Britain’s foremost scientific institution has suggested that reducing the amount of sunlight reaching the Earth could help slow global warming and mitigate some of the impacts of climate change. However, the Royal Society emphasizes that such interventions carry significant risks.
In a recent report, the society, historically known for driving the scientific revolution in the 17th century, stated that advanced technologies designed to reflect sunlight back into space could “buy time” for reductions in fossil fuel emissions to take effect. Two methods were highlighted as both technically feasible and potentially effective: injecting reflective particles into the upper atmosphere and increasing the reflectivity of clouds over oceans by spraying them with salt.
The report cautions, however, that unilateral action by a single nation could have severe unintended consequences, such as triggering extreme droughts or other disruptive weather events globally. Professor Keith Shine, who chairs the report’s working group, stressed that solar radiation modification (SRM) is inherently risky. Yet, he suggested that there could come a point where the dangers of SRM are considered smaller than the consequences of failing to adequately limit climate change.
According to the report, global efforts to cut greenhouse gas emissions appear unlikely to prevent temperatures from rising above 1.5°C—the level many scientists consider a “safe” threshold. With UN climate negotiations set to resume in Brazil, current policies suggest the planet could warm by at least 3°C above pre-industrial levels by 2100.
Of the proposed SRM techniques, the working group identified stratospheric aerosol injection as the most promising. This method involves high-altitude aircraft releasing sulfur dioxide, which forms particles capable of reflecting a portion of incoming sunlight. Historical evidence supports its potential: the 1991 eruption of Mount Pinatubo in the Philippines released approximately 15 million tonnes of sulfur dioxide into the stratosphere, temporarily lowering global temperatures by 0.5°C for one to two years. Modeling indicates that annual emissions of 8 to 16 million tonnes of sulfur dioxide, dispersed across both hemispheres, could reduce global temperatures by roughly 1°C.
