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PARIS, February 7 – Billions of tons of meltwater dumped into the world's oceans from the ice sheets of Greenland and Antarctica could improve extreme weather and destabilize the regional climate in a few decades, announced researchers yesterday.
These cast iron giants, especially Greenland, are about to further weaken the ocean currents that move cold waters southward along the seafloor while pushing the tropical waters to the north, have- they reported in the newspaper Nature.
Known as the Southern Rolling Circulation of the Atlantic (Amoc), this liquid conveyor belt plays a crucial role in the Earth's climate system and helps to ensure the relative warmth of the Northern Hemisphere.
"According to our models, this meltwater will cause significant disturbances in ocean currents and alter global warming levels," said lead author, Nicholas Golledge, associate professor at the Antarctic Research Center at Victoria University's Wellington, New Zealand.
The loss of mass of the Antarctic Ice Sheet, for its part, traps warmer waters beneath the surface, eroding glaciers from below, forming a vicious circle of accelerated melt that contributes to rising sea levels.
Most of the ice sheet studies have focused on how quickly they could decrease due to global warming and on increasing global temperatures before their disintegration, whether it continues over centuries or millennia become inevitable.
But much less research has been conducted on how meltwater could affect the climate system itself.
Colder temperatures
"The large-scale changes we observe in our simulations are conducive to a more chaotic climate with more extreme weather events and more intense and frequent heat waves," co-authored Natalya Gomez, a researcher in the Department of Earth Sciences. Earth and planets from McGill University. in Canada, told AFP.
"By the middle of the century," the researchers concluded, "the meltwaters of Greenland's ice cap are significantly disrupting the Amoc," which has already shown signs of slowing down.
This is "a much shorter time than expected," commented Helene Seroussi, a researcher at Sea Level and Ice's Jet Propulsion Laboratory Group in California, who did not participate in the study.
The results were based on highly detailed simulations combined with satellite observations of changes made to the ice sheets since 2010.
The weakening of the current in the Atlantic will likely result in an increase in air temperature in the High Arctic, eastern Canada and Central America, as well as colder temperatures northwest of Europe and on the east coast of North America.
The ice sheets of Antarctica and Greenland, which are no more than three kilometers thick, contain more than two-thirds of the world's freshwater, enough for the world's oceans to grow to 58 meters and seven meters, if they melted completely.
In addition to Greenland, the regions most exposed to global warming are West Antarctica and several large East Antarctic glaciers, which are much larger and more stable.
In a second study published yesterday in Nature, some of the same scientists have proposed new projections on the contribution of Antarctica to sea-level rise by 2100 – a very controversial subject.
Ice Cliffs
According to a controversial study conducted in 2016, the continent's ice cliffs – exposed to the disintegration of ice floes that extend beyond glaciers over ocean waters – were highly vulnerable to collapse and could lead to a rise in the level of the sea one meter by the end of the century.
That would have been enough to move up to 187 million people worldwide, especially in the densely populated deltas of low rivers of Asia and Africa, showed research.
But the new study challenges these results.
"Unstable ice cliffs have been proposed as a cause of the unstoppable collapse of large parts of the ice cap," said lead author Tamsin Edwards, a lecturer in geography at King's College London.
"But we have re-analyzed the data and found that it is not."
Edwards told AFP that the two new studies "predict a very likely contribution of 15 centimeters to Antarctica" by 2100, with an ascending limit of about 40 cm.
A special report on oceans published by the Intergovernmental Panel on Climate Change (IPCC), scheduled for September, will provide a much-awaited estimate of sea-level rise.
The last major IPCC assessment in 2013 did not take into account ice sheets – now considered the main contributor to thermal expansion and glaciers – due to lack of data. – AFP
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