News Review by Kip Hansen – 16 February 2020
Several media pieces have followed up on a study about the Thwaites Glacier in Antarctica. Even the (in)famous climatologist who shares my last name pulled out this story for the press in Australia. Newsweek ran with it as part of a catastrophe article: These Five Cities Are Vulnerable to Rising Seas, Including Miami and New York. Phys.org carried this: New study models impact of calving on retreat of Thwaites Glacier.
What are they saying?
“The Thwaites Glacier is about the size of a U.S. swing state and holds enough ice to raise sea levels by about 10 feet. This alone is scary enough to justify its nickname, the Doomsday Glacier, but there’s more. The Thwaites sits along a 75-mile stretch of shoreline in Antarctica that serves to partially shield the vast West Antarctic Ice Sheet from the warm ocean waters. The WAIS has enough ice to raise the seas by 200 feet.”
“These projections carry some uncertainty, but one thing seems pretty clear: the next century will be tough for coastal city dwellers. Sea levels are rising about 3 millimeters each year. By the end of the century, the oceans could rise at least 2 feet over 2005 levels, according to a 2018 study in the Proceedings of the National Academies of Science. Michael Mann, a climate scientist, told NBC News that unless emissions of greenhouse gases are abated, by the end of the century more than 650 million people will be living on land that is under water all or much of the time.”
“We think that possibly in a few years or decades, we don’t know yet, the remainder of the ice shelf in front of Thwaites might be gone,” explained Hongju Yu, an assistant specialist at the University of California, Irvine and lead author of the new study.
If the ice shelf disappeared, it would no longer provide resistance to the glacier’s flow, allowing the glacier to accelerate. The glacier would then begin losing mass mainly through increasing breakup of chunks of ice at its leading edge—a process called calving. The aim of the new study was to simulate how much Thwaites’ retreat would accelerate through calving once the ice shelf disappears.”
If Thwaites collapsed, it could raise global sea level by more than half a meter (nearly two feet) and lead to a domino effect of further glacier collapse in West Antarctica. Worst-case scenario, it is going to be gone in less than a century,” Yu said. “But it may also take much longer.” — Phys.org
That’s a lot of scary talk. What is it all about?
The Thwaites Glacier is one of the many West Antarctic glaciers.
Thwaites is inside the Red Box on the left, in West Antarctica. It is not the largest of the glaciers in Antarctica, but there has been long term concern about Thwaites because it is flowing faster than many others.
Part of the concern with Thwaites is the “grounding line” – will Thwaites retreat from the grounding line and thus allow the main glacier to flow faster into the sea?
The Thwaites story is part of the ongoing controversy over Antarctic ice gain/loss that has been being fought in the journals for the last five or ten years. NASA supports a variety of views — 1) NASA Study: Mass Gains of Antarctic Ice Sheet Greater than Losses ; 2) Antarctica’s contribution to sea level rise was mitigated by snowfall ; 3) Ramp-up in Antarctic ice loss speeds sea level rise
The first study, Zwally (2017), claims Antarctica is gaining mass — not losing. The second claims that even though Antarctica is getting more snow, it isn’t gaining overall. And the third claims “Ice losses from Antarctica have tripled since 2012, increasing global sea levels by 0.12 inch (3 millimeters) in that timeframe alone”. The controversy has spawned articles such as “What to Believe in Antarctica’s Great Ice Debate”, written by freelance science journalist, which says “In 2015 a study was published claiming that East Antarctica is in fact gaining mass, contrary to the majority of studies conducted thus far” [the study was done in 2015 but published in 2017] but fails to mention that the study is from Jay Zwally, a glaciologist with NASA Goddard Space Flight Center in Greenbelt, Maryland, which was published on Oct. 30 2017 in the Journal of Glaciology and which is still headlined on the NASA website. The Scientific American article was rushed into publication 4 days before the Zwally study appeared in the Journal of Glaciology.
In recent years, the media has often gone way overboard about Thwaites and Pine Island glaciers. “But if carbon emissions continue to track on something resembling a worst-case scenario, the full 11 feet of ice locked in West Antarctica might be freed up, their study showed.” [according to DeConto and Pollard]
The controversy hinges on whether the floating ice shelf of Thwaites will continually retreat and eventually lead to it losing its buttressing effect on the bulk of the glacier. Then if the buttressing is removed, will the bulk of the glacier then rush into the sea? Hongju Yu and his team do not think so: “…removing the ice shelf abruptly does not have a long-lasting impact on the retreat and cumulative mass loss of the glacier.” [study conclusions] – and yet Hongju Yu is seemingly quoted to the contrary in the media.
OPINION: Personally, I think Hongju Yu has been carefully interviewed into saying things that the study itself does not support – subtly coerced into statements desired for the narrative of climate alarm.
Interested readers can plow through the conflicting studies for themselves but the bottom line is that there is a “consensus” opinion, backed by many studies intended to confirm what may be the “prevailing bias in the field” and then there are other studies that find the opposite or show greatly reduced long-term concern.
What does the featured study really find?
The study being spoken of is “Impact of iceberg calving on the retreat of Thwaites Glacier, West Antarctica over the next century with different calving laws and ocean thermal forcing” [
Its published conclusions are:
“We investigate the impact of calving on the evolution of Thwaites Glacier, West Antarctica over the next century without its buttressing ice shelf. Our simulations suggest that removing the ice shelf abruptly does not have a long-lasting impact on the retreat and cumulative mass loss of the glacier. We calibrate a von Mises calving law with Haynes Glacier, which does not have an ice shelf. Within the calibrated range of the calving parameters, we find a considerable enhancement of the retreat of the glacier compared to the case where the glacier is only experiencing ice shelf melt. The retreat rate varies significantly depending on the selection of σmax. Conversely, we find that a buoyancy driven calving law does not influence the retreat by more than 20% and ice front melt by the ocean modulates the retreat by 15% to 50%, with the highest increase associated with a maximum thermal forcing of 4°C. Based on our experiments, we conclude that Thwaites Glacier will raise global sea level by 13-19 mm if the grounding line stabilizes on the western ridge; otherwise, its collapse will proceed and raise global sea level by 50 mm within this century.”
What was said in the media:
2 FEET — “By the end of the century, the oceans could rise at least 2 feet over 2005 levels,”
10 FEET — “The Thwaites Glacier is about the size of a U.S. swing state and holds enough ice to raise sea levels by about 10 feet.”
200 FEET — “The WAIS has enough ice to raise the seas by 200 feet.”
650 MILLION UNDER WATER – “…by the end of the century more than 650 million people will be living on land that is under water” — Michael Mann
ACTUAL MODELLED PREDICTIONS:
13-19 mm = 0.5 to 0.75 inches by 2100
Worst Case — 50 mm = 2 inches
(Of course, both of these scenarios are “IFs” based on a lot of computer modelling. )
We will have to wait on Thwaites to see what it is going to do. We don’t really understand the dynamics involved with Antarctic glaciers yet – what makes them speed up and slow down. But in any case, even Hongju Yu’s worst case conclusion only minimally adds to expected sea level rise of about 12 inches ( other opinions vary but possible values over 2 feet are extremely unlikely) by 2100.
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I have emailed Professor Hongju Yu and asked him about the apparent disconnect between his study’s conclusions and the statements attributed to him in the media. If he responds, I’ll either add it to Comments or the main body of the essay.
Despite repeated assertions of Antarctic ice melt and glacier collapse, the sea level record does not show discernible effects – global sea levels still rising at their centuries long 2-3 mm per year as the Earth climate warms from the Little Ice Age.
The study of the Antarctic is a valid scientific endeavor – but not if its only purpose is to attempt to raise more and more alarm about climate change.
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