Do we really want to play dice with our planet?
A recent series in declared “it’s about geoengineering.” So let’s discuss it, beginning with some fundamental truths about this cluster of techno-optimistic “quick fixes” that claim to offset our slow progress toward eliminating planet-warming carbon emissions.
Solar geoengineering methods—primarily those aimed at reducing sunlight—have attracted the most attention, but many desperate schemes have been proposed to “fix” the climate disruption caused by the increasing burden of carbon dioxide from human activities.
Many of these proposals threaten the most sensitive aspects of the climate system, extending even to wildly expensive ideas such as constructing massive dams in the Bering Strait. If implemented, geoengineering schemes would place Earth’s physical climate in a dangerously precarious state and introduce a major new destabilizing technology into an already turbulent political environment.
The essential point to understand is that carbon dioxide, once emitted, is removed from the atmosphere only very slowly. A sizable portion will continue to keep Earth dangerously warm for centuries.
Solar geoengineering proposals involve injecting substances whose effects, by contrast, decay within a matter of years. Some might consider this an advantage, thinking we could quickly turn it on and off if the damage to our planet becomes apparent. This is incorrect.
Recent analyses demonstrate that it would take decades to create the required infrastructure. By then we would be completely reliant on maintaining it – a tall task in a dangerous world with global conflict.
Solar geoengineering would only temporarily mask the pent-up warming caused by the ongoing buildup of carbon dioxide. This accumulated warming would be released in a catastrophically rapid “termination shock” if circumstances force the cessation of solar geoengineering.
Therefore, solar geoengineering does not “buy time” for decarbonization. The same applies to other geoengineering schemes, which also require sustained maintenance over centuries to millennia. Five hundred years from now, the fabled Bering dam may crumble, but the carbon dioxide wreaking havoc on the climate system will still be present.
A lot of unforeseen events can occur in a few decades, let alone over centuries. Do we really want to commit today’s and future generations to maintaining these approaches without fail?
Scientific expertise and the complexity of climate change
Collectively, the four of us have studied the physics of climate for well over 100 years; we understand its complexity and the many surprises it holds. Since 1990, the Intergovernmental Panel on Climate Change (IPCC) has produced six assessment reports, working with tens of thousands of scientists—from physicists to economists—to ensure thorough scientific evaluation of the impacts of increasing carbon dioxide concentrations.
It took more than a century of carbon emissions before we could detect climate change and even longer to unequivocally attribute those changes to anthropogenic carbon emissions. Only in 2015, at the Paris Agreement, did most countries accept that the world is warming and that fossil fuel emissions must be addressed (with the UNFCCC mentioning fossil fuels explicitly only in 2023).
Now, proponents of geoengineering propose to strike the climate with a new, poorly understood tool that engages some of the most uncertain aspects of the climate system, including aerosols, clouds, and regional rainfall patterns. This would trigger even greater uncertainty in outcomes, especially if injections of substances into the high atmosphere are poorly planned, unmanaged, and uncoordinated, all occurring without a governance framework.
Surely, we should demand the same level of scientific diligence devoted to understanding the regional consequences of greenhouse gas emissions.
Limitations of climate models and experiments
Climate model simulations can indicate potential risks but cannot guarantee positive outcomes. To date, no rigorous modeling assessment has explored different solar geoengineering scenarios or formally compared climate sensitivity to such interventions, including impacts on regional weather and climate variability.
What is known is that the few models used so far do not even agree on the level of intervention required. For example, after only 10 years of the same stratospheric aerosol injection, global cooling estimates range from less than 1°C to as much as 3°C—a rate of change more rapid than any observed from carbon dioxide emissions. We are essentially flying blind.
The notion that small-scale “safe” experiments can answer important questions about the magnitude and effects of deployment is misguided.
Any meteorologist or oceanographer knows that the massive forces involved in the global climate system—such as the great heat-redistributing currents of the ocean and atmosphere, or year-to-year fluctuations in cloud patterns—will swamp the effects of any experiment and provide no indication of the efficacy and the risks of deploying solar geoengineering.
Research priorities and funding concerns
If geoengineering is to be seriously considered, the scientific foundations must be firmly established. However, most current research funding is directed toward developing deployment technology, often without adequate consideration of potential consequences.
The solar geoengineering technological momentum continues with apparent disregard for potential planetary damage, despite several important assessments from leading scientific academies—including the UK Royal Society, US National Academy of Sciences, and French Academy of Sciences—to which we belong. Each has highlighted major uncertainties, ethical concerns, and governance issues, urging great caution.
This is especially true of the £60 million geoengineering program funded by the UK government’s ARIA agency. ARIA’s chief aim is technology development, and many projects it funds are conducted in collaboration with for-profit companies.
Even more concerning is the explicit involvement of venture-capital-funded startups seeking to profit from near-term solar geoengineering deployment. The Israeli-US startup Stardust has received over $60 million in venture capital, with their business plan assuming near-term deployment. Another company, Mirror, aims to place giant mirrors in low Earth orbit; while they market illumination sales rather than solar geoengineering, the underlying technology is identical, and it is likely they will soon seek to participate in “cooling credits” markets.
Governance and ethical challenges
All of this is occurring in the absence of governance. Some pro-geoengineering researchers call for governance, but the path to achieving it remains unclear. Is solar geoengineering governable at all?
It is reckless to invest in developing technology that, even if effective, could enable unrestricted, profit-driven deployment by companies such as Stardust.
As private companies with minimal regulation, these entities and their investors have no legal obligations to submit to public scrutiny or provide assurances regarding climate impacts. Will these technologies be deployed without serious scientific understanding of consequences or consideration of social, legal, and political concerns?
Conclusion: focus on reducing fossil fuel emissions
All of this represents a significant diversion of resources and deflection from the urgent task at hand. As one of us has said,
when you’re in a climate hole, stop digging … and burning fossil fuels.It really is that simple.
About the authors
Raymond Pierrehumbert is Professor of Planetary Science at the University of Oxford and was a lead author on the IPCC Third Assessment Report and the US National Academy’s first assessment report on solar geoengineering. He is a Fellow of the Royal Society.
Julia Slingo was formerly Chief Scientist of the UK Met Office and has received the Rossby Medal of the American Meteorological Society among other prestigious awards. She holds nine Honorary Doctorates including from Cambridge University, is a Fellow of the Royal Society, Dame Commander of the Order of the British Empire, and was a reviewer on the recent Royal Society report on solar geoengineering.
Michael E Mann is the Presidential Distinguished Professor in Earth and Environmental Science at the University of Pennsylvania and Director of the Center for Science, Sustainability and the Media. He is a Member of the US National Academy of Sciences and Foreign Member of the Royal Society.
Valerie Masson-Delmotte is Directeur de Recherche at the Climate and Environmental Sciences Laboratory. She co-chaired IPCC Working Group 1 during AR6, co-authored the French Académie des Sciences geoengineering report, and contributed to a peer-reviewed assessment of polar geoengineering options.
