Reduction of internal climate variability in surface temperature due to sea-ice loss since the mid-21st century

Understanding the internal climate variability (ICV) is a principal challenge in projecting future climate change. In this study, we define the ICV in projection of surface temperature as the ensemble spread of surface temperature using a 30-member ensemble simulated with the Community Earth System Model Large Ensemble (CESM-LE) experiment, and examine how this ICV changes from the present climate to the future climate under Representative Concentration Pathway 8.5 scenario (RCP8.5). First, ICV is reduced in the future climate, particularly since the mid-21st century. Such a decrease is primarily due to the reduction of ICV in both the Arctic (70°–90°N) and the Antarctic (65°–80°S). Our analysis further indicates that the decrease in ICV in Arctic is significant during boreal fall (September–October–November), and in particular, it is closely linked to the reduction in sea ice since the early and mid-21st century. This implies that realistic simulation of the Arctic sea ice is a key in reducing ICV in a changing climate.