Limiting man-made warming to a maximum of 1.5 °C above pre-industrial temperatures will significantly reduce the risk of ice-free Arctic conditions compared to a maximum increase of 2 °C, report two studies published online this week in Nature Climate Change. These results emphasize the need for greater efforts to reduce greenhouse gas emissions in order to preserve the fragile Arctic.

One of the most visible signs of climate change is the drastic decline in the extent of Arctic sea ice - the total area with ice concentrations over 15%. Since 1979, the minimum annual extent of sea ice in the Arctic, as observed each September, has dropped by about 40%. This has prompted considerable interest in quantifying when - and if - the Arctic could become ‘ice-free’; that is, having a sea ice extent of less than 1 million km2 during a September.

In two separate studies, Michael Sigmond and colleagues, and Alexandra Jahn model the probabilities of an ice-free Arctic under the 1.5 °C and 2 °C warming thresholds proposed in the Paris climate agreement. The authors report significant benefits in limiting man-made warming to a 1.5 °C increase. In such a world, ice-free Arctic conditions would be expected approximately once every forty years, compared to once every 3-5 years under 2 °C of warming. With the 3 °C increase expected from current emission pledges, however, ice-free conditions are expected most Septembers.

In an accompanying News & Views article, James Screen comments that “although the reduced odds of ice-free conditions at warming of 1.5 °C relative to 2 °C are clear, the exact probabilities should be interpreted with caution ... This is because the sensitivity of sea ice to global warming in the real world is highly uncertain, which makes it difficult to assess whether sea ice is lost at the correct rate in climate models.”