Climate more responsive to marine cloud brightening than ocean albedo modification: A model study

[Andrew Lockley]

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020JD033256

Climate more responsive to marine cloud brightening than ocean albedo modification: A model study

Mengying Zhao  Long Cao  Lei Duan  Govindasamy Bala  Ken Caldeira

First published: 19 December 2020

https://doi.org/10.1029/2020JD033256

This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1029/2020JD033256

About

 

Share on

Abstract

Solar radiation modification has been suggested as a backup option to reduce anthropogenic warming. Marine cloud brightening (MCB) and ocean albedo modification (OAM) are two proposed approaches to intentionally reflect sunlight back to space over oceanic regions. Using the NCAR Community Earth System Model, we compare climate response to MCB and OAM under the framework of fast adjustment and slow feedback. We implement MCB and OAM uniformly over the global ocean to offset CO2‐induced warming. We find that to offset 3.3 K global mean warming from a doubling of CO2, diagnosed effective radiative forcing is ‐4.8 and ‐3.6 W m‐2 for OAM and MCB, respectively. Correspondingly, radiative forcing efficacy of OAM is about 70% of MCB. Fast climate adjustment differs in response to MCB and OAM forcing. MCB cools the lower atmosphere by reflecting sunlight from cloud, causing a reduction in sunlight absorption in the atmosphere. In contrast, OAM, by reflecting more sunlight from surface, increases shortwave heating of the lower atmosphere, leading to a decrease in low marine clouds and hence a positive cloudy‐sky shortwave forcing that partly compensates the negative clearly‐sky shortwave forcing. The slow climate response and pattern of equilibrium climate change are similar between MCB and OAM. As for hydrological cycle, relative to the climate under a doubling of CO2, both MCB and OAM produce an increase in precipitation and runoff over tropical land.