The Oceans Are Going to Rise-but When?

"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."

A portion of the West Antarctic Ice Sheet shows apparent irreversible retreat as glaciers lose ice faster than snowfall, causing grounding lines to recede inland. Initial loss of those glaciers would raise sea level by more than a meter, affecting roughly 230 million people, and eventual collapse of the entire sheet could add about five meters. A proposed ice-cliff instability mechanism could accelerate retreat, prompting a worst-case IPCC scenario of over two meters by 2100 and up to 15 meters by 2300 if emissions continue. Scientific disagreement about timing creates major uncertainty for adaptation and coastal preparedness.

Read at WIRED