Oct 24, 2023 - Energy & Environment

Accelerated loss of West Antarctic Ice Sheet now "unavoidable": study

Marguerite Bay in Antarctica. Photo: British Antarctic Survey

A comprehensive look at ocean temperatures along West Antarctic coast shows that a faster melt of the region's ice shelves is all but "unavoidable" this century and implies a quicker rate of sea level rise.

Why it matters: The future of millions of coastal residents worldwide depends on the stability of the West Antarctic Ice Sheet. A more rapid loss of this ice threatens to send sea levels above existing projections of a one-to-three-foot rise by 2100.

Zoom in: The study, published in Nature Climate Change, uses a sophisticated computer model to simulate past, present and future ocean temperatures in the Amundsen Sea. The model also simulates the associated response from floating ice shelves, which are extensions of marine-terminating glaciers.

  • These ice shelves act as door stops, holding back land-based ice behind them. And when these shelves melt faster, largely from ocean heat eating away at them from below, inland ice can destabilize and hasten its movement into the sea, thereby raising sea levels.
  • The new study states it offers a "sobering" look at how much control humans still have over ocean temperatures in this particular region of Antarctica, already an area of increased scientific concern over its melt trends in recent years.
  • It finds that the time to effectively intervene to prevent further warming and faster ice shelf loss in this region of Antarctica this century has passed.
  • "We are now committed to an increasing trend" of ice shelf loss, lead author Kaitlin Naughten of the British Antarctic Survey, told reporters.

The intrigue: She said seas surrounding West Antarctica, where ice shelves buttress huge glaciers such as the Thwaites Glacier in the Amundsen Sea Embayment, would warm at up to three times the historical rate.

  • "Thwaites Glacier is directly in the study region, it would be directly impacted by these changes," she said.
  • Although the study does not produce sea level rise projections, Naughten said it is clear that sea level rise would increase through 2100 and beyond.
  • "We have every reason to conclude that sea level rise would speed up," she said. "It appears that we may have lost control of the West Antarctic ice sheet melting during the 21st century."

Between the lines: This study is unique in examining what is known as ice sheet basal melting, or ocean melting along the underside of ice shelves.

  • The new research paints a bleaker picture, with increased heating from the ocean over time, compared to other studies that have assumed the ocean-induced melting would remain stable throughout the century, Naughten said.
  • Interestingly, the study did not show significant differences in ocean warming rates through midcentury, whereas depending on the emissions scenario, they would begin to diverge toward the end of the 21st century and beyond.
  • However, decisions made during the next few decades would affect the course of sea level rise beyond 2100, studies have shown.

Yes, but: Naughten emphasized that the study results should not foster hopelessness or stymie climate action.

  • "We shouldn't give up — even if this particular impact is unavoidable," she said, noting the study region only comprises about 10% of Antarctica's ice.
  • Many other climate impacts, such as worsening heat waves and coral reef loss, would be minimized by greenhouse gas emissions cuts.

What they're saying: Naughten and her coauthors note one key limitation, which is that this is one modeling study, and the use of other models would increase confidence in the projections.

  • Scientists not involved in the new study said its findings are credible, though not yet definitive.
  • "While they do not show a lot of differences between various emission scenarios, they do point out that the Paris agreement won't be safe enough for these glaciers," said Eric Rignot, a climate scientist at UC Irvine and NASA.
  • "We know that since the glaciers are already in a galloping state of retreat, we observe that retreat year after year, that's not a projection," Rignot said.
  • "It is not a matter of depressing the readership; it is what it is," he said.
  • Ian Joughin, a climate scientist at the University of Washington, told Axios that the total amount of additional sea level rise for the period and area in the study may only amount to several centimeters through 2100.

The bottom line: The unsettling climate news helps illustrate why scientists emphasize the need to cut emissions with greater urgency.

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