A Semi-Analytical Model for Water Vapor, Temperature, and Surface-Albedo Feedbacks in Comprehensive Climate Models

Radiative feedbacks govern the Earth's climate sensitivity and elucidate the geographic patterns of climate change in response to a carbon-dioxide forcing. We develop an analytical model for patterned radiative feedbacks that depends only on changes in local surface temperature. The analytical model combines well-known moist adiabatic theory with the radiative-advective equilibrium that describes the energy balance in high latitudes. Together with a classic analytical function for surface albedo, all of the non-cloud feedbacks are represented. The kernel-based analytical feedbacks reproduce the feedbacks diagnosed from global climate models at the global, zonal-mean, and seasonal scales, including in the polar regions, though with less intermodel spread. The analytical model thus provides a framework for a quantitative understanding of radiative feedbacks from simple physics, independent of the detailed atmospheric and cryospheric responses simulated by comprehensive climate models. Given an increase in carbon dioxide concentration, individual radiative feedbacks stabilize or amplify the climate response. When diagnosed from comprehensive climate models, these feedbacks exhibit considerable variability, yet, single atmospheric columns have been successfully used as minimal models to quantify the effect of temperature and water vapor changes on global climate. Here, we bring together these perspectives by developing an analytical model for radiative feedbacks that, for projected changes, knows only of local surface temperature. That is, thermodynamic expressions for atmospheric temperature, water vapor, and sea-ice albedo are combined with radiative kernels, which characterize the top-of-atmosphere radiative response to a small perturbation, to yield estimates of radiative feedbacks independent of the simulated atmospheric and cryospheric changes from a climate model. The analytical model captures the equator-to-pole and seasonal feedback structure, including in the ice-covered polar regions, as well as the global feedback across an ensemble of global climate models. This research thus provides a framework for a quantitative understanding of radiative feedbacks from simple physics combined with geographic patterns of surface warming. Analytical approximations of atmospheric temperature and surface albedo are used to estimate feedbacks in comprehensive climate modelsMeridional, seasonal, and global variations in feedbacks are well-represented by the analytical model, including in the polar regionsAnalytical feedbacks have less intermodel spread than general circulation model feedbacks, suggesting that deviations from an adiabat contribute to uncertainty

Automated summary

An analytical model for patterned radiative feedbacks that depends only on changes in local surface temperature is developed. The model captures the feedbacks diagnosed from global climate models at different scales and provides a quantitative understanding of radiative feedbacks from simple physics.