Contraction of the World's Storm-Cloud Zones the Primary Contributor to the 21st Century Increase in the Earth's Sunlight Absorption

Abstract

Recent Earth energy budget observations show an increase in the sunlight absorbed by the Earth of 0.45 W/m2 per decade, caused primarily by a decrease in cloud reflection. Here we decompose the solar radiative budget trends into general circulation and cloud controlling process components. Regimes representing the midlatitude and tropical storm zones are defined, and the trends in the areal coverage of those regimes which are potentially induced by circulation changes are separated from trends in the cloud radiative effect within each regime which are potentially induced by changes in local cloud controlling processes. The regime area change component, which manifests itself as a contraction of the midlatitude and tropical storm regimes, constitutes the largest contribution to the solar absorption trend, causing decreased sunlight reflection of 0.37 W/m2 per decade. This result provides a crucial missing piece in the puzzle of the 21st century increase of the Earth's solar absorption.

Key Points

        Satellite observations show that in the past 24 years the worlds storm cloud zones have been contracting at a rate of 1.5%–3% per decade

    This contraction allows more solar radiation to reach the Earth's surface and constitutes the largest contribution to the observed 21st century trend of increased solar absorption


  

Plain Language Summary

Analysis of satellite observations shows that in the past 24 years the Earth's storm cloud zones in the tropics and the middle latitudes have been contracting at a rate of 1.5%–3% per decade. This cloud contraction, along with cloud cover decreases at low latitudes, allows more solar radiation to reach the Earth's surface. When the contribution of all cloud changes is calculated, the storm cloud contraction is found to be the main contributor to the observed increase of the Earth's solar absorption during the 21st century.