijopsrknw inp oro-··micle: 10 !088 !?JS-9116: 10 9/0()_j005 7 NASA. The Impact of Climate Change on .Vatural Disasters. 

https:/ /carthobsen:alory .nasa.gov /Features/RisingC ost/rising_ costS. php 8 Geert Jan van Oldenborgh, et. al ... Attribution of extreme rainfall from Hurricane Haney," Environmental Research Letters 12 

no 12 (20 18) 01950 I http:iiiopscience. iop.org/article/1 0.1 088!1748-9326/aa9et2 
54 

come 9 To cite two prominent examples, when comparing low and high emissions scenarios 

produced by the lPCC, neither global average temperatures nor sea level rise see significant 

divergence for decades or perhaps until late in this century or early in the 22nd century. 10 

4 

For these reasons, climate change has been a relatively low priority on the public agenda and is likely to 

remain so, despite longstanding eftorts on the part of some to increase the salience of the issue. The 

asymmetry in timescales, between mitigation measures with present day costs and very long-term benefits 

is the reason that policies demanding high mitigation costs in the present to avoid unquantifiable risks far 

into the future have reliably failed politically, not only here in the United States'' but almost everywhere 

else."·" Explicit climate policies have not much affected the trajectory of emissions anywhere."·" That 

fact has been obfuscated by both advocates of climate action, who have exaggerated the scope of the 

policies that have been proposed and initiated and opponents, who have exaggerated the cost of those 

policies. 

To put a finer point on that observation, almost a decade after the US Senate failed to bring climate 

legislation to a vote, US carbon emissions today remain lower than the level that would have been 

mandated by the Waxman Markey legislation that passed this house in 2009. 16 The Waxman Markey 

proposal is not an isolated case. Similar efforts to cap emissions in Europe and California have established 

emissions caps that have proven with the benefit of hindsight to be consistently above the actual trajectory 

of observed emissions. For these reasons, it is difficult to take very seriously claims that these measures 

would have led to economic catastrophe. for the simple reason that they would have changed much less 

than either proponents or opponents claimed. 

As such, policies to cap, price, or regulate greenhouse gas emissions, where they are established and well 

conceived, will likely very modestly tip the scales toward lower carbon fuels and technologies. The 

success or failure of efforts to substantially drive decarbonization to levels that diverge significantly from 

business as usual trajectories will depend primarily upon the availability of! ow carbon technologies that 

are cheap and scalable." Reasonable pricing and regulatory strategies will have a role to play. but will be 

9 Moss. Richard I i,, ct al. "'fht: next generation of scenarios for climate change research and assessment." 1\'ature 463. no. 7282 

(20 10): fig Sb, pg 753. http·i/,·nnps cnnpp1'fS n,~tirjdo.ol K II-!BBBS9-X 1 YO'"'CH~ fT/n'llmdJ!5871 pd!' 

10 lPCC. The Global Climate !~{the 21st Cenlllry, 2001. http:>: ·,\\W\\.ipcc.ch·ip~.:cn:ports. tor \\f! I figspm-5.htm 11 Cenkr for Climate and Energy Solutions. Congress Climate Histm:v. hllps· \\\\\\ c,;;; or't' content rnngrfs:s-djnufl~~hisliH) 

12 Sengupta. Somini. lhe .\'ew rork Times . .. Why China Wants to Lead on Climate. but Clings to Coal (for "Now):' Nov l-l, 

2017. hUTK·\n\\\ n; tjiDt') rom '

1 01 7'1 1 14/rljnn!s'.rhin'H'!)'ll htm! 0 

1

, Neslen. Arthur. The Guardwn. ··secret UK push to \\Caken EU climate la\vs 'completely mad'". ~1ay 9. 2018. 

h!lpy ", \\\Y\\ tbt'!'!)'mlhn com !.'ll\ jroll!ll"!lf11()J8, Ul'l) Q9.sl'C(\'t-q\.:~pusb-ttHH"Jkti!J-l'!!-clim'!lt'+m s-rpmpkt~•l)-mod 

14 van Renssen, Sonja. "The inconvenient truth of failed climate policies, .. Sarure Climate Change 8 (2t)i 8). 355~358. 

15 Nordhaus. Ted and Jessica Lo\·ering. Breakthrough Institute. --noes Climate Policy Maner?" Nov 28. 2016. 

http· •:Jb,•brt'(lhthrmJnb org iS)!I\'S·{'!jnn!c-Poljn ·dqes-r! jm'Jh'-pql ir; -m'tlter 

Jr, rhe Waxman-Markey legislation required a 3%emission cut from 2005levcls by 2012 and a 17%cmission cut by 2020. This 

requires a l. 75~'0 redu<::tion per year from 2012 to 20 !6. so emissions should be at 10~·"0 below 2005 levels in 2016. As it 

happened. they \\ere at an 11~,'0 cut from 2005. Sec bt1p;r· grist pp•··Jrtirk 1()09-06~01-\\'l\mrm-marb,>> -hi!!-br,·')kdm\o and 

http:.;· \\\\\\" s'P'l O!)\ ·site:.;·prod!!rtjon ljfryl0/8-0 I .'docp@,Dl'i IO! 8 rhapkr ) t(t'J)(h_in gn:enhooS•'dfilS ~·mj..;sjqns pdf 

17 International Energy Agency. The Way fOnvard. 20!4. 

ht!p'>·'/\\\\\\ ku oru'ppb!jq!inn._.'frs•epuh!jratjqo>'publjqtinn Tlw_ \V'l) t(m\ ·ml pdf 
55 

limited both by political limits to the short term costs that can be imposed in pursuit of uncertain climate 

benefits and the cost and availability of low carbon substitutes. 

5 

That should not, however. be the end of the story with regard to policy efforts to mitigate climate change. 

There is much beyond pricing or regulating emissions that policymakers can do to move us more rapidly 

in a cost-effective manner toward a lower carbon economy. Despite the industty's recent struggles, almost 

twenty percent of America's electricity still comes from nuclear energy," a technology that was 

developed and commercialized through a range of federal policies and initiatives. America's world 

leading decline in emissions over the last decade has been achieved in large part due to the shale gas 

rcvolution. 19 which was made possible by decades of federal research. development, and demonstration 

efforts in partnership with the private sector." Decades of policy support for wind and solar energy have 

begun to pay off as well. with costs falling rapidly and electricity penetration rising." 

There is much that federal policy makers can do to support continuing reductions in US emissions in the 

short term. 

• This includes. most especially, keeping America's nuclear power plants open. Continuing plant 

closures threaten to undo much of the progress that America has made over the last decade due to 

both the transition from coal to gas and growing renewable energy shares. Whether through state 

and federal clean energy standards. intervention at the Federal Energy Regulatory Commission. 

or other measures. it is imperative that we keep America's zero carbon nuclear power plants 

operating. 

• Natural gas. meanwhile, continues to displace coal-fired electricity generation."·"" Efforts to 

resuscitate the coal industry are misguided and doomed to fail due to the realities of energy 

economics. Coal is being displaced by a cleaner, cheaper, and more useful fuel due to market 

forces and we should let that transition run its course." 

• Finally. we should put claims that wind and solar energy are now economically competitive with 

fossil fuels to the test. I have long supported generous federal support for those technologies but it 

is clearly time to ramp those subsidies down and let existing wind and solar technologies stand on 

tx U.S. Energy InfOrmation Administration. C.S 1Vucfear Industry, May L 2018. 

http..;·/iw\\W da gmienng;nplajnni'jndt•y php')p·u,w::;:::;mwk'lf lJSt' 

19 rvtidd!eton. RichardS .. et al. "The shale gas revolution: Barriers. sustainability. and emerging opportuni[ics." Applied Energr 

199 {20 17): 88~95. h!!p;:,· \\\\\\ c;ri.·ncrdit¢bl rpm sris'!J('s' 'lftjr)s•·piJISO)OQ )b I I)! 7)0-l ~I) 

20 Jenkins. Jesse. et al. Breokthrough lnstitwe. ··us GoYt:rnrnent History in Shale Gas Fracking History: An Overview." March 2. 

1:012. hllJK thebrcobthroqk'b orv,arcbj\r 'ilnk <J"lS fnrkjiW hj.;:tof} -md 

"

1 Cusick. DanieL Scientific American ''Wind and Solar nrm-vth Outpace Gas:· Jan 12. 2017. 

hllp:.;·//\\\\ \\ srkntill("j!J)j>rfcan CQQ)!'artirk'\\ !Od~w~hwlar~gm\\jh~Q\J!p;)q'•gas I 

12 Nuccite!IL Daniel. The Guardian. "The war on coat is over. Coal lost." Oct 16.2017. 

hllpy >\\\\\ tlwomrdj·m rom 'I'm ironnwnt rlim'J1s'-const'nsus-97~ps:r-cenl 1()! 7.ocr. I!J<tbc-\\ 'l(-nn-cmHs-mer~>wll-lost 

23 Goft: MichaeL Breakthrough Institute . .. Hov. ~atural Gas and Wind Decarbonize the Grid," July 13.2017. 

h!!p:, · ;r!hrhn•·JktlmHJ"h oro:jndn pbp: jssJa's·deqrhonjc!l ion hp»-O'ltJ!['ll-u•Js-·ulih\ jnd-dt•prbonjzP-tl){'-grjd 

24 Nordhaus. Ted, eta!. Breakthrough institute . .. -:"Jatural Gas Overv.helmingl: Replaces Coal," Dec 14, 2015. 

h!!p:, · <'it!whrro ktbn 11 1g h 1 1ro/jndex php1isst ts•s/natma 1-g 'h/o;JI! l['l 1-aas-m en\ lw I m j no 1)- -rl'p!an'>-Cil'l I 

25 McBride. Jam~son. Breakthrough Institute . .. Clean Energ: Advocates Should Oppose Subsidizing CoaL" Dec 7. 2017. 

http::;·· Jlll'hrL·Jktbm!!<>h nro:jwks php \njrr-:. rksm-rnn'-') -'Bhnrats·,:;-:;hp!lld-opp!lSC-S!!bsidjtjno-coal 
56 

their own so that they might survive the market test necessary to penetrate even further into the 

economy. 

6 

There will clearly be limits, however, to how far we are going to get with present low carbon technology. 

Even if wind and solar energy gets much cheaper, their variable nature means that without new and very 

low cost technologies capable of storing vast quantities of electricity for weeks and months, not days at a 

time, there will be both technical and economic limitations to how much electricity we can count on26 

from those sources. N uclcar energy still represents our largest source of zero carbon power," but large 

conventional nuclear power plants are enormous public works projects that like many other similar 

endeavors have proven extremely costly to build." Any nuclear renaissance worth speaking of in the 

United States will require a new generation of nuclear reactors that are much smaller and can be 

manufactured offsite. And because natural gas still has significant carbon intensity, the environmental 

benefits of the coal to gas transition are ultimately limited.'" If natural gas is to fulfill its promise as a 

sustainable fossil fuel, we will need to develop and deploy at scale technologies of carbon capture and 

storage. 

Moreover, roughly 70% of US carbon emissions arise from outside the power sector.'0 We have made 

some progress in the transportation sector. due to fuel efficiency and the commercialization of hybrid 

electric engines. We are just beginning to see the entry of electric vehicles into the light duty 

transportation market. But both hybrid and fully electric vehicles still require significant cost premiums 

and. for the latter. a huge build-out of charging infrastructure. As a result. it will likely be decades before 

we see the end of the internal combustion engine, if at all. 

Outside of light duty transportation, the path to decarbonization is harder still. We have few viable low 

carbon substitutes for industrial heat and power, cement production, fertilizer, and heavy transportation. 

Carbon capture technologies could offer us a way to avoid emissions from fossil energy uses that we can't 

displace, but the path to economically viable carbon capture technologies for many applications is far 

from clear as well. 

All of these new and improved technologies will require a significant and sustained commitment to 

mission-driven innovation in collaborative fashion between the public and private sectors to offer viable 

alternatives to fossil fuels in the United States and globally. and most are likely decades away from 

commercialization. 

26 Beaudin, Marc. eta!. "Energy storage for mitigating the variability of renewable electricity sources: An updated re\·icw." 

Energyfor sustainable dn·e/opment 14, no . .f (2010}: 302-314. 27 Center for Climate and Energy Solutions. Climate Solutions: The Role ofXuclear PoH'er, April20l4. 

hllp'i· · '' \\'' r7Ps orn sjtc 'JSSets qplo·Hh '1() I 4 04 'rljm•J!t•-sohnjons-mk-mwk·Jr-po\\er pdf 

28 S~ napse Energy Economics. JVuclear Pmrer Plant Construction Costs, July 2008. 

b1tps·/·\\\\\\ sxnopsc-t'JJ\'[0) cpm/siks 1d;;tilt!lt1files 1S) nnrs··Papn JQ(}8~07 0 SJ!Ckor~P!nnt-( 'nnstwctjqn-Cnsl;) c\001) 0 pdf 

1

'

1 li .S. Energy Information Administration. HO\\' much carbon dioxide is produced when different fuels are burned? 

http:;··.\'\\" s:j-1 om. tpol)'foqs.'hq php')jd·=)'::&t= II 

30 EPA. Sources of Greenhouse Gas Emissions. https \\\\\\.~pa.oo\ O'ho~missi~ms.'soun.:cs-on.:!..'nhtHISt'-lla.:>-~missions 
57 

For this reason. the prospects for stabilizing atmospheric concentrations of greenhouse gases to levels 

consistent with limiting global warming to two degrees or less, the long-standing international target for 

climate stabilization, are extremely unlikely. Fossil ti.Jels still constitute over 80% of primary energy 

consumption globally and in the United States and that share has hardly fallen since the oil shocks of the 

1970's." Most IPCC scenarios for stabilizing temperatures at 2 degrees celsius assume that the world 

removes enormous quantities of carbon from the atmosphere in the latter half of this century. something 

that we have no idea how to do at the scale that would be required 32 

7 

The likelihood. however. that in the next several decades atmospheric concentrations of greenhouse gases 

will rise to levels inconsistent with limiting global temperature increase to less than two degrees. should 

not be taken as reason to abandon mitigation efforts. The two degree target represents a political 

convention. not a particularly well established biophysical boundary33 There is no particularly strong 

empirical basis for the view that catastrophic climate impacts might be avoided should we succeed at 

stabilizing temperature below the two degree threshold nor that catastrophe is assured should we fail. 

Irrespective of the international two degree convention, the basic relationship between emissions and 

climate risk remains. Lower emissions bring lower long-term climate risk-" That includes both impacts 

whose relationships to global temperatures are relatively linear and climate tipping points that could bring 

non-linear impacts. Lower emissions bring lower risk of crossing tipping points that may or may not exist 

and whose precise location with regard to global temperatures is highly uncertain. 

That basic relationship. between emissions and risk. is true today, when we have not yet surpassed two 

degrees of warming, and it will still be true several decades hence, when we have. All else being equal, 

cost-e!Tective mitigation brings lower climate risk even recognizing that global mitigation efforts are 

highly unlikely to result in stabilization of atmospheric concentration of greenhouse gases at levels 

consistent with limiting the temperature increase to two degrees. Developing and deploying cost-effective 

technologies that reduce carbon emissions can also bring a range of further benefits. including improved 

public health from cleaner energy. lower energy costs. global competitiveness, and access to global export 

markets. 

Adaptation for A Hotter World 

Given the likely trajectory of emissions and global temperature. even presupposing much more 

far-reaching mitigation success than the global community has thus far made, climate adaptation will play 

a large role in determining how well human societies weather a changing climate over the coming 

decades and centuries. Adaptation in the context of anthropogenic climate change is. in most of its 

particulars, not much different than the steps that human societies reliably undet1ake as they modernize 

and develop. As societies become wealthier, their populations have become more resilient to climate 

31 The World Bank, Fossil fue! energy consumption. 20 I..J. https:/iJata.worldhank.oro-/indicator/ECi.t :sLC0:\!1\I.H).ZS 

'

2 P¢ters. Glen P .. and Oli\·er Gedcn. "Catalys.ing a political shitt from low to negative carbon." :Vature Climate Change 7, no. 9 

(2017): 619. 33 Jaeger. Carlo C.. and Julia Jaegt:r. "Tlu~e views of two degrees." Regional Environmental Change I L no. l (201 l): 15-26. 

'"' Majkut, Joseph. Redudng Emission, Reducing Climate Risk. March 2016. 

bttp...:·/:njsbqntiJI't'!lts•r nroih!oo "redJ!Cjno-emi:l:>iou.;;~r-:dJwjno--dnnate-rjsks: 
58 

variability and extreme weather. 35·"' Modern, affluent societies are able to deploy infrastructure and 

technology to keep the weather at bay - sea walls and flood channels, modern housing and transportation 

networks, water and sewage systems. air conditioning to offer a few examples. Those measures are 

further amplified by modern institutions and practices- weather forecasts, emergency response systems. 

public health measures and the like.'-

8 

Citizens of wealthy economies are also much more mobile and integrated into national and global 

networks of trade and commerce that make them much less vulnerable to local and regional climatic 

disruptions. There has been a heavy focus among many concerned about climate adaptation upon 

increasing local resilience, mostly focused on localized food and energy production in the event that 

connections to regional and national networks are lost And while there is clearly some utility in having 

backup power generation and water resources available in the immediate aftermath of a natural disaster. it 

is precisely our integration into global and national networks that make developed world populations so 

resilient to climate variability and disruption. The ability, for instance, to purchase food produced halfway 

across the country, or the world, in the midst of a drought, makes us much more resilient to that sort of 

climate variability. especially if it is sustained, as may become increasingly frequent 

Wealthy societies are able to abandon areas that become indefensible in the face of a changing climate 

and citizens of those societies are able to leave in search of better climates. Over the last fifty years, about 

20% of the United States population has shifted from the northeast and midwest to the southeast and 

southwest. much of that due to voluntarily migration in search of better climates." Those climates were 

not always so. Much of the southeast was historically malarial wetlands. Much of the southwest was 

inhospitable desert. Infrastructure and technologies have transformed those regions to desirable places to 

live. Climate change over the course of the next century may occasion migrations and transformations of 

similar scale. Good infrastructure and good institutions will greatly minimize the disruption and 

dislocation that could result from those shifts. 

So the first critical thing to understand about climate adaptation is that we in the developed world are 

already very well adapted to climate change and, in many cases, also to the variability and change that we 

might experience in coming decades. The greatest risks to our continuing ability to be so will be our 

failure to invest in infrastructure and to tend to the institutions that we depend on to keep us safe. 

Hurricane Katrina was an extreme but otherwise ordinary hurricane that we should expect to see every so 

otten along the Gulf Coast But decades of neglected infrastructure exacerbated by neglect and 

incompetence on the part of state and federal emergency response officials turned it into a national 

tragedy. 39 We are watching a similar tragedy unfold in Puerto Rico today. 

'

5 The World Bank, Turn Dow11the Heat, November 2012. 

bttp·.idommrnl) \\orldbanb oro 'emoted ,'ni8b"i"q IJ6S 149107611 ipdfiSowh.:JjFjkN·JmrO pdf 36 Fankhauser. Samuel. and Thomas KJ ~kDermott. "Understanding the adaptation deficit: \\hy are poor countries more 

vulnerable to climate events than rich countries?" Global Environmental Change 27 (2014): 9·18. 37 Noh~~!, LR .. et al. "Adaptation needs and options.'' In Climate Change 201.1.- Impacts, Adaptation, and Vulnerability. Part A: 

Global and Sectoral Aspects. Contribution<~( Working Group II to the Fifth Assessment Report o.fthe Intergovernmental Panel 

on Climate Change (2014) pp. 833-868. 3

!1. Frey, William, CS. grov . .!/h rate hits neH' low as migration to the Sun Belt continues, December 2016. 

https· '·'\\ \)\\ hroob jngs s;du-'blog-'the~a\'!.'lll!l.' '){) 16' ]1, 1 ~:u.s~orowlh~wft>.bjt:.;-IW\\·Io\\ -'JS-m jpratjon.Jo-tbe-snn.hdH·ontjmws 

39 Griffis. F. H. "Engineering failures exposed by Hurricane Katrina." Technology in Societ)· 29. no. 2 (2007): 189~ 195. 
59 

9 

Neither of these disasters can be laid at the feet of a rapidly changing climate. They are what we should 

expect in these regions and storms like those will, with certainty, occur again. Both disasters resulted from 

neglecting infrastructure, institutions, and the people who depend upon them. Even as it may continue to 

debate the merits of various climate mitigation measures. this Congress would substantially improve our 

long term prospects of adapting to climate change well if it agreed on a bipartisan basis to dramatically 

raise national investment in infrastructure and recommitted itself to ensuring a comprehensive federal 

response to all natural disasters for all of America's citizens. 

What is true in the rich world is even more so in developing countries. Modem infrastructure is what 

makes us resilient to climate variability and natural disasters. The faster developing countries are able to 

build that infrastructure. the more resilient they will be to a changing climate. It is here that difficult 

tradeoff.s between mitigation and adaptation are most problematic. Institutions can make a big difference 

and they can't really be disentangled from infrastructure. But the existence of hard infrastructure- steel 

and cement for housing, roads, hospitals, water and sewage systems- is the critical physical fact that 

makes societies more resilient to climatic extremes. Building that infrastructure is energy intensive and. as 

noted above, there are few viable low carbon alternatives presently available for many of the activities 

entailed in doing so. 

This presents a quandary of sorts. Fossil fueled development globally increases climate risk. But it also 

makes developing world populations much more resilient to that risk. Infrastructure is an obvious 

example. But the basic dynamic is broadly applicable. Social and economic modernization is an energy 

intensive business and while there are some cases where that energy can be produced without carbon 

emissions. global development is, for at least the next several decades, almost certain to remain an 

enterprise that is primarily powered by fossil fuels. 

There have been a number efforts through US funded global development institutions to establish 

sweeping restrictions on fossil fuel development, including at the World Bank, USAID, and the Overseas 

Private Development Corporation. While there may be some limited cases where this has been wise. 

trading off present day development tor the poorest people in the world for uncertain climate mitigation 

benellts many decades hence is indefensible in my view. Development today makes poor populations 

much more resilient to both present day climate extremes and long term climate change. The United 

States should not stand in the way of poor nations around the world availing themselves of the same 

development and infrastructure that has made us so much more resilient to climate change, even if that 

development entails greater fossil fuel consumption. 

Conclusion 

[n closing, I would like to suggest that America and the world would be better served by a bit more 

moderation in this body from both sides of the aisle. Climate change is real, its origins are primarily 

anthropogenic, and it presents real risks to human societies. Whether those risks will prove catastrophic, 

much less apocalyptic, simply cannot be foretold. 
60 

10 

Lest anything I have said lead this committee to conclude that climate change docs not constitute a 

significant threat to the American people, let me return to the question of uncertainty. An increasingly 

wealthy world faced with impacts that unfold gradually, over century timescales, should be able to adapt 

to them reasonably well. But there are unquantifiable risks of significant impacts that could unfold over 

decadaL not century timescales, and these are the sorts of impacts that even wealthy nations may not 

weather well. These risks, I will note, exist even if one is more inclined towards the low end of estimates 

of climate sensitivity. I am skeptical of calls to stabilize temperature at 1.5 degrees celsius and 

atmospheric concentrations of carbon at 350ppm.40 But those demands are based in part upon studies of 

various climate impacts and tipping points that, while far from convincing in my view. cannot be 

dismissed out of hand either. 

If the impacts associated with rising emissions unfold slowly and in linear fashion, then there is good 

reason to think that the United States and much of the rest of the world will manage those changes 

relatively well. The gradual migration of large populations from the Rust Belt to the Sun Belt took place 

over many decades and brought faster economic growth and improvements to overall well being. A large 

and sudden migration necessitated by rapidly unfolding climate impacts would not be so benign and 

would almost certainly bring very significant costs and disruption. 

There are also impottant potential interactive effects between climate change and social and political 

institutions that should not be dismissed. I am skeptical of various claims that assert a causal link between 

civil strife in various parts of the world and climate change. But it is certainly plausible to suggest that 

worsening climate impacts in various parts of the nation and the world, in complex interactions with 

various other dynamics, might undermine the institutional capacities that allow us to establish and 

maintain resilience. 

It is for this reason that continuing decarbonization efforts should remain an important priority, nationally 

and globally- with an urgent effort to push the cost and technical envelope for low carbon technology in 

order to hasten and reduce the costs of mitigation. It is also for this reason that we should explore other 

means to mitigate climate impacts beyond decarbonization, including carbon removal and 

geoengineering. Neither of these latter strategies represents an existing mitigation pathway today. But 

clearly, a reasonable assessment of the many uncertain futures that climate change could bring suggests 

that further research into these mitigation strategies is wise, not out of any certainty that they will be 

necessary but in recognition of the possibility that they might be needed. 

The absence of much serious discussion among policy-makers regarding carbon removal and 

gee-engineering point to a broader challenge. Climate policy discussions have been overly dominated by 

a heavy focus on decarbonization and discussions of decarbonization have been further constrained by an 

overly narrow focus upon efforts to regulate or price emissions and promote renewable energy. Those 

measures will certainly have a role to play moving forward but mitigation efforts will need to take a range 

of other steps much more seriously, including the coal to gas transition, advanced nuclear energy, 

40 Nordhaus, T cd. Foreign Affairs. "The Truth About the Two-Degree Target," March 2018. 

h!tps 1 '\\\\\\ tjueign·1fh!t;; cmn.·artjch;:.; norld/2018~0~~07 twtb.)hPI!f-t\\p~dcors•t•~li]ros•t 
61 

ll 

advanced renewable energy technologies. carbon capture and removal, electrification, and 

geoengineering. Climate policy discussions will also be much better served to remember that adaptation 

to climate change is, in most cases, not appreciably different than the myriad measures we have already 

taken to make us more resilient to climate variability and extremes already. A broadening of the sorts of 

policies. technologies, and measures that we include in climate policy discussions might also bring the not 

inconsiderable benefit of substantially broadening the political coalition suppm1ing climate action. 

However we respond, climate change will under the best of circumstances be a chronic condition faced by 

human societies for many centuries to come. Accepting that reality, in non-apocalyptic terms, will allow 

us to mitigate. plan for, and adapt to that future most effectively and at the least cost to both present and 

future generations. 

Thank you for considering my testimony. 
62 

Chairman SMITH. Thank you, Mr. Nordhaus. 

And Dr. Duffy. 

TESTIMONY OF DR. PHIL DUFFY, 

PRESIDENT AND EXECUTIVE DIRECTOR, 

WOODS HOLE RESEARCH CENTER 

Dr. DUFFY. Thank you, Mr. Chairman, Ranking Member Johnson, and Members of the Committee for the opportunity to appear 

here today. 

In my remarks this morning, I’m going to discuss the threat of 

global climate change but I do want to mention that I started my 

career in the Nuclear Weapons Complex at Lawrence Livermore 

National Laboratory, where I worked on nuclear-weapons testing 

and also on protecting the United States against the threat of nuclear ballistic missile attack. 

The threat that I’ve devoted the bulk of my career to, global climate change, I believe to be equally important. In my remarks this 

morning, I’m going to focus on some of the science of climate 

change and on the role of technologies in addressing it, and on the 

leadership and business opportunities that I believe this presents. 

The fact of global warming should be beyond question, so I won’t 

review here the mountain of observational evidence we have documenting warming of the planet and associated related changes 

such as increases in some form of extreme weather, thawing permafrost, and so on. 

The scientific consensus on human causation of climate change 

is as strong as the consensus on the fact of climate change itself, 

and I would like to quote from volume one of the fourth National 

Climate Assessment. This was released last November by the 

Trump Administration, and I quote: ‘‘This assessment concludes 

that it is extremely likely that human activities, especially emissions of greenhouse gases, are the dominant cause of the observed 

warming since the mid-20th century. There’s no convincing alternative explanation.’’ 

Governments also recognize human causation of climate change. 

As of now, every country in the world is a party to the Paris Climate Agreement. It makes no sense to be part of that agreement 

if you do not recognize not only the seriousness of the climate 

threat but the human role in causing that threat. 

Turning to technologies, we need technologies for mitigation of 

climate change, that is, preventing unacceptable climate change; 

for adaptation, that is, coping with unpreventable climate change; 

and we also need technology for measuring emissions of greenhouse 

gases. And my topline message this morning is that I hope our government will lead the development of these technologies not only 

because we need them but because once again this presents an opportunity for the U.S. research and business communities, and 

that’s an opportunity that if we don’t take advantage of, someone 

else will. 

For mitigation, my first recommendation would be to accelerate 

deployment of the technologies we have now, namely wind and 

solar. We also do of course need new technologies for energy generation for energy storage and energy transmission. And because 

we’ve delayed so long in implementing effective climate policies, we 
63 

now also need technologies to remove carbon dioxide from the atmosphere. And while we’re developing those technologies, we do 

have an important opportunity to implement land management 

practices which can pull a significant quantity of carbon dioxide out 

of the atmosphere, and those same land management practices like 

reforestation and restoring wetlands and so on also have important 

benefits for climate adaptation. 

Turning now to adaptation, we need a host of technologies for 

coping with the range of climate impacts. These include extreme 

weather, infectious disease, water contamination, water scarcity, 

food scarcity, and so on. The good news is that adaptation measures are generally cost-effective because in fact we’re generally 

underadapted and underprepared for the climate we have today, 

and if you doubt that, you need look no farther than Houston or 

Puerto Rico. 

Finally, I want to mention that we do need technologies to better 

measure greenhouse gas emissions. They say that you can’t control 

what you can’t measure, and any effective climate policy needs reliable techniques for measuring greenhouse gas emissions. 

So in closing, I’d like to encourage you to support American efforts to do the research and to develop the technologies that we 

need to tackle climate change. Addressing this threat is an opportunity for American leadership that I would hate to see us miss. 

Thank you for the opportunity to appear here this morning. 

[The prepared statement of Dr. Duffy follows:] 
64 

TEO NOROHAUS 

EXECUTIVE DIRECTOR 

Ted Nordhaus is a leading global thinker on energy, environment, climate, human 

development, and politics. He is the co-founder and executive director of the 

Breakthrough Institute and a co-author of "An Ecomodernist Manifesto." 

Over the last decade, he has helped lead a paradigm shift in climate, energy, and 

environmental policy. He was among the first to emphasize the imperative to "make 

clean energy cheap" in explained why efforts to 

establish legally binding international limits on greenhouse gas emissions would fail in 

the and made the case for nuclear energy as a 

critical global warming solution in the has written on the limits to 

and the need to in the New York Times, 

and has argued for the importance of intensifying agricultural production in order to 

spare land for forests and biodiversity in and the 

His 2007 book co-authored with Michael Shellenberger, was called 

"prescient" by and "the best thing to happen to environmentalism since Rachel 

Carson's Silent Spring" by (An excerpt in can be read here.) 

Their 2004 essay, "The Death of Environmentalism," was featured on the front page of 

the Sunday sparked a national debate, and inspired a generation of 

young environmentalists. 

Over the years, Nordhaus been profiled in the ''·""'"--~--''"-"'-' 

the E'!.'lfiQLLC::L':'f]IIJ:-:J.\: -~-'--"~"-'-·'="''·'"'"·'-'•' 

award. 

Nordhaus is executive editor of the which called 

"among the most complete efforts to provide a fresh answer" to the question of how to 

modernize liberal thought, and the called "The most promising effort at 

self-criticism by our liberal cousins in a long time." 
65 

Testimony of Dr. Philip B. Duffy 

U.S. House of Representatives Committee on Science, Space, and Technology 

Hearing on "Using Technology to Address Climate Change" 

May 16,2018 

Thank you Mr. Chairman, ranking member Johnson, and members of the committee for the 

opportunity to appear today. 

I am Philip Duffy, President and Executive Director of the Woods Hole Research Center. 

I have a doctoral degree in applied physics from Stanford, and began my career in the nuclear 

weapons complex at Lawrence Livermore National Laboratory. There I worked in the group 

that tested nuclear weapons at the Nevada Test Site, and also on strategic defenses against 

ballistic missile attack. 

The bulk of my career, however, has been devoted to a different and equally important threat, 

global climate change. For more than 20 years I studied climate change as a research scientist; 

I spent 3 years at a climate change communications organization, Climate Central (ending as 

their Chief Scientist); and between 2011 and 2015 worked on designing and implementing climate policies in the Obama White House. 

Consensus on giQQ§l warmiiJgjl._nd its human causation 

Today I will discuss the need for technologies for mitigating (preventing) unacceptable climate 

change, for adapting to changes we can't prevent, and for monitoring greenhouse gas emissions. A top-line message is that development and deployment of these technologies present 

an important opportunity for US researchers and businesses. I will also mention the positive 

economic benefits that can be obtained from well-designed climate policies. 

I'll start, however, by reviewing some of what we know about climate change and its human 

causation. 

The fact of global warming is beyond question. An enormous quantity of observational evidence clearly demonstrates warming of the atmosphere and ocean, melting of land and sea 

ice, sea level rise, reductions in snow cover, and a host of other consequences of warming, 

such as increases in extreme precipitation and other forms of extreme weather. 

The scientific consensus on human causation of observed warming is as strong as on the fact 

of warming itself. The latest scientific estimate presented by the Intergovernmental Panel on 

Climate Change (IPCC) is that humans are responsible for essentially all of the warming observed over the past 60 or so years. This is supported by the latest US National Climate Assessment, the first volume of which was released by the Trump administration in November 

2017. This Assessment found that " ... based on extensive evidence, ... it is extremely likely 

that human activities, especially emissions of greenhouse gases, are the dominant cause 

of the observed warming since the mid-20th century. For the warming over the last century, 

there is no convincing alternative explanation supported by the extent of the observational evidence." 
66 

It is important to note that world governments also share the consensus on human causation 

of climate change. IPCC summary statements, including those on attribution of warming to 

human activities, are not only produced and reviewed by hundreds of scientists from nations 

around the world, they are approved by governments as well. In fact, every sentence in the 

IPCC summary documents, again including those on human causation of climate change', 

were approved unanimously by national representatives. Furthermore, every country in the 

world has signed onto the Paris climate agreement, which commits them to taking steps to reduce their contributions to climate change. There would be no reason to do that if they did not 

recognize both the importance of the climate threat and the human role in causing it. 

Let me add that any alternative explanation for recent climate change (other than human 

greenhouse gas emissions) faces two challenges: first, it must provide an alternative physical 

mechanism for observed warming, and second, it must explain why the observed increase in 

atmospheric greenhouse gases is not responsible for observed warming. This would require 

overturning the scientific understanding of the greenhouse effect, that has been developed 

over the course of nearly two centuries and that, in its current form, explains observational data 

with striking fidelity. 

Finally on this subject, while we understand more than enough about climate science to know 

that we need to urgently implement strong climate policies, there are important policy-relevant 

issues that need to be better understood. Chief among these may be "tipping points," climate 

processes which would be impossible to stop after they have been set in motion, and which 

would have severe societal consequences. These are discussed further below. I encourage this 

Congress to support increased funding for research into these questions and others that the 

Congress may feel need to be better understood. In particular, if despite the overwhelming evidence supporting human causation of climate change, the Congress feels that the human role 

in climate change needs to be better understood and debated, then I encourage them to support increased research funding, in order to ensure that that debate is as well-informed as possible. 

lipping points and the urgency of ad_c;!rt'1§l!ing_c:;limate change 

The oft-cited urgency of addressing climate change has a strong basis in science. Part of this 

basis is the long lifetime of C02 in the atmosphere. This implies that even if human greenhouse 

gas emissions were to instantly and completely cease, the elevated global temperature and its 

many climatic and human consequences would not materially improve for centuries. Sea level 

would continue to rise for a thousand years. The policy ramifications of this are fundamental: 

"wait and see" is a bad climate policy, because if the effects of climate change become intolerable it will be too late to avoid being forced to cope with them for centuries, if not longer. 

The urgency of addressing climate change is also driven by thresholds and tipping points such 

as the onset of large-scale emissions of greenhouse gases from thawing permafrost. The disintegration of major land ice sheets is another process which may become irreversible and which 

would produce devastating global consequences-massive sea level rise. Improved scientific 

understanding of these processes, and observations showing them starting to occur, are the 

main reasons why policy discussion increasingly focus on the stricter goal of limiting global 

' The most recent such statement is: "It is extremely likely that human influence has been the 

2 
67 

warming to 1.5°C rather than the older 2° goaL As noted above, we urgently need more research in order to understand as precisely as possible where these tipping points lie, to allow 

us to refine our top-line climate policy goals (e.g. should we limit warming to 1.5°, 2°, or something else?) in order to be sure to avoid the consequences of crossing these thresholds and 

tipping points. 

The urgency of addressing climate change is also driven by societal factors. For example, well 

before coastal areas are permanently or even usually inundated, property values in these areas 

may drop. Inability to get affordable insurance, or any insurance at all, may accelerate this decline. We urgently need policies to delay or prevent inundation and flooding, as well scientifically and economically sound policies on insurance, disaster response, rebuilding, and so on. 

Technology will play an essential role in minimizing the effects of climate change and adapting 

to the effects we cannot prevent, as well as in measuring greenhouse gas emissions. I would 

like to see our government help US businesses to develop these technologies and sell them to 

the rest of the world. If we don't, someone else will, and I would hate for our country to lose 

that opportunity. 

To begin with reducing emissions, both developed and developing countries want, deserve 

and will seek the best possible quality of life for their people. This means an increase in global 

energy use. It is very much in our own self-interest to help other countries to accomplish this 

with technologies that do not contribute to climate change. Otherwise, the greenhouse gas 

emissions from these countries will result in climate consequences that will be extremely harmful to all nations, including us. Key technologies needed for mitigation include those for carbonfree energy generation, storage, and transmission, as well as for climate-friendly agriculture 

and forest management In addition, we need technologies for energy efficiency, for electrification of the transportation and industrial sectors, and so on. Finally, I believe that we should at 

least investigate technologies for counteracting the effects of atmospheric greenhouses gases, 

a practice known as geoengineering. 

Because we have delayed so long at implementing effective emissions reductions measures, 

we also need technologies to remove C02 from the atmosphere. Although it may in the future 

be possible to achieve this using technological means, it is possible now to achieve significant 

C02 removal using land management practices like reforestation and climate-smart agriculture. I recommend adoption of these practices as they have significant positive side-benefits, 

including making us more resilient to climate threats. 

An enormous range of technologies is needed for climate adaptation. These include technologies to cope with extreme weather, water contamination, vector borne diseases, to increase 

resilience of crops, and so on. With respect to extreme weather, assessments have shown that 

we are under-prepared even for the present climate, meaning that investments in preparedness and resilience would produce net economic savings even absent human-caused climate 

change. Upgrading our physical infrastructure could be an important step in increasing resilience, if that infrastructure is designed with the climate of the 21st century in mind. 

New technologies are also needed to measure greenhouse gas emissions. Any policy to meaningfully control climate change will require the ability to accurately and verifiably measure these 

3 
68 

emissions. Needed technologies include those for measuring carbon in the atmosphere, 

ocean, forest, soils, etc. both remotely and in situ, as well as advanced modeling to understand 

where emissions are coming from. Here again, I would hope that our government would help 

the United States to be the leader in the development and deployment of such technologies. 

The recent decision to cancel NASA's Carbon Monitoring System is ill-advised as the information gathered by such systems will generate real value at low cost. 

Climate policies anqtb~ir economic conseg1.1ences 

Mitigation and adaptation are sometimes presented as alternatives, but this is a false dichotomy. Focusing exclusively on mitigation would leave us needlessly vulnerable to harms from unavoided climate change. Ignoring mitigation would expose us to potentially catastrophic consequences. We are already practicing both mitigation and adaptation, and this will continue to 

be true. As noted above, investments in adaptation often save more money than they cost. 

Results of early studies suggest that the same is true of mitigation policies. We are beginning 

to have enough real-world experience with these policies that we can learn valuable lessons by 

studying not only their effectiveness at reducing greenhouse gas emissions but also their immediate economic impacts. Forty countries and 20 subnational jurisdictions are now under a 

carbon pricing policy (carbon tax or emissions trading system). Assessments of these policies 

have found that well designed climate policies can not only reduce greenhouse gas emissions 

but have immediate positive economic impacts. Several recent studies, for example, found that 

the Regional Greenhouse Gas Initiative (RGGI), a "cap and trade system" on greenhouse gas 

emissions from the electric power sector in nine northeastern states, has resulted in billions of 

dollars of net economic benefit to the region2 , as well as $5.78 in savings due to improved 

health outcomes3

. While these studies are limited in scope, the idea that the same policies that 

address climate change can also improve the economy is powerful and important. 

Conclusion 

The threat of global climate change is real and urgent, and is recognized as such by scientists 

and governments around the world. Advanced technologies of many types will be essential in 

minimizing and adapting to this threat. 

I recommend specifically: 

·Accelerated deployment of carbon-free energy production technologies we have now, especially wind and solar; 

• Development of new such technologies, as well as technologies for energy storage and 

transmission; 

2 h!!Ps://www.dec.ny.gov/docs/lJJ:Iministration pdf/ag11 rggi.pdf 

www.analysisgroup.com/uploadedfiles/ .. ./analysis_group_rggi_reportjuly_2015.pdf 

www .a_lli!lys[sgr:Qup.com/uploadedfiles/ .. ./analysis qrQI.IQ_r_ggj_report april 201~,p<;!J 

3 http://abtassociates.com/RGGI 

4 
69 

• Development of technologies to remove C02 from the atmosphere; 

• Research into geoengineering; 

• Adoption of land-management practices that remove C02 from the atmosphere; 

• Development of improved technologies for measuring GHG emissions and global carbon 

stocks 

• Accelerated research into understanding climate thresholds and tipping points, in order to 

inform top-line climate police goals (e.g. 2° vs 1.5°); 

No nation is better position than ours to develop these technologies and to profit economically 

from their deployment. I enthusiastically encourage this Congress to support and enable US 

leadership in this area. 

5 
70 

Philip B. Duffy is President and Executive Director of the Woods Hole 

Research Center (WHRC). Dr. Duffy was trained in physics and 

started his career in the nuclear weapons complex at Lawrence 

Livermore National Laboratory. There he was involved with testing 

nuclear weapons at the Nevada Test Site, and also worked on 

strategic defenses against nuclear ballistic missile attack. Turning to 

the threat of global climate change, Dr. Duffy studied the problem for 

20 years as a research scientist. Between 2011 and 2015 he helped 

to formulate and implement domestic and international climate policy 

in the Obama White House. Prior to joining the White House he was 

Chief Scientist at Climate Central, a non-profit dedicated to increasing 

public understanding and awareness of climate change. He has been 

a Senior Scientist at Lawrence Livermore National Laboratory, an 

adjunct faculty member at UC Merced, and has held visiting academic 

posts at Stanford University and at the Carnegie Institution for 

Science. Dr. Duffy has over 75 peer reviewed publications, has served 

on committees of the National Academy of Sciences, and as an 

advisor to the US Department of State. He has a bachelor's degree 

from Harvard and a PhD from Stanford University. 
71 

Chairman SMITH. Thank you, Dr. Duffy, and I’ll recognize myself 

for questions. 

And Mr. Cass, let me direct my first one to you. You put up a 

couple of slides today. One had to do with the number of heat 

deaths increasing exponentially, particularly in the Northeast. 

Would you go into just some quick detail as to why that study was 

flawed? And you mentioned the Rhodium study as well, but take 

your pick. Just why are some of these studies flawed and why 

should we sort of discount them? 

Mr. CASS. Sure. Thank you. I think to understand conceptually 

why they’re flawed, it’s important to recognize that all regions, 

even within the United States, adapt to their local climate, and so 

when you look across the country you find, for instance, that people 

in the hotter parts of the country are not suffering from higher 

heat-related mortality than people in the cooler parts. The logical 

conclusion to draw from that would be that as the country gets 

warmer, we should not expect to see a lot more heat-related deaths 

because, again, people will adapt to whatever heat they face, and 

indeed, that’s what the most recent published literature shows. 

What studies do instead to generate large heat death estimates 

is to look at the reaction we have seen historically even per hot day 

or per days that are especially hot for a location and simply extrapolate forward if we see many more hot days than surely we will 

see that many more deaths. And the EPA study is the best example of this where they take a city like Pittsburgh and they say if 

one percent of Pittsburgh days have lows above 71 degrees, we will 

call that extreme heat for Pittsburgh, and whatever the death rate 

they experience on those days they will continue to experience that 

death rate on days when the temperature is above a low of 71 even 

if that becomes very common in the future and so you see the 

death rate in Pittsburgh skyrocket if you assume that. Of course, 

if the climate in Pittsburgh shifts to be more like that of a more 

southerly city, Pittsburgh’s use of air conditioning and other adaptive technologies will shift as well, and the result will likely be that 

we will see the same low death rate that we do today. 

Chairman SMITH. Okay. Thank you, Mr. Cass. 

Mr. Nordhaus, I appreciate your good point that given the uncertainties we all could use some moderation and humility. A good reminder. 

What I wanted to ask you about is, you mentioned that we 

couldn’t just rely upon renewable energy; we need to make better 

use of fossil fuels. Would you go into some detail or give examples 

of what you’re talking about? 

Mr. NORDHAUS. Well, I think the primary point that I would 

want to stress to this Committee, a couple of things. The first is 

that whatever we may think we should do, the evidence is pretty 

strong that 70 percent of U.S. energy, well over 70 percent of U.S. 

primary energy still comes from fossil fuels. That’s true globally. 

And despite longstanding efforts, that has not changed very much 

going all the way back to the oil shocks of the 1970s. So part of 

that we could do better. Part of that, there are a lot of uses of fossil 

fuels that we don’t have very good alternatives for. We spend a lot 

of time arguing and talking about various technological pathways 

in the power sector, which is a little bit like looking for your keys 
72 

under the light post because that’s where the light is. That’s the 

easy place where there really are good options for decarbonization 

so we like to argue about that, but once you get outside of the 

power sector into industry, heavy transportation, and agriculture, 

it gets much harder. 

Secondly, in the developed world, there are very significant 

tradeoffs. The things that make us resilient to climate extremes, 

whether they are caused by climate change or just normal climate 

variability, are infrastructure, and infrastructure, building infrastructure, is a really energy-intensive business—steel, cement, 

things like that, and again, those are exactly the sectors we don’t 

have particularly good alternatives, low-carbon alternatives in. So 

for that reason, I think there’s important tradeoffs, especially when 

we think about poor countries and their use of fossil fuels, that we 

need to keep in mind in terms of what will make those countries 

in the coming decades most resilient to a changing climate. 

Chairman SMITH. All right. Thank you, Mr. Nordhaus. 

And Dr. Duffy, I appreciated your mention of technology. Obviously I agree with that. You mentioned your background and your 

experience, let’s call it with nuclear energy, at least that’s the way 

you started at Lawrence Livermore, and I’m wondering if you feel 

that if we do develop nuclear fusion as many expect to in the next 

ten years, I mean, there’s almost nothing else we could do that 

would have more of a dramatic impact on reducing carbon emissions, I think, than nuclear fusion. Do you agree with that, or what 

impact do you think that would have if we came up with a costeffective way of producing that kind of energy? 

Dr. DUFFY. Well, Mr. Chair, thank you for the question. I just 

want to clarify. My experience at Lawrence Livermore National 

Lab was with nuclear weapons. 

Chairman SMITH. I knew that. I was actually—— 

Dr. DUFFY. And—— 

Chairman SMITH. It’s still nuclear. I was hoping—— 

Dr. DUFFY. I’m proud to be a tree hugger but I don’t think there’s 

too many tree huggers who’ve detonated nuclear bombs. 

Chairman SMITH. Okay. 

Dr. DUFFY. As far as nuclear fusion goes, I mean, it’s been 30 

years in the future for at least 30 years. 

Chairman SMITH. Okay. 

Dr. DUFFY. I will say I do support Mr. Nordhaus’s opinion that 

we need to make better use and more extensive use of nuclear fusion. 

Chairman SMITH. Okay. Thank you, Dr. Duffy. 

I’m going to do something that I don’t do very often, and that is, 

without objection yield myself an additional minute, and the reason 

I’d like to do so is because Dr. Curry is not here but I would like 

to put up a slide that I was going to use had she been here, and 

I’d like all Members to take a look at this. 

[Slide]You will see that for the last 100 years, sea-level rise has 

been basically constant. It’s been going up at about 1.8 millimeters 

per year, and you’ll see that there appears to be no correlation between the increase in the sea level and carbon emissions, and I just 

want to put that up there for our edification. I was going to ask 

Dr. Curry about it but I think it kind of speaks for itself. 
73 

Dr. DUFFY. I’d like to comment on that, Mr. Chair. You know, 

you’ve shown a sea-level record from one location. 

Chairman SMITH. Right. This is San Francisco. It’s also Boston, 

which appears to be—— 

Dr. DUFFY. The rate of global sea-level rise has accelerated and 

is now four times faster than it was 100 years ago. 

Chairman SMITH. Is this chart inaccurate then? 

Dr. DUFFY. It’s accurate but it doesn’t represent what’s happening globally. It represents what’s happening in San Francisco. 

Chairman SMITH. All the charts I’ve seen, whether it be San 

Francisco, whether it be Boston or anywhere else show about the 

same degree of increase. I’m welcome to look at whatever you want 

to propose but this is—— 

Dr. DUFFY. I’d be happy to show that to you. 

Chairman SMITH. These are objective charts that I’ve seen, so 

thank you, Dr. Duffy. 

That concludes my questions, and the Ranking Member, Ms. 

Johnson, is recognized for hers. 

Ms. JOHNSON. Thank you very much, Mr. Chairman. 

Our understanding of Earth’s climate system continues to improve, and within some of our lifetimes, we’ve seen the accuracy of 

our short-term weather forecasts improve dramatically. As a matter of fact, just the time that I’ve been in Congress, we’ve seen improvement in travel. Yesterday, for example, it took me about 

seven hours to get here from Dallas, Texas, because of weather. We 

didn’t see the weather but it was predicted, and we made it and 

we got here. 

So Dr. Duffy, how do you respond to those who suggest that we 

cannot adequately anticipate the consequences of climate change in 

order to develop effective mitigation and adaptation strategies? 

Dr. DUFFY. Thank you for the question, Ranking Member Johnson. I would say this. You know, the climate models that we have 

do faithfully reproduce the broader outlines of physical climate 

change, and these include increases in the global temperature, 

polar amplification, that is, more rapid warming, particularly in 

the North Pole, increases in precipitation and extreme precipitation, although those are actually underpredicted by climate models. 

The models also predict loss of sea ice, although again they’ve 

underpredicted the observed rate of loss of sea ice, and similarly, 

the models predict loss of land ice but once again have underpredicted the rate that that’s occurred. The models predict stratospheric cooling, thawing permafrost, increases in heat exchange. 

All of these phenomena have been very accurately representative 

models. 

And I’m glad that you actually mentioned the miracle of weather 

prediction because there is a connection between making climate 

projections and the miracle of weather prediction and actually some 

of the European centers that do a very, very good job at day-to-day 

weather forecasting use literally the same computer program for 

their climate predictions that they use to predict day-to-day weather, and again, those are literally the best weather forecasts in the 

world today. 

Ms. JOHNSON. Thank you very much. 
74 

If we veer away from looking into climate change and its effects 

and look in another direction or deny it’s there at all, I think we’ll 

fail to improve our predictions, and where do you think that will 

take us? Because if we can stop—we can stop anything we want 

to here but it doesn’t stop climate change. We can deny it happens 

but it does happen. And so if we look the other way and decide that 

we are not going to research, what do you think the outcome might 

be? 

Dr. DUFFY. Well, thank you for the question. You know, the outcomes from unmitigated climate change are not pretty, and I’m 

very happy to hear both of my co-witnesses supporting the need for 

both mitigation and adaptation. You know, one of the things that 

I’m most concerned about with climate change is the threat of 

crossing so-called thresholds and tipping points, and what that 

means essentially is processes which once underway become irreversible, and one of those is the thawing of permafrost, which I 

mentioned. Permafrost is mostly in the Arctic. It sounds far away 

but there’s an enormous quantity of carbon tied up in frozen permafrost. It’s starting to thaw. It’s starting to release greenhouse 

gases. That threatens to become an unstoppable process, which 

would greatly amplify global warming. 

And I’ll just mention one more, and that is the decay of the 

major land ice sheets. Similarly, those processes are probably slow 

but we may be very near the point where they become unstoppable 

and therefore commit the planet to many, many meters of sea-level 

rise. 

Ms. JOHNSON. Thank you very much. 

Thank you, Mr. Chairman. 

Chairman SMITH. Thank you, Ms. Johnson. 

Without objection, I’d like to put in the record, this is an op-ed 

in today’s Wall Street Journal by Fred Singer. He is a Professor 

Emeritus of Environmental Science at the University of Virginia, 

and he founded the Science and Environmental Policy Project. The 

headline on this op-ed is ‘‘The sea is rising but not because of climate change.’’ 

[The information appears in Appendix II] 

Chairman SMITH. We’ll now go to the gentleman from California, 

Mr. Rohrabacher, for his questions. 

Mr. ROHRABACHER. Well, thank you very much. Let me just note 

before I ask any questions, I have in my career been very supportive of trying to develop certain technologies that I consider to 

be more efficient at providing the energy needs for the people of the 

world, whether it’s nuclear energy, which we’re talking about now, 

and by the way I would hope, Mr. Chairman, that we don’t focus 

on the development of nuclear energy that is least likely to be developed. We can actually do fission reactors now that are very efficient and come to play in this issue as compared to fusion, which 

it seems always to be 20 years away, 30 years away, and always 

will be. We can produce safe nuclear reactors right now if we’d 

focus on fission and quit wasting our money on fusion, but that’s 

a disagreement. Thank you. 

But also, you know, I believe in solar and wind and all the rest 

of these as long as they pencil out and what we need is a new battery technology, which I understand is on the way, when those 
75 

things will actually become profitable and people will naturally go 

in that direction because, correct me if I’m wrong, doesn’t the 

amount of carbon that is put in the air reflect the fact that we are 

not efficiently producing energy? Isn’t that what we’re talking 

about here? I believe so. But when you come down to this debate 

over adaptation versus mitigation, there’s an insistence when people talk about mitigation that we control human behavior rather 

than having people naturally evolve in response to that need, and 

so I’m a little bit disturbed by, number one, that over and over 

again I hear don’t ever talk about whether or not mankind is the 

main cause of the temperature changing and the climate changing. 

That’s a little disturbing to hear constantly beaten into our heads 

in a Science Committee meeting when basically we should all be 

open to different points of view. 

Because the answer that we’ve been given in terms of mitigation 

versus adaptation is that we need controls over people’s lives and 

make their decisions for them rather than adapt economically and 

elsewise. Let me ask you whether or not any of you on the panel 

would agree that solutions—I’ve read a number of studies that 

have indicated there’s certain solutions that are being advocated. 

One study is that we should be eliminating pets, dogs. Dogs should 

be eliminated, and that’s part of their solution that we’re going to 

do that. There was one that talked about ending frequent-flier 

miles, and others who talk about how we need to have major increase in parking fees and gas taxes. Now, do any of you on the 

panel agree that that approach—no more dogs, you can’t have a 

dog as your pet, we’re going to outlaw those things, no more frequent-flier miles, and by the way, ordinary people benefit from frequent-flier miles and dogs, and now you have to see them on the 

airplanes actually—versus major increases in parking fees? Do any 

of you support that type of human control in order to come to grips 

with what you’re telling us is absolutely undebatable, that man 

caused global warming? Do any of you agree with any one of those 

solutions? Go ahead. 

Mr. NORDHAUS. No. 

Mr. ROHRABACHER. Okay. 

Mr. NORDHAUS. I will say that, as I indicated in my written testimony, I think that modest tax, regulatory pricing policies can help 

modestly move us at a cost-effective way towards lower carbon 

technologies but the underlying sort of fundamental facts that will 

determine how far we get will be the availability of low-cost, lowcarbon technologies, and that’s going to require a lot of continuing 

innovation. 

Mr. ROHRABACHER. And like as they say, the amount of carbon 

going into the air reflects that that technology is not as efficient 

as other means. Now, those of us who don’t believe that we should 

be expanding the control of the government over our lives and that 

people should actually have more decisions rather than less, that’s 

the area of contention that I see here. 

Mr. Chairman, thanks very much for this hearing. 

Chairman SMITH. Thank you, Mr. Rohrabacher. 

And the gentlewoman from Oregon, Ms. Bonamici, is recognized. 

Ms. BONAMICI. Thank you very much, Chairman, and thank you 

again to our witnesses. 
76 

Dr. Duffy, you mentioned when you were talking about clean, renewable energy sources, you mentioned wind and solar. In Oregon 

off our coast, we’re doing some great research on wave energy and 

harnessing the power of the oceans. There’s so much potential 

there. Our economy in the Northwest is really dependent on the 

health of the ocean and the lower Columbia River estuary, and people fish in our rivers and lakes and oceans and hike in our forests. 

We rely on those natural resources to support a significant portion 

of our economy, and many of those are vulnerable to the effects of 

climate change, and my constituents are already experiencing some 

challenges. We have wineries and farmers who are very concerned 

about drought as temperatures continue to rise. Our coastal communities are worried about the vitality of the commercial fishing 

and shellfish industries as high levels of carbon dioxide in the atmosphere are changing ocean chemistry, and I know they’re working hard on adaptation but they’re also very concerned about why 

the ocean conditions are changing and how they’re changing. 

We’ve had higher than usual spring and summer temperatures 

and earlier snowmelt, changing the dynamics of the tourism industry, and we understand that climate change can have significant effects on the economic stability of a region or a nation. 

So would you talk a little bit about how this economic growth 

could be stalled as a result of these challenges but also importantly, what is the cost of inaction? My colleague was just pointing 

out that renewables make sense when they pencil out but what are 

the costs of not taking action? 

Dr. DUFFY. Well, thanks so much for the question. I mean, you 

just mentioned—I mean, you just partially answered your own 

question. You listed a number of local impacts of climate change 

that are happening now, are affecting folks in your district. I also 

come from a coastal region. We have actually very, very similar 

concerns. A big part of our local and regional economy is based on 

fishing. We have serious problems with rapid ocean warming, with 

sea-level rise and so on. 

You know, you asked, you know, what are the economic concerns. 

I mean, there’s a range including consequences of extreme weather 

impacts on food scarcity, impacts on water scarcity and on and on. 

Ms. BONAMICI. Thank you. You know, we’ve had a lot of conversations in this Committee about the cost of regulation, especially with things like the Clean Power Plan, and should there be 

a regulation, should the market or technology solve the problem. 

Does not regulation drive the development of technology? If there 

is a regulation, does not that encourage the private sector and researchers to develop the technologies that we need to comply with 

regulations, Dr. Duffy? 

Dr. DUFFY. You know, that’s a great question, and you know, as 

I think you know, I worked for years in California, and there was 

a fascinating study done of the effect of regulation of both energy 

efficiency and refrigerants on the cost of refrigerators, and what it 

showed is that the cost of refrigerators historically went up, up, up, 

up, up until the onset of regulation at which point the cost of refrigerators went down, down, down, down, down as the size of the 

refrigerators and their energy use—well, the energy use went 
77 

down, the size continued to increase. So yes, actually regulation 

can be a stimulant for technological innovation. 

Ms. BONAMICI. I also wanted to mention, we had a lot of wildfires 

in Oregon last year. We had unusually hot and dry conditions, and 

of course, the fires and smoke created dangerous conditions for all 

populations but especially with, you know, women, seniors, children, people living with chronic health conditions, and even residents living miles away found ash throughout their neighborhoods. 

So could you discuss the difference between committing resources 

to understanding the connection between climate change and extreme weather events and simply adapting to those events as we 

experience them? 

Dr. DUFFY. Thanks for the question, and you know, you mentioned wildfires specifically. There have been huge increases, a sixfold increase in area burned by wildfire in the western United 

States in the last 30 years. Some of that is due to changes in forest 

management practices. I saw a study recently that attributed 

roughly half of the increase in area burned to human-caused climate change. It’s not hard to understand why that would be. The 

fire season is longer. Temperatures are hotter. By the end of the 

fire season, we have a lot of fuel that’s getting awfully, awfully 

crispy, and we have had record number of fires and record amounts 

of area burned. 

Ms. BONAMICI. Right, and my time is expired. I yield back. 

Thank you, Mr. Chairman. 

Chairman SMITH. Thank you, Ms. Bonamici. 

And the gentleman from Alabama, Mr. Brooks, is recognized for 

his questions. 

Mr. BROOKS. Thank you, Mr. Chairman. 

Ever since human beings have been on the planet, sea levels 

have risen relative to ground levels. Why is that? Any of you can 

opine as you wish. 

Dr. DUFFY. Well, I’d be happy to address that. Sea levels over the 

last three million years have gone up and down in line with the 

cycles of ice ages and interglacials, and I can expound on the 

science if you wish. The recent, the last 100-year increase in sealevel rise, as I mentioned earlier, has clearly been attributed to 

human activities. Greenhouse gas emissions—— 

Mr. BROOKS. That wasn’t the question. I appreciate your wanting 

to expound on that. My statement is that since human beings have 

been on Earth, sea levels have risen. What are the factors that 

have caused it to rise? 

Dr. DUFFY. Well, as I said, sea levels have gone up and down—— 

Mr. BROOKS. I’m talking net, not fluctuations. 

Let’s assume that for a moment that what you’re talking about 

has some kind of factual, rational basis for it that ice has melted. 

Are there other factors? 

Dr. DUFFY. No, look, you know—— 

Mr. BROOKS. No, there are not other factors, Mr. Duffy? 

Dr. DUFFY. Looking at the history of sea-level rise is very informative, and one of the things that we see, for example, is that the 

last time the global temperature was as high as it is—— 

Mr. BROOKS. Dr. Duffy, you’re not answering my question again. 

I’m conceding for the moment that there has been ice meltage com-
78 

pared to what it was three million years ago, whatever, since that’s 

the timeframe you used. I’m asking another question, and that is, 

what other factors have caused the sea levels to rise relative to dry 

land? Does anyone else have any—I mean—— 

Dr. DUFFY. Okay. 

Mr. BROOKS. —in particular, Dr. Duffy, you said they’re going to 

be massive. Isn’t that the word that you use in your remarks, massive sea-level rises? Don’t you think if you’re going to make that 

kind of statement you ought to have some idea as to what all the 

causes of sea-level rises have been? 

Dr. DUFFY. Sure, and if you’re referring to ground subsidence, 

that is a factor in some regions. 

Mr. BROOKS. Okay. What else? That’s one. So now we’ve gotten 

two. What else? 

Dr. DUFFY. Ground subsidence is not going to cause the levels of 

sea-level rise that arouse my concern. 

Mr. BROOKS. I’m just asking for factors. I was not asking for your 

prioritizing of one over the other but you mentioned two. What 

else? 

Dr. DUFFY. Those are all that I know of. 

Mr. BROOKS. What about erosion? Every single year that we’re 

on Earth, you have huge tons of silt deposited by the Mississippi 

River, by the Amazon River, by the Nile, by every major river system, and for that matter, creek all the way down to the smallest 

systems, and every time you have that soil or rock, whatever it is 

that is deposited into the seas, that forces the sea levels to rise because now you’ve got less space in those oceans because the bottom 

is moving up. What about—— 

Dr. DUFFY. I’m pretty sure that that’s—— 

Mr. BROOKS. —the white cliffs of Dover, California where you 

have the waves crashing against the shorelines and time and time 

again you’re having the cliffs crash into the sea? All of that displaces water, which forces it to rise, does it not? 

Dr. DUFFY. I’m pretty sure that on human time scales, those are 

miniscule effects. 

Mr. BROOKS. Okay. Well, let’s talk about ice for a moment. 

Where is most of the ice located on planet Earth? 

Dr. DUFFY. Antarctic ice sheet. 

Mr. BROOKS. And how much? 

Dr. DUFFY. I don’t have a number in my head. 

Mr. BROOKS. Do you have a rough estimation or idea of how—— 

Dr. DUFFY. The amount of ice in the Antarctic ice sheet if melted 

would raise global sea levels—— 

Mr. BROOKS. I’m not asking you how much—— 

Dr. DUFFY. —by 200 feet. 

Mr. BROOKS. Okay. You keep going and you don’t answer the 

question. My question is, how much of the ice on the Earth is in 

Antarctica? I’m not asking you to expound on anything else. I’m 

trying to limit you to that particular question. 

Dr. DUFFY. I don’t know the answer. 

Mr. BROOKS. Do you have any idea? 

Dr. DUFFY. I wouldn’t want to speculate in this forum. 
79 

Mr. BROOKS. Well, would it surprise you if it’s as high as 85 to 

90 percent, that that’s generally where the estimates are of the 

total amount of ice is in Antarctica? 

Dr. DUFFY. It would not surprise me. 

Mr. BROOKS. And would it surprise you to know that as global 

temperatures rise, assuming for the moment that they do, that that 

actually increases the amount of ice that is collected on Antarctica? 

Dr. DUFFY. That’s not true, sir. 

Mr. BROOKS. That’s not true? Well, I made a trip down to Antarctica and met with National Science Foundation scientists, and they 

all agreed with global warming, and they emphasized that you’re 

going to have an increase in the amount of ice in Antarctica because of global warming. Now, have you ever studied—I understand you studied climate but how about meteorology? Have you 

ever studied meteorology? 

Dr. DUFFY. I have, and I’ll be happy to—— 

Mr. BROOKS. So you understand that as the temperature—— 

Dr. DUFFY. We have satellite records—— 

Mr. BROOKS. Wait a second, please. You’ve answered my question. I don’t want you to orate because I have limited time. If the 

Chair would please permit as I try to get this point across? 

Chairman SMITH. Okay. Without objection, the gentleman is recognized for another 30 seconds. 

Mr. BROOKS. Do you understand that as temperatures rise, more 

moisture is contained in the atmosphere and then that moisture in 

Antarctica collects on land and it takes hundreds and hundreds of 

years for that ice that is deposited on Antarctica to actually ever 

even reach the shoreline where it touches the oceans where it can 

affect in some way sea-level increases? 

Dr. DUFFY. We have satellite records clearly documenting a 

shrinkage of the Antarctic ice sheet and an acceleration of that 

shrinkage. 

Mr. BROOKS. I’m sorry, but I don’t know where you’re getting 

your information but the scientific data that I have suggests—— 

Dr. DUFFY. The National Snow and Ice Data Center. 

Mr. BROOKS. Well, okay. I’m talking NASA and others. 

Dr. DUFFY. And the National Aeronautics and Space Administration. 

Mr. BROOKS. Well, I’ve got a NASA base in my district, and apparently they’re telling you one thing and me a different thing but 

there are plenty of studies that have come out that show that with 

respect to Antarctica, that the total ice sheet, particularly that 

above land, is increasing, not decreasing. Now, you can make a different argument if you want to talk about Greenland or the Artic 

but that having been said, thank you, Mr. Chairman, for the indulgence. 

Chairman SMITH. Thank you, Mr. Brooks, and the gentleman 

from Illinois, Mr. Lipinski, is recognized. 

Mr. LIPINSKI. Thank you. 

Dr. Duffy, in your testimony you state that technology will play 

an essential role in minimizing and adapting to the effects of climate change, something you think the U.S. government should 

support. You allude to the economic benefits that are likely to ac-
80 

crue to U.S. businesses as a result of developing these new technologies. 

I agree that the government has an important role to play in 

helping U.S. businesses lead the world in technology to address climate change. That’s why I introduced the bipartisan Challenges 

and Prizes for Climate Act along with 13 of my Democratic and Republican colleagues from the Climate Solutions Caucus. This bill 

requires the Department of Energy to organize prize competitions 

around climate challenges such as energy efficiency, grid energy 

storage, and carbon capture, and prioritizes market-ready solutions 

that are made in America. This is one important way the Federal 

Government can both incentivize and raise awareness of technology 

to address climate change. 

I’m wondering what you think some others might be. How else 

can the government leverage the private sector to develop technologies and solutions that we need to address climate change? 

Dr. DUFFY. Well, thanks for the question. You know, one really 

important measure which has been mentioned earlier would be to 

create the incentives, the economic incentives, to develop those 

technologies, and here, putting a price on carbon emissions, which 

after all corrects a market failure, is a very important step which 

would incentivize both the development and implementation of a 

lot of important technologies. 

Mr. LIPINSKI. Any other—well, let me move on. If we—if the 

United States, if we don’t really help lead the world in this, what 

do our—what do we have to lose economically? Where are we right 

now? Where are American businesses right now compared to the 

rest of the world in developing these climate solutions? And if we 

don’t do more, what do we lose economically? 

Dr. DUFFY. Well, that’s a great question, and you know, in the 

immediate term, no country is spending more on renewable energy 

than China is, and you know, I would hate to lose that race to 

them. 

You know, the other aspect of this that’s very concerning to me 

is the potential brain drain aspect, and you know, historically, the 

excellence of American education and American research has been 

a magnet for talented people from around the world to come here 

and those folks have added invaluably to our country in many, 

many ways including economically, and when I look in the job ads 

section now of international scientific journals, it saddens me to see 

that where are all the jobs now. Well, a lot of them are in China. 

Most of them are in China. And again, you know, I would much 

prefer to see Americans investing in both the science and the technology to address this threat. 

Mr. LIPINSKI. I want to focus on something a little more specific. 

How would you characterize the nature of geoengineering or carbon 

removal as a potential option to fight climate change? 

Dr. DUFFY. You know, I would treat those separately. Carbon removal is a—well, carbon removal in principal actually does in fact 

act to reverse climate change by lowering the concentration of carbon in the atmosphere. As I mentioned in my testimony, there are 

rather low-tech land management methods that can remove quite 

a bit of CO2 from the atmosphere, probably not as much as need 

to but make a really, really valuable contribution, and again, you 
81 

know, those measures have some very valuable co-benefits including, as I mentioned, benefits for adaptation. Technological measures to remove carbon dioxide from the atmosphere are under development at the moment. They’re very expensive, and at the moment we don’t have the ability to deploy them at the scale that we 

need. 

You also asked about so-called geoengineering, which I would 

characterize as measures to counteract the climatic effects of increasing greenhouse gases. I don’t know anyone in the scientific 

community who’s enthusiastic about deployment of geo engineering. I think a lot of us, however, recognize that this is something 

we need understand better. We need to understand the potential 

effectiveness, and most importantly, we need to understand the potential unintended consequences. 

Mr. LIPINSKI. Thank you. I’m out of time. I yield back. 

Chairman SMITH. The gentleman yields back. 

And the gentleman from Florida, Mr. Posey, is recognized for his 

questions. 

Mr. POSEY. Thank you, Mr. Chairman, and I thank the witnesses 

for their attendance here today. 

Mr. Cass and Mr. Nordhaus, do you believe Dr. Duffy’s claim 

that government regulation is responsible for lowering the cost of 

refrigerators in this country? Or do you tend to believe it might be 

due to competition and improved production and technical advancements? 

Mr. NORDHAUS. I would say probably a bit of both, and I don’t 

know the specific research that he is referring to, but I would assume that a significant amount of the cost savings there were not 

in the actual purchase cost of the refrigerator but just in the energy costs associated with running it as refrigerators have become 

more efficient. I do think that there’s a case that various regulatory 

measures like EnergyStar have significantly contributed to improving the energy efficiency of refrigerators—— 

Mr. POSEY. We’re talking about costs. Okay. Thank you. 

Mr. Cass? 

Mr. CASS. I think as Mr. Nordhaus emphasized, the key distinction is between the upfront cost of the product typically and then 

the operating cost, and what we find with regulation is that if 

you—and we see this now with, for instance, CAFE standards. If 

you require people to purchase more expensive cars that use less 

gas, you can claim to be saving them money. The problem is that 

typically they don’t agree, and if they did, you wouldn’t need the 

regulation. 

Mr. POSEY. That’s kind of what I thought. 

Dr. Duffy, you referenced a big threat from large-scale emissions 

of greenhouse gases from thawing permafrost. How did the greenhouse gases get captured into the permafrost in 15 seconds or less? 

Dr. DUFFY. It’s dead organic matter, dead animals and plants. 

Mr. POSEY. All right. What was the temperature on Earth before 

the last ice age? 

Dr. DUFFY. Before the last ice age—— 

Mr. POSEY. Yes, sir. 

Dr. DUFFY. —and the last interglacials? Well, similar to what it 

was about 100 years ago. 
82 

Mr. POSEY. You think? You don’t think maybe it was 30 degrees 

warmer when dinosaurs roamed the Earth? 

Dr. DUFFY. There certainly have been epics in the past when the 

global temperature was warmer than it is now, and there’s evidence that during those epics there was massive release of greenhouse gases from frozen ground, previously frozen ground. 

Mr. POSEY. Well, where did the greenhouse gases come from if 

we didn’t have people to create them? 

Dr. DUFFY. Oh, again, you know, the greenhouse gases that are 

tied up in permafrost, it’s not really gases, but the carbon that’s 

tied up in permafrost is undecayed organic matter. 

Mr. POSEY. So that’s a threat that would exist if people never existed? 

Dr. DUFFY. It’s a threat that would exist but the activities of people are unlocking that threat by warming the Arctic and causing 

that frozen ground to thaw. 

Mr. POSEY. How many ice ages do you think we’ve had on this 

planet? 

Dr. DUFFY. Dozens. 

Mr. POSEY. Okay. 

Dr. DUFFY. But, you know, just because it’s happened before 

doesn’t mean it’s benign. 

Mr. POSEY. What caused the end of the last ice age? 

Dr. DUFFY. The ice ages are caused by oscillations in the Earth’s 

orbital parameters. 

Mr. POSEY. Yeah, the last one was caused by a cataclysmic collision of an asteroid on this planet, I believe. 

What do you say to people who theorize that the Earth as it continues to warm is returning to its normal temperature? 

Dr. DUFFY. Look, you know, if you want to characterize a temperature above today’s temperature as normal, you’re free to do 

that, but that doesn’t mean that’s a planet that we want to live on. 

If we let—— 

Mr. POSEY. I don’t want to get philosophical. I’m trying to—— 

Dr. DUFFY. I’m not getting philosophical. I’m getting extremely 

practical. 

Mr. POSEY. You’re what? 

Dr. DUFFY. I’m being extremely practical. 

Mr. POSEY. Yeah. Well—— 

Dr. DUFFY. If we let the planet warm two or three degrees, we 

will have tens of meters of sea-level rise, and the community where 

I live will essentially cease to exist. 

Mr. POSEY. I don’t think anybody disputes that the Earth is getting warmer. I think what’s not clear is the exact amount of who 

caused what, and getting to that is I think where we’re trying to 

go with this Committee, just a little bit understanding of exactly 

how much different causes contribute to the warming that we see. 

Dr. DUFFY. Look, I encourage you to look at the last assessment 

report of the Intergovernmental Panel on Climate Change estimated the human contribution to warming over the last 60 or 70 

years is essentially equal to the observed warming. In other words, 

they’re saying humans caused essentially all of the observed warming over the last 60 or 70 years. 
83 

Mr. POSEY. When do you think the turn was made from the 

1970s prediction that we were going to have another ice age, and 

that was the big threat they were telling us when I was in school? 

Dr. DUFFY. Well, the scientific community in the 1970s never actually widely predicted an immediate cooling. There were a few 

popular press articles about it but it was never something that was 

widely believed in the scientific community. 

Chairman SMITH. The gentleman’s time has expired. 

And the gentlewoman from Connecticut, Ms. Esty, is recognized 

for her questions. 

Ms. ESTY. Thank you, Mr. Chairman. I want to thank our witnesses for joining us here today for this important hearing. 

I want to note, Mr. Nordhaus, I want to thank you as a member 

of the Transportation and Infrastructure Committee for your importantly making sure everyone on this Committee and anyone 

watching understands how much of the contribution towards carbon and how much of the fuel consumption, the carbon consumption is related to the transportation and the industrial sectors, and 

that is why it’s so important on that Committee, and we welcome 

your testimony on that in front of the T&I Committee to make that 

point, but I do think it also underscores the importance of technological innovation in a variety of sectors. It cannot be an appropriate answer to say the rest of the world doesn’t develop its technology or doesn’t advance economically but the United States is 

uniquely positioned, I would say, to advance research in all of those 

realms, which is why we have innovation being done in the Department of Defense, which has invested heavily because 30 percent of 

its costs are in the cost of transportation and has recognized the 

value it places as well as the DOD seen the threat of sea-level rise 

being enormously threatening to global security as well as threatening our bases. So that is real cost right now, and if any of you 

have the figures on that, we can also get you to those because those 

are real costs and DOD is really worried about them right now, 

and that is going to impact taxpayer dollars as well as military preparedness, something that is not integrated often enough in this 

Committee. 

I hail from the State of Connecticut. We are one of the RGGI 

states. Dr. Duffy, you have lived in several of them, California and 

Connecticut. In my State of Connecticut, which has decided to lean 

in to a lower carbon future because it sees both the short- and the 

long-term advantages of that, that is created with our first-in-thenation green bank over 13,000 jobs. Those are jobs that are selling 

technology out of my district around the world. We have fuel cells 

that are being sold in Korea. We are the largest supplier of fuel 

cells to Korea, in part as part of that carbon transition. 

If we were to lean away from that, I think about this being like 

insurance for a car, or better yet, insurance on your house. I’ve 

never lived in a house that has burned down but I get insurance 

anyway. The concerns—and there’s a lot of debate, especially with 

my colleagues saying exactly what percentage is due to human behavior, but if the consequences, if the most extreme predictions are 

right, are cataclysmic for the continuation of life on Earth for 

human beings, then it would seem prudent that we at least take 

some measure of action. 
84 

So Dr. Duffy, could you talk about both the opportunity that we 

have from the business point of view, which is I think in part why 

so much of the business community leaned in on, say, the Paris 

Climate Accords? U.S. business leaned in and said yes, we want to 

support this because they see that business opportunity to sell to 

the entire world. And could you also talk about the research importance? We are very concerned, and we talked a lot in this Committee about China’s investment across the board in research and 

getting ahead of us, whether it’s on solar technology or other things 

that they will then license to the world. And Dr. Duffy, if you could 

talk a little bit about those business opportunities and imperatives 

as decision makers about what we can do? 

Dr. DUFFY. Sure, I’d be happy to address that, and I’ll also just 

echo your comments about RGGI, the Regional Greenhouse Gas 

Initiative, and as I’m sure you know, a number of studies have 

shown positive economic impacts in the nearly ten years that RGGI 

has been in place, and some of those positive impacts, by the way, 

come from improved health outcomes. I think the latest study documented $5.7 billion in savings because of improved health outcomes. 

Regarding, you know, research on technologies and the business 

opportunity, you know, again, I think it’s an important opportunity. 

The world as a whole is mobilizing to address this global threat. 

It will take global cooperation to address this threat, and you 

know, look, we’re the United States. We should be leaders here, not 

followers. It’s as simple as that in my view. 

Ms. ESTY. Can you flag what are some of the research elements 

that you think the Federal Government is uniquely positioned to 

do the basic research? Because obviously the private sector is going 

to do that R&D but that basic research, whether it be fusion, which 

we have a variety of opinions you’ve heard here about fusion but 

certainly if we were to be successful at fusion, that would be transformative. What are some of those other areas? 

Dr. DUFFY. I think in general, you know, where the Federal Government has a role is in the early-stage research where, you know, 

the economic payoff is doubtful or is a ways down the road and fusion would certainly be an example of that. 

Ms. ESTY. Thank you, and I see I’m out of time. 

Chairman SMITH. Thank you, Ms. Esty. 

And the gentleman from Arizona, Mr. Biggs, is recognized. 

Mr. BIGGS. Thank you, Mr. Chairman, and thank you, gentlemen, for being here to testify today. I appreciate it very much. 

Mr. Cass, in your written materials you cite two studies, one by 

Little—or excuse me, one by Mills and one by Basera, or Barreca, 

I guess is—I had that wrong. They take two different approaches 

to mortality rates due to extreme temperature, and you said in 

there—let’s talk about that for just a second. They both take different approaches. Why did they take different approaches? What 

were they looking for, and why did they traverse the path that they 

did? 

Mr. CASS. Sure. I think the Mills study is kind of the quintessential example of ignoring adaptation. They look at different cities 

and assume that as temperatures change, cities will not change 

their response, and as a result, they produce very large cost esti-
85 

mates. The Barreca work I think is much more interesting and useful. They actually look at response to high temperatures over time, 

and so instead of just developing a homogenous response for, say, 

the second half of the 20th century, they say let’s compare what 

happened in the first half to the second half or let’s compare the 

1960s to the 1990s, and by looking at it in those terms and by taking the adoption of air conditioning into account in particular, what 

they find is that by the 1990s, mortality related to heat has plummeted, and essentially they find a decline of about 80 percent from 

the first half to the second half, a decline of about half within the 

second half, and by 2004, looking at the level of air conditioning 

that’s been adopted, the effect of heat on mortality is no longer statistically significant. 

Mr. BIGGS. And have you had a chance to engage with any of 

these researchers to kind of find out why they took the path they 

took? 

Mr. CASS. I’ve had a number of exchanges, some of them as I was 

doing the research, some of them more recently to sort of ask if I’ve 

missed anything or to understand the approach they’re taking. You 

know, one response I’ll hear is well, we were only trying to show 

what we were trying to show, so a study is we stated our assumptions and you can make of it whatever you want. Another response 

is to say first of all, yes, we do point out that we don’t take adaptation into account, and then in fact if you look elsewhere in the report, you’ll see we also provide an alternative calculation for that 

conclusion. So even the Mills study, for instance, actually also says 

well, what if we assume that cities do adapt, even just assume everyone gets as good as Dallas at dealing with heat, and just with 

that basic assumption they find their cost estimate I believe falls 

by about two-thirds. The interesting thing is that that’s the more 

interesting finding but that’s reported as an aside. It’s not something the Obama EPA chose to then incorporate in the estimate of 

costs that it highlighted. 

Mr. BIGGS. Well, I happen to come from the Phoenix metro area, 

which is one of the hottest areas in the United States, and if you 

look back 70 years ago, there was about 100,000 people. Today the 

metro area is five million people. So I guess my question to you is, 

have studies been done to determine what the variables or what— 

not variables but what activities have come about through adaptation to make, let’s say, life more bearable in the desert? 

Mr. CASS. I mean, I think the best evidence suggests air conditioning, you know, looking more broadly at the economic decision 

of so many people to move to the Southwest, and even today we 

see continued movement to the Southeast, and the analyses of mortality suggest that adopting air conditioning is the best explanation 

of why you don’t see more mortality. I would also say just that I 

think there’s an important lesson to be drawn from the fact that 

Americans looking at their options, taking everything that they 

wish to take into account are choosing to move further south. They 

are voluntarily opting for hotter temperatures, and—— 

Mr. BIGGS. I love the heat, by the way. 

Mr. CASS. There you go. That sort of behavior again underscores 

that places deal with the climates that they have, and there are 

pros and cons to whatever climate you have. It is not correct to 
86 

simply assume that if the climate changes people will behave as 

they did in the past. 

Mr. BIGGS. Thank you, and I just have about 20 seconds left. 

Mr. Nordhaus, you mentioned that you felt like we should 

incentivize clean fuel. What would you do to incentivize clean fuel? 

Mr. NORDHAUS. Well, I think the most important thing is taking 

steps to drive down the cost of the underling technologies, you 

know, whether that’s electricity technologies, transportation technologies. 

Mr. BIGGS. How would you do that, though? 

Mr. NORDHAUS. R&D, programs to demonstrate and commercialize some early-stage support—— 

Mr. BIGGS. Who would do that? 

Mr. NORDHAUS. Pardon? 

Mr. BIGGS. Who would do that? 

Mr. NORDHAUS. I think there are a variety of measures that 

could be taken at both the state and federal level. 

Mr. BIGGS. Thank you, Mr. Chairman. 

Chairman SMITH. Thank you, Mr. Biggs. 

And the gentleman from Illinois, Mr. Foster, is recognized for his 

questions. 

Mr. FOSTER. Thank you, Mr. Chairman. Thank you to our witnesses. 

First I’d like an opportunity to clear up this question about refrigerator capital costs and efficiency. 

Dr. Duffy, as the only one with an actual technical background 

on this panel of witnesses, can you just try to clarify this a little 

bit? 

Dr. DUFFY. Sure. The study was—the study I’m referring to was 

done, I don’t remember when, by the California Energy Commission, and the costs in question were the purchase price of refrigerators, not the lifetime energy costs. 

Mr. FOSTER. Right. And so the federal regulations regarding efficiency of refrigerators resulted in not only reduction in the electrical costs over time but also the purchase price, presumably because you can have a smaller motor, et cetera, and compressor. 

Dr. DUFFY. I think that’s right, and my guess is that what’s happened is that at the onset—and it was both federal and state regulations. At the onset of those regulations, the companies were making refrigerators the same way they had for decades because it 

worked and they were making money and everything was fine, and 

I believe that the advent of regulations caused the engineers to 

take another look at it and not surprisingly they realized that gee, 

we progressed and we now know how to do things better than we 

did 20 years ago. 

Mr. FOSTER. Thank you, and that’s a different narrative than we 

often hear in this. 

Staying with technical questions here, Mr. Cass, can you explain 

the plans that shellfish have to use air conditioning to adapt to climate change? 

Mr. CASS. I’m not familiar with any. It turns out that as a relative cost of climate change, though, and it is one that EPA took 

into account, it barely even shows up on the chart, and so my suggestion would not be that adaptation takes care of everything as 
87 

I think I emphasized several times, there are certainly real costs 

to climate change but the scale of those costs does not look anything like the type of cataclysmic rhetoric that we are hearing from 

some members of this Committee, to some degree from some members of this panel, and also from the dollar estimates that for instance the EPA produced. 

Mr. FOSTER. But—all right. There are difficulties when you talk 

about economic modeling of the intergenerational wealth transfers. 

You know, for example, underinvesting in research on low-carbon 

technologies, high-efficiency technology and so on, we are imposing 

huge costs on the next generation, and you know, those are real 

costs that should be modeled and are almost impossible to. On the 

other hand, you don’t always need a complete calculation, an accurate calculation, to know that we’re making big mistakes. So that 

from what you know of the rough estimates that have been made, 

is it clear that we are underinvesting in technologies actually, Mr. 

Nordhaus? For example, the big cuts that were proposed by the 

Trump Administration to research, fundamental research on energy efficiency and other green technologies, is that something 

which you believe is a step in the wrong direction as a society? 

Mr. NORDHAUS. I would say that cutting federal investment in 

energy research development and demonstration is unwise. 

Mr. FOSTER. Thank you. 

Mr. Cass, have you seen an economic analysis that would contradict that conclusion? 

Mr. CASS. I would agree with that, and my testimony specifically 

thanks Congress for maintaining that funding, and I think there’s 

a good case for increasing it, but I do think it’s also important to 

recognize that just as we ask the climate scientists to provide the 

best possible science on climate, we also need to ask economists to 

provide the best possible economics on climate, and if you look at 

the economics for climate change that are being produced, the cost 

estimates that they’re delivering are not defensible, and so—— 

Mr. FOSTER. How do you economically model, for example, the 

costs of the extinction of a species? 

Mr. CASS. I think that’s very difficult to model economically, and 

I think that we need to be realistic about what they are, and so 

when you describe the huge costs that we’re imposing on future 

generations, we need to define what those are, and certainly neither EPA nor GAO managed to find those. 

Mr. FOSTER. So you would advocate then for more effort in more 

accurately defining the climate—the cost of future climate change? 

Mr. CASS. Yes, absolutely, and I think it’s critical in doing that 

to emphasize that adaptation is not something to be put to the 

side. Adaptation is the central question to what the costs will be 

and in many respects to what the best policy responses will be. We 

need to understand what are the things we’re going to adapt to 

fairly naturally, what are the things we’re going to adapt to but 

with cost. Air conditioning, for instance, is not free, and what if 

anything are the things that maybe we will have difficulty adapting to and we need contingency plans for. I have not heard good 

definitions of things that it’s difficult to conceive of society adapting 

to but I certainly think that’s an exercise we should be asking 

about. 
88 

Mr. FOSTER. Any comments, Mr. Nordhaus? 

Mr. NORDHAUS. Yeah, I think that there are just huge uncertainties both ways when we try to look out a century and think about, 

you know, what we can adapt to, what we can’t adapt to, what the 

costs of mitigation will be. They’re just—we don’t know. So you 

have to—— 

Mr. FOSTER. And yet you both conclude that we’re underinvesting as a society in—— 

Mr. NORDHAUS. Absolutely, and I would just make one other 

point, which is that I do want to—there are very difficult to quantify if not unquantifiable risks of quite rapid impacts, and I think 

as Mr. Cass has also recognized, very rapid change would be much 

more costly and difficult to adapt to, and we just don’t know, and 

I think it will—I don’t think more climate science is likely to help 

us better understand the likelihoods on timeframes that we would 

need to take action to address them, so that’s not an argument 

against climate science but we should understand what sorts of uncertainties we’re likely to be able to resolve and what sorts of uncertainties we’re unlikely to resolve. 

Mr. FOSTER. Thank you, but I think it’s interesting that you both 

agree that actions like the recent cancellation of NASA’s carbon 

monitoring system are actually also steps in the wrong direction. 

We need more information on the time scale of which this problem 

will bite us. 

Thank you, and I yield back. 

Chairman SMITH. Thank you, Mr. Foster. 

The gentleman from Texas, Mr. Weber, is recognized. 

Mr. WEBER. Thank you, Mr. Chairman. 

Mr. Cass, you mentioned the study by the EPA that found that 

Pittsburgh extreme heat and mortality will rise exponentially beyond levels even in Phoenix or Houston, so I’ve got a couple of 

questions for you. Is it true that the closer to the equator you get, 

the warmer it is? 

Mr. CASS. Generally speaking, I believe that’s right. 

Mr. WEBER. You believe that’s right from your geography back 

in the sixth grade? 

Mr. CASS. And traveling south from time to time. 

Mr. WEBER. Well, you need to come to Galveston and spend lots 

of money. 

I owned an air conditioning company for over 35 years, so when 

you start—and by the way, we loved seasons changing. We loved 

heat in Texas. And I can tell you from firsthand experience a couple things being in the business 35 years. We’re not experiencing 

mass casualties. Now, Congressman Biggs from Arizona said that 

he loved the heat too. Over in Arizona they’ve got a dryer heat. Of 

course, we have the more humid heat. So I want you, Mr. Cass, to 

expand on what’s wrong with two things if you can. I realize one’s 

more scientific and one’s a little less. What’s wrong with the study 

of prediction of mortality in Pittsburgh, which is arguably further 

up north and a lot further away from the equator than we are in 

Texas, that they think there would be 75 times more mortalities in 

Pittsburgh than in Phoenix or in Houston? Number one, what’s 

wrong with that study? And number two, isn’t that a big hyperbole 
89 

to create some kind of need to really push forward on more regulations? 

Mr. CASS. Thank you. The technical way of describing the problem I think is to say that the study assumes all things are held 

constant, and of course, that’s traditionally how we expect economic 

analysis—— 

Mr. WEBER. But let me interject here real quick. So if that was 

true, we’re closer to the equator. If it was getting hotter in Pittsburgh, would it be getting hotter in Texas? Would that be a safe 

assumption? 

Mr. CASS. Yes. 

Mr. WEBER. And at the same rate? 

Mr. CASS. There are variations but generally speaking—— 

Mr. WEBER. Okay. Keep going. 

Mr. CASS. So I think the way to understand the problem is that 

they identified an effect of extreme heat days in Pittsburgh on mortality and assume that a day of that heat level will always have 

the same effect even if Pittsburgh’s climate changes. That’s a very 

poor assumption to make because we can see what places with 

warmer climates look like and how they respond to temperatures, 

and we know that they respond differently from Pittsburgh, and so 

if you were going to try to project how Pittsburgh would respond 

to a warmer climate, you need to look at how people in warmer climates respond. You can’t assume that Pittsburgh is going to respond as if it still had—— 

Mr. WEBER. You’d buy adequate air conditioning. I can tell you 

from experience how that happens in the Gulf Coast. 

Mr. CASS. That’s exactly right. And I think it’s important to point 

out when we talk about adaptation that, you know, technological 

adaptation—and certainly that’s the title of the hearing—is only 

one form of adaptation. There are biophysical adaptations. People 

do get used to the heat. There are behavioral adaptations. There 

are economic adaptations. There are social adaptations. 

Mr. WEBER. There’s probably a certain number of people in Pittsburgh who don’t buy air conditioning because of the cost because 

they figure they can tough it out in the warmer times because it 

has a cooler climate more often more so than Texas does, and then 

even though 71 degrees to us is very, very cool—you know, Texas 

can be 95 to 100, 105—and when they get caught with higher temperature, in my opinion, that should be 90, 95 or 100, depending 

on how much ventilation’s in that home, then people could suffer 

heat strokes and be in real dire danger. Do you think that’s part 

of the hype, trying to force more regulations on the energy industry? 

Mr. CASS. So just to clarify, the 71 degrees is the low, so a day 

with a low of 71 is a warm day, but I think you’re exactly right 

that people in Pittsburgh are not going to respond to one very 

warm day a year the way they would respond if they had 30, and 

so you’d expect to see them behave differently in the context of a 

changing climate. I do think that part of the impetus for not including good analyses of adaptation in topline cost estimates is to 

create large topline cost estimates, and the fact that a lot of these 

analyses actually do provide analyses with adaptation but put 
90 

those off to the side as an alternative case instead of as the main 

case I think is one of the problems. 

Mr. WEBER. Well, I will tell you—— 

Dr. DUFFY. If I could offer a comment on—— 

Mr. WEBER. No. I’m sorry, Mr. Duffy. I’m running out of time. 

I can tell you from experience, 35 years in the air conditioning 

business, that the higher the efficiency ratings went up and the 

price was driven up, the less likely customers were to buy. They 

were hard pressed to say they’ll spend $6,000 or $7,000 for a new 

air conditioning system. All of a sudden you’ve created one now 

where you’ve got to be more efficient, better compressors and more 

crawl space, and now those are 8,000 or 9,000. They’re having trouble coming up with the six much less the eight or nine. So what 

do they do? They fix the old clunker that’s terribly energy inefficient and keep it going for yet another year. 

Mr. Chairman, I yield back. 

Chairman SMITH. Thank you, Mr. Weber. 

And the gentleman from Pennsylvania, Mr. Lamb, is recognized 

for his questions. 

Mr. LAMB. Thank you, Mr. Chairman, and before I ask any questions, I’ll just testify as a southwestern Pennsylvanian that the 

good people of Pittsburgh are going to be just fine. We have 

throughout our history and I think our record of sports championships helps testify to the toughness that we have. Obviously we’re 

very concerned about how costly these changes will be, especially 

in a part of the country like ours. People are elderly, and the costs 

of cooling your home an extra 5 degrees will be difficult for people 

living on Social Security and pensions, but I just wanted to make 

that comment. 

Also, Mr. Chairman, if it’s all right, I would like to introduce a 

study without objection. It is from the NASA Jet Propulsion Laboratory in California. It addresses the issue of ice losses in the Antarctic that was discussed earlier. Dr. Duffy was asked several questions about it, and this is just meant simply to show that it is a 

complicated issue and that it was government-funded NASA research that has really helped us improve our understanding of this 

complicated problem. 

Chairman SMITH. Without objection, that will be made a part of 

the record. 

[The information follows:]*************** COMMITTEE INSERT 

*************** 

Mr. LAMB. Thank you, Mr. Chairman. 

Now, Dr. Nordhaus—or Mr. Nordhaus, I’m sorry—if I could ask 

you a question about the importance of America’s nuclear plants. 

Your testimony noted that it’s important to keep these plants open, 

and you noted a few things: state and federal clean energy standards, intervention at FERC, and other measures that could do this. 

Could you just briefly expand on that? What are some other options 

we have to help these nuclear plants that are at risk of closing? 

Mr. NORDHAUS. I think properly valuing both the reliability and 

the low-carbon nature of the electricity they produce, and there are 

a bunch of different ways to do that. I think that many states with 

nuclear plants that are threatened with closure also have renewable portfolio standards, and if we transition those to clean energy 
91 

standards, we could both significantly raise the bar in terms of 

what the requirements for zero carbon energy in those states was, 

keep those plants online for quite a while longer, and at some point 

if it makes sense to close them and replace them with other—we’ll 

know they’ll be replaced with other zero-carbon options as opposed 

to fossil fuel-powered options so—— 

Mr. LAMB. Are you aware of efforts in New Jersey, Illinois, New 

York to do exactly that? Do you support those efforts? 

Mr. NORDHAUS. Yeah, I support all of those efforts, and again, 

would only suggest that we’d be much better served moving from 

a sort of one-off bailing out nuclear plants plant by plant to a more 

broader strategy to increase low-carbon energy on the grid by keeping all of our nuclear plants operating. 

Mr. LAMB. I also wanted to ask about R&D spending. I’ve read 

a report recently from Boston Consulting Group, and it suggests 

that the United States still leads the world in frontend basic R&D 

spending like in basic research but that where we have been surpassed by China is in actually bringing these technologies to the 

market, and now they’re spending more than us in that regard. 

Can you talk about what we could do at our national labs or elsewhere to close that gap and try to get more American-funded research to the market in America and elsewhere? 

Mr. NORDHAUS. Yeah, I think there’s an old idea about R&D, 

which is that there’s this sort of thing called basic science that you 

put in a box and you fund that and then sort of private firms take 

that and do things with it. I think that when you look at the Chinese model, it’s very much state led. I think that in the United 

States when you really look at most of our greatest successes, certainly in energy but in many, many other technological arenas, 

what we’ve really seen are public-private partnerships where there 

is significant public support for applied research. Often first-of-akind technologies are quite costly to build, whether it’s your first 

nuclear plant or your first big carbon capture facility, and those 

things do require public support. The private sector isn’t going to 

do it alone. 

Mr. LAMB. And just lastly, before we run out of time, you had 

mentioned earlier the idea of federal and state combinations. I 

think you mentioned a federal transportation project or demonstration when you were asked about clean fuel earlier and how we 

might bring that to market. Could you just elaborate on that a little bit? 

Mr. NORDHAUS. Yeah. I think that there are a variety of efforts, 

longstanding efforts actually, to sort of get these technologies to 

market, and it’s been both state and federal policy that sort of have 

gotten us to the point where we do have cleaner fuels—— 

Mr. LAMB. Do you have like a specific example to illustrate that? 

Mr. NORDHAUS. You know, going back even to the 1990s, there 

was a big federal partnership with the automakers on battery technology that really sort of established the trajectory that we’re on 

now in terms of electric vehicles, so that would be one. 

Mr. LAMB. Thank you, Mr. Chairman. I yield back. 

Chairman SMITH. Thank you, Mr. Lamb. 

And the gentleman from Texas, Mr. Babin, is recognized. 
92 

Mr. BABIN. Yes, sir. Thank you, Mr. Chairman. Thank you to the 

witnesses as well. 

Mr. Nordhaus, it is unrealistic to assume that we will be able to 

rely on renewable energy like wind and solar in the near future for 

all of our energy needs. Is that a true or false statement? 

Mr. NORDHAUS. That would be my view. 

Mr. BABIN. Okay. How do we decide when it’s time to reduce 

wind and solar subsidies to allow the market to take over? 

Mr. NORDHAUS. I think that with mature wind and solar technologies, which is mostly what we’re subsidizing now, there is general agreement including among proponents of those technologies 

that they are competitive in many contexts with fossil fuel technologies. I think we’re probably at the point where we ought to put 

that proposition to the test and scale back subsidies. Now, I do 

think that there are probably a range of advanced renewable technologies that we may want to continue to provide some support for, 

but when you’re looking at cheap solar, 15 percent efficiency solar 

panels that are being mass produced in China, I’m not quite sure 

why we’re, you know, paying, you know, substantially continuing 

to subsidize them. 

Mr. BABIN. I got you, and I agree with you 100 percent. 

Dr. DUFFY. I’d be happy to add a comment on that if I may. 

Mr. BABIN. Well, I’m not through just yet. We had the Department of Energy Secretary here just last week, and we brought out 

the fact that some federal agencies had formally been articulating 

and reporting on the amount of subsidies for solar versus fossil fuel 

versus wind, et cetera, and it was astounding to see just a few 

years ago like 4 years ago that we were spending something like 

15 times more subsidizing solar than we were, say, fossil fuels, in 

fact, even 100 times in some cases, and all of a sudden this agency 

that was reporting this went silent. We’re not able to see those reports over the last few years, and we don’t know whether they 

don’t want the public to see these huge discrepancies or what the 

reason is, but Secretary Perry said that he was going to look into 

this and start printing these reports out again. Thank you. 

Thank you. Why is it important, Mr. Nordhaus, that the United 

States not stand in the way of developing countries’ efforts to build 

and improve infrastructure even if it means more fossil fuel consumption? 

Mr. NORDHAUS. Well, as I noted earlier, when it comes to infrastructure, that’s what makes us adaptable and resilient to a changing climate and to just existing climate extremes, so if you’re concerned about the impacts of climate change on poor populations in 

the developing world, the most important thing that they can do 

certainly over the next couple of decades is build infrastructure, 

and right now a lot of that infrastructure still requires fossil fuels, 

so we should be clear-eyed about the tradeoffs between mitigation 

and adaptation in those particular contexts. 

Mr. BABIN. Thank you. 

And Mr. Cass, in your testimony you mentioned that the Mills 

study included an alternative analysis from its main findings that 

excluded human adaptive response to temperatures. Do most temperature studies that you have analyzed come with such a dis-
93 

claimer to the public that human ability to adapt is not considered 

a factor? 

Mr. CASS. Usually the study itself will state that, and I would 

say fairly clearly if you go and find the original report and read it, 

you can understand what they’re doing. I think the problem is that 

by the time it gets summarized up to the GAO summary to policymakers, certainly by the time it gets reported in the newspaper, 

that kind of context is either lost entirely or put down at the bottom when in fact it’s the very heart of the issue. 

Mr. BABIN. And then also, back to you, Mr. Nordhaus, you testified that the U.S. carbon emissions are lower today than what 

would have been mandated by the Waxman-Markey legislation in 

2009 that failed to pass Congress. What has been the primary driver in this reduction? 

Mr. NORDHAUS. The biggest single driver has been the shale gas 

revolution, which I would note, you know, is a classic example of 

the sort of public-private partnership to develop, commercialize 

cheap scalable technology that we need a lot more of. I think that 

I will also note that once upon a time, we thought of natural gas 

as a bridge fuel in the power sector from high-carbon to low-carbon 

intensity. I think when you look at the record, having looked at 

generation shares in the power sector over the last decade, I think 

there’s a pretty strong case that natural gas is mostly doing exactly 

that, that it has been displacing coal, and that in more recent years 

a lot of natural gas generation has been displaced by wind, which 

is the other, the second largest driver of falling emissions in the 

power sector. 

Mr. BABIN. And I can vouch for that because my home district 

of southeast Texas had a brand-new biomass plant meant to take 

wood products and convert them into electricity to be sold on the 

grid, and yet within just a few short years later this brand-new 

plant is now sitting idle because of the cheap natural gas feedstocks that we have today, so anyway, thank you very much, and 

Mr. Chairman, I’ll yield back. 

Chairman SMITH. Thank you, Mr. Babin. 

The gentleman from Florida, Mr. Crist, is recognized. 

Mr. CRIST. Thank you, Mr. Chairman. 

I am from Florida. I first want to thank the witnesses for being 

here today. I appreciate your time. I represent on the west coast 

of Florida Pinellas County, which is the St. Petersburg, Clearwater 

area. Pinellas County happens to be a peninsula, and Florida, as 

you’re aware, is a peninsula also, and some make the argument 

that Florida may be the state that is most susceptible to rising sea 

levels. 

Having said that, Dr. Duffy, I’d like to ask you, what would you 

say are the three greatest causes of climate change, if you could do 

that? 

Dr. DUFFY. Well, there’s really two major causes, and the first 

is—well, human emissions of greenhouse gases generally and that 

comes from two sources. One is burning of fossil fuels, and the 

other is land-use practices like deforestation and also agriculture. 

Agriculture historically has released a large quantity of carbon dioxide into the atmosphere. 

Mr. CRIST. How so? 
94 

Dr. DUFFY. Through tilling of soil. Agriculture also releases other 

greenhouse gases besides CO2: methane, nitrous oxide, methane 

through livestock largely, nitrous oxide through fertilizers. Agriculture food production is a very significant source of human greenhouse gas emissions. 

Mr. CRIST. You said that the first cause is human emissions? Is 

that how you described it? 

Dr. DUFFY. Yes, sir, and within the category of human emissions, 

the biggest contribution historically has been burning of fossil 

fuels. 

Mr. CRIST. And what would be the simplest way to stem the tide 

of that level of fossil fuel burning? 

Dr. DUFFY. Well, what needs to happen is adoption of carbon-free 

energy sources as we’ve been discussing here this morning. 

Mr. CRIST. And which do you think are the most effective? 

Dr. DUFFY. Well, as I said, you know, I would argue for accelerated deployment of the technologies we have today, which are 

mainly wind and solar. I think Mr. Nordhaus has argued persuasively for the need to keep nuclear power in the mix, and I agree 

with that, but those are the technologies that we have today. I do 

also support the development of new technologies and new ideas. 

Mr. CRIST. You know, when you think about how much we utilize 

coal, fossil fuels as an energy source, and automobiles are, I assume, a big contributor to carbon emissions as well, if we had all 

cars become electric, would that have a significant impact on the 

reduction of emissions? 

Dr. DUFFY. It would. In the United States, the transportation 

sector, which is of course more than just cars, the transportation 

sector contributes roughly 25 percent of our greenhouse gas emissions. In California where I’ve spent most of my life, it’s actually 

much higher proportion, almost 50 percent, 40, 50 percent. You 

know, certain—— 

Mr. CRIST. Because of the amount of automobiles? 

Dr. DUFFY. We drive a lot in California. You know, I agree with 

Mr. Nordhaus that, you know, certain parts of the transportation 

sector are pretty easy to electrify, and cars are certainly an example of that. I mean, we have electric cars now. They’re treat. I drive 

one. Other parts of the transportation sector will be much, much 

more difficult. We haven’t mentioned aviation but that’s probably 

the best example. 

Mr. CRIST. Great. Thank you very much. I appreciate your time. 

I yield back. 

Chairman SMITH. Thank you, Mr. Crist. 

And the gentleman from California, Mr. Takano, is recognized. 

Mr. TAKANO. Thank you, Mr. Chairman. 

Mr. Duffy, did you have anything more to say about renewables, 

claims being made about the viability of renewables? 

Dr. DUFFY. Yeah. Well, on the economics, I mean, there are—and 

I guess there’s conflicting figures but fossil fuels have certainly 

been heavily subsidized as well, and I’ve seen figures suggesting 

that fossil fuels are actually more heavily subsidized than renewables. 

The other thing that’s important to mention about cost is that for 

fossil fuels, there’s tremendous environmental costs associated with 
95 

the use of fossil fuels, which are not reflected in the price, and 

we’ve been focusing today on the climate consequences of fossil 

fuels but there’s also very, very important public health consequences, and just to give you an example, particulate pollution 

from use of coal even today kills about 10,000 Americans a year. 

Now, that number has come down dramatically in large part because of EPA regulation on coal-burning power plants, and I’d also 

add to that that if you look and you compare mortality from coal 

use in China to mortality from coal use in the United States, and 

I’m not talking about different amounts of coal being used, I’m saying per ton of coal burned, the mortality in the United States is 20 

times less than that in China, and that’s because we have very effectively and cost-effectively regulated the air pollution from coal 

burning. 

Mr. TAKANO. I’m curious about something. I struggle with this 

idea of nuclear power being a carbon-free source. I mean, I hear 

you saying that you agree, Mr. Nordhaus, that you don’t want to 

rule it out as part of the mix that we need to employ to reduce the 

amount of carbon we emit. Is there—but isn’t there some problem 

that we have with managing the spent fuel? Isn’t there some enormous subsidy that the government will have to—or at least use the 

leverage of its power to force communities who don’t really want 

to have the risk of the spent fuel in their backyard or nearby for 

those communities that do produce the fuel? I mean, presumably 

everybody would benefit from it. There’s some generalized socialized good that comes from it but how do we think about this? 

Mr. NORDHAUS. Well, look, nuclear power is not without its 

issues, and you mentioned disposal of spent fuel. There’s, you 

know, also legitimate concerns about weapons proliferation. I will 

say, you know, a couple points though. I mean, it can be used effectively. At one point I think the country of France generated 80 percent of their electricity from nuclear power. I would also say that, 

you know, the safety issues with nuclear power have been greatly 

exaggerated, not to say they don’t exist but if you look at the actual 

safety record of nuclear power in the United States, I don’t think 

there’s been one human death attributed to nuclear power in the 

United States, and that’s remarkable. And as I said, fossil fuels are 

extraordinarily dangerous. You know, even solar panels, there’s 

some amount of mortality. People fall off roofs and so on. 

Mr. TAKANO. This is a much deeper conversation, I would say, 

but a recent report by the Department of Defense on climate risk 

to DOD infrastructure that was recently submitted to Congress 

was determined to have had significant edits made from a draft 

version from December 2016. Major changes in the report include 

omission of references to climate change. 

Dr. Duffy, how important is it to ensure that accurate scientific 

assessments regarding impacts due to climate change be made 

available to the broader public and to our military specifically? 

Dr. DUFFY. Thanks for the question. You know, the military leaders that I’ve talked to clearly recognize the threat that global climate change poses for their operations and their war-fighting capabilities, and I think that that threat needs to be recognized, and 

I would hate to see our fighting men and women placed at unnecessary risk because we’re afraid to confront this threat. 
96 

Mr. TAKANO. Well, what are the dangers of playing down the role 

of climate impacts on infrastructure, both military and non-military, to try and stay—in order to try and stay, quote, unquote, apolitical? 

Dr. DUFFY. You know, the danger is that we don’t build the right 

infrastructure, you know, and we do—we have—we face a backlog 

of decaying infrastructure in this country, infrastructure of all 

sorts, not just transportation infrastructure—energy infrastructure 

and so on. We need to invest in new infrastructure, and as we do 

that—and I’ve been involved in some major water infrastructure 

projects in California and, you know, these major physical infrastructures typically are designed to last 50 or 100 years, and you 

know, what we did when we designed water infrastructure in California is to think ahead and what is the climate and hydrology of 

the next 50 or 100 years going to look like, and that’s what the 

water agencies in California do and that’s what we should do generally. We need to design the infrastructure around the climate of 

the future, not the climate of the past. 

Mr. TAKANO. Thank you. My time is up. 

Chairman SMITH. Thank you, Mr. Takano. 

Let me thank you all for being here today. I think this was a 

very worthwhile discussion of various challenges that we face, and 

I was really pleased to see more agreement than disagreement on 

the need and reliance upon innovation and technology in the future 

to address climate change as well. I appreciate the testimony and 

the manner today. You all reflected the moderation and humility 

that Mr. Nordhaus mentioned, and we have not always had that 

when we discussed this subject, so I appreciate both, as I say, what 

you said and how you said it. So thanks again for being here. 

The record will remain open for two weeks for additional written 

comments and questions from Members, and we stand adjourned. 

[Whereupon, at 12:09 p.m., the Committee was adjourned.] 
(97) 

Appendix I 

ANSWERS TO POST-HEARING QUESTIONS
98 

ANSWERS TO POST-HEARING QUESTIONS

Responses by Dr. Phil Duffy 
99 

a. Do the trends in mean global sea level rise match the trends in global carbon 

emissions in the past 100 years? 

Recent observed sea levels are consistent with the expected effects of human-caused global 

warming. Sea levels are rising in large part due to melting land ice and to thermal expansion of 

the ocean water, both of which are a consequence of increasing atmospheric greenhouse gases 

(GHG) resulting from human activities (fossil fuel burning and land use change). The 

acceleration in the rate of sea-level rise is a lagged response to warming resulting from the longterm buildup of GHG in the atmosphere. There is not expected to be a I: 1 relationship between 

global carbon emissions and sea level. The rate of sea level rise corresponds more closely to 

temperature than to annual carbon emissions, but even this relationship is not linear. 

b. What are the primary contributing factors to sea level fluctuations since the 

turn of the 20'h century? 

The table below, from the IPCC's Fifth Assessment Report, estimates the global mean sea level 

(GMSL) rise budget for three different time intervals. Both observed and modeled GMSL 

contributions show that melting of land ice and thermal expansion of the ocean together are the 

dominant cause of sea-level rise in the 20'h and 21 ''centuries. 

Global Mean Sea Level Budget (mm yr-1), 1901-2010 

G!(I(H~rs ~xcep.l in Gretmlaod and AntarctiCil' 

Glaciers in G1een!and' 

Grt!!m!andkesheet 

Antan:tkke-sheet 

land water storage 

Total of (ontributlons 

Observed GMSl rise 

:~~~it4coitt~·to·GMsL;t~;, 

lhemlale;.:pansion 

Glacmrs exc~t in Grl!«<limd: ;md Antarctica 

Gl.lciefsinGreenland 

Total including land water stotage 

Residual< 

Data lor all gladus exttmd to 2009, not1010. 

This cunlributioo is not mdudffi in tho> total bec<~use glade.>rs in Greenland are illC!uded in thl<' obwvational ass~sment of tt1t Greenland k!! s~t. 

Obse1'111'!d GMSl rise- modelled tMrmal expansion- modelt!l'd glactel>- observ~ land water Stl:ltagf!, 

Source: Table 13.1, IPCC WGI AR5, Chapter 13 

0}6!0J9to1.1ll 

OJO [1101 toO.ll]~ 

1}33!0.15!00.411 

0.27 f£U6to0.38J 

0.38[0.26!00.49! 

a{2.lto3.4l 
100 

2. Please describe how Antarctic ice sheet extent has varied in recent years. 

The Antarctic ice sheet has been losing ice during the last two decades, and that net loss has been 

accelerating. The figure below illustrates an acceleration of the rate of mass loss of the Antarctic 

ice sheet through 2012. 

~3000 

Q. 

"' Sl 

~ 2000 

~ 

-~ ~ 1000 

~ 

"5 

E 

:> 

(.) 0 

1992 1994 

Acceleration of Antarctic Ice Sheet Decay 

Antarctica 

Cumulative ice mass loss 

Uncertainty range 

1998 2000 2002 2004 2006 2008 2010 

Year 

8 

6 

E' 

4 §. 

2 

0 

w 

...J 

(/) 

Flgur\1 4.1$ l CumulatiVe ~ mass loss (an<! sea ~e! equivalent, StE} from Antafttica demred as annual averages from 10 ~ent studies {~ main text and Appelldtx 4.A for detmls}. 

Source: Figure 4.16. IPCC WG1 ARS, Chapter 04. 

The IPCC's Fifth Assessment Report concludes the following: 

"The Antarctic ice sheet has been losing ice during the last two decades (high confidence). There 

is vety high confidence that these losses are mainly from the northern Antarctic Peninsula and 

the Amundsen Sea sector of West Antarctica. and high confidence that they result from the 

acceleration of outlet glaciers. 

The average rate of ice loss from Antarctica likely increased from 30 [~37 to 97) Gt yr~l (sea 

level equivalent. 0.08 [~0.10 to 0.27) mm yr~l) over the period 1992-·2001, to 147 [72 to 221) 

Gt yr~l over the period 2002-2011 (0.40 [0.20 to 0.61) mm yr--1). 

A more recent assessment (published in Nature on June 13. 2018) weighed the results of24 

studies of antarctic ice loss and found that the rate of ice loss has increased 3x in the past I 0 

years. 
101 

a. Can you please address the discrepancy with recently reported Antarctic ice 

sheet gains compared to an increase in global atmospheric and ocean 

temperatures? 

A 2015 NASA study based on satellite altimetry concluded that the Antarctic ice sheet was 

gaining ice overall. This conclusion contradicted those of both earlier and later studies. The 4th 

National Climate Assessment, released by the Trump administration in November 2017, weighed 

evidence available at the time and concluded that the Antarctic icc sheet is shrinking. 

b. Do ice sheet gains disprove the overall levels of rapid ice loss recently in the 

Antarctic? 

Gains in some regions of the Antarctic ice sheet are not enough to overcome losses of ice in 

other regions. 

3. How did energy conservation regulations for refrigerators impact the energy 

consumption, price, and size of refrigerators? 

Starting in the mid-l970s, California and the United States issued a series of energy conservation 

regulations for home refrigerators. As a result, the average energy demand per new refrigerator 

declined dramatically, from about 2,000 kilowatt hours used per year to about 500 kilowatt hours 

per year. 

Annual energy use of a new refrigerator, 1950 -2008 

kilowatthours per year 

2 000 

1 500 

1 000 

500 

0 

1950 1960 1970 1960 1990 2000 

Source: EIA (https://www.eia.gov/todayinenergy/detail.php?id= l 0491) 

federal standard 

2010 2020 

The two figures included here on home refrigerator appliance history demonstrate that 

refrigerator volume has increased while the purchase price has fallen over the same historical 

time period. 
102 

Price 

{ln2009$) 

2000 1200 23 

22 

1500 1000 

21 

1000 800 

20 

600 600 

19 

0 400 18 

1974 2008 

Source: U.S. Department of Energy (https://www.energy.gov/eere/buildings/articles/refrigeratorstandards-saveconsumers-billions). 

a. What impact have refrigerator standards had on the American consumer? 

The history illustrated here suggests that regulation has led to cheaper and more efficient 

refrigerators. 

b. Did the presence of regulations hinder or enhance the development of new 

refrigerators? 

It appears that regulation had a role in stimulating innovation in refrigerator design. 
(103) 

Appendix II 

ADDITIONAL MATERIAL FOR THE RECORD
104 

STATEMENT SUBMITTED BY DR. JUDITH CURRY

Major points: 

STATEMENT TO THE 

COMMITTEE ON SCIENCE, SPACE AND TECHNOLOGY 

OF THE UNITED STATES HOUSE OF REPRESENTATIVES 

Hearing on 

Using Technology to Address Climate Change 

16 May 2018 

Judith A. Curry 

Climate Forecast Applications Network 

Georgia Institute of Technology 

<;urryjl[Qith(,l:yahoo.com 

There are multiple causes of climate variability and change, and climate is just one element of the 

complex causes of vulnerability of human and natural systems. 

In adapting to climate variability and change, we need to acknowledge that we cannot know 

exactly how the climate will evolve in the 21 ''century, we are certain to be surprised and that we 

will make mistakes along the way. 

Possible scenarios of incremental worsening of weather and climate extremes don't change the 

fundamental storyline that the U.S. is highly vulnerable to current extreme weather and climate 

events and has an adaptation deficit relative to the current climate state and historical extreme 

events. 

Rather than 'bouncing back' from extreme weather and climate events, we can 'bounce forward' 

to reduce future vulnerability by evolving our infrastructures, institutions and practices. 

A focus on local policies that support resilience and anti-fragility avoids the hubris of thinking we 

can predict the future climate. 

Rather than negotiating an optimal policy based on a negotiated scientific consensus, robust and 

flexible policy strategies can be designed that account for uncertainty, ignorance and dissent. 

Climate models are not the only, or best, way to generate future scenarios of regional climate 

change. Current climate model predictions neglect important aspects of natural variability. 

All scientifically plausible scenarios of future climate change need to be on the table to inform 

adaptation, not just those selected by a particular heuristic, e.g. emissions scenarios. 

On regional and decadal time scales, the greatest vulnerability to climate change is not associated 

with the smooth long-term trend but rather with rapid shifts in frequencies and intensities of 

extreme weather and climate events that are driven by natural internal climate variability. 

Sea level rise is an issue for which anticipatory adaptation is justified by our scientific 

understanding of the direction (if not the magnitude) of future sea level change. 

Large-scale ocean circulations can cause regional sea level rise to exceed global mean sea level 

rise by an order of magnitude. 

In many of the locations that are most vulnerable to sea level rise, natural oceanic and geologic 

processes plus land usc practices are the dominant causes of current local sea level rise problems. 

The focus of climate science on mitigation-relevant science (e.g. attribution, sensitivity) has 

diverted resources away from regional climate dynamics and prediction of extreme events on 

weekly to seasonal time scales that would support tactical and strategic adaptation decisions. 
105 

STATEMENT TO THE 

COMMITTEE ON SCIENCE, SPACE AND TECHNOLO(;y 

OF THE UNITED STATES HOUSE OF REPRESENTATIVES 

Hearing on 

Using Technology to Address Climate Change 

16 May 2018 

Judith A. Curry 

Climate Forecast Applications Network 

Georgia Institute of Technology 

curry j ud~th@ yahsJO.com 

I thank the Chairman and the Committee for the opportunity to offer testimony today on 'Using 

Technology to Address Climate Change.' l am Professor Emeritus of the School of Earth and 

Atmospheric Sciences at the Georgia Institute of Technology. I have devoted four decades to 

conducting research on a variety of topics related to weather and climate. In recent years my focus 

has been on uncertainty and the interface between climate science and policy. As President of Climate 

Forecast Applications Network LLC, I have been working with decision makers to usc weather and 

climate information to reduce vulnerability to extreme weather and climate events. 

In 2014, I was privileged to host to host the UK-US Workshop on Climate Science Needed to Support 

Robust Adaptation Decisions.' The Workshop participants included some of the world's leading 

thinkers and practitioners on climate adaptation. The Workshop was motivated by the recognized gap 

between what science is currently providing in terms of infonnation about climate variability and 

change, versus the information desired by decision to make robust development and adaptation plans 

for managing climate-related risks and responding to opportunities. The focus was on timescalcs out 

to 2050 and regional scales. The Workshop addressed perspectives from the public and private 

sectors' on climate adaptation, strategies for robust decision making,3 limits of climate models." and 

broadening the portfolio of climate information-' The insights from this Workshop provide the 

framing for my testimony. 

Adapting to climate change 

In context of the debate on climate change, two overarching policy response options have been 

articulated: 

l. Mitigation of climate change through reduction of greenhouse gas emissions 

2. Pre-emptive adaptation to climate change through improved infrastructure, land usc practices 

and management of resources. 

1 https://judithcurry .com/20 14/02/ I 0/uk-us-workshop-on-climate-sciencc-needed-to-support-robust -adaptation-decisions/ 2 https:/ /judi thcurry .com/20 14/02/ 12/uk-us-workshop-part -ii-perspecti ves-from -the-private-sector-on-climate-adaptation/ 

J https:/ /judithcurry .com/20 14/02/14/uk -us-workshop-part-iii-strategies-for-robust-decision-making-for-climate-adaptation/ 

~ https://judithcurry .com/20 14/02/18/uk -us-workshop-part -iv -I imits-of-c limate-modcls-for -adaptation-decision-making/ 

::-. tmn~~ithcurnt.com 20!-!. 03 l9 uk-us-\V~Qr_k~_QQ_:Q~!!:!:-v-broad..:nimHb.c--portfo!to-of-climate-in[q.r.!l.J.?-t!9n· 

2 
106 

In stratcgizing about both mitigation and adaptation to climate change, it is important to recognize 

that both policy options exist in context of a broad and complex policy environment: 

[. Mitigation impacts global, national and regional policies on energy, transportation, 

agriculture and environmental quality, with concomitant issues related to economics and 

security 

2. Adaptation is in response to both human caused and natural climate variability and weather 

extremes, and is driven by local vulnerabilities, economic capacity, cultural values and 

governance. The impacts of weather and climate extremes arc exacerbated by growing 

populations and the associated resource requirements, plus increasing development on lowlying coastal regions, floodplains and hill slopes that are well known to be vulnerable to 

storms. 

Nearly all human societies and activities arc sensitive to weather and climate. People have always 

adapted to weather extremes and climate variability, and many community coping strategies already 

exist. The Intergovernmental Panel on Climate Change (IPCC) Special Report on Extreme Events" 

acknowledges that there is not yet evidence of changes in the global frequency or intensity of 

hurricanes, droughts, floods or wildfires. The existence of a signature of human-caused global 

warming on sea level rise acceleration is still being debated. Nevertheless, the focus of analyses of 

adaptation to human caused climate change has been on anticipatory adaptation to new conditions 

that arc outside of the range of those previously experienced, that arc predicted in response to humancaused warming based on climate model simulations. 

The extreme damages from recent hurricanes such as Katrina, Sandy and Harvey plus the recent 

billion dollar disasters from floods, droughts and wildfires, emphasize that the U.S. is highly 

vulnerable to current weather and climate disasters, not to mention the more extreme disasters that 

were encountered in the U.S. during the 1930's and 1950's. Possible scenarios of incremental 

worsening of weather and climate extremes over the course of the 21" century doesn't change the 

fundamental storyline that the U.S. is not well adapted to the current weather and climate variability, 

let alone the range that has been experienced over the past several centuries. 

As a practical matter, adaptation has been driven by local crises associated with extreme weather and 

climate events. emphasizing the role of 'surprises' in shaping responses. Advocates of adaptation to 

climate change are not arguing for simply responding to events and changes after they occur: they are 

arguing for anticipatory adaptation. But arguments for preparing for the consequences of global 

warming rest on an implicit assumption that we can reliably anticipate the changes to which we will 

be adapting and therefore that we can sensibly plan for those changes. Unfortunately, climate models 

do not provide us with the information needed to anticipate the local consequences of climate 

variability and change. 

The challenge for climate change adaptation is to work with a broad range of information about 

regional vulnerabilities and climate variability in the context of a decision-analytic framework that 

acknowledges deep uncertainty. 

Resilience, anti-fragility and thrivability 

In adapting to climate change, we need to acknowledge that we cannot know how the climate will 

evolve in the 21 '' century, we are certain to be surprised and we will make mistakes along the way. 

There is much to be learned from the extraordinary adaptations of species and ecosystems in the 

natural world. 

6 http://www.ipcc.ch/report/srex/ 

3 
107 

'Resilience' is the ability to 'bounce back' in the face of unexpected events. Resilience carries a 

connotation of returning to the original state as quickly as possible. Vulnerabilities to extreme events 

typically reveal a gap between the present situation and what is needed to reduce future vulnerability. 

Hence, we need to 'bounce forward' to reduce future vulnerability by evolving our infrastructures. 

institutions and practices. 

The concept of 'thrivability' has been articulated by Jean Russell:' 

"It isn't enough to repair the damage our progress has brought. It is also not enough to 

manage our risks and be more shock-resistant. Now is not only the time to course correct and 

he more resilient. It is a time to imagine a'lwt \<t'e can generate for the "1-1/0rld. Not on(v can we 

work to minimi::e our footprint but we can also create positive handprints. It L1 time to strive 

fbr a world that thrives. " 

A related concept is Nicholas Taleb's 'anti-fragility'' that focuses on approaches that enable us to 

thrive from high levels of volatility, particularly those unexpected extreme events. Taleb argues that 

the most profound and important of these unexpected events are by their very nature unpredictable. 

Taleb regards the real opportunity to be learning and growth from volatility and unexpected events -

not to return to where you were. but to become even better as a result of encountering and 

overcoming challenges. Anti-fragile systems are dynamic rather than static, thriving and growing in 

new directions rather than simply maintaining the status quo. Anti-fragile systems require random 

events to strengthen and grow, and so avoid becoming brittle and fragile. 

Strategies to increase anti-fragility include economic development, reducing the downside from 

volatility. developing a range of options, tinkering with small experiments, and developing and 

testing transformative ideas. Anti-fragility is consistent with decentralized models of policy 

innovation, that create !1cxibility and redundance in the face of volatility. This 'innovation dividend' 

is analogous to biodiversity in the natural world, enhancing resilience in the face of future shocks 9 

A focus on policies that support resilience and anti-fragility avoids the uncertainties of attributing 

climate change to humans versus nature and avoids the hubris of thinking we can predict the future 

climate. The questions then become: 

How can we best promote the development of transforrnative ideas and technologies" 

How much resilience can we afford'? 

Decision- analytic approaches 

Traditional approaches to risk management work well when the future is changing slowly. is 

predictable and docsn 't generate much disagreement. Predict-then-act methods can backfire when 

uncertainties arc underestimated, competing analyses engender disagreement and decision makers are 

blinded to surprises. Acting on fc>recasts of the unpredictable can contribute to bad decisions. 

Climate-related decisions involve incomplete information from a fast-moving and irreducibly 

uncertain science. There arc many different interests and values in play, the relevant time scales are 

https:/ rwww.amazon.com/Thrivability-Break ing-through-World· W orksidpi 19094 7028 7 

t\ Taleb, 'N 2012 Antifragile: Thing.~,· That Gain From Disorder. Random House. 9 Amanda Lynch, Climate Change Adaptation Policy Innovation: Subsidiarity, Diversity ad Redundancy. 

https:/ljudithcurry.com/2014/02/14/uk-us-workshop-part-iii-stratcgics-for-robust-dccision-making-for-climate~adaptation/ 

4 
108 

long and there is near certainty of surprise. Current policies often neglect known unknowns- leading 

to overconfidence and poor decisions. 

The bottom-up resource-based vulnerability perspective 10 determines the major threats to local and 

regional water, food, energy, human health, and ecosystem function resources from extreme events 

including those from climate but also from other social and environmental issues. Relative risks can 

be compared with other risks in order to adopt optimal preferred mitigation/adaptation strategies. This 

is a more inclusive approach for policy makers to deal with the complexity of the spectrum of social 

and environmental extreme events that may occur, beyond just the focus on greenhouse gases as 

emphasized in the IPCC assessments. 

Rather than seeking an optimal policy based on a negotiated scientific consensus. robust and flexible 

policy strategies can be designed that account for uncertainty, ignorance and dissent. Flexible 

strategies can be quickly adjusted to advancing scientific insights and new conditions that arise. 

Robust decision making strategies 11 manage deep uncertainty by nmning the analysis backwards: start 

with a proposed strategy, identify future scenarios where strategy docs and does not meet its goals, 

and identify steps that can be taken so strategy may succeed over a wider range of future 

scenarios. Stakeholders can then debate about how much robustness they can afford- which is more 

useful than debating what the future will be. 

Climate Informed Decision Analysis (CIDA)" is an approach that identifies which scenarios of 

climate change would affect the project and then determines the likelihood of those scenarios. As a 

process committed to acceptance of deep uncertainties, CIDA does not attempt to reduce uncertainties 

or make predictions, but rather focuses on determining which decision options arc robust to a range of 

plausible futures. 

Adaptive governanccL' focuses on decentralized decision-making structures in the face of the 

complexity and uncertainty associated with rapid environmental change. This allows large, complex 

problem like global climate change to be factored into many smaller, more tractable problems. In an 

integral sense, addressing these smaller problems corresponds to adaptation to profound uncertainties 

that are inherent in complex systems that limit predictability. Planning to meet projected targets and 

timetables is secondary to continuing appraisal of incremental steps toward long-term goals. Each 

step in such trial-and-error processes depends on politics to balance and integrate the interests of 

multiple participants to advance their common interest. 

The climate knowledge gap 

The focus of the UN Framework Convention on Climate Change'" on mitigation policies has arguably 

led the adaptation problem and its solutions in a direction that relics on mitigation-relevant science 

(i.e. attribution of global climate change and sensitivity to C02), rather than on understanding natural 

climate variability and regional risks in the context of vulnerability. 

Climate models consistently indicate that the mean global temperature of the planet will rise with 

increasing C02 emissions. However, models show systematic errors in the simulated global mean 

tcmperah1re that is similar in magnitude to the size of the historical change we arc seeking to 

10 https;i/pielkcclimatcsci.files.wordpress.com/2012/l O/r~365l.pdf 11 https://www .rand.org/pubs/research briefs/RB970 l.html 11 http:!.'elibrary.worldbank.org/content/workingpaperl! 0.159611813-9450-6193 13 http://press.uchicago.edu/ucp;books/bookldistributed/ A!bo8917780.html 1

" https: 1

/unfccc.int 

5 
109 

understand. 15 Further, it is important to recognize that mean global climate is not what any one locale 

or nation will be adapting to. 

There is a gap between the scale on which models produce consistent information and the scale that is 

relevant for human adaptation to climate change16 Attempts to 'downscale' the output of climate 

models are still in the early stages of development. Dynamical downscaling uses a higher-resolution 

regional model that is forced at the boundaries by outputs from the global climate models. The 

obvious problem with dynamical downscaling is that if the boundary conditions derived from the 

global climate model are in error, then these errors will propagate into the regional model. 

Finally, existing climate models are unable to simulate realistically extreme outcomes such as a rapid 

disintegration of the West Antarctic Ice Sheet. Hence global climate models provide little relevant 

information regarding unlikely but potentially catastrophic impacts. 

It is not at all obvious we will ever be able to model climate on scales that are quantitatively 

infonnative to adaptation decisions. Failure to appropriately communicate this 'weakest link' has 

been a critical failure of science-based policy-making. 

Scenarios of 21'1 century climate variations and change 

Adaptation strategies require information about future climate change, from both natural and human 

causes. Given the deep uncertainties surrounding regional climate change, a range of scenarios are 

needed in the context of robust decision making strategies. 

The primary narrative for communicating climate change to decision makers has been as a gradual 

and predictable process, driven by emissions scenarios. This allegedly predictable signal is distinct 

from the unpredictable natural climate variability. Hence .decision makers have focused on the 

apparently predictable trend associated with increasing emissions. However, to support decision 

making needs, all scientifically plausible scenarios need to be on the table, not just those selected by a 

particular heuristic, e.g. emissions scenarios. 17 

Natural climate variability refers to forcing from the sun, volcanic eruptions and natural internal 

variability associated with chaotic interactions between the atmosphere and ocean. The most familiar 

mode of natural internal variability is El Nino/La Nina. On longer multi-decadal time scales, there is a 

network of atmospheric and oceanic circulation regimes, including the Atlantic Multidccadal 

Oscillation and the Pacific Decadal Oscillation. It is these circulation regimes that dominate climate 

variability and extreme events on regional and decadal time scales. 

20'" century climate change is most often explained in terms of extemal forcing, with natural internal 

variability providing high frequency 'noise.' However, the role of large-scale multi-dccadal ocean 

oscillations is increasingly understood to play a more fundamental role," whereby the external 

forcing projects onto the modes of natural intcmal variability, producing 'shifts' in the climate 

system. 19 These circulation pattems act as a buffer on the climate system to small perturbations, but 

15 https:!lagupubs.onlinelibrary .wiley.com/doi/1 O.l 029/20 l2MSOOO 154 10 http://www .lsc.ac. uk/C A TS/Assets/PDF s/Publications/Papers/20 I 0/SO~AdaptationtoGlobal W anning-201 0. pdf 17https://ww\v .researchgate.net/publication/305 7238 70 _Reconciling_ anthropogenic_ eli mate_ change_ and_ variability _.on_ decad 

a! tirnescales 1 s-https://www .nature.com/anicles/197 45 

!<J Tsonis, A et aL 2007: A new dynamical mechanism for major climate shifts. Geophys. Res. Lett .. 34, Ll3705. 

https:!!panthcrtile.uwm.edu/aatsonisiwwwi2007GL030288.pdf 

6 
110 

over time can lead to an abrupt shift to a new state. These interactions on timescales from decades to 

centuries produce step changes in warming that integrate into a long-tenn complex trend. These 

complex interactions are a major determinant of changing climate risk, particularly with regards to 

extreme weather events and 'hot spots' of sea level rise. 

Significant climate shifts in the past 50 years include: 

1976/l977 Great Pacific Climate Shift: major shifts in atmospheric circulation patterns and 

extreme weather events, changes in the biota of the Pacific Ocean, greater frequency of El 

Nino cvents. 20 

1995 shift of the Atlantic Multidecadal Oscillation to the wann phase: shift to the active 

phase of Atlantic hurricanes, with a substantial increase in the number U.S. landfalls" 

200 I synchronization of multiple climate modes: early 21 ''century 'hiatus' in warming" 

The characterization of climate risk on regional and dccadal time scales changes substantially if 

climate change is characterized as being gradual versus subject to shifts. Prediction of trends over 

decadal time scales may not be useful if the climate does not behave in a trend-like fashion. Of 

greater relevance for decision making is understanding the statistics of extreme events and potential 

future shifts in the climate. 

For climate shifts, the main approach is no longer predicted trends based on global climate models, 

but rather a diagnostic approach based on the climate dynamics of the large-scale ocean circulation 

regimes. Step changes in climate can lead to significant changes in the frequency and magnitude of 

extremes and periodic shifts in means can be anticipated. A better understanding of how climate 

shifts, system complexity and systemic response may affect decision making should be a priority for 

developing scenarios of regional climate change. 

Scenarios of global climate change 

The scenarios of future global climate change provided by the IPCC AR5 arc incomplete, focusing 

only on emissions scenarios and ignoring natural climate variations: 

"With regard to solarforcing, the 1985-2005 solar cTcle is repeated. Neither projections of" 

/illure deviationsji-om this solar cycle, norfitture volcanic radiative forcing and their 

uncertainties are considered. ·· [IPCC AR5 WG I Section 12.2.3] 

"Any climate projection is su~ject to sampling uncertainties that arise because of internal 

variabilitv. [P}rediction of" the amplitude or phase of"some mode oj"variabilit\' that mav be 

important on long time .vca!es is not addressed" LIPCC AR5 \\i'GI Section 12.2.3] 

Additional scenarios that should be considered for the trend of 21st century global climate change 

(individually or in combination): 

Scenario of volcanic activity matching the 19th century eruptions 

Grand solar minimum in the mid 21st century 

Shift to the cold phase of the Atlantic Multidecadal Oscillation (AMO) 

Lower values of climate sensitivity to carbon dioxide that are consistent with observationallybased energy budget analyscs23 

0 http://horizon. ucsd.edu/miller/down!oad/c !imateshift/climate __ shift.pdf 1 Imps: \\ W\\ .rcsearch:mtc.net publica!ion ~3~~:±Jl§_~_II!~_f\S£CJ~Lln<::T~J!?.£__iJ1 Atlantic Hurricome Acti\·itv Cau?~S__i!_!l4_ 

Implication 

" https:/!agupubs.onlinelibrary.wiley.comidoi/ful\1 I 0.1 029/2008GL03 7022 23 Nicholas Lewis and Judith Curry, 20! 8: The impact of recent forcing and ocean heat uptake data on estimates of climate 

sensitivity. Journal of Climate, [h;t_[l~- ~Q_~,S!lJ!_lQJJ_25 Jl:!::L~Q_::l_7-0(J6 7.1] 

7 
111 

There are known structural inadequacies in global climate models (e.g. inadequate treatments of solar 

indirect effects, vertical ocean heat transfer and processes related to clouds). Hence in addition to 

sensitivity studies using climate models, semi-empirical methods should also be used in developing 

these additional scenarios. 

Scenarios of regional climate change 

Climate models are not the only, or best, way to generate future scenarios of regional climate change. 

Climate Informed Decision Analysis (CIDA) uses a broader range of climate scenarios": 

"Climate scenarios can be generated parametricaiZv or stochastically to explore uncertaintv in 

climate variables that affect the system olfnterest. This allows sampling changes in climate that 

include but are not constrained by the range of climate model projecrions. Scenarios can be 

developed as part of' a stakeholder-driven, negotiated process. and climate projections can be 

used in this process. For scenarios in 1vhich the climate consequences exceed coping thresholds. 

it is rhen jhtitfiil to evaluate the plausibilitv of the scenarios. Climate projections. paleoclimate 

reconstructions. and subjective climate knowledge could all infiJrm such discussions." 

Several empirical strategies have been developed for providing scenarios of regional climate change: 

Pattern scaling: the main assumption is that the spatial pattern of change is assumed to remain 

constant at any time horizon or forcing scenario14 

Projections based on regional estimates of Transient Climate Sensitivity25 

Ensemble random analog prediction'". 

On deeadal time scales, the greatest vulnerability is to extreme weather events such as floods, 

droughts, heat waves, heavy snowfalls and tropical cyclones. The future time series is of less 

relevance than decadal frequencies of extreme events (including clusters) and worst-case scenarios 

over the target time interval. Coarse-resolution global climate models do a poor job of simulating 

extreme weather events. A novel strategy has been proposed whereby high-resolution numerical 

weather prediction models arc used in a hvpothetical climate setting to provide tailored narratives 

for high-resolution simulations of high-impact weather in a future climate. 27 

My company Climate Forecast Applications Network (CFAN) has been developing a network-based 

dynamic climatology framework for developing regional dccadal scenarios of future climate. focused 

on the decadal statistics of extreme weather events." Central to this framework is the multi-decadal 

ocean oscillations, notably the Atlantic Mu!tidecadal Oscillation (AMO), and Pacific Dccadal 

Oscillation (PDO). These oscillations have a substantial impact on the frequency and intensity of 

tropical cyclones and on patterns of droughts and floods. The methodology for scenario generation 

includes generation of a synthetic climatology of the extreme events for each of the climate regimes 

as defined by the phase of ocean oscillations. 

The greatest vulnerability is not to the smooth long-term changes but rather to the prospect by 

relatively rapid shifts in the climate or a clustering of extreme weather events in a particular location. 

The network-based scenario generation framework is ideally suited to incorporating projections of 

2

"' http://www .lse.ac. uk/C A TS/ Assets/PDF s/Publ ications/Papers/20 14/Robustness~of~pattem~scaled~cl imate~change~ 

sccnarios-for-adaptation-dccision-support.pdf 25 https:/iauupubs.on!in_c.!i_Q@~'JkY-~m~49_~'aQ~_"LO-'---!QQ~-::~-Q_!_7_Q!-:Q_7_Q_942 6 http://wv.rw. lse.ac. uk/C A TS/ Assets/PDF s/Publications/Papers/ 1999-and-before/2 8·RandomAnalogue N onL in Processes1997-Paparella-ctal.pdf 27 ~!~~~\\"' .nature.com"artic!c-;'nc!imare~-t?Q 

" https:/ /docs. w ixstatic .com/ugd/867 d28 _ 83 8be4ad291 c4922857a0987 685d635 f. pdf 

8 
112 

future climate shifts. Several recent efforts have focused on predicting the next shift in ocean 

circulation regimes, but this remains at the forefront of climate dynamics research. 

1-Vorst-case scenario 

The worst-case scenario plays an important role in clarifying the upper bound of possible scenarios 

that would be genuinely catastrophic. The worst-case scenario is judged to be the most extreme 

scenario that cannot be falsified as impossible based upon our background knowledge. 

It is estimated that fully melting Antarctica would contribute over 60 meters of sea level rise, and 

Greenland would contribute more than 7 meters, with an additional 1.5 meters of sea level rise from 

glaciers. How much of this is potentially realizable in the 21st century? 

The lPCC AR5 predicted a likely range of sea level rise for the 21 ''century between 0.26 and 0.85 m 

(10 to 33 inches), depending on the emission scenario [Summary for Policy Makers]. This is 

compared to an observed sea level rise of 8 inches over the 20'h century. Additional sea level rise of I 

or 2 feet over a century can be a relatively minor problem if it is managed appropriately. The primary 

concern over future sea level rise is related to the potential collapse of the West Antarctic lee Sheet, 

which could cause global mean sea level to rise substantially above the IPCC's 'likely' range in the 

21 ''century. The IPCC AR5 has medium confidence that this additional contribution from the West 

Antarctic icc sheet would not exceed several tenths of a meter of sea level rise during the 21st century 

[AR5 WG I Chapter 13]. 

Subsequent to the 2013 IPCC AR5, there has been considerable focus on the worst-case scenario fix 

global sea level rise. Strategies for generating the worst-case scenarios include process modeling that 

employs the worst-case estimate for each component, estimates from the deglaciation of the last ice 

age and the previous interglacial, and expert judgment. 

Recent estimates of the worst-case scenario for global sea level rise in the 21" century range from 1.6 

to 2.9 m (5- 9.5 feet), with the recent NOAA Report29 using a value of 2.5 m (8 feet). These values 

of sea level rise imply rates of sea level rise as high as 50 mmiyr by the end of the 21" century. For 

reference, the current global rate of sea level rise is about 3 mmlyr. Arc these scenarios of sea level 

rise by 2100 plausible'' Or even possible? 

From the TPCC AR5: 

"These high rates are sustainable only when the Earth is emerging fi-·om periodv of extreme 

glaciation. During the transition qf the last glacial maximum about 21,000 years ago to the 

present interglacial. . coral reef' deposits indicate that global sea level ruse abruptlv by 14 

to 18 m in less than 500 years, in which the rate ol sea level rise reached more than 40 

mm~vr." [AR5 WGl FAQ 5.2] 

Rohling et a!. (20 13 )

31' provide a geologic/paleoclimatic perspective on the worst-case scenario for 

2 I" century sea level rise. These high projected rates of sea level rise are larger than the rates at the 

onset of the last deglaciation, even though today's global icc volume is only about a third of that at 

the onset of the last deglaciation. Starting from present-day conditions, such high rates of sea level 

rise would require unprecedented icc-loss mechanisms, such as collapse the West Antarctic lee Sheet 

or activation of major East Antarctic lee Sheet retreat. 

29 https://tidesandcurrents.noaa.govfpublications/techrpt83 _Global_ and_ Regional~ SLR _Scenarios_ for_ the_ US_ final.pdf 30 https://wv.'V.'.nature.com/articles/srep03461 

9 
113 

Can human caused global warming trigger such an extreme scenario on the time scale of the 21" 

century'> While on the subject of worst-case scenarios of sea level rise, we should not ignore potential 

geologic 'wild cards'. In the more likely category of geologic impacts on the time scale of the 21" 

century is geothermal heat flux in the vicinity of the Greenland and Antarctic icc sheets. 11 The worstcase scenario of a collapse of the West Antarctic Icc Sheet seems more likely to be caused by a 

geological event than by greenhouse gas emissions. However, it is impossible to assign probabilities 

to such unprecedented wild card events, and they are regarded as extremely unlikely. 

Sea level rise 

Global mean sea level has increased by about 8-9 inches since 1880, with about 3 inches occurring 

since 1993. There is no question that local sea levels are increasing in some coastal regions at rates 

that are causing damage. However attributing sea level rise to human-caused global warming is very 

challenging. This is because there are much larger impacts on local sea level rise from regional ocean 

circulations, local geological processes, land usc practices and coastal engineering. This challenge 

was recognized in the IPCC AR5 WGII Report: 

[L]ocal sea level trend> are also influenced by .fi1ctors such as regional variability in 

ocean and atmospheric circulation, subsidence, isostatic ac(justtnent, coastal erosion, and 

coastal modification. As a consequence. the detection of the impact of' climate change in 

observed changes in regional sea level remains challenging [AR5 WG [I Section 18.3.3] 

Anthropogenic causes of' regional sea level rise include sediment consolidation fi'om 

building loads. reduced sediment deliverv to the coast, and extraction of' suhsurf'ace 

resources such as gas, petroleum, and grounchrater. Subsidence rates ma_v also be 

sensitive to the rates of oil and gas removal. Regional sea level rise can exceed global 

mean sea level rise by an order of magnitude reaching more than 10 cmlvr. [AR5 WG II 

Section5.3.2.2] 

Sea level rise is one impact area where anticipatory adaptation strategies make sense; while there are 

substantial uncertainties about its magnitude, the sign of future sea level change is clearly positive. 

Causes of regional sea level change 

Sea levels have not been rising uniformly across the globe. One reason for the regional variations is 

dynamic redistribution of ocean mass via ocean circulations. Figure 1 shows that the Pacific Dccadal 

Oscillation has resulted in recent sea level trends ranging from > 10 mm/yr in the western Pacific to 

less than l mm/yr at several regions on the U.S. west coast [for reference, the global average value is 

- 3 mm/yr]. 

Short-term accelerations in sea level rise along the U.S. Atlantic coast have repeatedly occurred over 

the last century. These 'hot spots' can exceed rates of 4 inches in five years, and can occur anywhere 

along the U.S. Atlantic coast. A recent papcr3

' argues that the North Atlantic Oscillation (NAO), a 

seesaw pattern in air pressure over different regions of the North Atlantic Ocean, could explain the 

shift in the position of short-term variations in sea level rise. Shifts in the NAO alter the position of 

31 A new volcanic province: an inventory of subglacial volcanoes in West Antarctica. VanWyk, de Vries, Maximillian et al. 

Geological Society, London. Special Publications (2018) 

J:.: https://www.nature.com/articles/nature 14491 

10 
114 

the jet uti distrihuthm of in 

wh,;thcr will pile up to 

the north of Cap,, Hat \eras in 

A blain ct aL 

the ongoing rcspon,;;c of the solid 

and 

and thus global but aiso produce regionally 

gravitJ.tional field and rotatiun, and lead tn regional verticat land motion. 

enhance local sea lcYcl 

Northeast Atlantic and Oulf 

Local vulnerabilities and confinmdiugfactors 

ofn1can global sea level little n .. :lcvance for specific 

and local conl(mnding tiKtors that dominate 

to prcnidcd from of the vulnerable in the US 

'' Imps; 'linL-;pringeu:om ·article'! 0. 1007':; l0'12-016-93WI-S. 

ll 
115 

Barrier islands arc a type of dune system that forms by wave and tidal action parallel to the mainland 

coast. Barrier islands arc prominent on the U.S. East Coast and Gulf Coast. The morphology of 

barrier islands is very dynamic. Storms and engineering practices that influence the natural flow of 

sediment have a substantial influence on this morphology. independent of sea level rise. Particularly 

for the barrier islands that have wealthy communities, aggressive engineering strategies arc being 

developed. These most vulnerable islands arc becoming laboratories for coastal sea level rise 

adaptation strategies. But it is futile to expect these changeable islands to remain as geologically 

stable entities for a very long times. 

Isle de Jean Charles. Much ado has been made about the 'climate refugees' from Isle de Jean 

Charles off the coast of Louisiana, which is disappearing - in 1955, there were 22,000 acres while 

there are 320 acres today·". The principal problem traces back to the Great Mississippi Flood of 1927 

when the U.S. Am1y Corps of Engineers responded by building giant levees to constrain the river. 

which stopped the flow of sediment into its delta. These refugees arc more accurately referred to as 

'Mississippi flood mitigation refugees.' 

New Orleans. The issues of sea level rise and land loss in the Mississippi delta region are complex, 

with geological subsidence and the decline in sediment transported by the Mississippi river being the 

dominant drivers35 Since the 1950s, the suspended sediment load of the Mississippi River has 

decreased by -50% due primarily to the construction of dams in the Mississippi basin. A new 

subsidence map of coastal Louisiana·" tinds the coastal region to be sinking at about one third of an 

inch per year (or 9 mm/yr) [for reference. the average rate of global mean sea level rise of 3 

mm/yr]. For a city whose elevation averages one to two feet below sea level, sea level rise from 

human caused warming is not the dominant driver for the problems that New Orleans is facing. The 

Louisiana Coastal Protection and Restoration Authority, using funds from the British Petroleum oil 

spill settlement, is moving forward with two large sediment diversions. These diversions will start 

channeling huge volumes of river water in new directions, in a bid to protect areas around New 

Orleans in particular:" 

Miami. Miami has a population of more than 5.5 million living at an elevation of 6 feet above sea 

level. Around 2011. the slow upward creep of the accelerated: from 2011 to 2015, the rate of sea level 

rise across the southeastern U.S. increased by a factor of six, from 3 mm/year to 20 mm/year, which 

was caused by a change in the NAO ocean circulation pattern. In South Florida, the main problem is 

drainage.3

' The systems here were designed to let stonn water drain into the ocean when it rains. With 

sea levels now often higher than the exits to the run-off pipes. saltwater is instead running up through 

the system and into the streets. There is a growing recognition that at some point, certain areas in 

South Florida will no longer be viable places to live. The challenge is to ensure that the economy as a 

whole, including tourism, continues to thrive. 

New York City. In New York City. sea level has risen ll inches over the past century,39 which is a 

greater rate than mean global sea level rise. It has been estimated"" that land subsidence [sinking] in 

the New York City area has been roughly 3-4 inches per century. ?\lew York City is particularly 

34 https://www.indepcndcnt.eo.uk/news/worldlamericas/time-almost~up-island-louisiana-sinking-into-thc-sca-amcricanindians-coastal-erosion-isle-de-jean-a828040 l.htm I 35 https: i/www .sciencedirectcom/science.1

article/pii/S0025 3 22 7163035 5 3#bb0365 

y, https:/lphys.orglnews'20 I 7-06-highlights-louisiana-coast.html 37 https://www. washingtonpost.com/news/energy-environment/wp/20 18/04/11 /seas-are-rising-too-fast -to-save-much-of-them ississippi-dclta-scientists-say/'!utrn _ term=.dfa2 7 4d9c508 3

x http://www. bbc .com/future/story/20 I 70403-miamis-fight -against-sea-level-rise 

.w https://tidesandi:urrents.noaa.gov/sltrendsi 40 https;.'/www.c!imate.gov/news-fcatures/features/superstorm-sandy-and-sea-!evel-rise 

12 
116 

vulnerable to the effects of sea level rise because it is built primarily on islands and has 520 miles of 

coastline. The City's waterfront is among its greatest assets. There is also substantial infrastmcture 

and municipal facilities along the coast that are at risk from sea level rise, including roads, bridges, 

parks, waste transfer stations and wastewater treatment plants. Following Hurricane Sandy, a 

comprehensive plan has been developed: Cizv of New York: Building a Stronger, More Resilient Ne1r 

Yore' New York has developed a broad range of coastal protection measures that match the risks 

facing a given area: increase coastal edge elevations, minimize upland wave zones, infrastmcture to 

protect against storm surge, improve coastal design and govemance, restore estuaries wetlands. 

coastal nourishment, site elevation, and drainage systems. 

San Francisco Bay area. Sea level has been measured in the San Francisco Bay area since the 19th 

century. Over the past the past 100 years, sea level has risen by 7.7 inches, 42 which is slightly lower 

than the global average rate. Landfill zones are sinking due to soil compaction, at a rate as much as 

one-half inch per year, threatening coastal infrastructure including the San Francisco Intemational 

Airport. Another major contributor to sinking is groundwater pumping. Communities in the San 

Francisco Bay area have developed comprehensive plans to adapt to sea level rise.41 Nevertheless, 

the San Francisco Bay Bridge ramp was recently built without any consideration of sea level rise. 

Less than two years after its completion, a report by the Metropolitan Transportation Commission 

finds that sea level rise is expected to permanently inundate several areas of the new span of the Bay 

Bridge and recommends a series of construction projects to protect the Bay Bridge, costing taxpayers 

an additional $17 million. 44 

At the 2017 Conference on Regional Sea-ln·el Changes and Coastal Impacts, Kath lcen White of the 

U.S. Army Corps of Engineers made the following statement: 

"If we onzv look at the problem starting with just the climate signal, then it leads down a 

different path than if' we look at components of' sea level rise that are important to decisionmakers."45 

Conclusions 

Climate-related decisions involve incomplete information from fast-moving and irreducibly uncertain 

science. [n responding to climate change, we need to acknowledge that we cannot know exactly how 

the climate will evolve in the 21" century, we are certain to be surprised and that we will make 

mistakes along the way. 

Acting on forecasts of the unpredictable can contribute to bad decisions. Current policy making 

practices often neglect known unknowns leading to overconfidence. Rather than negotiating an 

optimal policy based on a negotiated scientific consensus, robust and flexible policy strategies can be 

designed that account for uncertainty, ignorance and dissent. Flexible strategies can be quickly 

adjusted to advancing scientific insights and new conditions that arise. 

41 http://s-media.nyc.gov/agencies/sirr/SIRR_ singles _Hi_ rcs.pdf 42 https://tidcsandcurrents.noaa.gov/sltrends/ 43 http://sf-planning.org/sea-level-risc-action-plan 44 https:i/blog.ucsusa.orgfjuliet-c_hristian~smith/a-bridoe-over-troub!ed-watcrs-how-the-b~ridge-\-vas-rebuilt::.':Vithoutconsidering-climatt;.:S.h.<l_!}g_~? 

) http://sciencedocbox.com/Geology/7 4213642-Conference-report -regional-sea-!evel-changes-and-coastal-impacts-july-20 17-

new-york-usa.html 

13 
117 

On regional and decadal time scales, the greatest vulnerability to climate change is not associated 

with the smooth long-term warming trend but rather with rapid shifts in frequencies and intensities of 

extreme weather and climate events that are associated with natural internal climate variability. The 

challenge for climate change adaptation is to work with a broad range of information about regional 

climate variability and vulnerabilities in the context of a decision-analytic framework that 

acknowledges deep uncertainty and that we arc almost certain to be surprised about future regional 

climate conditions and extreme weather events. 

Rather than 'bouncing back' from extreme weather and climate events. we can 'bounce forward' to 

reduce future vulnerability by evolving our infrastructures, institutions and practices. A focus on 

policies that support resilience and anti-fragility avoids the hubris of thinking we can predict the 

future climate. 

A regional focus on adapting to the risks of climate change allows for a range of bottom-up strategies 

to be integrated with other societal challenges, including growing population, environmental 

degradation, poorly planned land-use and over-exploitation of natural resources. Even if the threat 

from global warming turns out to be small, near-term benefits to the region can be realized in terms of 

reduced vulnerability to a broad range of threats, improved resource management, and improved 

environmental quality. 

The focus on mitigation policies has led climate science in the direction that is targeted at attribution 

of global climate change and determining the sensitivity of climate to C02• There has been little focus 

on understanding natural internal climate variability and regional climate dynamics that is needed to 

inform adaptation to climate variability and change. A new emphasis of climate science on 

understanding natural climate variability and its regional impacts is needed to better understand our 

vulnerabilities to climate change in the 21" century. 

14 
118 

Short Biography 

Judith Curry 

Professor, School of Earth and Atmospheric Sciences 

Georgia Institute of Technology 

Atlanta, GA 30332-0349 

curryja@eas.gatech.edu 

Dr. Judith Curry is President of Climate Forecast Applications Network (CFAN) and Professor 

Emerita of Earth and Atmospheric Sciences at the Georgia Institute of Technology. Dr. Curry 

received a Ph.D. in atmospheric science from the University of Chicago in 1982. Prior to joining the 

faculty at Georgia Tech, she held faculty positions at the University of Colorado, Penn State 

University and Purdue University. Dr. Curry's research interests span a range of topics in weather and 

climate. She has authored over 180 scientific papers, and is author of the textbooks Thermodynamics 

of' Atmospheres and Oceans and Thermodynamics. Kinetics and !Yficrophysics of Clouds. She is a 

prominent public spokesperson on issues associated with the integrity of climate science, and is 

proprietor the weblog Climate Etc. judithcurry.com. Dr. Curry has recently served on the NASA 

Advisory Council Earth Science Subcommittee, the DOE Biological and Environmental Research 

Advisory Committee, and the National Academies Climate Research Committee and the Space 

Studies Board and the NOAA Climate Working Group. Dr. Curry is a Fellow of the American 

Meteorological Society, the American Association for the Advancement of Science, and the 

American Geophysical Union. 

Financial declaration 

Funding sources for Curry's research have included NSF, NASA, NOAA, DOD and DOE. Recent 

contracts for CF AN include a NOAA contract to improve subseasonal weather forecasts, a DOE 

contract to develop extended range regional wind power forecasts and a DOD contract to predict 

extreme events associated with climate variability/change having implications for regional stability. 

CF AN clients include energy and power companies, reinsurance and asset management companies, 

other weather service providers, nongovernmental organizations and development banks. 

For more information: 

http://currv.eas.gatcch.edu/ 

http://wy;w.cfanclimat"."-"ml 

http://judithcurry.com/about/ 

15 
119 

SLIDE SUBMITTED BY CHAIRMAN LAMAR SMITH
120 

ARTICLE SUBMITTED BY RANKING MEMBER EDDIE BERNICE JOHNSON

5/17/2018 The Sea Is RISing, but Not Because of Climate Change- WSJ 

OPINION! COMMENTARY 

The Sea Is Rising, but Not Because of 

Climate Change There IS ncttw1g w<c on do dbout 1t, exteot to bwld d•kes and S<'J walls a !il1le b.: h1ghEY 

By Fred Singer 

May15.Z018627pm.f:f 

It is genem.lly thought that sea-level risl' accelerates mainly by thermal <>xpanslon of 

sea water. the so-called stenc component. But by studying a wry shmt timl' mtervaL it 

ispossibletosldestepmostofthl!cDmplicatirms,hki'"isostatitadjustment'"ofthe 

shor<'line (as continents nse after the overlying ice has me! ted) and "subsidence" of 

tlt~shorelme(Jsgroundwatl!"fandmineralsareextracted) 

t chose to a~se~s the se<Ht>vel trend from 191.'5-45, when a gt>nuin<>, indep€ndt>ntly 

confirmed warming of approximately 0.5 degree Celsius occurred. I note partinllat·!y 

that sea-level rise is not affected by the warming; it continu('S at the same rate, 1.8 

mil!inwt('rs a Y<'<lr, ~ccording to a 1990 review by AndrewS. Trupm and John Wahr.l 

therefore conclud\'-contra.ry to the g\.'neral wisdom-that th\.' lemp\.'rature of wa 

WJtPr has no din:•<.:t elect on sN-level risE'. ThJt means ndther does th<' atmospherk 

rontE'ntofc,trbondw:ode. 

This contluswn is wcrthhighlighting: It shows that st>a-ll'Vel rise does not deprnd on 

tlw use of fossil fuds Thf' Pvidenre shnuk\ allay fear that the r<>lease of additional C02 

wlllincrease<;ea-lev•lnse 

nuttherei<Jalsogooc,datashowingsealE'Vel5at<>infactrisingatacon>tantr<tte.The 

trt>nd has be<'n measured by a network of tidal gaug\'s, many of which have been 

co!lettingdataforoveracentury. 

sea water evide-ntly must be offset by Jomi'thing e-lse, What could that be? I .::ondude 

that it must be ice Jccumu!atwn, through evJporation of OC<'an W<lter, and subs("quent 

prc•dpitation turning into 1ce. Evid(':lC!' suggests that ,tccumu!ation of ice on th€ 

Antarctic continent has been offsf'tt!ng th<" stNk eff<•ct for dt least several crnturies. 

pht•nomeml: thermal E'xpanswn of water and evaporation ofwr~ter mo!erules. But tf 

evaporationoffsetsthermalexpanswn.thencteffectisofroursedosetozt.'ro.Whi1t 

then i~ the re<tl causeofsea-!evel rise of 1 to 2 millimeters a year7 

h•mce do<'S not affN:t thE' S\'a leveL) Aftt>r the rapid moi'lting away of northern ice 

sheets, the slow melLng of Antarcttc ice at the periphery of the continmt may bt• tho• 

maincauseofrum:n:sea-levelrisi' 

https./twww.wsj.com/articles/the-sea-is·rising-but-not-because-of.climate-changew1526423254 112 
121 

5/17/2018 The Sea Is R1sing. but Not Because of Climate Change- WSJ 

All this. because\\ ~~ much warmer now than 12,000 years ago, at the end of thE' most 

recent glaciation. Yet there is little h\'at available in the Antarctic to support me!tmg 

We can see melting hap~ning right now at tht> Ross ke Shelf of the West Antarctic Ice 

Sheet. Geologists have tracked Ross's slow disappearance, and glacwlogist Robert 

Bindschad!er predicts the ke shelf w1ll melt completely within about 7,000 yE'ars, 

gradt:allyraismgthesealevelasttgo€'s 

Of wurse, ~ lot Cd.n happ('n in 7,000 years. The onset of a new glaciation could cause the 

Sl'dl€'veltostoprismg.Itcouldevenfilll400fPt't,tothelevP!atthelastglaciation 

maximum 18,000 ye.ars ago. 

Currently, sea-k•vt•l nst' does not sepm to depend on ocean tf'mperature, a:ld rntainly 

not on C02. We• can expect the sea to continuo: nsing at about the present rate forth<' 

foreseeable future. By 2100 the sl'as Will rise another 6 inchPs or so-a far cry from Al 

Gore's alarming numbers. There is nothing we tfln do about rismg sea levels in the 

meantime. We'd better build dLkes and sea walls a little bit higher. 

Mr. Smger is a professor emuitus of !'nvironmental science at the Umversity of 

Virginia, HI' founded the Science and Emwonmental Policy Project and the 

Nongovernmental International Panel on Climate Change. 

Appeared in I he Mav 16, 20!8, print edition 

https:l/www.wsj.com/articles/the-sea-is-rising-but-not-because-of-climate-change-1526423254 212 
122 

STUDY SUBMITTED BY REPRESENTATIVE CONOR LAMB

The Cryosphere, 12,521-547,2018 

https://doi.org/l 0.5194/tc-12-521-20 18 

© Author(s) 2018. This work is distributed under 

the Creative Commons Attribution 3.0 License. 

Ellill 

u 

Increased West Antarctic and unchanged East Antarctic ice 

discharge over the last 7 years 

Alex S. Gardnert, Geir Moboldt2, Ted Scambos', Mark Fahnstock4, Stefan Ligtenberg5, Michie! van den Broeke5, 

and Johan Nilsson 1 

1 Jet Propulsion Laboratory, California Institute of Technology, Pasadena. CA 91109, USA 2Norwegian Polar Institute, Pram Centre, 9296 Tromsp, Norway 3National Snow and Ice Data Center (NSIDC), University of Colorado at Boulder, Boulder, CO 80303, USA 4Geophysical Institute, University of Alaska Fairbanks, Fairbanks, AK 99775, USA 5Institute for Marine and Atmospheric research Utrecht (IMAU), Utrecht University, Utrecht, the Netherlands 

Correspondence: Alex S. Gardner (alex.s.gardner@jpl.nasa.gov) 

Received: 25 April20!7- Discussion started: 4 May 2017 

Revised: 21 November 2017- Accepted: 27 November 2017- Published: 13 February 2018 

Abstract. Ice discharge from large ice sheets plays a direct 

role in determining rates of sea~level rise. We map presentday Antarctic-wide surface velocities using Landsat 7 and 

8 imagery spanning 2013-2015 and compare to earlier estimates derived from synthetic aperture radar, revealing heterogeneous changes in ice flow since ,....., 2008. The new mapping provides complete coastal and inland coverage of ice 

velocity north of82.4° S with a mean error of< lO m yr- 1, resulting from multiple overlapping image pairs acquired during the daylight period. Using an optimized flux gate, icc 

discharge from Antarctica is 1929 ± 40 Gigatons per year 

(GtyC1) in 2015. an increase of 36± 15Gtyr- 1 from the 

time of the radar mapping. Flow accelerations across the 

grounding lines of West Antarctica's Amundsen Sea Embayment. Getz Ice Shelf and Marguerite Bay on the western Antarctic Peninsula, account for 88% of this increase. 

In contrast, glaciers draining the East Antarctic Tee Sheet 

have been remarkably constant over the period of observation. Including modeled rates of snow accumulation and 

basal melt, the Antarctic ice sheet lost ice at an average rate 

of 183±94Gtyr- 1 between 2008 and 2015. The modest increase in ice discharge over the past 7 years is contrasted by 

high rates of ice sheet mass loss and distinct spatial patters 

of elevation lowering. The West Antarctic Ice Sheet is experiencing high rates of mass loss and displays distinct patterns 

of elevation lowering that point to a dynamic imbalance. We 

find modest increase in ice discharge over the past 7 years, 

which suggests that the recent pattern of mass loss in An taretica is part of a longer-term phase of enhanced glacier tlow 

initiated in the decades leading up to the first continent-wide 

radar mapping of icc flow. 

1 Introduction 

The Antarctic ice sheet receives roughly 2000Gt ('""' 5.5 mm 

sea-level equivalent) of precipitation each year with > 90% 

of this mass leaving as solid ice discharge to the ocean and 

the remaining < I 0% leaving in the form of sublimation, 

wind-driven snow transport, meltwater runoff and basal melt. 

Recent studies indicate significant mass loss from the Antarctic ice sheet that is likely accelerating (Harig and Simons, 

2015: Helmet al.. 2014; Martin-Espaiiolet aL, 2016: McMillan et aL, 20!4; Rignot et al., 201lb; Shepherd et aL, 2012: 

Velicogna, 2009). Understanding how this imbalance evolves 

is critical to providing meaningful projections of sea-level 

change. A major hurdle for improved attribution of mass 

changes determined from gravimetry and/or altimetry, and 

in determining mass changes themselves from the mass balance approach, is the difficulty in resolving continent-wide 

changes in ice discharge at high precision and accuracy for 

multiple epochs. This requires circum-Antarctic measurements of surface velocity on fine spatial scale and with sufficient accuracy (-....IOmyr- 1) to observe regionally coherent 

changes in flow. 

Published by Copernicus Publications on behalf of the European Geosciences Union. 
123 

522 A. S. Gardner et al.: Increased West Antarctic and unchanged East Antarctic ice discharge 

Earlier circum-Antarctic mappings of surface velocity 

have been based on synthetic aperture radar (SAR) data with 

incomplete coverage for 1996-2000 (Jezek et al., 2003: Rignot, 2006) and near~complete coverage for 2007~2009 (Rignot et al., 2011 a). Applications of optical imagery for surface velocity mapping have heretofore been limited to more 

local scales (e.g .. Bindschadler and Scambos, 1991: Scambas et aL, 1992) due to limited sensor capabilities, cloudiness 

and too few repeat~image acquisitions. Improvements in sensor technology (particularly in radiometric resolution) and 

far higher image acquisition rates for Landsat 8, launched in 

2013. largely overcome these limitations (Fahnestock et al.. 

2015: Jeong and Howat, 2015: Mouginot et al., 2017) and 

provide the ability to generate near-complete yearly mappings of surface velocity with high accuracy (""" I 0 m yr- 1 ). 

Here we describe the application of two newly developed 

and independent feature tracking methodologies (JPL and 

NSIDC) that we applied to hundreds of thousands of Landsat 

image pairs covering the entire Antarctic ice sheet north of 

82.4° S, producing six near-complete mappings of ice sheet 

surface velocities in both the 2013-2014 and 2014-2015 austral polar daylight periods. By differencing these velocity 

tlelds with the earlier SAR mapping (Rignot et al., 20lla) we 

resolve changes in ice surface velocity for the 7-year period 

between cin:a 2008 and 2015. Velocity changes are then used 

to estimate ice discharge on the basin scale and its change 

through time. For the determination of ice discharge we pro~ 

vide a novel approach to dcflning the cross-sectional area of 

i.:c Oow (flux gate; Sect 2.2) that greatly reduces uncertainties in estimates of ice discharge. By differencing estimates 

of ice discharge and basal melt rates (Van Lieffcringe and 

Pattyn. 20l3) from published estimates of the surface mass 

balance (van Wessem et al., 2016, 2014) we are able to estimate the net mass balance of the ice sheet on the basin scale, 

revealing recent patters of ice sheet imbalance. 

2 Methods 

2.1 Surface velocity 

Glacier velocities were determined by feature tracking of 

matching path-row Landsat Collection 0 LIT and LIGT image pairs in the panchromatic Band 8 (15m pixel size) using 

normalized cross correlation (NCC). To assess the sensitivity of our results to choices in Landsat processing methodology (e.g., search template size, spatial resolution, geolocation offset correction, data hltcring. image-pair date separation and compositing) we examine multiple velocity mosaics 

derived from two independent processing methodologies developed by JPL and NSIDC (Fig. I). Uncertainties in velocities were determined by comparing Landsat and SAR velocities measured at flux-gate nodes for basins with minimal 

change in ice discharge (basins Bl-19 and 827), i.e., where 

velocity differences are assumed to be indicative measureThe Cryosphere, 12, 521-547, 2018 

ment uncertainty. Uncertainties in velocities can be as high 

as 20-30 m yr- 1 locally but are largely uncorrelatcd on basin 

~cales (> IOOOkm; see Appendix A for validation of the velocity fields). All velocity mosaics are freely downloadable 

from the NSIDC (National Snow and Ice Data Center). JPL 

and NSIDC processing chains share many of the same characteristics, with main differences being how the image-pair 

data are corrected for geolocation errors, how the imagery 

is searched for matching features and the choice of search 

parameter" such as template size and spacing. 

2.Ll JPL auto-RIFT 

Image-pair pixel offsets 

The autonomous Repeat Image Feature Tracking (autoRIFf v0.1) processing scheme was applied to all Landsat 7 

and 8 images acquired between August 2013 and May 20 16 

with 80% cloud cover or less. Images were preprocessed using a 5 by 5 Wallis operator to normalize for local variability 

in image radiance caused by shadows, topography and sun 

angle. All image pairs with less than 910-day separation were 

searched. Preprocessed image pairs were searched for matching features by finding local NCC maxima at suhpixel resolution using Taylor rcflncmcnt (Pamgios ct al., 2006) within a 

specified search distance. A sparse ( l /16 of full search) NCC 

search was first used to determine areas of coherent correlation between image pairs. Results from the sparse search 

guide a dense search with search centers spaced such that 

there is no overlap between adjacent template search chips 

O.e., the distance between template centers is equal to the 

template size). Highest-quality image pairs (<20 1

/t cloud 

and< l-year separation) were searched using this approach, 

with a large search distance centered at zero pixel offset with 

a 32 by 32 pixel template chip. Spatially resolved statistics 

(mean and standard deviation of x andy displacements) are 

then used to guide a dense image search of all imagery with 

l6 x 16 or 32 x 32 pixel template chips depending on expected gradients in surface velocities. Areas of unsucces.sful 

retrievals were searched with progressively in<.::reasing template chip sizes of 32, 64 and 128 that increase the signal to 

noise at the expense of spatial resolution. 

Successful matches were identified using a noYcl normalized displacement coherence (!'\DC) filter. ln this approach 

filtering is applied on search-normalized displacements. i.e., 

displacements divided by the NCC search distance. Normal~ 

ized displacements are accepted if 7 or more of the values 

within a 5 by 5 pixel centered window are within one-quarter 

of a search distance for both x and y displacement components. This acceptance criterion is iterated on three times. 

Finally an iterative (two times) filter is applied to remove the 

few number of displacements that are retained by random 

agreement with neighbors. For this filter, displacements are 

compared to the centered 5 by 5 window median. Only val~ 

ues that agree within 4 times the centered 5 by 5 window 

www.the-cryosphere.netJI2/52112018/ 
124 

A. s. Gardner et al.: Increased \Vest Antarctic and unchanged East Antarctit.~ ice discharge 523 

between JPL auto~RIFT error-weighted NSlDC LISA 125m and Rignot et at. (20lla) surface vdocitie~. 

b shows close-ups the Hektoria Glacier, located on the eastern side of the Antarctic 

velocity counts and their interquatiile (lQR) for the auto-RIFT Wl5 

um~alistir:all\ low so we display the IQR <IS a proxy random error. 

generic 'md verv effective at removinn ran-

' " match bh;;1ttcrs 

blunmspmcernerus were cakulated 

rd'ertnced images. that are in Antarctic Polar Ste:rec>gntphic 

iEPSG 3031 l - This introduces scale 

that the latitude of origin (71" S). 

\Ve corrected for this scale distortion when converting from 

pixel to velocity fol!O\ving: the equations preheavy post-processing to isolate 

the geophysical signaL This was done by stacking all timenormalized displacements (velocities). them 

ovct stationary or slow flowing surfaces 

on the interquartile (!QR) determined for each 

the displacement All x and y displacernerrrs 

outside of the Qr- T x IQR to + T x lQR were 

culled from the set. where Q1 and Q3 arc the first and 

third quartile, respec1ive!y, and T is a scalar that defines the 

acceptance threshold. 

www.the-cryosphere.net/12/521/2018/ 

Reference velocity 

A reference velocity ( Vxo. Vyo) field was generated from all 

individual As a first step, gross outliers 

were Jata by setting T equal 

t0 3. Stacked displacement were then coregis.tered hy 

iteratively correcting for the median x and difference between individual 

reference velocity fields 

slow Howing surfaces. stopping after iterations, For each 

iteration, coregistcred displacctnents were filtered setting T 

to L5, and the effective chip size (resolution 

the velocity for low-velocity ~radicnts (< 

ice 

> were not 

met. V.rrcf and with Rignot ct 

aL (20 ll a) velocities Additionally. all pixels 

containing exposed rock were initially assigned a Vxrcf and 

V_Vref of Omyr- 1. rock was identified using the 

SCAR Antarctic Database (Thomson and Cooper. 

1993; Fig. 2). The initial size was set to the 

minimum chip size for the valid displacements in the stack were determined a chip of that size 

or smaller. After each coregistration data, Vxrt)f and 

VYref were set equal to the velocity for those 

pixels that have velocities and a \/x and Vy 

The Cryosphere, 12,521-547,2018 
125 

524 A. S. Gardner ct al.: Increased \Vest Antart:tic and unchanged East Antarctic ice discharge 

:Figure 2. Antarctic ice '>hcet velocities overlain on the MODIS tvtoof Ant.an.:tic.a (S.:ambos et aL 2007)< Ar~a~ of zeru 

change in are '>ho\vn in cyun. zero surbee v..:lo~.-'lt) :-,hown in red a:-. ddlned according 

to the Antarctic Dlgit<ll Databa-.;.e lhttp;//1.V\\ \\.adJ.scar.org) 

rock arc reas:·,igned a V X ref of uncertainty of 

e11ch imag.:-pair velocity ticld was determined as the standeviation of the residuals to Vxrer and VYrd· When 

th.::rc were fewer than J20 coregistration pixels within an impair. the uncertainty \Vas set to the RSS (roo! of sum of 

squares) of the pointing uncertainty of each image. 

.JPL auto-RIFT annual fields 

year r ( centcr date or 

image pair> 15 July, Y < 15 July Y) \v~re corcgiskred using the reference vducity field (Vxo, Vyo), where 

Vxref anU F Yref were set equal to the error-weighted 

( Vxo. V Yo) for those 

anJ Vxo and i\nnual error-weighted 

and vdocitlcs were fir~t calculated setting 

the limit;; based on the quartile of Vxo and F Yo 

and !>etting T = 3. Vekl~._-ities were rdlncd hy 

the liltcr llmits hasc.d on the quartile ranges of initial 

values and u~ing a more stringent acceptance threshold of 

T '" 1.5. 

Csing this approach we calculated four nt!arly complete 

Landsat g vclncity maps: median (,\1) and error-weighted average (\V) velocities for years 2014 and 2015. The .2014 and 

2015 velocities were derived from "'' 100 000 and ,.,._ .::!00 000 

unique image pair:.,. respectively (Fig. 1 ). 

2.1.2 1\SIDC LISA 

NSIDC's Landsat ice speed for Antarctica processing 

(LiSA v LO) used the Python image correlation, PyCorr 

v l.l 0, described in detail by Fahn~stock et aL (20 15). PyC'orr 

The Cryosphcrc, 12, 521-547, 2018 

to Landsat 8 data by 16 to .JOO days. 

26 September 2013 to April 2015 using a reference template size of 300 x 300m with 300m 

between search Images were manually 

of cloud~ free surf~1ce 

with less than 70 t.''/r cloud cover. 

pass tllter of appmximately 250m spatial scale \vas applied 

to the images to enhance surface detail and suppress topographic shading. 

PyCorr outputs a quality metric delcorr. v..-hich is the diff;;rcnce between the n.:grcssion cocfflcicnt of the 

and the second-highest match outside of a 3 x \..'d! area 

All displacement valut..'S with a ddcorr value 

were eliminated. Velncitics arc further tlltcrcJ 

by examining the difference between the velocities at the 

assessed pixel with the eight values. Velocities 

vvith no neighhors were masked. with one 

bor were masked when the absolute Jifference bct\veen 

two values was greater than ]65 m yr- 1• Velocities with two 

neighbors v.rere masked if they exceeded 3 standard devia.tions. of the mean. Finally the standard LlcYiation of each 

3 x 3 region was computed. and the center pixel of each re~ 

gion was masked when the ;.;orresponding stanJan.l deviation 

is greater than 365 m yr- 1. 

and near-zero icc 

ice vl?locity and >20myC1) 

areas according to Rignot t't al. (201 !a). Offset corrections were then \veightcd by count and applied to individual 

image~ pair results . 

Re:-.ulting veku:itit:s for ew.:h image were bilineady 

rcsampled to the target grid 750 or ! 25m. 

These grids were then using a weighting ::-;chemt.' 

that favors the more accurate long-interval velocity determinations ( 16-day pairs, 0.3 \veighting; 0.6; 48-

day pairs, 0.9; >48-day LOl. 

factor was applied to 

ddcorr values. Mosaics \.Verc then CO!Tected ror 

scale distortion, stackeJ and combined in a average 

scheme. The numher of in the LiSA v l.O grid 

ranges from ......._. ! 0 to over 1 ). 

2.2 Flux gates 

Estimation of icc. nux from rncasurcmcnts of surface velocity requires knowledge of the vertical density profile, How 

cross-sectional area (flux gatt!J and an a;:;sumption of the rclatiom,hip between surface and depth-averaged velocity. The 

most accurate estimates of ice thickness come from radioecho-sounding (RES) measurt':ments, but RES data only exist 

for about 19 q, of the ice sheet grounding line. For the calculation of discharge, we choose to compromise proximity to 

the line for inclusion of more upstream RES data 

www.the-cryosphere.net/121521/20181 
126 

.-\.. S. Gardner et al.: Increased \Vest Antarctic and unchanged East Antarctic ice discharge 525 

Figure 3. Radio-echo-sounding do.ta 

Tahle l. 

to c::ompitc nux fGI FG-:2. An prO\ idt'd in 

Table L Data -:ources and pcrcr.::ntagt::s fur radiC>-ccho-..;ounding data used to compile tlux 

Bedmap-2 data cell 

Sum 19.2 cr 

velocities, \Vc do so by modifying the be~t-knm,m 

line to go inland of major shear zones and tP 

RES flight lint.'" from 1shidt valid thickncs;-; data can ht: 

extracted. We prioritize the nearest and most recent RES data 

aY:ti!able from seven freely available data sets <Fig. 3 and ·nt- hlc l ). For Bux \Vith nn RES data \vithin I km distance. 

thickness values are exlra<:Led by bilinear interpolation 

from the icc thkkncs.s grid ofHuss and Farinotti (20!.f) over 

the Anlarctic Peninsula and Bedmap-2 (Fret\vell ct al., 20 13) 

for the rc,l,l nf Antarctica. \Vt:: ,p:cnaatc t!m:e altcrnatiw· flu,\ 

gatl:s: a groundinf!-linc flux gate (GLO) based on a 'Ynthc.sis 

of the grounding !inc, a lightly modified version 

impnwed by following RES profiles upstr~am and in 

close proximity to the grounding line (} .. G I) and a llux-gatt· 

www.the-cryospherc .net/ 121521120181 

(2010) 

cOLI) 

(lutlinc based s~1ldy on RES prolilcs: in favorable position-'> 

for cak:u!ating tlu.x. (FG2). 

GLO h a best-as:-.essmenl grounding-line 

a synthesis l1f incomplch:: data lirs.t 

et al. t20U) that has been 

grounding-line in the Amundsen Sea region (Rignot et aL 2014. l b) and for the Totten Glacier in East 

Antarctica (Li ct aL 20!5; Rig:not et aL 2013): two highly 

dynamic regions \.-Vith considerable icc !luxes and changes 

Ice thickness was mainly exof Bedmap-2 o/c) and 

grounding line (! 9 (:i" ). For that, we 

in Bedmap··2 that have been derived directly from RES data 

The Cryosphere.l2. 521-5-17.2018 
127 

526 A. S. Gardner et al.: Increased West Antarctic and unchanged East Antarctic ice discharge 

(7 9t ), as indicated in a data coverage mask. These thickness 

value" have a much lower uncertainty (mean 68 m) than the 

interpolated thicknesses in areas not covered by RES (mean 

168m). 

FG I is a modified version of GLO that follows RES flight 

lines (Fig. 3) or Bedmap-2 data cells that are in the vicinity of 

the grounding line. Vv'hether or not to divert from the grounding line in favor of RES profiles was determined ad hoc rather 

than applying a strict distance threshold. Long, continuous 

RES profiles further apart were more likely to be followed 

than short, scattered RES data doser to the grounding line. 

In general, the modified parts of fG l are within a few tens of 

kilometers from the GLO and even less so in the Amundsen 

and Bellingshausen Sea coasts and the Filchner-Ronne ice 

shelf regions. where RES llight lines are often aligned with 

the grounding line. Almost all of these important regions are 

covered by RES data in FG 1, and for Antarctica as a whole 

the RES coverage is 42 Sf (Table I). We found that FG l was 

the most suitable flux-gate line for estimating changes in ice 

discharge due to its close proximity to the grounding line and 

high coverage of RES data. 

FG2 is a modified version of FG 1 that further prioritizes 

RES flight lines over proximity to the grounding line around 

the entire continent Only slight moditlcations were made in 

regions like the Amundsen and Bellingshausen Sea coasts. 

the Filchner-Ronne ice shelf and Dronning Maud Land for 

which many near-grounding-line RES data exist. but for parts 

of East Antan:tka and along the Transantarctic ~ountains 

the modification can he several hundred kilometers (Fig. J;. 

The total co\'erage of RES data along FG2 is 96 'IC (Table I). 

We used this Jlux~gate line to estimate absolute discharge 

for the ice sheet, but not for assessing temporal changes in 

discharge, because they arc often most pronounced near the 

grounding line that is better sampled by FG 1. 

The average point spacing along the three llux~gatt.! lines 

is 198-265 m, with a maximum spacing of 400 m to ensure 

sufficiently dense sampling of ice thickness and surface velocity for ice llux calculations (see Sect. 2.3 for a dctailed discussion of resolution-dependent errors in nux calculations). 

Flux-gate points without RES data and within the rock mask 

of the SCAR Amarctk Digital Database (<4%; Thomson 

and Cooper, 1993; Fig. 2) were assigned a Lero ice thickness. 

Since the thickness data were provided as physical ice thickne~scs, we subtracted modeled average ( 1979, 2015) firn air 

content (FAC; see Sect. 2.5) to obtain ice-equivalent thicknesses, assuming ice has a density of 917 kg m-3, relevant 

for ice llux cakulations. 

For further analyses, we also extracted point attributes for 

source data and year, surface elevation. FAC and a!! available 

thickness data. Histograms of ice thickness. uncertainties in 

icc thickness. date of thickness measurement, FAC, uncertainty in FAC, surface velocity, ice thickness change rate and 

uncertainty ice thickness change rate for all three flux gates 

are shown in Fig. 4, Flux gates and extracted ancillary data 

are available from the National Snow and Ice Data Center. 

The Cryosphere, 12, 521-547, 2018 

2.3 Ice discharge 

We calculate ice nux (F) by multiplying the x andy velocity 

component (Vxjy) by the width of the flux gate projected in 

the x and)' coordinates (Wx jy) and ice-equivalent thickness 

(H) at each ftux node (i) and summing 

"" F L (Vxl Wxi + Vyi W_\'i) H;, (I) 

l=l 

where nn is the number of nodes at which ice flux is calculated. Here we defined the flux gate following polygon 

convention with the upstream side of the tlux gate being defined as to the right-hand side of the polygon gate vector as 

one moves from node n to node n + l. In this convention 

W x is negative when Yn+l > y11 and Wy is negative when 

Xn+ 1 < x 11 . Ice discharge (D) at the grounding line of the ice 

sheet corresponds to F for the GLO flux gate. Applying mass 

conserving principles (Morlighem et al.. 2011 ), Dis equal to 

F + SMB + d Vd,,/dt for the FG I and 1'02 flux gates. SMll 

is the unmeasured flux due to a positive surface mass budget or the area between the !lux gate and the grounding line 

and is estimated from RACY.102.3 climatology (1979-2015; 

see Sect. 1.4). SMB is corrected (reduced) for basal melt occurring between the tlux gate and the grounding line which 

does not contribute to solid ice discharge (Van Liefferinge 

and Pattyn, 2013). dVdyn/dt is the unmeasured flux_ due to 

ice How convergence and divergence bct\veen the flux gale 

and the grounding line. which we refer to as the dynamic 

volume change. This is accounted for by assuming that tim 

corrected CryoSat-2 elevation change rates (Sect. 2.6) measured over ice moving at >200m yr- 1 that lies between the 

flux-gate and the grounding line can be attributed to dynamic 

volume change. Rates of volume change in 2008 and 20 I 5 

were extrapolated using the measured acceleration in the rate 

of elevation change over the period ofCryoSat-2 data (2011-

20 15). Measured dynamic volume loss is considered to increase total discharge and vice versa. Uncertainty in the dynamic volume change can not be rigorously quantiiieU and 

are therefore conservatively assumed to be 0.1 m yr- 1 times 

the area between the grounding line and the flux_ gate having 

a surface velocity >200m yr- 1 or 30 Cft, of the magnitude of 

the estimated dynamic volume change, whichever is larger. 

A velocity cutoff of 200m yr- 1 was selected to separate vol~ 

ume changes resulting from changes surface mass balance 

and those resulting from changes in dynamics. This threshold 

is arbitrary. Even so, the dynamic volume change correction 

is very small and insensitive to the selected cutoff velocity. 

Calculation of discharge is highly sensitive to the definition of the flux gate and to any vertical gradient in the 

ice flow (Chuter et al., 2017: Mouginot el al.. 2014; Rig~ 

not. 2006; Rignot and Thomas, 2002). When calculating ice 

flux, we assum~ that there are no vertical gradients in icc 

velocity. This assumption introduces a small positive bias 

(<0.4 %) but is negligible relative to other sources of error. 

www,the-cryosphere,net/12/521/2018/ 
128 

A. S. Gardner et al.: Increased \Vest Antarctic and unchanged East Antarctic ice discharge 527 

Figure 4. Histograms of ice-equivalent thickness (a). uncertainty in 

ict:-equiva!ent thickne<;-; (b). year of ice thickness measurement (c), 

tim air content (d), in fim air content (e), surface ve!o.::-

rate of ice-equivalent thickne-;s (h) 

tlux gates. The y axis is the percentage of flux nodes that fall within 

each hi->togram bin. 

Set': Appendix A for the calculation of the expected vertical 

gradient in ice velocity. One known issue is the systematic 

underestimation of kc tlux with the coarsening of the resolution of the basal topography and/or the surface velocity 

(Fig. 5). This happens bccaust': fast-moving ice is concentrated in basal troughs: higher velocities multiplied hy larger 

icc thi<.::kn~ss and lower velocities multiplied by smaller ice 

thickness do not equate to average thickness multiplied by 

average velocity. FG2. which follows high-resolution RES 

prollle.s around almost the entire continent at the expense of 

proximity to the grounding line, provides the cross-sectional 

area with the lowest uncertainty and is most appropriate for 

the total discharge. even after having to account 

mass input between the gate and the grounding 

line. FG I strikes a balanct! between proximity to the grounding lin(: (GLO) and the distance from ice thickness observations. This gate is best suited for estimating changes in ice 

discharge. Our best estimate of total discharge is <.::01nputed 

using the 2015 error-weighted average auto-RIFT velocities, 

FG2 and an estimate of addi!ional mass flux between FG2 

and GLO. We then compute the change in discharge between 

the 2015 and 2008 period at FGI and subtract this from our 

best estimate of total discharge, accounting for dynamic volume change and changes in ice thickness between periods. 

www.the·cryosphere.net/12/521/2018/ 

60 

·SOL------·-·-

0 ' Resolullon [km] 

Figure 5. Error in total Antarctic discharge (relative to best esti~ 

mate) when velocity and ice thickness are averaged for increasing 

along-llux~gatc r~:.olutions prior to cornputinJ! flux. 

This muhi~t1ux-gatc approach greatly reduces errors in estimates of kc discharge. 

For areas south of the Landsat observation limit. we first 

cakulatt! the total flux across gates located > ~Q.4') S using 

the 1997 and 2009 SAR vdocity mappings of Scheuchl et 

a1. (2012). To determine a representative .2015 ilux rate we 

extrapolate the 2009 estimate assuming the same rate of 

change in discharge as observed for the 1997-2009 period. 

Changes in flux (dF) were calculated at all t1ux-gatc nodes 

(i) where both velocity mappings were valid and assumed 

to be unchanged elsewhere. In our analysis of velocities we 

found that there were some geocoding issues between the 

SAR (Rignot eta!.. 20!ia) and Landsat velocities. which are 

most likely due to errors in th~ elevation model used to convert from radar slant range coordinates to a location on the 

Earth surface. \Ve also found the SAR velot:ities unreliable 

for most of the northwest Antarctic Peninsula, where velocities near the grounding lines of narrow outlet glaciers were 

unrealistically low and likely tht' results of interpolation to 

areas of missing data. To minimize the impact of these artifacts in our flux-change analyses. we prescribed areas of 

zero change in nux along shear margins where changes are 

expected to be small and for much of the northwest Antarctic Peninsula (Fig. 2). Any residual geocoding errors arc expect~d to introduce noise into our analysis but arc unlikely to 

significantly bias our estimates of flux or flux change as errors will somewhat cancel when integrated across the entire 

glacier cross section (errors arc typically of similar magnitude but opposite sign along right and left flow margins). Sec 

Appendix A for a comprehensive dis<.::ussion of the un<.::ertainty quantification. 

One known limitation o[ our analysis is that the SAR velocity mosaic (Rignot ct al., 20 II a) that we difference our 

Landsat velocities with is derived from data spanning the 

period 1996-2009 with no information provided on the effective date of the data. \Ve assume that the SAR mosaic 

has a representative date of circa 2008 as most Jata used 

in the mosaic was colle<.::ted between 2007 and 2009. This 

data has been used previously to estimate total Antarctic disThe Cryospbere, 12,521-547,2018 
129 

528 A. S. Gardner et al.: Increased \Vest Antarctic and unchanged East Antarctic ice discharge 

charge in Rignot et al. (2013) with a reference date of2007 to 

2008 and in Depoorter et al. (2013) with a reference date of 

2007 to 2009. Individual year composites of the data used in 

older mosaic were recently made available (Mouginot et al., 

2017). These new data come with more precise time stamps 

but at the expense of reduced horizontal resolution (I km vs. 

450 m), reduced spatial coverage and larger uncertainties. To 

ensure that our stated time period of circa 2008 is appropriate 

we rcsamplc (linear interpolation) the original SAR velocity 

mosaic to 1 krn and compare to the error averaged 2007-2008 

and 2008-2009 velocities from the new data set Differences 

in flux across the FG I are less than 2 Gt yr- 1 for all basins 

except for basins 12, !3, 14 and 24 that differ by -4, -5, -6 

and 4 Gt yr- 1, respectively. Some of the difference can be attributed to real differences in flow hut also from differences 

in uncertainties between products (the original SAR mosaic 

having lower errors, particularly for the East Antarctic) and 

from differences in horizontal resolution. From this analysis 

we concluded that the best estimate of ftux for the- 2008 period is produced by the earlier mosaic that has higher spatial 

resolution and the lower uncertainty, which is derived from 

the same underlying data contained in the annual mosaics. 

We also determine the period "circa 2008" characterizes well 

the effective date of the earlier SAR mosaic. 

2.4 Surface mass budget 

Here we estimate SMB for the 2008-2015 period 

from Regional Atmospheric Climate Model version 2.3 

(RACM02.3) output at a horizontal resolution of 5.5 km 

for the Antarctic Peninsula (van Wessem et al., 2016) and 

27 km elsewhere (van Wessem et aL, 2014). In RACM02.3, 

SMB is calculated as the total precipitation (from snow and 

rain) minus total sublimation (directly from the surface and 

from drifting snow), wind-driven snow erosion and meltwater runoff. For the six Antarctic Peninsula basins (B 1, 

B23-27), entirely or partially covered by the high-resolution 

model, we use the 27 km model output for the missing years 

of 2014 and 2015. For these basins, the 27 km model output was scaled to better agree with the 5.5 km output using 

the delta scaling approach. Uncertainty in SMB is taken to 

be 20% and is treated as uncorrclated between basins. The 

reader is referred to the works of van Wessem et al. (20 14 and 

2016) for a thorough discussion of the model setup. model 

validation and SMB uncertainties. 

2.5 Firn air content 

To convert volume !luxes to mass !luxes, the depth-averaged 

ice-sheet density is needed. FAC is a measure of the residual column that would remain if the firn column were 

compressed to the density of glacier ice, assumed to be 

9l7kgm-3 We estimate FAC using the fim densification 

modellMAU-FDM (Ligtenberg et al., 20ll. 2014). IMAUFDM simulates fim densification by dry compaction and 

The Cryosphere, l2, 521-547, 2018 

through meltwater processes (percolation. retention and refreezing) and is forced at the surface by 3-hourly resolution 

output of RACM02.3 (van Wessem et al.. 2016, 2014): surface temperature. 10m wind speed, precipitation (solid and 

liquid), sublimation, wind-driven snow erosion/deposition 

and surface melt. The simulation over the entire Antarctic 

continent (at 27 km grid resolution) covers ! 979-2015, while 

the Antarctic Peninsula simulation (at 5.5 km grid resolution) only covers 1979-20!3. Both simulations output FAC 

at 2-day temporal resolution. The JMAU-FDM is calibrated 

using 48 depth-density observations from across Antarctica 

(Ligtenberg et aL, 2011), and results have been successfully 

used to convert satellite altimetry (e.g., Gardner et aL, 20l3; 

Scambos et al., 2014; Shepherd et al., 2012) and ice thickness measurements (e.g., Depoorter et aL, 2013; Fretwell 

et al., 2013) into estimates of ice mass change and iceequivalent thickness. Although time-evolving FAC is simulated throughout 1979-2015, we use the climatological average FAC as the most robust correction of our flux-gate thicknesses that are based on source data from many different 

times, sometimes unknown. 

Uncertainties in the simulated FAC originate from either 

the observations used in the IMAU-FDM calibration process or the RACM02.3 forcing data. This has been quantified at lO o/t. (Supplement of Dcpoortcr ct al., 2013), composed of measurements errors in the observations of the 

pinning points in a depth-density profile: surface density, 

depth of 550 kg m-3 level and depth of830 kg m-3 ievel. The 

RACM02.3 uncertainty is primarily caused by the assumption used for model initialization; to initialize the lMAUFDM, it is assumed that the climate over the past IOOlOOO years was equal to the J979-20!3/l5 average climate 

(Ligtenbcrg ct al., 20 ll ). Therefore, errors in the climatic 

forcing during the initialization period have a direct effect on 

the simulated lim density profile and subsequent FAC. Using sensitivity simulations. it was found that a 1 °k perturbation in accumulation during the initialization period causes 

a 0.75% error in FAC. Similarly. a 1 % perturbation in the 

melt/ accumulation ratio results in a 0.27 m error in FAC. 

The melt I accumulation ratio was used instead of the total 

melt, as the amount of annual snow that melts away in summer (i.e., the ratio between annual melt and annual accumulation) mainly dctcnnincs how much !lrn pore space remains 

rather than the total amount of melt. 

Along the ice-sheet grounding line the mean and standard 

deviation of FAC are 16.3 ± 6.1 m with associated uncertainties of 3.7 ± l.O nL The combined uncertainties of Lhe flrn observations and the RACM02.3 forcing of accumulation and 

surface melt showed the highest uncertainties on the western 

side of the Antarctic Peninsula, where high accumulation is 

combined with high melt. In areas where the modeled FAC 

uncertainty was higher than the actual FAC, the uncertainty 

was re~set to the same value as the FA C. 

www.the-cryosphere.net/12/521/2018/ 
130 

A. S. Gardner et at.: Increased West Antarctic and unchanged East Antarctic ice discharge 529 

for the period 2011 to 2015. 

line ant.l GLO <;hown with 

2.6 Surface elevation and elevation change 

To account for thickness changes between the times of dis~ 

chame calculation (2008 and 20 15) and to correct for Jy~ 

namic volume change between the flux gate and the grounding line, we use ;urface elevation rates estimated from 

c(yoSat~2 radar altimetry between January 2011 and January 2015 (Fig. 6). CryoSat-2 elevations were derived from 

the ESA L I c product using the methodology developed by 

Nilsson et aL (2016) .. For each CryoSat-2 observation mode 

(LARM and SARfn), the derived surface elevations were 

separated into grounded and floating icc using the grounded 

and floating ice definitions from Dcpoorter et aL (2013) grid~ 

ded to a 240m in stercographic (EPSG: 303!) projection. 

Geophysical range corrections were applied to all data ac~ 

..::orJing to Bouzinac (20l5). For floating ice. the tidal correctior;~ (ocean tide and ocean loading) were replaced with 

values generated from the CATS2008 tidal model (Padman 

et aL, 2008). 

Surface elevation changes and rates of acceleration were 

generated using the surfa;e fit method, described in Nilsson 

eta!. (2016), onto a l km polar-stereographic grid (EPSG: 

3031) for each mode. The derived elevation change distribution was edited to remove solutions with a magnitude larger 

than± 15 myr- 1, similar to the approach taken by \Vouters et 

a!. (20 15). The edited data was then interpolated onto a I km 

grid using the weighted average of the 16 closest grid points. 

weighted by their standard error from the least-squares solution and distance. The standard error of the rate of change is 

assumed to be indicative of the formal error of each measurement. No correction for potential trends in FAC and glacial 

isostatic adjustment are applied, which may cause surface elevation rates to deviate from ice-equivalent thickness rates. 

www,the-cryosphere.net/12/521/2018/ 

2. 7 Mass budget 

To assess the net ice sheet mass budget during the 2008-

2015 period, we combine our new estimates of discharge 

(Sect. 2.3) with estimates of surface mass budget (Sect. 2.4) 

and basal melt rates (Pattyn. 20!0; Van Liefferinge and Pattyn, 20 13). Discharge and surface mass budget for the northem Antarctic Peninsula (B25-26) are highly uncertain and 

only included for reference in Table 2. The complex basal 

topography. narrow glacial valleys and highly crevassed ice, 

make interpretation of the hed reflection in radar data diftlcult 

in this region. Estimating the surface mass budget is equally 

challenging with large interannual variability and steep spatial gradients in both precipitation and melt due to extreme 

surface topography over a large latitudinal range. For 825-

26, we therefore rely on net mass budgets determined from 

glacier elevation changes within the 2003-20 II period that 

~e update with estimated discharge changes for 2008-2015 

(Scambos et al., 2014; Berthier et al., 2012: Shuman et aL 

2017). A full discussion of the updated Antarctic Peninsula 

mass budget estimate is provided in Appendix B. 

3 Results 

3.1 Changes in surface velocity and ice discharge 

By combining uncertainties of ice velocity and its relation 

to depth-averaged velocity, ice thickness, dynamic volume 

change and SMB for each flux-gate configuration, we estirnate ... a total discharge uncertainty of 5.61?1(, for GLO. 4.5% 

for FG I and 2.1 % for FG2. The lower uncertainty for FG2 is 

due to the extensive use of RES data for ice thickness along 

the nux gate (fig. 4). Hence. we use FG2 in combination with 

the Landsat velocity ticld to estimate total discharge. Obtaining continent-wide discharge for"' 2008 using the SARbased velocity fic!J (Rignot ct al., 2011 a) at the FG2 nux 

gate is not possible due to data gaps inland of the grounding 

line. Instead, we estimate discharge change between the 2008 

and Landsat mappings at FG l and then subtract that from 

the Landsat estimate of discharge to obtain a total estimate 

for 2008. This approach reduces the impact of ice thickness 

errors at FG l since they get scaled by velocity differences 

rather than by velocity magnitudes that are typically much 

larger. Thickness changes at FG I and changes in the rate 

of dynamic volume change between FG I and the grounding line occurring between 2008 and Landsat mappings were 

accounted for in the estimates of discharge change using the 

derived CryoSat-2 elevation change rates for 2011-2015 (see 

Sect. 2.6). Rates of volume change in 2008 and 2015 \vere 

extrapolated using the measured acceleration over the 2011-

2015 period. Calculating nux in this way reduced the uncertainty in the total flux estimate generated from SAR velocities from 99 Gt yr- 1 when calculating total discharge only at 

The Cryosphere, 12,521-547,2018 
131 

530 A. S. Gardner et al.: Increased \Vest Antarctic and unchanged East Antarctic ice discharge 

Table 2. Surface area. cross sectional area for tlux gate FG2. discharge corrected for dynamic volume change and surface mass balance 

bet\VCI.'il flux gate FG2 and the grounding line, basal melting, surface mass balance (SMB) and net ma!.s balance for the 27 basin~ ddlnt'd by 

Zwally et al. (2002). Cumulative numbers are provided for the Ea~t Antarctk Ice Sheet (EAIS: B2-·17), the West Antarctic Ice Sheet iWAIS: 

BL 818~23) and the Antarctic Peninsula (AP: B24-B27). Basal melt rates are from Van Liefferinge and Pattyn (2013) and calculated 

according to Pattyn (2010). SMB is calculated using the RACM02.3 regional climate mode! at 5.5 km (van Wessem d aL 2016) resolution 

over the Antarctic Peninsula and 27 km ebewhere (van Wes-;em et al., 2014) and averaged over the 200R-2015 period. The net mass balance 

is calculated as the 2008-2015 SMB minu:-. the average rate of discharge minus hasal melt. Discharge for 2008 is derived from Rignot et 

a\. CO 11 a) and for 2015 from the mean of the JPL 2015 error-weighted Landsat velocity mapping. 

Ba"in Area Flux gate Basal melt SMB Net mass change 

km2 krn2 2!108 2015 D. Gtyr-l 200R-20!5 Gtyr- 1 kgm -2 yr-1 

474800 987 ±53 110±8 112± 7 2±3 3±0 121 :±:: 24 7±25 16±54 

765400 305 ± 33 48±6 47±4 -1±4 3±1 52± !0 2± 12 2± 16 

1556600 213± 18 59+4 60±4 J:t-2 5±2 74± 15 9+ 15 6± ]() 

241200 351 .i55 41 ±8 43.!. 7 2±3 1±0 45±9 2± 12 8.!.50 

185 300 196±30 30±5 31 ±4 1±2 1±0 36±7 5±9 26±47 

607700 501 ±59 60±7 60±6 -1±3 3±0 81± 16 17 ± 17 28±29 

-192 500 495 ± 62 68±8 70±8 2±2 2±0 93± 19 23±20 46±41 

161200 277 ± 32 17 ±4 18±3 1±2 1±0 36± 7 18 ± 8 Ill ±50 

146000 219± 18 17± 3 16±2 -1±2 1±0 17±3 0±5 -1 ±31 

10 919 300 55± 5 34±4 33± 3 -I ±2 3+ 1 42±8 6±9 6± 10 

II 255 200 187± 14 13±3 12±2 -l ±:2 !±I 16±3 1±4 6± 17 

12 727 100 610±74 102± II 101 = 10 0±3 5±1 128 ± 26 21 ± 28 29± 38 

!3 I 130800 667 ±50 226± 19 223 ± 18 -2±5 ?eLl 201±40 -31±45 -27 ± 39 

14 718500 714±48 130± !0 130± Ill 0±3 5±1 125±25 -10±27 -14±38 

15 123 800 i90.lll 26±6 26~t 5 0±2 1±0 25±5 -2+8 -16± 62 

16 262000 159± 13 13±2 14±2 0±2 1±0 10±2 -5±3 -18± 12 

17 I 825 800 646±51 67±8 67±7 -1±3 5±2 78± 16 5± 18 3+ 10 

18 261 400 125± 16 9±3 8±2 -I ±2 2±1 23::.::5 13±5 49::.!: 21 

19 367 700 258 ± 34 44±6 45±6 1±2 3± I 37 o=7 -II± 10 -30± 26 

20 180 !00 490± 54 171 ± 15 183 ± 14 12±4 2±0 112±22 -67±27 -375 _t 149 

21 207 500 179± 12 180± 12 !89± 12 9±4 2±1 98±20 -89± 23 -428 ±Ill 

22 2!0200 112 ±7 127±8 134± 8 7±2 2+:0 8-1± 17 -49± 19 -231+89 

23 74600 249±20 83± 8 83±7 0±3 1±0 65± !3 -18± 15 -242±204 

24 100600 211 ± 15 94±7 95±7 2±3 1±0 86± 17 -9± 19 -94± 186 

25 .14 700 78± 15 88 ± !3 91 ± 12 4±5 0±0 100±20 -10±21' -297±605' 

26 42000 116± 12 23±4 25 ± 3 2±2 1±0 29±6 -17±7' -406± 174' 

27 52000 89cl9 12±3 12cl2 0±2 0±0 18±4 6±5 120±88 

EAIS ]() 118500 5786± !65 952 ± 31 952 ± 29 -1±11 45±4 1058±66 61 ±73 6±7 

WAIS I 776 200 2400 ± 88 724± 24 754 + 23 

AP 229 200 493 ± 26 217± 15 223± 14 

All 121:13900 8679± 189 189+±43 1929+40 

the grounding line to 40 Gt yr- 1, a 60 7C reduction in uncertainty, when applying this combined approach . 

Comparing differences in discharge estimates between 

6 Landsat velocity mappings (Fig. 7, 4 auto-RIFf vOJ, 

2 LISA v l.O) shows good agreement despite differences in 

feature tracking methodologies, template chip size, horizontal resolution and time periods. The standard deviations between flux-change estimates are below the stated uncertainty 

in discharge lisled in Table 2 for all 27 basins. Differences 

The Cryosphere, 12, 521-547, 2018 

30l. 8 16± I 541 +45 -214±51 -120±29 

7±6 2±0 234± 27 -31 ±29 -1.13±128 

36± 15 63±4 18.14± 84 -183±94 -15+8 

that do exist can be attributed to product errors. Auto~ RIFT 

W 15 has the lowest uncertainties, followed by auto-RI:f-<1 

M15 !hen aulo-RIFT W14 and l\114 with the USA 125 

and 750 m products having the highest uncertainties (See 

Fig. AI). auto-RIFT uncertainties are lowest for the 2015 

mapping simply due to a much larger number of available 

image pairs. The reason for higher uncertainties of the LISA 

products is not entirely known but is likely due to differences in geolocation offset correction and merging procewww.the·cryosphere.net/12/521/2018/ 
132 

A. S. Gardner et al.: Increased \Vest Antarctic and unchanged East Antarctic ke discharge 531 

:Vkthodsl h1r th~ 27 ha~ins dclinc:d by Zwa!ly l't al. \2002) 

( 20! 1 a, circa 2008) ,,.·ith ~ix different Lands a! 

weighted <nerage of all 201-.J./!5 pans; 

!25m ave rag<: of a!l 20!-+-··20!5 image pair-.,). lhsin' 17 and !k are ..:omp!imentl."d 

of 82.5° S (Scheuch! ct aL 20 l2 ~- ~vluch of the difference between velocity 

the lowe'>t uncertaintie~ (used in thi" 'itudyL folkw,ed by ~'115. then \V!..J. and Yll..J., 

dures. Some diff~rence between 

pcdcd due to rea! changes in ice e!Tcctin: 

datt:s. This gnod agn?~mcnt het\vccn products gives us <.:nntidence that our results are not sensitive to the Landsat processing methodology. From here forward we only present results 

generated auto-RII-<J \Vl5 that 

certainties in discharge 

b cakuiatetl. 

3.l.J Amundsen Sea 

For the B:2! and B22 catchments, containing Pine Island, 

Thwaites, Haynes. Pope, Smith and Kohler glaciers (Fig. 

we tind a 6 r,:; increase in icc discharge or 

(Table This implies an average discharge increase of 

for 2008--2015 that is considerably lo\ver than 

the 6.5 Gt yr·- 2 previously estimated for 1994-2008 (Mouginot et aL 2014). This recent :-.lowing in the rate of acceleration is in exL'el!ent agreement with the previously published 

dense history or icc that a rate of 

increasc for this region of for overlapbut shorter of 2010-20!3 period CVIouginot et 

2014). Pine and Tlnvaites glaciers both shO\v dear 

www.the-cryosphere.net/12/521/20181 

signs of dynamic drawch)\V!l, with velocities increasing > 100m yr~ 1 up to 80-100 km inland from the 

grounding line 9). Figure 9 shows a peak in Pine Island 

velocity change at 50 km and a :;econdary peak at II 0 km 

upstream of the line. We see no such when 

comparing hctwet:n products. \\'hich us confldent that the se\.:ondary peak is not an artifact of the Landsat 

proce:-.sing. One possible non-gcophysicil a planation is that 

the radar mosaic includes data from a period signilkantly 

earlier than 200R for area or the second peak. East Kohler nnd 

Smith glaciers abo shO\v extensh·e speedups throughout their 

with increases or > 100m yr- 1 reaching more than 

inland likely driven by increased Oc<.'an melt rates and 

subs~quent grounding-line retreat (Khazendar d al.. 2016: 

Scheuchl et al., 2016 ). Patterns of velocity change for Pope 

and Kohkr glaciers are more complex, with slowing of up tn 

!OOmyr·--l near the grounding line and increas~:.·d speed hy 

""50 m yr~ 1 upstream reaching 40--80 km inland. Thl~ pattern of change is suggestive of an earlier period of dynamic 

drmvdown that is slowly propagating inland contrasted by 

more recent deceleration near the grounding line. Glacier:-. 

feeding the Get;: and Sulzberger k:e sht'lves (B20: including 

Berry, Hull and Land gla\.:iers) increased in speed by 10 to 

The Cryosphere, 12,521-547, 2018 
133 

532 A. S. Gardner et al.: Increased \Vest Antarctic and unchanged East Antarctic ice discharge 

Figure 8. 2015 Antarctic icc "hect :-.urfa~~ velocitie:- '>hown m lu~ <;ca!e Jeterrnined from featurt' tracking of >200000 Landsat image 

Glacier and ice qreams discu\sed in text lahckd with black numbering: (! l Ali'>on. {2) Berry. (3) Bind-;chadkr, (4) Bond, (5) Evan-;, 

Ferrigno. \7) f!a'ik, (8) Fox, (91 Haynes. (10) HulL ill l Kohler. 1 12! l.and.! 1.~) ( l4l \lacAyeaL (15) Pint" Island. (16) Popt", 

(17) Pmspect. 118) Rutford, t 19) Seller, (20) Sks'iOr. C!) Smith, (22) Stancomh-Wilb. Totten. and (24) T\vaite». ke sheh·c.\ labeled 

with white numbering: I l) Amery. (2l Filchner, en Fimbul. \4) George Vf, \5) Gett.. (6) ),!lo:;.cow U, (7) Rii'ier-Larsen. \8) Ronne. (9) Rns'>. 

t 10) Scar ln!cL and ( 10) Sul1berger. 

Figure 9. Change in 'iurface vdocitit''- between date ofpan-,\ntarctic SAR ct al .. 201 Ja, circa ~008) and new 2015 velocity 

produced here from feature tracking of Land,at 8 imagery. Change m -;hown for grounded ice only. l'vlissing data shmvn 

m and the 27 ha::-.Jn boundaries ddined hy Zwa!ly et al. (20021 Jre sho'Wn in hLKk 

I 00 m y-r-· 1 at their grounding lines. increasing discharge by 

6 c;r (Table 2). This result is in broad agreement with Chutcr 

et al. (2017) that obs.~rved increases in ice velocity Juring 

the 2007-2013 period alongside 20!0--2013 dynamic thinning rates of 0.7 m yr- 1 for the glaciers. feeding the Abbot 

and Getz ke s.helve5.. 

The Cryosphere, 12,521-547,2018 

3.1.2 Bellingshausen coast 

LocaliLed accelerations of 50-200m yr- 1 are observed near 

grounding lines for several of the major glaciers. the 

Bellingshausen Coast (823 and B2-+) including the 

Fox and Alison k:e streams and glaciers feeding into the 

southern George VI Icc SheiL Despite some areas of !low 

www.the-cryospherc.net/12/521/20 18/ 
134 

A. S. Gardner et al.: Increased West Antarctic and unchanged East Antarctic ice discharge 533 

acceleration, increases in discharge are highly localized. For 

many gladcrs, the flux-gate cro~s section is decreasing from 

regional thinning, resulting in negligible changes in discharge. This result is unexpected. but with high confidence. 

as this region has experienced high rates of ice shelf thinning 

{Paolo eta!., 2015) and grounding-line retreat (Christie et aL 

2016). both of which were inferred to have resulted in accelerated dynamic thinning that contributed 10 a 56± 8 Gt yr- 1 

increase in the rate of mass loss that began around 2009 and 

persisted until at least April 2014 (Wouters eta!., 2015). 

From our analysis we conclude that any changes in discharge contributing to observed rates of thinning must have 

occurred prior to the SAR mapping of ice velocities. This result agrees with a recent investigation of longer-term (1995-

2016) changes in ice discharge for this region (Hogg et al., 

2017) that found that the region's glacier experienced an increase in ice discharge between 1995 and 2008 and almost 

no change in discharge between 2{X)8 and 2016. 

3.1.3 Northern Antarctic Peninsula 

Along the west coast of the northern Antarctic Peninsula 

(B25) glaciers feeding into Marguerite Bay (Seller and 

Prospect) sped up by 400-800 m yr- 1 at their grounding 

lines, the largest speedup of all Antarctic glaciers, with an 

increase of> I 00 m yr- 1 reaching l 0·-15 km upstream. This 

speedup \Vas recently attributed to increa~ed ocean melt rates 

resulting from SOI!ENSO-driven ocean warming (Walker 

and Gardner, 2017). The majority of the west-coast glaciers 

to the north of Marguerite Bay are not sufficiently sampled in 

the earlier SAR mapping and are assumed to be unchanged 

between 2008 and 2015 (Fig. 2). Along the east coast of 

the northern Antarctic Peninsula (B26) most glacier..., feeding into the former Larsen A and B ice shelves that collapsed 

in 1995 and 2002, respectively, either have not changed significantly or show signs of slowing ncar their grounding lines 

(Wuite et al., 2015), with the exception of Leppard and Flask 

glaciers. These two glaciers have sped up by 50-I00myc 1 

at their grounding lines, likely in response lO reduced ke 

shelf butnessing and a resulting speedup of the abutting Scar 

Inlet Ice Shelf (Khazendar eta!., 20!5). Overall. this region 

shows a modest increase in ice discharge of 6 ± 6 Gt yr- 1, 

most of which comes from the glaciers tlowing into Marguerite Bay. Small changes in rates of discharge between periods are in good agreement with constant rates of RACMO~ 

derived surface mass budget and mass changes derived from 

GRACE data (Appendix B). 

3.L4 Ice streams feeding large ice shelves 

Our analysis suggests a 5-20 m yr- 1 slowdown of a broad 

region upstream of both Bindschadler and :\iacAyeal ice 

streams, which feed the Ross Ice Shelf. Ice streams feeding 

the Ronne-Filchner Ice Shelf show heterogeneous changes 

with slowing of 15--40 m yr- 1 upstream of the Rutford and 

www.the-cryosphere.neU12/521/2018/ 

Evans ice stream grounding lines and ......,. 20m yr- 1 :»peed up 

of the Slessor Ice Stream. Slowing in the Rutford lee Stream 

is consistent with the slowing observed between 1997 and 

2009 (Scheuchl et al., 2012). but the apparent increase in 

velocity of the Slessor Ice Stream is of equal magnitude 

but of opposite sign to the changes observed between 1997 

and 2009 (Scheuchl et al.. 20 12). Further to the east, the 

Stancomb-Wills Glacier increased in speed by 20-40 myr-- 1, 

just upstream of the grounding line, with glaciers feeding the 

Riiser-Larsen. Fimhul and Amery ice shelves showing little 

change. OveralL changes in surface velocity along grounding 

Jines of ice streams and glaciers feeding the major ice shelves 

of East and West Antarctica have not been large enough to 

significantly impact the net icc discharge for their respective 

basins (Table 2). 

3.L5 East Antarctic glaciers 

Ice discharge has remained remarkably steady for the East 

Antarctic glaciers, particularly along the coasts of Drenning Maud Land and Enderby Land. These basins (B5-B8) 

showed very little change in ice discharge. The region to the 

west of Law Dome, including Underwood and Bond glaciers, 

shows subtle evidence of some increased tlow speed and ice 

discharge, though the signal is near the limit of detection in 

part due to larger errors in the earlier radar mosaic for this 

region. However, the much larger Totten Glacier and the trib~ 

utaries of the Moscow University Ice Shelf (8 13) that drain a 

large fraction of the East Antarctic Ice Sheet show localized 

areas of ice speed variations hut little change in discharge 

(Fig, ! ), This result is consistent with recent findings of Li 

et al. (2016) showing that the Totten Glacier increased in velocity between 200 I and 2007, likely in response to elevated 

ocean temperature, but has been relatively unchanged since. 

3.1.6 Antarctic discharge 

In total we estimate that between the SAR and autoRifT WIS velocity mappings, the Antarctic ice sheet increased its solid ice discharge to the ocean from 1894 ± 43 

to 1929±40Gtyr- 1• This represents a 36± I5Gtyr- 1 increase in total discharge between 2008 and 2015; 78 0~ of 

the increases in discharge concentrated to glaci~rs flowing into the Amundsen Sea and another 10% coming from 

glaciers flowing into Marguerite Bay. Breaking it down to 

the main ice-sheet regions. the discharge of the West Antarctic Ice Sheet (B I, B 18-23) increased by 30 ± 8 Gt yr- 1 and 

the Antarctic Peninsula (B24-27) by 7 ± 6 Gt yr- 1, representing a 4 and 3 9'c increase in discharge, respectively. The 

discharge of the East Antarctic Ice Sheet (B2-l7) was remarkably unchanged with a total discharge of 952 ± 31 and 

952 ± 29 Gt yr- 1 in 2008 and 2015, respectively. 

Our estimate of 2008 total Antarctic ice discharge 

( 1894 ± 43 yr'' 1) is smaller than earlier estimates ~f 

2048± 146 and 2049 ± 86Gtyr- 1 by Rignot et aL (2013) 

The Cryosphere, 12,521-547, 2018 
135 

534 A. S. Gardner et al.: Increased West Antarctic and unchanged East Antarctic ice discharge 

and Depoorter et al. (2013), respectively. Both earlier studies use the same SAR velocity mosaic as used here (Rignot et al., 20 II a). Our estimate agrees with that of Rignot 

et aL (2013) within stated errors but not with that of De~ 

poorter et al. (2013). Rignot et al. (2013) used Operation 

Ice Bridge and BEDMAP-2 ice thickness data at lnSAR 

derived grounding lines to determine a total Antarctic discharge, with upscaling accounting for 352 Gt yr- 1 of the total discharge. The most obvious reason for the difference in 

the central estimates is the definition of the nux gates. Rignot et al. (2013) mostly rely on BEDMAP-2 data while our 

study draws almost entirely from flight data. Another possible reason for the difference is the upscaling of results for 

unmeasured basins. For these basins the total discharge is 

assumed to be the modeled climatological average surface 

mass balance integrated over the upstream basin. Such estimates have not been adjusted for losses due to basal melt, and 

they are sensitive to errors in the modeled SMB and to the 

delineation of the contributing basin area over which SMB is 

integrated. Upscaling for unmeasured areas by Depoorter et 

al. (2013) accounted for 476 Gt yr- 1 of their estimated discharge. The Depoorter et al. (2013} study uses a different 

definition of groundling hut otherwise uses the same data as 

used in Rignot et al. (2013). Again, much of the difference 

hctwccn estimates can be attributed to the definition of icc 

thickness and upscaling to unmeasured basins. It should also 

be noted that Depoorter et al. (2013) and Rignot et al. (2013) 

both used output from an earlier version of RACMO that 

produced larger total SMB than the version of the model 

used in our study. Since SMB is used to upscale discharge, 

this likely contributes some to the larger discharge estimates. 

Similar conclusions were made for updated Greenland Ice 

Sheet discharge estimates that were lower than previous estimates (Enderlin et al., 2014). 

3.2 Changes in net mass balance 

For the West Antarctic Ice Sheet, the 2008-2015 net 

mass budgets were negative for all but two basins (B l 

and Bl8) (Fig. 10), summing to a total imbalance of 

-214±51 Gtyr- 1 with largest rates of loss collocated with 

increased glacier velocities along the Amundsen Sea Embayment (B21 and B22) and Getz Ice Shelf (B20). The large 

mass Joss for the Getz Ice Shelf region is in contrast to 

the near balance conditions recently reported by Chuter et 

al. (2017) for the 2006-2008 period but is in agreement 

with the 2010-2013 estimate of net mass change by MartinEspafiol et al. (2016). The East Antarctic Ice Sheet is found 

to have increased slightly in mass at a rate of 61 ± 73 Gt yr-- 1 

with largest gains in Dronning Maud (B6) and Enderby Land 

(B7 and BS) that can be partially attributed to increase in 

precipitation rate (+28Gtyr- 1 relative to 1979-2007 mean) 

during the study period, which is consistent with earlier 

findings (Boening ct al., 2012; King ct al., 2012; Shepherd et al., 2012). For the whole of Antarctica, we estiThe Cryosphere, 12, 521-547, 2018 

mate an average mass budget of -l83±94Gtyr- 1 for the 

2008-2015 period. Other recent estimates of Antarctic mass 

change include those derived from CryoSat-2 altimetry of 

-159±48Gtyr- 1 for the period 2010-2013 (McMillan ct 

a!., 2014) and -116± 76Gtyr- 1 for the period 2011-2014 

(Helm et al., 2014, assuming density of ice) and a recent 

estimate from the joint inversion of gravity, altimetry and 

GPS data of -159:::22Gtyr- 1 for the period 2010-2013 

(Martin-Espafiol et al., 2016). All three studies show near 

balance to slightly positive mass changes for the East Antarc+ 

tic Ice Sheet and large losses for the West Antarctic Ice Sheet 

and the Antarctic Peninsula, all of which agree well with 

the results presented here when considering uncertainties and 

differences in study periods. 

4 Discussion 

Areas of accelerated surface velocity (Fig. 9) and increased 

ice discharge are in good agreement with basin-scale assessment of changes in ice flow and ice discharge (Li et al., 20 16; 

Mouginot et al., 2014) and with pa!terns of ice sheet thinning determined from laser and radar altimetry (Flament and 

Remy, 2012; Helmet al., 2014; Pritchard eta!., 2009). These 

show broad regions of surface lowering for glaciers feeding 

into the Amundsen Sea Embayment and Getz Ice Shelf and 

rapid drawdown of smaller glacier systems in the Antarctic 

Peninsula. Glaciers and ice streams feeding major ice shelves 

were remarkably steady with small heterogeneous changes 

in velocity. Apparent upstream slmving of Bindschadler and 

MacA yea! ice streams are at the limit of delectability and difficult to interpret. Recent assessments show varying changes 

in ice stream velocities for this region (Hulbe et aL, 2016; 

Scheuchl et al.. 20 12), suggesting that measured trends may 

be influenced by rapid changes in !he sub-icc-stream hydrology (Hulbc eta!.. 2016). 

Strongly negative net mass budgets are apparent for the 

West Antarctic Ice Sheet and are largely due to mean rates of 

ice discharge greatly exceeding rates of snow accumulation. 

The basin-averaged results (Fig. 1 0) match remarkably well 

with patterns of pan-Antarctic multi-decadal (1994-2012) 

changes in ice shelf thickness (Paolo et al., 20 15); high rates 

of mass Joss from glaciers feeding into the Amundsen Sea 

are collocated with high rates of icc shelf thinning and near 

balance conditions for \Vilkes Land glaciers and basins feeding the Filchner-Ronne. Ross and Amery ice shelves are collocated with ice shelves that have experienced little change 

in ice thickness over the past two decades. This result further supports the strong link between oceanic melting of ice 

shelves and ice sheet mass budget (Pritchard eta!., 2012). 

The link between basin mass budget and change in discharge is less obvious. This is primarily due to differences in 

representative periods as mass budgets represent the cumulative imbalance away from equilibrium state while changes 

in discharge are only representative of change in discharge 

www.the-cryosphere.nel/12/521!2018/ 
136 

A. S. Gardner et al.: Increased \Vest Antarctic and um:hanged East Antarctic icc discharge 535 

Figure 10. ~'t:tss and 1.:hange in discharg~ for the 27 basins ddined by calculated as described 

difTerenc!ng the pan-Antarctic SAR 

displacements supple-mented. \vith 2009 SAR 

in Table 2 using average surface mas-; balance. Change in discharge" 

of Rignot et at. (201 Ia: circa 200R.\ with of all 2015 

to fill Landsat 

provide an e~tirnalc disdlarge 

and da;;hed blue lines, respecti·vely. 

betv.een t\VO in time; e.g., a glacier can decelerate 

but still be ice at a rate that exceeds the "ur~ 

face mass budget minus ha.sal melt. Increased ice discharge 

from the Amundsen Sea Embayment and partial 

re~stabiiizatit.m have been a!lributed to changes ice shelf 

(Jacobs ct al., 1996: ;\1acgregor et aL 20 t 2) that 

increased icc shelf basal melt rates (Jacobs et 

Jenkins et aL 1997) and more recently to a decrease in ocean melting resulting from changes in the temperature of intermediate depth waters (Dutricux ct al., 2014 ). 

Increased discharge from glaciers feeding into the Gctz Icc 

Shelf is likely in response to rapid thinning of the lee shelf 

due to changes in ocean circulation and tht: depth of \varmcr 

modified Cin.:umpolar Deep \Vater (Jacobs. et aL, 20UJ. 

5 ('ondusion 

Applying mxvel feature tracking methods to hundr~ds of 

thousands of Landsat image pairs \Ve are now able construct a detailed and comprehensive record of recent changes 

in Antan::tic-wlde ice flow. \Vhen comhined with optimized 

t1ux-gatc definitions and an earlier mapping of surface vc~ 

locity (Rignot et aL, 20lla), such mea:.>urcments allow for 

accurate reconstructions of ice discharge and change:-. in 

ice discharge through timt:\ Applying these new capabilitie.<;, we determine that the Antarctic ice sheet dischanz:ed 

l894:t43Gtyr-l of :-olid ice into the oc~an 200f(.._inwww.the·cryosphere.net/12/521/2018/ 

time i..hfl:'cn.:nce" Ill 

creasing to 1929 ± 40 Gt yr- 1 in 2015 \Vith 78 9( of the increase in discharge concentrated to glaciers Howing into the 

Amumhcn Sea <md anoth~r 10 tTL conK'S from glacl!:rs. Howinto Bay. Glaciers and ice streams feeding 

ice were remarkably steady with small heterogeneous change" in Strongly net mas~ 

budgets are apparent for the Antarctk Sheet and 

are largely due to mean rates of ice di:>charge greatly exct~cding rates of snow accumulation. The East Antarctic Ice Sheet 

experienced near-balance conditions \Vith modest gains in 

Dronning :Vlaud and Enderby Land driven hy increased rate:-. 

of precipitation. 

Ov1.T the last decade, it is evident th<il larger-scale change:} 

in discharge are relatively modest(< 7 9( for all basins) comto the fractional imbalance between discharge and ~urrnass budget {up to several tens of percent). This suggests tbai th~ recent loss in Antarctica, domiSea sector. is likely a part of a longerterm phase of enhanced glacier How initiated in the 1990.-. as 

indicated by satdlite records (Konradet aL, 2017: Mouginot 

eta\., 2014) or as early as the 1940s as from subice-shelf sediment records (Smith et al., 

Glaciology is transitioning from an ob:::;ervationally to one with ample high-quality. 

high-volume satellite data sets suitahle for mapping ice flow 

on continental scales (e.g .. Landsat R, Sentinel 1afb. Sentinel I alb). This study a foundation ft)r C\1ntinued 

asSC\'>mcnt of kc sheet and discharge that will allow rcThe Cryosphere, 12. 521-547, 2018 
137 

536 A. S. Gardner et al.: Increased West Antarctic and unchanged East Antarctic ice discharge 

searches to observe both large and subtle changes ice sheet 

flow that may indicate early signs of ice sheet instability 

with low latency. Such a capability would help to diagnose 

unstable t1ow behavior and, in conjunction with high accuracy measurements of ice sheet elevation and mass change. 

would lead to improved assessment ice sheet surface mass 

balance and ice shelf melt rates. Low-latency monitoring 

of ice tlow and discharge would also allow field programs, 

flight planning and satellite tasking to coordinate the collection or complimentary observations in areas of changing ice 

behavior. These advances wiH ultimately lead to a deeper understanding of the causal mechanisms resulting in observed 

and future ice sheet instabilities. Any substantial improvement in our assessment of ice sheet discharge will require 

The Cryosphere, 12, 521-547, 2018 

more detailed knowledge of ice thickness just upstream of 

the grounding line. particularly for areas or complex now 

such as the Antarctic Peninsula and Victoria Land. Errors in 

discharge estimates can be greatly reduced if thickness profiles are acquired perpendicular to icc now. Improved estimates of net mass change calculated using the mass budget 

approach will come from continued rcflncmcnt of rc);2ional 

climate models and better estimates of basal melt. 

Data avaifahility. All velocity mosaics, grounding Jines. flux gates 

and ancillary data are available from the National Snow and Ice 

Data Center (Gardner et aL 2018a, b; Fahnestock et al.. 20!0). 

www.the·cryosphere.net/12/521/20 18/ 
138 

A. S. Gardner et al.: Increased \Vest Antarctic and unchanged East Antarctic ice discharge 537 

Appendix A: Uncertainty quantification 

A l Ice discharge 

The uncertainty in flux estimates were calculated for each of 

the 27 basins as 

uF 

where a FH is due to uncertainties in ice-equivalent thickness. a fJH is due to uncertainties in the change of iceequivalent thickness between the measurement times of ice 

thickness and surface velocily, nnd a Fr is due to uncertainties in measured velocity. due to the assumption that 

the depth-averaged velocity is equal to the surface veand is added as a bias (outside of the quadrature sum) 

to sides of the error envelope for simplicity. a Fdv,l\n!dt· 

a Fs.\1R and a Fr.m are uncertainties introduced by dynUmic 

volume change, surface mass balance and basal melt correcM 

between the flux gate and the true grounding 

was taken to be 0.! m yr~ 1 for surfaces moving faster than 200myr- 1, a FsMB \vas taken to be 20J:l0 of 

th0 SMB. Uncertainties in flux resulting from uncenainties 

in ice thickness, changes in ice thickness and surface velocity 

were propagated assuming a conservative conelation length 

along the flux gate as follows; 

(A2) 

(A3) 

"" aFv + LoVo;W;Hi, (A4) 

r=l 

where m is the numher of point estimates of flux (x) for each 

correlation length distance alnng the tlux gate and n is the 

number of discrete uncorrelated lengths for each basin for 

measurements of icc thickness (H), changes in ice thickness 

(dH) and the surface wlocity normal to the flux gate ( \1). 

Uncertainties in ice thickness (a fl;) arc taken as the RSS of 

the thicknc~s and the FAC. Cncertaintics in changes 

in ice thickne~s are determined as the RSS of uncertainty due to changes in FAC and surface elevation. dt is the 

difference in time between the measurement of ice thickness 

and the measurement of surface velocity. a FF is modeled 

using a velocity uncertainty component aVo that is fully correlated at lengths smaller than an estimated correlation length 

and uncorrelated at larger lengths (aV). Comparing Landsat 

and SAR velocities measured at tlux-gate nodes for basins 

with minimal in ice discharge (Bl-19 and B27): i.e., 

where are assumed to be indicative measurement uncertainty. we were able to model the ohserved 

www.the-cryosphere.net/12/521/20 18/ 

Figure Al. RMSE of the Landsat component of velocity that is 

nomutl to the !lux-gate cross section at FGJ (a) and FG:2 th) flux 

nodes relative to '""' 2008 SAR velodtks aL. 20 J I a) a-; a 

RMSE between Landsat and SAR observations (Fig. A l) set· 

ting aVo 3m y(···l and a V 1 m yr·· 1 with a cotTelation 

length of I 000 km for both the SAR and Landsat mappings. 

Uncertainties in velocities can be as high as 20-30myr- 1 

locally but are largely uncorrelated on basin scales. There 

arc insufficient data to determine rigorous estimates or the 

correlation lengths for ice thickness, change in icc thickness 

and surface velocity, all of which are likely spatially variable, Instead we took a conservative approach and assigned 

a con·elation length of I 000 km to all three measurements. 

When calculating icc flux \VC assumed that the surface 

velocity was equal to the depth-averaged velocity. This approach neglects vertical gradients in ice velocity that re:,.ult 

from the stress-dependent plastic deformation (creep) of ice. 

Since surface vdocities are always larger than the depthaveraged velocity this introduced a positive bias into our estimates of icc Hux. Neglecting sliding and assuming a depth 

constant creep parameter (A) the depth-averaged velocity is 

80 9C of the surface velocity (Cuffey and Paterson, 20 l 0). Asflow and a linear increase in shear stress with 

surface velocity due to creep (V~) can be calculated 

~t11 H. l+nb (A5) 

where n is the creep exponent. H is the ice thickness and lb 

is the driving stress at the bed. n is typically assumed to be 

3 and so is done here. fb is calculated using the surface slope 

and ice depth (Cuffey and Paterson. 20 I 0). The creep pa· 

rameter A (Fig. A2a) is taken from lee Sheet System Model 

(ISSM) output generated as part of the Sea-level Response 

to lee Sheet Evolution (SeaRISE) experiments (Bindschadler 

et al., 201J). We calculated surface slope from a CryoSat-2 

DEM that was smoothed on a scale of several times the ice 

thickness (20 km). Ice thickness was taken from Bcdmap-2 

(Fretwell et al., Vs varied between Omyr~l at the ice 

divides and in steeply sloped outlet glaciers near 

The Cryosphere, 12, 521-547, 2018 
139 

538 A. S. Gardner et al.: Increased West Antarctic and unchanged East Antarctic ice discharge 

Figure A2. Creep parameter (A: s- 1 Pa-3) shown in tog scale (a). Estimated surface velocity due to ice creep (\1s). 

the coast (Fig. A2b). We considered 20% of V, to be the upper bound or the bias introduced into our nux estimates due 

to Yertical gradients in the velocity field (a Fv-). calculated as 

"" a Fv= 0.2L Vsi WiHi. (A6) 

.\=I 

where nn is the number nodes along the basin flux gate. This 

is an upper bound scenario, as A increases rapidly with temperature, and ice sheet temperature is typically at a maximum 

near the hed. This results in a higher concentration of shear 

deformation near the base of the ice sheet than inferred from 

a depth-constant A. 

Uncertainties in nux estimates \vere assumed to be uncorrclatcd between basins. A detailed accountinp: of each flux 

term and their associated error is provided in Tables A 1 

through A3. Table A 1 provides detailed breakdown for the 

total discharge calculated using FG2 as the flux gate. This approach produces the discharge estimate with the lowest error 

and is the approach used in the main paper. For comparison, 

Tables A2 and A3 provide detailed breakdowns for the total 

discharge calculat~d using FG 1 and GLO, respectively. 

A2 Change in ice discharge 

Uncertainty in tlux-change estimates (ad F) are calculated as 

CTdF (A7) 

The Cryosphere, 12,521-547, 2018 

where adF H is the thickness-related uncertainty and is calculated as 

(AS) 

where dF is the change in flux and F is the total flux. adFdH 

is calculated in the same way as a FdH but setting dt to the 

time separation between repeat measurements of velocity. 

adFv is the flux-change uncertainty from the measured velocity and is determined as 

adFv= (A9) 

where a Fv is the uncertainty in flux introduced from uncertainties in surface velocity for two measurement epochs ( l 

and 2). adF00 data is the flux~changc uncertainty introduced 

by the assumPtion of zero change in t1ux for areas lacking 

reliable repeat measurements (a F11 o_data) and for areas between the tlux gate and the grounding line (a FsNm) and is 

calculated as 

adFno .. data = 0.1 (a FsMB +a Fno_data). (AIO) 

Uncertainties in flux-change estimates were assumed to be 

uncorrel.ated between basins. A detailed accounting of each 

change in nux term and their associated error is provided in 

Table A4. 

www.the-cryosphere.net/12/521/2018/ 
:; 

Er 

7 

i 

ii 

"" 

s 

:: 

..; 

::r 

" .~ ~ 3 

... 

.!" 

i!J 

;;;: ~ s 

"" 

HM and dVdyn/dt arc the surfa;:c ma:-.s 

propagation are describe in Sect. A I. 

-=-----::-:,---------- ID Surf;1ce ;m:a Length 

basin (km) 

GLO FG2 GLO-FG2 

I 474821 463 896 !0926 1170 

2 765 381 757 558 7824 359 

3 1556551 I 545527 II 024 253 

4 241 158 226961 14197 680 

5 185337 182 253 3084 415 

6 607737 583 513 24224 740 

7 492518 451677 40841 799 

8 161243 !44458 16785 485 

9 146003 !40392 5612 386 

10 919320 918041 1278 56 

II 255 178 249424 5753 275 

12 727088 698 205 28883 882 

13 I 130843 l 095837 35006 804 

14 718511 667028 51483 734 

15 123 780 14 735 !09044 187 

16 262005 236067 25937 339 

17 I 825799 I 667 954 !57845 775 

18 261 357 234457 26900 185 

19 367 678 347019 20659 353 

20 180072 139929 40143 71.\ 

21 207 491 203 265 4227 276 

22 210237 206351 3886 177 

23 74562 53294 21269 396 

24 100567 93479 7088 429 

25 34657 18312 16345 475 

26 42025 30162 II 863 469 

27 51962 40319 11643 297 

Total 12123881 I 1410110 713 770 13108 

rrFu aFou 

108.8 5.6 0.3 

46.0 3.2 (),() 

58.1 3.4 0.1 

39.5 7.0 0.4 

29.3 4.0 0.4 

53.8 5.3 0.2 

49.1 5.9 0.3 

11.9 1.9 0.2 

15,0 1.1 0.2 

33.0 2.9 0.2 

! !.9 0.7 0.1 

89.0 8.8 0.6 

192.7 15.9 {t9 

102.2 6.7 0.5 

L3 0.1 0.0 

10.7 0.7 0.1 

46,0 3.8 0.2 

7A Ll 0.0 

42.9 5.6 0.1 

140.6 11.4 0.9 

180.8 11.1 0.7 

130.9 7.8 0.3 

60.6 5.! 0.6 

86.3 5.9 0.5 

34.4 3.5 0.8 

17.3 L7 0.4 

6.9 0.6 0.1 

1606.3 3Ul 22 

weighted average velocity (W !5), F02 flux gate 

area between the flux gate and the grounding line. F is the total flux acros!'i 

change integrated over the area between lhc nux gate and the grounding line. All error terms an

aFv a Fv _lxtr IYF SMB 

3.3 0.2 6.8 2.7 

L8 0.1 3.7 0.9 

L6 0.0 3.8 L6 

2J) 0.1 7.4 3.8 

1.5 0.1 4.4 1.6 

2.4 0.2 6.0 6.0 

2.4 0.2 6.6 20,6 

1.8 O.l 2.7 6.2 

Ln 0.1 2.0 u 

1.2 0.1 3.2 0.0 

L5 0.7 2.4 0.4 

2.7 1.0 10.2 11.0 

2.8 1.4 17.5 27.5 

3.0 0.5 7.9 26.9 

!.5 0.1 1.7 245 

1.4 0.0 U\ 2.9 

2.8 0.4 5.2 22.9 

1.3 0.0 1.7 2.0 

1.7 0.0 5.8 2.4 

2.3 05 12.2 .B.9 

!.5 0.2 IIA 4.7 

1.3 0.0 7.9 2.8 

1.7 0.3 5.7 20.2 

1.6 0.2 6.3 7.5 

1.2 0.2 3.9 54.9 

J.J 05 2.7 7.2 

1.2 0.0 1.4 5.0 

10.2 2.2 35.2 301.5 

Addltionulllux between FG2 and GLO 

!Gtyr- 1] 

aFsMB BM a f'BM dVuyn/dl 

05 0.0 n.o O.J 

0.2 0.0 0.0 0.2 

0.3 (J,O 0.0 0.0 

0.8 -0.1 0.0 -0.1 

0.3 0.0 0.0 --0.1 

L2 -0,2 0.0 -0.2 

4.1 -0.4 0.0 -OJ 

1.2 -0.2 0.0 -0.5 

0.3 0.0 0.0 0.0 

(),() 0.0 0.0 0.0 

0.1 -0.1 0.0 0.0 

2.2 -0.6 0.0 0.7 

5.5 -0.7 0.0 2.5 

5.4 -0,8 0.0 0.1 

4.9 -05 0.1 0.2 

0.6 -0.2 0.0 0.0 

4.6 -0.4 0.0 -2.3 

0.4 0.0 0.0 -1.9 

0.5 -0.1 0.0 0.1 

6.8 -0.5 0.0 8.2 

0.9 -0,1 0.0 3.7 

0.6 0.0 0.0 0.8 

4.0 -0.3 rw 1.5 

1.5 -0.1 0.0 1.3 

11.0 -0.1 0.0 2.0 

lA 0.0 0.0 0.2 

LO 0.0 0.0 0.0 

17.9 -5.3 0.1 16.1 

I 

>l·jv,,,;u, D 

0.2 IIL7 

0.1 47.1 

0.! 59.8 

0.2 43.3 

0.0 30.R 

0.2 59.7 

0.6 69.9 

0.1 17.7 

OJ 16.4 

0.1 33.1 

ll.l 12.3 

1).8 101.2 

1.0 2233 

O.R 130.0 

0.4 26.4 

0.1 13.7 

1.8 67.0 

1.2 7.5 

0.8 45.5 

2.5 I 183.2 

1.1 189.3 

0.2 134.5 

0.5 82.5 

0.4 95.2 

0.6 91.4 

0.1 24.7 

0.0 ! 1.9 

4.1 1929.2 
A2. Same Table A 1 hut m.ing the FG I for the nux gate. 

Length 

(km) 

Flux through FG I 

(Gtyr- 1) 

AdJitionill flux hdween FG I rmd GUl 

jGtyr-11 

Total discharge 

(Gtyr- 1) 

GLO 

474HZ I 

7653KJ 

1550551 

241 !58 

185337 

607737 

492518 

161243 

146003 

919320 

255 178 

7270!\8 

I 130843 

718511 

123780 

262005 

I 825799 

261 357 

367678 

\80072 

207 491 210237 

74562 

100567 

34657 

42025 

51962 

HJl GLO H!l FGI F afu aFoH ffFv aFv_har aF I SMB rr FsMB HM a dVJyn/dT a I n an 

406855 7907 1287 109.8 53 O.l 3.2 0,2 65 1.8 0.4 0.0 0.0 0.1 0.21 II !.7 6.5 

761 534 3H47 370 46.9 2.9 0.1 1.9 0.0 3.6 0 5 0.1 OJJ 0.0 0.2 0.1 47.5 3.6 

I 553 I !5 3437 29'J 59.6 3.8 01 1.6 0.0 4.2 O.J 0.1 0.0 0.0 0.0 0.1 60.0 4.2 

239208 1950 843 44.5 10.7 0.5 !.9 0.0 10.9 0.6 0.1 0.0 0.0 ()J) 0.0 45.! 10.9 

184 737 600 489 30.4 4.6 0.4 L6 0.1 5.0 0.2 0.0 0.0 O.Cl 0.0 OJl 30.6 5.0 

60417K 3559 !ORO 59.0 9.1 0.2 2.3 0.1 9.4 O.K 0.2 0.0 OJ) -0.2 0.1 59.7 9.4 

492 159 359 1253 45.1 23.0 1.4 1.6 0.0 23.1 0.2 0.0 0.0 0.0 0.0 0.0 45.3 23.1 

100984 259 554 14.K 7.3 0.4 !.4 (J.O 7.5 0.2 0.0 0.0 0.0 0.0 0.0 14.9 7.5 145979 24 466 14.5 2.0 0.1 !.7 OJ) 2.7 0.0 0.0 0.0 0.0 0.0 0.0 14.5 2.7 

919149 171 36 37.3 3.6 0.1 !.2 0.2 4.0 ().f) 0.0 0.0 0.0 0.0 0.0 37.3 4.0 

255 033 145 333 9.0 1.3 0.1 1.6 0.8 2.8 0.0 0.0 0.0 0.0 0.0 0.0 9.0 2.8 

726 521 567 !072 I 24.6 38.6 1.8 2.0 0.1 38.8 O.J 0.1 0.0 0.0 0.0 0.0 124.9 38.8 

1125684 5159 1005 202.3 35.7 2.0 2.6 1.1 36.9 4.1 0.8 -0.1 0.0 1.3 0.4 207.8 36.9 

716677 1834 1129 134.0 24.6 1.6 2.2 0.1 24.8 1.2 0.2 0.0 0.0 0.1 0.1 135.1 24.R 

123620 160 1102 19.7 14.0 0.4 !.7 0.7 14.8 0.0 0.0 00 0.0 0.0 0.0 19.7 14.8 

26141!\ 587 5:'\·l 7.2 1.7 0.2 1.2 0.0 2.1 0.0 0.0 0.0 0.0 0.0 0.0 7.2 2.1 

1823861 1938 1235 53.8 10.9 0.3 2.1 0.1 !1.2 0.3 0.1 0.0 0.0 0.1 53.9 11.2 

259869 !4RH 444 10.6 2.0 0.1 1.6 0.0 2.6 0.1 0.0 0.0 0.0 0.0 10.6 2.6 

366 585 1094 419 44.9 6.2 0.! 1.7 0.0 6.4 0. I 0.0 0.0 0.0 0.0 0.1 45.0 6.4 

l73 18! 6H91 !382 146.9 23.4 1.1 2.1 0.4 23.9 7.4 1.5 -0.2 0.0 6.1 1.8 160.6 24.0 

205 221 2271 326 181.9 1 1.9 0.8 1.5 0.2 12.2 2.3 0.5 --0.1 0.0 3.7 1.1 I 88.0 12.3 208 363 1874 219 132.1 8.4 0.4 1.3 0.0 8.6 1.3 0.3 0.0 0.0 0.8 0.2 134.2 8.6 

72800 1763 881 78.2 17.3 1.1 1.9 0.0 17.4 2.7 0.5 0.0 0.0 0.7 0.2 81.6 17.5 

97 297 3171 5! 1 8tU H.9 0.7 1.6 0.2 9.3 2.9 0.6 0.0 0.0 1.0 0.3 92.0 9.3 

33 834 823 1360 62.9 25.6 1.9 I .3 0.0 25.8 I .7 0.3 0.0 OJ) 0.8 0.2 65.4 25.H 

41 888 138 1300 26.1 7.7 ()_(, I .5 0.5 8.4 0.0 0.0 0.0 0.0 0.0 0.0 26.2 8.4 

51 562 400 703 8.9 2.4 0.1 1.5 0.0 2.8 0.2 0.0 0.0 0.0 0.0 0.0 9.! 2.8 

12 I 23 881 12 071 JOt) 52 572 20653 1792.9 80.3 4.6 9.5 1.7 82.0 29.3 2.0 -0.6 0.0 14.4 2.3 1837.3 82. I 

s 

l 

t 

-a 

-5 

"" 

"' "' ::::! 

Q. 

u 
.; .; 

;, 

.g. 

"' 

il 

"" 

g: 

;;! 

n "' 

l 

Sl 

-

""' f:; 

e 

oe 

Table A3. Same as Table A! but usmg the GLO fur the !lux gate. 

Ill 

basin 

GLO GLO GLO-GLO 

474821 474821 

76538! 765381 

1556551 1556551 

241 158 241 158 

I 337 185 337 

607 7?.7 607 737 

4()2518 492518 

161 243 161243 

9 146003 146003 

10 ()19320 919320 

II 255178 25517R 

I 2 727 088 727 088 

13 1130843 1130843 

14 718511 718511 

15 123780 123780 

16 262 005 262 005 

I 7 I 825 799 I 825 799 

18 261 357 261357 19 367678 367678 

20 180072 180072 

21 207491 207491 

22 2102"H 210237 23 74 562 74 562 24 100567 100567 25 34 657 34 657 

26 -/.2 025 42 025 

27 51962 51962 

Total 12123881 12123881 

Length 

(km) ____ " 

GUl 

1651 112.1 

457 .N.4 

325 50.9 

920 47.3 

530 29.2 

1144 5!t5 

1265 4-LS 

57-t 13.7 554 14.1 

35 33.4 

343 1'1.8 

1144 125.7 1248 202.6 

I 162 129.7 

1121 20.3 

597 7.5 

1288 53.3 

510 lOA 

540 44.6 

1581 I.N.2 

370 181.7 

266 12l:L9 

936 80.7 

557 n.7 

1323 62.4 

1326 27.5 

784 10.6 

22 550 1755.6 

rrFu 

""2 

4.0 

7.4 

14.2 

5.0 

13.2 

22.5 

6.!) 

2.0 

3.2 

l.J 

40.2 

3V 

32.4 

14.3 

2.2 

4.Y 

2.2 

6.9 

34.6 

16.1 

10.6 

24.6 

23.0 

35.4 

g"y 

0 

98 () 

aFuH aFv 

()_J 3.9 

(U 2.3 

0.2 1.7 0.6 2.0 0.4 1.7 0.3 2.2 

1.4 1.6 

0.4 1.4 

0.2 1.9 

0.1 1.2 

0.1 1.6 

1.9 2.1 

1.9 2.8 

1.8 2.1 

0.4 1.7 0.2 1.3 0.3 2.2 0.1 1.7 0.2 1.9 

1.3 2.2 1.5 1.6 

0.5 1.3 

1.4 1.9 

lA LS 

2.4 L3 

0.7 1.5 0.3 1.5 

5.3 10.1 

Additional flux bcrwccn FG I and GLO 

""----"---------IGtyr11 

n Fv bur rr F I SMB 

0.4 9.5 0.0 0.0 4.6 0.0 0.0 7.0 (U) 0.0 !4.4 0.0 0.\ 5.3 0.0 0.0 11.4 0.0 0.0 22.6 0.0 0.0 7.0 0.0 0.0 2.8 0.0 0.2 3.5 0.0 

o.s 2.9 0.0 

0.1 40.4 0.0 

0.4 38.2 0.0 0.0 32.6 0.0 

0.8 15.2 0.0 0.0 2.6 0.0 0.1 10.3 0.0 0.0 2.8 0.0 0.0 7.1 0.0 0.1 34.7 0.0 0.2 16.4 0.0 0.0 10.7 0.0 0.0 24.7 0.0 0.0 23.1 I OD 0.0 35.5 0.0 0.2 9.2 0.0 0.0 -L9 0.0 

!.3 91) 2 ! 0.0 

a FsMB BM rr FsM d Fdyn/dt 

M M M M M M M M M M M M M M 

M M 

M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M M 

0.0 ()() 

M 

M 

M 

M 

M 

M M 

M 

M 

M 

M M M M M M M M M M M M M M M M M 

0.0 

M 

M 

M 

M M M 

M 

M 

M 

M 

M M M 

M M M M M M M M M M M M M M 

0.0 

[) 

0.0 112.1 

0.0 39.4 

0.0 50.9 0.0 47.3 0.0 29.2 0.0 58.5 0.0 44.5 ().() 13.7 ().() 14.1 

0.0 33.4 

0.0 8.8 0.0 125.7 0.0 202.6 

0.0 129.7 

0.0 20.3 0.0 7.5 0.0 53.3 0.0 10.4 0.0 44.6 

flO 139.2 0.0 18!.7 

0.0 128,9 (LO gJt7 

0.0 78.7 

0.0 62.4 0.0 27.5 0.0 10.6 

0.0 ! 1755.6 
143 

542 A. S. Gardner et al.: Increased West Antarctic and unchanged East Antarctic ice discharge 

Table A4. Detailed breakdown of the change in di-;charge ( ~ [)) estimate presented in Table 2 using JPL auto~ RIFf 2015 weighted awrage 

velocity (WI5). "'-'2008 veloc1ties from Rignot eta!. (20lla), the fGI flux gate and GLO grounding !inc. dF is change in flux acros~ 

the grounding line and ddVctvn/dt is the change in dynamic volume change for the area between FGI and GLO. All error term'i and their 

propagation are describe in sect. A2. 

J[) Length ,, AdJ!tlunal D. flux bet\\-ecn 

ba\m O..m) FGl and GL 1Gtyr~ 1 j 

GL FGI GL-FGJ FG! dF adFn rrdFdu adFv rrdFn"~dJtJ dd\1-t~n/dt dD adO 

47..1.82! 466855 7967 12X7 2.0 0.1 0.6 3.0 " -0.-l I 6 32 

76538! 761534 3847 370 -0.5 0.0 0.1 2.0 .l8 -0.3 -0.8 -LJ 

1556551 ! 553115 3-1-37 294 O.H 0.0 0.4 2.1 0.1 -0.! 07 ... 2-1-1158 239208 1450 8-D " OA 1.0 2A OA 0.0 " L7 

\85337 184737 600 489 0.7 0.1 0.8 2.0 O.l 0.1 0.7 .. 607737 604178 3559 1080 -0.6 0.1 0.7 2.5 0.6 0.2 -0.3 2.7 

492518 492159 359 1253 I 9 0.2 07 2.1 0.3 0.0 1.9 " 16! 243 160984 259 554 0.7 0.1 0.4 1.9 0.0 0.0 0.7 2.0 

!4600:'1 145979 2-~ 466 -0.7 0.1 0.2 " 0.0 -0.1 -0.8 2.2 

10 919320 9!9149 171 36 -1.2 0.1 0.3 1.6 0.0 0.0 -L2 1.7 

II 255178 255033 145 333 -1.2 0.1 ()_J 2.0 ()_() 0.0 -II 2.0 

12 727088 726521 567 1072 -03 0.0 !.3 2.8 0.4 0.0 -0.3 3.1 

I' I 130843 I 1.25684 5154 1005 -2.3 0 . .2 2.3 3.3 2.8 0.0 -2.3 4.9 

1., 718511 716677 UB4 1129 -O...t 0.0 !.5 28 0.5 0.4 0.0 3.2 

15 1.23 780 123620 160 1102 00 0.0 0.0 2.3 0.0 0.0 0.0 2.3 

16 262005 261418 5X7 554 0.3 0.0 0.3 1.7 00 0.0 0.4 1.7 

17 18.25799 1823861 1938 123S -0.5 0.0 ()_..j. 2.1 2.5 0.2 -tU 3.3 

IX 261357 259869 1-188 444 -1.5 0.0 0.0 lA !.2 0.1 -lA 1.9 

19 367678 366585 10(}4 419 1.0 0.1 0.3 2.0 0.1 0.2 L2 2.0 

.20 !S0072 !7318! 689! 1382 IL6 0.9 2.6 2.8 1.1 0.7 12.2 4.1 

21 207491 205221 2271 326 9.4 0.6 2.8 2.1 0.2 0.1 9.5 J.6 

n 210237 .208363 11-!74 219 7.2 0.4 1.1 1.8 OJ -0.1 7,1 " 23 7456.2 72800 1763 881 0.1 00 1.7 26 0.5 -0.1 0.0 3 . .2 

24 100567 97297 3271 511 1.7 0.1 2.1 .. 0.4 -0.8 O.S 31 

25 34657 33834 823 1360 3.6 0.3 09 1.6 4.3 -0.6 3.0 4.7 

26 -12025 41888 138 1300 1.7 0.2 09 2.1 0.4 0.0 17 2.3 

27 5! 962 51562 400 703 OJ 0.0 0.2 2.1 0.0 0.0 0 .. 1. 2.1 

Total 12!23881 1207JJ()lj 52572 20653 35.9 L3 6.2 11.7 -0.5 35.4 15.2 

The Cryospherc, 12, 521-547, 2018 www.thc-cryosphere.net/12/521/2018/ 
144 

A. S. Gardner et al.: Increased West Antarctic and unchanged East Antarctic ice discharge 543 

Appendix B: Northern Antarctk Peninsula net mass 

balance GRACE JPL"' -31 Gt vr 1t 

ch::~racterized uncer~ 

and o f~k/dr 

agated to highly uncertain estimates of net mass change. 

this reason, we derived our estimat~s of net mass change using previously published estimates 

tion measurements that we added to of change 

in ice discharge. Work by Scamhos et aL (20 14 ), based on el~ 

evation changes, and recent gravity work and Simons, 

20l5) both sugg~st that the northcm Antarctic 

gion (precise study extents vary) has seen continued 

losses at more or less a constant rate of for 

the period 2003-2015: this is further supported by examination of JPL mascon (\'/atkins et a!., 20 15) mass anomalies 

and RACMO surface mass budget anomalies (See B I). 

Estimates based on CryoSat-2 \McMillan et aL, 

a reduced mass loss for B25 and B26 (below the 

level) for the period 20 l 0-2013, hut usable data 

CryoSat-2 for this rugged region are sparse. 

To estimate the net mass balance for basins B:25 and B26. 

\VC used estimates of glacier mass loss dete,nnined from repeat elevation measurements for the 2003<!0 11 period as n 

(Scambos et aL 2014). Since this. study was 

to areas north of 66" S. v.,;e added our estimate of 

south of 66'S (6Gtyr-l: Table 2) 

net mass balances for 2008-2015. 

\Vas calculat~d as the RSS 

estimate of in disScamuncenainty in the surface mass budgeL Basin totals and uncertainties are provided in Tahle 2. 

www.thc-cryosphere.net/12/521/2018/ 

~ 

~ § 

j 

2004 2014 

Figure Bl. Rates of 2002-2014 mass as derived from linfits to cumulative anomalies <>urface ma~s balance 

determined at 5.) km (blue line) and 27 km (red line), and JPL 

The Cryospbere, 12,521-547, 2018 
145 

544 A. S. Gardner et al.: Increased West Antarctic and unchanged East Antarctic ice discharge 

Author comribwions. ASG devised the study, developed the JPL 

auto-RIFT software, did all calculations and wrote the paper. OM 

was r~spons1hlc for updating the grounding-line location and de lining the flux gates. he also spent considerable time revising the 

manuscript after the lead author broke his wrist while snowboardmg. TS and MF produced the USA velocity fields; SL and MvdB 

provided modeled FAC and SMB output and J~ produced surface 

elevation change rates from CryoSat-2 data. All author-; di"cus<;ed 

and commented on the manuscript at all stages. 

Competing interests. The authors declare that they have no conflict 

of interest. 

Acknmrledgemems. W~ thank Brice Van Lieffcringe and Prank Pattyn for kindly sharing their modeled estimates of basal melt rates. 

Bert Wouters for helpful dlscu..,sions regarding Bellingshausen 

Sea glacier mass changes, Ala Khazendar for helping to provide 

context for observed changes in glacier velocity. Ian Joughin for 

helpful discussion regarding SAR velocities and sharing of data 

not used in this study. Peter Fretwell for providing information on 

Bedmap-2 and Eric Rignot, Jeremie Mouginot and Bernd Scheuch! 

for making their SAR velocities publically available, without which 

this study would not have been possible. Ted Scambos i<> deeply 

appreciative of Terry Haran and Marin Klinger for all of their hard 

work creating the NSIDC velocity maps. This work wa<> supported 

by funding from the NASA Cryosphere program. The research was 

conducted at the Jet Propulsion Laboratory. California Institute 

of Technology, under contract with the National Aeronautics and 

Space Administration and at University of Colorado Boulder and 

University of Alaska Fairbanks under NASA grant N~X 16AJ88G. 

Edited by: G. Hilmar Gudmundsson 

Reviewed by: three anonymous referees 

References 

A!Uson, I. and Hyland. G.: Amery Ice Shelf compiled and merged 

ice thickne<>'i dataset<>, Australian Antarctic Data Centre, Metadata. available at: https:l/data.aad.gov.au/metadata!records/A!S_ 

thicknes-.,_bottom (last access: I June 20\6), 20!0 (updated 

2014). 

Berthier, E., Scambos, T. A., and Shuman, C. A.: Mass 

loss of Larsen B tributary glaciers \Antarctic Peninsula) 

unabated since 2002, Geophy<>. Res. Len., ~9. LIJSOL 

hups://doi.org!IO.l029/2012GL051755, 2012. 

Bindschadler, R. A. and Scambos, T. A.: Satellite-image-derived velocity field of an Antarctic ice stream. Science. 252. 242-246, 

199!. 

Bindschadler, R. A .. Nowicki, S .. Abe-Ouchi. A .. Aschwanden, A., 

Choi, H., Fastook, J., Granzow, G., Greve, R .. Gutowski, G .. 

Herzfeld, U., Jackson, C.. Johnson. J., Khrou!ev. C .. Levem1ann. 

A .. Lip~comb, W. H., Martin, M. A .. Mortighem, ~ .. Parizek. B. 

R .. Pollard, D., Price, S. E. Ren, D., Saito, F., Sato, T., Seddik. 

H., Scrow,si. H., Takahashi, K., Walker. R .. and Wang, W. L.: leesheet modd sensiriviti!!s to environmt!nta! forcing and their use 

The Cryosphere, 12, 521-547, 2018 

in projecting future <>ea level (the SeaRlSE project), J. Glacio!., 

59, 195-224. https://doi.org/10.3189/2013JoG12J125, 2013. 

Blanken<>hip. D. D., Kempf. S. D .. and Young, D. A.: IceRridge 

HiCARS 2 L2 Geolocated ke Thickness, Version I, edited. 

NASA National Snow and lee Data Center, Boulder. Colorado. 

USA, https://doi.org/1 0.506 7/9EBR2TOVXUDG. 2012 (updated 

2015). 

Boening, C .. Lebsack, M., Landcrer. F., and Stephem, G.: Snowfalldriven mass change on the East Antarctic ice sheet. Geophys. 

Res. Lett., 39, L2!501. https:l/doi.org/10.1029/2012GL053316. 

2012. 

Bouzinac, C.: CryoSat Product Handbook, edited. European 

Space Agency, available at: https:J/earth.esa.intldocuments/ 

10174/125272/CryoSat_Product_Handbook (last acce..,s: I June 

2016), 2015. 

Callen~, D., Matsuoka, K., Steinhage, D., Smith, B., Witrant, E., and 

Pattyn. E: Transition of flow regime along a marine-tenninating 

outlet glacier in East Antarctica, The Cryosphere, 8, 867-875. 

https://doi.org/!0.519-1/tc-8-867-20 14, 201-1. 

Catlens, D .. Thonnard, N., Lenaerts, J. T. !v1., Van Wessern, J. M .. 

Van De Bt!rg, W. J., Matsuoka. K., and Pattyn, F.: Mass balance of the Sor Rondane glacial ~:y~tem, Ea<;t Antarctica, Ann. 

Glaciol., 56, 63-09, https://doi.org/10.3189/2015AoG70A010, 

2015. 

Christie. F. D. W .. Bingham, R. G., Gourmelen. N., Tett. 

S. E B., and Muto. A.: Four-decade record of pen'asive grounding line retreat along the Bellingshausen mar~ 

gin of West Antarctica, Gcophys. Res. Lett., 43, 5741·-5749, 

httpd/doi.org/10.! 002/20 16GL068972, 2016. 

Chuter, S. J., :\.<1artfn-Espafiol. A., Wouters. B .. and Bamber. J. L.: 

Mass balance reassessment of glaciers draining into the Abbot 

and Getz Ice Shelves of West Antarctica, Geophy<>. Res. Lett.. 

44. 7328-7337. https://doi.org/1 0.1002/20 17GL073087. 2017. 

Coffey, K. and Pater,am. W. S. B.: The physic~ of glaciers, 

xii, 693 pp., Buttcnvorth-Heinemann/Elsevier, Amsterdam, the 

Netherlands, Boston. USA, 2010. 

Depoorter. M. A .. Bamber, J. L .. Griggs. J. A .. Lenaerts, J. T. M .. 

Ligtenberg, S. R. M., van den Broeke, M. R .. and Moholdt, G.: 

Calving tluxcs and basal melt rates of Antarctic ice shelves, Nature, 502. 89-92. http<>:!/doi.org/1 0.1 038/nature 12567, 2013. 

Dutrieux. P., De Rydt. L Jenkins, A., Holland, P. R., Ha. 

H. K., LC"e. S. IL. Steig. E. J., Ding. Q., Abraham~en, E. 

P., and S..:hrOder, M.: Strong Sensitivity of Pine Island IceShelf Melting to Climatic Variability. Science, 343, 174--178, 

http!-.:l/doi.org/JO.ll26/science.l244341, 2014. 

Enderlin, E. M .. Howat. I. M .. Jeong. S., :-.Joh, M.-J .. van Angelen. 

J. H .. and van den Broeke. M. R.: An improved mass budget 

for the Greenland ice :.heet, Geophys. Res. Leu .. 4 I. 866-872. 

http~://doi.org/10.! 002/20 13GL059010, 20 1-t. 

Fahnestock, M.. Scambos, T.. Moon, T.. Gardner, A., Haran, T .. and Klinger, M.: Rapid large-area mapping of ice 

flow using Landsat 8, Remote Sens. Environ .. 185, 84-94, 

https:l/doi.org/10.10!6/j.r<>e.2015.! 1.023, 2015. 

Fahnestock. M., Sc:.1mbos, T., Moon, T, Gardner. A., Haran, 

T .. and Klinger, M.: Landsat8 Ice Speed of Antarctica, available at: ftp://ftp.n~idc.org/pub/DATASETS/nsidc0733_1andsat_ 

ice_ <>peed_ vO 1/ (las! access: 8 February 10 18), 2016. 

www,the-cryosphere.net/12/52112018/ 
146 

A. S. Gardner et al.: Increased West Antarctic and unchanged East Antarctic ice discharge 545 

Flament, T and Remy, F: Dynamk thinning of Antarctic glaciers 

from a!ong~track repeat radar altimetry, J. GlaciaL 58,830 840. 

https://doi.org:l10.3l89/2012JoG! IJ118. 2012. 

Fretwell, P., Pritchard. H. D., Vaughan, D. G., et al.: Bedmap2: im~ 

proved ice bed, surfuce and thickness datasets for Antarctira, The 

Cryosphere. 7, 375 .. 393. hups://doi.org/10.5194/tc-7-375-2013. 

2013. 

Gardner, A. S., Moho!dt, G., Cogley, J. G., Wouters. B., Arendt. 

A. A., Wuhr. L Bcrthier, E., Hock, R., Pfe!Ter, W. T., Kaser, G., 

Ligtenberg, S. R. M .. Bolch. T.. Sharp, M. J., Hagen. J. 0., van 

den Broeke, M. R., and PauL F.: A reconciled estimate of glacier 

contributions to sea level rise: 2003 to 2009, Science, 340, 852-

857, https://doi.org/1 0.1 I 26/sclence.l23-l-532, 2013. 

Gardner, A. S., Moholdt, G., Scambo-;, T. Fahn-aock. M .. Ligtenberg, S., van den Broeke, M .. and Nilsson, J.: Grounding Line 

for Antarctic Discharge (GLAD) point Illes for flux estimates. 

available at: ftp://ftp.nsidc.org/pub/DATASETS/n~idc0732_ 

land'iat_antarctic_ice_ velocitie'i_ vO I /GardnerEtAI_20! 8_ 

SupData/GLAD _llux_g.ates/, !a~t access: 8 February 20 !Sa. 

Gardner, A. S .. Moholdt, G .. Scambos. T., Fahnstock, M., LigtenS., van den Brocke, M., and Nils~on, J.: JPL auto-RIFT 

surface velocities, available at: ftp://ftp.nsidc.org/pub/ 

DATASETS/nsidc0732_landsat_antarctic_ice _ ve!ocitie~_ vO J I 

GardncrEtA!_20 l8_SupData/GLAD_tlux.,...gate::./, last access: 

8 February 20i8b. 

Gogineni, P.: CReSIS Radar Depth Sounder Data. edited. Lawrence. 

Kansas, USA, avaialble at: http://data.cresis.ku.edu/ {la~t access: 

I June 2016), 2012 (updated 2015). 

Harig. C. and Simon'i. F. J.: Accelerated We~t Antarctic ice mas-. 

loss continues to outpace East Antarctic gain~. Earth Planet. Sc. 

Lett., 4!5, 134·-l-1-1, hHps:i/doi.org/10.1016/j.cpsL2015.01.029. 

2015. 

Helm, V., Humbert A, and Miller, H.: Elevution and elevation 

change of Greenland and Anturctica derived from CryoSat2, The Cryosphere, 8, 1539-1559, https://doi.org/10.5 !94/tc-R1539-2014_ 2014. 

Hogg. A. E., Shepherd, A., Comford. S. L.. Briggo.;, K. H., Gounne-

\en, N., Graham. J. A .. Joughin, L, Mouginot, J., Nagler, T.. 

Payne. A. L Rignot. E., and Wuite, J.: Increased ice flow in Western Palmer Land linked to ocean melting. Geophyo.;. Res. Lett. 

44.4159-4167, https:!/doi.orgltO. !002/2016GL072J 10, 20!7. 

Hu!be, C. L.. Scambo~. T A., Kling~r. M .. and Fahne,tock, M.A.: 

Flow variability and ongoing margin <;hifts on Bind~chad!er and 

~1acAyea! lee Streams, West Antarctica. J. Geophys. Res.~Earth, 

121. 283· 293. https://doi.orgll 0.1002/20! 5Jf003670, 2016 

Huss, .\1. and Farinotti, D.: A high-re:-.o!ution bedrock map 

for the Antarctic Peninsula, The Cryosphere, 8. I 26 I ·--1273, 

hUps://doi.orgll0.5194/tc-8-!26!~201-t 201-t 

Jacobs, S., Giulivi. C., Dutrieux. P .. Rignot. E .. Nitsche. F .. and 

Mouginot. J.: Getz Ice Shelf melting re.,pono.;e to changes 

in ocean forcing. J. Geophys. Res.-Oceans. 118, 4152--4168, 

https:J/doi.org/1 O.l002/jgrc.20298. 2013. 

Jacobs, S. S .. Hellmer. H. H., and Jenkins, A.: Antarctic lee Sheet 

melting m the southeast Pacifk. Geophys. Res. Lett., 23, 957-

960_ https://doi.org/1 0.1 029/96GL00723, 1996. 

Jacobs, S. S., Jenkins, A., Giu!ivi, C. F, and Dutrieux. P.: 

Stronger ocean circulation ami increased melting under Pine Island Glacier ice o.;he!f, Supplement, Nat. Geosci., 4. 519-523, 

https://doi.org/10.l038/ngeoll88. 2011. 

www.the-cryosphere,net/12/521/2018/ 

Jenkins, A., Vaughan, D. G., Jacobs, S. S., Hellmer, H. H .. and Keys, 

J. R.: Glaciological and oceanographic evidence of high melt 

rare-; beneath Pine Island Glacier, West Antarctica. J. Glacio!.. 

43, 114-121, 1997. 

Jeong, S. and Howat, I. M.: Performance of Landsat 8 Operational 

Land Imager for mapping ice sheet velocity. Remote Scns. Environ .. 170, 90-10!, https://doi.orgll0.10!6/j.rse.2015.08.023. 

2015. 

Jezek, K. C., Farne~s. K., Carande, R .. Wu, X., and LabelleHarner, N.: RADARSAT I synthetic aperture radar observation" 

of Antarctica: Modified Antarctic Mappmg Mission. 2000. Radio 

Sci., 38,8067, https://doi.orgii0.1029/2002RS002643, 2003. 

Khazendar, A., Bor~tad, C. P., Scheuchl, B .. Rignot, E., and 

Serous:-.i, H.: The evolving instability of the remnant Larsen B 

lee Shelf and its tributary glaciers, Earth Planet. Sc. Lett .. -l\9, 

199-210, https://doi.orgll0.1016/j.epsl.2015.03.014, 2015. 

Khazendar, A .. Rignot. E .. Schroeder, D. M .. Seroussi, H .. Schodlok. M. P., Scheuchl, B .. Mouginot, J.. Sutterley. T C .. and 

Velicogna, I.: Rapid submarine ice melting in the grounding 

zones of ice shelves in Wc<>t Antarctica, Supplement, NaL Commun., 7, 13243, https://doi.org/1 0.1 038/ncomms 13243, 2016. 

King. M. A., Bingham. R. J., Moore, P., Whitehouse. P. L .. Bentley. 

M. J.. and Milne, G. A.: Lower ~atel!ite-gravimetry estimates of 

Antarctic sea-level contribution, Supplement. :-.lature, 491, 586--

589, https:l/doi.org!JO.l038/naturel !621. 2012. 

Konrad, IL Gilbert, L., Comford. S. L. Puyne, A., Hogg. 

A.. ,1\luir. A., and Shepherd. A.: Uneven onset and pace 

of ice-dynamical imbalance in the Amundsen Sea Embayment, West Anturctica, Geophy<;. Res. Lett., 44. 910---918. 

https://Joi.org/10.1002/2016GL070733. 2017. 

Leuschen. C., Gogineni, P., Rodriguez-Morales, E. Paden, L and 

Allen, C.: lceBridge MCoRDS L2 lee Thickness, Version I. 

edited. NASA National Snow and lee Data Center, Boulder. Colorado. USA. httpd/doi.org/!0.5067/GDQOCUCVTE2Q. 20!0 

(updated 2015). 

Li. X .. Rignot, E., Morlighem, M .. Mouginot. J., ~nd ScheuchL 

B.: Grounding line retrear of Touen Glacier. East Antarctica, !996 to 2013, Geophy~. Res. Lett., 42, 8049-8056. 

http~://doi.org/10. !002/2015GL065701. 20!5. 

Li. X.. Rignot, E .. Mouginot, L and Schcuchl. B.: Icc flo~ 

dynamic~ and ma<;s \o<;s of Totten Glacier, East Antarctica, 

from 1989 to 2015. Geophys. Re~. Lett., 43, 6366 637J, 

http-;://doi.org/10.100:?:/20!6GL069173, 2016. 

Ligtenberg, S. R. M .. Helsen, M. M .. and van den Broeke. M. R.: An 

imprmcd ~emi-empirkal modd for the densitkarion of An! arctic 

tim. The Cryo~phere, 5, 809-819. https:I/Joi.org/10.519-1-/rc-5-

809-2011, 201 L 

Ligtenberg, S. R. M., Kuipers Munneke, P .. and van den Broeke. 

M. R: Prt.'sent and future variation:, in Antan:tk firn air content. The Cryo~phere, 8. 171 1·-1723, https://doi.orgll0.5!94/tc8-!711-2014, 2014. 

~acgregor. J. A .. Catania. G. A., Markowski. M. S., and Andrew:-., 

A. 0.: Widespread rifling and retreat of ice-shelf margins in the 

eastern Amundsen Sea Embayment between 1972 and 2011, J. 

Glacio!., 58, 458-466, https://doi.org/l0.3189/2012JoG 111262. 

2012. 

Martin-I.:\paiiol. A .. Zammit-Mangion. A .. Clarke, P. J., Flament. 

T., Helm, V.. King, M. A., Luthcke, S. B., Petrie, E., Remy, F., 

SchOn, N .. Wouters. B., and. Bamber. J. L: Spatial and tempoThe Cryosphere, 12,521-547, 2018 
147 

546 A. S. Gardner et al.: Increased West Antarctic and unchanged East Antarctic ice discharge 

raJ Antarctic Ice Sheet mass trends, glacio-isostatic adjustment, 

and surface processes from a joint inversion of satellite altimeter. 

gravity, and GPS data, J. Geophys. Res.-Earth. 12!. 182-200. 

https://doi.org/1 0.1002/20 15JF003550. 2016. 

McMillan. M .. Shepherd, A., Sundal, A., Briggs, K., Muir, A. 

Ridout, A.. Hogg, A .. and Wingham. D.: Increased icc losses 

from Antarctica detected by CryoSat<L Geophys. Res. Lett, -1!. 

3899-3905, https:lldoi.orgll0.100212014GL060111. 2014. 

Mor!ighem. M., Rignot, E., Seroussi, H., Larour, E., Ben Dhia, 

H., and Aubry, D.: A mass conservation approach for mapping glacier ice thickne~~. Gcophy'>. Res. Lett., 38, L! 9503. 

https:l/doi.org/10.1029/2011GL048659, 2011. 

Mouginot, J., Rignot, E .. and Scheuchl, B.: Sustained increase in 

ice discharge from the Amundsen Sea Embayment, We~t Antarctica, from 1973 to 2013, Geophy'>-. Rc$. Lett., 41. 1576--1584. 

https://doi.org/1 0.1002/20 13GL059069, 20 !4. 

:vtouginot, J., Rignot, E., Scheuch!, B .. and MiHan, R.: Comprehensive Annual Ice Sheet Velocity ~1apping Using Landsat-8. 

Sentinel-!, and RADARSAT-2 Data. Remote Sensing, 9, 364, 

https://doi.org/10.3390/rs9040364, 2017. 

Nilsson. J ., Gardner. A.. Sandberg Sorensen, L, and f.-Drsberg. R.: Improved retrieval of land ice topography from 

CryoSat-2 data and its impact for volume-change estimation 

of the Greenland lee Sheet, The Cryosphere. 10, 2953--2969, 

https:lldoi.org/10.5194/tc-10-2953-2016, 2016. 

Padman, L. Erofeeva, S. Y., and Frick~r. H. A.: Improving 

Antarctic tide models by assimilation of fCESat laser altimetry over ice shelves, Geophy-;. Res. Leu .. 35. L22504, 

https://doi.org/1 0.1 029/2008GL035592. 2008. 

Paolo. F. S .. Fricker, H. A, and Padman. L: Volume lo-;s from 

Antarctk ice shelves is accelerating. Science, 348. 327 · 331. 

https://doi.orgll0.1126/science.aaa0940. 2015. 

Paragios. N., Chen, Y .. and Faugeras. 0. D.; Handbook of mathematical models in computer vision. Springer Science & Bu:-,iness 

Media, New York, NY, USA. 2006. 

Pattyn. F.: Antarctic suhg!acial conditions infetTed from a hybrid 

ice sht:et!ice stream model. Earth Planet. Sc. Lett., 295.451-461, 

https://doi.org/1 0.10 l6(!.eps\.20 1 0.04.025, 2010. 

Pritchard, H. D., Arthem, R. J., Vaughan. D. G., and Edwards, L. 

A.: Extensive dynamic thinning on the margins of the Greenland 

and Antarctic ice sheet'i, ~ature. 461.971--975. 2009. 

Pritchard, H. D, Ligtenberg, S. R. ~f.. Fricker. H. A .. Vaughan, D. 

G .. van den Broeke. M. R .. and Padman, L.: Antarctic ice--.;heet 

loss driven by basal melting of ice -.;he!Yes. Supplement. Nature, 

484. 502~505, httpd/doi.org/1 0.1 038/nature I 096S. 20 I 2. 

Rignot. E.: Change<> in ice dynamics and mass balance of the 

Antarctic ice <iheet, Philos. T. Roy. Soc. Lond. A. 364. 1637-

! 655, https://doi.org/l0.1098/r~ta.2006.1793. 2006. 

Rignot E. and Thomas. R. H.: Mass balance of Polar ice <iheets, 

Science, 297, 1502-1506. 2002. 

Rignot, E., Mouginot. L and ScheuchL B.: Ice Flow 

of the Antarctic Ice Sheet, Science. 333. 1+27- 1430, 

https://doi.org/1 0.1 I 26/science.l208336, 20 ll a. 

Rig not, E., Velicogna. 1., van den Broeke. M. R., Monaghan, A .. and 

Lenaerts, J.: Acceleration of the contribution of the Greenland 

and Antarctic ice sheets to sea level rise, Geophys. Res. Lett . 38. 

L0550J, https:/ldoi.orgl10.102912011gl046583. 2011b. 

The Cryosphere, 12, 521-547, 2018 

Rignot, E., Jacobs, S., Mouginot, L and Scheuch!, B.: Ice~ 

Shelf Melting Around Antarctica, Science, 341, 266-270. 

https://doi.orgll0.1126/<;c]ence.1235798, 2013. 

Rignot, E .. Mouginot. J., Morlighem, M., Seroussi. H., and 

Scheuch!, B.: Widespread. rapid grounding line retreat of Pine 

Island. Thwaite-;, Smith. and Kohler glaciers. West Antarctica. from 1992 to 2011, Geophys. Res. Lett., 41, 3502-3509, 

https:lldoi.orgi10.100212014GL060140, 2014. 

Scambos, T. A., Dutkiewicz, M. J .• Wilson, J. C., and Bindschadler. 

R. A.: Application of Image Cross-Correlation to th~ Measurement of Glacier Velocity Using Satellite lmage Data, Remote 

Sens. Environ., 42. 177-186, 1992. 

Scambos, T. A., Haran, T. M.. Fahnestock, M. A., Painter. 

T. H., and Bohlander, J.: ~ODlS-ba~ed Mosaic of Antan.:-

tica C\rtOAJ data sets: Continent-wide -;urface morphology 

and snow grain <>ize, Remote Sens. Environ., 111, 242--257, 

https:l/doi.org/1 0.10 l6/j.rse.2006.12.020. 2007. 

Scambos. T. A .. Berthier, E .. Haran, T., Shuman. C. A .. Cook, 

A. J.. Ligtenberg, S. R. M .. and Bohlander. J.: Detailed ice 

loss pattern in the northern Antarctic Peninsula: wide<ipread decline driven by ice front retreats, The Cryosphere. 8, 2! 35-2145, 

http<;://doi.org/1 0.5194/tc-8-2135-2014. 2014. 

Scheuchl. B .. Mouginot, L and Rignot. E.: Ice velocity changes 

in the Ro-;s and Ronne sectors observed using satellite radar 

data from 1997 and 2009. The Cryosphere. 6. 1019-1030. 

hups://doi.org/10.5194/tc-6-1019-2012, 20!2. 

Scheuchl, B., Mouginot, L Rignot. E., Morlighem. M., and 

Khazendar. A.: Grounding line retreat of Pope, Smith. and 

Kohler Glaciers, West Antarctica, measured with Sentinel-! a 

radar interferometry data. Geophys. Res. Lett., 43, 8572-8579. 

https://doi.org/10.1 002/20 !6GL069287, 2016. 

Shepherd, A, Ivins, E. R .. A, G., et a!.: A Reconciled Estimate of Ice-Sheet Mass Balance. Science, 338. 1183··1189, 

https:l/doi.org/1 0.1 ! 26/science.l228102. 2012. 

Shuman. C. A., Berthier, E.. and Scambos, T. A.: 2001--

2009 elevation and mass los<>es in the Larsen A and B 

embayments, Antarctic Peninsula. J. Glacio!., 57, 737--754. 

https:lldoi.orgl10.31891002214311797409811. 2017. 

Smith. J. A .. Andersen, T. L Shortt, M., Gaffney, A. ~t.. Truffer, M .. 

Stanton. T. P., Bindschadler. R.. Dutrieux, P., Jenkins, A., Hillenbrand, C. D., Ehrmann. W .. Corr, H. F. J., Farley, N., CrowhuN, 

S., and Vaughan, D. G.: Sub-kc-:-.helf -.ediment:-. record hi:,tory 

of twentieth-century r~!reat of Pine Island Glacier, :-.lature, 541. 

77--80. http<.;://doi.org/JO.l038/nature20136. 2017. 

Snyder. J. P.: Map projectiom: A working manuaL Report Rep. 

1395. C. S. Govt:rnm~:nt Printing Offke. Washington. D.C. USA. 

1987. 

Thomson, J. and Cooper, A.: The SCAR Antarctic digital topographic database. Antarct. Sci., 5. 239··244, 1993. 

Van Lieffcringe. B. and Pattyn, F.: Using ice~ftow models to 

evaluate potential 'iites of million year-old ice in Antarctica. 

Clim. Past, 9, 2335-2345, https://doi.org/10.5194/cp-9-2335-

2013, 2013. 

van Wessem. J. M., Reijmer. C. H .. ~Iorlighem, M., :-vtouginot, 

1., Rignot, E.. Medley, B., Joughin, L, Wouters. B .. Depoorter. 

M. A .. Bamber. J. L., Lenaerts. J. T. M .. De Van Berg, W. 

J., Van Den Broeke. M. R., and Van Meijgaard, E.: Improved 

representation of East Antarctic surface mass balance in a rewww,the-cryosphere.net/12/521/2018/ 
148 

Æ 

A. S. Gardner et al.: Increased West Antarctic and unchanged East Antarctic ice discharge 547 

gional atmospheric climate model, J. Glacio!., 60. 761-770, 

https://doi.org/1 0.3189/20 14JoG !41051, 2014 

van Wes-;em, J. M., Ligtenberg, S. R. M .. Reijmer. C. H .. van de 

B~rg, W. 1., van den Broeke, M. R., Harrand, N. E., Thomas, E. 

R .• Turner, J., Wuite, J., Scambos, T. A., and van Meijgaard, E.: 

The modelled surface mass balanct: of the Antarctic Peninsula 

at 5.5 km horizontal re-.olution, The Cryosphere, 10, 271·-285. 

http;://doi.orgll0.5194/tc-10-271-2016. 2016. 

Yelicogna, I.: Increasing rares of ice ma:-.s lo<>:-. from the Greenland and Antarctic ice sheets revealed hy GRACE, Geophy<>. Res. 

Lett., 36, L 19503, https://doi.orgllO. 1029/2009g!040222, 2009. 

Walker, C. C. a1d Gardner. A. $.: Rapid drawdown of Antarctica's Wordie Ice Shdf glaciers in re-;pome to EN SO/Southern 

Annular Mode-driven warming in the Southern Ocean, 

Supplement C, Earth Planet. Sc. Lett., 476. 100 1 10, 

httpd/doi.org/10.1 0 16/j.epsl.2017.08.005, 2017. 

Watkins. M. M .. Wiese. D. N., Yuan. D.-N .. Boening, C.. and 

Landerer, F. W.: Improved methods for observing Earth's 

time variable ma~s di-;tribution with GRACE using spherical cap rnascons, J. Geophys. Res.-SoL Ea .. 120. 2648-267 t, 

http:-.://doi.orgf!0.1002/2014JBO! 1547. 2015 

www,the-cryosphere,net/12/521/2018/ 

Wouter-;. B .. Martin-EspaftoL A., Helm. V, Hament, T .. 

We<>sem, J. M., Ligtenberg, S R. M., van den Broeke, M 

Rq and Bamber, J. L.: Dynamic thinning of glacier-; on 

the Southern AntarctiC Pemnsula, Sc1ence, J4~. l'\99-903. 

hups:l/doi.org/l0.1126/<>cience.aaa5727. 2015 

Wuite. J., Rott, H., Hetzenecker. M., Floricioiu, D., Dt! 

L Gudmund~~on. G. H., Nagler, T., and Kern, M · 

tion of ... urface velocities and ice discharge of Larsen B outkt glaciers from t995 to 2013, The Cryosphere, 9, 957-969. 

https://doi.org/1 0.5194/tc-9-957-2015, 2015 

Zwally, H. J., Giovinetto, B- M., Beckley, M. A., and Saba, J. L 

Antarctic and Greenland Drainage GSFC Cryospheric 

Science" available at httf'://it:esut4.!:sfcnasa.g<lVi 

The Cryosphere, 12,521-547, 2018