Point of no return

More than half of Earth’s freshwater resources are held frozen in the Antarctic Ice Sheet, making the ice sheet’s long-term stability crucial to limiting global sea-level rise. In this week’s issue, Ricarda Winkelmann and her colleagues present model results that reveal how vulnerable the ice sheet is to climate change. The researchers show that as Earth’s climate becomes warmer, the ice sheet becomes progressively more sensitive to a given amount of warming. Even more concerning is the fact that, if warming levels persist, to restore the ice sheet to its current form would require more than just a reversion in temperature to the present-day level, it needs a cooling to lower than pre-industrial levels. The results suggest that, if the limits on warming set out in the Paris Agreement are not met, Antarctica’s long-term contribution to sea levels will dramatically increase and will be close to impossible to reverse.