September 23, 2020

expert reaction to Antarctic ice sheet and sea level rise

A study, published in Nature, looked at the Antarctic ice sheet and sea level rise.

Dr Helene Hewitt, a Met Office science fellow and ocean modelling expert, said:

“Sea level rise is one of the greatest societal impacts from climate change and it will continue for hundreds of years, even with attempts to limit global warming to 1.5 °C.

“The melting of the Antarctic Ice Sheet has the potential to add several metres to global sea level rise, but taking urgent measures to curb increasing global temperature will slow the rate of sea level rise, buying more time for millions of at-risk people.

“Without urgent mitigation the future for low-lying communities, including some of the world’s greatest cities, is even more under threat.”

Dr Matt Palmer, a Met Office sea level rise scientist, said:

“Recent projections developed by the Met Office as part of UKCP climate projections have shown that sea-level will continue to rise to 2300 and beyond, and that the largest uncertainty is what will happen to the Antarctic Ice Sheet.

“This very important and timely study makes clear the urgent need to stabilise surface temperature rise in-line with Paris Agreement targets to limit the total committed sea-level rise to a few metres.

“At higher warming levels, large parts of the Antarctic Ice Sheet may be lost permanently, with irreversible sea level rise of several metres or more.”

Prof Andrew Shepherd, Director of the Centre for Polar Observation and Modelling, University of Leeds, said:

“These are long-term predictions of how much ice Antarctica will have lost in perhaps 150,000 years’ time. Although we won’t be around to see it, it’s a stark warning that the melting can’t be reversed unless we can cool our planet to below pre-industrial temperatures. Now is the time to act.”

Prof Chris Rapley, Professor of Climate Science, University College London, said:

“Antarctica is so remote that it seems disconnected from our daily lives. The block of ice it holds is massive. It seems incredible that we could affect it, or it us. Yet observations show that ice-loss as a result of global warming is already under way. And sea level rise – to which it contributes – is increasingly a source of impacts and damages.  Beyond a certain threshold of warming, massive loss over time will be inevitable and irreversible. We have known this for a while. Even so, the results presented in the paper – and especially the video showing the way in which the ice sheet will disintegrate – are truly shocking.

“We are transforming a planet. Archimedes said ‘Give me a lever long enough and a fulcrum on which to place it and I will move the Earth’. Who would have guessed in his day that burning fossilised plant matter would constitute lever and pivot?!

“The message of the paper is that the level of warming we humans create will determine inevitable and irreversible consequences in Antarctica that will be of a planetary magnitude. 

“The idea that we might really commit future Earth to being ice-free (with all the related consequences) is a truly profound conclusion – one which we have speculated about until now – but which this work, if correct, shows to be real.”

Prof Jonathan Bamber, Professor of Glaciology, University of Bristol, said:

“This study provides compelling evidence that even moderate climate warming has incredibly serious consequences for humanity and those consequences grow exponentially as the temperature rises. The committed sea level rise from Antarctica even at 2 degrees warming represents an existential threat to entire nation states. We’re looking at removing nations from a map of the world because they no longer exist. It doesn’t get much more serious than that.”

Dr Robert Larter, Marine Geoscientist, British Antarctic Survey (BAS), said:

“The Antarctic ice sheet holds enough ice to raise global mean sea level by 58 m if it all melted. This study estimates how much of this ice will eventually melt for different temperature rises, if those elevated temperatures are sustained for a long time into the future. At present most ice is lost by calving of icebergs and by melting at the base of glaciers where they flow out over the ocean as ‘ice shelves’. Significant surface melting is limited to parts of the Antarctic Peninsula and low elevation area around the fringes of Antarctica. As temperatures increase it is clear that the extent of surface melting will also increase. Apart from being a direct addition to the ice losses, increased surface melt is also expected to trigger a set of feedback effects. Eventually it will impact the stability of ice shelves, compromising or eliminating their buttressing effect on the glaciers flowing into them and thus allowing those glaciers to flow faster and deliver more ice to the ocean. Where surface melt drains through a glacier to its bed it can also lubricate sliding of the ice over its bed, further increasing the glacier flow rate.

“The study also highlights how changes in the ice sheet are not easily reversible, the so-called ‘hysteresis’ phenomenon. Once an ice sheet has lost a substantial proportion of its ice through accelerated glacier flow and surface melting its surface will sit at lower elevation in warmer air. Even if the air temperature profile returns to how it was before ice sheet change was initiated, the air temperature at the surface will not be as cold as it was at the initially higher elevation. For the ice sheet to regrow to its original size even colder temperatures will be necessary. Higher surface temperatures over an ice sheet on which the surface elevation has decreased will eventually affect the temperature of ice throughout the ice sheet. Warmer ice can deform and flow more quickly and is more prone to basal melting, which facilitates flow of glaciers over their bed by sliding. Despite these factors that increase ice loss, a smaller, warmer ice sheet may achieve a new equilibrium state as a result of increased snowfall from the warmer air over its surface.

“Numerical ice sheet models simulate a range of physical processes and feedbacks, so the accuracy of their predictions depends on a detailed understanding of each of these. Therefore, in order to obtain more accurate predictions of future ice loss and to reduce their uncertainties further field and laboratory research to improve understanding of processes and feedbacks is important.”

‘The hysteresis of the Antarctic Ice Sheet’ by Julius Garbe et al. was published in Nature at 4pm UK time on Wednesday 23 September.

https://doi.org/10.1038/s41586-020-2727-5

Declared interests

None received.