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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 warm up, as long as it stays 2 degrees warmer for a long enough time, it's the end of the game," said David Wilson, 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. That's what the researchers deduced by studying sediment traces in the seabed off the current 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.
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're already beyond pre-industrial," Wilson said. "So, these are potentially the types of temperatures that we could see this century."
However, the study can not reveal the speed with which the ice was removed from the Wilkes Basin. The past hot periods in question are thought to have been caused by slight variations in the orbit of the Earth that revolves around the sun, resulting in stronger summer heat. This heat has been maintained for thousands of years.
"What we can certainly say is that during the [geological] The stages where temperatures have been warm for a few millennia is where we see a distinct signature in our records, "said Wilson." We can not necessarily say things did not happen quickly, but we can not solve that 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 this makes it more interesting to study this part. of East Antarctica, "she wrote.
"The only way to obtain unequivocal evidence of ice sheet removal 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 to date that the eastern and western glaciers of Antarctica threaten 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, located in Western Antarctica and considered the greatest risk for coastal of this century.
The Thwaites and Wilkes situations are strangely similar: both have huge amounts of bottom- and bottom-facing ice, and descending slopes that create what scientists call "ice cap instability." Marine". And both contain enough ice to unlock 10 feet or more from sea level.
Thwaites is "sitting in a very unhappy place, resting on one of the deepest foundations of Western Antarctica," said Ted Scambos, principal investigator at the National Snow and Ice Data Center in New York. Boulder, Colorado. Columbia 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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