Diminished Efficacy of Regional Marine Cloud Brightening in a Warmer World (Invited)

Marine cloud brightening (MCB) is a solar geoengineering proposal to cool atmospheric temperatures and reduce climate change impacts by increasing the reflectivity of low marine clouds. As large-scale approaches to stabilize global mean temperatures pose substantial governance challenges, regional climate interventions may become more attractive in the near-term. Using the Community Earth System Model version 2, we investigate the efficacy of regional MCB in the North Pacific to mitigate extreme heat in the Western United States. Under present-day conditions, we find MCB in the remote mid-latitudes or proximate subtropics reduces the relative risk of dangerous summer heat exposure by 55% and 16%, respectively. However, the same interventions under mid-century warming minimally reduce or even increase heat stress in the Western United States and across the world. This loss of efficacy may arise from a state-dependent response of the Atlantic Meridional Overturning Circulation to both anthropogenic warming and regional MCB. Our result demonstrates a risk in assuming that interventions effective under certain conditions will remain effective as the climate continues to change.