Solar radiation modification refers to large-scale methods designed to reflect sunlight and cool Earth. The President's Science Advisory Committee first mentioned deliberately bringing about countervailing climatic changes in the 1965 report titled Restoring the Quality of Our Environment.
Russian climatologist Mikhail Budyko suggested releasing aerosols into the stratosphere in 1974 if global warming became a serious threat. He proposed aircraft burning sulfur to generate aerosols that would reflect sunlight away from Earth.
Major reports evaluating potential benefits and risks followed from organizations like the Royal Society in 2009. The US National Academies released assessments in 2015 and 2021 while the United Nations Environment Programme issued a report in 2023.
Through 2024 roughly 200 million dollars had been spent on SRM research with annual rates increasing to more than 30 million dollars recently. As of May 2025 another 164 million dollars has been committed for the period 2025 through 2029.
In 2023 Mexico announced it would prohibit SRM experiments within its borders. Several US states implemented prohibitions on geoengineering in 2025 targeting purported chemtrails rather than SRM per se including Tennessee and Florida.