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A flotilla of tabular icebergs drifts in the Southern Ocean, near the outlet of the subglacial Wilkes Basin, eastern Antarctica. (Christina Riesselman)
Chris Mooney
Reporter covering climate change, energy and the environment.
Scientists reported on Wednesday that temperatures not much warmer than the planet is currently experiencing are enough to melt much of the eastern Antarctic ice cap, including at one time about 125,000 years ago. higher than now.
"It does not need to be a very big warming, as long as it stays 2 degrees warmer for a long enough time, that's the final game," said David Wilson, a geologist at Imperial College London and one of the authors of the new research, which was published in Nature. Scientists from Australia, New Zealand, Japan and Spain also contributed to the work.
The research is being done in a poorly studied area called the Wilkes Subglacial Basin, which is about the size of California and Texas combined and contains more than 10 feet of potential sea level rise. Led by three huge glaciers called Cook Mertz and Ninnis, the Wilkes are known to be vulnerable to rapid withdrawal because the ice is not on land and rises from a deep depression in the seabed.
In addition, this depression increases deeper as you move from the current Wilkes inland icy coast to the South Pole, a slope that could facilitate rapid ice loss.
The new science adds that during the warm periods of Earth's history, some or all of the ice in Wilkes' subglacial basin appears to have disappeared. This is a deduction made by researchers by studying the state of sediments in the seabed off the coast of the present ice front.
Here, they found several layers of sediment that appeared to be from where the ice is now, suggesting that when these layers of the seabed were laid, Wilkes contained either less ice or no ice at all. .
These sediments have corresponded in time to several well known warm periods, when the seas have increased considerably. But what is disturbing is that in many cases these times were not much hotter than what the planet is already at this moment.
The shape of the substratum under Antarctica, showing the very deep subglacial Wilkes Basin, using data from the Bedmap2 project. (Stewart Jamieson / Durham University).
Humans caused a warming of about 1 degree Celsius (1.8 degrees Fahrenheit) above pre-industrial planetary temperatures prior to about 1880. The world is committed to avoiding global warming above 2 degrees Celsius and even hopes to keep warming to 1.5 degrees, but current country promises are not enough to prevent these results.
In other words, we are already on a trajectory that could warm the planet enough to melt all or part of the Wilkes Basin.
"We are saying 2 degrees beyond the pre-industrial period and we are already beyond pre-industrialization," Wilson said. "So, it's potentially the kind of temperatures we could see this century."
However, the study can not reveal the speed with which the ice was removed from the Wilkes Basin. Warm past periods are thought to have been caused by slight variations in the Earth's orbit as it rotates around the sun, resulting in stronger summer heat. This heat has been maintained for thousands of years.
"What we can say is that during the [geological] The stadiums where temperatures were hot for a few millennia, that's where we see a separate signature in our records, "Wilson said. "We can not necessarily say that things have not been fast, but we can not solve them in our data."
The new research "contributes to the growing evidence that East Antarctica is not as stable as we thought," Isabella Velicogna, a glaciologist at the University of California at Irvine, said by email. Velicogna was not directly involved in the document.
"What I found particularly interesting is that the authors came to their conclusions using an offshore recording, not directly under the ice (which would be ideal), but that makes it more interesting to study this part. East Antarctica. ," she wrote.
"The only way to get unequivocal evidence of the ice cap retreat is to pierce the ice sheet itself in the basin," said Reed Scherer, an Antarctic expert at Northern Illinois University. "As long as this is not done, this study done just off the coast provides the clearest evidence so far that the glaciers of East and West Antarctic are threatening the Future with rising global temperatures ".
The new research comes as the US and British governments prepare to launch a multi-year research project to study the vast and isolated Thwaites Glacier of Antarctica, in western Antarctica, considered the greatest risk to coastal waters. this century.
The Thwaites and Wilkes situations are strangely similar: both have huge amounts of ice on the seabed rather than on the ground, and descending slopes that create what scientists call "marine cap instability." ". feet or more of sea level rise.
Twait Scambos, senior researcher at the National Snow and Ice Data Center in Boulder, Colorado, said at an event held in Columbia that Thwaites was "in a very unfortunate place … resting on one of the foundations rocky of West Antarctica. University Wednesday
The new study suggests that Thwaites is the beginning and not the end of our concerns. One of the main differences is that Thwaites already loses 50 billion tons of ice a year, while the Wilkes area seems to be relatively unchanged for the moment, according to Wilson.
But it may be that the world is already warm enough to wake up West Antarctica, but a little more heat will cause the same phenomenon in parts of the East Antarctic Ice Sheet. This would not only greatly explain the connection between past sea level and past temperatures in Earth's history – it would further illuminate the future we are heading towards.
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