An Update on the Thermosteric Sea Level Rise Commitment to Global Warming

Thermosteric sea level rise is a large component of the ongoing sea level rise, and historic thermal expansion is reasonably well captured by current climate models. However, the thermosteric sea level rise per degree warming one would experience in equilibrium, that is, after the ocean has stopped taking up heat is poorly constrained.

Here we evaluate the equilibrium thermosteric sea level rise caused by global warming in several coupled climate models. The thermosteric sea level rise is found to be well approximated as a linear function of the mean ocean temperature increase in the models. However, the mean ocean temperature increase as a function of the mean surface temperature increase differs between the models. Our models can be divided into two branches; models with an Atlantic meridional overturning circulation that increases with warming have large mean ocean temperature increases and vice versa. These two different branches give estimates of the equilibrium thermosteric sea level rise per degree of surface warming that are respectively 98% and 21% larger than the estimate given in the IPCC Fifth Assessment Report. Our estimates of the equilibrium thermosteric sea level rise are also used to infer an equilibrium sea level sensitivity, a parameter akin to the often used equilibrium climate sensitivity metric.