Has coarse ocean resolution biased simulations of transient climate sensitivity?

We investigate the influence of ocean component resolution on simulation of climate sensitivity using variants of the GFDL CM2.5 climate model incorporating eddy-resolving (1/10 degrees) and eddy-parameterizing (1 degrees) ocean resolutions. Two parameterization configurations of the coarse-resolution model are used yielding a three-model suite with significant variation in the transient climate response (TCR). The variation of TCR in this suite and in an enhanced group of 10 GFDL models is found to be strongly associated with the control climate Atlantic meridional overturning circulation (AMOC) magnitude and its decline under forcing. We find that it is the AMOC behavior rather than resolution per se that accounts for most of the TCR differences. A smaller difference in TCR stems from the eddy-resolving model having more Southern Ocean surface warming than the coarse models.