Taking Antartica's Temperature: Frozen Continent May Not Be Immune to Global Warming

Article excerpt

[ILLUSTRATION OMITTED]

Antarctica is a land of extremes: the driest, windiest, coldest place on Earth. The ice sheet that blankets the continent is, on average, 2 kilometers thick and covers nearly 14 million square kilometers. Antarctica is so remote and so isolated that as recently as 2007 scientists thought that it might be unaffected by global warming.

That year the Intergovernmental Panel on Climate Change concluded in its Fourth Assessment Report that Antarctica was the only continent where anthropogenic temperature change had not been detected. In contrast to the Arctic, the report said, ice in the far south wasn't experiencing alarming, widespread melting. Some data even suggested that the continent was moderately cooling. "As best we knew," says David Bromwich, a climate scientist at Ohio State University, "there was not much changing."

Climate change skeptics latched onto the report to bolster their own conclusions. But in truth scientists didn't really know much about Antarctica's climate, past or future, at the time. Few long-term, on-the-ground temperature records exist, and those that do date back only to the 1940s and '50s. And most of the long-running research stations that collected these data line the coastal perimeter; just a handful dot the expansive interior. It's like trying to measure what's happening on the coasts of the United States to determine what's going on in North Dakota, Bromwich says.

Yet, over the last six years researchers have found clever ways to take Antarctica's temperature and piece together its complicated climate history. Those efforts reveal that the continent is home to some of the most rapidly warming places on Earth. Whether natural or human-caused, Antarctica's changing climate makes it clear that the continent isn't as isolated as was once thought.

If these warming trends continue, what happens in Antarctica will have important consequences for the rest of the world. The Antarctic ice sheet stores roughly 70 percent of the planet's freshwater. If it melted entirely and drained into the ocean, global sea level would rise more than 60 meters--enough to submerge New York City, London, Copenhagen, Bangkok, all of Florida, much of the Netherlands, Bangladesh and many other low-lying coastal and island locales.

Fortunately, researchers don't expect the massive ice sheet to disappear anytime soon. But to plan for the future, officials need to know how much ice will melt and how quickly sea level will rise. When it comes to these sorts of estimates, Antarctica is the biggest unknown.

Geographic differences between Antarctica and the Arctic help explain why it has been easier to spot signs of climate change in the North. The Arctic is naturally warmer than the Antarctic--Greenland, for example, sits at a lower latitude than Antarctica--so it doesn't require as much warming to thaw out. Thus, rising Arctic temperatures have already caused startling changes. Last summer, 97 percent of Greenland's ice sheet experienced some degree of surface melting.

Another difference is that Antarctica is land surrounded by ocean while the Arctic is ocean surrounded by land. Much of the Arctic's melting ice is sea ice, or frozen seawater. When sea ice melts, nothing happens to sea level because the ice is already in the ocean and its melting doesn't change the ocean's volume. Disappearing sea ice does lead to more warming, however. As the white ice thins and reveals the darker ocean below, the Arctic absorbs more solar radiation, leading to more warming and ultimately more melting.

The Arctic is also just simpler to study. A trip to the far north is effortless compared with the journey to Antarctica. And people live in the Arctic, so scientists have a much longer history of climate observations and measurements, including knowledge from native cultures that have inhabited the region for thousands of years.

[ILLUSTRATION OMITTED]

[ILLUSTRATION OMITTED]

"Antarctic science tends to lag at least a decade behind Arctic science," says climate scientist David Schneider of the National Center for Atmospheric Research in Boulder, Colo. …