Assessing the potential efficacy of marine cloud brightening for cooling Earth using a simple heuristic model

Abstract:

Marine cloud brightening (MCB) is the idea that the amount of solar radiation reflected by low clouds might be deliberately increased by augmenting the existing population of aerosol particles with salt particles created from seawater. MCB has been suggested as one of the potentially feasible climate intervention approaches to counteract anthropogenic global warming. Global and process modeling studies have been conducted to assess various aspects of MCB, but many questions remain.

Observations evaluating the brightening of clouds using pollution from commercial shipping serve as a useful tool for evaluating potential for brightening, as do studies using detailed microphysical models and large eddy simulations. In this presentation, these different pieces of knowledge will be synthesized using the framework of a simple heuristic model, which aims to estimate bounds on the global radiative forcing possible from MCB given assumptions regarding: (a) the quantity, size, and lifetime of salt particles injected from each vessel; (b) the number of vessels deployed; (c) the relationship between cloud droplet concentration and the aerosol size distribution; (d) the albedo susceptibility of clouds; (e) the strength of the cloud liquid water adjustments to aerosol. This presentation will use the heuristic model to explore questions such as: How much salt mass must be sprayed to achieve a certain forcing, what is the optimal size for the injected particles, and how many ships are really needed to achieve significant cooling?