# Presentation: 467565

## ICESat-1

***ICESat-1***
***Is detecting large changes in polar ice  associated with climate warming***

***Exploring the 3******rd****** Dimension:***
***A unique capability with laser altimetry.***

## "The Arctic is screaming," Mark Serreze, U. of Colorado, Assoc. Press.

“The tipping point for perennial sea ice has likely already been reached.”,  Joey Comiso, NASA, AGU presentation reported in Science. 

"At this rate, the Arctic Ocean could be nearly ice-free at the end of summer by 2012, much faster than previous predictions."  Jay Zwally, NASA, Assoc. Press.

"Our projection of 2013 for the removal of ice in summer is not accounting for the last two minima, in 2005 and 2007," Wieslaw Maslowski, Naval Postgraduate School, BBC News.

***“******The tipping point for perennial sea ice has likely already been reached.”,******  ****Joey Comiso, NASA, AGU presentation reported in Science.**** ***
***"At this rate, the Arctic Ocean could be nearly ice-free at the end of summer by 2012, much faster than previous predictions."***  *Jay Zwally, NASA, Assoc. Press.*
***"Our projection of 2013 for the removal of ice in summer is not accounting for the last two minima, in 2005 and 2007,"****** Wieslaw Maslowski, ****Naval Postgraduate School, BBC News.*

***Recent News on Arctic Sea Ice ***

## Climate Warming Signal is Largest in the Arctic

**Goddard Institute for Space Studies (GISS) Temperature Analysis**

***Climate Warming Signal is Largest in the Arctic***

## Arctic Sea Ice Declining Faster than 18 Models in IPCC 2007

**Arctic sea ice decline: Faster than forecast, *****GRL May 2007. ***
- J. Stroeve, M. Holland, W. Meier,T. Scambos, and M. Serreze, U. Colorado and NCAR

***Arctic Sea Ice Declining Faster than 18 Models in IPCC 2007***

**Principal Model Limitations:**
**1. Treatment of SEA ICE THICKNESS.**
**2. Treatment of OCEAN CIRCULATION.**

## ICESat Measurement of Freeboard

***ICESat Measurement of Freeboard***

## ICESat’s First Sea Ice Thickness Estimates

**Thickness**

**Freeboard**

***ICESat’s First Sea Ice Thickness Estimates***

## Decline in Age and Thickness of Arctic Sea Ice

**A younger, thinner Arctic ice cover: Increased potential for rapid,**
**extensive sea-ice loss, *****GRL Dec 2007,***
- J. A. Maslanik, C. Fowler, J. Stroeve, S. Drobot, J. Zwally, D. Yi, and W. Emery, U. Colorado and NASA Goddard
** ****Oldest and thickest multiyear ice has declined significantly.**
** ****Remaining ice is thinner and more vulnerable to increasing summer melting.**

## Model Suggests A Tipping Point In Ice Thickness 

***Model Suggests A Tipping Point In Ice Thickness ***

**NCAR CCSM3 Model: Marika Holland, Cecilia Bitz, Bruno Tremblay, Julienne Stroeve**

**Slide Credit: Adapted from Mark Serreze.**

## COUPLED SEA ICE/ATMOSPHERE/ OCEAN MODEL 

-  Model indicated that the _**thickness and volume**_ of sea ice declined even faster than the _**area**_ from 1997 through 2003.

** **Model and data both show a fundamental loss of thick 3 to 5 m in recent years.

***COUPLED SEA ICE/ATMOSPHERE/ OCEAN MODEL****** ***
***Wieslaw Maslowski et al, Naval Post Graduate School***

## Attribution Of Change (Maslowski, NPS)

- Background: atmospheric and radiative forcing only explained about 50% of the observed sea ice variations.

- RESULT:
-   Increased flow of ocean heat into the Arctic from the Pacific in the 2000’s coincides with the strong sea ice retreat in the 2000’s.
-   Oceanic forcing explains about 60% of the sea ice decrease (area and thickness) in the Western Arctic.

**Increased heat flow**

- Alaska

## Observed Thinning of Ice Remaining in Late October

**Large areas of 2 m ice replaced by < 1 m ice.**

**Most thick 3 to 4 m multiyear ice near Canada & Greenland is gone.**

**About half of the ice was thicker than 2 m in 2003.**

**Most of ice thicker than  2 m was gone by 2007.**

**Sea ice thickness derived from ICESat freeboard measurements**

## Changes in Arctic Sea Ice Thickness and Volume From ICESat-1 Data

***Changes in Arctic Sea Ice Thickness and Volume From ICESat-1 Data***

-  **Thickness and volume of sea ice are declining even faster than the area**
** ****Observations are consistent with the Maslowski ice-ocean model “prediction”.**

**Note: The methodology of deriving sea ice thickness from ICESat data and thickness maps have been published in several peer-reviewed papers, but these particular results are not yet published.**

## Ice Sheet Changes with Changing Climate

***Ice Sheet Changes with Changing Climate***

**Notes:**
Sea level is now rising 1 foot per 100 yrs.
Results from DECADES of ocean altimetry (in which NASA has been a major player since Seasat 1978) show current rate of 3.3 mm/yr.
Just 5 or 10 yrs ago, rate was about 2 mm/yr, now about 50% larger.
Can not account for all the causes.  Ice sheets remain the largest uncertainty.   Not so much for current mass balance, because we are getting new results from ICESat and GRACE, but for the future.

How do ice sheets respond to climate?: surface processes well know, but new processes. Not all accounted for in models.

Precipitation increase in Antarctica.  Could mitigate Greenland losses.   Inconsistency between models and what is happening ---- new IPPC report.

## Greenland Ice Sheet Changes from ICESat

***Greenland Ice Sheet Changes from ICESat***

## Thank You!

**Thank You!**

## BACKUP

## Ice Thickness Changes of Greenland Ice Sheet from ICESat

***Ice Thickness Changes of Greenland Ice Sheet from ICESat***

_** **__**Enhanced thickening inland and enhanced thinning at edges **_since the 1990’s.
-   _**Mass losses**_ from increased melting near margins and accelerating glacier outflow (mainly in Southeast and West ) _**exceed gains**_ from increased precipitation inland.
-   _**Net mass loss of about 120 Gt/yr**_ (0.3 mm/yr sea level rise) is consistent with GRACE mascon solutions (GSFC, Lutchke et al., Science 2006).
-   ICESat and GRACE consistently show _**increased mass losses mainly in drainage systems 3, 4, and 6. **_

## ICESat-1 and Future ICESat-2 based on Decades of Science Needs and Community Recommendations

***“******Possible changes in the mass balance of the Antarctic and Greenland ice sheets are ***_***fundamental gaps in our understanding***_*** and are crucial to the quantification and refinement of sea-level forecasts.”***
**Sea-Level Change report, NRC (1990).**

***“******Continued observations with satellite altimeters, including ... the ***_***laser altimeter***_*** on ICESat ... ***_***should be continued for at least 15 years***_*** ... to establish the climate sensitivities of the mass balance and decadal scale trends.”***
*** *****Climate Change 2001, IPCC (2001).**

***2007 NRC Decadal Survey: need long-term polar ice measurements, ICESat-2.***

***ICESat-1 and Future ICESat-2 based on Decades of Science Needs and Community Recommendations***

***“******Repetitive mapping of ice sheet elevation by ***_***satellite laser altimetry offers a unique opportunity to study the time-dependent behavior of the ice sheets***_***.***
**Antarctic Climate Research, Scientific Committee on Antarctic Research (1983)**