Remarkable separability of circulation response to Arctic sea ice loss and greenhouse gas forcing

Arctic sea ice loss may influence midlatitude climate by changing large-scale circulation. The extent to which climate change can be understood as greenhouse gas-induced changes that are modulated by this loss depends on how additive the responses to the separate influences are. A novel sea ice nudging methodology in a fully coupled climate model reveals that the separate effects of doubled atmospheric carbon dioxide (CO2) concentrations and associated Arctic sea ice loss are remarkably additive and insensitive to the mean climate state. This separability is evident in several fields throughout most of the year, from hemispheric to synoptic scales. The extent to which the regional response to sea ice loss sometimes agrees with and sometimes cancels the response to CO2 is quantified. The separability of the responses might provide a means to better interpret the diverse array of modeling and observational studies of Arctic change and influence. Plain Language Summary The decrease in Arctic sea ice area may influence midlatitude climate and weather by changing hemispheric-scale winds. Whether the change in winds due to this Arctic sea ice loss can be cleanly separated from the wind changes due to human-induced greenhouse gas increase remains a question. Here using a global climate computer model, we explicitly separate the climate response to Arctic sea ice loss from the climate response to a doubling of atmospheric carbon dioxide (CO2) concentration with fixed Arctic sea ice. We show that the two separate responses add up to the full climate response to a doubling of CO2 concentration. We also show that it is not important whether CO2 is doubled with a large amount of Arctic sea ice or a small amount or whether Arctic sea ice decreases in a warm climate or in a cold climate. These results imply that some features of human-induced climate change may be explained by Arctic sea ice melting and may help to explain the many different greenhouse gas-induced wind changes found in modeling and observational studies.