The Shortwave Radiative Flux Response to an Injection of Sea Salt Aerosols in the Gulf of Mexico

Abstract

As climate change progresses and continues to cause increased risks and damages to society, there are increasing discussions focused on solar geoengineering as a means of temporarily and deliberately reducing some of the impacts of human-caused greenhouse gas emissions (NASEM, 2021). Marine cloud brightening (MCB; Latham, 1990) has emerged as one of the more commonly discussed ideas. This idea involves taking advantage of aerosol-cloud interactions (Haywood & Boucher, 2000): injecting sea salt aerosols into marine low clouds can, under certain meteorological conditions, cause their albedo to increase (Twomey, 1974(Twomey, , 1977, which would cool the planet if done on a large enough scale (Latham et al., 2008).To maximize the radiative flux response of MCB, previous studies have established that marine stratocumulus clouds off the west coasts of North America, South America, and southwest Africa are most susceptible to cloud brightening (Jones et al., 2009;Salter et al., 2008). Additionally, studies show that injecting Aitken mode particles with dry-diameters between 50 and 100 nm invoke greater aerosol-cloud indirect effects and require less injected mass to achieve a similar forcing as compared to larger, accumulation mode particles (Connolly et al., 2014;Partanen et al., 2012;Wood, 2021). Nonetheless, additional studies demonstrate that an injection of

Unexpected failure of regional marine cloud brightening in a warmer world

“…We also model MCB by simply increasing cloud droplet number concentration, rather than injecting any aerosols. Prior studies show that the direct radiative effect of sea salt aerosols contributes non-negligible cooling 41,42 , which would lead to an underestimation of cooling from midlatitude MCB in our study. Other ESMs also have different mean-state AMOCs and AMOC sensitivities to forcing which would likely lead to different outcomes.…”

“…This approach allows us to focus on the climate responses to MCB by perturbing the model in the next step of the causal chain (inject aerosols → aerosolize and activate into CCN → increase CDNC → enhance cloud reflectivity). We note that the direct radiative effect of sea salt aerosols has been found to contribute a non-negligible cooling 41,42 , so the results from our study likely underestimate the total radiative effect of MCB. We also only apply MCB in March through November when MCB would be most effective due to higher Northern Hemisphere solar insolation.…”