More ice and yet rising sea levels due to melting ice sheets | Polarjournal
The amounts of fresh water flowing into the sea from the melting Antarctic ice sheets have the potential to provide sufficient cooling on the surface by increasing sea ice formation to slow down the melt there. But the advancing warming in other places would cause the ice shelf to melt more quickly from below, thereby causing sea levels to rise. Picture: Michael Wenger

The Antarctic ice sheets are the largest ice masses on Earth. Melting and calfing of these amounts of ice would take a long time, but it would be an unstoppable process once it is in progress. As a result, global sea levels would rise by more than 60 meters, scientists agree with their models. It is also undisputed that this has an impact on the global climate. But the speed at which global temperatures would rise and which feedback processes in Antarctica are influencing this increase is not yet sufficiently clear. A US team of researchers has now included a previously unnoticed factor in the models and found surprising findings.

According to the team led by master student Shaina Sadai of the University of Massachusetts Amherst and Professor David Pollard of Pennsylvania State, the amounts of meltwater created by global warming in Antarctica, will provide enough cooling to should slow down the melting beyond 2250. “We found that future melt water coming off Antarctica leads to huge amounts of thick sea ice around the continent. With higher greenhouse gas emissions, the ice sheet melts faster, which in turn leads to more freshwater flowing into the ocean and more sea ice production,” says Shaina Sadai. This would lead to a slowdown in the future warming of Antarctica.

The concentration of sea ice around Antarctica had increased in the past, but this was due to increased global warming. However, the warmer water masses under the ice lead to a faster melting of the ice shelf and this in turn to a faster rise in sea level. Picture: Michael Wenger

Average global temperatures would still be roughly 3 degrees Celsius warmer than today due to human greenhouse gas emissions, even with the cooling effects of this melt water on climate.

Alan Cordon, Woods Hole Oceanographic Institute

The simulations currently used to predict the earth’s future climate lack the accelerated melting processes of the Antarctic ice sheets and icebergs, as the research group notes in its work. When and where the amounts of meltwater flowing into the ocean, the scientists modeled in their study, published in the journal Science Advances. In their calculations, the researchers also discovered that this slowdown would be felt not only in Antarctica, but worldwide. In the Arctic, too, the decline in winter sea ice would be delayed by several decades, the team writes. But Dr Alan Condron of the Woods Hole Oceanographic Institute and co-author of the study, warns: “All that said, it’s important to note that this is not a global ‘cooling’ scenario”. Average global temperatures would still be roughly 3 degrees Celsius warmer than today due to human greenhouse gas emissions, even with the cooling effects of this melt water on climate.”

The researchers also incorporated the amount of fresh water from the melting icebergs into their calculations. Due to the warming, more icebergs would break off from the ice sheets and the ice sheets would recede faster. Picture: Michael Wenger

The results of the research team go even further and not in the direction of “good news”: their new model shows that the subsurface water masses around Antarctica would warm faster due to the larger amounts of sea ice. This ice prevents the heat from being released into the atmosphere, as Alan Condron explains. “The subsurface ocean waters warm by as much as one degree Celsius, which can increase melting below parts of the ice sheet,” says the researcher. “This could make the ice sheet more unstable and accelerate rates of sea level rise beyond current projections.” The study’s two other authors, Rob DeConto of the University of Massachusetts and David Pollard, agree. Both add that the future stability of Antarctic ice sheets depends on which process wins first: ocean warming or surface cooling. The answer to this question is now the subject of further investigation.

Dr Michael Wenger, PolarJournal

Link to the study: Sadai et al (2020) Sci Adv 6 (39) Future climate response to Antarctic Ice Sheet melt caused by anthropogenic warming; DOI: 10.1126/sciadv.aaz1169

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