The Montreal Protocol is delaying the occurrence of the first ice-free Arctic summer

The rapid melting of Arctic sea ice is the largest and clearest signal of anthropogenic climate change. Current projections indicate that the first ice-free Arctic summer will likely occur by mid-century, owing to increasing carbon dioxide concentrations in the atmosphere. However, other powerful greenhouse gases have also contributed to Arctic sea ice loss, notably ozone-depleting substances (ODSs). In the late 1980s, ODSs became strictly regulated by the Montreal Protocol, and their atmospheric concentrations have been declining since the mid-1990s. Here, analyzing new climate model simulations, we demonstrate that the Montreal Protocol, designed to protect the ozone layer, is delaying the first appearance of an ice-free Arctic summer, by up to 15 y, depending on future emissions. We also show that this important climate mitigation stems entirely from the reduced greenhouse gas warming from the regulated ODSs, with the avoided stratospheric ozone losses playing no role. Finally, we estimate that each Gg of averted ODS emissions results in approximately 7 km2 of avoided Arctic sea ice loss.

Automated summary

The melting of Arctic sea ice, largely due to anthropogenic climate change, is projected to result in the first ice-free Arctic summer by mid-century. Ozone-depleting substances (ODSs), which have been regulated since the late 1980s by the Montreal Protocol, have also contributed to this ice loss. Using climate model simulations, it is demonstrated that the Montreal Protocol is delaying the occurrence of an ice-free Arctic summer by up to 15 years, solely due to the reduction in greenhouse gas warming from regulated ODSs. Furthermore, it is estimated that each Gg of reduced ODS emissions leads to 7 km2 of avoided Arctic sea ice loss.