Nature - Antarctic Ice Loss Now Inevitable; 2.5 Meters SLR On The Way Even If Paris Goals Met

[hatrack]

The melting of the Antarctic Ice Sheet is well underway and will be almost impossible to reverse, even if global emissions reduction targets are met, according to new research published in Nature.

The study, which seeks to uncover the complexities of the Antarctic ice system, finds that partial, but major, melting of the south polar region’s ice sheet will raise global sea levels roughly 2.5 meters (8.2 feet) over a period of time extending beyond 2100. Importantly, it will be difficult to counteract these changes, even if temperatures were to fall after reaching 2 degrees Celsius (3.6 degrees Fahrenheit) of warming above pre-industrial levels. In particular, “the West Antarctic Ice Sheet will not regrow to its modern extent until temperatures are at least one degree Celsius [1.8 degrees Fahrenheit] lower than pre-Industrial levels,” according to the study. With carbon emissions soaring annually, such a turnaround isn’t expected any time soon.

In the discourse around climate change, Antarctica has long been the elephant in the room. Much of the world’s attention has been focused on the Arctic, and its Greenland Ice Sheet, because the northern region is warming at twice the rate of the rest of the world. Unlike Arctic sea ice which responds rapidly to changes in the planetary energy balance and to inputs of greenhouse gas emissions, Antarctica’s response is far slower, and being so far away, is less in the public mind. For many decades, scientists didn’t believe it was even possible for humans to drastically affect the Antarctic ice cap. But more recent research shows that not only is it possible, it’s already happening. In fact, the ice sheet is losing mass at an accelerating rate.

“A lot of the models of Antarctic ice loss are fitting to shorter time scales — projections of 100 or 200 years out,” says Torsten Albrecht, study co-author and a postdoctoral researcher at the Potsdam Institute for Climate Impact Research. “We trained our model over paleo time scales… to understand certain events in the past which tell us a lot about the future.”

EDIT

https://ctmirror.org/2020/11/01/researchers-antarctic-ice-sheet-is-primed-to-pass-irreversible-climate-thresholds/

Abstract

More than half of Earth’s freshwater resources are held by the Antarctic Ice Sheet, which thus represents by far the largest potential source for global sea-level rise under future warming conditions1. Its long-term stability determines the fate of our coastal cities and cultural heritage. Feedbacks between ice, atmosphere, ocean, and the solid Earth give rise to potential nonlinearities in its response to temperature changes. So far, we are lacking a comprehensive stability analysis of the Antarctic Ice Sheet for different amounts of global warming. Here we show that the Antarctic Ice Sheet exhibits a multitude of temperature thresholds beyond which ice loss is irreversible. Consistent with palaeodata2 we find, using the Parallel Ice Sheet Model3,4,5, that at global warming levels around 2 degrees Celsius above pre-industrial levels, West Antarctica is committed to long-term partial collapse owing to the marine ice-sheet instability. Between 6 and 9 degrees of warming above pre-industrial levels, the loss of more than 70 per cent of the present-day ice volume is triggered, mainly caused by the surface elevation feedback. At more than 10 degrees of warming above pre-industrial levels, Antarctica is committed to become virtually ice-free. The ice sheet’s temperature sensitivity is 1.3 metres of sea-level equivalent per degree of warming up to 2 degrees above pre-industrial levels, almost doubling to 2.4 metres per degree of warming between 2 and 6 degrees and increasing to about 10 metres per degree of warming between 6 and 9 degrees. Each of these thresholds gives rise to hysteresis behaviour: that is, the currently observed ice-sheet configuration is not regained even if temperatures are reversed to present-day levels. In particular, the West Antarctic Ice Sheet does not regrow to its modern extent until temperatures are at least one degree Celsius lower than pre-industrial levels. Our results show that if the Paris Agreement is not met, Antarctica’s long-term sea-level contribution will dramatically increase and exceed that of all other sources.

EDIT

https://www.nature.com/articles/s41586-020-2727-5#citeas

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[Boomer]

1. I'm not a trained climate scientist

My lack of training is probably why I find it so difficult to understand how we could possibly reverse this trend by any action on our part at this time. Not that we're taking any actions, mind you, which I suppose renders my curiosity a moot point anyway.