From present to future: New study examines climate response to Arctic sea ice loss and its contribution to climate change
Arctic sea ice extent has declined rapidly in the past three decades and climate models driven by increased greenhouse gases project an ice-free Arctic Ocean by the second half of this century. In a new study to be published in the Journal of Climate, CIRES and NOAA researchers from the Physical Sciences Division and an NCAR collaborator use NOAA GFDL’s Coupled Model version 3 (CM3) simulations to explore the ocean and atmospheric response to Arctic sea ice loss for the time period 1990-2090, and its contribution to anthropogenic climate change. In their experiment, greenhouse gases increased in all simulations, but one set of simulations held ice fixed at its 1990 value, while in a second set of simulations sea ice evolved over time. A comparison between the two sets of simulations enabled the team to identify the effects of Arctic sea ice loss on climate from the recent past to the end of the 21st century.
The results showed that Arctic sea ice loss is a crucial factor for greenhouse gas-induced changes in the Atlantic Ocean, such as weakening of the Atlantic Meridional Overturning Circulation (AMOC) and the absence of warming sea surface temperatures south of Greenland—referred to as the North Atlantic “warming hole.” The response of the jet stream to sea ice loss in the near term is very small compared to internal variability, but it increases over time, and by the end of the 21st century it differs from the overall response to anthropogenic climate change. Sea ice loss warms the Northern Hemisphere extratropical continents especially over high latitudes and the eastern United States. Lastly, there is increased tropical precipitation and warming in the tropical upper atmosphere in response to continued Arctic sea ice loss. This is termed a “mini-global warming” because it has the same general pattern, but a much weaker amplitude, as the overall tropical response to increased greenhouse gas emissions.
While previous modeling studies have examined the role of sea ice between a time period in the recent past and a time period in the future, this study is the first to examine the contribution of Arctic sea ice loss to anthropogenic climate change over time. The researchers’ findings generally agree with similar modeling studies focusing on the later part of the 21st century, including the prediction of a “mini-global warming” signal in the tropics. However, their results differ from some observational studies. For example, some observational studies suggest that sea ice loss cools the Northern Hemisphere extratropical continents in winter instead of warming them. However, observational studies do not allow to determine cause and effect. This can only be determined by model experiments.
Posted: August 20, 2018