Friday, March 31, 2006

Antarctic air is warming faster than rest of world; New finding could have implications for sea level rises

The Times
Antarctic air is warming faster than rest of world
New finding could have implications for sea level rises
By Mark Henderson

AIR temperatures above the entire frozen continent of Antarctica have risen three times faster than the rest of the world during the past 30 years.

While it is well established that temperatures are increasing rapidly in the Antarctic Peninsula, the land tongue that protrudes towards South America, the trend has been harder to confirm over the continent as a whole.

Now analysis of weather balloon data by scientists at the British Antarctic Survey (BAS) has shown that not only are the lower reaches of the Antarctic atmosphere warming, but that they are doing so at the fastest rate observed anywhere on Earth.

Temperatures in the troposphere — the lowest 8km (5 miles) of the atmosphere — have increased by between 0.5C and 0.7 C (0.9F and 1.3F) per decade over the past 30 years.

This signature of climate change is three times stronger than the average observed around the world, suggesting that global warming is having an uneven impact and that it could be greater for Antarctica.

It is already known that temperatures in the Arctic are rising steeply, but with the exception of the Antarctic peninsula, the data for the southern ice-cap are more mixed.

Although the Antarctic peninsula has warmed by more than 2.5C during the past 50 years, most surface measurements suggest that there have been no pronounced temperature changes elsewhere on the continent, while some have indicated a small cooling effect.

The new research, led by John Turner, of the BAS, shows that the air above the surface of Antarctica is definitely warming, in ways that are not predicted by climate models and that cannot yet be explained. The results are published today in the journal Science.

“The rapid surface warming of the Antarctic Peninsula and the enhanced global warming signal over the whole continent shows the complexity of climate change,” Dr Turner said.

“Greenhouses gases could be having a bigger impact in Antarctica than across the rest of the world and we don’t understand why.

“The warming above the Antarctic could have implications for snowfall across the Antarctic and sea level rise. Current climate model simulations don’t reproduce the observed warming, pointing to weaknesses in their ability to represent the Antarctic climate system. Our next step is to try to improve the models.”

The weather balloons from which the data has been collected have been launched daily from many of Antarctica’s research stations since 1957. These balloons carry instrument packages known as radiosondes, which measure temperature, humidity and winds at altitudes of 20km and beyond.

The radiosonde data showed a pronounced warming effect throughout the troposphere during the winter months, while the stratosphere above cooled appreciably.

There is increasing evidence that greenhouse gases such as carbon dioxide are creating a blanket about the Earth that traps heat at lower levels, warming the troposphere and surface, while cooling the stratosphere above.

The study is the third to be published this month to suggest that the effects of global warming on Antarctica are likely to be more pronounced than has often been predicted.

Research has indicated that the melting of the Greenland ice-cap in the Arctic could produce sea level rises that destabilise Antarctic ice-shelves, and Nasa satellite data have shown the internal Antarctic ice-sheets to be thinning.