Antarctica's Atmosphere Warming Dramatically, Study Finds

Source:  Copyright 2006, National Geographic
Date:  March 30, 2006
Byline:  John Roach

The air over Antarctica has warmed dramatically over the past 30 years, according to a new study of archived data collected by weather balloons floated over the icy continent.

The greatest warming—nearly 1.4ºF (0.75ºC) per decade in the winter—has occurred about 3 miles (5 kilometers) above the surface.

Scientists are hard pressed to explain the temperature spike, which is three times larger than the global average. The rise cannot be explained by the climate models scientists use to predict the effects of global warming from increased greenhouse gases.

(Read National Geographic magazine's "Global Warning: Signs from Earth.")

"That could point to some mechanism of climate change we don't understand, a failing in these models, or just a result of natural climate variability," said John Turner, a climate scientist with the British Antarctic Survey in Cambridge, England.

Meanwhile, surface temperatures have increased 4.5ºF (2.5ºC) in the last 50 years on the Antarctic Peninsula, the mountainous arm that trails toward the southern tip of South America.

"But the rest of Antarctica has done virtually nothing [at the surface]", Turner said.

Turner is the lead author of the study, which appears in tomorrow's issue of the journal Science.

David Bromwich, a meteorologist with the Byrd Polar Research Center at Ohio State University in Columbus, said there's "no doubt this [warming] is real."

But, he added, the finding only "deepens the mystery of what's going on over Antarctica."

Potential Implications

According to Turner, the unexpected warming could affect snowfall across the continent, which might have implications for global sea-level rise.

Snowfall records of the past three decades show no change, Turner said. "But measuring snowfall is hard. Measuring temperature is obviously easier," he added.

Scientists expect the warming to create a small increase in snowfall over Antarctica, as the warmer, moister air blows over the continent and is cooled to form snow.

This in turn could mitigate, to a small extent, sea-level rise by "locking up" meltwater in the form of snow.

Since the atmospheric warming is greatest three miles (five kilometers) up in the atmosphere, Turner said it is unlikely to result in extensive melting of ice on the surface. The continent's tallest mountains are 2.5 miles (4 kilometers) high.

Complex Signals

Turner and his colleagues are now trying to understand why the atmosphere warming is disconnected from surface temperatures.

One possibility, he said, is that the region is showing a greater than expected sensitivity to greenhouse gases in the winter.

Antarctica is dark during the winter months, which means there is no sunlight to heat the surface.

However, the heat that is on the surface continues to radiate into the atmosphere, where it is trapped by the blanket of greenhouse gases, Turner explained.

Alternatively, the warming may reflect a change in air circulation patterns, though data collected at Antarctic weather stations suggest this has not happened, he said.

Bromwich, of the Byrd Center, said the findings fit the emerging picture of Earth experiencing the effects of global warming, such as the widely reported melting in the Arctic.

"To understand what is happening to our world, we also need to understand what is happening in Antarctica," Bromwich said.

"This [research] deepens the mystery rather than solves it, but it shows us the direction we should be looking."