Climate feedbacks with latitude derived from climatological data and theory

Abstract. Most current methods for evaluating climate feedbacks utilise variation with time in Earth’s energy balance and surface temperatures, either from observations or Earth system model perturbation experiments. This study presents a new semi-empirical evaluation of Earth’s climate feedbacks at equilibrium, constrained instead by variation with latitude in recent mean climatology. Latitudinally binned surface temperature and outgoing radiation climatology provides a first order net climate feedback estimate  λ= -1.3±0.1 Wm^-2 K^-1, but this does not isolate the temperature influence on outgoing radiation from other factors. To isolate the surface temperature influence: First, we derive approximated functional relations for outgoing shortwave and longwave radiation in terms of surface temperature, surface relative humidity, fractional cloud amount, tropopause height and incident solar radiation. Second, we use observations of current zonal-mean climatology to constrain the relations and apply calculus to evaluate non-cloud climate feedbacks with latitude, including the Planck, water vapour-lapse rate and surface albedo. Our novel climatology-based evaluations of climate feedbacks weighted by the recent warming pattern, when combined with a recent estimate of cloud feedback from multiple lines of evidence, implies a global mean total net climate feedback λ= -1.1 (-0.8 to -1.4 at 66 % range) Wm^-2 K^-1 consistent with recent assessments of the literature. Our latitudinal method to constrain non-cloud climate feedback is independent of previous temporal approaches, using different observational lines of evidence, and so our method complements existing methods to help constrain climate feedback and climate sensitivity.