A less cloudy future: the role of subtropical subsidence in climate sensitivity

An observable constraint on climate sensitivity, based on variations in mid-tropospheric relative humidity (RH) and their impact on clouds, is proposed. We show that the tropics and subtropics are linked by teleconnections that induce seasonal RH variations that relate strongly to albedo (via clouds), and that this covariability is mimicked in a warming climate. A present-day analog for future trends is thus identified whereby the intensity of subtropical dry zones in models associated with the boreal monsoon is strongly linked to projected cloud trends, reflected solar radiation, and model sensitivity. Many models, particularly those with low climate sensitivity, fail to adequately resolve these teleconnections and hence are identifiably biased. Improving model fidelity in matching observed variations provides a viable path forward for better predicting future climate. Estimates of how much Earth’s global sur-face temperature would increase if theconcentration of atmospheric carbon di-oxide were double its pre-industrial concentra-tion vary across climate models by a factor of about 2 (1). This metric, termed equilibrium cli-mate sensitivity (ECS), serves as a canonica