Antarctica’s massive ice sheet, equivalent to 190 feet of sea-level rise if it all melted, will shed more water into the oceans as the planet continues warming. But there is a concerning nuance to this that graduate student Julius Garbe and Professor Ricarda Winkelmann discovered. Beyond certain warming thresholds, melting will drastically accelerate, and the ice sheet won’t fully recover even if we lower the planet’s temperature back to today’s level. The first threshold requires temperatures not much higher than recent yearly averages: another 1°C. The findings were published this month in Nature.

The scientists made their discovery by running state-of-the-art computer simulations on the ice sheet under a few warming scenarios. Relying on computer models may give you pause. But they ensured their computer model works by testing whether it can accurately simulate Antarctica’s behavior through past glacial cycles. Once they confirmed they can accurately simulate the past, they examined the future. Thus far, increased snowfall has prevented Antarctica from losing ice overall, but this is expected to change soon. The authors confirmed the ice sheet’s melting will soon outweigh the gains from snowfall, but they also found key thresholds where Antarctica becomes unable to recover all of its lost ice.

The first threshold of another 1 °C increase is the extent of global warming that the internationally signed Paris Climate Agreement sought to avoid (the same agreement from which the Trump administration formally began withdrawing last year, after President Obama signed it in 2015). Climate scientists have generally agreed that we are unlikely to avoid this. After exceeding this threshold, Antarctic melting is projected to increase average sea level to almost 8 feet for every degree of warming. The number of feet increases four-fold if the planet reaches 5°C higher than recent years. Another final threshold is much more concerning, albeit one we probably won’t see this century—or at all if global temperatures can be curbed in time. If the planet warms by another 9°C, Antarctica is on track to be essentially ice-free, releasing all of its frozen water into the oceans. And don’t forget that the Antarctic ice sheet is not the only contributor to sea-level rise; Greenland also houses an immense volume of ice that it’s losing at a faster rate.

Around 600 million people live along the coast. As sea level rises, millions of people are expected to be displaced from their homes along with trillions of dollars in economic damage suffered by countries across the globe. While drastic sea-level rise may be a distant threat, the recent findings suggest that its inevitability is decided by the actions taken sooner rather than later.

Julius Garbe is a Ph.D. student at the University of Potsdam in Professor Ricarda Winkelmann’s lab . Ricarda Winkelmann is a professor of climate science.

Managing Correspondent: Jordan Wilkerson

Original Press Article: The hysteresis of the Antarctic Ice Sheet

Image Credit: NASA/Jeremy Harbeck