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West Antarctica Warming in Triple Time

December 26, 2012

discovery.com

Bromwich

The study by Bromwich and colleagues suggests that such exceptional melting events as in January 2005 could become more frequent in the future. Top: Map of Antarctica showing the extent of surface melting in January 2005 observed from space. Bottom: Time series of mean January temperature at Byrd Station from 1957 to 2011 with the warm January 2005 highlighted with a yellow circle. Credit: background map from Google Earth; satellite observations of surface melting courtesy of G. Picard (LGGE)

The West Antarctic Ice Sheet is warming at twice the rate previously thought, say scientists who have teased the information from more than 50 years of temperature data at Byrd Station, in the center of the ice. The average temperature at that station has risen 4.3 degrees F (2.4 degrees C) since 1958, which is triple the warming rate of most of the planet and on par with the very fastest warming parts of the world.

Of particular concern is that the warming is partially taking place in the summer months. That’s when the already seasonal warmth, plus the new higher average air temperatures, combine and increase the likelihood of major melting events that destabilize the ice shelves. Those shelves hold back a lot of Antarctic glacial ice from reaching the sea, explained Ohio State University’s David Bromwich, the lead author on the study, which was published in the latest issue of Nature Geoscience.

“Lots of melting can do lots of damage to the ice shelves,” Bromwich told Discovery News. And that can ramp up Antarctica’s contribution to sea level rise worldwide. “We know that these melting events can happen today and we are likely to see more melting events.”

Researchers have already documented accelerating of glaciers along the Amundsen Sea coast, which is dumping more West Antarctic ice into the sea, but warmer sea temperatures had been seen as the primary cause of that. Air temperatures have been harder to pin down, due to large gaps in the records at Byrd Station.

“There are very, very few observations for that part of the world,” said Davis Schneider an Antarctic researcher at the National Center for Atmospheric Research, and not a contributor to the new study. Thinning ice sheets, borehole temperature readings and ice cores all provide indirect evidence of warming, he said, but what’s been needed is “ground-truthing” with old fashioned thermometer data.

“It’s those kind of data, that are fragmented, that this study has skillfully reconstructed,” said Schneider.

Two previous studies using the fragmented Byrd Station air temperature data had come to conflicting conclusions, which prompted Bromwich and his colleagues to do the most detailed and careful analysis yet. That included reconstructing data using climate models and temperature data from other Antarctic sites.

“We did a very, very careful job of it,” said Bromwich.

The new work is welcome, said Schneider, because getting a handle on what’s happening in Antarctic air temperatures has not been easy, but it’s essential.

“This is a very first-order question,” said Schneider. “Hopefully we can move beyond that. There is a lot less known about Antarctica than the Arctic and we have a lot of catching up to do.”

Bromwich3

Henry Brecher, research associate (now retired) at Byrd Polar Research Center at Ohio State University, took this picture when he was among scientists who “wintered over” at Byrd Station in 1959-1960, close to the time the region’s first temperature data were gathered. Credit: Henry Brecher, courtesy of Ohio State University.
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