Albedo enhancement of marine clouds to counteract global warming: impacts on the hydrological cycle

Bala, G and Caldeira, Ken and Nemani, Rama and Cao, Long and Ban-Weiss, George and Shin, Ho-Jeong (2011) Albedo enhancement of marine clouds to counteract global warming: impacts on the hydrological cycle. In: Climate Dynamics, 37 (5-6). pp. 915-931.

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Abstract

Recent studies have shown that changes in solar radiation affect the hydrological cycle more strongly than equivalent CO(2) changes for the same change in global mean surface temperature. Thus, solar radiation management ``geoengineering'' proposals to completely offset global mean temperature increases by reducing the amount of absorbed sunlight might be expected to slow the global water cycle and reduce runoff over land. However, proposed countering of global warming by increasing the albedo of marine clouds would reduce surface solar radiation only over the oceans. Here, for an idealized scenario, we analyze the response of temperature and the hydrological cycle to increased reflection by clouds over the ocean using an atmospheric general circulation model coupled to a mixed layer ocean model. When cloud droplets are reduced in size over all oceans uniformly to offset the temperature increase from a doubling of atmospheric CO(2), the global-mean precipitation and evaporation decreases by about 1.3% but runoff over land increases by 7.5% primarily due to increases over tropical land. In the model, more reflective marine clouds cool the atmospheric column over ocean. The result is a sinking motion over oceans and upward motion over land. We attribute the increased runoff over land to this increased upward motion over land when marine clouds are made more reflective. Our results suggest that, in contrast to other proposals to increase planetary albedo, offsetting mean global warming by reducing marine cloud droplet size does not necessarily lead to a drying, on average, of the continents. However, we note that the changes in precipitation, evaporation and P-E are dominated by small but significant areas, and given the highly idealized nature of this study, a more thorough and broader assessment would be required for proposals of altering marine cloud properties on a large scale.

Item Type:	Journal Article
Publication:	Climate Dynamics
Publisher:	Springer
Additional Information:	Copyright of this article belongs to Springer.
Keywords:	Climate change;Global warming;Geoengineering;Solar radiation management;Marine cloud-albedo enhancement;Hydrological cycle
Department/Centre:	Division of Mechanical Sciences > Divecha Centre for Climate Change Division of Mechanical Sciences > Centre for Atmospheric & Oceanic Sciences
Date Deposited:	20 Sep 2011 08:49
Last Modified:	20 Sep 2011 08:49
URI:	http://eprints.iisc.ac.in/id/eprint/40546

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