Antarctica less frigid in last ice age than scientists previously estimated

Antarctica, the coldest place on Earth, was very, very cold during the last ice age -- but new research, published Thursday in the journal Science, suggests the Southern Continent wasn't quite as frigid as previously predicted.

Previous studies estimated temperatures across Antarctica dipped 9 degrees Celsius below present temperatures at the maximum extent of the last ice age, some 20,000 years ago.

The latest findings, however, suggest some parts of Antarctica were 10 degrees Celsius colder than they are today, while large portions of the continent, including central East Antarctica, were just 4 to 5 degrees colder.

"This is the first conclusive and consistent answer we have for all of Antarctica," lead study author Christo Buizert said in a press release.

"The surprising finding is that the amount of cooling is very different depending on where you are in Antarctica. This pattern of cooling is likely due to changes in the ice sheet elevation that happened between the ice age and today," said Buizert, an assistant professor of atmospheric sciences and climate change specialist at Oregon State University.

Efforts to predict how Earth and its natural systems will be affected by climate change rely upon accurate records of past climate patterns. It's especially important for climate scientists interested in the future of Antarctica's ice sheet to accurately model its past.

Like previous studies of the last ice age, the latest research effort relied on massive ice cores drilled from a variety of Antarctic glaciers. Traditionally, climate scientists have used water isotope ratios in different layers to estimate changes in temperature.

In Greenland, researchers use other types of paleoclimate data and analysis to calibrate the measured changes in water isotopes, ensuring more accurate temperature predictions.

However, in Antarctica, they don't have the benchmarks necessary for proper calibration.

"It is as if we had a thermometer, but we could not read the scale," said Buizert. "One of the places where we had no calibration is East Antarctica, where the oldest continuous records of ice cores have been drilled, making it a critical location for understanding climate history."

For the new study, researchers used two methods to estimate ancient temperatures and calibrate previous isotope measurements.

First, scientists used what's called borehole thermometry, which captures the temperature of different ice layers deep beneath the glacier's surface.

Because temperatures at the surface affect temperature distribution deep beneath Antarctica, deep-lying ice layers can contain the signatures of historic temperature changes.

Second, researchers studied patterns in the snowpack, which is converted to ice as it becomes layered and compacted over time. This conversion process is highly sensitive to changes in temperature.

Both analysis methods yielded similar results.

The data showed that in places where Antarctica's ice sheet was thickest, temperatures plunged a solid 10 degrees below current temperatures.

However, the last ice age reduced snowfall totals across much of the continent. In these areas -- because they weren't as elevated -- temperatures weren't quite as frigid.

"This relationship between elevation and temperature is well-known to mountaineers and pilots -- the higher you go, the colder it gets," Buizert said.

The authors of the latest study said their findings don't undermine estimates about how sensitive the planet is to rising or falling CO2 levels, the main culprit of human-caused climate change.

"This paper is consistent with the leading theories about sensitivity," Buizert said. "We are the same amount of worried today about climate change as we were yesterday."

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