August 10, 2022

expert reaction to review paper looking at the response of the East Antarctic Ice Sheet to past and future climate change

A review paper published in Nature looks at the response of the East Antarctic ice sheet to past and future climate change.

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

“The review is definitely robust, no problems there, and it is timely because there is recent evidence of ocean warming around East Antarctica and this was the origin of rapid imbalance in West Antarctica.  However, the authors report that parts of the East Antarctica ice sheet are showing signs of imbalance today, and I think we still don’t have a hard line of evidence to support this suggestion.  Although there are a few locations which show ice sheet thinning (Totten Glacier being the most prominent), there is no real sign of glacier speedup during the satellite era – the primary indicator of dynamical imbalance – which means we can’t rule out a shortfall in snowfall as the source of thinning.  This is important, because we know that changes in ice sheet mass associated with meteorology are quite slow and predictable, whereas changes associated with glacier imbalance can evolve rapidly and are difficult to predict.  So I think the jury is still out on whether EAIS is showing the initial signs of imbalance, despite the warming offshore.”

Dr Joel Hirschi, Associate Head of Marine Systems Modelling, the National Oceanography Centre, said:

Is this good quality research?

“This is not actually a research article but a review article.  In my view it is of very good quality and nicely compiles what we know about the past evolution of the East Antarctic Ice Sheet (EAIS) and how it may change in the next few centuries.

Are the conclusions backed up by solid data?

“Yes, what the authors say in the review article is based on findings from many peer-reviewed articles which cover the most relevant research about the Antarctic ice sheet undertaken to date.

How does this work fit with the existing evidence?

“It is well documented that, as our climate warms, some ice sheets (such as the Greenland Ice Sheet) are losing mass (i.e. ice) – contributing to a rising sea level.

“For the East Atlantic Ice Sheet it is not yet clear how much it will contribute to sea level rise in the coming centuries.  The aim of this review is to provide an overview of our the current understanding of the EAIS and its evolution.

Have the authors accounted for confounders?

“Yes, the authors acknowledge that there is still much uncertainty about how much the EAIS will contribute to sea level rise in year to come.

Are there important limitations to be aware of?

“By how much the EAIS will contribute to rising sea levels doesn’t just depend on how much the climate will warm but equally also on how much the amount of snow falling onto the ice sheet will change.  Model projections suggest a wide range of possible contributions of EAIS to global sea level rise.

What are the implications in the real world?  

“The EAIS is by far the largest potential source of sea level rise.  The water contained in its ice is equivalent to more than 50 m sea level i.e. without the EAIS the global sea level would be more than 50 m higher than it is today.  Yet, our understanding of its stability and how it will respond to climate change is lacking and, therefore, one of the main messages of the article is that we should address this knowledge gap.

Is there any overspeculation?

“No, the authors clearly state that while the EAIS may become a important contributor to global sea level rise it the coming centuries there is no indication that it could “collapse”.” 

Prof Eric Wolff, Royal Society Research Professor, University of Cambridge, said:

“The East Antarctic Ice Sheet is the largest ice mass on Earth, containing ice equivalent to 50 metres of sea level.  While there is great anxiety about the smaller West Antarctic and Greenland ice sheets, most scientists have hoped and assumed that the larger East Antarctic Ice Sheet is stable.  This study looks carefully at how the East Antarctic Ice sheet behaved in warm periods of the past, and at what models say will happen in the future.  The good news is that, if we keep to the 2 degrees of global warming that the Paris agreement promises, the sea level rise due to the East Antarctic Ice Sheet should be modest.  However if emissions of greenhouse gases are not controlled, there is a risk that even the very cold East Antarctic Ice Sheet starts to retreat and that it could contribute many metres of sea level rise over the next few centuries.  The study emphasises that keeping emissions under control now can avert a disastrous sea level rise for future generations.”

Dr Florence Colleoni, paleo-glaciologist at the National Institute of Oceanography and Applied Geophysics, Trieste, Italy, said:

“Geological and geomorphological records of past periods clearly show that the future sea level rise scenarios, related to the carbon emmission scenarios, are not science fiction.  EAIS responded during past warming period by large ice discharges into the ocean on a timescale of a few centuries, as a result of instability processes mainly caused by oceanic warming.  I was this year on a marine geophysical expedition (37 expedition of PNRA – National italian Programme for Antarctic Research) in the EAIS sector and preliminary results show that EAIS has been very active and very responsive to past climatic fluctuations, even in the relatively recent past.  Even if we don’t know what will be the trajectory of carbon emmissions by 2100 and beyond, paleo-evidence suggest that even with past CO2 concentration only slightly lower than today, the Antarctic Ice Sheet experienced some large ice discharges in its marine-based sectors.  This implies that the role of a very modest ocean warming, on the long-term, in the Antarctic ice sheet instability is larger than thought when only considering present-day observations as a baseline.

Does the press release accurately reflect the science?

“Yes.

Is this good quality research?  Are the conclusions backed up by solid data?

“Yes.

How does this work fit with the existing evidence?

“This work is a review of existing evidence.

Have the authors accounted for confounders?  Are there important limitations to be aware of?

“Not really.  Technical limitations comes from models physics that do not always agree on the marine ice sheet instability processes and the way the ice sheet grounding line retreats in the simulations.  Which leads to some substantial uncertainties in the projections.

What are the implications in the real world?  Is there any overspeculation?

“No overpseculation.  The implications are: those future sea level rise scenarios are not science fiction, paleoevidence clearly show that large ice discharged form this sector happened in the past.”

Dr Robert Larter, Marine Geophysicist, British Antarctic Survey, said:

“The vast amount of water locked up as ice in the East Antarctic Ice Sheet would cause global mean sea level to rise by 52 m if it was all released into the ocean.  Geological evidence indicates that sea-level changes of tens of metres have resulted from past changes in the ice sheet over timescales of millions of years.  Despite recent climate change, scientific observations over the past few decades show that the East Antarctic Ice Sheet’s inputs and outputs have remained close to balance, in contrast to accelerating ice loss from the neighbouring West Antarctic Ice Sheet.  However, in more detail observations reveal that changes have occurred and the approximate state of balance of the East Antarctic Ice Sheet is the result of increased ice losses around parts of the ice sheet margin being offset by increased snow accumulation over its interior.

“This study uses the latest available data and models to assess how this ice sheet will change over the next few centuries under different emissions scenarios.  The projections come with large uncertainties, particularly over the longer timescales considered, but highlight the potential for multi-metre contributions to sea-level rise over the next few centuries if high emissions continue to 2100 and beyond.

“The analysis indicates that the East Antarctic Ice Sheet is unlikely to make a major contribution to sea level before 2100, and therefore over this timescale changes in the West Antarctic and Greenland ice sheets remain the largest concern.  However, the study shows that continued high emissions over the remainder of this century are likely to result in a commitment to multi-metre sea-level rise contributions from the East Antarctic Ice Sheet over the ones that follow.  Furthermore, the authors highlight that early-warning signs that this sleeping giant is awakening will come from changes in the sectors where the ice rests on a bed below sea level, and therefore future research in these regions should be a high priority.”

Dr Helen Millman, Antarctica Director & Postdoctoral Fellow, International Cryosphere Climate Initiative (ICCI), University of New South Wales, said:

“This paper confirms what scientists studying Antarctica’s past have been saying for years: past sea levels suggest that East Antarctica is vulnerable at temperatures we may reach by mid-century if we stay on our current emissions path.  It is an especially strong study because it combines what we know about Antarctica’s behaviour in the past with current observations, and uses those to evaluate modelled projections of Antarctica’s future.  We need to keep in mind that the 3-5 metres projected by 2500 at high emissions would be joined by equal or greater amounts from the West Antarctic Ice Sheet and Greenland.  It is vital that urgent action is taken to reduce our greenhouse gas emissions.”

‘Response of the East Antarctic Ice Sheet to past and future climate change’ by Chris R. Stokes et al. was published in Nature at 16:00 UK time on Wednesday 10 August 2022.

DOI: 10.1038/s41586-022-04946-0

Declared interests

Prof Eric Wolff has previously co-authored papers with some of this study’s authors.

Dr Florence Colleoni: “I don’t have any conflict of interest to declare.”

Dr Robert Larter: “My role at UK Science Lead for the Science Coordination Office of the International Thwaites Glacier Collaboration could be viewed as a vested interest, in that research in West Antarctic competes for resources with research in East Antarctica. However, my view is that we need to increase the science effort in both regions.”

Dr Helen Millman: “I declare that I have no competing interests in my evaluation of this research.”

For all other experts, no reply to our request for DOIs was received.