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Antarctic instability is spreading & # 39; – BBC News

Thwaites Glacier

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Jeremy Harbeck

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The Thwaites glacier is unbalanced and its ice loss is accelerating

According to a new evaluation of 25 years of satellite data, almost a quarter of the West Antarctic ice sheet can now be considered unstable.

As unstable, the scientists mean that more ice is being lost from the region than the one that is being replenished through the snowfall.

Some of the largest glaciers have been reduced by more than 120 m in some places.

The losses of the two largest ice streams, Pine Island and Thwaites, have multiplied fivefold during the period of spacecraft observations.

And the changes have seen a marked acceleration in the last decade.

It is believed that the conductor is warm oceanic water that attacks the edges of the continent where its drainage glaciers enter the sea.

The British-led study was presented here in Milan at the Living Planet Symposium, the largest Earth observation conference in Europe.

It has also been published at the same time in the journal Geophysical Research Letters.

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Work: Esa's satellite registry incorporates more than 800 million measurements of ice height

The overview unites data from four superimposed satellite missions of the European Space Agency (Esa): ERS-1, ERS-2, Envisat and Cryosat.

All these spacecraft were launched with radar altimeters to measure the change in height in the east and west sectors of the ice sheet.

Their unified record from 1992 to 2017 was combined with weather models to distinguish elevation trends due to short-term variations in snowfall due to long-term changes in the ice mass as a result of melting and the birth of the iceberg .

"By using this unique dataset, we have been able to identify parts of Antarctica that are experiencing sustained and rapid thinning, regions that are changing faster than we might expect due to normal weather patterns," said Dr. Malcolm. McMillan from the University of Lancaster. Center of the United Kingdom for polar observation and modeling.

"We can now clearly see how these regions have expanded over time, extending inland through some of the most vulnerable parts of West Antarctica, which is critical to understanding the contribution of the ice sheet to the increase in sea ​​level worldwide, "he told BBC News.

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Title of the mediaRecent years in the satellite record show an accelerated loss.

If the western and eastern Antarctic is considered as a whole, this contribution is 4.6 mm during the study period. It would have been more than a millimeter higher even if the eastern sector of the ice sheet had not gained mass slightly during the period.

Even so, the losses observed in the west mean that the entrance of the continent to the ever-increasing surface of the world's oceans is now heading towards the higher end of the projections.

The computer models contained in the last major evaluation of the Intergovernmental Panel on Climate Change (IPCC) predicted, in the central range, 5 cm of sea level rise from the Antarctic by 2100.

As things stand, it is likely to be another 10 cm taller, says CPOM colleague and lead author of the newspaper, Professor Andrew Shepherd, of the University of Leeds.

"There is a stretch of 3,000 km of coastline, including the stretches of Bellingshausen, Amundsen and Marie Byrd Land, which clearly is not modeled properly because that's where all the ice comes from and more ice than expected," he explained.

"Then, we must go back to those models to try to understand what part of the signal they are not capturing, and certainly the altimeter data, which gives a very detailed description of the imbalance, should be the first people.

Now there is a concerted international effort to investigate the areas that change most rapidly.

This past expedition season saw a mission led by the United States and the United Kingdom to collect geophysical information from the ocean in front of the Thwaites glacier. Repeats of expeditions are planned to the surface of the ice for the next seasons.

Thwaites, and its neighboring Pine Island glacier, appear to be the Achilles heel of the West Antarctic ice sheet.

Located in the Amundsen sea sector, they represent by far the greatest sign of imbalance. About 50% of its drainage basins are now losing mass, at average rates since 1992 of 28 trillion tons per year in Pine Island and 46 trillion tons per year in Thwaites.

But it's acceleration that says, scientists say.

Between 1992 and 1997, the loss rates were 2 billion tons per year and 12 billion tons per year, respectively. During the last period of the survey (2012 to 2016), the rate increases to 55 billion tons and 76 billion tons per year.

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