Melting Arctic sea ice slow down the projected warming of the North Atlantic

Projected warming is inhomogeneous over the globe. The North Atlantic Ocean is one of the regions with minimum projected warming according to climate model projections. Several models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) even projected a slight cooling in 2081-2100 relative to 1986-2005 for the North Atlantic Ocean.  In the paper Sea-ice free Arctic contributes to the projected warming minimum in North Atlantic accepted to be published in Environmental Research Letters, series of numerical model simulations using both the Bergen Climate Model (BCM) and the atmospheric component of BCM, are used to document that an autumn sea-ice free Arctic Ocean contributes to the slow-down of the projected warming of the North Atlantic.

Simulated annual mean changes in surface air temperature with BCM. a) between the future projection (Proj) during the Arctic sea ice free period and the present-day climate (Ctrl), b) in response to the sea-ice free Arctic, c) in response to the sea-ice free Arctic with atmospheric component of BCM. The dots in a, b and c) show where the responses simulated with BCM / ARPEGE pass the 95% significance testSimulated annual mean changes in surface air temperature with BCM. a) between the future projection (Proj) during the Arctic sea ice free period and the present-day climate (Ctrl), b) in response to the sea-ice free Arctic, c) in response to the sea-ice free Arctic with atmospheric component of BCM. The dots in a, b and c) show where the responses simulated with BCM / ARPEGE pass the 95% significance testThe authors are from the Nansen and Bjerknes Centers and Uni Research Climate in Bergen, as well as the Nansen-Zhu Centre and the Climate Change Research Centre of the Chinese Academy of Sciences in Beijing. In the paper, led by Dr. Lingling Suo from the Nansen Center, they describes the mechanism causing the slow-down of the projected warming of the North Atlantic by the fact that the autumn sea-ice free conditions in the Arctic triggers a weaker Icelandic low during autumn. This is further associated with the weakened wind stress over the subpolar gyre reducing the intensity of the deep convection over the subpolar north Atlantic and accordingly contributing to a weakening of the Atlantic meridional overturning circulation (AMOC).  The weakened AMOC leads to a decrease in northward heat transport and a cooling of the ocean surface in the mid-latitude of the North Atlantic. The role of the air-sea interaction in the response to changes in the Arctic sea ice extent (see figure) , which so fare has not been widely discussed in the literature, has been highlighted by the results presented in this paper.

 

Paper citation: Suo, L., Gao, Y., Guo, D., and Bethke, I. Sea-ice free Arctic contributes to the projected warming minimum in North Atlantic. Environ Res Lett (at press). https://doi.org/10.1088/1748-9326/aa6a5e