Reduced probability of ice-free summers for 1.5 °C compared to 2 °C warming

Arctic sea ice has declined rapidly with increasing global temperatures. However, it is largely unknown how Arctic summer seaice impacts would vary under the 1.5 degrees C Paris target compared to scenarios with greater warming. Using the Community Earth System Model, I show that constraining warming to 1.5 degrees C rather than 2.0 degrees C reduces the probability of any summer ice-free conditions by 2100 from 100% to 30%. It also reduces the late-century probability of an ice cover below the 2012 record minimum from 98% to 55%. For warming above 2 degrees C, frequent ice-free conditions can be expected, potentially for several months per year. Although sea-ice loss is generally reversible for decreasing temperatures, sea ice will only recover to current conditions if atmospheric CO2 is reduced below present-day concentrations. Due to model biases, these results provide a lower bound on summer sea-ice impacts, but clearly demonstrate the benefits of constraining warming to 1.5 degrees C.