Fast recovery of North Atlantic sea level in response to atmospheric CO2 removal

Abstract

Sea level rise (SLR) due to anthropogenic warming has received growing attention because of its impacts on the coastal environments and associated damages to human societies. It has been reported that such a global mean SLR is unlikely to be restored within the human-relevant time scales, even if climate mitigation is successfully implemented. However, the regional aspect of SLR reversibility in response to the stabilization or reduction of atmospheric carbon dioxide (CO2) concentrations remains unclear. In this study, we found dramatic sea level fluctuations in the Subpolar North Atlantic (SPNA) under idealized CO2 ramp-up and -down experiments. In particular, during the ramp-up period, the SPNA experiences a faster SLR than the global mean. Subsequently, it experiences a rapid decline in response to the subsequent reduction in CO2 levels. The substantial sea level changes are mainly attributed to the response of the Atlantic Meridional Overturning Circulation (AMOC)−the northward transport of heat and salinity. The enhanced meridional salinity transport, resulting from the rapid recovery of the AMOC, triggered by the build-up of the meridional salinity gradient during the ramp-up period, plays a key role in the rapid recovery of the SPNA sea level. Our study highlights that the SPNA and surrounding coastal areas may experience abrupt changes in sea level and associated coastal environments under climate mitigation scenarios. Key words: Sea level rise, Atlantic Meridional Overturning Circulation (AMOC), CO2 removal, Subpolar North Atlantic (SPNA)