Forcing Susceptibility and Climate Sensitivity to Midlatitude Marine Cloud Brightening

[Geoengineering News]

https://journals.ametsoc.org/view/journals/clim/aop/JCLI-D-25-0337.1/JCLI-D-25-0337.1.xml

Authors: Haruki Hirasawa, Matthew Henry, Alex M. Mason, Philip J. Rasch, Sarah J. Doherty, Robert Wood, James Haywood, and Knut von Salzen

Online Publication: 12 Dec 2025

Abstract

The climate intervention approach marine cloud brightening (MCB) would aim to reduce climate warming by injecting sea salt aerosol (iSSA) into the lower troposphere to increase cloud albedo, reflect more sunlight, and cool the surface. Due to the short atmospheric lifetime of tropospheric aerosol, MCB iSSA emissions and their resulting radiative forcing are regional by nature. This presents a significant challenge and opportunity, as there are many potential MCB implementation patterns that could produce widely varying climate responses. Previous modeling studies suggest that MCB implementation in the subtropical oceans can cause global cooling, but often result in remote regional temperature and precipitation responses that may be considered undesirable. Here, we use three Earth System Models (ESMs) to estimate the impact of MCB implementation in fourteen different ocean regions, assessing MCB forcing and cooling efficiency in each region and examining the patterns of temperature response from each case. We find that iSSA emissions in the midlatitude oceans produce stronger cloud forcing, greater cooling efficiency, and more spatially uniform cooling. With this information, we evaluate a novel MCB emission strategy that emits iSSA in the midlatitude oceans. The ESMs show this iSSA emission pattern produces temperature and precipitation responses across all three ESMs that are quite similar in pattern (but of opposite sign) to the greenhouse gas (GHG) response. Thus, compared to previously tested iSSA injection patterns, midlatitude MCB implementations may be more suitable when intending to maintain climates close to present day conditions.

Source: AMSO