内容来源：https://www.quantamagazine.org/how-soon-will-the-seas-rise-20251020/

内容总结：

【新闻总结】南极冰盖加速消融，海平面上升危机迫近

长期以来被视为"沉睡巨人"的南极西部冰盖正显现苏醒迹象。2014年，美国宇航局首次确认该区域冰川已进入不可逆消退阶段。这片厚度达两公里的冰原若完全消融，将使全球海平面上升5米，足以重塑世界海岸线格局。

科学界争议焦点在于消融速度。2016年《自然》杂志提出"海洋冰崖不稳定性"理论，认为90米以上冰崖可能发生连锁崩塌，导致海平面在2100年前上升超2米。但最新研究指出，冰川流动与冰屑堆积可能减缓这一进程，将预期升幅修正至40厘米以内。

南极西部冰盖的特殊地质结构是其脆弱性的根源。与东部冰盖不同，它坐落于海平面以下的盆地中，温暖海水持续侵蚀其基底。2017年命名的"末日冰川"思韦茨冰川正以每年1.6公里速度后退，其完全崩塌可能单独导致海平面上升65厘米。

尽管存在科学争议，但观测数据表明危机正在加速。卫星监测显示，自1990年代以来，阿蒙森海沿岸冰川持续消退。科罗拉多大学冰川学家泰德·斯坎博斯指出："我们已从讨论冰盖增减转为关注消融速度。"

联合国政府间气候变化专门委员会最新预测显示，到2100年海平面可能上升0.5至1米。若南极冰盖失控崩塌，这一数字或将翻倍。罗格斯大学气候专家罗伯特·科普警告："唯一确定的是，排放的二氧化碳越多，我们面临的风险就越大。"

随着冰川学研究的深入，科学界逐渐认识到：人类沿海文明发展的数千年，恰逢地质史上罕见的低海平面时期。如今，海洋正在回归，而回归的速度，很大程度上取决于人类当下的选择。

中文翻译：

海平面上升倒计时
2014年5月，美国国家航空航天局在新闻发布会上宣布：西南极冰盖的部分区域似乎已进入不可逆的消退阶段。在这片厚达两公里的冰层边缘，流向海洋的冰川消融速度已超过降雪补充速度，导致冰缘不断向陆地方向退缩。至此，问题的核心不再是西南极冰盖是否会消失，而是何时消失。当这些冰川彻底消融，海平面将上升逾一米，淹没目前2.3亿人居住的土地。而这仅是整部灾难片的序幕——整个冰盖的崩塌最终可能使海面升高5米，重塑全球海岸线。

当时科学界预估这些冰川的消融将绵延数个世纪。但2016年《自然》杂志发表的重磅研究指出，冰崖崩解可能引发失控的消退链式反应，极大加速进程。政府间气候变化专门委员会据此制定了严峻的新版最坏情景：到2100年，南极洲、格陵兰岛及山地冰川的融水，加上海水热膨胀效应，可能使全球海平面上升超2米。这仅仅是个开端。若温室气体排放持续失控，到2300年海平面将暴涨15米。

不过并非所有科学家都认同这种失控情景。关于西南极巨型冰川还能存续多久的争论由此形成拉锯战。若消退过程持续数百年，人类尚有适应时间；但若未来几十年内通过争议性的失控过程加速崩塌，后果将超越我们的应对能力。科学家警告，纽约、新奥尔良、迈阿密、休斯敦等人口稠密都市可能无力招架。

"我们绝对没有排除这种可能性，"马尼托巴大学冰川学家卡伦·阿利表示，她的研究支持失控过程存在的可能，"但我尚不能断言近期会发生，也不敢断言绝不会发生。"

数千年来，人类在海岸线繁衍生息，却不知自己正生活在地质学的偶然中——这段海平面偏低的异常时期终将结束。海洋终将归来，但何时来临？关于冰盖消退机制的科学认知，将如何决定我们的港口家园与数十亿沿海居民的命运？

冰与海的生死线
1978年，俄亥俄州立大学特立独行的冰川学家约翰·默瑟（据传曾裸体进行野外考察）率先指出全球变暖对西南极冰盖的威胁。其理论根基在于该冰盖与海洋之间独特的危险关系。

面积超过阿拉斯加与得克萨斯总和的西南极洲，被横贯南极山脉与大陆东部分隔。与大部分冰层位于海平面以上陆地的东南极洲（及格陵兰）不同，西南极冰盖深陷于海平面以下的碗状洼地，边缘与海水相接。这种结构使其成为最易崩塌的冰盖。

这座穹顶状冰盖在自重作用下通过触手般的冰川向外流动。但冰川并未止步于海岸线，而是形成厚达数百米的巨型漂浮冰架延伸入海。这些"冰架"如同系留的巨筏，通过水下隆起物和山脊产生的阻力固定，抵御着冰川向海洋不可避免的重力牵引。

冰盖最脆弱的前沿是"接地线"——冰层从海底基岩过渡为漂浮冰架的分界线。当相对温暖的海水侵蚀保护性冰架底部，冰架逐渐变薄，接地线不断向内陆推移。漂浮冰架崩解分离后，失去支撑的上游冰川会加速流向海洋。与此同时，海水如进军般涌向更厚的冰层，这些冰层下方是朝向大陆碗状中心倾斜的基岩。

"这是极其严峻的警示，"诺森比亚大学冰川学家希尔马·古德蒙德森指出，随着接地线在"海洋冰盖不稳定性"进程中向内陆厚冰区推进，"全球海平面将急剧上升，且进程会非常迅速。"

2002年，科学家目睹了这场预演。南极半岛外侧面积近似罗德岛的拉森B冰架，在短短一个月内土崩瓦解，令科学界震惊。地表融水聚集迫使冰裂扩大（即水力压裂过程），导致这座冰川唯一屏障分崩离析。其后冰川入海速度激增八倍。其中克雷恩冰川的冰崖在2003年连续崩塌，导致冰体急剧收缩。若西南极海岸规模更大的思韦茨冰川和松岛冰川发生类似情况，后果将如何？

崩塌加速器
后续对古海岸线的研究揭示了地球系统的惊人敏感性：历史上比现今稍暖的时期，海平面竟比现在高出6-9米。

为此，冰川学家罗伯特·德康托和戴维·波拉德提出了颠覆性的冰盖崩塌新理论。他们基于拉森B崩解与格陵兰冰川崩裂数据建立计算机模型，并参照地质史记录进行校准，推演出的未来融化量与古海平面研究预期相符。

2016年研究描绘了近乎难以置信的冰量流失与海平面上升速度。在"海洋冰崖不稳定性"机制中，超过90米的冰川悬崖失稳崩塌，通过链式反应暴露更厚冰层，加速消退进程。该模型显示，仅南极冰盖（尚未计入格陵兰、山地冰川及热膨胀因素）就可能在2100年前使海平面上升超1米。

在2021年纳入更多因素的模型更新中，德康托团队将预估大幅下调，预测高排放情景下本世纪末海平面上升不足40厘米。尽管数据波动，德康托仍坚信该机制："其理论基础是无可辩驳的基础物理与冰川学原理。"

延缓消退的机制
2016年研究后，科学界开始检验高耸冰崖是否真会发生失控崩塌。很快许多学者提出质疑。

基本物理原理鲜有争议：若拉森B这类冰架快速崩塌，暴露其后足够高的冰崖，这些冰崖确实会在自重下弯曲。"摩天大楼存在高度极限是有道理的，"密歇根大学冰川学与断裂力学专家杰里米·巴西斯解释道。但批评者指出，自然界尚未观测到冰崖失控崩塌，或许存在抑制因素。

"暴露的高冰崖确实会崩解，但存在两种稳定机制，"达特茅斯学院冰川学家马蒂厄·莫利格姆指出，他领导的2024年研究确认了这些机制。首先，新暴露的冰崖崩塌时，后方冰体伸展变薄，"高冰崖的高度随之降低"；其次，流动冰川会向前补充崩解冰体，延缓冰崖向内陆消退，降低链式反应概率。

另一项挑战该理论的研究指出，破碎冰体常会形成密集混杂的冰山碎屑浆。这种冰冻混合物能充当挡土墙，至少能暂时稳定冰崖。

冰下基岩也可能是关键角色。"固体地球对海平面变化的影响远超预期，"伦敦帝国学院地球动力学家弗雷德里克·理查兹表示。科学界早已认识到冰川融化时陆地会像释重床垫般回弹，但传统观点认为该过程过于缓慢，数世纪内可忽略不计。如今高精度GPS等地球物理数据显示，回弹可在数十年甚至数年内发生。

这种影响的好坏取决于冰体消退速度。若消退平缓，基岩抬升冰体，减少侵蚀水量；但若通过冰崖失控等机制快速消退，地球响应速度将无法跟上。2024年研究显示，此时基岩仍在抬升，却会将融水推入海洋："相当于把西南极洲碗状洼地里的水挤进全球海洋系统，反而加剧海平面上升。"

地球的动态特性也影响着古海平面模型。理查兹团队在2023年研究发现，澳大利亚300万年前的上新世海岸线随地幔缓慢起伏而变动，考虑垂直运动后估算的古海平面高度更低。理查兹强调这意味着修订后的记录与更保守的冰退模型更吻合："我们必须谨慎，[古代]海平面估值可能偏高，进而导致对冰盖敏感性的高估。"

德康托则以拉森B崩解和格陵兰雅各布港冰川碎裂作为反证。他指出拉森B失去对克雷恩冰川的支撑后，冰体崩解速度远超冰川补给能力，"这有力证明断裂速度可以超越流动速度"。

从历史照见未来
"我职业生涯初期，学界还在争论南极冰盖是在增厚还是变薄，"科罗拉多大学博尔德分校冰川学家特德·斯坎博斯回忆。政府间气候变化专门委员会曾长期认为，本世纪冰盖将保持相对稳定，理由是升温会带来更多降雪抵消融化。

这个假设随着21世纪初拉森B的崩塌而瓦解，科学界很快达成冰量持续流失的共识。卫星观测显示阿蒙森海沿岸冰川（包括松岛和思韦茨）流速较数十年前加快。冰盖已失衡。到2014年美国国家航空航天局召开新闻发布会时，已明确西南极多数巨型冰川自1990年代起持续消退。

"那是我们首次掌握足够证据表明这些接地线在连年后退，"当年发布会研究合著者莫利格姆指出。这种持续流失意味着冰川必然消失。"理论上终止融化可遏止进程，但现实绝无可能实现。"

当讨论聚焦海水侵蚀冰架时，部分科学家日益关注冰盖上方的变化——暖空气正持续融化冰盖表面。惠灵顿维多利亚大学冰川学家尼古拉斯·戈莱奇认为，西南极洲正在向格陵兰的模式转变：格陵兰易受海洋侵蚀的冰体大多已消失，表面融化已成主导。他相信南极洲的表面融化作用将很快超越多数模型预期。

例如融水积聚曾促成拉森B崩塌。融水渗入冰隙润滑基岩和沉积物，使整体更易滑动。哥伦比亚大学冰川学家乔尼·金斯莱克指出，数值模拟过度简化或忽略了这些水文过程："忽视水文变化就会低估消退速度。"

2020年研究证实，渗入南极冰架的融水可能侵入裂缝并使其扩张，这正是德康托团队预言的海洋冰崖不稳定性前兆。

根据未来排放情景，政府间气候变化专门委员会现预测2100年前海平面平均上升0.5-1米（含所有融水源与热膨胀）。若海洋冰崖不稳定性机制成立，南极洲的贡献可能使总升幅翻倍。"这些过程存在深层不确定性，"罗格斯大学气候学家兼科学政策专家罗伯特·科普强调，"唯一能确定的是：大气中二氧化碳越多，风险越大。"

巴西斯对此总结道："无论通过海洋冰崖不稳定性还是海洋冰盖不稳定性，到2100年，我们面对的海岸线必将与我成长时截然不同。"

英文来源：

How Soon Will the Seas Rise?
Introduction
In May 2014, NASA announced at a press conference that a portion of the West Antarctic Ice Sheet appeared to have reached a point of irreversible retreat. Glaciers flowing toward the sea at the periphery of the 2-kilometer-thick sheet of ice were losing ice faster than snowfall could replenish them, causing their edges to recede inland. With that, the question was no longer whether the West Antarctic Ice Sheet would disappear, but when. When those glaciers go, sea levels will rise by more than a meter, inundating land currently inhabited by 230 million people. And that would be just the first act before the collapse of the entire ice sheet, which could raise seas 5 meters and redraw the world’s coastlines.
At the time, scientists assumed that the loss of those glaciers would unfold over centuries. But in 2016, a bombshell study in Nature concluded that crumbling ice cliffs could trigger a runaway process of retreat, dramatically hastening the timeline. The Intergovernmental Panel on Climate Change (IPCC) took notice, establishing a sobering new worst-case scenario: By 2100, meltwater from Antarctica, Greenland and mountain glaciers combined with the thermal expansion of seawater could raise global sea levels by over 2 meters. And that would only be the beginning. If greenhouse gas emissions continue unabated, seas would rise a staggering 15 meters by 2300.
However, not all scientists are convinced by the runaway scenario. Thus, a tension has emerged over how long we have until West Antarctica’s huge glaciers vanish. If their retreat unfolds over centuries, humanity may have time to adapt. But if rapid destabilization begins in the coming decades through the controversial runaway process, the consequences could outpace our ability to respond. Scientists warn that major population centers — New York City, New Orleans, Miami and Houston — may not be ready.
“We’ve definitely not ruled this out,” said Karen Alley, a glaciologist at the University of Manitoba whose research supports the possibility of the runaway process. “But I’m not ready to say it’s going to happen soon. I’m also not going to say it can’t happen, either.”
For millennia, humanity has flourished along the shore, unaware that we were living in a geological fluke — an unusual spell of low seas. The oceans will return, but how soon? What does the science say about how ice sheets retreat, and therefore, about the future of our ports, our homes, and the billions who live near the coast?
Grounded by the Sea
In 1978, John Mercer, an eccentric glaciologist at Ohio State University who allegedly conducted fieldwork nude, was among the first to predict that global warming threatened the West Antarctic Ice Sheet. He based his theory on the ice sheet’s uniquely precarious relationship with the sea.
Bigger than Alaska and Texas combined, West Antarctica is split from the eastern half of the continent by the Transantarctic Mountains, whose peaks are buried to their chins in ice. Unlike in East Antarctica (and Greenland), where most ice rests on land high above the water, in West Antarctica the ice sheet has settled into a bowl-shaped depression deep below sea level, with seawater lapping at its edges. This makes West Antarctica’s ice sheet the most vulnerable to collapse.
A heaping dome of ice, the ice sheet flows outward under its own weight through tentaclelike glaciers. But the glaciers don’t stop at the shoreline; instead, colossal floating plates of ice hundreds of meters thick extend over the sea. These “ice shelves” float like giant rafts, tethered by drag forces and contact with underwater rises and ridges. They buttress the glaciers against an inexorable gravitational draw toward the sea.
Mark Belan/Quanta Magazine
The critical frontline of the ice sheet’s vulnerability is the “grounding line,” where ice transitions from resting on the seafloor to floating as an ice shelf. As the relatively warm sea works its way below the protective shelves, it thins them from below, shifting the grounding line inland. The floating shelves fragment and break away. The upstream glaciers, now without their buttressing support, flow faster toward the sea. Meanwhile, seawater intrudes like an advancing army toward thicker ice, which rests on bedrock that slopes inward toward the bowl-like center of the continent.
“There’s a very serious message here,” said Hilmar Gudmundsson, a glaciologist at Northumbria University: As the grounding line marches inland toward ever-thicker ice in a process called marine ice sheet instability, “you will have a very sharp increase in global sea level, and it will happen very quickly.”
In 2002, scientists got a live view of how that process may play out. The Larsen B ice shelf, a floating mass off the Antarctic Peninsula roughly the size of Rhode Island, broke apart in just over a month, stunning scientists. Pooling surface meltwater had forced open cracks — a process called hydrofracturing — which splintered the shelf, the only barrier for the glaciers behind it. The glaciers began flowing seaward up to eight times faster. One of these, Crane Glacier, lost its cliff edge in a series of collapses over the course of 2003, causing it to shrink rapidly. What if something similar happened to far larger glaciers on the coast of West Antarctica, like Thwaites and Pine Island?
NASA Earth Observatory
In the years that followed, studies of ancient shorelines revealed a stunning sensitivity in the Earth system: It appeared that epochs only slightly warmer than today featured seas 6 to 9 meters above present-day levels.
In response, glaciologists Robert DeConto and David Pollard developed a bold new theory of ice sheet collapse. They created a computer simulation based on Larsen B’s breakup and Greenland’s calving glaciers that was also calibrated to the geologic past — projecting future melt that matched expectations derived from ancient sea levels.
Their 2016 study outlined a scenario of almost unimaginably quick ice loss and sea-level rise. In a process called marine ice cliff instability (MICI), cliffs taller than 90 meters at the edges of glaciers become unstable and collapse, exposing ever-thicker ice in a chain reaction that accelerates retreat. The model suggested that ice from Antarctica alone — before any additions from Greenland, mountain glaciers or thermal expansion — could raise the seas by more than a meter by 2100.
In a 2021 update that incorporated additional factors into the simulations, DeConto and colleagues revised that estimate sharply downward, projecting less than 40 centimeters of sea-level rise by the century’s end under high-emission scenarios. Yet even as the numbers have shifted, DeConto remains convinced of the MICI concept. “It’s founded on super basic physical and glaciological principles that are pretty undeniable,” he said.
Mechanisms to Slow Retreat
After the 2016 study, the scientific community set out to test whether towering ice cliffs really could undergo runaway collapse. Many soon found reasons for doubt.
Few dispute the basic physics: If ice shelves like Larsen B collapse quickly and expose tall-enough cliffs on the glaciers behind them, those cliffs will indeed buckle under their own weight. “There’s a reason why skyscrapers are only so tall,” said Jeremy Bassis, a glaciologist and expert in fracture mechanics at the University of Michigan. However, critics argue that runaway cliff collapse hasn’t been seen in nature, and there might be good reasons why not.
“Yes, ice breaks off if you expose tall cliffs, but you have two stabilizing factors,” said Mathieu Morlighem, a glaciologist at Dartmouth College who led a 2024 study that identified these factors. First, as newly exposed glacier cliffs topple, the ice behind stretches and thins. As this happens, rapidly, “your ice cliff is going to be less of a tall cliff,” Morlighem said. Second, the flowing glacier brings more ice forward to replace what breaks off, slowing the cliff’s inland retreat and making a chain reaction of cliff toppling less likely.
NASA
Another study challenging the MICI scenario noted that breaking ice also tends to form a mélange, a dense, jumbled slurry of icebergs and sea ice. This frozen slurry can act as a retaining wall, at least temporarily stabilizing the cliffs against collapse.
The bedrock beneath the ice might also be a key player. “The solid Earth is having much bigger impacts on our understanding of sea-level change than we ever expected,” said Frederick Richards, a geodynamicist at Imperial College London. Scientists have long recognized that when glaciers melt, the land rebounds like a mattress relieved of weight. But this rebound has been mostly dismissed as too sluggish to matter for several centuries. Now, high-precision GPS and other geophysical data reveal rebound occurring over decades, even years.
Whether that’s good or bad depends on how quickly ice retreats. If it goes at a modest clip, the bedrock lifts the ice, reducing the amount of water that can lap away at it. But if retreat happens quickly enough through something like runaway cliff collapse, the Earth can’t keep up. A 2024 study showed that the bedrock still rises, but in that scenario it pushes meltwater into the ocean. “You’re actually getting more sea-level rise,” Richards said. “You’re pushing all this water out of a bowl underneath West Antarctica and into the global ocean system.”
Earth’s restlessness also affects models of ancient sea-level rise. In a 2023 study, Richards and colleagues found that Australia’s 3-million-year-old Pliocene shorelines had ridden the slow heave and sigh of Earth’s mantle, and that accounting for that vertical motion resulted in lower estimates for ancient sea levels. This matters, according to Richards, because the revised record is a better match for more conservative ice retreat models. “Hold on, guys,” he said. “We have to be a little bit careful. [Ancient] sea-level estimates might be overestimates, and therefore we might be overestimating how sensitive the ice sheets are.”
DeConto points to the Larsen B breakup and the crumbling of Greenland’s Jakobshavn Glacier as evidence to the contrary. Once Larsen B stopped holding back the Crane Glacier, he says, ice began breaking away faster than the glacier could replenish it. That is “really strong evidence that fracture can outpace flow.”
From Past to Future
“When I started my career, the question was whether Antarctica was growing or shrinking,” said Ted Scambos, a glaciologist at the University of Colorado, Boulder. The IPCC long held that the ice sheet would remain relatively stable through the 21st century, on the logic that rising temperatures would bring more snow, offsetting melt.
That assumption collapsed along with Larsen B in the early 2000s, and scientists soon came to a consensus that ice loss was well underway. Satellite observations revealed that glaciers along the Amundsen Sea, including Pine Island and Thwaites, were flowing faster than in previous decades. The ice sheet was not in balance. By the time NASA called the 2014 press conference, it was clear that many of West Antarctica’s enormous glaciers had been retreating steadily since the 1990s.
National Guard/Alamy
“It was the first time we had enough observations to say, hey, look, these grounding lines have been retreating year after year,” said Morlighem, a co-author on one of the studies presented at the press conference. This steady loss signaled that the glaciers would inevitably disappear. “In theory, if we turn off melt, we can stop it,” he noted. “But there’s absolutely zero chance we can do that.”
While the conversation has centered on how the sea will lap away at the ice shelves, some scientists are increasingly concerned about what’s happening up top, as warming air melts the ice sheet’s surface. Nicholas Golledge, a glaciologist at Victoria University of Wellington, sees West Antarctica today as transitioning to the status of Greenland: Most of Greenland’s marine-vulnerable ice has already vanished, and surface melt dominates. That process, Golledge believes, may soon play a bigger role in Antarctica than most models assume.
Pooling meltwater, for example, contributed to the Larsen B collapse. As the water trickles into crevasses, it lubricates the bedrock and sediments below, making everything more slippery. The Columbia University glaciologist Jonny Kingslake says these processes are oversimplified or omitted in numerical simulations. “If you ignore hydrology change, you are underestimating retreat,” he said.
Indeed, a 2020 study found that meltwater trickling into Antarctica’s ice shelves could infiltrate cracks and force them open, a precursor to marine ice cliff instability that DeConto and colleagues envisioned.
Depending on future emissions, the IPCC now projects an average sea-level rise of half a meter to 1 meter by 2100, a total that includes all melt sources and the expansion of warming water. The MICI process, if correct, could accelerate Antarctica’s contribution enough to double that overall rise. “There’s deep uncertainty around some of these processes,” said Robert Kopp, a climate scientist and science policy expert at Rutgers University. “The one thing we do know is that the more carbon dioxide we put into the atmosphere, the greater the risk.”
In Bassis’ view, “Whether it’s with marine ice cliff instability or marine ice sheet instability, it’s a bit of a distraction. By 2100, we will be talking about a coastline radically different than what I grew up with.”