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Abstract

We examine the seasonal cycle of Arctic sea ice in scenarios with limited future global warming. To do so, we analyse 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 MPI-ESM Grand Ensemble. Based on the high-sensitivity observations, we find that Arctic September sea ice is lost with low probability (P≈10%) for global warming of +1.5 ° C above pre-industrial levels and with very high probability (P>99%) for global warming of +2 ° C above pre-industrial levels. For the low-sensitivity observations, September sea ice is extremely unlikely to disappear for +1.5 ° C warming (P<<1%) and has low likelihood (P≈10%) to disappear even for +2 ° C global warming. For March, both observational records suggest a loss of 15% to 20% of Arctic sea-ice area for 1.5 ° C to 2 ° C global warming.