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?