Marine Cloud Brightening : an environmentally friendly geoengineering approach to counteract the climate emergency

Abstract

Human activities such as burning of fossil fuels have increased the global average atmospheric carbon dioxide level from 280 ppm in 1750 to 419 ppm in 2021, contributing to the rise in Earth’s temperature. In addition to the global effort to reduce greenhouse gas emissions, scientists and engineers raised the need for additional support via geoengineering technologies to accomplish the Paris Agreement temperature goals. The Marine Cloud Brightening (MCB) originally proposed by John Latham in 1990 is a solar radiation management (SRM) technique that aims to mitigate global warming by artificially increasing the reflectivity of marine cloud through seeding them with sub-micrometer seawater aerosol. By increasing the albedo of marine stratocumulus clouds, it can reflect more sunlight, cool the ocean, and offset the global warming. In the simulation using aerosol-climate model, -1.5 W/m² of the global mean direct forcing and -2.6 W/m² of the indirect effect were expected when all oceans were geoengineered with the MBC. Also, modeling study indicated that the MCB might be deployed on regional scale to mitigate certain consequences of global warming at a regional scale such as polar ice loss, typhoon occurrence, and coral bleaching. Implementation and assessment of the MCB, however, needs a collaboration among various fields of scientists and engineers. The major issues concerning the MCB are (i) to develop the seawater spray techniques that generate optimal sizes and volumes of seawater particles in sufficient numbers (10¹⁷ nuclei/s) and (ii) to improve aerosol-climate models to predict the aerosol-cloud interactions for accurate modeling of the potential efficacy of the MCB and its environmental impacts. In this presentation, we will introduce basic principles and recent research trends on the MCB and discuss critical issues associated with the MCB.