Solar Radiation Management: A Climate Tool with Geopolitical Implications

However, a temperature overshoot is anticipated.  The United Nations Environment Programme (UNEP) forecasts that the 1.5 °C threshold will be exceeded in the coming years, with warming potentially peaking between 2.2 °C and 3.6 °C this century.  Against this backdrop, three trends characterize the climate policy debate.

First, while initially viewed as distracting from mitigation, adaptation measures—such as building seawalls, selecting heat-resistant crops, or greening urban areas—are now fully integrated into the policy toolbox. Second, carbon dioxide removal (CDR) has emerged as a contentious complement to mitigation and adaptation.  Since 2007, the Intergovernmental Panel on Climate Change (IPCC) has included CDR methods in most scenarios that meet the 2 °C target. Forestry, bioenergy with carbon capture and storage (BECCS), or direct air capture and storage (DACS) could hasten carbon neutrality by compensating for residual emissions from hard-to-abate sectors like cement production and aviation. This could lead to negative emissions (where sequestered CO2 exceeds emitted CO2), causing atmospheric concentrations to decline. Third, solar radiation management (SRM)—techniques that aim to stimulate Earth’s albedo, reflect part of solar radiation and induce artificial cooling—are garnering significant attention.

This Memo is devoted to SRM, specifically stratospheric aerosol injection (SAI), which seeks to mimic the cooling effect of particles released during volcanic eruptions. Since Nobel laureate Paul Crutzen warned in 2006 that SAI should be investigated if mitigation falls short,  SAI has dominated SRM discussions. This prominence stems from a lack of major technological hurdles, modest projected costs, and the promise of rapid cooling with immediate benefits against heatwaves, droughts, hurricanes, and coral bleaching. Yet SAI also carries potentially deleterious side effects, including acid rain, ozone layer depletion, hydrological disruption, and the risk of termination shock.