Exploring the Relationships Between Marine Cloud Brightening, the Walker Circulation, and Boreal Summer Asian Monsoon Precipitation

Abstract

Because current efforts to mitigate global carbon emissions are insufficient to limit warming to 2C above preindustrial levels, some have proposed geoengineering, the deliberate large-scale manipulation of the planetary environment to counteract anthropogenic climate change, as a method of slowing the rise of global mean temperature (GMT). Marine cloud brightening (MCB), a solar radiation management geoengineering technique that involves the deliberate brightening of clouds by injecting aerosols or sea salt into regions of the atmosphere that are most susceptible to cloud formation, is one proposed method to mitigate the effects of global warming by increasing albedo and reflecting sunlight, thereby reducing GMT. While simulation studies suggest that MCB could counteract the global mean warming from a doubling in carbon dioxide concentration, there is still uncertainty regarding the extent and magnitude of its unintended side effects. Using the output from a version of the Geophysical Fluid Dynamics Laboratory’s Atmosphere-Ocean General Circulation Model, this study finds a link between a westward shift and intensification of the Walker circulation and increased (decreased) summer monsoon precipitation in the Indian Monsoon (East Asian Monsoon) region, when MCB is implemented exclusively in the South Pacific, as well as when MCB is implemented in the South Pacific, North Pacific, and South Atlantic simultaneously. These findings invite important questions about how societies will adapt to changes of weather patterns induced by MCB, and serve as a necessary step in assessing the tradeoffs between worlds with and without MCB.