• Poles: Towards a world without ice?
  • Wildlife: The domino effect of rapid melting ice in the Arctic
  • Report: Sea level will rise even faster than previously forecast

Satellites have been monitoring the Antarctic and Arctic ice masses for decades, but usually the results obtained combine data collected by different types of instruments. Now, a team led by scientists from the University of Washington has followed the evolution of those ice masses over a period of 16 years with the same technology: the lasers from the ICESat and ICESat-2 satellites.

Their data, published Thursday in the journal Science , shows that the net loss of ice from Antarctica and Greenland between 2003 and 2019 increased sea level by 1.4 centimeters. Greenland is responsible for two thirds of this increase and Antarctica for the other third, according to this study, which has measured the evolution of ice sheets, glaciers and ice shelves that detach and float in the ocean and that therefore it is one of the most detailed that has been done so far.

Every year Greenland loses, on average, 200 gigatons of ice and Antarctica 118 gigatons (one gigaton of ice would serve to fill 400,000 Olympic swimming pools).

Why does the Arctic thaw faster than Antarctica? "The contribution of Antarctica to sea level rise is almost entirely due to the ice that flows more rapidly towards the ocean. Snow melts very little every year because it is very cold there, even in summer. In contrast, areas Greenland's coasts are much warmer , so a lot of ice and snow melts every summer and at the same time, glacier ice goes to the ocean faster, "explains Benjamin Smith, glaciologist at the University of Washington and lead author of the research.

Worrying results

According to Smith, his results "are quite troubling because we are seeing substantial contributions from ice sheets at sea level . When these contributions remain stable over a long period, low-lying regions become more vulnerable areas to floods and storms, and these are areas where many people live. Our results also show a rapid thinning of the ice shelves in West Antarctica, which suggests that we are expecting further rises in sea level, "he says. .

In Antarctica they have seen two trends: on the one hand, the ice sheet is increasing in thickness in some areas of the interior of the continent , probably as a result of increased snow. But in other areas, such as the West and the Antarctic Peninsula, glaciers are decreasing as a result of the entry of warmer water that erodes and melts them. The Thwaites and Crosson ice shelves (or platforms) have lost the most weight, with an annual loss of five and three meters respectively.

Greenland has also seen significant thinning of coastal glaciers. For example, the Kangerdulgssuaq glacier and the Jakobshavn lost between four and six meters each year.

" If you look at a glacier or ice sheet for a month or a year, you're not going to be able to find out much about the impact of the climate . Now we have data from a 16-year period and we can be much more sure that the changes we see in Ice is about long-term changes in the climate, "says the glaciologist.

Smith believes that climate change "is most likely playing a major role in the changes" they are observing with their radars: "In Greenland, losses [of ice] are associated with warmer temperatures and more melted surface. In Antarctica, those Changes are linked to the presence of more warm water melting the ice that is floating in the ocean. And those changes in ocean water that cause that melting are consistent with what we expect from climate change, "he argues.

Last fall, the IPCC experts' special report on oceans and cryosphere warned that global sea level had risen 15 centimeters globally during the 20th century and is now accelerating, reaching 3.6 millimeters per year. The forecasts for the end of the century were not more hopeful. According to the UN group of experts, if the temperature rise remains well below two degrees compared to the beginning of the industrial era, the rise in sea level in 2100 could be between 30 and 60 centimeters but if not emissions were reduced could exceed the meter.

Smith points out that his study results fit well with the recent IPCC report: "Although our research is limited to the 2003-2019 period, it is consistent with the scientific consensus that higher surface and ocean temperatures will lead to a rise in sea level, "he concludes.

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