66496 Federal Register / Vol. 74, No. 239 / Tuesday, December 15, 2009 / Rules and Regulations 

ENVIRONMENTAL PROTECTION 

AGENCY 

40 CFR Chapter I 

[EPA–HQ–OAR–2009–0171; FRL–9091–8] 

RIN 2060–ZA14 

Endangerment and Cause or 

Contribute Findings for Greenhouse 

Gases Under Section 202(a) of the 

Clean Air Act 

AGENCY: Environmental Protection 

Agency (EPA). 

ACTION: Final rule. 

SUMMARY: The Administrator finds that 

six greenhouse gases taken in 

combination endanger both the public 

health and the public welfare of current 

and future generations. The 

Administrator also finds that the 

combined emissions of these 

greenhouse gases from new motor 

vehicles and new motor vehicle engines 

contribute to the greenhouse gas air 

pollution that endangers public health 

and welfare under CAA section 202(a). 

These Findings are based on careful 

consideration of the full weight of 

scientific evidence and a thorough 

review of numerous public comments 

received on the Proposed Findings 

published April 24, 2009. 

DATES: These Findings are effective on 

January 14, 2010. 

ADDRESSES: EPA has established a 

docket for this action under Docket ID 

No. EPA–HQ–OAR–2009–0171. All 

documents in the docket are listed on 

the www.regulations.gov Web site. 

Although listed in the index, some 

information is not publicly available, 

e.g., confidential business information 

(CBI) or other information whose 

disclosure is restricted by statute. 

Certain other material, such as 

copyrighted material, is not placed on 

the Internet and will be publicly 

available only in hard copy form. 

Publicly available docket materials are 

available either electronically through 

www.regulations.gov or in hard copy at 

EPA’s Docket Center, Public Reading 

Room, EPA West Building, Room 3334, 

1301 Constitution Avenue, NW., 

Washington, DC 20004. This Docket 

Facility is open from 8:30 a.m. to 4:30 

p.m., Monday through Friday, excluding 

legal holidays. The telephone number 

for the Public Reading Room is (202) 

566–1744, and the telephone number for 

the Air Docket is (202) 566–1742. 

FOR FURTHER INFORMATION CONTACT: 

Jeremy Martinich, Climate Change 

Division, Office of Atmospheric 

Programs (MC–6207J), Environmental 

Protection Agency, 1200 Pennsylvania 

Ave., NW., Washington, DC 20460; 

telephone number: (202) 343–9927; fax 

number: (202) 343–2202; e-mail address: 

ghgendangerment@epa.gov. For 

additional information regarding these 

Findings, please go to the Web site 

http://www.epa.gov/climatechange/ 

endangerment.html. 

SUPPLEMENTARY INFORMATION: 

Judicial Review 

Under CAA section 307(b)(1), judicial 

review of this final action is available 

only by filing a petition for review in 

the U.S. Court of Appeals for the District 

of Columbia Circuit by February 16, 

2010. Under CAA section 307(d)(7)(B), 

only an objection to this final action that 

was raised with reasonable specificity 

during the period for public comment 

can be raised during judicial review. 

This section also provides a mechanism 

for us to convene a proceeding for 

reconsideration, ‘‘ ‘[i]f the person raising 

an objection can demonstrate to EPA 

that it was impracticable to raise such 

objection within [the period for public 

comment] or if the grounds for such 

objection arose after the period for 

public comment (but within the time 

specified for judicial review) and if such 

objection is of central relevance to the 

outcome of this rule.’ ’’ Any person 

seeking to make such a demonstration to 

us should submit a Petition for 

Reconsideration to the Office of the 

Administrator, Environmental 

Protection Agency, Room 3000, Ariel 

Rios Building, 1200 Pennsylvania Ave., 

NW., Washington, DC 20004, with a 

copy to the person listed in the 

preceding FOR FURTHER INFORMATION

CONTACT section, and the Associate 

General Counsel for the Air and 

Radiation Law Office, Office of General 

Counsel (Mail Code 2344A), 

Environmental Protection Agency, 1200 

Pennsylvania Ave., NW., Washington, 

DC 20004. 

Acronyms and Abbreviations. The 

following acronyms and abbreviations 

are used in this document. 

ACUS Administrative Conference of the 

United States 

ANPR Advance Notice of Proposed 

Rulemaking 

APA Administrative Procedure Act 

CAA Clean Air Act 

CAFE Corporate Average Fuel Economy 

CAIT Climate Analysis Indicators Tool 

CASAC Clean Air Scientific Advisory 

Committee 

CBI Confidential Business Information 

CCSP Climate Change Science Program 

CFCs chlorofluorocarbons 

CFR Code of Federal Regulations 

CH4 methane 

CO2 carbon dioxide 

CO2e CO2-equivalent 

CRU Climate Research Unit 

DOT U.S. Department of Transportation 

EO Executive Order 

EPA U.S. Environmental Protection Agency 

FR Federal Register 

GHG greenhouse gas 

GWP global warming potential 

HadCRUT Hadley Centre/Climate Research 

Unit (CRU) temperature record 

HCFCs hydrochlorofluorocarbons 

HFCs hydrofluorocarbons 

IA Interim Assessment report 

IPCC Intergovernmental Panel on Climate 

Change 

MPG miles per gallon 

MWP Medieval Warm Period 

N2O nitrous oxide 

NAAQS National Ambient Air Quality 

Standards 

NAICS North American Industry 

Classification System 

NASA National Aeronautics and Space 

Administration 

NF3 nitrogen trifluoride 

NHTSA National Highway Traffic Safety 

Administration 

NOAA National Oceanic and Atmospheric 

Administration 

NOI Notice of Intent 

NOX nitrogen oxides 

NRC National Research Council 

NSPS new source performance standards 

NTTAA National Technology Transfer and 

Advancement Act of 1995 

OMB Office of Management and Budget 

PFCs perfluorocarbons 

PM particulate matter 

PSD Prevention of Significant Deterioration 

RFA Regulatory Flexibility Act 

SF6 sulfur hexafluoride 

SIP State Implementation Plan 

TSD technical support document 

U.S. United States 

UMRA Unfunded Mandates Reform Act of 

1995 

UNFCCC United Nations Framework 

Convention on Climate Change 

USGCRP U.S. Global Climate Research 

Program 

VOC volatile organic compound(s) 

WCI Western Climate Initiative 

WRI World Resources Institute 

TABLE OF CONTENTS 

I. Introduction 

A. Overview 

B. Background Information Helpful To 

Understand These Findings 

1. Greenhouse Gases and Transportation 

Sources Under CAA Section 202(a) 

2. Joint EPA and Department of 

Transportation Proposed Greenhouse 

Gas Rule 

C. Public Involvement 

1. EPA’s Initial Work on Endangerment 

2. Public Involvement Since the April 2009 

Proposed Endangerment Finding 

3. Issues Raised Regarding the Rulemaking 

Process 

II. Legal Framework for This Action 

A. Section 202(a) of the CAA— 

Endangerment and Cause or Contribute 

1. The Statutory Framework 

2. Summary of Response to Key Legal 

Comments on the Interpretation of the 

CAA Section 202(a) Endangerment and 

Cause or Contribute Test 


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1Section III of these Findings discusses the 

science on which these Findings are based. In 

addition, the Technical Support Document (TSD) 

accompanying these Findings summarizes the 

major assessments from the USGCRP, IPCC, and 

NRC. 

B. Air Pollutant, Public Health and Welfare 

III. EPA’s Approach for Evaluating the 

Evidence Before It 

A. The Science on Which the Decisions 

Are Based 

B. The Law on Which the Decisions Are 

Based 

C. Adaptation and Mitigation 

D. Geographic Scope of Impacts 

E. Temporal Scope of Impacts 

F. Impacts of Potential Future Regulations 

and Processes that Generate Greenhouse 

Gas Emissions 

IV. The Administrator’s Finding That 

Emissions of Greenhouse Gases 

Endanger Public Health and Welfare 

A. The Air Pollution Consists of Six Key 

Greenhouse Gases 

1. Common Physical Properties of the Six 

Greenhouse Gases 

2. Evidence That the Six Greenhouse Gases 

Are the Primary Driver of Current and 

Projected Climate Change 

3. The Six Greenhouse Gases Are Currently 

the Common Focus of the Climate 

Change Science and Policy Communities 

4. Defining Air Pollution as the Aggregate 

Group of Six Greenhouse Gases Is 

Consistent With Evaluation of Risks and 

Impacts Due to Human-Induced Climate 

Change 

5. Defining the Air Pollution as the 

Aggregate Group of Six Greenhouse 

Gases Is Consistent With Past EPA 

Practice 

6. Other Climate Forcers Not Being 

Included in the Definition of Air 

Pollution for This Finding 

7. Summary of Key Comments on 

Definition of Air Pollution 

B. The Air Pollution Is Reasonably 

Anticipated To Endanger Both Public 

Health and Welfare 

1. The Air Pollution Is Reasonably 

Anticipated To Endanger Public Health 

2. The Air Pollution Is Reasonably 

Anticipated To Endanger Public Welfare 

V. The Administrator’s Finding That 

Greenhouse Gases From CAA Section 

202(a) Sources Cause or Contribute to the 

Endangerment of Public Health and 

Welfare 

A. The Administrator’s Definition of the 

‘‘Air Pollutant’’ 

B. The Administrator’s Finding Whether 

Emissions of the Air Pollutant From 

Section 202(a) Source Categories Cause 

or Contribute to the Air Pollution That 

May Be Reasonably Anticipated To 

Endanger Public Health and Welfare 

C. Response to Key Comments on the 

Administrator’s Cause or Contribute 

Finding 

1. The Administrator Reasonably Defined 

the ‘‘Air Pollutant’’ for the Cause or 

Contribute Analysis 

2. The Administrator’s Cause or Contribute 

Analysis Was Reasonable 

VI. Statutory and Executive Reviews 

A. Executive Order 12866: Regulatory 

Planning and Review 

B. Paperwork Reduction Act 

C. Regulatory Flexibility Act 

D. Unfunded Mandates Reform Act 

E. Executive Order 13132: Federalism 

F. Executive Order 13175: Consultation 

and Coordination With Indian Tribal 

Governments 

G. Executive Order 13045: Protection of 

Children From Environmental Health 

Risks and Safety Risks 

H. Executive Order 13211: Actions 

Concerning Regulations That 

Significantly Affect Energy Supply, 

Distribution, or Use 

I. National Technology Transfer and 

Advancement Act 

J. Executive Order 12898: Federal Actions 

To Address Environmental Justice in 

Minority Populations and Low-Income 

Populations 

K. Congressional Review Act 

I. Introduction 

A. Overview 

Pursuant to CAA section 202(a), the 

Administrator finds that greenhouse 

gases in the atmosphere may reasonably 

be anticipated both to endanger public 

health and to endanger public welfare. 

Specifically, the Administrator is 

defining the ‘‘air pollution’’ referred to 

in CAA section 202(a) to be the mix of 

six long-lived and directly-emitted 

greenhouse gases: carbon dioxide (CO2), 

methane (CH4), nitrous oxide (N2O), 

hydrofluorocarbons (HFCs), 

perfluorocarbons (PFCs), and sulfur 

hexafluoride (SF6). In this document, 

these six greenhouse gases are referred 

to as ‘‘well-mixed greenhouse gases’’ in 

this document (with more precise 

meanings of ‘‘long lived’’ and ‘‘well 

mixed’’ provided in Section IV.A). 

The Administrator has determined 

that the body of scientific evidence 

compellingly supports this finding. The 

major assessments by the U.S. Global 

Climate Research Program (USGCRP), 

the Intergovernmental Panel on Climate 

Change (IPCC), and the National 

Research Council (NRC) serve as the 

primary scientific basis supporting the 

Administrator’s endangerment finding.1

The Administrator reached her 

determination by considering both 

observed and projected effects of 

greenhouse gases in the atmosphere, 

their effect on climate, and the public 

health and welfare risks and impacts 

associated with such climate change. 

The Administrator’s assessment focused 

on public health and public welfare 

impacts within the United States. She 

also examined the evidence with respect 

to impacts in other world regions, and 

she concluded that these impacts 

strengthen the case for endangerment to 

public health and welfare because 

impacts in other world regions can in 

turn adversely affect the United States. 

The Administrator recognizes that 

human-induced climate change has the 

potential to be far-reaching and multidimensional, and in light of existing 

knowledge, that not all risks and 

potential impacts can be quantified or 

characterized with uniform metrics. 

There is variety not only in the nature 

and potential magnitude of risks and 

impacts, but also in our ability to 

characterize, quantify and project such 

impacts into the future. The 

Administrator is using her judgment, 

based on existing science, to weigh the 

threat for each of the identifiable risks, 

to weigh the potential benefits where 

relevant, and ultimately to assess 

whether these risks and effects, when 

viewed in total, endanger public health 

or welfare. 

The Administrator has considered 

how elevated concentrations of the wellmixed greenhouse gases and associated 

climate change affect public health by 

evaluating the risks associated with 

changes in air quality, increases in 

temperatures, changes in extreme 

weather events, increases in food- and 

water-borne pathogens, and changes in 

aeroallergens. The evidence concerning 

adverse air quality impacts provides 

strong and clear support for an 

endangerment finding. Increases in 

ambient ozone are expected to occur 

over broad areas of the country, and 

they are expected to increase serious 

adverse health effects in large 

population areas that are and may 

continue to be in nonattainment. The 

evaluation of the potential risks 

associated with increases in ozone in 

attainment areas also supports such a 

finding. 

The impact on mortality and 

morbidity associated with increases in 

average temperatures, which increase 

the likelihood of heat waves, also 

provides support for a public health 

endangerment finding. There are 

uncertainties over the net health 

impacts of a temperature increase due to 

decreases in cold-related mortality, but 

some recent evidence suggests that the 

net impact on mortality is more likely 

to be adverse, in a context where heat 

is already the leading cause of weatherrelated deaths in the United States. 

The evidence concerning how humaninduced climate change may alter 

extreme weather events also clearly 

supports a finding of endangerment, 

given the serious adverse impacts that 

can result from such events and the 

increase in risk, even if small, of the 

occurrence and intensity of events such 

as hurricanes and floods. Additionally, 

public health is expected to be 


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2The temporal scope of impacts is discussed in 

more detail in Section III.C. The phrase ‘‘near term’’ 

as used in this document generally refers to the 

current time period from and the next few decades. 

The phrase ‘‘long term’’ generally refers to a time 

frame extending beyond that to approximately the 

middle to the end of this century. 

adversely affected by an increase in the 

severity of coastal storm events due to 

rising sea levels. 

There is some evidence that elevated 

carbon dioxide concentrations and 

climate changes can lead to changes in 

aeroallergens that could increase the 

potential for allergenic illnesses. The 

evidence on pathogen borne disease 

vectors provides directional support for 

an endangerment finding. The 

Administrator acknowledges the many 

uncertainties in these areas. Although 

these adverse effects provide some 

support for an endangerment finding, 

the Administrator is not placing primary 

weight on these factors. 

Finally, the Administrator places 

weight on the fact that certain groups, 

including children, the elderly, and the 

poor, are most vulnerable to these 

climate-related health effects. 

The Administrator has considered 

how elevated concentrations of the wellmixed greenhouse gases and associated 

climate change affect public welfare by 

evaluating numerous and far-ranging 

risks to food production and agriculture, 

forestry, water resources, sea level rise 

and coastal areas, energy, infrastructure, 

and settlements, and ecosystems and 

wildlife. For each of these sectors, the 

evidence provides support for a finding 

of endangerment to public welfare. The 

evidence concerning adverse impacts in 

the areas of water resources and sea 

level rise and coastal areas provides the 

clearest and strongest support for an 

endangerment finding, both for current 

and future generations. Strong support 

is also found in the evidence concerning 

infrastructure and settlements, as well 

ecosystems and wildlife. Across the 

sectors, the potential serious adverse 

impacts of extreme events, such as 

wildfires, flooding, drought, and 

extreme weather conditions, provide 

strong support for such a finding. 

Water resources across large areas of 

the country are at serious risk from 

climate change, with effects on water 

supplies, water quality, and adverse 

effects from extreme events such as 

floods and droughts. Even areas of the 

country where an increase in water flow 

is projected could face water resource 

problems from the supply and water 

quality problems associated with 

temperature increases and precipitation 

variability, as well as the increased risk 

of serious adverse effects from extreme 

events, such as floods and drought. The 

severity of risks and impacts is likely to 

increase over time with accumulating 

greenhouse gas concentrations and 

associated temperature increases and 

precipitation changes. 

Overall, the evidence on risk of 

adverse impacts for coastal areas 

provides clear support for a finding that 

greenhouse gas air pollution endangers 

the welfare of current and future 

generations. The most serious potential 

adverse effects are the increased risk of 

storm surge and flooding in coastal 

areas from sea level rise and more 

intense storms. Observed sea level rise 

is already increasing the risk of storm 

surge and flooding in some coastal 

areas. The conclusion in the assessment 

literature that there is the potential for 

hurricanes to become more intense (and 

even some evidence that Atlantic 

hurricanes have already become more 

intense) reinforces the judgment that 

coastal communities are now 

endangered by human-induced climate 

change, and may face substantially 

greater risk in the future. Even if there 

is a low probability of raising the 

destructive power of hurricanes, this 

threat is enough to support a finding 

that coastal communities are 

endangered by greenhouse gas air 

pollution. In addition, coastal areas face 

other adverse impacts from sea level rise 

such as land loss due to inundation, 

erosion, wetland submergence, and 

habitat loss. The increased risk 

associated with these adverse impacts 

also endangers public welfare, with an 

increasing risk of greater adverse 

impacts in the future. 

Strong support for an endangerment 

finding is also found in the evidence 

concerning energy, infrastructure, and 

settlements, as well ecosystems and 

wildlife. While the impacts on net 

energy demand may be viewed as 

generally neutral for purposes of making 

an endangerment determination, climate 

change is expected to result in an 

increase in electricity production, 

especially supply for peak demand. This 

may be exacerbated by the potential for 

adverse impacts from climate change on 

hydropower resources as well as the 

potential risk of serious adverse effects 

on energy infrastructure from extreme 

events. Changes in extreme weather 

events threaten energy, transportation, 

and water resource infrastructure. 

Vulnerabilities of industry, 

infrastructure, and settlements to 

climate change are generally greater in 

high-risk locations, particularly coastal 

and riverine areas, and areas whose 

economies are closely linked with 

climate-sensitive resources. Climate 

change will likely interact with and 

possibly exacerbate ongoing 

environmental change and 

environmental pressures in settlements, 

particularly in Alaska where indigenous 

communities are facing major 

environmental and cultural impacts on 

their historic lifestyles. Over the 21st 

century, changes in climate will cause 

some species to shift north and to higher 

elevations and fundamentally rearrange 

U.S. ecosystems. Differential capacities 

for range shifts and constraints from 

development, habitat fragmentation, 

invasive species, and broken ecological 

connections will likely alter ecosystem 

structure, function, and services, 

leading to predominantly negative 

consequences for biodiversity and the 

provision of ecosystem goods and 

services. 

There is a potential for a net benefit 

in the near term 2 for certain crops, but 

there is significant uncertainty about 

whether this benefit will be achieved 

given the various potential adverse 

impacts of climate change on crop yield, 

such as the increasing risk of extreme 

weather events. Other aspects of this 

sector may be adversely affected by 

climate change, including livestock 

management and irrigation 

requirements, and there is a risk of 

adverse effect on a large segment of the 

total crop market. For the near term, the 

concern over the potential for adverse 

effects in certain parts of the agriculture 

sector appears generally comparable to 

the potential for benefits for certain 

crops. However, The body of evidence 

points towards increasing risk of net 

adverse impacts on U.S. food 

production and agriculture over time, 

with the potential for significant 

disruptions and crop failure in the 

future. 

For the near term, the Administrator 

finds the beneficial impact on forest 

growth and productivity in certain parts 

of the country from elevated carbon 

dioxide concentrations and temperature 

increases to date is offset by the clear 

risk from the observed increases in 

wildfires, combined with risks from the 

spread of destructive pests and disease. 

For the longer term, the risk from 

adverse effects increases over time, such 

that overall climate change presents 

serious adverse risks for forest 

productivity. There is compelling 

reason to find that the support for a 

positive endangerment finding increases 

as one considers expected future 

conditions where temperatures continue 

to rise. 

Looking across all of the sectors 

discussed above, the evidence provides 

compelling support for finding that 

greenhouse gas air pollution endangers 

the public welfare of both current and 


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3Section 202(a) source categories include 

passenger cars, heavy-, medium and light-duty 

trucks, motorcycles, and buses. 

4The units for greenhouse gas emissions in these 

findings are provided in carbon dioxide equivalent 

units, where carbon dioxide is the reference gas and 

every other greenhouse gas is converted to its 

carbon dioxide equivalent by using the 100-year 

global warming potential (as estimated by the 

Intergovernmental Panel on Climate Change (IPCC). 

assigned to each gas. The reference gas used is CO2, 

and therefore Global Warming Potential (GWP)- 

weighted emissions are measured in teragrams of 

CO2 equivalent (Tg CO2 eq.). In accordance with 

UNFCCC reporting procedures, the United States 

quantifies greenhouse gas emissions using the 100- 

year time frame values for GWPs established in the 

IPCC Second Assessment Report. 

future generations. The risk and the 

severity of adverse impacts on public 

welfare are expected to increase over 

time. 

The Administrator also finds that 

emissions of well-mixed greenhouse 

gases from the transportation sources 

covered under CAA section 202(a) 3

contribute to the total greenhouse gas air 

pollution, and thus to the climate 

change problem, which is reasonably 

anticipated to endanger public health 

and welfare. The Administrator is 

defining the air pollutant that 

contributes to climate change as the 

aggregate group of the well-mixed 

greenhouse gases. The definition of air 

pollutant used by the Administrator is 

based on the similar attributes of these 

substances. These attributes include the 

fact that they are sufficiently long-lived 

to be well mixed globally in the 

atmosphere, that they are directly 

emitted, and that they exert a climate 

warming effect by trapping outgoing, 

infrared heat that would otherwise 

escape to space, and that they are the 

focus of climate change science and 

policy. 

In order to determine if emissions of 

the well-mixed greenhouse gases from 

CAA section 202(a) source categories 

contribute to the air pollution that 

endangers public health and welfare, 

the Administrator compared the 

emissions from these CAA section 

202(a) source categories to total global 

and total U.S. greenhouse gas emissions, 

finding that these source categories are 

responsible for about 4 percent of total 

global well-mixed greenhouse gas 

emissions and just over 23 percent of 

total U.S. well-mixed greenhouse gas 

emissions. The Administrator found 

that these comparisons, independently 

and together, clearly establish that these 

emissions contribute to greenhouse gas 

concentrations. For example, the 

emissions of well-mixed greenhouse 

gases from CAA section 202(a) sources 

are larger in magnitude than the total 

well-mixed greenhouse gas emissions 

from every other individual nation with 

the exception of China, Russia, and 

India, and are the second largest emitter 

within the United States behind the 

electricity generating sector. As the 

Supreme Court noted, ‘‘[j]udged by any 

standard, U.S. motor-vehicle emissions 

make a meaningful contribution to 

greenhouse gas concentrations and 

hence, * * * to global warming.’’ 

Massachusetts v. EPA, 549 U.S. 497, 525 

(2007). 

The Administrator’s findings are in 

response to the Supreme Court’s 

decision in Massachusetts v. EPA. That 

case involved a 1999 petition submitted 

by the International Center for 

Technology Assessment and 18 other 

environmental and renewable energy 

industry organizations requesting that 

EPA issue standards under CAA section 

202(a) for the emissions of carbon 

dioxide, methane, nitrous oxide, and 

hydrofluorocarbons from new motor 

vehicles and engines. The 

Administrator’s findings are in response 

to this petition and are for purposes of 

CAA section 202(a). 

B. Background Information Helpful To 

Understand These Findings 

This section provides some basic 

information regarding greenhouse gases 

and the CAA section 202(a) source 

categories, as well as the ongoing jointrulemaking on greenhouse gases by EPA 

and the Department of Transportation. 

Additional technical and legal 

background, including a summary of the 

Supreme Court’s Massachusetts v. EPA 

decision, can be found in the Proposed 

Endangerment and Contribution 

Findings (74 FR 18886, April 24, 2009). 

1. Greenhouse Gases and Transportation 

Sources Under CAA Section 202(a) 

Greenhouse gases are naturally 

present in the atmosphere and are also 

emitted by human activities. 

Greenhouse gases trap the Earth’s heat 

that would otherwise escape from the 

atmosphere, and thus form the 

greenhouse effect that helps keep the 

Earth warm enough for life. Human 

activities are intensifying the naturallyoccurring greenhouse effect by adding 

greenhouse gases to the atmosphere. 

The primary greenhouse gases of 

concern that are directly emitted by 

human activities include carbon 

dioxide, methane, nitrous oxide, 

hydrofluorocarbons, perfluorocarbons, 

and sulfur hexafluoride. Other 

pollutants (such as aerosols) and other 

human activities, such as land use 

changes that alter the reflectivity of the 

Earth’s surface, also cause climatic 

warming and cooling effects. In these 

Findings, the term ‘‘climate change’’ 

generally refers to the global warming 

effect plus other associated changes 

(e.g., precipitation effects, sea level rise, 

changes in the frequency and severity of 

extreme weather events) being induced 

by human activities, including activities 

that emit greenhouse gases. Natural 

causes also, contribute to climate 

change and climatic changes have 

occurred throughout the Earth’s history. 

The concern now, however, is that the 

changes taking place in our atmosphere 

as a result of the well-documented 

buildup of greenhouse gases due to 

human activities are changing the 

climate at a pace and in a way that 

threatens human health, society, and the 

natural environment. Further detail on 

the state of climate change science can 

be found in Section III of these Findings 

as well as the technical support 

document (TSD) that accompanies this 

action (www.epa.gov/climatechange/ 

endangerment.html). 

The transportation sector is a major 

source of greenhouse gas emissions both 

in the United States and in the rest of 

the world. The transportation sources 

covered under CAA section 202(a)—the 

section of the CAA under which these 

Findings occur—include passenger cars, 

light- and heavy-duty trucks, buses, and 

motorcycles. These transportation 

sources emit four key greenhouse gases: 

carbon dioxide, methane, nitrous oxide, 

and hydrofluorocarbons. Together, these 

transportation sources are responsible 

for 23 percent of total annual U.S. 

greenhouse gas emissions, making this 

source the second largest in the United 

States behind electricity generation.4

Further discussion of the emissions 

data supporting the Administrator’s 

cause or contribute finding can be found 

in Section V of these Findings, and the 

detailed greenhouse gas emissions data 

for section 202(a) source categories can 

be found in Appendix B of EPA’s TSD. 

2. Joint EPA and Department of 

Transportation Proposed Greenhouse 

Gas Rule 

On September 15, 2009, EPA and the 

Department of Transportation’s National 

Highway Safety Administration 

(NHTSA) proposed a National Program 

that would dramatically reduce 

greenhouse gas emissions and improve 

fuel economy for new cars and trucks 

sold in the United States. The combined 

EPA and NHTSA standards that make 

up this proposed National Program 

would apply to passenger cars, lightduty trucks, and medium-duty 

passenger vehicles, covering model 

years 2012 through 2016. They 

proposed to require these vehicles to 

meet an estimated combined average 


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emissions level of 250 grams of carbon 

dioxide per mile, equivalent to 35.5 

miles per gallon (MPG) if the 

automobile industry were to meet this 

carbon dioxide level solely through fuel 

economy improvements. Together, these 

proposed standards would cut carbon 

dioxide emissions by an estimated 950 

million metric tons and 1.8 billion 

barrels of oil over the lifetime of the 

vehicles sold under the program (model 

years 2012–2016). The proposed 

rulemaking can be viewed at (74 FR 

49454, September 28, 2009). 

C. Public Involvement 

In response to the Supreme Court’s 

decision, EPA has been examining the 

scientific and technical basis for the 

endangerment and cause or contribute 

decisions under CAA section 202(a) 

since 2007. The science informing the 

decision-making process has grown 

stronger since our work began. EPA’s 

approach to evaluating the science, 

including comments submitted during 

the public comment period, is further 

discussed in Section III.A of these 

Findings. Public review and comment 

has always been a major component of 

EPA’s process. 

1. EPA’s Initial Work on Endangerment 

As part of the Advance Notice of 

Proposed Rulemaking: Regulating 

Greenhouse Gas Emissions under the 

Clean Air Act (73 FR 44353) published 

in July 2008, EPA provided a thorough 

discussion of the issues and options 

pertaining to endangerment and cause 

or contribute findings under the CAA. 

The Agency also issued a TSD providing 

an overview of all the major scientific 

assessments available at the time and 

emission inventory data relevant to the 

contribution finding (Docket ID No. 

EPA–HQ–OAR–2008–0318). The 

comment period for that Advance 

Notice was 120 days, and it provided an 

opportunity for EPA to hear from the 

public with regard to the issues 

involved in endangerment and cause or 

contribute findings as well as the 

supporting science. EPA received, 

reviewed and considered numerous 

comments at that time and this public 

input was reflected in the Findings that 

the Administrator proposed in April 

2009. In addition, many comments were 

received on the TSD released with the 

Advance Notice and reflected in 

revisions to the TSD released in April 

2009 to accompany the Administrator’s 

proposal. All public comments on the 

Advance Notice are contained in the 

public docket for this action (Docket ID 

No. EPA–HQ–OAR–2008–0318) 

accessible through www.regulations.gov. 

2. Public Involvement Since the April 

2009 Proposed Endangerment Finding 

The Proposed Endangerment and 

Cause or Contribute Findings for 

Greenhouse Gases (Proposed Findings) 

was published on April 24, 2009 (74 FR 

18886). The Administrator’s proposal 

was subject to a 60-day public comment 

period, which ended June 23, 2009, and 

also included two public hearings. Over 

380,000 public comments were received 

on the Administrator’s proposed 

endangerment and cause or contribute 

findings, including comments on the 

elements of the Administrator’s April 

2009 proposal, the legal issues 

pertaining to the Administrator’s 

decisions, and the underlying TSD 

containing the scientific and technical 

information. 

A majority of the comments 

(approximately 370,000) were the result 

of mass mail campaigns, which are 

defined as groups of comments that are 

identical or very similar in form and 

content. Overall, about two-thirds of the 

mass-mail comments received are 

supportive of the Findings and generally 

encouraged the Administrator both to 

make a positive endangerment 

determination and implement 

greenhouse gas emission regulations. Of 

the mass mail campaigns in 

disagreement with the Proposed 

Findings most either oppose the 

proposal on economic grounds (e.g., due 

to concern for regulatory measures 

following an endangerment finding) or 

take issue with the proposed finding 

that atmospheric greenhouse gas 

concentrations endanger public health 

and welfare. Please note that for mass 

mailer campaigns, a representative copy 

of the comment is posted in the public 

docket for this Action (Docket ID No. 

EPA–HQ–OAR–2009–0171) at 

www.regulations.gov. 

Approximately 11,000 other public 

comments were received. These 

comments raised a variety of issues 

related to the scientific and technical 

information EPA relied upon in making 

the Proposed Findings, legal and 

procedural issues, the content of the 

Proposed Findings, and the implications 

of the Proposed Findings. 

In light of the very large number of 

comments received and the significant 

overlap between many comments, EPA 

has not responded to each comment 

individually. Rather, EPA has 

summarized and provided responses to 

each significant argument, assertion and 

question contained within the totality of 

the comments. EPA’s responses to some 

of the most significant comments are 

provided in these Findings. Responses 

to all significant issues raised by the 

comments are contained in the 11 

volumes of the Response to Comments 

document, organized by subject area 

(found in docket EPA–HQ–OAR–2009– 

0171). 

3. Issues Raised Regarding the 

Rulemaking Process 

EPA received numerous comments on 

process-related issues, including 

comments urging the Administrator to 

delay issuing the final findings, arguing 

that it was improper for the 

Administrator to sever the 

endangerment and cause or contribute 

findings from the attendant section 

202(a) standards, arguing the final 

decision was preordained by the 

President’s May vehicle announcement, 

and questioning the adequacy of the 

comment period. Summaries of key 

comments and EPA’s responses are 

discussed in this section. Additional 

and more detailed responses can be 

found in the Response to Comments 

document, Volume 11. As noted in the 

Response to Comments document, EPA 

also received comments supporting the 

overall process. 

a. It Is Reasonable for the Administrator 

To Issue the Endangerment and Cause 

or Contribute Findings Now 

Though the Supreme Court did not 

establish a specific deadline for EPA to 

act, more than two and a half years have 

passed since the remand from the 

Supreme Court, and it has been 10 years 

since EPA received the original petition 

requesting that EPA regulate greenhouse 

gas emissions from new motor vehicles. 

EPA has a responsibility to respond to 

the Supreme Court’s decision and to 

fulfill its obligations under current law, 

and there is good reason to act now 

given the urgency of the threat of 

climate change and the compelling 

scientific evidence. 

Many commenters urge EPA to delay 

making final findings for a variety of 

reasons. They note that the Supreme 

Court did not establish a deadline for 

EPA to act on remand. Commenters also 

argue that the Supreme Court’s decision 

does not require that EPA make a final 

endangerment finding, and thus that 

EPA has discretionary power and may 

decline to issue an endangerment 

finding, not only if the science is too 

uncertain, but also if EPA can provide 

‘‘some reasonable explanation’’ for 

exercising its discretion. These 

commenters interpret the Supreme 

Court decision not as rejecting all policy 

reasons for declining to undertake an 

endangerment finding, but rather as 

dismissing solely the policy reasons 

EPA set forth in 2003. Some 

commenters cite language in the 


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Supreme Court decision regarding 

EPA’s discretion regarding ‘‘the manner, 

timing, content, and coordination of its 

regulations,’’ and the Court’s declining 

to rule on ‘‘whether policy concerns can 

inform EPA’s actions in the event that it 

makes’’ a CAA section 202(a) finding to 

support their position. 

Commenters then suggest a variety of 

policy reasons that EPA can and should 

make to support a decision not to 

undertake a finding of endangerment 

under CAA section 202(a)(1). For 

example, they argue that a finding of 

endangerment would trigger several 

other regulatory programs—such as the 

Prevention of Significant Deterioration 

(PSD) provisions—that would impose 

an unreasonable burden on the economy 

and government, without providing a 

benefit to the environment. Some 

commenters contend that EPA should 

defer issuing a final endangerment 

finding while Congress considers 

legislation. Many commenters note the 

ongoing international discussions 

regarding climate change and state their 

belief that unilateral EPA action would 

interfere with those negotiations. Others 

suggest deferring the EPA portion of the 

joint U.S. Department of Transportation 

(DOT)/EPA rulemaking because they 

argue that the new Corporate Average 

Fuel Economy (CAFE) standards will 

effectively result in lower greenhouse 

gas emissions from new motor vehicles, 

while avoiding the inevitable problems 

and concerns of regulating greenhouse 

gases under the CAA. 

Other commenters argue that the 

endangerment determination has to be 

made on the basis of scientific 

considerations only. These commenters 

state that the Court was clear that ‘‘[t]he 

statutory question is whether sufficient 

information exists to make an 

endangerment finding,’’ and thus, only 

if ‘‘the scientific uncertainty is so 

profound that it precludes EPA from 

making a reasoned judgment as to 

whether greenhouse gases contribute to 

global warming,’’ may EPA avoid 

making a positive or negative 

endangerment finding. Many 

commenters urge EPA to take action 

quickly. They note that it has been 10 

years since the original petition 

requesting that EPA regulate greenhouse 

gas emissions from motor vehicles was 

submitted to EPA. They argue that 

climate change is a serious problem that 

requires immediate action. 

EPA agrees with the commenters who 

argue that the Supreme Court decision 

held that EPA is limited to 

consideration of science when 

undertaking an endangerment finding, 

and that we cannot delay issuing a 

finding due to policy concerns if the 

science is sufficiently certain (as it is 

here). The Supreme Court stated that 

‘‘EPA can avoid taking further action 

only if it determines that greenhouse 

gases do not contribute to climate 

change or if it provides some reasonable 

explanation as to why it cannot or will 

not exercise its discretion to determine 

whether they do’’ 549 U.S. at 533. Some 

commenters point to this last provision, 

arguing that the policy reasons they 

provide are a ‘‘reasonable explanation’’ 

for not moving forward at this time. 

However, this ignores other language in 

the decision that clearly indicates that 

the Court interprets the statute to allow 

for the consideration only of science. 

For example, in rejecting the policy 

concerns expressed by EPA in its 2003 

denial of the rulemaking petition, the 

Court noted that ‘‘it is evident [the 

policy considerations] have nothing to 

do with whether greenhouse gas 

emissions contribute to climate change. 

Still less do they amount to a reasoned 

justification for declining to form a 

scientific judgment’’ Id. at 533–34 

(emphasis added). 

Moreover, the Court also held that 

‘‘[t]he statutory question is whether 

sufficient information exists to make an 

endangerment finding’’ Id. at 534. Taken 

as a whole, the Supreme Court’s 

decision clearly indicates that policy 

reasons do not justify the Administrator 

avoiding taking further action on the 

question here. 

We also note that the language many 

commenters quoted from the Supreme 

Court decision about EPA’s discretion 

regarding the manner, timing and 

content of Agency actions, and the 

ability to consider policy concerns, 

relate to the motor vehicle standards 

required in the event that EPA makes a 

positive endangerment finding, and not 

the finding itself. EPA has long taken 

the position that it does have such 

discretion in the standard-setting step 

under CAA section 202(a). 

b. The Administrator Reasonably 

Proceeded With the Endangerment and 

Cause or Contribute Findings Separate 

From the CAA Section 202(a) Standard 

Rulemaking 

As discussed in the Proposed 

Findings, typically endangerment and 

cause or contribute findings have been 

proposed concurrently with proposed 

standards under various sections of the 

CAA, including CAA section 202(a). 

EPA received numerous comments on 

its decision to propose the 

endangerment and cause or contribute 

findings separate from any standards 

under CAA section 202(a). 

Commenters argue that EPA has no 

authority to issue an endangerment 

determination under CAA section 202(a) 

separate and apart from the rulemaking 

to establish emissions standards under 

CAA section 202(a). According to these 

commenters, CAA section 202(a) 

provides only one reason to issue an 

endangerment determination, and that 

is as the basis for promulgating 

emissions standards for new motor 

vehicles; thus, it does not authorize 

such a stand-alone endangerment 

finding, and EPA may not create its own 

procedural rules completely divorced 

from the statutory text. They continue 

by stating that while CAA section 202(a) 

says EPA may issue emissions standards 

conditioned on such a finding, it does 

not say EPA may first issue an 

endangerment determination and then 

issue emissions standards. In addition, 

they contend, the endangerment 

proposal and the emissions standards 

proposal need to be issued together so 

commenters can fully understand the 

implications of the endangerment 

determination. Failure to do so, they 

argue, deprives the commenters of the 

opportunity to assess the regulations 

that will presumably follow from an 

endangerment finding. They also argue 

that the expected overlap between 

reductions in emissions of greenhouse 

gases from CAA section 202(a) 

standards issued by EPA and CAFE 

standards issued by DOT calls into 

question the basis for the CAA section 

202(a) standards and the related 

endangerment finding, and that EPA is 

improperly motivated by an attempt to 

trigger a cascade of regulations under 

the CAA and/or to promote legislation 

by Congress. 

EPA disagrees with the commenters’ 

claims and arguments. The text of CAA 

section 202(a) is silent on this issue. It 

does not specify the timing of an 

endangerment finding, other than to be 

clear that emissions standards may not 

be issued unless such a determination 

has been made. EPA is exercising the 

procedural discretion that is provided 

by CAA section 202(a)’s lack of specific 

direction. The text of CAA section 

202(a) envisions two separate actions by 

the Administrator: (1) A determination 

on whether emissions from classes or 

categories of new motor vehicles cause 

or contribute to air pollution that may 

reasonably be anticipated to endanger, 

and (2) a separate decision on issuance 

of appropriate emissions standards for 

such classes or categories. The 

procedure followed in this rulemaking, 

and the companion rulemaking 

involving emissions standards for light 

duty motor vehicles, is consistent with 

CAA section 202(a). EPA will issue final 

emissions standards for new motor 


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vehicles only if affirmative findings are 

made concerning contribution and 

endangerment, and such emissions 

standards will not be finalized prior to 

making any such determinations. While 

it would also be consistent with CAA 

section 202(a) to issue the greenhouse 

gas endangerment and contribution 

findings and emissions standards for 

new light-duty vehicles in the same 

rulemaking, e.g., a single proposal 

covering them and a single final rule 

covering them, nothing in CAA section 

202(a) requires such a procedural 

approach, and nothing in the approach 

taken in this case violates the text of 

CAA section 202(a). Since Congress was 

silent on this issue, and more than one 

procedural approach may accomplish 

the requirements of CAA section 202(a), 

EPA has the discretion to use the 

approach considered appropriate in this 

case. Once the final affirmative 

contribution and endangerment findings 

are made, EPA has the authority to issue 

the final emissions standards for new 

light-duty motor vehicles; however, as 

the Supreme Court has noted, the 

agency has ‘significant latitude as to the 

manner, timing, [and] content * * * of 

its regulations . * * *’ Massachusetts v. 

EPA, 549 U.S. at 533. That includes the 

discretion to issue them in a separate 

rulemaking. 

Commenters’ argument would also 

lead to the conclusion that EPA could 

not make an endangerment finding for 

the entire category of new motor 

vehicles, as it is doing here, unless EPA 

also conducted a rulemaking that set 

emissions standards for all the classes 

and categories of new motor vehicles at 

the same time. This narrow procedural 

limitation would improperly remove 

discretion that CAA section 202(a) 

provides to EPA. 

EPA has the discretion under CAA 

section 202(a) to consider classes or 

categories of new motor vehicles 

separately or together in making a 

contribution and endangerment 

determination. This discretion would be 

removed under commenters’ 

interpretation, by limiting this to only 

those cases in which EPA was also 

ready to issue emissions standards for 

all of the classes or categories covered 

by the endangerment finding. However, 

nothing in the text of CAA section 

202(a) places such a limit on EPA’s 

discretion in determining how to group 

classes or categories of new motor 

vehicles for purposes of the contribution 

and endangerment findings. This 

limitation would not be appropriate, 

because the issues of contribution and 

endangerment are separate and distinct 

from the issues of setting emissions 

standards. EPA, in this case, is fully 

prepared to go forward with the 

contribution and endangerment 

determination, while it is not ready to 

proceed with rulemaking for each and 

every category of new motor vehicles in 

the first rulemaking to set emissions 

standards. Section 202(a) of the CAA 

provides EPA discretion with regard to 

when and how it conducts its 

rulemakings to make contribution and 

endangerment findings, and to set 

emissions standards, and the text of 

CAA section 202(a) does not support 

commenters attempt to limit such 

discretion. 

Concerns have been raised that the 

failure to issue the proposed 

endangerment finding and the proposed 

emissions standard together preclude 

commenters from assessing and 

considering the implications of the 

endangerment finding and the 

regulations that would likely flow from 

such a finding. However, commenters 

have failed to explain how this 

interferes in any way with their ability 

to comment on the endangerment 

finding. In fact it does not interfere, 

because the two proposals address 

separate and distinct issues. The 

endangerment finding concerns the 

contribution of new motor vehicles to 

air pollution and the effect of that air 

pollution on public health or welfare. 

The emissions standards, which have 

been proposed (74 FR 49454, September 

28, 2009), concern the appropriate 

regulatory emissions standards if 

affirmative findings are made on 

contribution and endangerment. These 

two proposals address different issues. 

While commenters have the opportunity 

to comment on the proposed emissions 

standards in that rulemaking, they have 

not shown, and cannot show, that they 

need to have the emissions standards 

proposal before them in order to provide 

relevant comments on the proposed 

contribution or endangerment findings. 

Further discussion of this issue can be 

found in Section II of these Findings, 

and discussion of the timing of this 

action and its relationship to other CAA 

provisions and Congressional action can 

be found in Section III of these Findings 

and Volume 11 of the Response to 

Comments document. 

c. The Administrator’s Final Decision 

Was Not Preordained by the President’s 

May Vehicle Announcement 

EPA received numerous comments 

arguing that the President’s 

announcement of a new ‘‘National Fuel 

Efficiency Policy’’ on May 19, 2009 

seriously undermines EPA’s ability to 

provide objective consideration of and a 

legally adequate response to comments 

objecting to the previously proposed 

endangerment findings. 

Commenters’ conclusion is based on 

the view that the President’s announced 

policy requires EPA to promulgate 

greenhouse gas emissions standards 

under CAA section 202(a), that the 

President’s and Administrator Jackson’s 

announcement indicated that the 

endangerment rulemaking was but a 

formality and that a final endangerment 

finding was a fait accompli. 

Commenters argue that this means the 

result of this rulemaking has been 

preordained and the merits of the issues 

have been prejudged. 

EPA disagrees. Commenters’ 

arguments wholly exaggerate and 

mischaracterize the circumstances. In 

the April 24, 2009 endangerment 

proposal EPA was clear that the two 

steps in the endangerment provision 

have to be satisfied in order for EPA to 

issue emissions standards for new motor 

vehicles under CAA section 202(a) (74 

FR at 18888, April 24, 2009). This was 

repeated when EPA issued the Notice of 

Upcoming Joint Rulemaking to Establish 

Vehicle GHG Emissions and CAFE 

Standards (74 FR 24007 May 22, 2009) 

(Notice of Intent or NOI). This was 

repeated again when EPA issued 

proposed greenhouse gas emissions 

standards for certain new motor 

vehicles (74 FR 49454, September 28, 

2009). EPA has consistently made it 

clear that issuance of new motor vehicle 

standards requires and is contingent 

upon satisfaction of the two-part 

endangerment test. 

On May 19, 2009 EPA issued the joint 

Notice of Intent, which indicated EPA’s 

intention to propose new motor vehicle 

standards. All of the major motor 

vehicle manufacturers, their trade 

associations, the State of California, and 

several environmental organizations 

announced their full support for the 

upcoming rulemaking. Not surprisingly, 

on the same day the President also 

announced his full support for this 

action. Commenters, however, 

erroneously equate this Presidential 

support with a Presidential directive 

that requires EPA to prejudge and 

preordain the result of this rulemaking. 

The only evidence they point to are 

simply indications of Presidential 

support. Commenters point to a press 

release, which unsurprisingly refers to 

the Agency’s announcement as 

delivering on the President’s 

commitment to enact more stringent 

fuel economy standards, by bringing 

‘‘all stakeholders to the table and 

[coming] up with a plan’’ for solving a 

serious problem. The plan that was 

announced, of course, was a plan to 

conduct notice and comment 


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rulemaking. The press release itself 

states that President Obama ‘‘set in 

motion a new national policy,’’ with the 

policy ‘‘aimed’’ at reducing greenhouse 

gas emissions for new cars and trucks. 

What was ‘‘set in motion’’ was a notice 

and comment rulemaking described in 

the NOI issued by EPA on the same day. 

Neither the President nor EPA 

announced a final rule or a final 

direction that day, but instead did no 

more than announce a plan to go 

forward with a notice and comment 

rulemaking. That is how the plan 

‘‘delivers on the President’s 

commitment’’ to enact more stringent 

standards. The announcement was that 

a notice and comment rulemaking 

would be initiated with the aim of 

adopting certain emissions standards. 

That is no different from what EPA or 

any other agency states when it issues 

a notice of proposed rulemaking. It 

starts a process that has the aim of 

issuing final regulations if they are 

deemed appropriate at the end of the 

public process. The fact that an Agency 

proposes a certain result, and expects 

that a final rule will be the result of 

setting such a process in motion, is the 

ordinary course of affairs in notice and 

comment rulemakings. This does not 

translate into prejudging the final result 

or having a preordained result that de 

facto negates the public comment 

process. The President’s press release of 

May 19, 2009 was a recognition that this 

notice and comment rulemaking process 

would be set in motion, as well as 

providing his full support for the 

Agency to go forward in this direction; 

it was no more than that. 

The various stakeholders who 

announced their support for the plan 

that had been set in motion all 

recognized that full notice and comment 

rulemaking was part of the plan, and 

they all reserved their rights to 

participate in such notice and comment 

rulemaking. For example, see the letter 

of support from Ford Motor Company, 

which states that ‘‘Ford fully supports 

proposal and adoption of such a 

National Program, which we understand 

will be subject to full notice-andcomment rulemaking, affording all 

interested parties including Ford the 

right to participate fully, comment, and 

submit information, the results of which 

are not pre-determined but depend 

upon processes set by law.’’ 

d. The Notice and Comment Period Was 

Adequate 

Many commenters argue that the 60- 

day comment period was inadequate. 

Commenters claim that a 60-day period 

was insufficient time to fully evaluate 

the science and other information that 

informed the Administrator’s proposal. 

Some commenters assert that because 

the comment period for the Proposed 

Finding substantially overlapped with 

the comment period for the Mandatory 

Greenhouse Gas Reporting Rule, as well 

as Congress’ consideration of climate 

legislation, their ability to fully 

participate in the notice and comment 

period was ‘‘seriously compromised.’’ 

Moreover, they continue, because EPA 

had not yet proposed CAA section 

202(a) standards, there was no valid 

reason to fail to extend the comment 

period. Several commenters and other 

entities had also requested that EPA 

extend the comment period. 

Some commenters assert that the 

notice provided by this rulemaking was 

‘‘defective’’ because the Federal 

Register notice announcing the proposal 

had an error in the e-mail address for 

the docket. At least one commenter 

suggests that this error deprives 

potential commenters of their Due 

Process under the Fifth Amendment of 

the Constitution, citing Armstrong v. 

Manzo, 380 U.S. 545, 552 (1965), and 

that failure to ‘‘correct’’ the minor 

typographical error in the e-mail 

address and extend the comment period 

would make the rule ‘‘subject to 

reversal’’ in violation of the CAA, 

Administrative Procedure Act (APA), 

the Due Process clause of the 

Constitution, and EO 12866. 

Finally, for many of the same reasons 

that commenters argue a 60-day 

comment period was inadequate, 

several commenters request that EPA 

reopen and/or extend the comment 

period. One commenter requests that 

the comment period be reopened 

because there was new information 

regarding data used by EPA in the 

Proposed Findings. In particular, the 

commenter alleges that it recently 

became aware that one of the sources of 

global climate data had destroyed the 

raw data for its data set of global surface 

temperatures. The commenter argues 

that this alleged destruction of raw data 

violates scientific standards, calls into 

question EPA’s reliance on that data in 

these Findings, and necessitates a 

reopening of the proceedings. Other 

commenters request that the comment 

period be extended and/or reopened 

due to the release of a Federal 

government document on the impact of 

climate change in the United States near 

the end of the comment period, as well 

as the release of an internal EPA staff 

document discussing the science. 

The official public comment period 

on the proposed rule was adequate. 

First, a 60-day comment period satisfies 

the procedural requirements of CAA 

section 307 of the CAA, which requires 

a 30-day comment period, and that the 

docket be kept open to receive rebuttal 

or supplemental information as followup to any hearings for 30 days following 

the hearings. EPA met those obligations 

here—the comment period opened on 

April 24, 2009, the last hearing was on 

May 21, 2009 and the comment period 

closed June 23, 2009. 

Second, as explained in letters 

denying requests to extend the comment 

period, a very large part of the 

information and analyses for the 

Proposed Findings had been previously 

released in July 30, 2008, as part of the 

Advance Notice of Proposed 

Rulemaking: Regulating Greenhouse 

Gas Emissions under the Clean Air Act 

(ANPR) (73 FR 44353). The public 

comment period for the ANPR is 

discussed above in Section I.C.1 of these 

Findings. The Administrator explained 

that the comment period for that ANPR 

was 120 days and that the major recent 

scientific assessments that EPA relied 

upon in the TSD released with the 

ANPR had previously each gone 

through their own public review 

processes and have been publicly 

available for some time. In other words, 

EPA has provided ample time for 

review, particularly with regard to the 

technical support for the Findings. See, 

for example, EPA Letter to Congressman 

Issa dated June 17, 2009, a copy of 

which is available at http://epa.gov/ 

climatechange/endangerment.html. 

Moreover, the comment period was 

not rendered insufficient merely 

because other climate-related 

proceedings were occurring 

simultaneously. 

While one commenter suggests that 

the convergence of several different 

climate-related activities has ‘‘seriously 

compromised’’ their ability to 

participate in the comment process, that 

commenter was able to submit an 89 

page comment on this proposal alone. 

Moreover, it is hardly rare that more 

than one rule is out for comment at the 

same time. As noted above, EPA has 

received a substantial number of 

significant comments on the Proposed 

Findings, and has thoroughly 

considered and responded to significant 

comments. 

EPA finds no evidence that a 

typographical error in the docket e-mail 

address of the Federal Register notice 

announcing the proposal prevented the 

public from having a meaningful 

opportunity to comment, and therefore 

deprived them of due process. Although 

the minor error—which involved a word 

processing auto-correction that turned a 

short dash into a long dash—appeared 

in the FR version of the Proposed 

Findings, the e-mail address is correct 


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5Peterson, T.C., and M.O. Baringer (Eds.) (2009) 

State of the Climate in 2008. Bull. Amer. Meteor. 

Soc., 90, S1–S196. 

in the signature version of the Proposed 

Findings posted on EPA’s Web site until 

publication in the Federal Register, and 

in the ‘‘Instructions for Submitting 

Written Comments’’ document on the 

Web site for the rulemaking. EPA has 

received over 190,000 e-mails to the 

docket e-mail address to date, so the 

minor typographical error appearing in 

only one location has not been an 

impediment to interested parties’ 

e-mailing comments. Moreover, EPA 

provided many other avenues for 

interested parties to submit comments 

in addition to the docket e-mail address, 

including via www.regulations.gov, 

mail, and fax; each of these options have 

been utilized by many commenters. EPA 

is confident that the minor 

typographical error did not prevent 

anyone from submitting written 

comments, by e-mail or otherwise, and 

that the public was provided 

‘‘meaningful participation in the 

regulatory process’’ as mentioned in EO 

12866. 

Our response regarding the request to 

reopen the comment period due to 

concerns about alleged destruction of 

raw global surface data is discussed 

more fully in the Response to Comments 

document, Volume 11. The commenter 

did not provide any compelling reason 

to conclude that the absence of these 

data would materially affect the trends 

in the temperature records or 

conclusions drawn about them in the 

assessment literature and reflected in 

the TSD. The Hadley Centre/Climate 

Research Unit (CRU) temperature record 

(referred to as HadCRUT) is just one of 

three global surface temperature records 

that EPA and the assessment literature 

refer to and cite. National Oceanic and 

Atmospheric Administration (NOAA) 

and National Aeronautics and Space 

Administration (NASA) also produce 

temperature records, and all three 

temperature records have been 

extensively peer reviewed. Analyses of 

the three global temperature records 

produce essentially the same long-term 

trends as noted in the Climate Change 

Science Program (CCSP) (2006) report 

‘‘Temperature Trends in the Lower 

Atmosphere,’’ IPCC (2007), and NOAA’s 

study 5 ‘‘State of the Climate in 2008’’. 

Furthermore, the commenter did not 

demonstrate that the allegedly destroyed 

data would materially alter the 

HadCRUT record or meaningfully 

hinder its replication. The raw data, a 

small part of which has not been public 

(for reasons described at: https:// 

www.uea.ac.uk/mac/comm/media/ 

press/2009/nov/CRUupdate), are 

available in a quality-controlled (or 

homogenized, value-added) format and 

the methodology for developing the 

quality-controlled data is described in 

the peer reviewed literature (as 

documented at http:// 

www.cru.uea.ac.uk/cru/data/ 

temperature/). 

The release of the U.S. Global Climate 

Research Program (USGCRP) report on 

impacts of climate change in the United 

States in June 2009 also did not 

necessitate extending the comment 

period. This report was issued by the 

USGCRP, formerly the Climate Change 

Science Program (CCSP), and 

synthesized information contained in 

prior CCSP reports and other synthesis 

reports, many of which had already 

been published (and were included in 

the TSD for the Proposed Findings). 

Further, the USGCRP report itself 

underwent notice and comment before 

it was finalized and released. 

Regarding the internal EPA staff paper 

that came to light during the comment 

period, several commenters submitted a 

copy of the EPA staff paper with their 

comments; EPA’s response to the issues 

raised by the staff paper are discussed 

in the Response to Comments 

document, Volume 1. The fact that some 

internal agency deliberations were made 

public during the comment period does 

not in and of itself call into question 

those deliberations. As our responses to 

comments explain, EPA considered the 

concerns noted in the staff paper during 

the proposal stage, as well as when 

finalizing the Findings. There was 

nothing about those internal comments 

that required an extension or reopening 

of the comment period. 

Thus, the opportunity for comment 

fully satisfies the CAA and 

Constitutional requirement of Due 

Process. Cases cited by commenters do 

not indicate otherwise. The comment 

period and thorough response to 

comment documents in the docket 

indicate that EPA has given people an 

opportunity to be heard in a 

‘‘meaningful time and a meaningful 

matter.’’ Armstrong v. Manzo, 380 U.S. 

545, 552 (1965). Interested parties had 

full notice of the rulemaking 

proceedings and a significant 

opportunity to participate through the 

comment process and multiple hearings. 

For all the above reasons, EPA’s 

denial of the requests for extension or 

reopening of the comment period was 

entirely reasonable in light of the 

extensive opportunity for public 

comment and heavy amount of public 

participation during the comment 

period. EPA has fully complied with all 

applicable public participation 

requirements for this rulemaking. 

e. These Findings Did Not Necessitate a 

Formal Rulemaking Under the 

Administrative Procedure Act 

One commenter, with the support of 

others, requests that EPA undertake a 

formal rulemaking process for the 

Findings, on the record, in accordance 

with the procedures described in 

sections 556–557 of the Administrative 

Procedure Act (APA). The commenter 

requests a multi-step process, involving 

additional public notice, an on-therecord proceeding (e.g., formal 

administrative hearing) with the right of 

appeal, utilization of the Clean Air 

Scientific Advisory Committee (CASAC) 

and its advisory proceedings, and 

designation of representatives from 

other executive branch agencies to 

participate in the formal proceeding and 

any CASAC advisory proceeding. 

The commenter asserts that while 

EPA is not obligated under the CAA to 

undertake these additional procedures, 

the Agency nonetheless has the legal 

authority to engage in such a 

proceeding. The commenter believes 

this proceeding would show that EPA is 

‘‘truly committed to scientific integrity 

and transparency.’’ The commenter cites 

several cases to argue that refusal to 

proceed on the record would be 

‘‘arbitrary and capricious’’ or would be 

an ‘‘abuse of discretion.’’ The allegation 

at the core of the commenter’s argument 

is that profound and wide-ranging 

scientific uncertainties exist in the 

Proposed Findings and in the impacts 

on health and welfare discussed in the 

TSD. To support this argument, the 

commenter provides lengthy criticisms 

of the science. The commenter also 

argues that the regulatory cascade that 

would be ‘‘unleashed’’ by a positive 

endangerment finding warrants the 

more formal proceedings. 

Finally, the commenter suggests that 

EPA engage in ‘‘formal rulemaking’’ 

procedures in part due to the 

Administrative Conference of the 

United States’ (ACUS) recommended 

factors for engaging in formal 

rulemaking. The commenter argues that 

the current action is ‘‘complex,’’ ‘‘openended,’’ and the costs that errors in the 

action may pose are ‘‘significant.’’ 

EPA is denying the request to 

undertake an ‘‘on the record’’ formal 

rulemaking. EPA is under no obligation 

to follow the extraordinarily rarely used 

formal rulemaking provisions of the 

APA. First, CAA section 307(d) of the 

CAA clearly states that the rulemaking 

provisions of CAA section 307(d), not 

APA sections 553 through 557, apply to 

certain specified actions, such as this 


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one. EPA has satisfied all the 

requirements of CAA section 307(d). 

Indeed, the commenter itself ‘‘is not 

asserting that the Clean Air Act 

expressly requires’’ the additional 

procedures it requests. Moreover, the 

commenter does not discuss how the 

suggested formal proceeding would fit 

into the informal rulemaking 

requirements of CAA section 307(d) that 

do apply. 

Formal rulemaking is very rarely used 

by Federal agencies. The formal 

rulemaking provisions of the APA are 

only triggered when the statute 

explicitly calls for proceedings ‘‘on the 

record after opportunity for an agency 

hearing.’’ United States v. Florida East 

Coast Ry. Co., 410 U.S. 224, 241 (1973). 

The mere mention of the word 

‘‘hearing’’ does not trigger the formal 

rulemaking provisions of the APA. Id. 

The CAA does not include the statutory 

phrase required to trigger the formal 

rulemaking provisions of the APA (and 

as noted above the APA does not apply 

in the first place). Congress specified 

that certain rulemakings under the CAA 

follow the rulemaking procedures 

outlined in CAA section 307(d) rather 

than the APA ‘‘formal rulemaking’’ 

commenter suggests. 

Despite the inapplicability of the 

formal rulemaking provisions to this 

action, commenters suggest that to 

refuse to voluntarily undertake 

rulemaking provisions not preferred by 

Congress would make EPA’s rulemaking 

action an ‘‘abuse of discretion.’’ EPA 

disagrees with this claim, and cases 

cited by the commenter do not indicate 

otherwise. To support the idea that an 

agency decision to engage in informal 

rulemaking could be an abuse of 

discretion, commenter cites Ford Motor 

Co. v. FTC, 673 F.2d 1008 (9th Cir. 

1981). In Ford Motor Co., the court ruled 

that the FTC’s decision regarding an 

automobile dealership should have been 

resolved through a rulemaking rather 

than an individualized adjudication. Id. 

at 1010. In that instance, the court 

favored ‘‘rulemaking’’ over 

adjudication—not ‘‘formal rulemaking’’ 

over the far more common ‘‘informal 

rulemaking.’’ The case stands only for 

the non-controversial proposition that 

sometimes agency use of adjudications 

may rise to an abuse of discretion where 

a rulemaking would be more 

appropriate—whether formal or 

informal. The Commenter does not cite 

a single judicial opinion stating that an 

agency abused its discretion by 

following the time-tested and 

Congressionally-favored informal 

rulemaking provisions of the CAA or the 

APA instead of the rarely used formal 

APA rulemaking provisions. 

The commenter also alludes to the 

possibility that the choice of informal 

rulemaking may be ‘‘arbitrary and 

capricious. EPA disagrees that the 

choice to follow the frequently used, 

and CAA required, informal rulemaking 

procedures is arbitrary and capricious. 

The commenter cites Vermont Yankee 

Nuclear Power Corp. v. NRDC, 435 U.S. 

519 (1978) for the proposition that 

‘‘extremely compelling circumstances’’ 

could lead to a court overturning agency 

action for declining to follow extraneous 

procedures. As the commenter notes, in 

Vermont Yankee the Supreme Court 

overturned a lower court decision for 

imposing additional requirements not 

required by applicable statutes. Even if 

the dicta in Vermont Yankee could be 

applied contrary to the holding of the 

case in the way the commenter suggests, 

EPA’s decision to follow frequently 

used informal rulemaking procedures 

for this action is highly reasonable. 

As for the ACUS factors the 

commenter cites in support of its 

request, as the commenter notes, the 

ACUS factors are mere 

recommendations. While EPA certainly 

respects the views of ACUS, the 

recommendations are not binding on the 

Agency. In addition, EPA has engaged 

in a thorough, traditional rulemaking 

process that ensures that any concerns 

expressed by the commenter have been 

addressed. EPA has fully satisfied all 

applicable law in their consideration of 

this rulemaking. 

Finally, as explained in Section III of 

these Findings and the Response to 

Comments document, EPA’s approach 

to evaluating the evidence before it was 

entirely reasonable, and did not require 

a formal hearing. EPA relied primarily 

on robust synthesis reports that have 

undergone peer review and comment. 

The Agency also carefully considered 

the comments received on the Proposed 

Findings and TSD, including review of 

attached studies and documents. The 

public has had ample opportunity to 

provide its views on the science, and 

the record supporting these final 

findings indicates that EPA carefully 

considered and responded to significant 

public comments. To the extent the 

commenter’s concern is that a formal 

proceeding will help ensure the right 

action in response to climate change is 

taken, that is not an issue for these 

Findings. As discussed in Section III of 

these Findings, this science-based 

judgment is not the forum for 

considering the potential mitigation 

options or their impact. 

II. Legal Framework for This Action 

As discussed in the Proposed 

Findings, two statutory provisions of the 

CAA govern the Administrator’s 

Findings. Section 202(a) of the CAA sets 

forth a two-part test for regulatory action 

under that provision: Endangerment and 

cause or contribute. Section 302 of the 

CAA contains definitions of the terms 

‘‘air pollutant’’ and ‘‘effects on welfare’’. 

Below is a brief discussion of these 

statutory provisions and how they 

govern the Administrator’s decision, as 

well as a summary of significant legal 

comments and EPA’s responses to them. 

A. Section 202(a) of the CAA— 

Endangerment and Cause or Contribute 

1. The Statutory Framework 

Section 202(a)(1) of the CAA states 

that: 

The Administrator shall by regulation 

prescribe (and from time to time revise) 

standards applicable to the emission of 

any air pollutant from any class or 

classes of new motor vehicles or new 

motor vehicle engines, which in [her] 

judgment cause, or contribute to, air 

pollution which may reasonably be 

anticipated to endanger public health or 

welfare. 

Based on the text of CAA section 

202(a) and its legislative history, the 

Administrator interprets the two-part 

test as follows. Further discussion of 

this two-part test can be found in 

Section II of the preamble for the 

Proposed Findings. First, the 

Administrator is required to protect 

public health and welfare, but she is not 

asked to wait until harm has occurred. 

EPA must be ready to take regulatory 

action to prevent harm before it occurs. 

Section 202(a)(1) requires the 

Administrator to ‘‘anticipate’’ ‘‘danger’’ 

to public health or welfare. The 

Administrator is thus to consider both 

current and future risks. Second, the 

Administrator is to exercise judgment 

by weighing risks, assessing potential 

harms, and making reasonable 

projections of future trends and 

possibilities. It follows that when 

exercising her judgment the 

Administrator balances the likelihood 

and severity of effects. This balance 

involves a sliding scale; on one end the 

severity of the effects may be of great 

concern, but the likelihood low, while 

on the other end the severity may be 

less, but the likelihood high. Under 

either scenario, the Administrator is 

permitted to find endangerment. If the 

harm would be catastrophic, the 

Administrator is permitted to find 

endangerment even if the likelihood is 

small. 

Because scientific knowledge is 

constantly evolving, the Administrator 

may be called upon to make decisions 

while recognizing the uncertainties and 


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limitations of the data or information 

available, as risks to public health or 

welfare may involve the frontiers of 

scientific or medical knowledge. At the 

same time, the Administrator must 

exercise reasoned decision making, and 

avoid speculative inquiries. Third, as 

discussed further below, the 

Administrator is to consider the 

cumulative impact of sources of a 

pollutant in assessing the risks from air 

pollution, and is not to look only at the 

risks attributable to a single source or 

class of sources. Fourth, the 

Administrator is to consider the risks to 

all parts of our population, including 

those who are at greater risk for reasons 

such as increased susceptibility to 

adverse health effects. If vulnerable 

subpopulations are especially at risk, 

the Administrator is entitled to take that 

point into account in deciding the 

question of endangerment. Here too, 

both likelihood and severity of adverse 

effects are relevant, including 

catastrophic scenarios and their 

probabilities as well as the less severe 

effects. As explained below, vulnerable 

subpopulations face serious health risks 

as a result of climate change. 

In addition, by instructing the 

Administrator to consider whether 

emissions of an air pollutant cause or 

contribute to air pollution, the statute is 

clear that she need not find that 

emissions from any one sector or group 

of sources are the sole or even the major 

part of an air pollution problem. The 

use of the term ‘‘contribute’’ clearly 

indicates a lower threshold than the sole 

or major cause. Moreover, the statutory 

language in CAA section 202(a) does not 

contain a modifier on its use of the term 

contribute. Unlike other CAA 

provisions, it does not require 

‘‘significant’’ contribution. See, e.g., 

CAA sections 111(b); 213(a)(2), (4). To 

be sure, any finding of a ‘‘contribution’’ 

requires some threshold to be met; a 

truly trivial or de minimis 

‘‘contribution’’ might not count as such. 

The Administrator therefore has ample 

discretion in exercising her reasonable 

judgment in determining whether, 

under the circumstances presented, the 

cause or contribute criterion has been 

met. Congress made it clear that the 

Administrator is to exercise her 

judgment in determining contribution, 

and authorized regulatory controls to 

address air pollution even if the air 

pollution problem results from a wide 

variety of sources. While the 

endangerment test looks at the entire air 

pollution problem and the risks it poses, 

the cause or contribute test is designed 

to authorize EPA to identify and then 

address what may well be many 

different sectors or groups of sources 

that are each part of—and thus 

contributing to—the problem. 

This framework recognizes that 

regulatory agencies such as EPA must be 

able to deal with the reality that 

‘‘[m]an’s ability to alter his environment 

has developed far more rapidly than his 

ability to foresee with certainty the 

effects of his alterations.’’ See Ethyl 

Corp v. EPA, 541 F.2d 1, 6 (DC Cir.), 

cert. denied 426 U.S. 941 (1976). Both 

‘‘the Clean Air Act ‘and common sense 

* * * demand regulatory action to 

prevent harm, even if the regulator is 

less than certain that harm is otherwise 

inevitable.’ ’’ See Massachusetts v. EPA, 

549 U.S. at 506, n.7 (citing Ethyl Corp.). 

The Administrator recognizes that the 

context for this action is unique. There 

is a very large and comprehensive base 

of scientific information that has been 

developed over many years through a 

global consensus process involving 

numerous scientists from many 

countries and representing many 

disciplines. She also recognizes that 

there are varying degrees of uncertainty 

across many of these scientific issues. It 

is in this context that she is exercising 

her judgment and applying the statutory 

framework. As discussed in the 

Proposed Findings, this interpretation is 

based on and supported by the language 

in CAA section 202(a), its legislative 

history and case law. 

2. Summary of Response to Key Legal 

Comments on the Interpretation of the 

CAA Section 202(a) Endangerment and 

Cause or Contribute Test 

EPA received numerous comments 

regarding the interpretation of CAA 

section 202(a) set forth in the Proposed 

Findings. Below is a brief discussion of 

some of the key adverse legal comments 

and EPA’s responses. Other key legal 

comments and EPA’s responses are 

provided in later sections discussing the 

Administrator’s findings. 

Additional and more detailed 

summaries and responses can be found 

in the Response to Comments 

document. As noted in the Response to 

Comments document, EPA also received 

comments supporting its legal 

interpretations. 

a. The Administrator Properly 

Interpreted the Precautionary and 

Preventive Nature of the Statutory 

Language 

Various commenters argue either that 

the endangerment test under CAA 

section 202(a) is not precautionary and 

preventive in nature, or that EPA’s 

interpretation and application is so 

extreme that it is contrary to what 

Congress intended in 1977, and 

effectively guarantees an affirmative 

endangerment finding. Commenters also 

argue that the endangerment test 

improperly shifts the burdens to the 

opponents of an endangerment finding 

and is tantamount to assuming the air 

pollution is harmful unless it is shown 

to be safe. 

EPA rejects the argument that the 

endangerment test in CAA section 

202(a) is not precautionary or 

preventive in nature. As discussed in 

more detail in the proposal, Congress 

relied heavily on the en banc decision 

in Ethyl when it revised section 202(a) 

and other CAA provisions to adopt the 

current language on endangerment and 

contribution. 74 FR 18886, 18891–2. 

The Ethyl court could not have been 

clearer on the precautionary nature of a 

criteria based on endangerment. The 

court rejected the argument that EPA 

had to find actual harm was occurring 

before it could make the required 

endangerment finding. The court stated 

that: 

The Precautionary Nature of ‘‘Will 

Endanger.’’ Simply as a matter of plain 

meaning, we have difficulty crediting 

petitioners’ reading of the ‘‘will endanger’’ 

standard. The meaning of ‘‘endanger’’ is not 

disputed. Case law and dictionary definition 

agree that endanger means something less 

than actual harm. When one is endangered, 

harm is threatened; no actual injury need 

ever occur. Thus, for example, a town may 

be ‘‘endangered’’ by a threatening plague or 

hurricane and yet emerge from the danger 

completely unscathed. A statute allowing for 

regulation in the face of danger is, 

necessarily, a precautionary statute. 

Regulatory action may be taken before the 

threatened harm occurs; indeed, the very 

existence of such precautionary legislation 

would seem to demand that regulatory action 

precede, and, optimally, prevent, the 

perceived threat. As should be apparent, the 

‘‘will endanger’’ language of Section 

211(c)(1)(A) makes it such a precautionary 

statute. Ethyl at 13 (footnotes omitted). 

Similarly, the court stated that ‘‘[i]n 

sum, based on the plain meaning of the 

statute, the juxtaposition of CAA section 

211 with CAA sections 108 and 202, 

and the Reserve Mining precedent, we 

conclude that the ‘‘will endanger’’ 

standard is precautionary in nature and 

does not require proof of actual harm 

before regulation is appropriate.’’ Ethyl 

at 17. It is this authority to act before 

harm has occurred that makes it a 

preventive, precautionary provision. 

It is important to note that this 

statement was in the context of rejecting 

an argument that EPA had to prove 

actual harm before it could adopt fuel 

control regulations under then CAA 

section 211(c)(1). The court likewise 

rejected the argument that EPA had to 

show that such harm was ‘‘probable.’’ 


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6The Supreme Court recognized that the current 

language in section 202(a), adopted in 1977, is 

‘‘more protective’’ than the 1970 version that was 

similar to the section 211 language before the DC 

Circuit in Ethyl. Massachusetts v. EPA, 549 U.S. at 

506, fn 7. 

The court made it clear that determining 

endangerment entails judgments 

involving both the risk or likelihood of 

harm and the severity of the harm if it 

were to occur. Nowhere did the court 

indicate that the burden was on the 

opponents of an endangerment finding 

to show that there was no 

endangerment. The opinion focuses on 

describing the burden the statute places 

on EPA, rejecting Ethyl’s arguments of a 

burden to show actual or probable harm. 

Congress intentionally adopted a 

precautionary and preventive approach. 

It stated that the purpose of the 1977 

amendments was to ‘‘emphasize the 

preventive or precautionary nature of 

the act, i.e., to assure that regulatory 

action can effectively prevent harm 

before it occurs; to emphasize the 

predominate value of protection to 

public health.’’ 6 Congress also stated 

that it authorized the Administrator to 

weigh risks and make projections of 

future trends, a ‘‘middle road between 

those who would impose a nearly 

impossible standard of proof on the 

Administrator before he may move to 

protect public health and those who 

would shift the burden of proof for all 

pollutants to make the pollutant source 

prove the safety of its emissions as a 

condition of operation.’’ Leg. His. at 

2516. 

Thus, EPA rejects commenters’ 

arguments. Congress intended this 

provision to be preventive and 

precautionary in nature, however it did 

not shift the burden of proof to 

opponents of an endangerment finding 

to show safety or no endangerment. 

Moreover, as is demonstrated in the 

following, EPA has not shifted the 

burden of proof in the final 

endangerment finding, but rather is 

weighing the likelihood and severity of 

harms to arrive at the final finding. EPA 

has not applied an exaggerated or 

dramatically expanded precautionary 

principle, and instead has exercised 

judgment by weighing and balancing the 

factors that are relevant under this 

provision. 

b. The Administrator Does Not Need To 

Find That the Control Measures 

Following an Endangerment Finding 

Would Prevent at Least a Substantial 

Part of the Danger in Order To Find 

Endangerment 

Several commenters argue that it is 

unlawful for EPA to make an affirmative 

endangerment finding unless EPA finds 

that the regulatory control measures 

contemplated to follow such a finding 

would prevent at least a substantial part 

of the danger from the global climate 

change at which the regulation is aimed. 

This hurdle is also described by 

commenters as the regulation 

‘‘achieving the statutory objective of 

preventing damage’’, or ‘‘fruitfully 

attacking’’ the environmental and public 

health danger at hand by meaningfully 

and substantially reducing it. 

Commenters point to Ethyl Corp. v. 

EPA, 541 F.2d 1 (DC Cir. 1976) (en banc) 

as support for this view, as well as 

portions of the legislative history of this 

provision. 

Commenters contend that EPA has 

failed to show that this required degree 

of meaningful reduction of 

endangerment would be achieved 

through regulation of new motor 

vehicles based on an endangerment 

finding. In making any such showing, 

commenters argue that EPA would need 

to account for the following: (1) The fact 

that any regulation would be limited to 

new motor vehicles, if not the subset of 

new motor vehicles discussed in the 

President’s May 2009 announcement, 

(2) any increase in emissions from 

purchasers delaying purchases of new 

vehicles subject to any greenhouse gas 

emissions standards, or increasing the 

miles traveled of new vehicles with 

greater fuel economy, (3) the fact that 

only a limited portion of the new motor 

vehicle emissions of greenhouse gases 

would be controlled, (4) the fact that 

CAFE standards would effectively 

achieve the same reductions, and (5) the 

fact that any vehicle standards would 

not themselves reduce global 

temperatures. Some commenters refer to 

EPA’s proposal for greenhouse gas 

emissions standards for new motor 

vehicles as support for these arguments, 

claiming the proposed new motor 

vehicle emission standards are largely 

duplicative of the standards proposed 

by the National Highway Traffic Safety 

Administration (NHTSA), and the 

estimates of the impacts of the proposed 

standards confirm that EPA’s proposed 

standards cannot ‘‘fruitfully attack’’ 

global climate change (74 FR 49454, 

September 28, 2009). 

Commenters attempt to read into the 

statute a requirement that is not there. 

EPA interprets the endangerment 

provision of CAA section 202(a) as not 

requiring any such finding or showing 

as described by commenters. The text of 

CAA section 202(a) does not support 

such an interpretation. The 

endangerment provision calls for EPA, 

in its judgment, to determine whether 

air pollution is reasonably anticipated to 

endanger public health or welfare, and 

whether emissions from certain sources 

cause or contribute to such air 

pollution. If EPA makes an affirmative 

finding, then it shall set emissions 

standards applicable to emissions of 

such air pollutants from new motor 

vehicles. There is no reference in the 

text of the endangerment or cause or 

contribute provision to anything 

concerning the degree of reductions that 

would be achieved by the emissions 

standards that would follow such a 

finding. The Administrator’s judgment 

is directed at the issues of 

endangerment and cause or contribute, 

not at how effective the resulting 

emissions control standards will be. 

As in the several other similar 

provisions adopted in the 1977 

amendments, in CAA section 202(a) 

Congress explicitly separated two 

different decisions to be made, 

providing different criteria for them. 

The first decision involves the air 

pollution and the endangerment criteria, 

and the contribution to the air pollution 

by the sources. The second decision 

involves how to regulate the sources to 

control the emissions if an affirmative 

endangerment and contribution finding 

are made. In all of the various 

provisions, there is broad similarity in 

the phrasing of the endangerment and 

contribution decision. However, for the 

decision on how to regulate, there are a 

wide variety of different approaches 

adopted by Congress. In some case, EPA 

has discretion whether to issue 

standards or not, while in other cases, 

as in CAA section 202(a), EPA is 

required to issue standards. In some 

cases, the regulatory criteria are general, 

as in CAA section 202(a); in others, they 

provide significantly more direction as 

to how standards are to be set, as in 

CAA section 213(a)(4). 

As the Supreme Court made clear in 

Massachusetts v. EPA, EPA’s judgment 

in making the endangerment and 

contribution findings is constrained by 

the statute, and EPA is to decide these 

issues based solely on the scientific and 

other evidence relevant to that decision. 

EPA may not ‘‘rest[] on reasoning 

divorced from the statutory text,’’ and 

instead EPA’s exercise of judgment must 

relate to whether an air pollutant causes 

or contributes to air pollution that 

endangers. Massachusetts v. EPA, 549 

U.S. at 532. As the Supreme Court 

noted, EPA must ‘‘exercise discretion 

within defined statutory limits.’’ Id. at 

533. EPA’s belief one way or the other 

regarding whether regulation of 

greenhouse gases from new motor 

vehicles would be ‘‘effective’’ is 

irrelevant in making the endangerment 

and contribution decisions before EPA. 

Id. Instead ‘‘[t]he statutory question is 


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whether sufficient information exists to 

make an endangerment finding’’ Id. at 

534. 

The effectiveness of a potential future 

control strategy is not relevant to 

deciding whether air pollution levels in 

the atmosphere endanger. It is also not 

relevant to deciding whether emissions 

of greenhouse gases from new motor 

vehicles contribute to such air 

pollution. Commenters argue that 

Congress implicitly imposed a third 

requirement, that the future control 

strategy have a certain degree of 

effectiveness in reducing the 

endangerment before EPA could make 

the affirmative findings that would 

authorize such regulation. There is no 

statutory text that supports such an 

interpretation, and the Supreme Court 

makes it clear that EPA has no 

discretion to read this kind of additional 

factor into CAA section 202(a)’s 

endangerment and contribution criteria. 

In fact, the Supreme Court rejected 

similar arguments that EPA had the 

discretion to consider various other 

factors besides endangerment and 

contribution in deciding whether to 

deny a petition. Massachusetts v. EPA, 

549 U.S. at 532–35. 

Commenters point to language from 

the Ethyl case to support their position, 

noting that the DC Circuit referred to the 

emissions control regulation adopted by 

EPA under CAA section 211(c) as one 

that would ‘‘fruitfully attack’’ the 

environmental and public health danger 

by meaningfully and substantially 

reducing the danger. It is important to 

understand the context for this 

discussion in Ethyl. The petitioner Ethyl 

Corp. argued that EPA had to show that 

the health threat from the emissions of 

lead from the fuel additive being 

regulated had to be considered in 

isolation, and the threat ‘‘in and of 

itself’’ from the additive had to meet the 

test of endangerment in CAA section 

211(c). EPA had rejected this approach, 

and had interpreted CAA section 

211(c)(1) as calling for EPA to look at 

the cumulative impact of lead, and to 

consider the impact of lead from 

emissions related to use of the fuel 

additive in the context all other human 

exposure to lead. The court rejected 

Ethyl’s approach and supported EPA’s 

interpretation. The DC Circuit noted 

that Congress was fully aware that the 

burden of lead on the body was caused 

by multiple sources and that it would be 

of no value to try and determine the 

effect on human health from the lead 

automobile emissions by themselves. 

The court specifically noted that ‘‘the 

incremental effect of lead emissions on 

the total body lead burden is of no 

practical value in determining whether 

health is endangered,’’ but recognized 

that this incremental effect is of value 

‘‘in deciding whether the lead exposure 

problem can fruitfully be attacked 

through control of lead additives.’’ 

Ethyl, 541 F.2d at 31 fn 62. The court 

made clear that the factor that was 

critically important to determining the 

effectiveness of the resulting control 

strategy—the incremental effect of 

automobile lead emissions on total body 

burden—was irrelevant and of no value 

in determining whether the 

endangerment criteria was met. Thus it 

is clear that the court in Ethyl did not 

interpret then CAA section 211(c)(1)(A) 

as requiring EPA to make a showing of 

the effectiveness of the resulting 

emissions control strategy, and instead 

found just the opposite, that the factors 

that would determine effectiveness are 

irrelevant to determining endangerment. 

Commenters also cite to the legislative 

history, noting that Congress referred to 

the ‘‘preventive or precautionary nature 

of the Act, i.e., to assure that regulatory 

action can effectively prevent harm 

before it occurs.’’ Leg. Hist. at 2516. 

However, this statement by Congress is 

presented as an answer to the question 

on page 2515, ‘‘Should the 

Administrator act to prevent harm 

before it occurs or should he be 

authorized to regulate an air pollutant 

only if he finds actual harm has already 

occurred.’’ Leg. Hist. at 2515. In this 

context, the discussion on page 2516 

clearly indicates that there is no 

opportunity for prevention or 

precaution if the test is one of actual 

harm already occurring. This discussion 

does not say or imply that even if the 

harm has not occurred, you can not act 

unless you also show that your action 

will effectively address it. This 

discussion concerns the endangerment 

test, not the criteria for standard setting. 

The criteria for standard setting address 

how the agency should act to address 

the harm, and as the Ethyl case notes, 

the factors relevant to how to ‘‘fruitfully 

attack’’ the harm are irrelevant to 

determining whether the harm is one 

that endangers the public health or 

welfare. 

As with current CAA section 202(a), 

there is no basis to conflate these two 

separate decisions and to read into the 

endangerment criteria an obligation that 

EPA show that the resulting emissions 

control strategy or strategies will have 

some significant degree of harm 

reduction or effectiveness in addressing 

the endangerment. The conflating of the 

two decisions is not supported in the 

text of this provision, by the Supreme 

Court in Massachusetts v. EPA, by the 

DC Circuit in Ethyl, or by Congress in 

the legislative history of this provision. 

It would be an unworkable 

interpretation, calling for EPA to project 

out the result of perhaps not one, but 

even several, future rulemakings 

stretching over perhaps a decade or 

decades. Especially in the context of 

global climate change, the effectiveness 

of a control strategy for new motor 

vehicles would have to be viewed in the 

context of a number of future motor 

vehicle regulations, as well as in the 

larger context of the CAA and perhaps 

even global context. That would be an 

unworkable and speculative 

requirement to impose on EPA as a 

precondition to answering the public 

health and welfare issues before it, as 

they are separate and apart from the 

issues involved with developing, 

implementing and evaluating the 

effectiveness of emissions control 

strategies. 

c. The Administrator Does Not Need To 

Find There Is Significant Risk of Harm 

Commenters argue that Congress 

established a minimum requirement 

that there be a ‘‘significant risk of harm’’ 

to find endangerment. They contend 

that this requirement stemmed from the 

Ethyl case, and that Congress adopted 

this view. According to the commenters, 

the risk is the function of two variables: 

the nature of the hazard at issue and the 

likelihood of its occurrence. 

Commenters argue that Congress 

imposed a requirement that this balance 

demonstrate a ‘‘significant risk of harm’’ 

to strike a balance between the 

precautionary nature of the CAA and 

the burdensome economic and societal 

consequences of regulation. 

There are two basic problems with the 

commenters’ arguments. First, 

commenters equate ‘‘significant risk of 

harm’’ as the overall test for 

endangerment, however the Ethyl case 

and the legislative history treat the risk 

of harm as only one of the two 

components that are to be considered in 

determining endangerment.—, The two 

components are the likelihood or risk of 

a harm occurring, and the severity of 

harm if it were to occur. Second, 

commenters equate it to a minimum 

statutory requirement. However, while 

the court in the Ethyl case made it clear 

that the facts in that case met the then 

applicable endangerment criteria, it also 

clearly said it was not determining what 

other facts or circumstances might 

amount to endangerment, including 

cases where the likelihood of a harm 

occurring was less than a significant risk 

of the harm. 

In the EPA rulemaking that led to the 

Ethyl case, EPA stated that the 

requirement to reduce lead in gasoline 

‘‘is based on the finding that lead 


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Federal Register / Vol. 74, No. 239 / Tuesday, December 15, 2009 / Rules and Regulations 66509 

7Commenters point to Amer. Farm Bureau Ass’n 

v. EPA, 559 F.3d 512, 533 (DC Cir. 2009) as 

supporting their argument. However, in that case 

the Court made clear that EPA’s action was not 

subject to the endangerment criterion in CAA 

section 108 but instead was subject to CAA section 

109’s requirement that the primary NAAQS be 

requisite to protect the public health with an 

adequate margin of safety. Under that provision and 

its case law, the Court upheld EPA’s reasoned 

balancing of the uncertainty regarding the link 

between non-urban thoracic coarse PM and adverse 

health effects, the large population groups 

potentially exposed to these particles, and the 

nature and degree of the health effects at issue. 

Citing to EPA’s reasoning at 71 FR 61193 in the 

final PM rule, the court explained that EPA need 

not wait for conclusive proof of harm before setting 

a NAAQS under section 109 for this kind of coarse 

PM. The Court’s reference to EPA’s belief that there 

may be a significant risk to public health is not 

stated as any sort of statutory minimum, but instead 

refers to the Agency’s reasoning at 71 FR 61193, 

which displays a reasoned balancing of possibility 

of harm and severity of harm if it were to occur. 

particle emissions from motor vehicles 

present a significant risk of harm to the 

health of urban populations, 

particularly to the health of city 

children’’ (38 FR 33734, December 6, 

1973). The court in Ethyl supported 

EPA’s determination, and addressed a 

variety of issues. First, it determined 

that the ‘‘will endanger’’ criteria of then 

CAA section 211(c) was intended to be 

precautionary in nature. It rejected 

arguments that EPA had to show proof 

of actual harm, or probable harm. Ethyl, 

541 F.2d at 13–20. It was in this context, 

evaluating petitioner’s arguments on 

whether the likelihood of a harm 

occurring had to rise to the level of 

actual or probable harm, that the court 

approved of EPA’s view that a 

significant risk of harm could satisfy the 

statutory criteria. The precautionary 

nature of the provision meant that EPA 

did not need to show that either harm 

was actually occurring or was probable. 

Instead, the court made it clear that 

the concept of endangerment is 

‘‘composed of reciprocal elements of 

risk and harm,’’ Ethyl at 18. This means 

‘‘the public health may properly be 

found endangered both by a lesser risk 

of a greater harm and by a greater risk 

of lesser harm. Danger depends upon 

the relation between the risk and harm 

presented by each case, and cannot 

legitimately be pegged to ‘probable’ 

harm, regardless of whether that harm 

be great or small.’’ The Ethyl court 

pointed to the decision by the 8th 

Circuit in Reserve Mining Co. v. EPA, 

514 F.2d 492 (8th Cir, 1975), which 

interpreted similar language under the 

Federal Water Pollution Control Act, 

where the 8th Circuit upheld an 

endangerment finding in a case 

involving ‘‘reasonable medical 

concern,’’ or a ‘‘potential’’ showing of 

harm. This was further evidence that a 

minimum ‘‘probable’’ likelihood of 

harm was not required. 

The Ethyl court made it clear that 

there was no specific magnitude of risk 

of harm occurring that was required. 

‘‘Reserve Mining convincingly 

demonstrates that the magnitude of risk 

sufficient to justify regulation is 

inversely proportional to the harm to be 

avoided.’’ Ethyl at 19. This means there 

is no minimum requirement that the 

magnitude of risk be ‘‘significant’’ or 

another specific level of likelihood of 

occurrence. You need to evaluate the 

risk of harm in the context of the 

severity of the harm if it were to occur. 

In the case before it, the Ethyl court 

noted that ‘‘the harm caused by lead 

poisoning is severe.’’ Even with harm as 

severe as lead poisoning, EPA did not 

rely on ‘‘potential’’ risk or a ‘‘reasonable 

medical concern.’’ Instead, EPA found 

that there was a significant risk of this 

harm to health. This finding of a 

significant risk was less than the level 

of ‘‘probable’’ harm called for by the 

petitioner Ethyl Corporation but was 

‘‘considerably more certain than the risk 

that justified regulation in Reserve 

Mining of a comparably ‘fright-laden’ 

harm.’’ Ethyl at 19–20. The Ethyl court 

concluded that this combination of risk 

(likelihood of harm) and severity of 

harm was sufficient under CAA section 

211(c). ‘‘Thus we conclude that however 

far the parameters of risk and harm 

inherent in the ‘will endanger’ standard 

might reach in an appropriate case, they 

certainly present a ‘danger’ that can be 

regulated when the harm to be avoided 

is widespread lead poisoning and the 

risk of that occurrence is ‘significant’.’’ 

Ethyl at 20. 

Thus, the court made it clear that the 

endangerment criteria was intended to 

be precautionary in nature, that the risk 

of harm was one of the elements to 

consider in determining endangerment, 

and that the risk of harm needed to be 

considered in the context of the severity 

of the potential harm. It also concluded 

that a significant risk of harm coupled 

with an appropriate severity of the 

potential harm would satisfy the 

statutory criteria, and in the case before 

it the Administrator was clearly 

authorized to determine endangerment 

where there was a significant risk of 

harm that was coupled with a severe 

harm such as lead poisoning. 

Importantly, the court also made it 

clear that it was not determining a 

minimum threshold that always had to 

be met. Instead, it emphasized that the 

risk of harm and severity of the 

potential harm had to be evaluated on 

a case by case basis. The court 

specifically said it was not determining 

‘‘however far the parameters of risk and 

harm * * * might reach in an 

appropriate case.’’ Ethyl at 20. Also see 

Ethyl fn 17 at 13. The court recognized 

that this balancing of risk and harm 

‘‘must be confined to reasonable limits’’ 

and even absolute certainty of a de 

minimis harm might not justify 

government action. However, ‘‘whether 

a particular combination of slight risk 

and great harm, or great risk and slight 

harm constitutes a danger must depend 

on the facts of each case.’’ Ethyl at fn 32 

at 18.7

In some cases, commenters confuse 

matters by switching the terminology, 

and instead refer to effects that 

‘‘significantly harm’’ the public health 

or welfare. As with the reference to 

‘‘significant risk of harm,’’ commenters 

fail to recognize that there are two 

different aspects that must be 

considered, risk of harm and severity of 

harm, and neither of these aspects has 

a requirement that there be a finding of 

‘‘significance.’’ The DC Circuit in Ethyl 

makes clear that it is the combination of 

these two aspects that must be evaluated 

for purposes of endangerment, and there 

is no requirement of ‘‘significance’’ 

assigned to either of the two aspects that 

must instead be evaluated in 

combination. Congress addressed 

concerns over burdensome economic 

and societal consequences in the 

various statutory provisions that 

provide the criteria for standard setting 

or other agency action if there is an 

affirmative endangerment finding. 

Those statutory provisions, for example, 

make standard setting discretionary or 

specify how cost and other factors are to 

be taken into consideration in setting 

standards. However, the issues of risk of 

harm and severity of harm if it were to 

occur are separate from the issues of the 

economic impacts of any resulting 

regulatory provisions (see below). 

As is clear in the prior summary of 

the endangerment findings and the more 

detailed discussion later, the breadth of 

the sectors of our society that are 

affected by climate change and the time 

frames at issue mean there is a very 

wide range of risks and harms that need 

to be considered, from evidence of 

various harms occurring now to 

evidence of risks of future harms. The 

Administrator has determined that the 

body of scientific evidence compellingly 

supports her endangerment finding. 

B. Air Pollutant, Public Health and 

Welfare 

The CAA defines both ‘‘air pollutant’’ 

and ‘‘effects on welfare.’’ We provide 

both definitions here again for 

convenience. 

Air pollutant is defined as: 


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66510 Federal Register / Vol. 74, No. 239 / Tuesday, December 15, 2009 / Rules and Regulations 

8 Karl, T., J. Melillo, and T. Peterson (Eds.) (2009) 

Global Climate Change Impacts in the United 

States. Cambridge University Press, Cambridge, 

United Kingdom. 

9U.S. EPA (2009) Inventory of U.S. Greenhouse 

Gas Emissions and Sinks: 1990–2007. EPA–430–R– 

09–004, Washington, DC. 

10EPA has placed within the docket a separate 

memo ‘‘Summary of Major Changes to the 

Technical Support Document’’ identifying where 

within the TSD such changes were made relative to 

the draft TSD released in April 2009. 

‘‘Any air pollution agent or 

combination of such agents, including 

any physical, chemical, biological, 

radioactive (including source material, 

special nuclear material, and byproduct 

material) substance or matter which is 

emitted into or otherwise enters the 

ambient air. Such term includes any 

precursors to the formation of any air 

pollutant, to the extent the 

Administrator has identified such 

precursor or precursors for the 

particular purpose for which the term 

‘‘air pollutant’’ is used.’’ CAA section 

302(g). As the Supreme Court held, 

greenhouse gases fit well within this 

capacious definition. See Massachusetts 

v. EPA, 549 U.S. at 532. They are 

‘‘without a doubt’’ physical chemical 

substances emitted into the ambient air. 

Id. at 529. 

‘‘Regarding ‘effects on welfare’, the 

CAA states that [a]ll language referring 

to effects on welfare includes, but is not 

limited to, effects on soils, water, crops, 

vegetation, man-made materials, 

animals, wildlife, weather, visibility, 

and climate, damage to and 

deterioration of property, and hazards to 

transportation, as well as effects on 

economic values and on personal 

comfort and well-being, whether caused 

by transformation, conversion, or 

combination with other air pollutants.’’ 

CAA section 302(h). 

As noted in the Proposed Findings, 

this definition is quite broad. 

Importantly, it is not an exclusive list 

due to the use of the term ‘‘includes, but 

is not limited to, * * * .’’ Effects other 

than those listed here may also be 

considered effects on welfare. Moreover, 

the terms contained within the 

definition are themselves expansive. 

Although the CAA defines ‘‘effects on 

welfare’’ as discussed above, there are 

no definitions of ‘‘public health’’ or 

‘‘public welfare’’ in the CAA. The 

Supreme Court has discussed the 

concept of public health in the context 

of whether costs of implementation can 

be considered when setting the health 

based primary National Ambient Air 

Quality Standards. Whitman v. 

American Trucking Ass’n, 531 U.S. 457 

(2001). In Whitman, the Court imbued 

the term with its most natural meaning: 

‘‘the health of the public. Id. at 466. In 

the past, when considering public 

health, EPA has looked at morbidity, 

such as impairment of lung function, 

aggravation of respiratory and 

cardiovascular disease, and other acute 

and chronic health effects, as well as 

mortality. See, e.g., Final National 

Ambient Air Quality Standard for 

Ozone, (73 FR 16436, 2007). 

EPA received numerous comments 

regarding its proposed interpretations of 

air pollutant and public health and 

welfare. Summaries of key comments 

and EPA’s responses are discussed in 

Sections IV and V of these Findings. 

Additional and more detailed 

summaries and responses can be found 

in the Response to Comments 

document. As noted in the Response to 

Comments document, EPA also received 

comments supporting its legal 

interpretations. 

III. EPA’s Approach for Evaluating the 

Evidence Before It 

This section discusses EPA’s 

approach to evaluating the evidence 

before it, including the approach taken 

to the scientific evidence, the legal 

framework for this decision making, and 

several issues critical to determining the 

scope of the evaluation performed. 

A. The Science on Which the Decisions 

Are Based 

In 2007, EPA initiated its assessment 

of the science and other technical 

information to use in addressing the 

endangerment and cause or contribute 

issues before it under CAA section 

202(a). This scientific and technical 

information was developed in the form 

of a TSD in 2007. An earlier draft of this 

document was released as part of the 

ANPR published July 30, 2008 (73 FR 

44353). That earlier draft of the TSD 

relied heavily on the IPCC Fourth 

Assessment Report of 2007, key NRC 

reports, and a limited number of thenavailable synthesis and assessment 

products of the U.S. Climate Change 

Science Program (CCSP; now 

encompassed by USGCRP). EPA 

received a number of comments 

specifically focused on the TSD during 

the 120-day public comment period for 

the ANPR. 

EPA revised and updated the TSD in 

preparing the Proposed Findings on 

endangerment and cause or contribute. 

Many of the comments received on the 

ANPR were reflected in the draft TSD 

released in April 2009 that served as the 

underlying scientific and technical basis 

for the Administrator’s Proposed 

Findings, published April 24, 2009 (74 

FR 18886). The draft TSD released in 

April 2009 also reflected the findings of 

11 new synthesis and assessment 

products under the U.S. CCSP that had 

been published since July 2008. 

The TSD that summarizes scientific 

findings from the major assessments of 

the USGCRP, the IPCC, and the NRC 

accompanies these Findings. The TSD is 

available at www.epa.gov/ 

climatechange/endangerment.html and 

in the docket for this action. It also 

includes the most recent comprehensive 

assessment of the USGCRP, Global 

Climate Change Impacts in the United 

States,8 published in June 2009. In 

addition, the TSD incorporates up-todate observational data for a number of 

key climate variables from the NOAA, 

and the most up-to-date emissions data 

from EPA’s annual Inventory of U.S. 

Greenhouse Gas Emissions and Sinks, 

published in April, 2009.9 And finally, 

as discussed in Section I.B of these 

Findings, EPA received a large number 

of public comments on the 

Administrator’s Proposed Findings, 

many of which addressed science issues 

either generally or specifically as 

reflected in the draft TSD released with 

the April 2009 proposal. A number of 

edits and updates were made to the 

draft TSD as a result of these 

comments.10

EPA is giving careful consideration to 

all of the scientific and technical 

information in the record, as discussed 

below. However, the Administrator is 

relying on the major assessments of the 

USGCRP, IPCC, and NRC as the primary 

scientific and technical basis of her 

endangerment decision for a number of 

reasons. 

First, these assessments address the 

scientific issues that the Administrator 

must examine for the endangerment 

analysis. When viewed in total, these 

assessments address the issue of 

greenhouse gas endangerment by 

providing data and information on: (1) 

The amount of greenhouse gases being 

emitted by human activities; (2) how 

greenhouse gases have been and 

continue to accumulate in the 

atmosphere as a result of human 

activities; (3) changes to the Earth’s 

energy balance as a result of the buildup 

of atmospheric greenhouse gases; (4) 

observed temperature and other climatic 

changes at the global and regional 

scales; (5) observed changes in other 

climate-sensitive sectors and systems of 

the human and natural environment; (6) 

the extent to which observed climate 

change and other changes in climatesensitive systems can be attributed to 

the human-induced buildup of 

atmospheric greenhouse gases; (7) future 

projected climate change under a range 

of different scenarios of changing 

greenhouse gas emission rates; and (8) 

the projected risks and impacts to 


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Federal Register / Vol. 74, No. 239 / Tuesday, December 15, 2009 / Rules and Regulations 66511 

11http://www.globalchange.gov/publications/ 

reports/ipcc-reports. 

12CCSP (2009) Coastal Sensitivity to Sea-Level 

Rise: A Focus on the Mid-Atlantic Region. A Report 

by the U.S. Climate Change Science Program and 

the Subcommittee on Global Change Research. 

[James G. Titus (Coordinating Lead Author), K. Eric 

Anderson, Donald R. Cahoon, Dean B. Gesch, 

Stephen K. Gill, Benjamin T. Gutierrez, E. Robert 

Thieler, and S. Jeffress Williams (Lead Authors)], 

U.S. Environmental Protection Agency, Washington 

DC, USA, 320 pp. CCSP (2008) Preliminary review 

of adaptation options for climate-sensitive 

ecosystems and resources. A Report by the U.S. 

Climate Change Science Program and the 

Subcommittee on Global Change Research. [Julius, 

S.H., J.M. West (eds.), J.S. Baron, B. Griffith, L.A. 

Joyce, P. Kareiva, B.D. Keller, M.A. Palmer, C.H. 

Peterson, and J.M. Scott (Authors)]. U.S. 

Environmental Protection Agency, Washington, DC, 

USA, 873 pp. CCSP (2008) Analyses of the effects 

of global change on human health and welfare and 

human systems. A Report by the U.S. Climate 

Change Science Program and the Subcommittee on 

Global Change Research. [Gamble, J.L. (ed.), K.L. 

Ebi, F.G. Sussman, T.J. Wilbanks, (Authors)]. U.S. 

Environmental Protection Agency, Washington, DC, 

USA. 13 IPCC (2007) Climate Change 2007: Impacts, 

Adaptation and Vulnerability. Contribution of 

Working Group II to the Fourth Assessment Report 

of the Intergovernmental Panel on Climate Change, 

M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der 

Linden and C.E. Hanson, Eds., Cambridge 

University Press, Cambridge, UK, 976pp. 14 It maintains the highest level of adherence to 

Agency and OMB guidelines for data and scientific 

integrity and transparency. This is discussed in 

greater detail in EPA’s Response to Comments 

document. 

human health, society and the 

environment. 

Second, as indicated above, these 

assessments are recent and represent the 

current state of knowledge on the key 

elements for the endangerment analysis. 

It is worth noting that the June 2009 

assessment of the USGCRP incorporates 

a number of key findings from the 2007 

IPCC Fourth Assessment Report; such 

findings include the attribution of 

observed climate change to human 

emissions of greenhouse gases, and the 

future projected scenarios of climate 

change for the global and regional 

scales. This demonstrates that much of 

the underlying science that EPA has 

been utilizing since 2007 has not only 

been in the public domain for some 

time, but also has remained relevant and 

robust. 

Third, these assessments are 

comprehensive in their coverage of the 

greenhouse gas and climate change 

problem, and address the different 

stages of the emissions-to-potentialharm chain necessary for the 

endangerment analysis. In so doing, 

they evaluate the findings of numerous 

individual peer-reviewed studies in 

order to draw more general and 

overarching conclusions about the state 

of science. The USGCRP, IPCC, and 

NRC assessments synthesize literally 

thousands of individual studies and 

convey the consensus conclusions on 

what the body of scientific literature 

tells us. 

Fourth, these assessment reports 

undergo a rigorous and exacting 

standard of peer review by the expert 

community, as well as rigorous levels of 

U.S. government review and acceptance. 

Individual studies that appear in 

scientific journals, even if peer 

reviewed, do not go through as many 

review stages, nor are they reviewed and 

commented on by as many scientists. 

The review processes of the IPCC, 

USGCRP, and NRC (explained in fuller 

detail in the TSD and the Response to 

Comments document, Volume 1) 

provide EPA with strong assurance that 

this material has been well vetted by 

both the climate change research 

community and by the U.S. government. 

These assessments therefore essentially 

represent the U.S. government’s view of 

the state of knowledge on greenhouse 

gases and climate change. For example, 

with regard to government acceptance 

and approval of IPCC assessment 

reports, the USGCRP Web site states 

that: ‘‘When governments accept the 

IPCC reports and approve their 

Summary for Policymakers, they 

acknowledge the legitimacy of their 

scientific content.’’ 11 It is the 

Administrator’s view that such review 

and acceptance by the U.S. Government 

lends further support for placing 

primary weight on these major 

assessments. 

It is EPA’s view that the scientific 

assessments of the IPCC, USGRCP, and 

the NRC represent the best reference 

materials for determining the general 

state of knowledge on the scientific and 

technical issues before the agency in 

making an endangerment decision. No 

other source of information provides 

such a comprehensive and in-depth 

analysis across such a large body of 

scientific studies, adheres to such a high 

and exacting standard of peer review, 

and synthesizes the resulting consensus 

view of a large body of scientific experts 

across the world. For these reasons, the 

Administrator is placing primary and 

significant weight on these assessment 

reports in making her decision on 

endangerment. 

A number of commenters called upon 

EPA to perform a new and independent 

assessment of all of the underlying 

climate change science, separate and 

apart from USGCRP, IPCC, and NRC. In 

effect, commenters suggest that EPA is 

either required to or should ignore the 

attributes discussed above concerning 

these assessment reports, and should 

instead perform its own assessment of 

all of the underlying studies and 

information. 

In addition to the significant reasons 

discussed above for relying on and 

placing primary weight on these 

assessment reports, EPA has been a very 

active part of the U.S. government 

climate change research enterprise, and 

has taken an active part in the review, 

writing, and approval of these 

assessments. EPA was the lead agency 

for three significant reports under the 

USGCRP 12, and recently completed an 

assessment addressing the climate 

change impacts on U.S. air quality—a 

report on which the TSD heavily relies 

for that particular issue. EPA was also 

involved in review of the IPCC Fourth 

Assessment Report, and in particular 

took part in the approval of the 

summary for policymakers for the 

Working Group II Volume, Impacts, 

Adaptation and Vulnerability.13 The 

USGCRP, IPCC, and NRC assessments 

have been reviewed and formally 

accepted by, commissioned by, or in 

some cases authored by, U.S. 

government agencies and individual 

government scientists. These reports 

already reflect significant input from 

EPA’s scientists and the scientists of 

many other government agencies. 

EPA has no reason to believe that the 

assessment reports do not represent the 

best source material to determine the 

state of science and the consensus view 

of the world’s scientific experts on the 

issues central to making an 

endangerment decision with respect to 

greenhouse gases. EPA also has no 

reason to believe that putting this 

significant body of work aside and 

attempting to develop a new and 

separate assessment would provide any 

better basis for making the 

endangerment decision, especially 

because any such new assessment by 

EPA would still have to give proper 

weight to these same consensus 

assessment reports. 

In summary, EPA concludes that its 

reliance on existing and recent synthesis 

and assessment reports is entirely 

reasonable and allows EPA to rely on 

the best available science.14 EPA also 

recognizes that scientific research is 

very active in many areas addressed in 

the TSD (e.g., aerosol effects on climate, 

climate feedbacks such as water vapor, 

and internal and external climate 

forcing mechanisms), as well as for 

some emerging issues (e.g., ocean 

acidification and climate change effects 

on water quality). EPA recognizes the 

potential importance of new scientific 

research, and the value of an ongoing 

process to take more recent science into 

account. EPA reviewed new literature in 


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66512 Federal Register / Vol. 74, No. 239 / Tuesday, December 15, 2009 / Rules and Regulations 

15The IPCC definition of adaptation: ‘‘Adaptation 

to climate change takes place through adjustments 

to reduce vulnerability or enhance resilience in 

response to observed or expected changes in 

climate and associated extreme weather events. 

Adaptation occurs in physical, ecological and 

human systems. It involves changes in social and 

environmental processes, perceptions of climate 

risk, practices and functions to reduce potential 

damages or to realize new opportunities.’’ The IPCC 

defines autonomous adaptation as ‘‘Adaptation that 

does not constitute a conscious response to climatic 

stimuli but is triggered by ecological changes in 

natural systems and by market or welfare changes 

in human systems.’’ 

preparation of this TSD to evaluate its 

consistency with recent scientific 

assessments. We also considered public 

comments received and studies 

incorporated by reference. In a number 

of cases, the TSD was updated based on 

such information to add context for 

assessment literature findings, which 

includes supporting information and/or 

qualifying statements. In other cases, 

material that was not incorporated into 

the TSD is discussed within the 

Response to Comments document. 

EPA reviewed these individual 

studies that were not considered or 

reflected in these major assessments to 

evaluate how they inform our 

understanding of how greenhouse gas 

emissions affect climate change, and 

how climate change may affect public 

health and welfare. Given the very large 

body of studies reviewed and assessed 

in developing the assessment reports, 

and the rigor and breadth of that review 

and assessment, EPA placed limited 

weight on the much smaller number of 

individual studies that were not 

considered or reflected in the major 

assessments. EPA reviewed them largely 

to see if they would lead EPA to change 

or place less weight on the judgments 

reflected in the assessment report. 

While EPA recognizes that some studies 

are more useful or informative than 

others, and gave each study it reviewed 

the weight it was due, the overall 

conclusion EPA drew from its review of 

studies submitted by commenters was 

that the studies did not change the 

various conclusions or judgments EPA 

would draw based on the assessment 

reports. 

Many comments focus on the 

scientific and technical data underlying 

the Proposed Findings, such as climate 

change science and greenhouse gas 

emissions data. These comments cover 

a range of topics and are summarized 

and responded to in the Response to 

Public Comments document. The 

responses note those cases where a 

technical or scientific comment resulted 

in an editorial or substantive change to 

the TSD. The final TSD reflects all 

changes made as a result of public 

comments. 

B. The Law on Which the Decisions Are 

Based 

In addition to grounding these 

determinations on the science, they are 

also firmly grounded in EPA’s legal 

authority. Section II of these Findings 

provides an in-depth discussion of the 

legal framework for the endangerment 

and cause or contribute decisions under 

CAA section 202(a), with additional 

discussion in Section II of the Proposed 

Finding (74 FR 18886, 18890, April 24, 

2009). A variety of important legal 

issues are also discussed in Sections III, 

IV, and V of these Findings, as well as 

in the Response to Comments 

document, Volume 11. Section IV and V 

of these Findings explain the 

Administrator’s decisions, and how she 

exercised her judgment in making the 

endangerment and contribution 

determinations, based on the entire 

scientific record before her and the legal 

framework structuring her decision 

making. 

C. Adaptation and Mitigation 

Following the language of CAA 

section 202(a), in which the 

Administrator, in her judgment, must 

determine if greenhouse gases constitute 

the air pollution that may be reasonably 

anticipated to endanger public health or 

welfare, EPA evaluated, based primarily 

on the scientific reports discussed 

above, how greenhouse gases and other 

climate-relevant substances are affecting 

the atmosphere and climate, and how 

these climate changes affect public 

health and welfare, now and in the 

future. Consistent with EPA’s scientific 

approach underlying the 

Administrator’s Proposed Findings, EPA 

did not undertake a separate analysis to 

evaluate potential societal and policy 

responses to any threat (i.e., the 

endangerment) that may exist due to 

anthropogenic emissions of greenhouse 

gases. Risk reduction through 

adaptation and greenhouse gas 

mitigation measures is of course a strong 

focal area of scientists and policy 

makers, including EPA; however, EPA 

considers adaptation and mitigation to 

be potential responses to endangerment, 

and as such has determined that they 

are outside the scope of the 

endangerment analysis. 

The Administrator’s position is not 

that adaptation will not occur or cannot 

help protect public health and welfare 

from certain impacts of climate change, 

as some commenters intimated. To the 

contrary, EPA recognizes that some 

level of autonomous adaptation 15 will 

occur, and commenters are correct that 

autonomous adaptation can affect the 

severity of climate change impacts. 

Indeed, there are some cases in the TSD 

in which some degree of adaptation is 

accounted for; these cases occur where 

the literature on which the TSD relies 

already uses assumptions about 

autonomous adaptation when projecting 

the future effects of climate change. 

Such cases are noted in the TSD. We 

also view planned adaptation as an 

important near-term risk-minimizing 

strategy given that some degree of 

climate change will continue to occur as 

a result of past and current emissions of 

greenhouse gases that remain in the 

atmosphere for decades to centuries. 

However, it is the Administrator’s 

position that projections of adaptation 

and mitigation in response to risks and 

impacts associated with climate change 

are not appropriate for EPA to consider 

in making a decision on whether the air 

pollution endangers. The issue before 

EPA involves evaluating the risks to 

public health and welfare from the air 

pollution if we do not take action to 

address it. Adaptation and mitigation 

address an important but different 

issue—how much risk will remain 

assuming some projection of how 

people and society will respond to the 

threat. 

Several commenters argue that it is 

arbitrary not to consider adaptation in 

determining endangerment. They 

contend that because endangerment is a 

forward-looking exercise, the 

fundamental inquiry concerns the type 

and extent of harm that is believed 

likely to occur in the future. Just as the 

Administrator makes projections of 

potential harms in the future, these 

commenters contend that the 

Administrator needs to consider the 

literature on adaptation that addresses 

the likelihood and the severity of 

potential effects. Commenters also note 

that since adaption is one of the likely 

impacts of climate change, it is 

irrational to exclude it from 

consideration when the goal is to 

evaluate the risks and harms in the real 

world in the future, not the risks and 

harms in the hypothetical scenario that 

result if you ignore adaptation. 

According to commenters, the 

Administrator must consider both 

autonomous adaptation and anticipatory 

adaptation. They contend that literature 

on adaptation makes it clear there is a 

significant potential for adaptation, and 

that it can reduce the likelihood or 

severity of various effects, including 

health effects, and could even avert 

what might otherwise constitute 

endangerment. Commenters note that 

EPA considered the adaptation of 

species in nature, and it is arbitrary to 

not also consider adaptation by humans. 

Moreover, they argue that there is great 


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certainty that adaptation will occur, and 

thus EPA is required to address it and 

make projections. They recommend that 

EPA look to historic responses to 

changes in conditions as an analogue in 

making projections, recognizing that life 

in the United States is likely to be quite 

different 50 or 100 years from now, 

irrespective of climate change. 

Commenters argue that adaption 

needs to be considered because it is 

central to the statutory requirements 

governing the endangerment inquiry. 

EPA is charged to determine the type 

and extent of harms that are likely to 

occur, and they argue that this can not 

rationally be considered without 

considering adaptation. Since some 

degree of adaptation is likely to occur, 

they continue that such a projection of 

future actual conditions requires 

consideration of adaption to evaluate 

whether the future conditions amount to 

endangerment from the air pollution. 

According to commenters, the issue 

therefore is focused on human and 

societal adaptation, which can come in 

a wide variety of forms, ranging from 

changes in personal behavioral patterns 

to expenditures of resources to change 

infrastructure, such as building and 

maintaining barriers to protect against 

sea level rise. 

With regard to mitigation, 

commenters argue that EPA should 

consider mitigation strategies and their 

potential to alleviate harm from 

greenhouse gas emissions. They contend 

that it is unreasonable for EPA to 

assume that society will not undertake 

mitigation. 

Section 202(a) of the CAA reflects the 

basic approach of many CAA sections— 

the threshold inquiry is whether the 

endangerment and cause or contribute 

criteria are satisfied, and only if they are 

met do the criteria for regulatory action 

go into effect. This reflects the basic 

separation of two different decisions—is 

this a health and welfare problem that 

should be addressed, and if so what are 

the appropriate mechanisms to address 

it? There is a division between 

identifying the health and welfare 

problem associated with the air 

pollution, and identifying the 

mechanisms used to address or solve 

the problem. 

In evaluating endangerment, EPA is 

determining whether the risks to health 

and welfare from the air pollution 

amount to endangerment. As 

commenters recognize, that calls for 

evaluating and projecting the nature and 

types of risks from the air pollution, 

including the probability or likelihood 

of the occurrence of an impact and the 

degree of adversity (or benefit) of such 

an impact. This issue focuses on how 

EPA makes such an evaluation in 

determining endangerment—does EPA 

look at the risks assuming no planned 

adaptation and/or mitigation, although 

EPA projects some degree is likely to 

occur, or does EPA look at the risks 

remaining after some projection of 

adaptation and/or mitigation? 

These two approaches reflect different 

views of the core question EPA is trying 

to answer. The first approach most 

clearly focuses on just the air pollution 

and its impacts, and aims to separate 

this from the human and societal 

responses that may or should be taken 

in response to the risks from the air 

pollution. By its nature, this separation 

means this approach may not reflect the 

actual conditions in the real world in 

the future, because adaptation and/or 

mitigation may occur and change the 

risks. For example, adaptation would 

not change the atmospheric 

concentrations, or the likelihood or 

probability of various impacts occurring 

(e.g., it would not change the degree of 

sea level rise), but adaptation has the 

potential to reduce the adversity of the 

effects that do occur from these impacts. 

Mitigation could reduce the 

atmospheric concentrations that would 

otherwise occur, having the potential to 

reduce the likelihood or probability of 

various impacts occurring. Under this 

approach, the evaluation of risk is 

focused on the risk if we do not address 

the problem. It does not answer the 

question of how much risk we project 

will remain after we do address the 

problem, through either adaptation or 

mitigation or some combination of the 

two. 

The second approach, suggested by 

commenters, would call for EPA to 

project into the future adaptation and/ 

or mitigation, and the effect of these 

measures in reducing the risks to health 

or welfare from the air pollution. 

Commenters argue this will better 

reflect likely real world conditions, and 

therefore is needed to allow for an 

appropriate determination of whether 

EPA should, at this time, make an 

affirmative endangerment finding. 

However, this approach would not 

separate the air pollution and its 

impacts from the human and societal 

responses to the air pollution. It would 

intentionally and inextricably 

intertwine them. It would inexorably 

change the focus from how serious is 

the air pollution problem we need to 

address to how good a job are people 

and society likely to do in addressing or 

solving the problem. In addition it 

would dramatically increase the 

complexity of the issues before EPA. 

The context for this endangerment 

finding is a time span of several decades 

into the future. It involves a wide 

variety of differing health and welfare 

effects, and almost every sector in our 

society. This somewhat unique context 

tends to amplify the differences between 

the two different approaches. It also 

means that it is hard to cleanly 

implement either approach. For 

example, it is hard under the first 

approach to clearly separate impacts 

with and without adaption, given the 

nature of the scientific studies and 

information before us. Under the second 

approach it would be extremely hard to 

make a reasoned projection of human 

and societal adaptation and mitigation 

responses, because these are basically 

not scientific or technical judgments, 

but are largely political judgments for 

society or individual personal 

judgments. 

However, the context for this 

endangerment finding does not change 

the fact that at their core the two 

different approaches are aimed at 

answering different questions. The first 

approach is focused on answering the 

question of what are the risks to public 

health and welfare from the air 

pollution if we do not take action to 

address it. The second approach is 

focused on answering the question of 

how much risk will remain assuming 

some projection of how people and 

society will respond. 

EPA believes that it is appropriate and 

reasonable to interpret CAA section 

202(a) as calling for the first approach. 

The structure of CAA section 202(a) and 

the various other similar provisions 

indicate an intention by Congress to 

separate the question of what is the 

problem we need to address from the 

question of what is the appropriate way 

to address it. The first approach is 

clearly more consistent with this 

statutory structure. The amount of 

reduction in risk that might be achieved 

through adaptation and/or mitigation is 

closely related to the way to address a 

problem, and is not focused on what is 

the problem that needs to be addressed. 

It helps gauge the likelihood of success 

in addressing a problem, and how good 

a job society may do in reducing risk; 

it is not at all as useful in determining 

the severity of the problem that needs to 

be addressed. 

The endangerment issue at its core is 

a decision on whether there is a risk to 

health and welfare that needs to be 

addressed, and the second approach 

would tend to indicate that the more 

likely a society is to solve a problem, the 

less likely there is a problem that needs 

to be addressed. This would mask the 

issue and provide a directionally wrong 

signal. Assume two different situations, 

both presenting the same serious risks to 


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public health or welfare without 

consideration of adaptation or 

mitigation. The more successful society 

is projected to be in solving the serious 

problem in the future would mean the 

less likely we would be to make an 

endangerment finding at the inception 

identifying it as a problem that needs to 

be addressed. This is much less 

consistent with the logic embodied in 

CAA section 202(a), which separates the 

issue of whether there is a problem from 

the issue of what can be done to 

successfully address it. 

In addition, the second approach 

would dramatically increase the 

complexity of the issues to resolve, and 

would do this by bringing in issues that 

are not the subject of the kind of 

scientific or technical judgments that 

Congress envisioned for the 

endangerment test. The legislative 

history indicates Congress was focused 

on issues of science and medicine, 

including issues at the frontiers of these 

fields. It referred to data, research 

resources, science and medicine, 

chemistry, biology, and statistics. There 

is no indication Congress envisioned 

exercising judgment on the very 

different types of issues involved in 

projecting the political actions likely to 

be taken by various local, State, and 

Federal governments, or judgments on 

the business or other decisions that are 

likely to be made by companies or other 

organizations, or the changes in 

personal behavior that may be 

occasioned by the adverse impacts of air 

pollution. The second approach would 

take EPA far away from the kind of 

judgments Congress envisioned for the 

endangerment test. 

D. Geographic Scope of Impacts 

It is the Administrator’s view that the 

primary focus of the vulnerability, risk, 

and impact assessment is the United 

States. As described in Section IV of 

these Findings, the Administrator gives 

some consideration to climate change 

effects in world regions outside of the 

United States. Given the global nature of 

climate change, she has also examined 

potential impacts in other regions of the 

world. Greenhouse gases, once emitted, 

become well mixed in the atmosphere, 

meaning U.S. emissions can affect not 

only the U.S. population and 

environment, but other regions of the 

world as well. Likewise, emissions in 

other countries can affect the United 

States. Furthermore, impacts in other 

regions of the world may have 

consequences that in turn raise 

humanitarian, trade, and national 

security concerns for the United States. 

Commenters argue that EPA does not 

have the authority to consider 

international effects. They contend that 

the burden is on EPA is to show 

endangerment based on impacts in the 

United States. They note that EPA 

proposed this approach, which is the 

only relevant issue for EPA. The 

purpose of CAA section 202(a), as the 

stated purpose of the CAA, commenters 

note, is to protect the quality of the 

nation’s air resources and to protect the 

health and welfare of the U.S. 

population. Thus, they continue, 

international public health and welfare 

are not listed or stated, and are not 

encompassed by these provisions. 

Moreover, they argue that Congress 

addressed international impacts 

expressly in two other provisions of the 

CAA. They note that under CAA section 

115, EPA considers emissions of 

pollutants that cause or contribute to air 

pollution that is reasonably anticipated 

to endanger public health or welfare in 

a foreign country, and that CAA section 

179B addresses emissions of air 

pollutants in foreign countries that 

interfere with attainment of a National 

Ambient Air Quality Standards 

(NAAQS) in the United States. Because 

Congress intentionally addressed 

international impacts in those 

provision, commenters argue that the 

absence of this direction in CAA section 

202(a) means that EPA is not to consider 

international effects when assessing 

endangerment under this provision. 

Commenters fail to recognize that 

EPA’s consideration of international 

effects is directed at evaluating their 

impact on the public health and welfare 

of the U.S. population. EPA is not 

considering international effects to 

determine whether the health and 

welfare of the public in a foreign 

country is endangered. Instead, EPA’s 

consideration of international effects for 

purposes of determining endangerment 

is limited to how those international 

effects impact the health and welfare of 

the U.S. population. 

The Administrator looked first at 

impacts in the United States itself, and 

determined that these impacts are 

reasonably anticipated to endanger the 

public health and the welfare of the U.S. 

population. That remains the 

Administrator’s position, and by itself 

supports her determination of 

endangerment. The Administrator also 

considered the effects of global climate 

change outside the borders of the United 

States and evaluated them to determine 

whether these international effects 

impact the U.S. population, and if so 

whether it impacts the U.S. population 

in a manner that supports or does not 

support endangerment to the health and 

welfare of the U.S. public. She is not 

evaluating international effects to 

determine whether populations in a 

foreign country are endangered. The 

Administrator is looking at international 

effects solely for the purpose of 

evaluating their effects on the U.S. 

population. 

For example, the U.S. population can 

be impacted by effects in other 

countries. These international effects 

can impact U.S. economic, trade, and 

humanitarian and national security 

interests. These would be potential 

effects on the U.S. population, brought 

about by the effects of climate change 

occurring outside the United States. It is 

fully reasonable and rational to expect 

that events occurring outside our 

borders can affect the U.S. population. 

Thus, commenters misunderstand the 

role that international effects played in 

the proposal. The Administrator is not 

evaluating the impact of international 

effects on populations outside the 

United States; she is considering what 

impact these international effects could 

have on the U.S. population. That is 

fully consistent with the CAA’s stated 

purpose of protecting the health and 

welfare of this nation’s population. 

E. Temporal Scope of Impacts 

An additional parameter of the 

endangerment analysis is the timeframe. 

The Administrator’s view is that the 

timeframe over which vulnerabilities, 

risks, and impacts are considered 

should be consistent with the timeframe 

over which greenhouse gases, once 

emitted, have an effect on climate. Thus 

the relevant time frame is decades to 

centuries for the primary greenhouse 

gases of concern. Therefore, in addition 

to reviewing recent observations, the 

underlying science upon which the 

Administrator is basing her findings 

generally considers the next several 

decades—the time period out to around 

2100, and for certain impacts, the time 

period beyond 2100. How the 

accumulation of atmospheric 

greenhouse gases and resultant climate 

change may affect current and future 

generations is discussed in section IV in 

these Findings. By current generations 

we mean a near-term time frame of 

approximately the next 10 to 20 years; 

by future generations we mean a longerterm time frame extending beyond that. 

Some public comments were received 

that questioned making an 

endangerment finding based on current 

conditions, while others questioned 

EPA’s ability to make an endangerment 

finding based on future projected 

conditions. Some of these comments are 

likewise addressed in Section IV in 

these Findings; and all comments on 

these temporal issues are addressed in 

the Response to Comments document. 


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F. Impacts of Potential Future 

Regulations and Processes That 

Generate Greenhouse Gas Emissions 

This action is a stand-alone set of 

findings regarding endangerment and 

cause or contribute for greenhouse gases 

under CAA section 202(a), and does not 

contain any regulatory requirements. 

Therefore, this action does not attempt 

to assess the impacts of any future 

regulation. Although EPA would 

evaluate any future proposed regulation, 

many commenters argue that such a 

regulatory analysis should be part of the 

endangerment analysis. 

Numerous commenters argue that 

EPA must fully consider the adverse 

and beneficial impacts of regulation 

together with the impacts of inaction, 

and describe this balancing as ‘‘risk-risk 

analysis,’’ ‘‘health-health analysis,’’ and 

most predominantly ‘‘risk tradeoff 

analysis.’’ Commenters argue that EPA’s 

final endangerment finding would be 

arbitrary unless EPA undertakes this 

type of risk trade-off analysis. 

Commenters specifically argue that 

EPA must consider the economic impact 

of regulation, including the Prevention 

of Significant Deterioration (PSD) 

permitting program for major stationary 

sources because it is triggered by a CAA 

section 202(a) standard, when assessing 

whether there is endangerment to public 

welfare. In other words, they argue that 

the Administrator should determine if 

finding endangerment and regulating 

greenhouse gases under the CAA would 

be worse for public health and welfare 

than not regulating. Commenters also 

argue that the reference to ‘‘public’’ 

health or welfare in CAA section 202, as 

well as the fact that impacts on the 

economy should be considered impacts 

to welfare, especially requires EPA to 

consider the full range of possible 

impacts of regulation. Commenters 

provide various predictions regarding 

how regulating greenhouse gases under 

the CAA more broadly will impact the 

public, industry, states the overall 

economy, and thus, they conclude, 

public health and welfare. Examples of 

commenters’ predictions include 

potential adverse impacts on (1) the 

housing industry and the availability of 

affordable housing, (2) jobs and income 

due to industry moving overseas, (3) the 

agriculture industry and its ability to 

provide affordable food, and (4) the 

nation’s energy supply. They also cite to 

the letter from the Office of Management 

and Budget provided with the ANPR, as 

well as interagency comments on the 

draft Proposed Findings, in support of 

their argument. 

At least one commenter argues that 

EPA fails to discuss the public health or 

welfare benefits of the processes that 

produce the emissions. The commenter 

contends that for purposes of CAA 

section 202(a), this process would be the 

combustion of gasoline or other 

transportation fuel in new motor 

vehicles, and that for purposes of other 

CAA provisions with similar 

endangerment finding triggers, the 

processes would be the combustion of 

fossil fuel for electric generation and 

other activities. The commenter 

continues that EPA’s decision to limit 

its analysis to the perceived detrimental 

aspects of emissions after they enter the 

atmosphere—as opposed to the possible 

positive aspects of emissions because of 

the processes that create the 

emissions—is based on EPA’s overly 

narrow interpretation of both the 

meaning of the term ‘‘emission’’ in CAA 

section 202(a) (and therefore in other 

endangerment finding provisions) and 

the intent of these provisions. The 

commenter states that logically, it makes 

little sense to limit the definition of the 

term ‘‘emission’’ to only the ‘‘air 

pollutants’’ that are emitted. The 

commenter concludes that when EPA 

assesses whether the emission of 

greenhouse gases endanger public 

health and welfare, EPA must assess the 

dangers and benefits on both sides of 

the point where the emissions occur: in 

the atmosphere where the emissions 

lodge and, on the other side of the 

emitting stack or structure, in the 

processes that create the emissions. 

Otherwise, EPA will not be able to 

accurately assess whether the fact that 

society emits greenhouse gases is a 

benefit or a detriment. The commenter 

states that because greenhouse gas 

emissions, particularly carbon dioxide 

emissions, are so closely tied with all 

facets of modern life, a finding that 

greenhouse gas emissions endanger 

public health and welfare is akin to 

saying that modern life endangers 

public health or welfare. The 

commenter states that simply cannot be 

true because the lack of industrial 

activity that causes greenhouse gas 

emissions would pose other, almost 

certainly more serious health and 

welfare consequences. 

Finally, some commenters argue that 

the impact of regulating under CAA 

section 202(a) supports making a final, 

negative endangerment finding. These 

commenters contend that the incredible 

costs associated with using the 

inflexible regulatory structure of the 

CAA will harm public health and 

welfare, and therefore EPA should 

exercise its discretion and find that 

greenhouse gases do not endanger 

public health and welfare because once 

EPA makes an endangerment finding 

under CAA section 202(a), it will be 

forced to regulate greenhouse gases 

under a number of other sections of the 

CAA, resulting in regulatory chaos. 

At their core, these comments are not 

about whether commenters believe 

greenhouse gases may reasonably be 

anticipated to endanger public health or 

welfare, but rather about commenters’ 

dissatisfaction with the decisions that 

Congress made regarding the response 

to any endangerment finding that EPA 

makes under CAA section 202(a). These 

comments do not discuss the science of 

greenhouse gases or climate change, or 

the impacts of climate change on public 

health or welfare. Instead they muddle 

the rather straightforward scientific 

judgment about whether there may be 

endangerment by throwing the potential 

impact of responding to the danger into 

the initial question. To use an analogy, 

the question of whether the cure is 

worse than the illness is different than 

the question of whether there is an 

illness in the first place. The question of 

whether there is endangerment is like 

the question of whether there is an 

illness. Once one knows there is an 

illness, then the next question is what 

to do, if anything, in response to that 

illness. 

What these comments object to is that 

Congress has already made some 

decisions about next steps after a 

finding of endangerment, and 

commenters are displeased with the 

results. But if this is the case, 

commenters should take up their 

concerns with Congress, not EPA. EPA’s 

charge is to issue new motor vehicle 

standards under CAA section 202(a) 

applicable to emissions of air pollutants 

that cause or contribute to air pollution 

which may reasonably be anticipated to 

endanger public health or welfare. It is 

not to find that there is no 

endangerment in order to avoid issuing 

those standards, and dealing with any 

additional regulatory impact. 

Indeed, commenters’ argument would 

insert policy considerations into the 

endangerment decision, an approach 

already rejected by the Supreme Court. 

First, as discussed in Section I.B of 

these Findings, in Massachusetts v. 

EPA, the court clearly indicated that the 

Administrator’s decision must be a 

‘‘scientific judgment.’’ 549 U.S. at 534. 

She must base her decision about 

endangerment on the science, and not 

on policy considerations about the 

repercussions or impact of such a 

finding. 

Second, in considering whether the 

CAA allowed for economic 

considerations to play a role in the 

promulgation of the NAAQS, the 


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16 Indeed, some persons may argue that due to the 

similarities between setting a NAAQS and making 

an endangerment finding, EPA cannot consider the 

impacts of implementation of the statute. 

17Note that it is EPA’s current position that these 

Final Findings do not make well-mixed greenhouse 

gases ‘‘subject to regulation’’ for purposes of the 

CAA’s Prevention of Significant Deterioration (PSD) 

and title V programs. See, e.g., memorandum 

entitled ‘‘EPA’s Interpretation of Regulations that 

Determine Pollutants Covered By Federal 

Prevention of Significant Deterioration (PSD) Permit 

Program’’ (Dec. 18, 2008). While EPA is 

reconsidering this memorandum and is seeking 

public comment on the issues raised in it generally, 

including whether a final endangerment finding 

should trigger PSD, the effectiveness of the 

positions provided in the memorandum was not 

stayed pending that reconsideration. Prevention of 

Significant Deterioration (PSD): Reconsideration of 

Interpretation of Regulations That Determine 

Pollutants Covered by the Federal PSD Permit 

Program, 74 FR 515135, 51543–44 (Oct. 7, 2009). In 

addition, EPA has proposed new temporary 

thresholds for greenhouse gas emissions that define 

when PSD and title V permits are required for new 

or existing facilities. Prevention of Significant 

Deterioration and Title V Greenhouse Gas Tailoring 

Rule (74 FR 55292, October 27, 2009). The proposed 

thresholds would ‘‘tailor’’ the permit programs to 

limit which facilities would be required to obtain 

PSD and title V permits. As noted in the preamble 

for the tailoring rule proposal, EPA also intends to 

evaluate ways to streamline the process for 

identifying GHG emissions control requirements 

and issuing permits. See the Response to Comments 

Document, Volume 11, and the Tailoring Rule, for 

more information. 

Supreme Court rejected arguments that 

because many more factors than air 

pollution might affect public health, 

EPA should consider compliance costs 

that produce health losses in setting the 

NAAQS. Whitman v. ATA, 531 U.S. at 

457, 466 (2001). To be sure, the 

language in CAA section 109(b) 

applicable to the setting of a NAAQS is 

different than that in CAA section 

202(a) regarding endangerment. But the 

concepts are similar—the NAAQS are 

about setting standards at a level 

requisite to protect public health (with 

an adequate margin of safety) and public 

welfare, and endangerment is about 

whether the current or projected future 

levels may reasonably be anticipated to 

endanger public health or welfare. In 

other words, both decisions essentially 

are based on assessing the harm 

associated with a certain level of air 

pollution. 

Given this similarity in purpose, as 

well as the Court’s instructions in 

Massachusetts v. EPA that the 

Administrator should base her decision 

on the science, EPA reasonably 

interprets the statutory endangerment 

language to be analogous to setting the 

NAAQS. Therefore, it is reasonable to 

interpret the endangerment test as not 

requiring the consideration of the 

impacts of implementing the statute in 

the event of an endangerment finding as 

part of the endangerment finding 

itself.16

Moreover, EPA does not believe that 

the impact of regulation under the CAA 

as a whole, let alone that which will 

result from this particular endangerment 

finding, will lead to the panoply of 

adverse consequences that commenters 

predict. EPA has the ability to fashion 

a reasonable and common-sense 

approach to address greenhouse gas 

emissions and climate change. The 

Administrator thinks that EPA has and 

will continue to take a measured 

approach to address greenhouse gas 

emissions. For example, the Agency’s 

recent Mandatory Greenhouse Gas 

Reporting Rule focuses on only the 

largest sources of greenhouse gases in 

order to reduce the burden on smaller 

facilities.17

We also note that commenters’ 

approach also is another version of the 

argument that EPA must consider 

adaptation and mitigation in the 

endangerment determination. Just as 

EPA should consider whether 

mitigation would reduce endangerment, 

commenters argue we should consider 

whether mitigation would increase 

endangerment. But as discussed 

previously, EPA disagrees and believes 

its approach better achieves the goals of 

the statute. 

Finally, EPA simply disagrees with 

the commenter who argues that because 

we are better off now than before the 

industrial revolution, greenhouse gases 

cannot be found to endanger public 

health or welfare. As the DC Circuit 

noted in the Ethyl decision, ‘‘[m]an’s 

ability to alter his environment has 

developed far more rapidly than his 

ability to foresee with certainty the 

effects of his alterations.’’ See Ethyl 

Corp., 541 F.2d at 6. The fact that we as 

a society are better off now than 100 

years ago, and that processes that 

produce greenhouse gases are a large 

part of this improvement, does not mean 

that those processes do not have 

unintended adverse impacts. It also was 

entirely reasonable for EPA to look at 

‘‘emissions’’ as the pollution once it is 

emitted from the source into the air, and 

not also as the process that generates the 

pollution. Indeed, the definition of ‘‘air 

pollutant’’ talks in terms of substances 

‘‘emitted into or otherwise enter[ing] the 

ambient air’’ (CAA section 302(g)). It is 

entirely appropriate for EPA to consider 

only the substance being emitted as the 

air pollution or air pollutant. 

IV. The Administrator’s Finding That 

Greenhouse Gases Endanger Public 

Health and Welfare 

The Administrator finds that elevated 

concentrations of greenhouse gases in 

the atmosphere may reasonably be 

anticipated to endanger the public 

health and to endanger the public 

welfare of current and future 

generations. The Administrator is 

making this finding specifically with 

regard to six key directly-emitted, longlived and well-mixed greenhouse gases: 

Carbon dioxide, methane, nitrous oxide, 

hydrofluorocarbons, perfluorocarbons, 

and sulfur hexafluoride. The 

Administrator is making this judgment 

based on both current observations and 

projected risks and impacts into the 

future. Furthermore, the Administrator 

is basing this finding on impacts of 

climate change within the United States. 

However, the Administrator finds that 

when she considers the impacts on the 

U.S. population of risks and impacts 

occurring in other world regions, the 

case for endangerment to public health 

and welfare is only strengthened. 

A. The Air Pollution Consists of Six Key 

Greenhouse Gases 

The Administrator must define the 

scope and nature of the relevant air 

pollution for the endangerment finding 

under CAA section 202(a). In this final 

action, the Administrator finds that the 

air pollution is the combined mix of six 

key directly-emitted, long-lived and 

well-mixed greenhouse gases 

(henceforth ‘‘well-mixed greenhouse 

gases’’), which together, constitute the 

root cause of human-induced climate 

change and the resulting impacts on 

public health and welfare. These six 

greenhouse gases are carbon dioxide, 

methane, nitrous oxide, 

hydrofluorocarbons, perfluorocarbons, 

and sulfur hexafluoride. 

EPA received public comments on 

this definition of air pollution from the 

Proposed Findings, and summarizes 

responses to some of those key 

comments below; fuller responses to 

public comments can be found in EPA’s 

Response to Comments document, 

Volume 9. The Administrator 

acknowledges that other anthropogenic 

climate forcers also play a role in 

climate change. Many public comments 

either supported or opposed inclusion 

of other substances in addition to the six 

greenhouse gases for the definition of air 

pollution. EPA’s responses to those 

comments are also summarized below, 

and in volume 9 of the Response to 

Comments document. 

The Administrator explained her 

rationale for defining air pollution 

under CAA section 202(a) as the 

combined mix of the six greenhouse 

gases in the Proposed Findings. After 

review of the public comments, the 

Administrator is using the same 

definition of the air pollution in the 


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Federal Register / Vol. 74, No. 239 / Tuesday, December 15, 2009 / Rules and Regulations 66517 

18The IPCC also refers to these six GHGs as longlived. Methane has an atmospheric lifetime of 

roughly a decade. One of the most commonly used 

hydrofluorocarbons (HFC–134a) has a lifetime of 14 

years. Nitrous oxide has a lifetime of 114 years; 

sulfur hexafluoride over 3,000 years; and some 

PFCs up to 10,000 to 50,000 years. Carbon dioxide 

in the atmosphere is sometimes approximated as 

having a lifetime of roughly 100 years, but for a 

given amount of carbon dioxide emitted a better 

description is that some fraction of the atmospheric 

increase in concentration is quickly absorbed by the 

oceans and terrestrial vegetation, some fraction of 

the atmospheric increase will only slowly decrease 

over a number of years, and a small portion of the 

increase will remain for many centuries or more. 

19As summarized in EPA’s TSD, the global 

average net effect of the increase in atmospheric 

greenhouse gas concentrations, plus other human 

activities (e.g., land use change and aerosol 

emissions), on the global energy balance since 1750 

has been one of warming. This total net heating 

effect, referred to as forcing, is estimated to be +1.6 

(+0.6 to +2.4) Watts per square meter (W/m2), with 

much of the range surrounding this estimate due to 

uncertainties about the cooling and warming effects 

of aerosols. The combined radiative forcing due to 

the cumulative (i.e., 1750 to 2005) increase in 

atmospheric concentrations of CO2, CH4, and N2O 

is estimated to be +2.30 (+2.07 to +2.53) W/m2. The 

rate of increase in positive radiative forcing due to 

these three GHGs during the industrial era is very 

likely to have been unprecedented in more than 

10,000 years. 

20See section 4 of the TSD for more detailed 

information about the three global temperature 

datasets. 

final finding, for the following reasons: 

(1) These six greenhouse gas share 

common properties regarding their 

climate effects; (2) these six greenhouse 

gases have been estimated to be the 

primary cause of human-induced 

climate change, are the best understood 

drivers of climate change, and are 

expected to remain the key driver of 

future climate change; (3) these six 

greenhouse gases are the common focus 

of climate change science research and 

policy analyses and discussions; (4) 

using the combined mix of these gases 

as the definition (versus an individual 

gas-by-gas approach) is consistent with 

the science, because risks and impacts 

associated with greenhouse gas-induced 

climate change are not assessed on an 

individual gas approach; and (5) using 

the combined mix of these gases is 

consistent with past EPA practice, 

where separate substances from 

different sources, but with common 

properties, may be treated as a class 

(e.g., oxides of nitrogen). 

1. Common Physical Properties of the 

Six Greenhouse Gases 

The common physical properties 

relevant to the climate change problem 

shared by the six greenhouse gases 

include the fact that they are long-lived 

in the atmosphere. ‘‘Long-lived’’ is used 

here to mean that the gas has a lifetime 

in the atmosphere sufficient to become 

globally well mixed throughout the 

entire atmosphere, which requires a 

minimum atmospheric lifetime of about 

one year.18 Thus, this definition of air 

pollution is global in nature because the 

greenhouse gas emissions emitted from 

the United States (or from any other 

region of the world) become globally 

well mixed, such that it would not be 

meaningful to define the air pollution as 

the greenhouse gas concentrations over 

the United States as somehow being 

distinct from the greenhouse gas 

concentrations over other regions of the 

world. 

It is also well established that each of 

these gases can exert a warming effect 

on the climate by trapping in heat that 

would otherwise escape to space. These 

six gases are directly emitted as 

greenhouse gases rather than forming as 

a greenhouse gas in the atmosphere after 

emission of a pre-cursor gas. Given 

these properties, the magnitude of the 

warming effect of each of these gases is 

generally better understood than other 

climate forcing agents that do not share 

these same properties (addressed in 

more detail below). The ozone-depleting 

substances that include 

chlorofluorocarbons (CFCs) and 

hydrochlorofluorocarbons (HFCs) also 

share the same physical attributes 

discussed here, but for reasons 

discussed throughout the remainder of 

this section are not being included in 

the Administrator’s definition of air 

pollution for this finding. 

2. Evidence That the Six Greenhouse 

Gases Are the Primary Driver of Current 

and Projected Climate Change 

a. Key Observations Driven Primarily by 

the Six Greenhouse Gases 

The latest assessment of the USGCRP, 

as summarized in EPA’s TSD, confirms 

the evidence presented in the Proposed 

Findings that current atmospheric 

greenhouse gas concentrations are now 

at elevated and essentially 

unprecedented levels as a result of both 

historic and current anthropogenic 

emissions. The global atmospheric 

carbon dioxide concentration has 

increased about 38 percent from preindustrial levels to 2009, and almost all 

of the increase is due to anthropogenic 

emissions. The global atmospheric 

concentration of methane has increased 

by 149 percent since pre-industrial 

levels (through 2007); and the nitrous 

oxide concentration has increased 23 

percent (through 2007). The observed 

concentration increase in these gases 

can also be attributed primarily to 

anthropogenic emissions. The industrial 

fluorinated gases have relatively low 

concentrations, but these concentrations 

have also been increasing and are 

almost entirely anthropogenic in origin. 

Historic data show that current 

atmospheric concentrations of the two 

most important directly emitted, longlived greenhouse gases (carbon dioxide 

and methane) are well above the natural 

range of atmospheric concentrations 

compared to at least the last 650,000 

years. Atmospheric greenhouse gas 

concentrations have been increasing 

because anthropogenic emissions are 

outpacing the rate at which greenhouse 

gases are removed from the atmosphere 

by natural processes over timescales of 

decades to centuries. It also remains 

clear that these high atmospheric 

concentrations of greenhouse gases are 

the unambiguous result of human 

activities. 

Together the six well-mixed 

greenhouse gases constitute the largest 

anthropogenic driver of climate 

change.19 Of the total anthropogenic 

heating effect caused by the 

accumulation of the six well-mixed 

greenhouse gases plus other warming 

agents (that do not meet all of the 

Administrator’s criteria that pertain to 

the six greenhouse gases) since preindustrial times, the combined heating 

effect of the six well-mixed greenhouses 

is responsible for roughly 75 percent, 

and it is expected that this share may 

grow larger over time, as discussed 

below. 

Warming of the climate system is 

unequivocal, as is now evident from 

observations of increases in global 

average air and ocean temperatures, 

widespread melting of snow and ice, 

and rising global average sea level. 

Global mean surface temperatures have 

risen by 0.74 °C (1.3 °F) (±0.18 °C) over 

the last 100 years. Eight of the 10 

warmest years on record have occurred 

since 2001. Global mean surface 

temperature was higher during the last 

few decades of the 20th century than 

during any comparable period during 

the preceding four centuries. 

The global surface temperature record 

relies on three major global temperature 

datasets, developed by NOAA, NASA, 

and the United Kingdom’s Hadley 

Center. All three show an unambiguous 

warming trend over the last 100 years, 

with the greatest warming occurring 

over the past 30 years.20 Furthermore, 

all three datasets show that eight of the 

10 warmest years on record have 

occurred since 2001; that the 10 

warmest years have all occurred in the 

past 12 years; and that the 20 warmest 

years have all occurred since 1981. 

Though most of the warmest years on 

record have occurred in the last decade 

in all available datasets, the rate of 

warming has, for a short time in the 


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66518 Federal Register / Vol. 74, No. 239 / Tuesday, December 15, 2009 / Rules and Regulations 

21 Karl T. et al., (2009). 

22The IPCC Fourth Assessment Report uses 

specific terminology to convey likelihood and 

confidence. Likelihood refers to a probability that 

the statement is correct or that something will 

occur. ‘‘Virtually certain’’ conveys greater than 99 

percent probability of occurrence; ‘‘very likely’’ 90 

to 99 percent; ‘‘likely’’ 66 to 90 percent. IPCC 

assigns confidence levels as to the correctness of a 

statement. ‘‘Very high confidence’’ conveys at least 

9 out of 10 chance of being correct; ‘‘high 

confidence’’ about 8 out of 10 chance; ‘‘medium 

confidence’’ about 5 out of 10 chance. The USGCRP 

uses the same or similar terminology in its reports. 

See also Box 1.2 of the TSD. Throughout this 

document, this terminology is used in conjunction 

with statements from the IPCC and USGCRP reports 

to convey the same meaning that those reports 

intended. In instances where a word such as 

‘‘likely’’ may appear outside the context of a 

specific IPCC or USGCRP statement, it is not meant 

to necessarily convey the same quantitative 

meaning as the IPCC terminology. 

23 Karl T. et al. (2009). 

Hadley Center record, slowed. However, 

the NOAA and NASA trends do not 

show the same marked slowdown for 

the 1999–2008 period. Year-to-year 

fluctuations in natural weather and 

climate patterns can produce a period 

that does not follow the long-term trend. 

Thus, each year may not necessarily be 

warmer than every year before it, though 

the long-term warming trend 

continues.21

The scientific evidence is compelling 

that elevated concentrations of heattrapping greenhouse gases are the root 

cause of recently observed climate 

change. The IPCC conclusion from 2007 

has been re-confirmed by the June 2009 

USGCRP assessment that most of the 

observed increase in global average 

temperatures since the mid-20th century 

is very likely 22 due to the observed 

increase in anthropogenic greenhouse 

gas concentrations. Climate model 

simulations suggest natural forcing 

alone (e.g., changes in solar irradiance) 

cannot explain the observed warming. 

The attribution of observed climate 

change to anthropogenic activities is 

based on multiple lines of evidence. The 

first line of evidence arises from our 

basic physical understanding of the 

effects of changing concentrations of 

greenhouse gases, natural factors, and 

other human impacts on the climate 

system. The second line of evidence 

arises from indirect, historical estimates 

of past climate changes that suggest that 

the changes in global surface 

temperature over the last several 

decades are unusual.23 The third line of 

evidence arises from the use of 

computer-based climate models to 

simulate the likely patterns of response 

of the climate system to different forcing 

mechanisms (both natural and 

anthropogenic). 

The claim that natural internal 

variability or known natural external 

forcings can explain most (more than 

half) of the observed global warming of 

the past 50 years is inconsistent with 

the vast majority of the scientific 

literature, which has been synthesized 

in several assessment reports. Based on 

analyses of widespread temperature 

increases throughout the climate system 

and changes in other climate variables, 

the IPCC has reached the following 

conclusions about external climate 

forcing: ‘‘It is extremely unlikely (<5 

percent) that the global pattern of 

warming during the past half century 

can be explained without external 

forcing, and very unlikely that it is due 

to known natural external causes alone’’ 

(Hegerl et al., 2007). With respect to 

internal variability, the IPCC reports the 

following: ‘‘The simultaneous increase 

in energy content of all the major 

components of the climate system as 

well as the magnitude and pattern of 

warming within and across the different 

components supports the conclusion 

that the cause of the [20th century] 

warming is extremely unlikely (<5 

percent) to be the result of internal 

processes’’ (Hegerl et al., 2007). As 

noted in the TSD, the observed warming 

can only be reproduced with models 

that contain both natural and 

anthropogenic forcings, and the 

warming of the past half century has 

taken place at a time when known 

natural forcing factors alone (solar 

activity and volcanoes) would likely 

have produced cooling, not warming. 

United States temperatures also 

warmed during the 20th and into the 

21st century; temperatures are now 

approximately 0.7 °C (1.3 °F) warmer 

than at the start of the 20th century, 

with an increased rate of warming over 

the past 30 years. Both the IPCC and 

CCSP reports attributed recent North 

American warming to elevated 

greenhouse gas concentrations. The 

CCSP (2008g) report finds that for North 

America, ‘‘more than half of this 

warming [for the period 1951–2006] is 

likely the result of human-caused 

greenhouse gas forcing of climate 

change.’’ 

Observations show that changes are 

occurring in the amount, intensity, 

frequency, and type of precipitation. 

Over the contiguous United States, total 

annual precipitation increased by 6.1 

percent from 1901–2008. It is likely that 

there have been increases in the number 

of heavy precipitation events within 

many land regions, even in those where 

there has been a reduction in total 

precipitation amount, consistent with a 

warming climate. 

There is strong evidence that global 

sea level gradually rose in the 20th 

century and is currently rising at an 

increased rate. It is very likely that the 

response to anthropogenic forcing 

contributed to sea level rise during the 

latter half of the 20th century. It is not 

clear whether the increasing rate of sea 

level rise is a reflection of short-term 

variability or an increase in the longerterm trend. Nearly all of the Atlantic 

Ocean shows sea level rise during the 

last 50 years with the rate of rise 

reaching a maximum (over 2 mm per 

year) in a band along the U.S. east coast 

running east-northeast. 

Satellite data since 1979 show that 

annual average Arctic sea ice extent has 

shrunk by 4.1 percent per decade. The 

size and speed of recent Arctic summer 

sea ice loss is highly anomalous relative 

to the previous few thousands of years. 

Widespread changes in extreme 

temperatures have been observed in the 

last 50 years across all world regions 

including the United States. Cold days, 

cold nights, and frost have become less 

frequent, while hot days, hot nights, and 

heat waves have become more frequent. 

Observational evidence from all 

continents and most oceans shows that 

many natural systems are being affected 

by regional climate changes, particularly 

temperature increases. However, 

directly attributing specific regional 

changes in climate to emissions of 

greenhouse gases from human activities 

is difficult, especially for precipitation. 

Ocean carbon dioxide uptake has 

lowered the average ocean pH 

(increased the acidity) level by 

approximately 0.1 since 1750. 

Consequences for marine ecosystems 

may include reduced calcification by 

shell-forming organisms, and in the 

longer term, the dissolution of carbonate 

sediments. 

Observations show that climate 

change is currently affecting U.S. 

physical and biological systems in 

significant ways. The consistency of 

these observed changes in physical and 

biological systems and the observed 

significant warming likely cannot be 

explained entirely due to natural 

variability or other confounding nonclimate factors. 

b. Key Projections Based Primarily on 

Future Scenarios of the Six Greenhouse 

Gases 

There continues to be no reason to 

expect that, without substantial and 

near-term efforts to significantly reduce 

emissions, atmospheric levels of 

greenhouse gases will not continue to 

climb, and thus lead to ever greater rates 

of climate change. Given the long 

atmospheric lifetime of the six 

greenhouse gases, which range from 

roughly a decade to centuries, future 

atmospheric greenhouse gas 


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Federal Register / Vol. 74, No. 239 / Tuesday, December 15, 2009 / Rules and Regulations 66519 

24 Due to the cumulative purpose of the statutory 

language, even if the Administrator were to look at 

the atmospheric concentration of each greenhouse 

gas individually, she would still consider the 

impact of the concentration of a single greenhouse 

gas in combination with that caused by the other 

greenhouse gases. 

25The range of uncertainty in the current 

magnitude of black carbon’s climate forcing effect 

is evidenced by the ranges presented by the IPCC 

Fourth Assessment Report (2007) and the more 

recent study by Ramanathan, V. and Carmichael, G. 

(2008) Global and regional climate changes due to 

black carbon. Nature Geoscience, 1(4): 221–227. 

concentrations for the remainder of this 

century and beyond will be influenced 

not only by future emissions but indeed 

by present-day and near-term emissions. 

Consideration of future plausible 

scenarios, and how our current 

greenhouse gas emissions essentially 

commit present and future generations 

to cope with an altered atmosphere and 

climate, reinforces the Administrator’s 

judgment that it is appropriate to define 

the combination of the six key 

greenhouse gases as the air pollution. 

Most future scenarios that assume no 

explicit greenhouse gas mitigation 

actions (beyond those already enacted) 

project increasing global greenhouse gas 

emissions over the century, which in 

turn result in climbing greenhouse gas 

concentrations. Under the range of 

future emission scenarios evaluated by 

the assessment literature, carbon 

dioxide is expected to remain the 

dominant anthropogenic greenhouse 

gas, and thus driver of climate change, 

over the course of the 21st century. In 

fact, carbon dioxide is projected to be 

the largest contributor to total radiative 

forcing in all periods and the radiative 

forcing associated with carbon dioxide 

is projected to be the fastest growing. 

For the year 2030, projections of the six 

greenhouse gases show an increase of 25 

to 90 percent compared with 2000 

emissions. Concentrations of carbon 

dioxide and the other well-mixed gases 

increase even for those scenarios where 

annual emissions toward the end of the 

century are assumed to be lower than 

current annual emissions. The radiative 

forcing associated with the non-carbon 

dioxide well-mixed greenhouse gases is 

still important and increasing over time. 

Emissions of the ozone-depleting 

substances are projected to continue 

decreasing due to the phase-out 

schedule under the Montreal Protocol 

on Substances that Deplete the Ozone 

Layer. Considerable uncertainties 

surround the estimates and future 

projections of anthropogenic aerosols; 

future atmospheric concentrations of 

aerosols, and thus their respective 

heating or cooling effects, will depend 

much more on assumptions about future 

emissions because of their short 

atmospheric lifetimes compared to the 

six well-mixed greenhouse gases. 

Future warming over the course of the 

21st century, even under scenarios of 

low emissions growth, is very likely to 

be greater than observed warming over 

the past century. According to climate 

model simulations summarized by the 

IPCC, through about 2030, the global 

warming rate is affected little by the 

choice of different future emission 

scenarios. By the end of the century, 

projected average global warming 

(compared to average temperature 

around 1990) varies significantly 

depending on emissions scenario and 

climate sensitivity assumptions, ranging 

from 1.8 to 4.0 °C (3.2 to 7.2 °F), with an 

uncertainty range of 1.1 to 6.4 °C (2.0 to 

11.5 °F). 

All of the United States is very likely 

to warm during this century, and most 

areas of the United States are expected 

to warm by more than the global 

average. The largest warming is 

projected to occur in winter over 

northern parts of Alaska. In western, 

central and eastern regions of North 

America, the projected warming has less 

seasonal variation and is not as large, 

especially near the coast, consistent 

with less warming over the oceans. 

3. The Six Greenhouse Gases Are 

Currently the Common Focus of the 

Climate Change Science and Policy 

Communities 

The well-mixed greenhouse gases are 

currently the common focus of climate 

science and policy analyses and 

discussions. For example, the United 

Nations Framework Convention on 

Climate Change (UNFCCC), signed and 

ratified by the United States in 1992, 

requires its signatories to ‘‘develop, 

periodically update, publish and make 

available * * * national inventories of 

anthropogenic emissions by sources and 

removals by sinks of all greenhouse 

gases not controlled by the Montreal 

Protocol, using comparable 

methodologies * * *’’ 24 25 To date, the 

focus of UNFCCC actions and 

discussions has been on the six 

greenhouse gases that are the same focus 

of these Findings. 

Because of these common properties, 

it has also become common practice to 

compare these gases on a carbon dioxide 

equivalent basis, based on each gas’s 

warming effect relative to carbon 

dioxide (the designated reference gas) 

over a specified timeframe. For 

example, both the annual Inventory of 

U.S. Greenhouse Gases and Sinks 

published by EPA and the recently 

finalized EPA Mandatory Greenhouse 

Gas Reporting Rule (74 FR 56260), use 

the carbon dioxide equivalent metric to 

sum and compare these gases, and thus 

accept the common climate-relevant 

properties of these gases for their 

treatment as a group. This is also 

common practice internationally as the 

UNFCCC reporting guidelines for 

developed countries, and the Clean 

Development Mechanism procedures for 

developing countries both require the 

use of global warming potentials 

published by the IPCC to convert the six 

greenhouse gases into their respective 

carbon dioxide equivalent units. 

4. Defining Air Pollution as the 

Aggregate Group of Six Greenhouse 

Gases Is Consistent With Evaluation of 

Risks and Impacts Due to HumanInduced Climate Change 

Because the well-mixed greenhouse 

gases are collectively the primary driver 

of current and projected human-induced 

climate change, all current and future 

risks due to human-induced climate 

change—whether these risks are 

associated with increases in 

temperature, changes in precipitation, a 

rise in sea levels, changes in the 

frequency and intensity of weather 

events, or more directly with the 

elevated greenhouse gas concentrations 

themselves—can be associated with this 

definition of air pollution. 

5. Defining the Air Pollution as the 

Aggregate Group of Six Greenhouse 

Gases Is Consistent With Past EPA 

Practice 

Treating the air pollution as the 

aggregate of the well-mixed greenhouse 

gases is consistent with other provisions 

of the CAA and previous EPA practice 

under the CAA, where separate 

emissions from different sources but 

with common properties may be treated 

as a class (e.g., particulate matter (PM)). 

This approach addresses the total, 

cumulative effect that the elevated 

concentrations of the six well-mixed 

greenhouse gases have on climate, and 

thus on different elements of health, 

society and the environment.24

EPA treats, for example, PM as a 

common class of air pollution; PM is a 

complex mixture of extremely small 

particles and liquid droplets. Particle 

pollution is made up of a number of 

components, including acids (such as 

nitrates and sulfates), organic chemicals, 

metals, and soil or dust particles. 

6. Other Climate Forcers Not Being 

Included in the Definition of Air 

Pollution for This Finding 

Though the well-mixed greenhouse 

gases that make up the definition of air 

pollution for purposes of making the 

endangerment decision under CAA 

section 202(a) constitute the primary 


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66520 Federal Register / Vol. 74, No. 239 / Tuesday, December 15, 2009 / Rules and Regulations 

26UNFCCC, Art. 4.1(b). 

driver of human-induced climate 

change, there are other substances 

emitted from human activities that 

contribute to climate change and 

deserve careful attention, but are not 

being included in the air pollution 

definition for this particular action. 

These substances are discussed 

immediately below. 

a. Black Carbon 

Several commenters request that black 

carbon be included in the definition of 

air pollution because of its warming 

effect on the climate. Black carbon is not 

a greenhouse gas, rather, it is an aerosol 

particle that results from the incomplete 

combustion of carbon contained in 

fossil fuels and biomass, and remains in 

the atmosphere for only about a week. 

Unlike any of the greenhouse gases 

being addressed by this action, black 

carbon is a component of particulate 

matter (PM), where PM is a criteria air 

pollutant under section 108 of the CAA. 

The extent to which black carbon makes 

up total PM varies by emission source, 

where, for example, diesel vehicle PM 

emissions contain a higher fraction of 

black carbon compared to most other 

PM emission sources. Black carbon 

causes a warming effect primarily by 

absorbing incoming and reflected 

sunlight (whereas greenhouse gases 

cause warming by trapping outgoing, 

infrared heat), and by darkening bright 

surfaces such as snow and ice, which 

reduces reflectivity. This latter effect, in 

particular, has been raising concerns 

about the role black carbon may be 

playing in observed warming and ice 

melt in the Arctic. 

As stated in the April 2009 Proposed 

Findings, there remain some significant 

scientific uncertainties about black 

carbon’s total climate effect,25 as well as 

concerns about how to treat the shortlived black carbon emissions alongside 

the long-lived, well-mixed greenhouse 

gases in a common framework (e.g., 

what are the appropriate metrics to 

compare the warming and/or climate 

effects of the different substances, given 

that, unlike greenhouse gases, the 

magnitude of aerosol effects can vary 

immensely with location and season of 

emissions). Nevertheless, the 

Administrator recognizes that black 

carbon is an important climate forcing 

agent and takes very seriously the 

emerging science on black carbon’s 

contribution to global climate change in 

general and the high rates of observed 

climate change in the Arctic in 

particular. As noted in the Proposed 

Findings, EPA has various pending 

petitions under the CAA calling on the 

Agency to make an endangerment 

finding and regulate black carbon 

emissions. 

b. Other Climate Forcers 

There are other climate forcers that 

play a role in human-induced climate 

change that were mentioned in the 

Proposed Findings, and were the subject 

of some public comments. These 

include the stratospheric ozonedepleting substances, nitrogen 

trifluoride (NF3), water vapor, and 

tropospheric ozone. 

As mentioned above, the ozonedepleting substances (CFCs and HCFCs) 

do share the same physical, climaterelevant attributes as the six well-mixed 

greenhouse gases; however, emissions of 

these substances are playing a 

diminishing role in human-induced 

climate change. They are being 

controlled and phased out under the 

Montreal Protocol on Substances that 

Deplete the Ozone Layer. Because of 

this, the major scientific assessment 

reports such as those from IPCC focus 

primarily on the same six well-mixed 

greenhouse gases included in the 

definition of air pollution in these 

Findings. It is also worth noting that the 

UNFCCC, to which the United States is 

a signatory, addresses ‘‘all greenhouse 

gases not controlled by the Montreal 

Protocol.’’ 26 One commenter noted that 

because the Montreal Protocol controls 

production and consumption of ozonedepleting substances, but not existing 

banks of the substances, that CFCs 

should be included in the definition of 

air pollution in this finding, which 

might, in turn, create some future action 

under the CAA to address the banks of 

ozone-depleting substances as a climate 

issue. However, the primary criteria for 

defining the air pollution in this finding 

is the focus on the core of the climate 

change problem, and concerns over 

future actions to control depletion of 

stratospheric ozone are separate from 

and not central to the air pollution 

causing climate change. 

Nitrogen trifluoride also shares the 

same climate-relevant attributes as the 

six well-mixed greenhouse gases, and it 

is also included in EPA’s Mandatory 

Greenhouse Gas Reporting Rule (FR 74 

56260). However, the Administrator is 

maintaining the reasoning laid out in 

the Proposed Findings to not include 

NF3 in the definition of air pollution for 

this finding because the overall 

magnitude of its forcing effect on 

climate is not yet well quantified. EPA 

will continue to track the science on 

NF3. 

A number of public comments 

question the exclusion of water vapor 

from the definition of air pollution 

because it is the most important 

greenhouse gas responsible for the 

natural, background greenhouse effect. 

The Administrator’s reasoning for 

excluding water vapor, was described in 

the Proposed Findings and is 

summarized here with additional 

information in Volume 10 of the 

Response to Comments document. First, 

climate change is being driven by the 

buildup in the atmosphere of 

greenhouse gases. The direct emissions 

primarily responsible for this are the six 

well-mixed greenhouse gases. Direct 

anthropogenic emissions of water vapor, 

in general, have a negligible effect and 

are thus not considered a primary driver 

of human-induced climate change. EPA 

plans to further evaluate the issues of 

emissions of water that are implicated 

in the formation of contrails and also 

changes in water vapor due to local 

irrigation. At this time, however, the 

findings of the IPCC state that the total 

forcing from these sources is small and 

that the level of understanding is low. 

Water produced as a byproduct of 

combustion at low altitudes has a 

negligible contribution to climate 

change. The residence time of water 

vapor is very short (days) and the water 

content of the air in the long term is a 

function of temperature and partial 

pressure, with emissions playing no 

role. Additionally, the radiative forcing 

of a given mass of water at low altitudes 

is much less than the same mass of 

carbon dioxide. Water produced at 

higher altitudes could potentially have 

a larger impact. The IPCC estimated the 

contribution of changes in stratospheric 

water vapor due to methane and other 

sources, as well as high altitude 

contributions from contrails, but 

concluded that both contributions were 

small, with a low level of 

understanding. The report also 

addressed anthropogenic contributions 

to water vapor arising from large scale 

irrigation, but assigned it a very low 

level of understanding, and suggested 

that the cooling from evaporation might 

outweigh the warming from its small 

radiative contribution. 

Increases in tropospheric ozone 

concentrations have exerted a 

significant anthropogenic warming 

effect since pre-industrial times. 

However, as explained in the Proposed 

Findings, tropospheric ozone is not a 

long-lived, well-mixed greenhouse gas, 

and it is not directly emitted. Rather it 

forms in the atmosphere from emissions 

of pre-cursor gases. There is increasing 

attention in climate change research and 

the policy community about the extent 

to which further reductions in 

tropospheric ozone levels may help 


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slow down climate change in the near 

term. The Administrator views this 

issue seriously but maintains that 

tropospheric ozone is sufficiently 

different such that it deserves an 

evaluation and treatment separate from 

this finding. 

7. Summary of Key Comments on 

Definition of Air Pollution 

a. It Is Reasonable for the Administrator 

To Define the Air Pollution as Global 

Concentrations of the Well-Mixed 

Greenhouse Gases 

Many commenters argue that EPA 

does not have the authority to establish 

domestic rights and obligations based 

on environmental conditions that are 

largely attributed to foreign nations and 

entities that are outside the jurisdiction 

of EPA under the CAA. They contend 

that in this case, the bulk of emissions 

that would lead to mandatory emissions 

controls under the CAA would not and 

could not be regulated under the CAA. 

They state that CAA requirements 

cannot be enforced against foreign 

sources of air pollution, and likewise 

domestic obligations under the CAA 

cannot be caused by foreign emissions 

that are outside the United States. The 

commenters argue that EPA committed 

procedural error by not addressing this 

legal issue of authority in the proposal. 

Commenters cite no statutory text or 

judicial authority for this argument, and 

instead rely entirely on an analogy to 

the issues concerning the exercise of 

extra-territorial jurisdiction. The text of 

CAA section 202(a), however, does not 

support this claim. Nothing in CAA 

section 202(a) limits the term air 

pollution to those air pollution matters 

that are caused solely or in large part by 

domestic emissions. The only issue 

under CAA section 202(a) is whether 

the air pollution is reasonably 

anticipated to endanger, and whether 

emissions from one domestic source 

category—new motor vehicles—cause or 

contribute to this air pollution. 

Commenters would read into this an 

additional cause or contribute test— 

whether foreign sources cause or 

contribute to the air pollution in such a 

way that the air pollution is largely 

attributable to the foreign emissions, or 

the bulk of emissions causing the air 

pollution are from foreign sources. 

There is no such provision in CAA 

section 202(a). Congress was explicit 

about the contribution test it imposed, 

and the only source that is relevant for 

purposes of contribution is new motor 

vehicles. Commenters suggest an illdefined criterion that is not in the 

statute. 

In addition, as discussed in Section II 

of these Findings, Congress 

intentionally meant the agency to judge 

the air pollution endangerment criteria 

based on the ‘‘cumulative impact of all 

sources of a pollutant,’’ and not an 

incremental look at just the 

endangerment from a subset of sources. 

Commenters’ arguments appear to lead 

to this result. Under the commenters’ 

approach, in those cases where the bulk 

of emissions which form the air 

pollution come from foreign sources, 

EPA apparently would have no 

authority to make an endangerment 

finding. Logically, EPA would be left 

with the option of identifying and 

evaluating the air pollution attributable 

to domestic sources alone, and 

determining whether that narrowly 

defined form of air pollution endangers 

public health or welfare. This is the 

kind of unworkable, incremental 

approach that was rejected by the court 

in Ethyl and by Congress in the 1977 

amendments adopting this provision. 

The analogy to extra-territorial 

jurisdiction is also not appropriate. The 

endangerment finding itself does not 

exercise jurisdiction over any source, 

domestic or foreign. It is a judgment that 

is a precondition for exercising 

regulatory authority. Under CAA section 

202(a), any exercise of regulatory 

authority following from this 

endangerment finding would be for new 

motor vehicles either manufactured in 

the United States or imported into the 

United States. There would be no extraterritorial exercise of jurisdiction. The 

core issues for endangerment focus on 

impacts inside the United States, not 

outside the United States. In addition, 

the contribution finding is based solely 

on the contribution from new motor 

vehicles built in or imported to the 

United States. The core judgments that 

need to be made under CAA section 

202(a) are all focused on actions and 

impacts inside the United States. This 

does not raise any concerns about an 

extra-territorial exercise of jurisdiction. 

The basis for the endangerment and 

contribution findings is fully consistent 

with the principles underlying the 

desire to avoid exercises of extraterritorial jurisdiction. Any limitations 

on the ability to exercise control over 

foreign sources of emissions does not, 

however, call into question the 

authority under CAA section 202 to 

exercise control over domestic sources 

of emissions based on their contribution 

to an air pollution problem that is 

judged to endanger public health or 

welfare based on impacts occurring in 

the United States or otherwise affecting 

the United States and its citizens. 

In essence, commenters are concerned 

about the effectiveness of the domestic 

control strategies that can be adopted to 

address a global air pollution problem 

that is caused only in part by domestic 

sources of emissions. While that is a 

quite valid and important policy 

concern, it does not translate into a legal 

limitation on EPA’s authority to make 

an endangerment finding. Neither the 

text nor the legislative history of CAA 

section 202(a) support such an 

interpretation and Congress explicitly 

separated the decision on endangerment 

from the decision on what controls are 

required or appropriate once an 

affirmative endangerment finding has 

been made. The effectiveness of the 

resulting regulatory controls is not a 

relevant factor to determining 

endangerment. 

EPA also committed no procedural 

flaw as argued by commenters. The 

proposal fully explored the 

interpretation of endangerment and 

cause or contribution under CAA 

section 202(a), and was very clear that 

EPA was considering air pollution to 

mean the elevated global concentration 

of greenhouse gases in the atmosphere, 

recognizing that these atmospheric 

concentrations were the result of world 

wide emissions, not just or even largely 

U.S. emissions. The separation of the 

effectiveness of the control strategy from 

the endangerment criteria, and the need 

to consider the cumulative impact of all 

sources in evaluating endangerment was 

clearly discussed. Commenters received 

fair notice of EPA’s proposal and the 

basis for it. 

Similarly, some commenters argue 

that EPA’s proposal defines air 

pollution as global air pollution, but 

EPA is limited to evaluating domestic 

air only; in other words that EPA may 

only regulate domestic emissions with 

localized effects. They argue this 

limitation derives from the purpose of 

the CAA—to enhance the quality of the 

Nation’s air resources, recognizing that 

air pollution prevention and control 

focus on the sources of the emissions, 

and are the primary responsibility of 

States and local governments. Therefore, 

commenters continue, that ‘‘air 

pollution’’ has to be air pollution that 

originates domestically and is to be 

addressed only at the domestic source. 

Sections 115 and 179B of the CAA, as 

discussed below, reflect this intention 

as well. The result, they conclude, is 

that ‘‘air pollution’’ as used in CAA 

section 202(a), includes only pollution 

that originates domestically, where the 

effects occur locally. They argue EPA 

has improperly circumvented this by a 

‘‘local-global-local’’ analysis that injects 


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global air pollution into the middle of 

the endangerment test. 

The statutory arguments made by the 

commenters attempt to read an 

unrealistic limitation into the general 

provisions discussed. The issues are 

similar in nature to those raised by the 

commenters arguing that EPA has no 

authority to establish domestic rights 

and obligations based on environmental 

conditions that are largely attributable 

to emissions from foreign nations and 

entities that are outside the jurisdiction 

of EPA under the CAA. In both cases, 

the question is whether EPA has 

authority to make an endangerment 

finding when the air pollution of 

concern is a relatively homogenous 

atmospheric concentration of 

greenhouse gases. According to the 

commenters, although this global pool 

includes the air over the United States, 

and leads to impacts in the United 

States and on the U.S. population, 

Congress prohibited EPA from 

addressing this air pollution problem 

because of its global aspects. 

The text of the CAA does not 

specifically address this, as the term air 

pollution is not defined. EPA interprets 

this term as including the air pollution 

problem involved in this case—elevated 

atmospheric concentration of 

greenhouse gases that occur in the air 

above the United States as well as across 

the globe, and where this pool of global 

gases leads to impacts in the United 

States and on the U.S. population. This 

is fully consistent with the statutory 

provisions discussed by commenters. 

This approach seeks to protect the 

Nation’s air resources, as clearly the 

Nation’s air resources are an integral 

part of this global pool. The Nation’s air 

resources by definition are not an 

isolated atmosphere that only contains 

molecules emitted within the United 

States, or an atmosphere that bears no 

relationship to the rest of the globe’s 

atmosphere. There is no such real world 

body of air. Protecting the Nation’s 

resources of clean air means to protect 

the air in the real world, not an artificial 

construct of ‘‘air’’ that ignores the many 

situations where the air over our borders 

includes compounds and pollutants 

emitted outside our borders, and in this 

case to ignore the fact that the air over 

our borders will by definition have 

elevated concentrations of greenhouse 

gases only when the air around the 

globe also has such concentrations. The 

suggested narrow view of ‘‘air 

pollution’’ does not further the 

protection of the Nation’s air resources, 

but instead attempts to limit such 

protection by defining these resources 

in a scientifically artificial way that 

does not comport with how the air in 

the atmosphere is formed or changes 

over time, how it relates to and interacts 

with air around the globe, and how the 

result of this can affect the U.S. 

population. 

The approach suggested by 

commenters fails to provide an actual 

definition for EPA to follow—for 

example, would U.S. or domestic ‘‘air 

pollution’’ be limited to only those air 

concentrations composed of molecules 

that originated in the United States? Is 

there a degree of external gases or 

compounds that could be allowed? 

Would it ignore the interaction and 

relationship between the air over the 

U.S. borders and the air around the rest 

of the globe? The latter approach 

appears to be the one suggested by 

commenters. Commenters’ approach 

presumably would call for EPA to only 

consider the effects that derive solely 

from the air over our borders, and to 

ignore any effects that occur within the 

United States that are caused by air 

around the globe. However the air over 

the United States will by definition 

affect climate change only in 

circumstances where the air around the 

world is also doing so. The impacts of 

the air over the United States cannot be 

assessed separately from the impacts 

from the global pool, as they occur 

together and work together to affect the 

climate. Ignoring the real world nature 

of the Nation’s air resources, in the 

manner presumably suggested by the 

commenters, would involve the kind of 

unworkable, incremental, and 

artificially isolating approach that was 

rejected by the court in Ethyl and by 

Congress in 1977. Congress intended 

EPA to interpret this provision by 

looking at air pollutants and air 

pollution problems in a broad manner, 

not narrowly, to evaluate problems 

within their broader context and not to 

attempt to isolate matters in an artificial 

way that fails to account for the real 

world context that lead to health and 

welfare impacts on the public. 

Commenters’ suggested interpretation 

fails to implement this intention of 

Congress. 

Commenters in various places refer to 

the control of the pollution, and the 

need for it to be aimed at local sources. 

That is addressed in the standard setting 

portion of CAA section 202(a), as in 

other similar provisions. The 

endangerment provision does not 

address how the air pollution problem 

should be addressed—who should be 

regulated and how they should be 

regulated. The endangerment provision 

addresses a different issue—is there an 

air pollution problem that should be 

addressed? In that context, EPA rejects 

the artificially narrow interpretation 

suggested by the commenters, and 

believes its broader interpretation in 

this case is reasonable and consistent 

with the intention of Congress. 

b. Consideration of Greenhouse Gases as 

Air Pollution Given Their Impact Is 

Through Climate Rather Than Direct 

Toxic Effects 

A number of commenters argue that 

carbon dioxide and the other 

greenhouse gases should not be defined 

as the air pollution because these gases 

do not cause direct human health 

effects, such as through inhalation. 

Responses to such comments are 

summarized in Section IV.B.1 of these 

Findings in the discussion of the public 

health and welfare nature of the 

endangerment finding. 

c. The Administrator’s Reliance on the 

Global Temperature Data Is a 

Reasonable Indicator of Human-Induced 

Climate Change 

We received many comments 

suggesting global temperatures have 

stopped warming. The commenters base 

this conclusion on temperature trends 

over only the last decade. While there 

have not been strong trends over the last 

seven to ten years in global surface 

temperature or lower troposphere 

temperatures measured by satellites, 

this pause in warming should not be 

interpreted as a sign that the Earth is 

cooling or that the science supporting 

continued warming is in error. Year-toyear variability in natural weather and 

climate patterns make it impossible to 

draw any conclusions about whether the 

climate system is warming or cooling 

from such a limited analysis. Historical 

data indicate short-term trends in longterm time series occasionally run 

counter to the overall trend. All three 

major global surface temperature 

records show a continuation of longterm warming. Over the last century, the 

global average temperature has warmed 

at the rate of about 0.13 °F (0.072 °C) per 

decade in all three records. Over the last 

30 years, the global average surface 

temperature has warmed by about 0.30 

°F (0.17 °C) per decade. Eight of the 10 

warmest years on record have occurred 

since 2001 and the 20 warmest years 

have all occurred since 1981. Satellite 

measurements of the troposphere also 

indicate warming over the last 30 years 

at a rate of 0.20 to 0.27 °F (0.11 °C to 

0.15 °C) per decade. Please see the 

relevant volume of the Response to 

Comments document for more detailed 

responses. 

Some commenters indicate the global 

surface temperature records are biased 

by urbanization, poor siting of 

instruments, observation methods, and 


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27Solomon, S., D. Qin, M. Manning, R.B. Alley, 

T. Berntsen, N.L. Bindoff, Z. Chen, A. Chidthaisong, 

J.M. Gregory, G.C. Hegerl, M. Heimann, B. 

Hewitson, B.J. Hoskins, F. Joos, J. Jouzel, V. Kattsov, 

U. Lohmann, T. Matsuno, M. Molina, N. Nicholls, 

J. Overpeck, G. Raga, V. Ramaswamy, J. Ren, M. 

Rusticucci, R. Somerville, T.F. Stocker, P. Whetton, 

R.A. Wood and D. Wratt (2007) Technical 

Summary. In: Climate Change 2007: The Physical 

Science Basis. Contribution of Working Group I to 

the Fourth Assessment Report of the 

Intergovernmental Panel on Climate Change 

[Solomon, S., D. Qin, M. Manning, Z. Chen, M. 

Marquis, K.B. Averyt, M. Tignor, and H.L. Miller 

(eds.)]. Cambridge University Press, Cambridge, 

United Kingdom and New York, NY, USA. Karl, T. 

et al. (2009). 

other factors. Our review of the 

literature suggests that these biases have 

in many cases been corrected for, are 

largely random where they remain, and 

therefore cancel out over large regions. 

Furthermore, we note that though the 

three global surface temperature records 

use differing techniques to analyze 

much of the same data, they produce 

almost the same results, increasing our 

confidence in their legitimacy. The 

assessment literature has concluded that 

warming of the climate system is 

unequivocal. The warming trend that is 

evident in all of the temperature records 

is confirmed by other independent 

observations, such as the melting of 

Arctic sea ice, the retreat of mountain 

glaciers on every continent, reductions 

in the extent of snow cover, earlier 

blooming of plants in the spring, and 

increased melting of the Greenland and 

Antarctic ice sheets. Please see the 

relevant volume of the Response to 

Comments document for more detailed 

responses. 

A number of commenters argue that 

the warmth of the late 20th century is 

not unusual relative to the past 1,000 

years. They maintain temperatures were 

comparably warm during the Medieval 

Warm Period (MWP) centered around 

1000 A.D. We agree there was a 

Medieval Warm Period in many regions 

but find the evidence is insufficient to 

assess whether it was globally coherent. 

Our review of the available evidence 

suggests that Northern Hemisphere 

temperatures in the MWP were probably 

between 0.1 °C and 0.2 °C below the 

1961–1990 mean and significantly 

below the level shown by instrumental 

data after 1980. However, we note 

significant uncertainty in the 

temperature record prior to 1600 A.D. 

Please see the relevant volume of the 

Response to Comments document for 

more detailed responses. 

d. Ability To Attribute Observed 

Climate Change to Anthropogenic, WellMixed Greenhouse Gases 

Many commenters question the link 

between observed temperatures and 

anthropogenic greenhouse gas 

emissions. They suggest internal 

variability of the climate system and 

natural forcings explain observed 

temperature trends and that 

anthropogenic greenhouse gases play, at 

most, a minor role. However, the 

attribution of most of the recent 

warming to anthropogenic activities is 

based on multiple lines of evidence. The 

first line of evidence arises from our 

basic physical understanding of the 

effects of changing concentrations of 

greenhouse gases, natural factors, and 

other human impacts on the climate 

system. Greenhouse gas concentrations 

have indisputably increased and their 

radiative properties are well established. 

The second line of evidence arises from 

indirect, historical estimates of past 

climate changes that suggest that the 

changes in global surface temperature 

over the last several decades are 

unusual. The third line of evidence 

arises from the use of computer-based 

climate models to simulate the likely 

patterns of response of the climate 

system to different forcing mechanisms 

(both natural and anthropogenic). These 

models are unable to replicate the 

observed warming unless anthropogenic 

emissions of greenhouse gases are 

included in the simulations. Natural 

forcing alone cannot explain the 

observed warming. In fact, the 

assessment literature 27 indicates the 

sum of solar and volcanic forcing in the 

past half century would likely have 

produced cooling, not warming. Please 

see the relevant volume of the Response 

to Comments for more detailed 

responses. 

B. The Air Pollution Is Reasonably 

Anticipated To Endanger Both Public 

Health and Welfare 

The Administrator finds that the 

elevated atmospheric concentrations of 

the well-mixed greenhouse gases may 

reasonably be anticipated to endanger 

the public health and welfare of current 

and future generations. This section 

describes the major pieces of scientific 

evidence supporting the Administrator’s 

endangerment finding, discusses both 

the public health and welfare nature of 

the endangerment finding, and 

addresses a number of key issues the 

Administrator considered when 

evaluating the state of the science as 

well as key public comments on the 

Proposed Findings. Additional detail 

can be found in the TSD and the 

Response to Comments document. 

As described in Section II of these 

Findings, the endangerment test under 

CAA section 202(a) does not require the 

Administrator to identify a bright line, 

quantitative threshold above which a 

positive endangerment finding can be 

made. The statutory language explicitly 

calls upon the Administrator to use her 

judgment. This section describes the 

general approach used by the 

Administrator in reaching the judgment 

that a positive endangerment finding 

should be made, as well as the specific 

rationale for finding that the greenhouse 

gas air pollution may reasonably be 

anticipated to endanger both public 

health and welfare. 

First, the Administrator finds the 

scientific evidence linking human 

emissions and resulting elevated 

atmospheric concentrations of the six 

well-mixed greenhouse gases to 

observed global and regional 

temperature increases and other climate 

changes to be sufficiently robust and 

compelling. This evidence is briefly 

explained in more detail in Section V of 

these Findings. The Administrator 

recognizes that the climate change 

associated with elevated atmospheric 

concentrations of carbon dioxide and 

the other well-mixed greenhouse gases 

have the potential to affect essentially 

every aspect of human health, society 

and the natural environment. The 

Administrator is therefore not limiting 

her consideration of potential risks and 

impacts associated with human 

emissions of greenhouse gases to any 

one particular element of human health, 

sector of the economy, region of the 

country, or to any one particular aspect 

of the natural environment. Rather, the 

Administrator is basing her finding on 

the total weight of scientific evidence, 

and what the science has to say 

regarding the nature and potential 

magnitude of the risks and impacts 

across all climate-sensitive elements of 

public health and welfare, now and 

projected out into the foreseeable future. 

The Administrator has considered the 

state of the science on how human 

emissions and the resulting elevated 

atmospheric concentrations of wellmixed greenhouse gases may affect each 

of the major risk categories, i.e., those 

that are described in the TSD, which 

include human health, air quality, food 

production and agriculture, forestry, 

water resources, sea level rise and 

coastal areas, the energy sector, 

infrastructure and settlements, and 

ecosystems and wildlife. The 

Administrator understands that the 

nature and potential severity of impacts 

can vary across these different elements 

of public health and welfare, and that 

they can vary by region, as well as over 

time. 

The Administrator is therefore aware 

that, because human-induced climate 

change has the potential to be farreaching and multi-dimensional, not all 


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risks and potential impacts can be 

characterized with a uniform level of 

quantification or understanding, nor can 

they be characterized with uniform 

metrics. Given this variety in not only 

the nature and potential magnitude of 

risks and impacts, but also in our ability 

to characterize, quantify and project into 

the future such impacts, the 

Administrator must use her judgment to 

weigh the threat in each of the risk 

categories, weigh the potential benefits 

where relevant, and ultimately judge 

whether these risks and benefits, when 

viewed in total, are judged to be 

endangerment to public health and/or 

welfare. 

This has a number of implications for 

the Administrator’s approach in 

assessing the nature and magnitude of 

risk and impacts across each of the risk 

categories. First, the Administrator has 

not established a specific threshold 

metric for each category of risk and 

impacts. Also, the Administrator is not 

necessarily placing the greatest weight 

on those risks and impacts which have 

been the subject of the most study or 

quantification. 

Part of the variation in risks and 

impacts is the fact that climbing 

atmospheric concentrations of 

greenhouse gases and associated 

temperature increases can bring about 

some potential benefits to public health 

and welfare in addition to adverse risks. 

The current understanding of any 

potential benefits associated with 

human-induced climate change is 

described in the TSD and is taken into 

consideration here. The potential for 

both adverse and beneficial effects are 

considered, as well as the relative 

magnitude of such effects, to the extent 

that the relative magnitudes can be 

quantified or characterized. 

Furthermore, given the multiple ways in 

which the buildup of atmospheric 

greenhouse gases can cause effects (e.g., 

via elevated carbon dioxide 

concentrations, via temperature 

increases, via precipitation increases, 

via sea level rise, and via changes in 

extreme events), these multiple 

pathways are considered. For example, 

elevated carbon dioxide concentrations 

may be beneficial to crop yields, but 

changes in temperature and 

precipitation may be adverse and must 

also be considered. Likewise, modest 

temperature increases may have some 

public health benefits as well as harms, 

and other pathways such as changes in 

air quality and extreme events must also 

be considered. 

The Administrator has balanced and 

weighed the varying risks and effects for 

each sector. She has judged whether 

there is a pattern across the sector that 

supports or does not support an 

endangerment finding, and if so 

whether the support is of more or less 

weight. In cases where there is both a 

potential for benefits and risks of harm, 

the Administrator has balanced these 

factors by determining whether there 

appears to be any directional trend in 

the overall evidence that would support 

placing more weight on one than the 

other, taking into consideration all that 

is known about the likelihood of the 

various risks and effects and their 

seriousness. In all of these cases, the 

judgment is largely qualitative in nature, 

and is not reducible to precise metrics 

or quantification. 

Regarding the timeframe for the 

endangerment test, it is the 

Administrator’s view that both current 

and future conditions must be 

considered. The Administrator is thus 

taking the view that the endangerment 

period of analysis extend from the 

current time to the next several decades, 

and in some cases to the end of this 

century. This consideration is also 

consistent with the timeframes used in 

the underlying scientific assessments. 

The future timeframe under 

consideration is consistent with the 

atmospheric lifetime and climate effects 

of the six well-mixed greenhouse gases, 

and also with our ability to make 

reasonable and plausible projections of 

future conditions. 

The Administrator acknowledges that 

some aspects of climate change science 

and the projected impacts are more 

certain than others. Our state of 

knowledge is strongest for recently 

observed, large-scale changes. 

Uncertainty tends to increase in 

characterizing changes at smaller 

(regional) scales relative to large (global) 

scales. Uncertainty also increases as the 

temporal scales move away from 

present, either backward, but more 

importantly forward in time. 

Nonetheless, the current state of 

knowledge of observed and past climate 

changes and their causes enables 

projections of plausible future changes 

under different scenarios of 

anthropogenic forcing for a range of 

spatial and temporal scales. 

In some cases, where the level of 

sensitivity to climate of a particular 

sector has been extensively studied, 

future impacts can be quantified 

whereas in other instances only a 

qualitative description of a directional 

change, if that, may be possible. The 

inherent uncertainty in the direction, 

magnitude, and/or rate of certain future 

climate change impacts opens up the 

possibility that some changes could be 

more or less severe than expected, and 

the possibility of unanticipated 

outcomes. In some cases, low 

probability, high impact outcomes (i.e., 

known unknowns) are possibilities but 

cannot be explicitly assessed. 

1. The Air Pollution Is Reasonably 

Anticipated To Endanger Public Health 

The Administrator finds that the wellmixed greenhouse gas air pollution is 

reasonably anticipated to endanger 

public health, for both current and 

future generations. The Administrator 

finds that the public health of current 

generations is endangered and that the 

threat to public health for both current 

and future generations will likely mount 

over time as greenhouse gases continue 

to accumulate in the atmosphere and 

result in ever greater rates of climate 

change. 

After review of public comments, the 

Administrator continues to believe that 

climate change can increase the risk of 

morbidity and mortality and that these 

public health impacts can and should be 

considered when determining 

endangerment to public health under 

CAA section 202(a). As described in 

Section IV.B.1 of these Findings, the 

Administrator is not limited to only 

considering whether there are any direct 

health effects such as respiratory or 

toxic effects associated with exposure to 

greenhouse gases. 

In making this public health finding, 

the Administrator considered direct 

temperature effects, air quality effects, 

the potential for changes in vector-borne 

diseases, and the potential for changes 

in the severity and frequency of extreme 

weather events. In addition, the 

Administrator considered whether and 

how susceptible populations may be 

particularly at risk. The current state of 

science on these effects from the major 

assessment reports is described in 

greater detail in the TSD, and our 

responses to public comments are 

provided in the Response to Comments 

Documents. 

a. Direct Temperature Effects 

It has been estimated that unusually 

hot days and heat waves are becoming 

more frequent, and that unusually cold 

days are becoming less frequent, as 

noted above. Heat is already the leading 

cause of weather-related deaths in the 

United States. In the future, severe heat 

waves are projected to intensify in 

magnitude and duration over the 

portions of the United States where 

these events already occur. Heat waves 

are associated with marked short-term 

increases in mortality. Hot temperatures 

have also been associated with 

increased morbidity. The projected 

warming is therefore projected to 

increase heat related mortality and 


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28U.S. EPA (2009) Assessment of the Impacts of 

Global Change on Regional U.S. Air Quality: A 

Synthesis of Climate Change Impacts on GroundLevel Ozone. An Interim Report of the U.S. EPA 

Global Change Research Program. U.S. 

Environmental Protection Agency, Washington, DC, 

EPA/600/R–07/094. 

morbidity, especially among the elderly, 

young and frail. The populations most 

sensitive to hot temperatures are older 

adults, the chronically sick, the very 

young, city-dwellers, those taking 

medications that disrupt 

thermoregulation, the mentally ill, those 

lacking access to air conditioning, those 

working or playing outdoors, and 

socially isolated persons. As warming 

increases over time, these adverse 

effects would be expected to increase as 

the serious heat events become more 

serious. 

Increases in temperature are also 

expected to lead to some reduction in 

the risk of death related to extreme cold. 

Cold waves continue to pose health 

risks in northern latitudes in 

temperature regions where very low 

temperatures can be reached in a few 

hours and extend over long periods. 

Globally, the IPCC projects reduced 

human mortality from cold exposure 

through 2100. It is not clear whether 

reduced mortality in the United States 

from cold would be greater or less than 

increased heat-related mortality in the 

United States due to climate change. 

However, there is a risk that projections 

of cold-related deaths, and the potential 

for decreasing their numbers due to 

warmer winters, can be overestimated 

unless they take into account the effects 

of season and influenza, which is not 

strongly associated with monthly winter 

temperature. In addition, the latest 

USGCRP report refers to a study that 

analyzed daily mortality and weather 

data in 50 U.S. cities from 1989 to 2000 

and found that, on average, cold snaps 

in the United States increased death 

rates by 1.6 percent, while heat waves 

triggered a 5.7 percent increase in death 

rates. The study concludes that 

increases in heat-related mortality due 

to global warming in the United States 

are unlikely to be compensated for by 

decreases in cold-related mortality. 

b. Air Quality Effects 

Increases in regional ozone pollution 

relative to ozone levels without climate 

change are expected due to higher 

temperatures and weaker circulation in 

the United States relative to air quality 

levels without climate change. Climate 

change is expected to increase regional 

ozone pollution, with associated risks in 

respiratory illnesses and premature 

death. In addition to human health 

effects, tropospheric ozone has 

significant adverse effects on crop 

yields, pasture and forest growth, and 

species composition. The directional 

effect of climate change on ambient 

particulate matter levels remains less 

certain. 

Climate change can affect ozone by 

modifying emissions of precursors, 

atmospheric chemistry, and transport 

and removal. There is now consistent 

evidence from models and observations 

that 21st century climate change will 

worsen summertime surface ozone in 

polluted regions of North America 

compared to a future with no climate 

change. 

Modeling studies discussed in EPA’s 

Interim Assessment 28 show that 

simulated climate change causes 

increases in summertime ozone 

concentrations over substantial regions 

of the country, though this was not 

uniform, and some areas showed little 

change or decreases, though the 

decreases tend to be less pronounced 

than the increases. For those regions 

that showed climate-induced increases, 

the increase in maximum daily 8-hour 

average ozone concentration, a key 

metric for regulating U.S. air quality, 

was in the range of 2 to 8 ppb, averaged 

over the summer season. The increases 

were substantially greater than this 

during the peak pollution episodes that 

tend to occur over a number of days 

each summer. The overall effect of 

climate change was projected to 

increase ozone levels, compared to what 

would occur without this climate 

change, over broad areas of the country, 

especially on the highest ozone days 

and in the largest metropolitan areas 

with the worst ozone problems. Ozone 

decreases are projected to be less 

pronounced, and generally to be limited 

to some regions of the country with 

smaller population. 

c. Effects on Extreme Weather Events 

In addition to the direct effects of 

temperature on heat- and cold-related 

mortality, the Administrator considers 

the potential for increased deaths, 

injuries, infectious diseases, and stressrelated disorders and other adverse 

effects associated with social disruption 

and migration from more frequent 

extreme weather. The Administrator 

notes that the vulnerability to weather 

disasters depends on the attributes of 

the people at risk (including where they 

live, age, income, education, and 

disability) and on broader social and 

environmental factors (level of disaster 

preparedness, health sector responses, 

and environmental degradation). The 

IPCC finds the following with regard to 

extreme events and human health: 

Increases in the frequency of heavy 

precipitation events are associated with 

increased risk of deaths and injuries as 

well as infectious, respiratory, and skin 

diseases. Floods are low-probability, 

high-impact events that can overwhelm 

physical infrastructure, human 

resilience, and social organization. 

Flood health impacts include deaths, 

injuries, infectious diseases, 

intoxications, and mental health 

problems. 

Increases in tropical cyclone intensity 

are linked to increases in the risk of 

deaths, injuries, waterborne and food 

borne diseases, as well as post-traumatic 

stress disorders. Drowning by storm 

surge, heightened by rising sea levels 

and more intense storms (as projected 

by IPCC), is the major killer in coastal 

storms where there are large numbers of 

deaths. Flooding can cause health 

impacts including direct injuries as well 

as increased incidence of waterborne 

diseases due to pathogens such as 

Cryptosporidium and Giardia. 

d. Effects on Climate-Sensitive Diseases 

and Aeroallergens 

According to the assessment 

literature, there will likely be an 

increase in the spread of several food 

and water-borne pathogens among 

susceptible populations depending on 

the pathogens’ survival, persistence, 

habitat range and transmission under 

changing climate and environmental 

conditions. Food borne diseases show 

some relationship with temperature, 

and the range of some zoonotic disease 

carriers such as the Lyme disease 

carrying tick may increase with 

temperature. 

Climate change, including changes in 

carbon dioxide concentrations, could 

impact the production, distribution, 

dispersion and allergenicity of 

aeroallergens and the growth and 

distribution of weeds, grasses, and trees 

that produce them. These changes in 

aeroallergens and subsequent human 

exposures could affect the prevalence 

and severity of allergy symptoms. 

However, the scientific literature does 

not provide definitive data or 

conclusions on how climate change 

might impact aeroallergens and 

subsequently the prevalence of 

allergenic illnesses in the United States. 

It has generally been observed that the 

presence of elevated carbon dioxide 

concentrations and temperatures 

stimulate plants to increase 

photosynthesis, biomass, water use 

efficiency, and reproductive effort. The 

IPCC concluded that pollens are likely 

to increase with elevated temperature 

and carbon dioxide. 


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e. Summary of the Administrator’s 

Finding of Endangerment to Public 

Health 

The Administrator has considered 

how elevated concentrations of the wellmixed greenhouse gases and associated 

climate change affect public health by 

evaluating the risks associated with 

changes in air quality, increases in 

temperatures, changes in extreme 

weather events, increases in food and 

water borne pathogens, and changes in 

aeroallergens. The evidence concerning 

adverse air quality impacts provides 

strong and clear support for an 

endangerment finding. Increases in 

ambient ozone are expected to occur 

over broad areas of the country, and 

they are expected to increase serious 

adverse health effects in large 

population areas that are and may 

continue to be in nonattainment. The 

evaluation of the potential risks 

associated with increases in ozone in 

attainment areas also supports such a 

finding. 

The impact on mortality and 

morbidity associated with increases in 

average temperatures which increase the 

likelihood of heat waves also provides 

support for a public health 

endangerment finding. There are 

uncertainties over the net health 

impacts of a temperature increase due to 

decreases in cold-related mortality, but 

there is some recent evidence that 

suggests that the net impact on mortality 

is more likely to be adverse, in a context 

where heat is already the leading cause 

of weather-related deaths in the United 

States. 

The evidence concerning how humaninduced climate change may alter 

extreme weather events also clearly 

supports a finding of endangerment, 

given the serious adverse impacts that 

can result from such events and the 

increase in risk, even if small, of the 

occurrence and intensity of events such 

as hurricanes and floods. Additionally, 

public health is expected to be 

adversely affected by an increase in the 

severity of coastal storm events due to 

rising sea levels. 

There is some evidence that elevated 

carbon dioxide concentrations and 

climate changes can lead to changes in 

aeroallergens that could increase the 

potential for allergenic illnesses. The 

evidence on pathogen borne disease 

vectors provides directional support for 

an endangerment finding. The 

Administrator acknowledges the many 

uncertainties in these areas. Although 

these adverse effects, provide some 

support for an endangerment finding, 

the Administrator is not placing primary 

weight on these factors. 

Finally, the Administrator places 

weight on the fact that certain groups, 

including children, the elderly, and the 

poor, are most vulnerable to these 

climate-related health effects. 

f. Key Comments on the Finding of 

Endangerment to Public Health 

EPA received many comments on 

public health issues and the proposed 

finding of endangerment to public 

health. 

i. EPA’s Consideration of the Climate 

Impacts as Public Health Issues Is 

Reasonable 

Several commenters argue that EPA 

may only consider the health effects 

from direct exposure to pollutants in 

determining whether a pollutant 

endangers public health. The 

commenters state that EPA’s proposal 

acknowledges that there is no evidence 

that greenhouse gases directly cause 

health effects, citing 74 FR 18901. To 

support their claim that EPA can only 

consider health effects that result from 

direct exposure to a pollutant, 

commenters cite several sources, 

discussed below. 

Clean Air Act and Legislative History. 

Several commenters argue that the text 

of the CAA and the legislative history of 

the 1977 amendments demonstrate that 

Congress intended public health effects 

to relate to risks from direct exposure to 

a pollutant. They also argue that by 

considering health effects that result 

from welfare effects, EPA was 

essentially combining the two categories 

into one, contrary to the statute and 

Congressional intent. 

Commenters state that the CAA, 

including CAA section 202(a)(1), 

requires EPA to consider endangerment 

of public health separately from 

endangerment of public welfare. 

Commenters note that while the CAA 

does not provide a definition of public 

health, CAA section 302(h) addresses 

the meaning of ‘‘welfare,’’ which 

includes weather and climate. Thus, 

they argue, Congress has instructed that 

effects on weather and climate are to be 

considered as potentially endangering 

welfare—not human health. They 

continue that Congress surely knew that 

weather and climatic events such as 

flooding and heat waves could affect 

human health, but Congress nonetheless 

classified air pollutants’ effects on 

weather and climate as effects on 

welfare. 

Commenters also argue that the 

legislative history confirms that 

Congress intended for the definition of 

‘‘public health’’ to only include the 

consequences of direct human exposure 

to ambient air pollutants. They note an 

early version of section 109(b) would 

have required only a single NAAQS 

standard to protect ‘‘public health,’’ 

with the protection of ‘‘welfare’’ being a 

co-benefit of the single standard. 

Commenters note that the proponents of 

this early bill explained, ‘‘[i]n many 

cases, a level of protection of health 

would take care of the welfare 

situation’’ Sen. Hearing, Subcommittee 

on Air and Water Pollution, Comm. On 

Public Works (Mar. 17, 1970) (statement 

of Dr. Middleton, Comm’r, Nat’l Air 

Pollution Control Admin., HEW), 1970 

Leg. Hist. 1194. Commenters state that 

the Senate bill that ultimately passed 

rejected this combined standard, 

requiring separate national ambient air 

quality standards and national ambient 

air quality goals. Commenters contend 

that Congress intended that the national 

ambient air quality goals be set ‘‘to 

protect the public health and welfare 

from any known or anticipated effects 

associated with’’ air pollution, 

including the list of ‘‘welfare’’ effects 

currently found in CAA section 302(h), 

such as effects on water, vegetation, 

animals, wildlife, weather and climate. 

Commenters note the Senate Committee 

Report stated that the national ambient 

air quality standards were created to 

protect public health, while the national 

ambient air quality goals were intended 

to address broader issues because ‘‘the 

Committee also recognizes that man’s 

natural and man-made environment 

must be preserved and protected. 

Therefore, the bill provides for the 

setting of national ambient air quality 

goals at levels necessary to protect 

public health and welfare from any 

known or anticipated adverse effects of 

air pollution—including effects on soils, 

water, vegetation, man-made materials, 

animals, wildlife, visibility, climate, and 

economic values.’’ Commenters argue 

this statement is clearly the source of 

the current definition of welfare effects 

in CAA section 302(h), which also 

includes ‘‘personal comfort and well 

being.’’ They argue the Senate bill 

contemplated the NAAQS would 

include only direct health effects, while 

the goals would encompass effects on 

both the public health and welfare. 

Commenters continue that considering 

both public health effects and welfare 

effects under a combined standard, as 

the Administrator attempts to do in the 

proposed endangerment finding, would 

resurrect the combined approach to 

NAAQS that the Senate emphatically 

rejected. 

The commenters also cite language 

from the House Report in support of 

their view that Congress only intended 

that EPA consider direct health effects 


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29As discussed later, in the past EPA took the 

position that this kind of potential indirect 

beneficial impact on public health should not be 

considered when setting the primary health based 

NAAQS for ozone. This was not based on the view 

that it was not a potential public health impact, or 

that it was a public welfare impact instead of a 

public health impact. Instead EPA was interpreting 

the NAAQS standard setting provisions of section 

109, and argued that they were intended to address 

only certain public health impacts, those that were 

adverse, and were not intended to address indirect, 

beneficial public health impacts. This interpretation 

of section 109 was rejected in ATA v. EPA, 175 F.3d 

1027 (1999) reh’g granted in part and denied in 

part, 195 F.3d 4 (DC Cir. 1999). The court made it 

clear that the potential indirect beneficial impact of 

ambient ozone on public health from screening 

UVB rays needed to be considered when setting the 

NAAQS to protect public health. 

when assessing endangerment to public 

health: ‘‘By the words ‘cause or 

contribute to air pollution,’ the 

committee intends to require the 

Administrator to consider all sources of 

the contaminant which contributes to 

air pollution and to consider all sources 

of exposure to the contaminant—food, 

water, air, etc.—in determining health 

risks’’ 7 H.R. Rep. No. 95–294, at 49–50 

(1977). Commenters also cite language 

in the Senate Report: ‘‘Knowledge of the 

relationship between the exposure to 

many air pollution agents and acute and 

chronic health effects is sufficient to 

develop air quality criteria related to 

such effects’’ S. Rep. No. 91–1196, at 7 

(1970). 

The specific issue here is whether an 

effect on human health that results from 

a change in climate should be 

considered when EPA determines 

whether the air pollution of well-mixed 

greenhouse gases is reasonably 

anticipated to endanger public health. 

In this case, the air pollution has an 

effect on climate. For example the air 

pollution raises surface, air, and water 

temperatures. Among the many effects 

that flow from this is the expectation 

that there will be an increase in the risk 

of mortality and morbidity associated 

with increased intensity of heat waves. 

In addition, there is an expectation that 

there will be an increase in levels of 

ambient ozone, leading to increased risk 

of morbidity and mortality from 

exposure to ozone. All of these are 

effects on human health, and all of them 

are associated with the effect on climate 

from elevated atmospheric 

concentrations of greenhouse gases. 

None of these human health effects are 

associated with direct exposure to 

greenhouse gases. 

In the past, EPA has not had to 

resolve the issue presented here, as it 

has been clear whether the effects relate 

to public health or relate to public 

welfare, with no confusion over what 

category was at issue. In those cases 

EPA has routinely looked at what effect 

the air pollution has on people. If the 

effect on people is to their health, we 

have considered it an issue of public 

health. If the effect on people is to their 

interest in matters other than health, we 

have considered it public welfare. 

For example, there are serious health 

risks associated with inhalation of 

ozone, and they have logically been 

considered as public health issues. 

Ambient levels of ozone have also 

raised the question of indirect health 

benefits through screening of harmful 

UVB rays. EPA has also considered this 

indirect health effect of ozone to be a 

public health issue.29 Ozone pollution 

also affects people by impacting their 

interests in various vegetation through 

foliar damage to trees, reduced crop 

yield, adverse impacts on horticultural 

plants, and the like. EPA has 

consistently considered these issues 

when evaluating the public welfare 

based NAAQS standards under CAA 

section 109. 

In all of these situations the use of the 

term ‘‘public’’ has focused EPA on how 

people are affected by the air pollution. 

If the effect on people is to their health 

then we have considered it a public 

health issue. If the effect on people is to 

their interest in matters other than 

health, then we have treated it as a 

public welfare issue. 

The situation presented here is 

somewhat unique. The focus again is on 

the effect the air pollution has on 

people. Here the effect on people is to 

their health. However this effect flows 

from the change in climate and effects 

on climate are included in the definition 

of effects on welfare. That raises the 

issue of how to categorize the health 

effects—should we consider them when 

evaluating endangerment to public 

health? When we evaluate 

endangerment to public welfare? Or 

both? 

The text of the CAA does not resolve 

this question. While Congress defined 

‘‘effects on welfare,’’ it did not define 

either ‘‘public health’’ or ‘‘public 

welfare’’. In addition, the definition of 

‘‘effects on welfare’’ does not clearly 

address how to categorize health effects 

that flow from effects on soils, water, 

crops, vegetation, weather, climate, or 

any of the other factors listed in CAA 

section 302(h). It is clear that effects on 

climate are an effect on welfare, but the 

definition does not address whether 

health impacts that are caused by these 

changes in climate are also effects on 

welfare. The health effects at issue are 

not themselves effects on soils, water, 

crops, vegetation, weather, or climate. 

They are instead effects on health. They 

derive from the effects on climate, but 

they are not themselves effects on 

climate or on anything else listed in 

CAA section 302(h). So the definition of 

effects on welfare does not address 

whether an effect on health, which is 

not itself listed in CAA section 302(h), 

is also an effect on welfare if it results 

from an effect on welfare. The text of the 

CAA also does not address the issue of 

direct and indirect health effects. 

Contrary to commenters’ assertions, the 

legislative history does not address or 

resolve this issue. 

In this context, EPA is interpreting the 

endangerment provision in CAA section 

202(a) as meaning that the effects on 

peoples’ health from changes to climate 

can and should be included in EPA’s 

evaluation of whether the air pollution 

at issue endangers public health. EPA is 

not deciding whether these health 

effects also could or should be 

considered in evaluating endangerment 

to public welfare. 

The stating of the issue makes the 

answer seem straightforward. If air 

pollution causes sickness or death, then 

these health effects should be 

considered when evaluating whether 

the air pollution endangers public 

health. The term public health is 

undefined, and by itself this is an 

eminently reasonable way to interpret it. 

This focuses on the actual effect on 

people, as compared to ignoring that 

and focusing on the pathway from the 

air pollution to the effect. The question 

then becomes whether there is a valid 

basis in the CAA to take the different 

approach suggested by commenters, an 

approach contrary to the common sense 

meaning of public health. 

Notably, the term ‘‘public welfare’’ is 

undefined. While it clearly means 

something other than public health, 

there is no obvious indication whether 

Congress intended there to be a clear 

boundary between the two terms or 

whether there might be some overlap 

where some impacts could be 

considered both a public health and a 

public welfare impact. Neither the text 

nor the legislative history resolves this 

issue. Under either approach, EPA 

believes the proper interpretation is that 

these effects on health should be 

considered when evaluating 

endangerment to public health. 

If we assume Congress intended that 

effects on public welfare could not 

include effects on public health and 

vice versa, then the effects at issue here 

should most reasonably be considered 

in the public health category. 

Indisputably they are health effects, and 

the plain meaning of the term public 

health would call for their inclusion in 

that term. The term public welfare is 


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undefined. If Congress intended that 

public welfare not include matters 

included in the public health category, 

then a reasonable interpretation of this 

undefined term would include those 

effects on welfare that impact people in 

ways other than impacting their health. 

The definition of ‘‘effects on welfare’’ 

does not clearly address how to 

categorize health effects that flow from 

effects on water, soil, land, climate, or 

weather. As noted above, the definition 

does not address whether health 

impacts that are caused by these 

changes in climate are also ‘‘effects on 

welfare.’’ Certainly effects on health are 

not included in the list in CAA section 

302(h). The lack of clarity in the 

definition of effects on welfare, 

combined with the lack of definition of 

public welfare, do not warrant 

interpreting the term public health 

differently from its straightforward and 

common sense meaning. 

The inclusion of the phrase ‘‘effects 

on * * * personal comfort and wellbeing’’ as an effect on welfare supports 

this view. The term would logically 

mean something other than the different 

term public health. The term ‘‘wellbeing’’ is not defined, and generally has 

a broader and different connotation of 

positive physical, emotional, and 

mental status. The most straightforward 

meaning of this term, in a context where 

Congress used the different term public 

health in a wide variety of other 

provisions, would be to include effects 

on people that do not rise to the level 

of health effects, but otherwise impact 

their physical, emotional, and mental 

status. This gives full meaning to both 

terms. 

The term well-being is a general term, 

and in isolation arguably could include 

health effects. However there is no 

textual basis to say it would include 

some health effects but not others, as 

argued by commenters. If sickness 

impacts your well-being, then it impacts 

your well-being whether it results 

directly or indirectly from the pollution 

in the air. Nothing in CAA section 

302(h) limits the term well-being to 

indirect impacts on people, or to health 

effects that occur because of other 

welfare effects, such as climate change. 

It is listed as its own effect on welfare. 

Instead of interpreting well-being as 

including all health effects, or some 

health effects, the much more logical 

way to interpret this provision in the 

context of all of the other provisions of 

the CAA is to interpret it as meaning 

effects on people other than health 

effects. 

Thus, if Congress intended to draw a 

strict line between the two categories of 

public health and public welfare, for 

purposes of determining endangerment 

under CAA section 202(a), then EPA 

believes that its interpretation is a 

reasonable and straightforward way to 

categorize the health effects at issue 

here. This gives weight to the common 

sense meaning of the term public health, 

where the terms public health and 

public welfare are undefined and the 

definition of effects on welfare is at best 

ambiguous on this issue. 

In the alternative, if Congress did not 

intend any such bright line between 

these two categories and there could be 

an overlap, then it is also reasonable for 

EPA to include these health effects in its 

consideration of whether the air 

pollution endangers public health. 

Neither approach condenses or conflates 

the two different terms. Under either 

approach EPA’s interpretation, as 

demonstrated in this rulemaking, would 

still consider numerous and varied 

effects from climate change as 

indisputable impacts on public welfare 

and not impacts on public health. In 

addition, this interpretation will not 

change the fact that in almost all cases 

impacts on public health would not also 

be considered impacts on public 

welfare. 

Prior EPA actions. Several 

commenters argue that EPA’s decision 

to include health impacts that occur 

because of climate change is 

inconsistent with its past approach, 

which has been to treat indirect health 

effects as welfare effects. Commenters 

contend that in the latest Criteria 

Document for ozone EPA listed 

tropospheric ozone’s effects on UVBinduced human diseases, as well as its 

effects on climate change, as welfare 

effects, even though the agency 

acknowledged significant health effects 

such as sunburn and skin cancer. 

Commenters also argue that EPA listed 

‘‘risks to human health’’ from toxins 

released by algal blooms due to excess 

nitrogen as ‘‘ecological and other 

welfare effects’’ in the recent Criteria 

Document for oxides of nitrogen and 

sulfur. Finally, commenters argue that 

EPA’s proposed action was contrary to 

the Agency decision to list new 

municipal solid waste landfills as a 

source category under CAA section 111. 

Commenters state that EPA listed 

climate change as a welfare effect in that 

action, (citing 56 FR 24469). 

The Agency’s recent approach 

regarding UVB-induced health effects is 

consistent with the endangerment 

findings, and demonstrates that the 

Agency considers indirect effects on 

human health as public health issues 

rather than public welfare issues. While 

the ozone Criteria Document may have 

placed the discussion of UV–B related 

health effects among chapters on 

welfare effects, in evaluating the 

evidence presented in the Criteria 

Document for purposes of preparing the 

policy assessment document, EPA staff 

clearly viewed UVB-induced effects as 

human health effects that were relevant 

in determining the public health based 

primary NAAQS for ozone, rather than 

welfare effects, regardless of which 

chapter in the Criteria Document 

described those effects. The evaluation 

of the UVB-related evidence is 

discussed with other human health 

effects evidence. The policy assessment 

document noted that Chapter 10 of the 

Criteria Document, ‘‘provides a 

thorough analysis of the current 

understanding of the relationship 

between reducing tropospheric [ozone] 

concentrations and the potential impact 

these reductions might have on UV–B 

surface fluxes and indirectly 

contributing to increased UV–B related 

health effects.’’ See, Review of the 

National Ambient Air Quality 

Standards for Ozone: Policy Assessment 

of Scientific and Technical Information, 

p 3–36 (January 2007) (emphasis 

added). 

EPA repeated this view in the 2007 

proposed ozone NAAQS rule. In 

presenting its evaluation of the human 

health evidence for purposes of setting 

the public health based primary 

NAAQS, EPA stated: ‘‘This section also 

summarizes the uncertainty about the 

potential indirect effects on public 

health associated with changes due to 

increases in UV–B radiation exposure, 

such as UV–B radiation-related skin 

cancers, that may be associated with 

reductions in ambient levels of groundlevel [ozone], as discussed in chapter 10 

of the Criteria Document and chapter 3 

of the Staff Paper.’’ 72 FR 37818, 37827. 

See also, 72 FR 37837 (‘‘* * * the 

Criteria Document also assesses the 

potential indirect effects related to the 

presence of [ozone] in the ambient air 

by considering the role of ground-level 

[ozone] in mediating human health 

effects that may be directly attributable 

to exposure to solar ultraviolet radiation 

(UV–B).’’) 

Thus, EPA’s approach to UV–B 

related health effects clearly shows the 

Agency has treated indirect health 

effects not as welfare effects, as 

commenters suggest, but as human 

health effects that need to be evaluated 

when setting the public health based 

primary NAAQS. In this ozone NAAQS 

rulemaking, EPA did not draw a line 

between direct and indirect health 

effects for purposes of evaluating UV–B 

related health effects and the public 

health based primary NAAQS. 


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30 Karl et al. (2009). 

Similarly, the NOX/SOX criteria 

document does not establish a 

precedent that indirect human health 

effects are welfare effects. Toxic algal 

blooms themselves are a welfare effect, 

so it is not surprising a discussion of 

algal blooms appears in sections dealing 

with welfare effects. The more relevant 

question is how EPA evaluated 

information regarding human health 

risks resulting from algal blooms. In the 

case of the Criteria Document, the role 

of nitrogen in causing algal blooms was 

unclear. As a result, the Agency did not 

have occasion to evaluate any resulting 

human health effects and the Criteria 

Document does not support the view 

that EPA treats indirect health effects as 

anything other than a public health 

issue. 

Finally, EPA disagrees that its action 

here is at odds with the listing of 

municipal solid waste landfills under 

CAA section 111. In the landfills New 

Source Performance Standard (NSPS) 

EPA did not consider health effects 

resulting from climate change much less 

draw any conclusions about health 

effects from climate change being health 

or welfare effects. If anything, the 

landfills NSPS is consistent with EPA’s 

approach. In the proposed rule, EPA 

stated: ‘‘The EPA has documented many 

cases of acute injury and death caused 

by explosions and fires related to 

municipal landfill gas emissions. In 

addition to these health effects, the 

associated property damage is a welfare 

effect’’ (56 FR 24474). EPA considered 

injury and death from fires resulting 

from landfill gasses to be health effects. 

Yet the injury did not result from direct 

exposure to the pollutant (landfill gas). 

Instead, the injury resulted from the 

combustion of the pollutant—the injury 

is essentially an indirect effect of the 

pollutant. Yet, as with this action, EPA 

considered the injury as a human health 

effect. 

Case law. Several commenters argue 

that EPA’s proposed endangerment 

finding was inconsistent with NRDC v. 

EPA, 902 F.2d 962 (DC Cir 1990). 

Commenters argue that in rejecting the 

argument that EPA must consider the 

health effects of increased 

unemployment that could result from a 

more stringent primary NAAQS 

standard, the DC Circuit explained that, 

‘‘[i]t is only the health effects relating to 

pollutants in the air that EPA may 

consider.’’ Id. at 973. Several 

commenters further argue that EPA later 

relied on that holding to defend its 

decision to set a primary NAAQS for 

ozone based solely on direct health 

effects of ozone. Citing, EPA Pet’n for 

Rehearing, Am. Trucking Ass’n v. EPA, 

No. 97–1440 (DC Cir. June 28, 1999) 

(‘‘ATA I’’) (arguing that the primary 

NAAQS should be set through 

consideration of only ‘‘direct adverse 

effects on public health, and not 

indirect, allegedly beneficial effects.’’) 

The NRDC case is not contrary to 

EPA’s endangerment finding. In NRDC, 

petitioner American Iron and Steel 

Institute argued that EPA had to 

consider the costs of health 

consequences that might arise from 

increased unemployment. The court 

ruled that, ‘‘[c]onsideration of costs 

associated with alleged health risks 

from unemployment would be flatly 

inconsistent with the statute, legislative 

history and case law on this point.’’ 902 

F.2d at 973. The cases cited by the court 

in support of its decision all hold that 

EPA may not consider economic or 

technological feasibility in establishing 

a NAAQS. The NRDC decision does not 

establish a precedent that the CAA 

prohibits EPA from considering indirect 

health effects as a public health issue 

rather than a public welfare issue. 

EPA also believes reliance on the 

Agency’s petition for rehearing in noted 

above is misplaced. In that case, EPA 

did not argue that indirect beneficial 

health effects were not public health 

issues. Instead EPA argued that under 

the CAA, it did not have to consider 

such indirect beneficial health effects of 

an air pollutant when setting the health 

based primary NAAQS. EPA was 

interpreting the NAAQS standard 

setting provisions of CAA section 109, 

and argued that they were intended to 

address only certain public health 

impacts, those that were adverse, and 

were not intended to address indirect, 

beneficial public health impacts. The 

issue in the case was not whether 

indirect health effects are relevant for 

purposes of making an endangerment 

decision concerning public health, but 

rather whether EPA must consider such 

beneficial health effects in establishing 

a primary NAAQS under CAA section 

109. EPA’s interpretation of CAA 

section 109 was rejected in ATA v. EPA, 

175 F.3d at 1027 (1999) reh’g granted in 

part and denied in part, 195 F.3d at 4 

(DC Cir. 1999). The court made it clear 

that the potential indirect beneficial 

impact of ambient ozone on public 

health from screening UVB rays needed 

to be considered when setting the 

NAAQS to protect public health. As 

discussed above, EPA has done just that 

as noted above in the UV–B context. 

Moreover, as discussed in Section II of 

these Findings, EPA is doing that here 

as well (e.g., considering any benefits 

from reduced cold weather related 

deaths). 

ii. EPA’s Treatment and Balancing of 

Heat- vs. Cold-Related Public Health 

Risks Was Reasonable 

A number of public commenters 

maintain that the risk of heat waves in 

the future will be modulated by 

adaptive measures. The Administrator is 

aware of the potential benefits of 

adaptation in reducing heat-related 

morbidity and mortality and recognizes 

most heat-related deaths are 

preventable. Nonetheless, the 

Administrator notes the assessment 

literature 30 indicates heat is the leading 

weather-related killer in the United 

States even though countermeasures 

have been employed in many vulnerable 

areas. Given projections for heat waves 

of greater frequency, magnitude, and 

duration coupled with a growing 

population of older adults (among the 

most vulnerable groups to this hazard), 

the risk of adverse health outcomes from 

heat waves is expected to increase. 

Intervention and response measures 

could certainly reduce the risk, but as 

we have noted, the need to adapt 

supports an increase in risk or 

endangerment. For a general discussion 

about EPA’s treatment of adaptation see 

Section III.C of these Findings. 

Several commenters also suggest coldrelated mortality will decrease more 

than heat-related mortality will 

increase, which indicates a net 

reduction in temperature-related 

mortality. Some commenters point to 

research suggesting migration to warmer 

climates has contributed to the 

increased longevity of some Americans, 

implying climate warming will have 

benefits for health. The Administrator is 

very clear that the exact balance of how 

heat- versus cold-related mortality will 

change in the future is uncertain; 

however, the assessment literature 

points to evidence suggesting that the 

increased risk from heat would exceed 

the decreased risk from cold in a 

warming climate. The Administrator 

does not dispute research indicating the 

benefits of migration to a warmer 

climate and nor that average climate 

warming may indeed provide health 

benefits in some areas. These points are 

reflected in the TSD’s statement 

projecting less cold-related health 

effects. The Administrator considers 

these potential warming benefits 

independent of the potential negative 

effects of extreme heat events which are 

projected to increase under future 

climate change scenarios affecting 

vulnerable groups and communities. 


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31U.S. EPA (2008) National Air Quality: Status 

and Trends Through 2007. EPA–454/R–08–006, 

November 2008. 

iii. EPA Was Reasonable To Find That 

the Air Quality Impacts of Climate 

Change Contribute to the Endangerment 

of Public Health 

Several commenters suggest that air 

quality effects of climate change will be 

addressed through the CAA’s NAAQS 

process, as implemented by the State 

Implementation Plans (SIP) and national 

regulatory programs. According to these 

commenters, these programs will ensure 

no adverse impact on public health due 

to climate change. Though climate 

change may cause certain air pollutant 

ambient concentrations to increase, 

States will continue to be compelled to 

meet the standards. So, while additional 

measures may be necessary, and result 

in increased costs, these commenters 

assert that, ultimately, public health 

will be protected by the continued 

existence of the NAAQS and therefore 

no endangerment with respect to this 

particular climate change-related impact 

will occur. One commenter states that 

EPA inappropriately assigns air quality 

risk to climate change that will be 

addressed through other programs. The 

CAA provides a mechanism to meet the 

standards and additional control 

measures consistent with the CAA will 

be adopted in the future, keeping 

pollution below unhealthy levels. The 

commenters state that the fact that 

NAAQS are in place that require EPA to 

fulfill its legal obligation to prevent this 

particular form of endangerment to 

public health. 

EPA does have in place NAAQS for 

ozone, which are premised on the 

harmfulness of ozone to public health 

and welfare. These standards and their 

accompanying regulatory regime have 

helped to reduce the dangers from 

ozone in the United States. However, 

substantial challenges remain with 

respect to achieving the air quality 

protection promised by the NAAQS for 

ozone. It is the Administrator’s view 

that these challenges will be 

exacerbated by climate change. 

In addition, the control measures to 

achieve attainment with a NAAQS are a 

mitigation measure aimed at reducing 

emissions of ozone precursors. As 

discussed in Section III.C of these 

Findings, EPA is not considering the 

impacts of mitigation with respect to 

future reductions in emissions of 

greenhouse gases. For the same reasons, 

EPA is reasonably not considering 

mitigation in the form of the control 

measures that will need to be adopted 

in the future to reduce emissions of 

ozone precursors and thereby address 

the increased ambient ozone levels that 

can occur because of climate change. 

It is important to note that controls to 

meet the NAAQS are typically put in 

place only after air quality 

concentrations exceeding the standard 

are detected. Furthermore, 

implementation of controls to reduce 

ambient concentrations of pollutants 

occurs over an extended time period, 

ranging from three years to more than 

twenty years depending on the pollutant 

and the seriousness of the 

nonattainment problem. Thus, while the 

CAA provides mechanisms for 

addressing adverse health effects and 

the underlying air quality exacerbation 

over time, it will not prevent the 

adverse impacts in the interim. Given 

the serious nature of the health effects 

at issue—including respiratory and 

cardiovascular disease leading to 

hospital admissions, emergency 

department visits, and premature 

mortality—this increase in adverse 

impacts during the time before 

additional controls can be implemented 

is a serious public health concern. 

Historically, a large segment of the U.S. 

population has lived in areas exceeding 

the NAAQS, despite the CAA and its 

implementation efforts. Half of all 

Americans, 158 million people, live in 

counties where air pollution exceeds 

national health standards.31 Where 

attainment of the NAAQS is especially 

difficult, leading to delays in meeting 

attainment deadlines, the health effects 

of increased ozone due to climate 

change may be substantial. 

It is also important to note that it may 

not be possible for States and Tribes to 

plan accurately for the impacts of 

climate change in developing control 

strategies for nonattainment areas. As 

noted in the TSD and EPA’s 2009 

Interim Assessment report (IA), climate 

change is projected to lead to an 

increase in the variability of weather, 

and this may increase peak pollution 

events including increases in ozone 

exceedances. While the modeling 

studies in the IA all show significant 

future changes in meteorological 

quantities, there is also significant 

variability across the simulations in the 

spatial patterns of these future changes, 

making it difficult to select a set of 

future meteorological data for planning 

purposes. At this time, models used to 

develop plans to attain the NAAQS do 

not take potential changes in future 

meteorology into consideration. 

Inability to predict the frequency and 

magnitude of such events could lead to 

an underestimation of the controls 

needed to bring areas into attainment, 

and a prolonged period during which 

adverse health impacts continue to 

occur. 

Even in areas that meet the NAAQS 

currently, air quality may deteriorate 

sufficiently to cause adverse health 

effects for some individuals. Some atrisk individuals, for example those with 

preexisting health conditions or other 

characteristics which increase their risk 

for adverse effects upon exposure to PM 

or ozone, may experience health effects 

at levels below the standard. Current 

evidence suggests that there is no 

threshold for PM or ozone 

concentrations below which no effects 

can be observed. Therefore, increases in 

ozone or PM in locations that currently 

meet the standards would likely result 

in additional adverse health effects for 

some individuals, even though the 

pollution increase might not be 

sufficient to cause the area to be 

designated nonattainment. While the 

NAAQS is set to protect public health 

with an adequate margin of safety, it is 

recognized that in attainment areas 

there may be individuals who remain at 

greater risk from an increase in ozone 

levels. The clear risk to the public from 

ozone increases in nonattainment areas, 

in combination with the risk to some 

individuals in attainment areas, 

supports the finding that overall the 

public health is endangered by increases 

in ozone resulting from climate change. 

Finally, it is also important to note 

that not all air pollution events are 

subject to CAA controls under the 

NAAQS implementation provisions. 

‘‘Exceptional events’’ are events for 

which the normal planning and 

regulatory process established by the 

CAA is not appropriate (72 FR 13561). 

Emissions from some events, including 

some wildfires, are not reasonably 

controllable or preventable. Such 

emissions, however, can adversely 

impact public health and welfare and 

are expected to increase due to climate 

change. As described in the TSD, PM 

emissions from wildfires can contribute 

to acute and chronic illnesses of the 

respiratory system, particularly in 

children, including pneumonia, upper 

respiratory diseases, asthma and chronic 

obstructive pulmonary disease. The 

IPCC (Field et al., 2007) reported with 

very high confidence that in North 

America, disturbances like wildfires are 

increasing and are likely to intensify in 

a warmer future with drier soils and 

longer growing seasons. 

2. The Air Pollution Is Reasonably 

Anticipated to Endanger Public Welfare 

The Administrator also finds that the 

well-mixed greenhouse gas air pollution 

may reasonably be anticipated to 


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endanger public welfare, both for 

current and future generations. 

As with public health, the 

Administrator considered the multiple 

pathways in which the greenhouse gas 

air pollution and resultant climate 

change affect climate-sensitive sectors, 

and the impact this may have on public 

welfare. These sectors include food 

production and agriculture; forestry; 

water resources; sea level rise and 

coastal areas; energy, infrastructure, and 

settlements; and ecosystems and 

wildlife. The Administrator also 

considered impacts on the U.S. 

population from climate change effects 

occurring outside of the United States, 

such as national security concerns for 

the United States that may arise as a 

result of climate change impacts in 

other regions of the world. The 

Administrator examined each climatesensitive sector individually, informed 

by the summary of the scientific 

assessments contained in the TSD, and 

the full record before EPA, and weighed 

the extent to which the risks and 

impacts within each sector support or 

do not support a positive endangerment 

finding in her judgment. The 

Administer then viewed the full weight 

of evidence looking across all sectors to 

reach her decision regarding 

endangerment to public welfare. 

a. Food Production and Agriculture 

Food production and agriculture 

within the United States is a sector that 

will be affected by the combined effects 

of elevated carbon dioxide 

concentrations and associated climate 

change. The Administrator considered 

how these effects, both adverse and 

beneficial, are affecting the agricultural 

sector now and in the future, and over 

different regions of the United States, 

taking into account that different 

regions of the country specialize in 

different agricultural products with 

varying degrees of sensitivity and 

vulnerability to elevated carbon dioxide 

levels and associated climate change. 

Elevated carbon dioxide 

concentrations can have a stimulatory 

effect on grain and oilseed crop yield, as 

may modest temperature increases and 

a longer growing season that results. A 

report under the USGCRP concluded 

that, with increased carbon dioxide and 

temperature, the life cycle of grain and 

oilseed crops will likely progress more 

rapidly. However, such beneficial 

influences need to be considered in 

light of various other effects. For 

example, the literature indicates that 

elevated carbon dioxide concentrations 

may also enhance pest and weed 

growth. Pests and weeds can reduce 

crop yields, cause economic losses to 

farmers, and require management 

control options. How climate change 

(elevated carbon dioxide, increased 

temperatures, altered precipitation 

patterns, and changes in the frequency 

and intensity of extreme events) may 

affect the prevalence of pests and weeds 

is an issue of concern for food 

production and the agricultural sector. 

Research on the combined effects of 

elevated carbon dioxide and climate 

change on pests, weeds, and disease is 

still limited. In addition, higher 

temperature increases, changing 

precipitation patterns and variability, 

and any increases in ground-level ozone 

induced by higher temperatures, can 

work to counteract any direct 

stimulatory carbon dioxide effect, as 

well as lead to their own adverse 

impacts. There may be large regional 

variability in the response of food 

production and agriculture to climate 

change. 

For grain and oilseed crop yields, 

there is support for the view that in the 

near term climate change may have a 

beneficial effect, largely through 

increased temperature and increased 

carbon dioxide levels. However there 

are also factors noted above, some of 

which are less well studied and 

understood, which would tend to offset 

any near term benefit, leaving 

significant uncertainty about the actual 

magnitude of any overall benefit. The 

USGCRP report also concluded that as 

temperature rises, these crops will 

increasingly begin to experience failure, 

especially if climate variability 

increases and precipitation lessens or 

becomes more variable. 

A key uncertainty is how humaninduced climate change may affect the 

intensity and frequency of extreme 

weather events such as droughts and 

heavy storms. These events have the 

potential to have serious negative 

impact on U.S. food production and 

agriculture, but are not always taken 

into account in studies that examine 

how average conditions may change as 

a result of carbon dioxide and 

temperature increases. Changing 

precipitation patterns, in addition to 

increasing temperatures and longer 

growing seasons, can change the 

demand for irrigation requirements, 

potentially increasing irrigation 

demand. 

Another key uncertainty concerns the 

many horticultural crops (e.g., tomatoes, 

onions, fruits), which make up roughly 

40 percent of total crop value in the 

United States. There is relatively little 

information on their response to carbon 

dioxide, and few crop simulation 

models, but according to the literature, 

they are very likely to be more sensitive 

to the various effects of climate change 

than grain and oilseed crops. 

With respect to livestock, higher 

temperatures will very likely reduce 

livestock production during the summer 

season in some areas, but these losses 

will very likely be partially offset by 

warmer temperatures during the winter 

season. The impact on livestock 

productivity due to increased variability 

in weather patterns will likely be far 

greater than effects associated with the 

average change in climatic conditions. 

Cold-water fisheries will likely be 

negatively affected; warm-water 

fisheries will generally benefit; and the 

results for cool-water fisheries will be 

mixed, with gains in the northern and 

losses in the southern portions of 

ranges. 

Finally, with respect to irrigation 

requirements, the adverse impacts of 

climate change on irrigation water 

requirements may be significant. 

There is support for the view that 

there may be a benefit in the near term 

in the crop yield for certain crops. This 

potential benefit is subject to significant 

uncertainty, however, given the 

offsetting impact on the yield of these 

crops from a variety of other climate 

change impacts that are less well 

understood and more variable. Any 

potential net benefit is expected to 

change to a disbenefit in the longer 

term. In addition, there is clear risk that 

the sensitivity of a major segment of the 

total crop market, the horticultural 

sector, may lead to adverse affects from 

climate change. With respect to 

livestock production and irrigation 

requirements, climate change is likely to 

have adverse effects in both the near 

and long terms. The impact on fisheries 

varies, and would appear to be best 

viewed as neutral overall. 

There is a potential for a net benefit 

in the near term for certain crops, but 

there is significant uncertainty about 

whether this benefit will be achieved 

given the various potential adverse 

impacts of climate change on crop yield, 

such as the increasing risk of extreme 

weather events. Other aspects of this 

sector are expected to be adversely 

affected by climate change, including 

livestock management and irrigation 

requirements, and there is a risk of 

adverse effect on a large segment of the 

total crop market. For the near term, the 

concern over the potential for adverse 

effects in certain parts of the agriculture 

sector appears generally comparable to 

the potential for benefits for certain 

crops. 

However, considering the trend over 

near- and long-term future conditions, 

the Administrator finds that the body of 

evidence points towards increasing risk 


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of net adverse impacts on U.S. food 

production and agriculture, with the 

potential for significant disruptions and 

crop failure in the future. 

b. Forestry 

The factors that the Administrator 

considered for the U.S. forest sector are 

similar to those for food production and 

agriculture. There is the potential for 

beneficial effects due to elevated 

concentrations of carbon dioxide and 

increased temperature, as well as the 

potential for adverse effects from 

increasing temperatures, changing 

precipitation patterns, increased insects 

and disease, and the potential for more 

frequent and severe extreme weather 

events. The potential beneficial effects 

are better understood and studied, and 

are limited to certain areas of the 

country and types of forests. The 

adverse effects are less certain, more 

variable, and also include some of the 

most serious adverse effects such as 

increased wildfire, drought, and major 

losses from insects and disease. As with 

food production and agriculture, the 

judgment to be made is largely a 

qualitative one, balancing impacts that 

vary in certainty and magnitude, with 

the end result being a judgment as to the 

overall direction and general level of 

concern. 

According to the underlying science 

assessment reports, climate change has 

very likely increased the size and 

number of wildfires, insect outbreaks, 

and tree mortality in the Interior West, 

the Southwest, and Alaska, and will 

continue to do so. Rising atmospheric 

carbon dioxide levels will very likely 

increase photosynthesis for forests, but 

the increased photosynthesis will likely 

only increase wood production in young 

forests on fertile soils. Nitrogen 

deposition and warmer temperatures 

have very likely increased forest growth 

where water is not limiting and will 

continue to do so in the near future. 

An increased frequency of 

disturbance (such as drought, storms, 

insect-outbreaks, and wildfire) is at least 

as important to forest ecosystem 

function as incremental changes in 

temperature, precipitation, atmospheric 

carbon dioxide, nitrogen deposition, 

and ozone pollution. Disturbances 

partially or completely change forest 

ecosystem structure and species 

composition, cause short-term 

productivity and carbon storage loss, 

allow better opportunities for invasive 

alien species to become established, and 

command more public and management 

attention and resources. The combined 

effects of expected increased 

temperature, carbon dioxide, nitrogen 

deposition, ozone, and forest 

disturbance on soil processes and soil 

carbon storage remain unclear. 

Precipitation and weather extremes 

are key to many forestry impacts, 

accounting for part of the regional 

variability in forest response. If existing 

trends in precipitation continue, it is 

expected that forest productivity will 

likely decrease in the Interior West, the 

Southwest, eastern portions of the 

Southeast, and Alaska, and that forest 

productivity will likely increase in the 

northeastern United States, the Lake 

States, and in western portions of the 

Southeast. An increase in drought 

events will very likely reduce forest 

productivity wherever such events 

occur. 

Changes in disturbance patterns are 

expected to have a substantial impact on 

overall gains or losses. More prevalent 

wildfire disturbances have recently been 

observed in the United States. Wildfires 

and droughts, among other extreme 

events (e.g., hurricanes) that can cause 

forest damage, pose the largest threats 

over time to forest ecosystems. 

For the near term, the Administrator 

believes the beneficial impact on forest 

growth and productivity in certain parts 

of the country from climate change to be 

more than offset by the clear risk from 

the more significant and serious adverse 

effects from the observed increases in 

wildfires, combined with the adverse 

impacts on growth and productivity in 

other areas of the country and the 

serious risks from the spread of 

destructive pests and disease. Increased 

wildfires can also increase particulate 

matter and thus create public health 

concerns as well. For the longer term, 

the Administrator views the risk from 

adverse effects to increase over time, 

such that overall climate change 

presents serious adverse risks for forest 

productivity. The Administrator 

therefore finds there is compelling 

reason to find that the greenhouse gas 

air pollution endangers U.S. forestry in 

both the near and long term, with the 

support for a positive endangerment 

finding only increasing as one considers 

expected future conditions in which 

temperatures continue to rise. 

c. Water Resources 

The sensitivity of water resources to 

climate change is very important given 

the increasing demand for adequate 

water supplies and services for 

agricultural, municipal, and energy and 

industrial uses, and the current strains 

on this resource in many parts of the 

country. 

According to the assessment 

literature, climate change has already 

altered, and will likely continue to alter, 

the water cycle, affecting where, when, 

and how much water is available for all 

uses. With higher temperatures, the 

water-holding capacity of the 

atmosphere and evaporation into the 

atmosphere increase, and this favors 

increased climate variability, with more 

intense precipitation and more 

droughts. 

Climate change is causing and will 

increasingly cause shrinking snowpack 

induced by increasing temperature. In 

the western United States, there is 

already well-documented evidence of 

shrinking snowpack due to warming. 

Earlier meltings, with increased runoff 

in the winter and early spring, increase 

flood concerns and also result in 

substantially decreased summer flows. 

This pattern of reduced snowpack and 

changes to the flow regime pose very 

serious risks to major population 

regions, such as California, that rely on 

snowmelt-dominated watersheds for 

their water supply. While increased 

precipitation is expected to increase 

water flow levels in some eastern areas, 

this may be tempered by increased 

variability in the precipitation and the 

accompanying increased risk of floods 

and other concerns such as water 

pollution. 

Warmer temperatures and decreasing 

precipitation in other parts of the 

country, such as the Southwest, can 

sustain and amplify drought impacts. 

Although drought has been more 

frequent and intense in the western part 

of the United States, the East is also 

vulnerable to droughts and attendant 

reductions in water supply, changes in 

water quality and ecosystem function, 

and challenges in allocation. The stress 

on water supplies on islands is expected 

to increase. 

The impact of climate change on 

groundwater as a water supply is 

regionally variable; efforts to offset 

declining surface water availability due 

to increasing precipitation variability 

may be hampered by the fact that 

groundwater recharge will decrease 

considerably in some already waterstressed regions. In coastal areas, the 

increased salinization from intrusion of 

salt water is projected to have negative 

effects on the supply of fresh water. 

Climate change is expected to have 

adverse effects on water quality. The 

IPCC concluded with high confidence 

that higher water temperatures, 

increased precipitation intensity, and 

longer periods of low flows exacerbate 

many forms of water pollution and can 

impact ecosystems, human health, and 

water system reliability and operating 

costs. These changes will also 

exacerbate many forms of water 

pollution, potentially making 

attainment of water quality goals more 


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difficult. Water pollutants of concern 

that are particularly relevant to climate 

change effects include sediment, 

nutrients, organic matter, pathogens, 

pesticides, salt, and thermal pollution. 

As waters become warmer, the aquatic 

life they now support will be replaced 

by other species better adapted to 

warmer water. In the long term, warmer 

water, changing flows, and decreased 

water quality may result in deterioration 

of aquatic ecosystems. 

Climate change will likely further 

constrain already over-allocated water 

resources in some regions of the United 

States, increasing competition among 

agricultural, municipal, industrial, and 

ecological uses. Although water 

management practices in the United 

States are generally advanced, 

particularly in the West, the reliance on 

past conditions as the basis for current 

and future planning may no longer be 

appropriate, as climate change 

increasingly creates conditions well 

outside of historical observations. 

Increased incidence of extreme weather 

and floods may also overwhelm or 

damage water treatment and 

management systems, resulting in water 

quality impairments. In the Great Lakes 

and major river systems, lower water 

levels are likely to exacerbate challenges 

relating to water quality, navigation, 

recreation, hydropower generation, 

water transfers, and bi-national 

relationships. 

The Administrator finds that the total 

scientific literature provides compelling 

support for finding that greenhouse gas 

air pollution endangers the water 

resources important for public welfare 

in the United States, both for current 

and future generations. The adequacy of 

water supplies across large areas of the 

country is at serious risk from climate 

change. Even areas of the country where 

an increase in water flow is projected 

could face water resource problems 

from the variability of the supply and 

water quality problems associated with 

precipitation variability, and could face 

the serious adverse effects from risks 

from floods and drought. Climate 

change is expected to adversely affect 

water quality. There is an increased risk 

of serious adverse effects from extreme 

events of flooding and drought. The 

severity of risks and impacts may only 

increase over time with accumulating 

greenhouse gas concentrations and 

associated temperature increases and 

precipitation changes. 

d. Sea Level Rise and Coastal Areas 

A large percentage of the U.S. 

population lives in coastal areas, which 

are particularly vulnerable to the risks 

posed by climate change. The most 

vulnerable areas are the Atlantic and 

Gulf Coasts, the Pacific Islands, and 

parts of Alaska. 

According to the assessment 

literature, sea level is rising along much 

of the U.S. coast, and the rate of change 

will very likely increase in the future, 

exacerbating the impacts of progressive 

inundation, storm-surge flooding, and 

shoreline erosion. Cities such as New 

Orleans, Miami, and New York are 

particularly at risk, and could have 

difficulty coping with the sea level rise 

projected by the end of the century 

under a higher emissions scenario. 

Population growth and the rising value 

of infrastructure increases the 

vulnerability to climate variability and 

future climate change in coastal areas. 

Adverse impacts on islands present 

concerns for Hawaii and the U.S. 

territories. Reductions in Arctic sea ice 

increases extreme coastal erosion in 

Alaska, due to the increased exposure of 

the coastline to strong wave action. In 

the Great Lakes, where sea level rise is 

not a concern, both extremely high and 

low water levels resulting from changes 

to the hydrological cycle have been 

damaging and disruptive to shoreline 

communities. 

Coastal wetland loss is being observed 

in the United States where these 

ecosystems are squeezed between 

natural and artificial landward 

boundaries and rising sea levels. Up to 

21 percent of the remaining coastal 

wetlands in the U.S. mid-Atlantic region 

are potentially at risk of inundation 

between 2000 and 2100. Coastal habitats 

will likely be increasingly stressed by 

climate change impacts interacting with 

development and pollution. 

Although increases in mean sea level 

over the 21st century and beyond will 

inundate unprotected, low-lying areas, 

the most devastating impacts are likely 

to be associated with storm surge. 

Superimposed on expected rates of sea 

level rise, projected storm intensity, 

wave height, and storm surge suggest 

more severe coastal flooding and 

erosion hazards. Higher sea level 

provides an elevated base for storm 

surges to build upon and diminishes the 

rate at which low-lying areas drain, 

thereby increasing the risk of flooding 

from rainstorms. In New York City and 

Long Island, flooding from a 

combination of sea level rise and storm 

surge could be several meters deep. 

Projections suggest that the return 

period of a 100-year flood event in this 

area might be reduced to 19–68 years, 

on average, by the 2050s, and to 4–60 

years by the 2080s. Additionally, some 

major urban centers in the United 

States, such as areas of New Orleans are 

situated in low-lying flood plains, 

presenting increased risk from storm 

surges. 

The Administrator finds that the most 

serious risk of adverse effects is 

presented by the increased risk of storm 

surge and flooding in coastal areas from 

sea level rise. Current observations of 

sea level rise are now contributing to 

increased risk of storm surge and 

flooding in coastal areas, and there is 

reason to find that these areas are now 

endangered by human-induced climate 

change. The conclusion in the 

assessment literature that there is the 

potential for hurricanes to become more 

intense with increasing temperatures 

(and even some evidence that Atlantic 

hurricanes have already become more 

intense) reinforces the judgment that 

coastal communities are now 

endangered by human-induced climate 

change, and may face substantially 

greater risk in the future. The 

Administrator has concluded that even 

if there is a low probability of raising 

the destructive power of hurricanes, this 

threat is enough to support a finding 

that coastal communities are 

endangered by greenhouse gas air 

pollution. 

In addition, coastal areas face other 

adverse impacts from sea level rise such 

as shoreline retreat, erosion, wetland 

loss and other effects. The increased risk 

associated with these adverse impacts 

also endangers the welfare of current 

and future generations, with an 

increasing risk of greater adverse 

impacts in the future. 

Overall, the evidence on risk of 

adverse impacts for coastal areas from 

sea level rise provides clear support for 

finding that greenhouse gas air pollution 

endangers the welfare of current and 

future generations. 

e. Energy, Infrastructure and 

Settlements 

The Administrator also considered 

the impacts of climate change on energy 

consumption and production, and on 

key climate-sensitive aspects of the 

nation’s infrastructure and settlements. 

For the energy sector, the 

Administrator finds clear evidence that 

temperature increases will change 

heating and cooling demand, and to 

varying degrees across the country; 

however, under current conditions it is 

unclear whether or not net demand will 

increase or decrease. While the impacts 

on net energy demand may be viewed 

as generally neutral for purposes of 

making an endangerment determination, 

climate change is expected to call for an 

increase in electricity production, 

especially supply for peak demand. The 

U.S. energy sector, which relies heavily 

on water for cooling capacity and 


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hydropower, may be adversely impacted 

by changes to water supply in reservoirs 

and other water bodies. 

With respect to infrastructure, climate 

change vulnerabilities of industry, 

settlement and society are mainly 

related to extreme weather events rather 

than to gradual climate change. The 

significance of gradual climate change, 

e.g., increases in the mean temperature, 

lies mainly in changes in the intensity 

and frequency of extreme events. 

Extreme weather events could threaten 

U.S. energy infrastructure (transmission 

and distribution), transportation 

infrastructure (roads, bridges, airports 

and seaports), water infrastructure, and 

other built aspects of human 

settlements. Moreover, soil subsidence 

caused by the melting of permafrost in 

the Arctic region is a risk to gas and oil 

pipelines, electrical transmission 

towers, roads, and water systems. 

Vulnerabilities for industry, 

infrastructures, settlements, and society 

to climate change are generally greater 

in certain high-risk locations, 

particularly coastal and riverine areas, 

and areas whose economies are closely 

linked with climate-sensitive resources. 

Additionally, infrastructures are often 

connected, meaning that an impact on 

one can also affect others. 

A significant fraction of U.S. 

infrastructure is located in coastal areas. 

In these locations, rising sea levels are 

likely to lead to direct losses (e.g., 

equipment damage from flooding) as 

well as indirect effects such as the costs 

associated with raising vulnerable assets 

to higher levels. Water infrastructure, 

including drinking water and 

wastewater treatment plants, and sewer 

and storm water management systems, 

may be at greater risk of flooding, sea 

level rise and storm surge, low flows, 

saltwater intrusion, and other factors 

that could impair performance and 

damage costly investments. 

Within settlements experiencing 

climate change stressors, certain parts of 

the population may be especially 

vulnerable based on their 

circumstances. These include the poor, 

the elderly, the very young, those 

already in poor health, the disabled, 

those living alone, and/or indigenous 

populations dependent on one or a few 

resources. In Alaska, indigenous 

communities are likely to experience 

disruptive impacts, including shifts in 

the range or abundance of wild species 

crucial to their livelihoods and wellbeing. 

Overall, the evidence strongly 

supports the view that climate change 

presents risks of serious adverse impacts 

on public welfare from the risk to 

energy production and distribution as 

well as risks to infrastructure and 

settlements. 

f. Ecosystems and Wildlife 

The Administrator considered the 

impacts of climate change on 

ecosystems and wildlife and the 

services they provide. The 

Administrator finds clear evidence that 

climate change is exerting major 

influences on natural environments and 

biodiversity, and these influences are 

generally expected to grow with 

increased warming. Observed changes 

in the life cycles of plants and animals 

include shifts in habitat ranges, timing 

of migration patterns, and changes in 

reproductive timing and behavior. 

The underlying assessment literature 

finds with high confidence that 

substantial changes in the structure and 

functioning of terrestrial ecosystems are 

very likely to occur with a global 

warming greater than 2 to 3 °C above 

pre-industrial levels, with 

predominantly negative consequences 

for biodiversity and the provisioning of 

ecosystem goods and services. With 

global average temperature changes 

above 2 °C, many terrestrial, freshwater, 

and marine species (particularly 

endemic species) are at a far greater risk 

of extinction than in the geological past. 

Climate change and ocean acidification 

will likely impair a wide range of 

planktonic and other marine calcifiers 

such as corals. Even without ocean 

acidification effects, increases in sea 

surface temperature of about 1–3 °C are 

projected to result in more frequent 

coral bleaching events and widespread 

mortality. In the Arctic, wildlife faces 

great challenges from the effects of 

climatic warming, as projected 

reductions in sea ice will drastically 

shrink marine habitat for polar bears, 

ice-inhabiting seals, and other animals. 

Some common forest types are 

projected to expand, such as oakhickory, while others are projected to 

contract, such as maple-beech-birch. 

Still others, such as spruce-fir, are likely 

to disappear from the contiguous United 

States. Changes in plant species 

composition in response to climate 

change can increase ecosystem 

vulnerability to other disturbances, 

including wildfires and biological 

invasion. Disturbances such as wildfires 

and insect outbreaks are increasing in 

the United States and are likely to 

intensify in a warmer future with 

warmer winters, drier soils and longer 

growing seasons. The areal extent of 

drought-limited ecosystems is projected 

to increase 11 percent per °C warming 

in the United States. In California, 

temperature increases greater than 2 °C 

may lead to conversion of shrubland 

into desert and grassland ecosystems 

and evergreen conifer forests into mixed 

deciduous forests. Greater intensity of 

extreme events may alter disturbance 

regimes in coastal ecosystems leading to 

changes in diversity and ecosystem 

functioning. Species inhabiting salt 

marshes, mangroves, and coral reefs are 

likely to be particularly vulnerable to 

these effects. 

The Administrator finds that the total 

scientific record provides compelling 

support for finding that the greenhouse 

gas air pollution leads to predominantly 

negative consequences for biodiversity 

and the provisioning of ecosystem goods 

and services for ecosystems and wildlife 

important for public welfare in the U.S., 

both for current and future generations. 

The severity of risks and impacts may 

only increase over time with 

accumulating greenhouse gas 

concentrations and associated 

temperature increases and precipitation 

changes. 

g. Summary of the Administrator’s 

Finding of Endangerment to Public 

Welfare 

The Administrator has considered 

how elevated concentrations of the wellmixed greenhouse gases and associated 

climate change affect public welfare by 

evaluating numerous and far-ranging 

risks to food production and agriculture, 

forestry, water resources, sea level rise 

and coastal areas, energy, infrastructure, 

and settlements, and ecosystems and 

wildlife. For each of these sectors, the 

evidence provides support for a finding 

of endangerment to public welfare. The 

evidence concerning adverse impacts in 

the areas of water resources and sea 

level rise and coastal areas provide the 

clearest and strongest support for an 

endangerment finding, both for current 

and future generations. Strong support 

is also found in the evidence concerning 

infrastructure and settlements, as well 

ecosystems and wildlife. Across the 

sectors, the potential serious adverse 

impacts of extreme events, such as 

wildfires, flooding, drought, and 

extreme weather conditions provide 

strong support for such a finding. 

Water resources across large areas of 

the country are at serious risk from 

climate change, with effects on water 

supplies, water quality, and adverse 

effects from extreme events such as 

floods and droughts. Even areas of the 

country where an increase in water flow 

is projected could face water resource 

problems from the supply and water 

quality problems associated with 

temperature increases and precipitation 

variability, and could face the increased 

risk of serious adverse effects from 

extreme events, such as floods and 


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32 ‘‘In an increasingly interdependent world, U.S. 

vulnerability to climate change is linked to the fates 

of other nations. For example, conflicts or mass 

migrations of people resulting from food scarcity 

and other resource limits, health impacts or 

environmental stresses in other parts of the world 

could threaten U.S. national security.’’ (Karl et al., 

2009). 

drought. The severity of risks and 

impacts is likely to increase over time 

with accumulating greenhouse gas 

concentrations and associated 

temperature increases and precipitation 

changes. 

Overall, the evidence on risk of 

adverse impacts for coastal areas 

provides clear support for a finding that 

greenhouse gas air pollution endangers 

the welfare of current and future 

generations. The most serious potential 

adverse effects are the increased risk of 

storm surge and flooding in coastal 

areas from sea level rise and more 

intense storms. Observed sea level rise 

is already increasing the risk of storm 

surge and flooding in some coastal 

areas. The conclusion in the assessment 

literature that there is the potential for 

hurricanes to become more intense (and 

even some evidence that Atlantic 

hurricanes have already become more 

intense) reinforces the judgment that 

coastal communities are now 

endangered by human-induced climate 

change, and may face substantially 

greater risk in the future. Even if there 

is a low probability of increasing the 

destructive power of hurricanes, this 

threat is enough to support a finding 

that coastal communities are 

endangered by greenhouse gas air 

pollution. In addition, coastal areas face 

other adverse impacts from sea level rise 

such as land loss due to inundation, 

erosion, wetland submergence, and 

habitat loss. The increased risk 

associated with these adverse impacts 

also endangers public welfare, with an 

increasing risk of greater adverse 

impacts in the future. 

Strong support for an endangerment 

finding is also found in the evidence 

concerning energy, infrastructure, and 

settlements, as well ecosystems and 

wildlife. While the impacts on net 

energy demand may be viewed as 

generally neutral for purposes of making 

an endangerment determination, climate 

change is expected to result in an 

increase in electricity production, 

especially to meet peak demand. This 

increase may be exacerbated by the 

potential for adverse impacts from 

climate change on hydropower 

resources as well as the potential risk of 

serious adverse effects on energy 

infrastructure from extreme events. 

Changes in extreme weather events 

threaten energy, transportation, and 

water resource infrastructure. 

Vulnerabilities of industry, 

infrastructure, and settlements to 

climate change are generally greater in 

high-risk locations, particularly coastal 

and riverine areas, and areas whose 

economies are closely linked with 

climate-sensitive resources. Climate 

change will likely interact with and 

possibly exacerbate ongoing 

environmental change and 

environmental pressures in settlements, 

particularly in Alaska where indigenous 

communities are facing major 

environmental and cultural impacts on 

their historic lifestyles. Over the 21st 

century, changes in climate will cause 

some species to shift north and to higher 

elevations and fundamentally rearrange 

U.S. ecosystems. Differential capacities 

for range shifts and constraints from 

development, habitat fragmentation, 

invasive species, and broken ecological 

connections will likely alter ecosystem 

structure, function, and services, 

leading to predominantly negative 

consequences for biodiversity and the 

provision of ecosystem goods and 

services. 

With respect to food production and 

agriculture, there is a potential for a net 

benefit in the near term for certain 

crops, but there is significant 

uncertainty about whether this benefit 

will be achieved given the various 

potential adverse impacts of climate 

change on crop yield, such as the 

increasing risk of extreme weather 

events. Other aspects of this sector may 

be adversely affected by climate change, 

including livestock management and 

irrigation requirements, and there is a 

risk of adverse effect on a large segment 

of the total crop market. For the near 

term, the concern over the potential for 

adverse effects in certain parts of the 

agriculture sector appears generally 

comparable to the potential for benefits 

for certain crops. However, the body of 

evidence points towards increasing risk 

of net adverse impacts on U.S. food 

production and agriculture over time, 

with the potential for significant 

disruptions and crop failure in the 

future. 

For the near term, the Administrator 

finds the beneficial impact on forest 

growth and productivity in certain parts 

of the country from elevated carbon 

dioxide concentrations and temperature 

increases to date is offset by the clear 

risk from the observed increases in 

wildfires, combined with risks from the 

spread of destructive pests and disease. 

For the longer term, the risk from 

adverse effects increases over time, such 

that overall climate change presents 

serious adverse risks for forest 

productivity. There is compelling 

reason to find that the support for a 

positive endangerment finding increases 

as one considers expected future 

conditions where temperatures continue 

to rise. 

Looking across all of the sectors 

discussed above, the evidence provides 

compelling support for finding that 

greenhouse gas air pollution endangers 

the public welfare of both current and 

future generations. The risk and the 

severity of adverse impacts on public 

welfare are expected to increase over 

time. 

h. Impacts in Other World Regions That 

Can Affect the U.S Population 

While the finding of endangerment to 

public health and welfare discussed 

above is based on impacts in the United 

States, the Administrator also 

considered how human-induced climate 

change in other regions of the world 

may in turn affect public welfare in the 

United States. According to the 

USGCRP report of June 2009 and other 

sources, climate change impacts in 

certain regions of the world may 

exacerbate problems that raise 

humanitarian, trade, and national 

security issues for the United States.32

The IPCC identifies the most vulnerable 

world regions as the Arctic, because of 

the effects of high rates of projected 

warming on natural systems; Africa, 

especially the sub-Saharan region, 

because of current low adaptive 

capacity as well as climate change; 

small islands, due to high exposure of 

population and infrastructure to risk of 

sea-level rise and increased storm surge; 

and Asian mega-deltas, such as the 

Ganges-Brahmaputra and the Zhujiang, 

due to large populations and high 

exposure to sea level rise, storm surge, 

and river flooding. Climate change has 

been described as a potential threat 

multiplier with regard to national 

security issues. 

The Administrator acknowledges 

these kinds of risks do not readily lend 

themselves to precise analyses or future 

projections. However, given the 

unavoidable global nature of the climate 

change problem, it is appropriate and 

prudent to consider how impacts in 

other world regions may present risks to 

the U.S. population. Because humaninduced climate change has the 

potential to aggravate natural resource, 

trade, and humanitarian issues in other 

world regions, which in turn may 

contribute to the endangerment of 

public welfare in the United States, this 

provides additional support for the 

Administrator’s finding that the 

greenhouse gas air pollution is 

reasonably anticipated to endanger the 

public welfare of current and future 


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generations of the United States 

population. 

i. Summary of Key Public Comments on 

Endangerment to Public Welfare 

Several public commenters point out 

the anticipated benefits that increasing 

carbon dioxide levels and temperatures 

will have on agricultural crops. In 

addition, commenters note how U.S. 

agricultural productivity, in particular, 

has been steadily rising over the last 100 

years. Responses to major comments are 

found here and more detailed responses 

are found in the Response to Comments 

document. 

The Administrator acknowledges that 

plants including agricultural crops 

respond to carbon dioxide positively 

based on numerous well-documented 

studies. However, previous assessments 

of food production and agriculture have 

been modified to highlight increasing 

vulnerability, stress, and adverse 

impacts from climate change over time, 

based on improvements in the 

understanding of plant physiology, 

concern over impacts on plant pests and 

pathogens, and the implications of 

changes in average temperatures for 

temperature extremes and for changes in 

the patterns of precipitation and 

evaporation. While it is still the case 

today and for the next few years that 

climate change benefits agriculture in 

some places and harms them in others, 

the Administrator considers that the far 

larger temperature increases expected 

over coming decades and beyond on the 

‘‘business as usual’’ trajectory will put 

significant stresses on agriculture and 

land resources in all regions of the 

United States. The Administrator 

prudently considers increased climate 

variability associated with a warming 

climate, which may overwhelm the 

positive plant responses from elevated 

carbon dioxide over time. Further, the 

effects of climate change on weeds, 

insect pests, and pathogens are 

recognized as key factors in determining 

plant damage in future decades. The 

Administrator also notes that scientific 

literature clearly supports the finding 

that drought frequency and severity are 

projected to increase in the future over 

much of the United States, which will 

likely reduce crop yields because of 

excesses or deficits of water. 

Vulnerability to extended drought, 

according to IPCC, has been 

documented as already increasing 

across North America. Further, based on 

review of the assessment literature, the 

Administrator considers multiple 

stresses, such as limited availability of 

water resources, loss of biodiversity, 

and air pollution, which are likely to 

increase sensitivity and reduce 

resilience in the agricultural sector to 

climate change over time. 

Similar to food production and 

agriculture, public commenters often 

noted that forest productivity is 

projected to increase in the coming 

years due to the direct stimulatory effect 

of carbon dioxide on plant growth 

combined with warmer temperatures 

and thus extended growing seasons. The 

Administrator notes this phenomenon 

has been well documented by numerous 

studies but recognizes that increased 

productivity will be associated with 

significant variation at local and 

regional scales. The Administrator 

considers that climate strongly 

influences forest productivity and 

composition, and the frequency and 

magnitude of disturbances that impact 

forests. Based on the most recent IPCC 

assessment of the scientific literature, 

several recent studies confirm previous 

findings that temperature and 

precipitation changes in future decades 

will modify, and often limit, direct 

carbon dioxide effects on plants. For 

example, increased temperatures may 

reduce carbon dioxide effects indirectly, 

by increasing water demand. The 

Administrator also considers that new 

research more firmly establishes the 

negative impacts of increased climate 

variability. Projected changes in the 

frequency and severity of extreme 

climate events have significant 

consequences for forestry production 

and amplify existing stresses to land 

resources in the future. 

Several public commenters maintain 

that wildfires are primarily the result of 

natural climatic factors and not climate 

change and dispute that they are or will 

increase in the future. The 

Administrator notes the scientific 

literature and assessment reports 

provide several lines of evidence that 

suggest wildfires will likely increase in 

frequency over the next several decades 

because of climate warming. Wildfires 

and droughts, among other extreme 

events (e.g., hurricanes) that cause forest 

damage, pose the largest threats over 

time to forest ecosystems. The 

assessment literature suggests that large, 

stand-replacing wildfires will likely 

increase in frequency over the next 

several decades because of climate 

warming and general climate warming 

encourages wildfires by extending the 

summer period that dries fuels, 

promoting easier ignition and faster 

spread. Furthermore, current climate 

modeling studies suggest that increased 

temperatures and longer growing 

seasons will elevate wildfire risk in 

connection with increased aridity. 

V. The Administrator’s Finding That 

Emissions of Greenhouse Gases From 

CAA Section 202(a) Sources Cause or 

Contribute to the Endangerment of 

Public Health and Welfare 

As discussed in Section IV.A of these 

Findings, the Administrator is defining 

the air pollution for purposes of the 

endangerment finding to be the elevated 

concentration of well-mixed greenhouse 

gases in the atmosphere. The second 

step of the two-part endangerment test 

is for the Administrator to determine 

whether the emission of any air 

pollutant emitted from new motor 

vehicles cause or contribute to this air 

pollution. This is referred to as the 

cause or contribute finding, and is the 

second finding by the Administrator in 

this action. 

Section V.A of these Findings 

describes the Administrator’s definition 

and scope of the air pollutant ‘‘wellmixed greenhouse gases.’’ Section V.B 

of these Findings puts forth the 

Administrator’s finding that emissions 

of well-mixed greenhouse gases from 

new motor vehicles contribute to the air 

pollution which is reasonably 

anticipated to endanger public health 

and welfare. Section V.C of these 

Findings provides responses to some of 

the key comments on these issues. See 

Response to Comments document 

Volume 10 for responses to other 

significant comments on the cause or 

contribute finding. More detailed 

emissions data summarized in the 

discussion below can be found in 

Appendix B of the TSD. 

A. The Administrator’s Definition of the 

‘‘Air Pollutant’’ 

As discussed in the Proposed 

Findings, to help appreciate the 

distinction between air pollution and air 

pollutant, the air pollution can be 

thought of as the total, cumulative stock 

in the atmosphere, while the air 

pollutant, can be thought of as the flow 

that changes the size of the total stock. 

Given this relationship, it is not 

surprising that the Administrator is 

defining the air pollutant similar to the 

air pollution; while the air pollution is 

the concentration (e.g., stock) of the 

well-mixed greenhouse gases in the 

atmosphere, the air pollutant is the 

same combined grouping of the wellmixed greenhouse gases, the emissions 

of which are analyzed for contribution 

(e.g., the flow into the stock). 

Thus, the Administrator is defining 

the air pollutant as the aggregate group 

of the same six long-lived and directlyemitted greenhouse gases: Carbon 

dioxide, methane, nitrous oxide, 

hydrofluorocarbons, perfluorocarbons, 


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33The Montreal Protocol covers ozone-depleting 

substances which may also share physical attributes 

of the six key greenhouse gases in this action, but 

they do not share other attributes such as being the 

focus of climate science and policy. See section 

* * *. 

34UNFCCC Art. 4.1(b). 

35 Indeed, the greenhouse gases 

hydrofluorocarbons and perfluorocarbons each are 

already a combination of multiple compounds. 

36The term ‘‘well-mixed greenhouse gases’’ is 

based on one of the shared attributes discussed 

above—these greenhouse gases are sufficiently longlived in the atmosphere such that, once emitted, 

concentrations of each gas become well mixed 

throughout the entire global atmosphere. Defining 

the air pollutant to be the combination of these six 

well-mixed greenhouse gases is based in part on 

this attribute—after the gases are emitted, they are 

sufficiently long-lived in the atmosphere to become 

well mixed as part of the air pollution. 

37For section 202(a) source categories, only the 

hydrofluorocarbon emissions related to passenger 

compartment cooling are included. Emissions from 

refrigeration units that may be attached to trucks are 

considered emissions from nonroad engines under 

CAA section 213. 

and sulfur hexafluoride. As noted 

above, this definition of a single air 

pollutant made up of these well-mixed 

greenhouse gases is similar to 

definitions of other air pollutants that 

are comprised of substances that share 

common attributes with similar effects 

on public health or welfare (e.g., 

particulate matter and volatile organic 

compounds). 

The common attributes shared by 

these six greenhouse gases are discussed 

in detail in Section IV.A of these 

Findings, where the Administrator 

defined the ‘‘air pollution’’ for purposes 

of the endangerment finding. These 

same common attributes support the 

Administrator grouping these six 

greenhouse gases for purposes of 

defining a single air pollutant as well. 

These attributes include the fact that 

they are all greenhouse gases that are 

directly emitted (i.e., they are not 

formed through secondary processes in 

the atmosphere from precursor 

emissions); they are sufficiently longlived in the atmosphere such that, once 

emitted, concentrations of each gas 

become well mixed throughout the 

entire global atmosphere; and they exert 

a climate warming effect by trapping 

outgoing, infrared heat that would 

otherwise escape to space. Moreover, 

the radiative forcing effect of these six 

greenhouse gases is well understood. 

Furthermore, these six greenhouse 

gases are currently the common focus of 

climate science and policy. For 

example, the UNFCCC, signed and 

ratified by the U.S. in 1992, requires its 

signatories to ‘‘develop, periodically 

update, publish and make available 

* * * national inventories of 

anthropogenic emissions by sources and 

removals by sinks of all greenhouse 

gases not controlled by the Montreal 

Protocol 33, using comparable 

methodologies * * * ’’ 34 To date, the 

focus of UNFCCC actions and 

discussions has been on the six 

greenhouse gases that are the same focus 

of these findings. As a Party to the 

UNFCCC, EPA annually submits the 

Inventory of U.S. Greenhouse Gas 

Emissions and Sinks to the Convention, 

which reports on national emissions of 

anthropogenic emissions of the wellmixed greenhouse gases. International 

discussions about a post-Kyoto 

agreement also focus on the well-mixed 

greenhouse gases. 

As noted above, grouping of many 

substances with common attributes as a 

single pollutant is common practice 

under the CAA. Thus, doing so here is 

not novel. Indeed CAA section 302(g) 

defines air pollutant as ‘‘any air 

pollutant agent or combination of such 

agents, * * * ’’ CAA § 302(g) (emphasis 

added). Thus, it is clear that the term 

‘‘air pollutant’’ is not limited to 

individual chemical compounds. In 

determining that greenhouse gases are 

within the scope of this definition, the 

Supreme Court described section 302(g) 

as a ‘‘sweeping’’ and ‘‘capacious’’ 

definition that unambiguously included 

greenhouse gases, that are 

‘‘unquestionably ‘agents’ of air 

pollution.’’ Massachusetts v. EPA, 549 

U.S. at 528, 532, 529 n.26. Although the 

Court did not interpret the term 

‘‘combination of’’ air pollution agents, 

there is no reason this phrase would be 

interpreted any less broadly. Congress 

used the term ‘‘any’’, and did not 

qualify the kind of combinations that 

the agency could define as a single air 

pollutant. Congress provided EPA broad 

discretion to determine appropriate 

combinations of compounds that should 

be treated as a singe air pollutant.35

For the same reasons discussed in 

Section IV.A above, at this time, only 

carbon dioxide, methane, nitrous oxide, 

hydrofluorocarbons, perfluorocarbons, 

and sulfur hexafluoride share all of 

these common attributes and thus they 

are the only substances that the 

Administrator finds to meet the 

definition of ‘‘well-mixed greenhouse 

gas’’ at this time.36 Also as noted above, 

if in the future other substances are 

shown to meet the same criteria they 

may be added to the definition of this 

single air pollutant. 

The Administrator is aware that CAA 

section 202(a) source categories do not 

emit all of the substances meeting the 

definition of well-mixed greenhouse 

gases. But that does not change the fact 

that all of these greenhouse gases share 

the attributes that make grouping them 

as a single air pollutant reasonable. As 

discussed further below, the 

reasonableness of this grouping does not 

turn on the particular source category 

being evaluated in a contribution 

finding. 

B. The Administrator’s Finding 

Regarding Whether Emissions of the Air 

Pollutant From Section 202(a) Source 

Categories Cause or Contribute to the 

Air Pollution That May Be Reasonably 

Anticipated To Endanger Public Health 

and Welfare 

The Administrator finds that 

emissions of the well-mixed greenhouse 

gases from new motor vehicles 

contribute to the air pollution that may 

reasonably be anticipated to endanger 

public health and welfare. This 

contribution finding is for all of the 

CAA section 202(a) source categories 

and the Administrator considered 

emissions from all of these source 

categories. The relevant mobile sources 

under CAA section 202 (a)(1) are ‘‘any 

class or classes of new motor vehicles or 

new motor vehicle engines, * * *.’’ 

CAA section 202(a)(1) (emphasis 

added). The new motor vehicles and 

new motor vehicle engines (hereinafter 

‘‘CAA section 202(a) source categories’’) 

addressed are: Passenger cars, light-duty 

trucks, motorcycles, buses, and medium 

and heavy-duty trucks. Detailed 

combined greenhouse gas emissions 

data for CAA section 202(a) source 

categories are presented in Appendix B 

of the TSD.37

The Administrator reached her 

decision after reviewing emissions data 

on the contribution of CAA section 

202(a) source categories relative to both 

global greenhouse gas emissions and 

U.S. greenhouse gas emissions. Given 

that CAA section 202(a) source 

categories are responsible for about 4 

percent of total global greenhouse gas 

emissions, and for just over 23 percent 

of total U.S. greenhouse gas emissions, 

the Administrator finds that both of 

these comparisons, independently and 

together, support a finding that CAA 

section 202(a) source categories 

contribute to the air pollution that may 

be reasonably anticipated to endanger 

public health and welfare. The 

Administrator is not placing primary 

weight on either approach; rather she 

finds that both approaches clearly 

establish that emissions of the wellmixed greenhouse gases from section 

202(a) source categories contribute to air 

pollution with may reasonably be 

anticipated to endanger public health 

and welfare. As the Supreme Court 

noted, ‘‘[j]udged by any standard, U.S. 


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38Because the Administrator is defining the air 

pollutant as the combination of well-mixed 

greenhouse gases, she is not issuing a final 

contribution finding based on the alternative 

definition discussed in the proposed findings (e.g., 

each greenhouse gas as an individual air pollutant). 

motor-vehicle emissions make a 

meaningful contribution to greenhouse 

gas concentrations and hence, * * * to 

global warming.’’ Massachusetts v. EPA, 

549 U.S. at 525.38

1. Administrator’s Approach in Making 

This Finding 

Section 202(a) of the CAA source 

categories consist of passenger cars, 

light-duty trucks, motorcycles, buses, 

and heavy- and medium-duty trucks. As 

noted in the Proposed Findings, in the 

past the requisite contribution findings 

have been proposed concurrently with 

proposing emission standards for the 

relevant mobile source category. Thus, 

prior contribution findings often 

focused on a subset of the CAA section 

202(a) (or other section) source 

categories. This final cause or contribute 

finding, however, is for all of the CAA 

section 202(a) source categories. The 

Administrator is considering emissions 

from all of these source categories in the 

determination. 

Section 202(a) source categories emit 

the following well-mixed greenhouse 

gases: carbon dioxide, methane, nitrous 

oxide, and hydrofluorocarbons. As the 

basis for the Administrator’s 

determination, EPA analyzed historical 

data of emissions of the well-mixed 

greenhouse gases for motor vehicles and 

motor vehicle engines in the United 

States from 1990 to 2007. 

The Proposed Findings discussed a 

number of possible ways of assessing 

cause or contribute and the point was 

made that no single approach is 

required by the statute or has been used 

exclusively in previous determinations 

under the CAA. The Administrator also 

discussed how, consistent with prior 

cause or contribute findings and the 

science, she is using emissions as a 

proxy for contributions to atmospheric 

concentrations. This approach is 

reasonable for the well-mixed 

greenhouse gases, because cumulative 

emissions are responsible for the 

cumulative change in the concentrations 

in the atmosphere. Similarly, annual 

emissions are a perfectly reasonable 

proxy for annual incremental changes in 

atmospheric concentrations. 

In making a judgment about the 

contribution of emissions from CAA 

section 202(a) source categories, the 

Administrator focused on making a 

reasoned overall comparison of 

emissions from the CAA section 202(a) 

source categories to emissions from 

other sources of greenhouse gases. This 

allows a determination of how the CAA 

section 202(a) source categories 

compare to all of the other sources that 

together as a group make up the total 

emissions contributors to the air 

pollution problem. The relative 

importance of the CAA section 202(a) 

source categories is central to making 

the contribution determination. Both the 

magnitude of these emissions and the 

comparison of these emissions to other 

sources provide the basis to determine 

whether the CAA section 202(a) source 

categories may reasonably be judged as 

contributing to the air pollution 

problem. 

In many cases EPA makes this kind of 

comparison of source categories by a 

simple percentage calculation that 

compares the emissions from the source 

category at issue to a larger total group 

of emissions. Depending on the 

circumstances, a larger percentage often 

means a greater relative impact from 

that source category compared to the 

other sources that make up the total of 

emissions, and vice versa. However, the 

actual numerical percentages may have 

little meaning when viewed in isolation. 

The context of the comparison is needed 

to ensure the information is useful in 

evaluating the relative impact of one 

source compared to others. For example, 

the number of sources involved and the 

distribution of emissions across all of 

the sources can make a significant 

difference when evaluating the results 

of a percentage calculation. In some 

cases a certain percentage might mean 

almost all other sources are larger or 

much larger than the source at issue, 

while in other circumstances the same 

percentage could mean that the source 

at issue is in fact one of the larger 

contributors to the total. 

The Administrator therefore 

considered the totality of the 

circumstances in order to best 

understand the role played by CAA 

section 202(a) source categories. This is 

consistent with Congress’ intention for 

EPA to consider the cumulative impact 

of all sources of pollution. In that 

context, the global nature of the air 

pollution problem and the breadth of 

countries and sources emitting 

greenhouse gases means that no single 

country and no single source category 

dominate or are even close to 

dominating on a global scale. For 

example, the United States as a country 

is the second largest emitter of 

greenhouse gases, and emits 

approximately 18 percent of the world’s 

total greenhouse gases. The total 

emissions of greenhouse gases 

worldwide are from numerous sources 

and countries, with each country and 

each source category contributing a 

relatively small percentage of the total 

emissions. That means that the relative 

ranking of countries or sources is not at 

all obvious from the magnitude of the 

percentage by itself. A country or a 

source may be a large contributor, in 

comparison to other countries or 

sources, even though its percentage 

contribution may appear relatively 

small. 

In this situation, addressing a global 

air pollution problem may call for many 

different sources and countries to 

address emissions even if none by itself 

dominates or comes close to dominating 

the global inventory. A somewhat 

analogous situation can be found in the 

ozone air pollution problem in the 

United States. Emissions of NOx and 

volatile organic compounds (VOCs) 

often come from numerous small 

sources, as well as certain large source 

categories. We have learned that 

successful ozone control strategies often 

need to take this into account, and 

address both the larger sources of NOx 

and VOCs as well as the many smaller 

sources, given the breadth of sources 

that as a group lead to the total 

inventory of VOCs and NOx. 

The global aspects of the greenhouse 

gas air pollution problem amplify this 

kind of situation many times over, 

where no single country or source 

category dominates or comes close to 

dominating the global inventory of 

greenhouse gas emissions. These 

unique, global aspects of the climate 

change problem tend to support 

consideration of contribution at lower 

percentage levels of emissions than 

might otherwise be considered 

appropriate when addressing a more 

typical local or regional air pollution 

problem. In this situation it is quite 

reasonable to consider emissions from 

source categories that are more 

important in relation to other sources, 

even if their absolute contribution 

initially may appear to be small. 

In addition, the Administrator is 

aware of the fact that the United States 

is the second largest emitter of wellmixed greenhouse gases in the world. 

As the United States evaluates how to 

address climate change, the 

Administrator will analyze the various 

sources of emissions and the source’s 

share of U.S. emissions. Thus, when 

analyzing whether a source category 

that emits well-mixed greenhouse gases 

in the United States contributes to the 

global problem, it is appropriate for the 

Administrator to consider how that 

source category fits into the larger 

picture of U.S. emissions. This ranking 

process within the United States allows 

the importance of the source category to 


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39The source of global greenhouse gas emissions 

data, against which comparisons are made, is the 

Climate Analysis Indicators Tool of the World 

Resources Institute (WRI) (2007). Note that for 

global comparisons, all emissions are from the year 

2005, the most recent year for which data for all 

greenhouse gas emissions and all countries are 

available. WRI (2007) Climate Analysis Indicators 

Tool (CAIT). Available at http://cait.wri.org. 

Accessed August 5, 2009. 

40One teragram (Tg) = 1 million metric tons. 1 

metric ton = 1,000 kg = 1.102 short tons = 2,205 

lbs. Long-lived greenhouse gases are compared and 

summed together on a CO2 equivalent basis by 

multiplying each gas by its Global Warming 

Potential (GWPs), as estimated by IPCC. In 

accordance with UNFCCC reporting procedures, the 

U.S. quantifies greenhouse gas emissions using the 

100-year time frame values for GWPs established in 

the IPCC Second Assessment Report. 

41 Greenhouse gas emissions data for the United 

States in this section have been updated since the 

Proposed Findings to reflect EPA’s most up-to-date 

information, which includes data for the year 2007. 

The source of the U.S. greenhouse gas emissions 

data is the Inventory of U.S. Greenhouse Gas 

Emissions and Sinks: 1990–2007, published in 2009 

(hereinafter ‘‘U.S. Inventory’’). 

be seen compared to other U.S. sources, 

informing the judgment of the 

importance of emissions from this 

source category in any overall national 

strategy to address greenhouse gas 

emissions. 

It is in this broader context that EPA 

considered the contribution of CAA 

section 202(a) sources. This provides 

useful information in determining the 

importance that should be attached to 

the emissions from the CAA section 

202(a) sources. 

In reaching her determination, the 

Administrator used two simple and 

straightforward comparisons to assess 

cause or contribute for CAA section 

202(a) source categories: (1) As a share 

of total current global aggregate 

emissions of the well-mixed greenhouse 

gases; and (2) as a share of total current 

U.S. aggregate emissions of the wellmixed greenhouse gases. 

Total well-mixed greenhouse gas 

emissions from CAA section 202(a) 

source categories were compared to total 

global emissions of the well-mixed 

greenhouse gases. The total air pollution 

problem, as already discussed, is the 

elevated and climbing levels of the six 

greenhouse gas concentrations in the 

atmosphere, which are global in nature 

because these concentrations are 

globally well mixed (whether they are 

emitted from CAA section 202(a) source 

categories or any other source within or 

outside the United States). In addition, 

comparisons were also made to U.S. 

total well-mixed greenhouse gases 

emissions to appreciate how CAA 

section 202(a) source categories fit into 

the larger U.S. contribution to the global 

problem. It is typical for the 

Administrator to consider these kinds of 

comparisons of emissions of a pollutant 

in evaluating contribution to air 

pollution, such as the concentrations of 

that same pollutant in the atmosphere 

(e.g., the Administrator analyzes PM2.5

emissions to determine if a source 

category contributes to PM2.5 air 

pollution). When viewed in the 

circumstances discussed above, both of 

these comparisons provide useful 

information in determining whether 

these source categories should be judged 

as contributing to the total air pollution 

problem. 

a. Section 202(a) of the CAA—Share of 

Global Aggregate Emissions of the WellMixed Greenhouse Gases 

Global emissions of well-mixed 

greenhouse gases have been increasing, 

and are projected to continue increasing 

unless the major emitters take action to 

reduce emissions. Total global 

emissions of well-mixed greenhouse 

gases in 2005 (the most recent year for 

which data for all countries and all 

greenhouse gases are available) 39 were 

38,726 teragrams of CO2-equivlant 

(TgCO2eq.) 40 This represents an 

increase in global greenhouse gas 

emissions of about 26 percent since 

1990 (excluding land use, land use 

change and forestry). In 2005, total U.S. 

emissions of well-mixed greenhouse 

gases were responsible for 18 percent of 

global emissions, ranking only behind 

China, which was responsible for 19 

percent of global emissions of wellmixed greenhouse gases. 

In 2005 emissions of the well-mixed 

greenhouse gas pollutant from CAA 

section 202(a) source categories 

represented 4.3 percent of total global 

well-mixed greenhouse gas emissions 

and 28 percent of global transport wellmixed greenhouse gas emissions (Table 

1 of these Findings). If CAA section 

202(a) source categories’ emissions of 

well-mixed greenhouse gas were ranked 

against total well-mixed greenhouse gas 

emissions for entire countries, CAA 

section 202(a) source category emissions 

would rank behind only China, the 

United States as a whole, Russia, and 

India, and would rank ahead of Japan, 

Brazil, Germany and every other 

country in the world. Indeed, countries 

with lower emissions than the CAA 

section 202(a) source categories are 

members of the 17 ‘‘major economies’’ 

‘‘that meet to advance the exploration of 

concrete initiatives and joint ventures 

that increase the supply of clean energy 

while cutting greenhouse gas 

emissions.’’ See http://www.state.gov/g/ 

oes/climate/mem/. It would be 

anomalous, to say the least, to consider 

Japan and these other countries as major 

players in the global climate change 

community and an integral part of the 

solution, but not find that CAA section 

202(a) source category emissions 

contribute to the global problem. Thus, 

the Administrator finds that emission of 

well-mixed greenhouse gases from CAA 

section 202(a) source categories 

contribute to the air pollution of wellmixed greenhouse gases. 

TABLE 1—COMPARISON TO GLOBAL GREENHOUSE GAS (GHG) EMISSIONS (TG CO2E) 

2005 Sec 202(a) share 

(percent) 

All U.S. GHG emissions .............................................................................................................................. 7,109 23.5 

Global transport GHG emissions ................................................................................................................. 5,968 28.0 

All global GHG emissions ............................................................................................................................ 38,726 4.3 

b. Section 202(a) of the CAA—Share of 

U.S. Aggregate Emissions of the WellMixed Greenhouse Gases 

The Administrator considered 

compared total emissions of the wellmixed greenhouse gases from CAA 

section 202(a) source categories to total 

U.S. emissions of the well-mixed 

greenhouse gases as an indication of the 

role these sources play in the total U.S. 

contribution to the air pollution 

problem causing climate change.41

In 2007, U.S. well-mixed greenhouse 

gas emissions were 7,150 TgCO2eq. The 

dominant gas emitted was carbon 

dioxide, mostly from fossil fuel 

combustion. Methane was the second 

largest well-mixed greenhouse gas, 

followed by N2O, and the fluorinated 

gases (HFCs, PFCs, and SF6). Electricity 

generation was the largest emitting 

sector (2,445 TgCO2eq or 34 percent of 


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total U.S. greenhouse gas emissions), 

followed by transportation (1,995 

TgCO2eq or 28 percent) and industry 

(1,386 TgCO2eq or 19 percent). 

Emissions from the CAA section 202(a) 

source categories constitute the major 

part of the transportation sector. Land 

use, land use change, and forestry offset 

almost 15 percent of total U.S. 

emissions through net sequestration. 

Total U.S. well-mixed greenhouse gas 

emissions have increased by over 17 

percent between 1990 and 2007. The 

electricity generation and transportation 

sectors have contributed the most to this 

increase. 

In 2007 emissions of well-mixed 

greenhouse gases from CAA section 

202(a) source categories collectively 

were the second largest emitter of wellmixed greenhouse gases within the 

United States (behind the electricity 

generating sector), emitting 1,663 

TgCO2eq and representing 23 percent of 

total U.S. emissions of well-mixed 

greenhouse gases (Table 2 of these 

Findings). The Administrator is keenly 

aware that the United States is the 

second largest emitter of well-mixed 

greenhouse gases. Part of analyzing 

whether a sector within the United 

States contributes to the global problem 

is to see how those emissions fit into the 

contribution from the United States as a 

whole. This informs her judgment as to 

the importance of emissions from this 

source category in any overall national 

strategy to address greenhouse gas 

emissions. Thus, it is relevant that CAA 

section 202(a) source categories are the 

second largest emitter of well-mixed 

greenhouse gases in the country. This is 

part of the Administrator looking at the 

totality of the circumstances. Based on 

this the Administrator finds that 

emission of well-mixed greenhouse 

gases from CAA section 202(a) source 

categories contribute to the air pollution 

of well-mixed greenhouse gases. 

TABLE 2—SECTORAL COMPARISON TO TOTAL U.S. GREENHOUSE GAS (GHG) EMISSIONS (TG CO2E) 

U.S. emissions 1990 1995 2000 2005 2006 2007 

Section 202(a) GHG emissions ....................................... 1231.9 1364.4 1568.1 1670.5 1665.7 1663.1 

Share of U.S. (%) ............................................................ 20.2% 21.1% 22.4% 23.5% 23.6% 23.3% 

Electricity Sector emissions ............................................. 1859.1 1989.0 2329.3 2429.4 2375.5 2445.1 

Share of U.S. (%) ............................................................ 30.5% 30.8% 33.2% 34.2% 33.7% 34.2% 

Industrial Sector emissions .............................................. 1496.0 1524.5 1467.5 1364.9 1388.4 1386.3 

Share of U.S. (%) ............................................................ 24.5% 23.6% 20.9% 19.2% 19.7% 19.4% 

Total U.S. GHG emissions ....................................... 6098.7 6463.3 7008.2 7108.6 7051.1 7150.1 

C. Response to Key Comments on the 

Administrator’s Cause or Contribute 

Finding 

EPA received numerous public 

comments regarding the Administrator’s 

proposed cause or contribute finding. 

Below is a brief discussion of some of 

the key comments. Responses to 

comments on this issue are also 

contained in the Response to Comments 

document, Volume 10. 

1. The Administrator Reasonably 

Defined the ‘‘Air Pollutant’’ for the 

Cause or Contribute Analysis 

a. The Supreme Court Held that 

Greenhouse Gases Fit Within the 

Definition of ‘‘Air Pollutant’’ in the CAA 

Several commenters reiterate 

arguments already rejected by the 

Supreme Court, arguing that greenhouse 

gases do not fit into the definition of 

‘‘air pollutant’’ under the CAA. In 

particular, at least one commenter 

contends that EPA must show how 

greenhouse gases impact or materially 

change ‘‘ambient air’’ when defining air 

pollutant and making the endangerment 

finding. This commenter argues that 

because carbon dioxide is a naturally 

occurring and necessary element in the 

atmosphere, it cannot be considered to 

materially change air. 

These and similar arguments were 

already rejected by the Supreme Court 

in Massachusetts v. EPA, 549 U.S. 497 

(2007). Briefs before the Supreme Court 

also argued that carbon dioxide is an 

essential role for life on earth and 

therefore cannot be considered an air 

pollutant, and that the concentrations of 

greenhouse gases that are a potential 

problem are not in the ‘‘ambient air’’ 

that people breathe. 

The Court rejected all of these and 

other arguments, noting that the 

statutory text forecloses these 

arguments. ‘‘The Clean Air Act’s 

sweeping definition of ‘air pollutant’ 

includes ‘any air pollution agent or 

combination of such agents, including 

any physical, chemical * * * substance 

or matter which is emitted into or 

otherwise enters the ambient air . * * *’ 

§ 7602(g) (emphasis added). On its face, 

the definition embraces all airborne 

compounds of whatever stripe, and 

underscores that intent through the 

repeated use of the word ‘any.’ Carbon 

dioxide, methane, nitrous oxide, and 

hydrofluorocarbons are without a doubt 

‘physical [and] chemical * * * 

substance[s] which [are] emitted into 

* * * the ambient air.’ The statute is 

unambiguous.’’ 

547 U.S. at 529–30 (footnotes 

omitted); see also id. at 530, n26 (the 

distinction regarding ambient air, 

however, finds no support in the text of 

the statute, which uses the phrase ‘‘the 

ambient air’’ without distinguishing 

between atmospheric layer.). Thus, the 

question of whether greenhouse gases fit 

within the definition of air pollutant 

under the CAA has been decided by the 

Supreme Court and is not being 

revisited here. 

b. The Definition of Air Pollutant May 

Include Substances Not Emitted by CAA 

Section 202(a) Sources 

Many commenters argue that the 

definition of ‘‘air pollutant’’—here wellmixed greenhouse gases—cannot 

include PFCs and SF6 because they are 

not emitted by CAA section 202(a) 

motor vehicles and hence, cannot be 

part of any ‘‘air pollutant’’ emitted by 

such sources. They argue that by 

improperly defining ‘‘air pollutant’’ to 

include substances that are not present 

in motor vehicle emissions, the Agency 

has exceeded its statutory authority 

under CAA section 202(a). Commenters 

contend that past endangerment 

findings under CAA section 202(a) 

demonstrate EPA’s consistent approach 

of defining ‘‘air pollutant(s)’’ in 

accordance with the CAA’s clear 

direction, to include only those 

pollutants emitted from the relevant 

source category (citing Notice of 

Proposed Rulemaking for Heavy-Duty 

Engine and Vehicle Standards finding 

that ‘‘emissions of NOX, VOCs, SOX, and 

PM from heavy-duty trucks can 

reasonably be anticipated to endanger 

the public health or welfare.’’ (65 FR 

35436, June 2, 2000). Commenters argue 

that EPA itself is inconsistent in the 

Proposed Findings, sometimes referring 


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to ‘‘air pollutant’’ as the group of six 

greenhouse gases, and other times 

falling back on the four greenhouse 

gases emitted by motor vehicles. 

EPA acknowledges that the Proposed 

Findings could have been clearer 

regarding the proposed definition of air 

pollutant, and how it was being applied 

to CAA section 202(a) sources, which 

emit only four of the six substances that 

meet the definition of well-mixed 

greenhouse gases. However, our 

interpretation does not exceed EPA’s 

authority under CAA section 202(a). It 

is reasonable to define the air pollutant 

under CAA section 202(a) to include 

substances that have similar attributes 

(as discussed above), even if not all of 

the substances that meet that definition 

are emitted by motor vehicles. For 

example, as commenters note, EPA has 

heavy duty truck standards applicable 

to VOCs and PM, but it is highly 

unlikely that heavy duty trucks emit 

every substance that is included in the 

group defined as VOC or PM. See 40 

CFR 51.100(s) (defining volatile organic 

compound (VOC) as ‘‘any compound of 

carbon, excluding carbon monoxide, 

carbon dioxide, carbonic acid, metallic 

carbides or carbonates, and ammonium 

carbonate, which participates in 

atmospheric photochemical reactions’’, 

a list of exemptions are also included in 

the definition); 40 CFR 51.100(oo) 

(defining particulate matter (PM) as 

‘‘any airborne finely divided solid or 

liquid material with an aerodynamic 

diameter smaller than 100 

micrometers’’). 

In this circumstance the number of 

substances included in the definition of 

well-mixed greenhouse gases is much 

smaller than other ‘‘group’’ air 

pollutants (e.g., six greenhouse gases 

versus hundreds of VOCs), and CAA 

section 202(a) sources emit an easily 

discernible number of these six 

substances. However, this does not 

mean that the definition of the wellmixed greenhouse gases as the air 

pollutant is unreasonable. By defining 

well-mixed greenhouse gases as a single 

air pollutant comprised of six 

substances with common attributes, the 

Administrator is giving effect to these 

shared attributes and how they are 

relevant to the air pollution to which 

they contribute. The fact that these six 

substances share these common, 

relevant attributes is true regardless of 

the source category being evaluated for 

contribution. Grouping these six 

substances as one air pollutant is 

reasonable regardless of whether a 

contribution analysis is undertaken for 

CAA section 202(a) sources that emit 

one subset of the six substances (e.g., 

carbon dioxide, CH4, N20 and HFCs, but 

not PFCs and SF6), or for another 

category of sources that may emit 

another subset. For example, electronics 

manufacturers that may emit N2O, PFCs, 

HFCs, SF6 and other fluorinated 

compounds, but not carbon dioxide or 

CH4 unless there is on-site fuel 

combustion. In other words, it is not 

necessarily the source category being 

evaluated for contribution that 

determines the reasonableness of 

defining a group air pollutant based on 

the shared attributes of the group. 

Even if EPA agreed with commenters, 

and defined the air pollutant as the 

group of four compounds emitted by 

CAA section 202(a) sources, it would 

not change the result. The 

Administrator would make the same 

contribution finding as it would have no 

material effect on the emissions 

comparisons discussed above. 

c. It Was Reasonable for the 

Administrator To Define the Single Air 

Pollutant as the Group of Substances 

With Common Attributes 

Several commenters disagree with 

EPA’s proposed definition of a single air 

pollutant composed of the six wellmixed greenhouse gases as a class. 

Commenters argue that the analogy to 

VOCs is misplaced because VOCs are all 

part of a defined group of chemicals, for 

which there are established 

quantification procedures, and for 

which there were extensive data 

showing that the group of compounds 

had demonstrated and quantifiable 

effects on ambient air and human health 

and welfare, and for which verifiable 

dispersion models existed. They 

contend this is in stark contrast to the 

entirely diverse set of organic and 

inorganic compounds EPA has lumped 

together for purposes of the Proposed 

Findings, and for which no model can 

accurately predict or quantify the actual 

impact or improvement resulting from 

controlling the compounds. Moreover, 

they argue that the gases EPA is 

proposing to list together as one 

pollutant are all generated by different 

processes and, if regulated, would 

require different types of controls; the 

four gases emitted by mobile sources 

can generally be limited only by using 

controls that are specific to each. 

At least one commenter argues that 

EPA cannot combine greenhouse gases 

into one pollutant because their 

common attribute is not a ‘‘physical, 

chemical, biological or radioactive 

property’’ (quoting from CAA section 

302(g)), but rather their effect or impacts 

on the environment. They say this 

differs from VOCs, which share the 

common attribute of volatility, or PM 

which shares the physical property of 

being particles. 

As discussed above, the well-mixed 

greenhouse gases share physical 

attributes, as well as attributes based on 

sound policy considerations. The 

definition of ‘‘air pollutant’’ in CAA 

section 302(g) does not limit 

consideration of common attributes to 

those that are ‘‘physical, chemical, 

biological or radioactive property’’ as 

one commenter claims. Rather, the 

definition’s use of the adjectives 

‘‘physical, chemical, biological or 

radioactive’’ refer to the different types 

of substance or matter that is emitted. It 

is not a limitation on what 

characteristics the Administrator may 

consider when deciding how to group 

similar substances when defining a 

single air pollutant. 

The common attributes that the 

Administrator considered when 

defining the well-mixed greenhouse 

gases are reasonable. While these six 

substances may originate from different 

processes, and require different control 

strategies, that does not detract from the 

fact that they are all long-lived, wellmixed in the atmosphere, directly 

emitted, of well-known radiative 

forcing, and generally grouped and 

considered together in climate change 

scientific and policy forums. Indeed, 

other group pollutants also originate 

from a variety of processes and a result 

may require different control 

technologies. For example, both a power 

plant and a dirt road can result in PM 

emissions, and the method to control 

such emissions at each source would be 

different. But these differences in origin 

or control do not undermine the 

reasonableness of considering PM as a 

single air pollutant. The fact that there 

are differences, as well as similarities, 

among the well-mixed greenhouse gases 

does not render the decision to group 

them together as one air pollutant 

unreasonable. 

2. The Administrator’s Cause or 

Contribute Analysis Was Reasonable 

a. The Administrator Does Not Need To 

Find Significant Contribution, or 

Establish a Bright Line 

Many commenters essentially argue 

that EPA must establish a bright line 

below which it would never find 

contribution regardless of the air 

pollutant, air pollution, and other 

factors before the Agency. For example, 

some commenters argue that EPA must 

provide some basis for determining de 

minimis amounts that fall below the 

threshold of ‘‘contributing’’ to the 

endangerment of public health and 

welfare under CAA section 202(a). 


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Commenters take issue with EPA’s 

statement that it ‘‘need not determine at 

this time the circumstances in which 

emissions would be trivial or de 

minimis and would not warrant a 

finding of contribution.’’ Commenters 

argue that EPA cannot act arbitrarily by 

determining that a constituent 

contributing a certain percent to 

endangerment in one instance is de 

minimis and in another is contributing 

to endangerment of public health and 

welfare. They request that EPA revise 

the preamble language to make clear 

that the regulated community can rely 

on its past determinations with respect 

to ‘‘contribution’’ determinations to 

predict future agency action and argue 

that EPA should promulgate guidance 

on how it determines whether a 

contribution exceeds a de minimis level 

for purposes of CAA section 202(a) 

before finalizing the proposal. 

The commenters that argue that the 

air pollution EPA must analyze to 

determine endangerment is limited to 

the air pollution resulting from new 

motor vehicles also argue that as a 

result, the contribution of emissions 

from new motor vehicles must be 

significant. They essentially contend 

that the endangerment and cause or 

contribute tests are inter-related and the 

universe of both tests is the same. In 

support of their argument, commenters 

argue that because the clause ‘‘cause, or 

contribute to, air pollution’’ is in plural 

form, it must be referring back to ‘‘any 

class or classes of new motor vehicles or 

new motor vehicle engines,’’ 

demonstrating that EPA must consider 

only the emissions from new motor 

vehicles which emit the air pollution 

which endangers. 

Since the Administrator issued the 

Proposed Findings, the DC Circuit 

issued another opinion discussing the 

concept of contribution. See Catawba 

County v. EPA, 571 F.3d 20 (DC Cir. 

2009). This decision, along with others, 

supports the Administrator’s 

interpretation that the level of 

contribution under CAA section 202(a) 

does not need to be significant. The 

Administrator is not required to 

establish a bright line below which she 

would never find contribution under 

any circumstances. Finally, it is 

reasonable for the Administrator to 

apply a ‘‘totality-of-the-circumstances 

test to implement a statute that confers 

broad discretionary authority, even if 

the test lacks a definite ‘threshold’ or 

‘clear line of demarcation to define an 

open-ended term.’’ Id. at 39 (citations 

omitted). 

In upholding EPA’s PM2.5 attainment 

and nonattainment designation 

decisions, the DC Circuit analyzed CAA 

section 107(d), which requires EPA to 

designate an area as nonattainment if it 

‘‘contributes to ambient air quality in a 

nearby area’’ not attaining the national 

ambient air quality standards. Id. at 35. 

The court noted that it had previously 

held that the term ‘‘contributes’’ is 

ambiguous in the context of CAA 

language. See EDF v. EPA, 82 F.3d 451, 

459 (DC Cir. 1996). ‘‘[A]mbiguities in 

statutes within an agency’s jurisdiction 

to administer are delegations of 

authority to the agency to fill the 

statutory gap in reasonable fashion.’’ 

571 F.3d at 35 (citing Nat’s Cable & 

Telecomms. Ass’c v. Brand X Internet 

Servs, 545 U.S. 967, 980 (2005)). 

The court then proceeded to consider 

and reject petitioners’ argument that the 

verb ‘‘contributes’’ in CAA section 

107(d) necessarily connotes a significant 

causal relationship. Specifically, the DC 

Circuit again noted that the term is 

ambiguous, leaving it to EPA to 

interpret in a reasonable manner. In the 

context of this discussion, the court 

noted that ‘‘a contribution may simply 

exacerbate a problem rather than cause 

it * * * ’’ 571 F.3d at 39. This is 

consistent with the DC Circuit’s 

decision in Bluewater Network v. EPA, 

370 F.3d 1 (DC Cir. 2004), in which the 

court noted that the term contribute in 

CAA section 213(a)(3) ‘‘[s]tanding alone, 

* * * has no inherent connotation as to 

the magnitude or importance of the 

relevant ‘share’ in the effect; certainly it 

does not incorporate any ‘significance’ 

requirement.’’ 370 F.3d at 13. The court 

found that the bare ‘‘contribute’’ 

language invests the Administrator with 

discretion to exercise judgment 

regarding what constitutes a sufficient 

contribution for the purpose of making 

an endangerment finding. Id. at 14. 

Finally, in Catawba County, the DC 

Circuit also rejected ‘‘petitioners’ 

argument that EPA violated the statute 

by failing to articulate a quantified 

amount of contribution that would 

trigger’’ the regulatory action. 571 F.3d 

at 39. Although petitioners preferred 

that EPA establish a bright-line test, the 

court recognized that the statute did not 

require that EPA ‘‘quantify a uniform 

amount of contribution.’’ Id. 

Given this context, it is entirely 

reasonable for the Administrator to 

interpret CAA section 202(a) to require 

some level of contribution that, while 

more than de minimis or trivial, does 

not rise to the level of significance. 

Moreover, the approach suggested by at 

least one commenter collapses the two 

prongs of the test by requiring that 

contribution must be significant because 

any climate change impacts upon which 

an endangerment determination is made 

result solely from the greenhouse gas 

emissions of motor vehicles. It 

essentially eliminates the ‘‘contribute’’ 

part of the ‘‘cause or contribute’’ portion 

of the test. This approach was clearly 

rejected by the en banc court in Ethyl. 

541 F.2d at 29 (rejecting the argument 

that the emissions of the fuel additive to 

be regulated must ‘‘in and of itself, i.e. 

considered in isolation, endanger[ ] 

public health.’’); see also Catawba 

County, 571 F.3d at 39 (noting that even 

if the test required significant 

contribution it would be reasonable for 

EPA to find a county’s addition of PM2.5

is significant even though the problem 

would persist in its absence). It is the 

commenter, not EPA that is ignoring the 

statutory language. Whether or not the 

clause ‘‘cause, or contribute to, air 

pollution’’ refers back to ‘‘any class or 

classes of new motor vehicles or new 

motor vehicle engines,’’ or to ‘‘emission 

of any air pollutant,’’ the language of 

CAA section 202(a) clearly contemplates 

that emission of an air pollutant from 

any class or classes may merely 

contribute to, versus cause, the air 

pollution which endangers. 

It is also reasonable for EPA to decline 

to establish a ‘‘bright-line ‘objective’ test 

of contribution.’’ 571 F.3d at 39. As 

noted in the Proposed Findings, when 

exercising her judgment, the 

Administrator not only considers the 

cumulative impact, but also looks at the 

totality of the circumstances (e.g., the air 

pollutant, the air pollution, the nature of 

the endangerment, the type of source 

category, the number of sources in the 

source category, and the number and 

type of other source categories that may 

emit the air pollutant) when 

determining whether the emissions 

justify regulation under the CAA. Id. (It 

is reasonable for an agency to adopt a 

totality-of-the-circumstances test). 

Even if EPA agreed that a level of 

significance was required to find 

contribution, for the reasons discussed 

above, EPA would find that the 

contribution from CAA section 202(a) 

source categories is significant. Their 

emissions are larger than the great 

majority of emitting countries, larger 

than several major emitting countries, 

and they constitute one of the largest 

parts of the U.S. emissions inventory. 

b. The Unique Global Aspects of 

Climate Change Are an Appropriate 

Consideration in the Contribution 

Analysis 

Some commenters disagree with 

statements in the Proposed Findings 

that the ‘‘unique, global aspects of the 

climate change problem tend to support 

a finding that lower levels of emissions 

should be considered to contribute to 

the air pollution than might otherwise 


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be appropriate when considering 

contribution to a local or regional air 

pollution problem.’’ They argue there is 

no basis in the CAA or existing EPA 

policy for this position, and that it 

reveals an apparent effort to expand 

EPA’s authority to the ‘‘truly trivial or 

de minimis’’ sources that are 

acknowledged to be outside the scope of 

regulation, in that it expands EPA’s 

authority to regulate pollutants to 

address global effects. 

Commenters also assert that contrary 

to EPA’s position, lower contribution 

numbers are appropriate when looking 

at local pollution, like nonattainment 

concerns—in other words, in the 

context of a statutory provision like 

CAA section 213 specifically aimed at 

targeting small source categories to help 

nonattainment areas meet air quality 

standards. However, they conclude this 

policy is simply inapplicable in the 

context of global climate change. 

As discussed above, the term 

‘‘contribute’’ is ambiguous and subject 

to the Administrator’s reasonable 

interpretation. It is entirely appropriate 

for the Administrator to look at the 

totality of the circumstances when 

making a finding of contribution. In this 

case, the Administrator believes that the 

global nature of the problem justifies 

looking at contribution in a way that 

takes account of these circumstances. 

More specifically, because climate 

change is a global problem that results 

from global greenhouse gas emissions, 

there are more sources emitting 

greenhouse gases (in terms both of 

absolute numbers of sources and types 

of sources) than EPA typically 

encounters when analyzing contribution 

towards a more localized air pollution 

problem. From a percentage perspective, 

there are no dominating sources and 

fewer sources that would even be 

considered to be close to dominating. 

The global problem is much more the 

result of numerous and varied sources 

each of which emit what might seem to 

be smaller percentage amounts when 

compared to the total. The 

Administrator’s approach recognizes 

this reality, and focuses on evaluating 

the relative importance of the CAA 

section 202(a) source categories 

compared to other sources when viewed 

in this context. 

This recognition of the unique totality 

of the circumstances before the 

Administrator now as compared to 

previous contribution decisions is 

entirely appropriate. It is not an attempt 

by the Administrator to regulate ‘‘truly 

trivial or de minimis’’ sources, or to 

regulate sources based on their global 

effects. The Administrator is 

determining whether greenhouse gas 

emissions from CAA section 202(a) 

sources contribute to an air pollution 

problem is endangering U.S. public 

health and welfare. As discussed in the 

Proposed Findings, no single 

greenhouse gas source category 

dominates on the global scale, and many 

(if not all) individual greenhouse gas 

source categories could appear small in 

comparison to the total, when, in fact, 

they could be very important 

contributors in terms of both absolute 

emissions or in comparison to other 

source categories, globally or within the 

United States. If the United States and 

the rest of the world are to combat the 

risks associated with global climate 

change, contributors must do their part 

even if their contributions to the global 

problem, measured in terms of 

percentage, are smaller than typically 

encountered when tackling solely 

regional or local environmental issues. 

The commenters’ approach, if used 

globally, would effectively lead to a 

tragedy of the commons, whereby no 

country or source category would be 

accountable for contributing to the 

global problem of climate change, and 

nobody would take action as the 

problem persists and worsens. The 

Administrator’s approach, on the 

contrary, avoids this kind of approach, 

and is a reasonable exercise of her 

discretion to determine contribution in 

the global context in which this issue 

arises. 

Importantly, as discussed above, the 

contribution from CAA section 202(a) 

sources is anything but trivial or de 

minimis under any interpretation of 

contribution. See, Massachusetts v. 

EPA, 549 U.S. at 1457–58 (‘‘Judged by 

any standard, U.S. motor-vehicle 

emissions make a meaningful 

contribution to greenhouse gas 

concentrations and hence, * * * to 

global warming’’). 

c. The Administrator Reasonably Relied 

on Comparisons of Emissions From 

Existing CAA Section 202(a) Source 

Categories 

i. It Was Reasonable To Use Existing 

Emissions From Existing CAA Section 

202(a) Source Categories Instead of 

Projecting Future Emissions From New 

CAA Section 202(a) Source Categories 

Many commenters argue that EPA 

improperly evaluated the emissions 

from the entire motor vehicle fleet, and 

it is required to limit its calculation to 

just emissions from new motor vehicles. 

Thus the emissions that EPA should 

consider in the cause or contribute 

determination is far less than the 4.3 

percent of U.S. greenhouse gas 

emissions attributed to motor vehicles 

in the Proposed Findings, because this 

number includes both new and existing 

motor vehicles. One commenter 

calculated the emissions from new 

motor vehicles as being 1.8 percent of 

global emissions, assuming 

approximately one year of new motor 

vehicle production in the United States 

(11 million vehicles) in a total global 

count currently of approximately 600 

million motor vehicles. 

In the Proposed Findings, EPA 

determined the emissions from the 

entire fleet of motor vehicles in the 

United States for a certain calendar year. 

EPA explained that, consistent with its 

traditional practice, it used the recent 

motor vehicle emissions inventory for 

the entire fleet as a surrogate for 

estimates of emissions for just new 

motor vehicles and engines. This was 

appropriate because future projected 

emissions are uncertain and current 

emissions data are a reasonable proxy 

for near-term emissions. 

In effect, EPA is using the inventory 

for the current fleet of motor vehicles as 

a reasonable surrogate for a projection of 

the inventory from new motor vehicles 

over the upcoming years. New motor 

vehicles are produced year in and year 

out, and over time the fleet changes over 

to a fleet composed of such vehicles. 

This occurs in a relatively short time 

frame, compared to the time period at 

issue for endangerment. Because new 

motor vehicles are produced each year, 

and continue to emit over their entire 

life, over a relatively short period of 

time the emission from the entire fleet 

is from vehicles produced after a certain 

date. In addition, the emissions from 

new motor vehicles are not limited to 

the emissions that occur only during the 

one year when they are new, but are 

emissions over the entire life of the 

vehicle. 

In such cases, EPA has traditionally 

used the recent emissions from the 

entire current fleet of motor vehicles as 

a reasonable surrogate for such a 

projection instead of trying to project 

and model those emissions. While this 

introduces some limited degree of 

uncertainty, the difference between 

recent actual emissions from the fleet 

and projected future emissions from the 

fleet is not expected to differ in any way 

that would substantively change the 

decision made concerning cause or 

contribution. There is not a specific 

numerical bright line that must be 

achieved, and the numerical 

percentages are not treated and do not 

need to be treated as precise values. 

This approach provides a reasonable 

and clear indication of the relative 

magnitudes involved, and EPA does not 

believe that attempting to make future 


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projections (for both vehicles and the 

emissions value they are compared to) 

would provide any greater degree of 

accuracy or precision in developing 

such a relative comparison. 

ii. The Administrator Did Not Have To 

Use a Subset or Reduced Emissions 

Estimate From Existing CAA Section 

202(a) Source Categories 

Several commenters note that 

although EPA looks at emissions from 

all motor vehicles regulated under CAA 

section 202(a) in its contribution 

analysis, the Presidential announcement 

in May 2009 indicated that EPA was 

planning to regulate only a subset of 

202(a) sources. Thus, they question 

whether the correct contribution 

analysis should look only at the 

emissions from that subset and not all 

CAA section 202(a) sources. Some 

commenters also argue that because 

emission standards will not eliminate 

all greenhouse gas emissions from motor 

vehicles, the comparison should 

compare the amount of greenhouse gas 

emissions ‘‘reduced’’ by those standards 

to the global greenhouse emissions. 

They also contend that the cost of the 

new standards will cause individual 

consumers, businesses, and other 

vehicle purchasers to hold on to their 

existing vehicles to a greater extent, 

thereby decreasing the amount of 

emissions reductions attributable to the 

standard and appropriately considered 

in the contribution analysis. Some 

commenters go further and contend that 

EPA also can only include that 

incremental reduction that the EPA 

regulations will achieve beyond any 

reductions resulting from CAFE 

standards that NHTSA will set. 

Although the May announcement and 

September proposed rule involved only 

the light duty motor vehicle sector, the 

Administrator is making this finding for 

all classes of new motor vehicles under 

CAA section 202(a). Thus, although the 

announcement and proposed rule 

involve light duty vehicles, EPA is 

working to develop standards for the 

rest of the classes of new motor vehicles 

under CAA section 202(a). As the 

Supreme Court noted, EPA has 

‘‘significant latitude as to the manner, 

timing, content, and coordination of its 

regulations with those of other agencies. 

Massachusetts v. EPA, 549 U.S. at 533. 

The argument that the Administrator 

can only look at that portion of 

emissions that will be reduced by any 

CAA section 202(a) standards, and even 

then only the reduction beyond those 

attributable to CAFE rules, finds no 

basis in the statutory language. The 

language in CAA section 202(a) requires 

that the Administrator set ‘‘standards 

applicable to the emission of any air 

pollutant from [new motor vehicles], 

which in [her] judgment cause, or 

contribute to, air pollution which 

[endangers].’’ It does not say set 

‘‘standards applicable to the emission of 

any air pollutant from [new motor 

vehicles], if in [her] judgment the 

emissions of that air pollutant as 

reduced by that standard cause, or 

contribute to, air pollution which 

[endangers].’’ As discussed above, the 

decisions on cause or contribute and 

endangerment are separate and distinct 

from the decisions on what emissions 

standards to set under CAA section 

202(a). The commenter’s approach 

would improperly integrate these 

separate decisions. Indeed, because, as 

discussed above, the Administrator does 

not have to propose standards 

concurrent with the endangerment and 

cause or contribute findings, she would 

have to be prescient to know at the time 

of the contribution finding exactly the 

amount of the reduction that would be 

achieved by the standards to be set. As 

discussed above, for purposes of these 

findings we look at what would be the 

emissions from new motor vehicles if no 

action were taken. Current emissions 

from the existing CAA section 202(a) 

vehicle fleet are an appropriate estimate. 

d. The Administrator Reasonably 

Compared CAA Section 202(a) Source 

Emissions to Both Global and Domestic 

Emissions of Well-Mixed Greenhouse 

Gases 

EPA received many comments on the 

appropriate comparison(s) for the 

contribution analysis. Several 

commenters argue that in order to get 

around the ‘‘problem’’ of basing an 

endangerment finding upon a source 

category that contributes only 1.8 

percent annually to global greenhouse 

gas emissions, EPA inappropriately also 

made comparisons to total U.S. 

greenhouse gas emissions. These 

commenters argue that a comparison of 

CAA section 202(a) source emissions to 

U.S. greenhouse gas emissions, versus 

global emissions, is arbitrary for 

purposes of the cause or contribute 

analysis, because it conflicts with the 

Administrator’s definition of ‘‘air 

pollution,’’ as well as the nature of 

global warming. They note that 

throughout the Proposed Findings, the 

Administrator focuses on the global 

nature of greenhouse gas. Thus, they 

continue, while the percentage share of 

motor vehicle emissions at the U.S. 

level may be relevant for some 

purposes, it is irrelevant to a finding of 

whether these emissions contribute to 

the air pollution, which the 

Administrator has proposed to define on 

a global rather than a domestic basis. 

Commenters also accuse EPA of 

arbitrarily picking and choosing when it 

takes a global approach (e.g., 

endangerment finding) and when it does 

not (e.g., contribution findings). 

The language of CAA section 202(a) is 

silent regarding how the Administrator 

is to make her contribution analysis. 

While it requires that the Administrator 

assess whether emission of an air 

pollutant contributes to air pollution 

which endangers, it does not limit how 

she may undertake that assessment. It 

surely is reasonable that the 

Administrator look at how CAA section 

202(a) source category emissions 

compare to global emissions on an 

absolute basis, by themselves. But the 

United States as a nation is the second 

largest emitter of greenhouse gases. It is 

entirely appropriate for the 

Administrator to decide that part of 

understanding how a U.S. source 

category emitting greenhouse gases fits 

into the bigger picture of global climate 

change is to appreciate how that source 

category fits into the contribution from 

the United States as a whole, where the 

United States as a country is a major 

emitter of greenhouse gases. Knowing 

that CAA section 202(a) source 

categories are the second largest emitter 

of well-mixed greenhouse gases in the 

country is relevant to understanding 

what role they play in the global 

problem and hence whether they 

‘‘contribute’’ to the global problem. 

Moreover, the Administrator is not 

‘‘picking and choosing’’ when she 

applies a global or domestic approach in 

these Findings. Rather, she is looking at 

both of these emissions comparisons as 

appropriate under the applicable 

science, facts, and law. 

e. The Amount of Well-Mixed 

Greenhouse Gas Emissions From CAA 

Section 202(a) Sources Reasonably 

Supports a Finding of Contribution 

Many commenters argue that the 

‘‘cause or contribute’’ prong of the 

Proposal’s endangerment analysis fails 

to satisfy the applicable legal standard, 

which requires more than a minimal 

contribution to the ‘‘air pollution 

reasonably anticipated to endanger 

public health or welfare.’’ They contend 

that emissions representing 

approximately four percent of total 

global greenhouse gas emissions are a 

minimal contribution to global 

greenhouse gas concentrations. 

EPA disagrees. As stated above, CAA 

section 202(a) source category total 

emissions of well-mixed greenhouse 

gases are higher than most countries in 

the world; countries that the U.S. and 

others believe play a major role in the 


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global climate change problem. 

Moreover, the percent of global wellmixed greenhouse gas emissions that 

CAA section 202(a) source categories 

represent is higher than percentages that 

the EPA has found contribute to air 

pollution problems. See Bluewater 

Network, 370 F.3d at 15 (‘‘For 

Fairbanks, this contribution was 

equivalent to 1.2 percent of the total 

daily CO inventory for 2001.’’) As noted 

above, there is no bright line for 

assessing contribution, but as discussed 

in the Proposed Findings and above, 

when looking at a global problem like 

climate change, with many sources of 

emissions and no dominating sources 

from a global perspective, it is 

reasonable to consider that lower 

percentages contribute than one may 

consider when looking at a local or 

regional problem involving fewer 

sources of emissions. The Administrator 

agrees that ‘‘[j]udged by any standard, 

U.S. motor-vehicle emissions make a 

meaningful contribution to greenhouse 

gas concentrations and hence, * * * to 

global warming.’’ Massachusetts v. EPA, 

549 U.S. at 525. 

VI. Statutory and Executive Order 

Reviews 

A. Executive Order 12866: Regulatory 

Planning and Review 

Under Executive Order (EO) 12866 

(58 FR 51735, October 4, 1993), this 

action is a ‘‘significant regulatory 

action’’ because it raises novel policy 

issues. Accordingly, EPA submitted this 

action to the Office of Management and 

Budget (OMB) for review under EO 

12866 and any changes made in 

response to Office of Management and 

Budget (OMB) recommendations have 

been documented in the docket for this 

action. 

B. Paperwork Reduction Act 

This action does not impose an 

information collection burden under the 

provisions of the Paperwork Reduction 

Act, 44 U.S.C. 3501 et seq. Burden is 

defined at 5 CFR 1320.3(b). These 

Findings do not impose an information 

collection request on any person. 

C. Regulatory Flexibility Act 

The Regulatory Flexibility Act (RFA) 

generally requires an agency to prepare 

a regulatory flexibility analysis of any 

rule subject to notice and comment 

rulemaking requirements under the 

Administrative Procedure Act or any 

other statute unless the agency certifies 

that the rule will not have a significant 

economic impact on a substantial 

number of small entities. Small entities 

include small businesses, small 

organizations, and small governmental 

jurisdictions. 

For purposes of assessing the impacts 

of this action on small entities, small 

entity is defined as: (1) A small business 

as defined by the Small Business 

Administration’s (SBA) regulations at 13 

CFR 121.201; (2) a small governmental 

jurisdiction that is a government of a 

city, county, town, school district, or 

special district with a population of less 

than 50,000; and (3) a small 

organization that is any not-for-profit 

enterprise which is independently 

owned and operated and is not 

dominant in its field. 

Because these Findings do not impose 

any requirements, the Administrator 

certifies that this action will not have a 

significant economic impact on a 

substantial number of small entities. 

This action does not impose any 

requirements on small entities. The 

endangerment and cause or contribute 

findings do not in-and-of-themselves 

impose any new requirements but rather 

set forth the Administrator’s 

determination on whether greenhouse 

gases in the atmosphere may reasonably 

be anticipated to endanger public health 

or welfare, and whether emissions of 

greenhouse gases from new motor 

vehicles and engines contribute to this 

air pollution. Accordingly, the action 

affords no opportunity for EPA to 

fashion for small entities less 

burdensome compliance or reporting 

requirements or timetables or 

exemptions from all or part of the 

Findings. 

D. Unfunded Mandates Reform Act 

This action contains no Federal 

mandates under the provisions of Title 

II of the Unfunded Mandates Reform 

Act of 1995 (UMRA), 2 U.S.C. 1531– 

1538 for State, local, or tribal 

governments or the private sector. The 

action imposes no enforceable duty on 

any State, local or tribal governments or 

the private sector. Therefore, this action 

is not subject to the requirements of 

sections 202 or 205 of the UMRA. 

This action is also not subject to the 

requirements of section 203 of UMRA 

because it contains no regulatory 

requirements that might significantly or 

uniquely affect small governments. This 

finding does not impose any 

requirements on industry or other 

entities. 

E. Executive Order 13132: Federalism 

This action does not have federalism 

implications. Because this action does 

not impose requirements on any 

entities, it will not have substantial 

direct effects on the States, on the 

relationship between the national 

government and the States, or on the 

distribution of power and 

responsibilities among the various 

levels of government, as specified in 

Executive Order 13132. Thus, Executive 

Order 13132 does not apply to this 

action. 

F. Executive Order 13175: Consultation 

and Coordination With Indian Tribal 

Governments 

This action does not have tribal 

implications, as specified in Executive 

Order 13175 (65 FR 67249, November 9, 

2000). This action does not have 

substantial direct effects on one or more 

Indian tribes, on the relationship 

between the Federal Government and 

Indian tribes, or on the distribution of 

power and responsibilities between the 

Federal Government and Indian tribes, 

nor does it impose any enforceable 

duties on any Indian tribes. Thus, 

Executive Order 13175 does not apply 

to this action. 

G. Executive Order 13045: Protection of 

Children From Environmental Health 

Risks and Safety Risks 

EPA interprets EO 13045 (62 FR 

19885, April 23, 1997) as applying only 

to those regulatory actions that concern 

health or safety risks, such that the 

analysis required under section 5–501 of 

the EO has the potential to influence the 

regulation. This action is not subject to 

EO 13045 because it does not establish 

an environmental standard intended to 

mitigate health or safety risks. Although 

the Administrator considered health 

and safety risks as part of these 

Findings, the Findings themselves do 

not impose a standard intended to 

mitigate those risks. 

H. Executive Order 13211: Actions 

Concerning Regulations That 

Significantly Affect Energy Supply, 

Distribution, or Use 

This action is not a ‘‘significant 

energy action’’ as defined in Executive 

Order 13211 (66 FR 28355 (May 22, 

2001)), because it is not likely to have 

a significant adverse effect on the 

supply, distribution, or use of energy 

because it does not impose any 

requirements. 

I. National Technology Transfer and 

Advancement Act 

Section 12(d) of the National 

Technology Transfer and Advancement 

Act of 1995 (‘‘NTTAA’’), Public Law 

104–113, 12(d) (15 U.S.C. at 272 note) 

directs EPA to use voluntary consensus 

standards in its regulatory activities 

unless to do so would be inconsistent 

with applicable law or otherwise 

impractical. Voluntary consensus 


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66546 Federal Register / Vol. 74, No. 239 / Tuesday, December 15, 2009 / Rules and Regulations 

standards are technical standards (e.g., 

materials specifications, test methods, 

sampling procedures, and business 

practices) that are developed or adopted 

by voluntary consensus standards 

bodies. NTTAA directs EPA to provide 

Congress, through OMB, explanations 

when the Agency decides not to use 

available and applicable voluntary 

consensus standards. 

This action does not involve technical 

standards. Therefore, EPA did not 

consider the use of any voluntary 

consensus standards. 

J. Executive Order 12898: Federal 

Actions To Address Environmental 

Justice in Minority Populations and 

Low-Income Populations 

Executive Order (EO) 12898 (59 FR 

7629, Feb. 16, 1994) establishes federal 

executive policy on environmental 

justice. Its main provision directs 

federal agencies, to the greatest extent 

practicable and permitted by law, to 

make environmental justice part of their 

mission by identifying and addressing, 

as appropriate, disproportionately high 

and adverse human health or 

environmental effects of their programs, 

policies, and activities on minority 

populations and low-income 

populations in the United States. 

EPA has determined that these 

Findings will not have 

disproportionately high and adverse 

human health or environmental effects 

on minority or low-income populations 

because it does not affect the level of 

protection provided to human health or 

the environment. Although the 

Administrator considered climate 

change risks to minority or low-income 

populations as part of these Findings, 

this action does not impose a standard 

intended to mitigate those risks and 

does not impose requirements on any 

entities. 

K. Congressional Review Act 

The Congressional Review Act, 5 

U.S.C. 801 et seq., as added by the Small 

Business Regulatory Enforcement 

Fairness Act of 1996, generally provides 

that before a rule may take effect, the 

agency promulgating the rule must 

submit a rule report, which includes a 

copy of the rule, to each House of the 

Congress and to the Comptroller General 

of the United States. EPA will submit a 

report containing this rule and other 

required information to the U.S. Senate, 

the U.S. House of Representatives, and 

the Comptroller General of the United 

States. This action is not a ‘‘major rule’’ 

as defined by 5 U.S.C. 804(2). This rule 

will be effective January 14, 2010. 

Dated: December 7, 2009. 

Lisa P. Jackson, 

Administrator. 

[FR Doc. E9–29537 Filed 12–14–09; 8:45 am] 

BILLING CODE 6560–50–P 


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