Leading climate scientists have issued a stark warning against solar geoengineering, arguing that it does not 'buy time' for decarbonisation and could lead to catastrophic consequences. In a joint statement, Raymond Pierrehumbert, Julia Slingo, Michael Mann, and Valerie Masson-Delmotte—experts with over a century of combined climate research experience—urge caution against techno-optimistic quick fixes for the climate crisis.
The Illusion of a Quick Fix
Solar geoengineering proposals, which involve reducing sunlight to offset global warming, have gained attention as a potential solution. However, the scientists argue that these schemes are fraught with risks. Carbon dioxide, once emitted, remains in the atmosphere for millennia, while the effects of solar geoengineering decay within years. This mismatch means that any temporary cooling would be followed by a rapid 'termination shock' if the intervention were to stop.
Recent analyses show that building the necessary infrastructure for solar geoengineering could take up to two decades. By then, the world would be completely reliant on maintaining it—a daunting prospect in a world plagued by conflict. The pent-up warming from ongoing carbon emissions would be released catastrophically if the geoengineering were to cease.
Uncertainty and Risks
The scientists highlight the profound uncertainty surrounding geoengineering. Climate models disagree on the level of intervention needed and the response. After just ten years of stratospheric aerosol injection, global cooling could range from less than 1°C to as much as 30°C—a change more rapid than anything seen from carbon dioxide emissions. 'We are essentially flying blind,' they warn.
Small-scale experiments cannot answer critical questions about deployment risks. The massive forces of the global climate system, such as ocean currents and cloud patterns, would swamp any experimental effects, providing no reliable indication of efficacy or safety.
Governance and Profit Motives
The scientists express concern over the lack of governance and the growing involvement of for-profit companies. Startups like Stardust and Reflect Orbital are developing geoengineering technologies with venture capital funding, aiming for near-term deployment. 'All of this is happening in the total absence of governance,' they note, calling for rigorous scientific diligence and ethical considerations before any deployment.
A Call for Real Action
The experts conclude that geoengineering is a dangerous distraction from the real task: reducing fossil fuel emissions. 'When you're in a climate hole, stop digging... and burning fossil fuels,' they say. They urge policymakers to focus on proven solutions like renewable energy and energy efficiency, rather than risky technological gambles.
Raymond Pierrehumbert is Professor of Planetary Science at the University of Oxford and a former IPCC lead author. Julia Slingo is former Chief Scientist of the UK Met Office and a Fellow of the Royal Society. Michael E. Mann is Presidential Distinguished Professor at the University of Pennsylvania. Valerie Masson-Delmotte is a co-chair of IPCC Working Group 1 and a co-author of the French Académie des Sciences geoengineering report.
