Trend Solar radiation modification back on the agenda and the need for preventive atmospheric governance

Summary

The report says the climate emergency and slow progress on emissions have brought solar radiation modification back into international debate. SRM covers interventions that reflect part of incoming sunlight to cool the planet temporarily, spanning stratospheric aerosol injection, marine cloud brightening, cirrus cloud modification and orbital reflectors. Although known for decades, these ideas drew limited research attention, none has been deployed at scale and analysis rests almost entirely on climate models, with major uncertainty about regional effects and ecological and social impacts. Models suggest SRM could quickly lower global average temperature, much like the temporary cooling after the 1991 Pinatubo eruption, but it could also unevenly alter rainfall patterns and the water cycle. The report contrasts a scenario of preventive atmospheric governance, built on international coordination, scientific transparency and a consensus on non-use or very restricted use, with a fragmented one in which actors go it alone. It judges that the emerging trend is not deployment but the need to decide collectively which limits must not be crossed.