Scientists find Doomsday Glacier is melting ‘more aggressively’ than thought, with big impacts for sea level rise

The planet’s widest glacier is melting “more aggressively” than previously projected, meaning its impacts on global sea level rise could be double current estimates, according to new research by a team of glaciologists.

Thwaites Glacier in West Antarctica — nicknamed the Doomsday Glacier because of the catastrophe its collapse would trigger — is a huge wildcard when it comes to forecasting global sea level rise.

The Florida-sized glacier, which lies in one of the least accessible places on Earth, has been retreating for decades and its melting ice currently contributes around 4% to global sea level rise.

But the mechanisms behind its retreat are exceptionally complex, making it tricky to precisely map out its future.

It’s a vital task, however, as Thwaites holds enough water to raise sea levels by more than 2 feet if it were to collapse. Because it also acts as a cork holding back the vast Antarctic ice sheet, it could ultimately lead to around 10 feet of sea level rise, devastating coastal communities from Miami to Manila.

Rob Larter/British Antarctic Survey

Glaciologists from the University of California, Irvine and NASA’s Jet Propulsion Laboratory have developed a new ice sheet model they say better reflects what’s happening underneath this ice giant.

Thwaites’ rapid retreat is driven by processes at its “grounding line” — the point at which the ice rises up from the seabed and starts to float on the ocean as an ice shelf.

But while typical ice sheet models have tended to view the grounding line as something fixed and mostly stable, “we have come to acknowledge a different arrangement beneath Earth’s major ocean-terminating glaciers,” said the report’s lead author Mattia Poinelli, a project scientist at UCLA who was an Earth system science researcher at UC Irvine at the time of the study.

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Satellite data reveals the grounding line is actually a “grounding zone,” sometimes miles wide, where seawater constantly flushes in and out with the tides, lifting and lowering the thick ice in a process known as “tidal pumping.” This allows relatively warm ocean water to penetrate “deep underneath the ice sheets and causing vigorous melting,” Poinelli said.

When the scientists adjusted models to include the concept of a grounding zone, they found Thwaites could contribute up to 1.2 inches of sea level rise by 2100 — twice previous estimates — even without further global warming, according to the findings published Monday in the journal Nature Communications.

Scientists looked deep beneath the Doomsday Glacier. What they found spells potential disaster for the planet

The land on which Thwaites sits slopes downward, meaning as the glacier melts, more ice is exposed to warm ocean water. The topography is complicated, however, by two key underwater ridges, which “pin” the ice, holding it back from flowing into the ocean more rapidly.

The melting processes at Thwaites’ grounding zone are accelerating the “unpinning” of ice from a large ridge called the Mouginot Ridge, the study found. There is a 60% chance that it will be unpinned by the end of the century, the study found, after which the glacier is likely to retreat quickly down the sloping bedrock toward the next major ridge.

The findings suggest the impacts of losing Thwaites might have been underestimated. A sea level rise of 1.2 inches may not sound much but it’s enough to greatly magnify dangers to coastal populations.

The results “predict greater risk of and exposure for coastal flooding than anticipated in the coming decades,” said Eric Rignot, a report author and professor of Earth system science at UC Irvine.

Jeremy Harbeck/OIB/NASA

Ted Scambos, a senior research scientist for the Earth Science and Observation Center at the University of Colorado Boulder, who was not involved in the research, said the findings could be “a real gamechanger for sea level forecasting from Thwaites.”

But he and other experts caution that more research is needed to understand the impacts of different grounding zone melting processes, not least by getting direct data from underneath the glacier.

Journey to the disappearing edge of the Arctic

“The reality is that there is a lot we still need to find out about grounding zone processes to be able to make confident predictions about how fast ice will be lost,” said Robert Larter, a marine geophysicist at British Antarctic Survey, who was also not involved in the study. The environment beneath Thwaites, which is very difficult to access, is even more complex than the paper describes, he added.

Getting observational data from Thwaites’ grounding line is the next step, Rignot said. The scientists are planning to travel there in 2028 to deploy instruments able to document the flushing in and out of seawater.

“We have been aware of the impacts of climate change on our planet’s sensitive ice sheets for decades,” Rignot said, “but a mounting realization gained in recent years of what is really happening on the undersides of glaciers like Thwaites is leading to an even greater sense of alarm.”

He said the world must cut planet-heating pollution now to limit the impacts but warned, “even if we do, we can expect higher sea levels in the future resulting from the damage that has already been done.”

一组冰川学家的最新研究表明，地球上最宽的冰川正在以比之前预测“更猛烈”的速度融化，这意味着它对全球海平面上升的影响可能是目前估计的两倍。

位于南极洲西部的斯韦茨冰川（因其崩塌可能引发的灾难而被昵称为“末日冰川”）是预测全球海平面上升时的一个巨大不确定因素。

这座面积相当于佛罗里达州大小的冰川位于地球上最难到达的地区之一，几十年来一直在消退，其融化的冰目前对全球海平面上升的贡献约为 4%。

但其退却背后的机制极其复杂，因此很难精确地规划其未来。

然而，这是一项至关重要的任务，因为斯韦茨冰川蓄水量巨大，一旦崩塌，足以使海平面上升超过2英尺。由于它还像软木塞一样阻挡着巨大的南极冰盖，最终可能导致海平面上升约10英尺，对从迈阿密到马尼拉的沿海社区造成毁灭性打击。

罗布·拉特/英国南极调查局

加州大学欧文分校和美国宇航局喷气推进实验室的冰川学家开发了一种新的冰盖模型，他们表示该模型能更好地反映这个冰山巨石下正在发生的事情。

斯韦茨冰盖的快速消退是由其“接地线”处的过程驱动的——接地线是冰从海底升起并开始作为冰架漂浮在海洋上的点。

但报告的主要作者马蒂亚·波伊内利（Mattia Poinelli）表示，尽管典型的冰盖模型倾向于将接地线视为固定且基本稳定的东西，“我们已经认识到地球主要海洋末端冰川下方存在着不同的安排”。波伊内利是加州大学洛杉矶分校的项目科学家，在进行这项研究时，他还是加州大学欧文分校的地球系统科学研究员。

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卫星数据显示，所谓的接地线实际上是一个“接地区”，有时宽达数英里，海水随着潮汐不断涌入涌出，抬升和降低厚厚的冰层，这一过程被称为“潮汐泵送”。波伊内利表示，这使得相对温暖的海水能够“深入冰盖下方，导致剧烈融化”。

根据周一发表在《自然通讯》杂志上的研究结果，当科学家们调整模型，将接地带的概念纳入其中时，他们发现，即使没有进一步的全球变暖，到 2100 年，斯韦茨地幔也可能导致海平面上升高达 1.2 英寸——是之前估计的两倍。

科学家们深入探索了末日冰川之下。他们的发现预示着地球可能面临灾难。

斯韦茨冰川所在的地势向下倾斜，这意味着随着冰川融化，更多的冰体暴露在温暖的海水中。然而，两道关键的水下山脊使地形变得复杂，它们像钉子一样固定着冰体，阻止其更快地流入海洋。

研究发现，斯韦茨冰川接地带的融化过程正在加速冰川从名为穆吉诺山脊的大山脊上“脱离”。研究还发现，到本世纪末，穆吉诺山脊有60%的概率会脱离山脊，之后冰川很可能会沿着倾斜的基岩迅速退缩，向下一个主要山脊方向移动。

研究结果表明，斯韦茨湖消失的影响可能被低估了。海平面上升1.2英寸听起来不多，但足以大大加剧沿海居民面临的危险。

报告作者之一、加州大学欧文分校地球系统科学教授埃里克·里格诺特表示，研究结果“预测未来几十年沿海地区发生洪水的风险和暴露程度将比预期更大”。

杰里米·哈贝克/OIB/NASA

科罗拉多大学博尔德分校地球科学与观测中心的高级研究科学家泰德·斯坎博斯（Ted Scambos）并未参与这项研究，但他表示，研究结果可能会“真正改变斯韦茨海平面预测的局面”。

但他和其他专家警告说，需要进行更多研究才能了解不同接地带融化过程的影响，尤其需要从冰川下方获取直接数据。

前往北极消失的边缘地带

“事实上，我们仍需深入了解冰川接地带的形成过程，才能对冰川消融的速度做出可靠的预测，”英国南极调查局的海洋地球物理学家罗伯特·拉特尔说道，他并未参与这项研究。他还补充说，斯韦茨冰川下方的环境极其难以接近，其复杂程度甚至超过了论文中的描述。

里格诺特表示，下一步是从斯韦茨岛的接地线获取观测数据。科学家们计划于2028年前往那里，部署能够记录海水流入和流出的仪器。

“几十年来，我们一直意识到气候变化对地球脆弱的冰盖的影响，”里格诺特说，“但近年来，人们越来越意识到像斯韦茨冰川这样的冰川底部正在发生的事情，这导致人们更加感到担忧。”

他表示，世界必须立即减少导致全球变暖的污染，以限制其影响，但他警告说，“即使我们这样做，由于已经造成的破坏，我们也可以预料到未来海平面会上升。”