Sea ice in the Arctic is more likely to persist through summers if the goals of the Paris climate agreement are met.

The 2015 Paris accord calls for limiting global warming to 1.5–2 °C above preindustrial levels. Michael Sigmond and his colleagues at the Canadian Centre for Climate Modelling and Analysis in Victoria modelled how likely ice-free summers would be if temperatures stabilized at those levels indefinitely. The team found that ice-free summers would be expected once every 5 years with 2 °C of warming, and once every 40 years with a 1.5 °C rise.

Even the latter scenario produces an 85% probability of an ice-free summer within roughly a century. Prospects are worse if countries don’t achieve the steep greenhouse-gas cuts necessary to limit warming to 1.5–2 °C. So far nations have committed to cut emissions only enough to stabilize global temperatures at roughly 3 °C above pre-industrial levels; under that scenario, every Arctic summer will be free of sea ice.