Geoengineering methods designed to reduce global temperatures could inadvertently worsen droughts and hurricanes in other parts of the world, scientists have cautioned. A new report from the Royal Society examines the current science surrounding solar radiation modification (SRM) — a suite of techniques intended to reflect a portion of the sun’s rays back into space. The study found that a globally coordinated effort could, in theory, help lower global temperatures and mitigate some impacts of climate change. However, the report also stressed that such measures are no substitute for cutting greenhouse gas emissions, which remain the primary driver of global warming. The authors warned that any unilateral action by individual nations could have severe repercussions for others.
Interest in geoengineering has grown amid faltering progress to reduce emissions and limit global temperature rises to 1.5°C, or “well below” 2°C, above pre-industrial levels. According to the latest UN assessment ahead of climate talks in Brazil, the world remains on course for as much as 2.8°C of warming under current policies.
Yet, despite its potential, SRM raises profound technological and ethical concerns. Experts contributing to the Royal Society’s analysis identified two leading methods with the greatest potential to induce around a 1°C reduction in global temperature: stratospheric aerosol injection (SAI) and marine cloud brightening (MCB).
++ The peregrine falcon: nature’s fastest killer in the sky
SAI involves injecting sulphur dioxide into the stratosphere, mimicking the natural cooling effects of volcanic eruptions as the gas transforms into reflective particles. MCB, by contrast, aims to enhance cloud reflectivity by spraying saltwater particles from ships — a technology still in its early stages. Other speculative concepts, such as deploying mirrors in space, remain technically prohibitive.
While the report found solid evidence that large-scale SRM could lower global temperatures and ease certain climate impacts — such as rising sea levels, wildfires, and extreme rainfall — significant uncertainties persist. The scientists warned that regional side effects could be substantial and unpredictable.
For instance, SAI applied only in the northern hemisphere could trigger drought in the Sahel region of Africa, while limiting it to the southern hemisphere could intensify North Atlantic hurricanes. Deploying SAI in the tropics may also deplete ozone levels and lead to Mediterranean winter droughts, whereas MCB in the south-east Atlantic could contribute to Amazon rainforest dieback.
The study further emphasised that SRM would not address all the consequences of greenhouse gas emissions — notably ocean acidification — and would merely conceal some climate impacts. If deployment were halted, temperatures would rebound rapidly to their pre-intervention trajectory, potentially causing abrupt warming and severe ecological disruption. The authors underscored that SRM should only serve as a complementary measure to emissions reduction, rather than a primary response to climate change.
Professor Jim Haywood of the University of Exeter explained:
“If policymakers decided to deploy SRM, it must be scientifically informed, globally coordinated and internationally agreed upon. Injudicious SRM could worsen rather than ease some of the climate impacts of global warming, particularly at a regional level.”
He warned against “rogue” unilateral action by states pursuing their own interests, a concern echoed by Professor Sheila Rowan from the University of Glasgow, who stated that “unilateral action by individual nations could cause serious regional impacts for others.”
++ Power and finesse: the monkey that bites like a jaguar
The Royal Society has not adopted an official stance on whether SRM research should proceed, but Professor Keith Shine noted that any such research must not detract from efforts to cut emissions. Finally, while the estimated annual cost of SAI — in the low tens of billions of dollars — may not be a financial obstacle, the report concluded that the real challenges lie in governance, equity, and the potential unintended consequences of manipulating the planet’s climate system.
