Wednesday, August 13, 2008

Antarctic climate: Short-term spikes, long-term warming linked to tropical Pacific

National Center for Atmospheric Research: Dramatic year-to-year temperature swings and a century-long warming trend across West Antarctica are linked to conditions in the tropical Pacific Ocean, according to a new analysis of ice cores conducted by scientists at the National Center for Atmospheric Research (NCAR) and the University of Washington (UW). The findings show the connection of the world's coldest continent to global warming, as well as to periodic events such as El Niño.

"As the tropics warm, so too will West Antarctica," says NCAR's David Schneider, who conducted the research with UW's Eric Steig. "These ice cores reveal that West Antarctica's climate is influenced by atmospheric and oceanic changes thousands of miles to the north." The research appears this week in the online Early Edition of Proceedings of the National Academy of Sciences. The work was supported by the National Science Foundation, NCAR's sponsor.

Scientists are keenly interested in whether warming will destabilize the West Antarctic ice sheet over a period of decades or centuries. The ice sheet covers an area the size of Mexico, averages about 6,500 feet deep, and, if melted, would raise global sea levels by about 8 to 16 feet (2.5-5 meters).

Antarctica's climate is difficult to study, partly because there are few observations of this vast and remote region and partly because the cold, dry atmosphere is unlike that of the other six continents. Scientists previously determined that Antarctica overall probably warmed by about 0.4 degrees Fahrenheit (0.2 degrees Celsius) in the last century. But it has not been apparent until now that low-lying West Antarctica is more responsive to global warming trends than East Antarctica, where wind patterns have largely kept out comparatively warm air.

…Although the heart of El Niño's oceanic warming is in the tropical Pacific, it often fosters a circulation pattern that pushes relatively mild, moist air toward West Antarctica, where it can temporarily displace much colder air. As a result, West Antarctica has one of the world's most variable climates. "These results help put Antarctica's recent climate trends into a global context," says Schneider. Steig adds that while the influence of tropical climate on West Antarctica climate was not unknown, "these results are the first to demonstrate that we can unambiguously detect that influence in ice core records."….

When a strong El Niño develops across the tropical Pacific, it can influence weather and climate as far away as the southern polar region. This occurs via a "wave train" of areas with unusually high or low pressure in the upper atmosphere (H's and L's) that leads to warmer-than-normal temperatures in West Antarctica. Bright reds near the equator show the unusually warm sea-surface temperatures (SSTs) associated with an El Niño during 1940-41. There are no SST data for that period for the portions of the Southern Ocean shown here. Analysis of ice cores drilled in West Antarctica (red dots) reveals that air temperatures there warmed by as much as 10° Fahrenheit as this three-year-long El Niño unfolded, then dropped by as much as 13° F afterward. (Image by Steve Deyo, ©UCAR.) News media terms of use*

No comments: