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Viewable Images

Caption for Item 1: Southern Hemisphere Surface Air Temperature Projection

This graphics shows the surface air temperature (Celsius) trend averaged over the years 2000 to 2050, based on model simulations that combine projected greenhouse gas and ozone trends. Most areas warm by 1 to 3 degrees Celsius (~3 to 6 Fahrenheit) in the model. Credit: Drew Shindell, Gavin Schmidt, NASA GISS

Caption for Item 2: Southern Ocean and Antarctica

Map of Antarctica and the surrounding seas and oceans. Credit: Claire Parkinson, NASA GSFC

Caption for Item 3: Antarctic Temperature Response to Positive Shift in SAM (in Celsius)

This image shows how temperatures (in degrees Celsius) respond in the Antarctic to a positive shift in the Southern Annular Mode (or Antarctic Oscillation) of approximately the same size as has taken place over the past three decades. The temperatures were based on two decades of satellite data. Credit: From Schneider, Steig and Comiso, J. Clim., 2004

Caption for Item 4: Antarctica Animation

This animation shows the globe tilting up to reveal Antarctica through the eyes of Canadian Space Agency's RADARSAT satellite.
Credit: NASA/Goddard Space Flight Center Scientific Visualization Studio.

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October 06, 2004 - (date of web publication)

STUDY SHOWS POTENTIAL FOR ANTARCTIC CLIMATE CHANGE

 

 

This graphics shows the surface air temperature (Celsius) trend averaged over the years 2000 to 2050, based on model simulations that combine projected greenhouse gas and ozone trends.

Item 1

Click on image to enlarge.

While Antarctica has mostly cooled over the last 30 years, the trend is likely to rapidly reverse, according to a computer model study by NASA researchers. The study indicates the South Polar Region is expected to warm during the next 50 years.

Findings from the study, conducted by researchers Drew Shindell and Gavin Schmidt of NASA's Goddard Institute of Space Studies (GISS), New York, appear in this week's Geophysical Research Letters. Shindell and Schmidt found depleted ozone levels and greenhouse gases are contributing to cooler South Pole temperatures.

Low ozone levels in the stratosphere and increasing greenhouse gases promote a positive phase of a shifting atmospheric climate pattern in the Southern Hemisphere, called the Southern Annular Mode (SAM). A positive SAM isolates colder air in the Antarctic interior.

In the coming decades, ozone levels are expected to recover due to international treaties that banned ozone-depleting chemicals. Higher ozone in the stratosphere protects Earth's surface from harmful ultraviolet radiation. The study found higher ozone levels might have a reverse impact on the SAM, promoting a warming, negative phase. In this way, the effects of ozone and greenhouse gases on the SAM may cancel each other out in the future. This could nullify the SAM's affects and cause Antarctica to warm.

 

 

Map of Antarctica and the surrounding seas and oceans.

Item 2

Click on the image to enlarge.

"Antarctica has been cooling, and one could argue some regions could escape warming, but this study finds this is not very likely," Shindell said. "Global warming is expected to dominate in future trends."

The SAM, similar to the Arctic Oscillation or Northern Annular Mode in the Northern Hemisphere, is a seesaw in atmospheric pressure between the pole and the lower latitudes over the Southern Ocean and the tip of South America.

These pressure shifts between positive and negative phases speed-up and slow down the westerly winds that encircle Antarctica. Since the late 1960s, the SAM has more and more favored its positive phase, leading to stronger westerly winds. These stronger westerly winds act as a kind of wall that isolates cold Antarctic air from warmer air in the lower latitudes, which leads to cooler temperatures.

Greenhouse gases and ozone depletion both lower temperatures in the high latitude stratosphere. The cooling strengthens the stratospheric whirling of westerly winds, which in turn influences the westerly winds in the lower atmosphere. According to the study, greenhouse gases and ozone have contributed roughly equally in promoting a strong-wind, positive SAM phase in the troposphere, the lowest part of the atmosphere.

 

 

This image shows how temperatures (in degrees Celsius) respond in the Antarctic to a positive shift in the Southern Annular Mode

Item 3

 

Shindell and Schmidt used the NASA GISS Climate Model to run three sets of tests, each three times. For each scenario, the three runs were averaged together. Scenarios included the individual effects of greenhouse gases and ozone on the SAM, and then a third run that examined the effects of the two together.

The model included interactions between the oceans and atmosphere. Each model run began in 1945 and extended through 2055. For the most part, the simulations matched well compared with past observations.

Model inputs of increasing greenhouse gases were based upon observations through 1999, and upon the Intergovernmental Panel on Climate Change mid-range estimates of future emissions. Stratospheric ozone changes were based on earlier NASA GISS model runs that were found to be in good agreement with past observations and similar to those found in other chemistry-climate models for the future.

 

 

This animation shows the globe tilting up to reveal Antarctica through the eyes of Canadian Space Agency's RADARSAT satellite.

Item 4

Click on image to view animation.

Shindell said the biggest long-term danger of global warming in this region would be ice sheets melting and sliding into the ocean. "If Antarctica really does warm up like this, then we have to think seriously about what level of warming might cause the ice sheets to break free and greatly increase global sea levels," he said.

In the Antarctic Peninsula, ice sheets as big as Rhode Island have already collapsed into the ocean due to warming. The warming in this area is at least partially a result of the strengthened westerly winds that pass at latitudes of about 60 to 65 degrees south. As the peninsula sticks out from the continent, these winds carry warm maritime air that heats the peninsula.

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