The diverse role of clouds in Earth’s observed hemispheric albedo symmetry

December 02, 2022

Aiden Jonsson

Hosted by Maria Rugenstein

Abstract

Observations of Earth’s radiative energy system have shown that Earth’s albedo is symmetric between the northern and southern hemispheres, despite significant hemispheric differences in the clear-sky albedo due to the distribution of land and aerosol sources. This symmetry is given by the annual mean cloud cover compensating almost exactly for the clear-sky albedo asymmetries. I will present the main features of global cloud cover that allow for the hemispheric albedo symmetry, beginning with the role of tropical and subtropical clouds, and then highlighting the role of midlatitude clouds. While planetary albedo symmetry has been observed since the earliest satellite measurements, a theoretical explanation has proven elusive, although there have been speculations of albedo symmetry-maintaining mechanisms within the climate system. Since an albedo symmetry-maintaining mechanism would play a role in determining the features of global cloud cover in response to any clear-sky albedo perturbation, such as aerosol emissions and changes in the cryosphere under warming, it would also have implications for cloud radiative feedbacks. To illustrate the potential that discovering such a mechanism would provide, I will present the implications of such a mechanism for the strength of currently poorly constrained shortwave cloud feedbacks.