Arctic Sea Ice in a 1.5°C Warmer World

We examine the seasonal cycle of Arctic sea ice in scenarios with limited future global warming. To do so, we analyze two sets of observational records that cover the observational uncertainty of Arctic sea ice loss per degree of global warming. The observations are combined with 100 simulations of historical and future climate evolution from the Max Planck Institute Earth System Model Grand Ensemble. Based on the high-sensitivity observations, we find that Arctic September sea ice is lost with low probability (P approximate to 10%) for global warming of +1.5 degrees C above preindustrial levels and with very high probability (P>99%) for global warming of +2 degrees C above preindustrial levels. For the low-sensitivity observations, September sea ice is extremely unlikely to disappear for +1.5 degrees C warming (P<<1%) and has low likelihood (P approximate to 10%) to disappear even for +2 degrees C global warming. For March, both observational records suggest a loss of 15% to 20% of Arctic sea ice area for 1.5 degrees C to 2 degrees C global warming.