Geoengineering: a horrible idea we might have to do

01What Solar Geoengineering Actually Means

Solar geoengineering — also known as solar radiation modification — is the deliberate large-scale intervention in Earth's climate system to reduce surface temperatures by reflecting a small fraction of incoming sunlight back into space. It does not address the root cause of climate change, which is greenhouse gas accumulation, but it could temporarily lower temperatures while the world works to decarbonize.

The concept draws inspiration from nature: large volcanic eruptions, such as Mount Pinatubo in 1991, injected millions of tons of sulfur dioxide into the stratosphere and cooled the planet by roughly 0.5°C for over a year. The idea behind solar geoengineering is to replicate this effect deliberately, continuously, and at a controlled scale. The technology is controversial precisely because it works — which means someone might actually do it.

02Stratospheric Aerosol Injection Explained

Stratospheric aerosol injection (SAI) is the most studied and most feasible solar geoengineering approach. It involves dispersing reflective particles — typically sulfur dioxide, calcium carbonate, or diamond dust — into the stratosphere at altitudes of roughly 20 kilometers. Once there, these particles form a fine aerosol mist that scatters sunlight, reducing the amount of solar radiation that reaches Earth's surface.

Delivery mechanisms remain a major engineering challenge. Existing aircraft cannot fly high enough to reach the stratosphere efficiently, so purpose-built high-altitude planes would need to be developed. A 2020 Harvard-led study estimated that a sustained global SAI program could cost approximately $2.25 billion per year per degree of cooling — remarkably cheap compared to the economic damage of unmitigated warming. This low cost is what makes the technology both promising and dangerous: a single nation could deploy it unilaterally.

03The Potential Benefits and Risks

The benefits are straightforward: SAI could reduce global average temperatures within months, potentially averting catastrophic climate thresholds like the collapse of major ice sheets or the dieback of the Amazon rainforest. It could reduce the intensity of extreme heat events, protecting vulnerable populations. And it could buy time for the world to transition away from fossil fuels without breaching tipping points that would make warming self-reinforcing.

The risks, however, are profound and poorly understood. SAI could alter global precipitation patterns, potentially disrupting the Asian monsoon on which billions depend for agriculture. It could deplete the ozone layer, particularly if sulfur-based aerosols are used. It would do nothing to address ocean acidification, which is driven by CO2 absorption independent of temperature. And because aerosols fall out of the stratosphere within a few years, any deployment would require continuous, uninterrupted maintenance — potentially for centuries.

04The Termination Shock Problem

Of all the risks associated with solar geoengineering, termination shock may be the most alarming. If an SAI program is deployed and then abruptly stopped — whether due to war, political collapse, economic crisis, or sabotage — the masking effect disappears within a few years. The planet would warm at a rate potentially 10 times faster than it is warming today, an ecological shock that ecosystems and human societies would have little time to adapt to.

This creates a paradox: the longer SAI is deployed, the more dependent the planet becomes on its continuation. The world would be locked into maintaining the program indefinitely, creating a new form of infrastructure as critical as the electrical grid. Any disruption — a pandemic, a financial crisis, a change in political leadership — could trigger catastrophic warming. This irreversibility is what makes many climate scientists deeply uneasy about SAI as a serious policy option.

05Who Gets to Decide the Earth's Thermostat

Perhaps the most intractable problem is governance. There is currently no international framework for deciding whether, when, or how to deploy solar geoengineering. The United Nations has no dedicated body with authority over it. The Paris Agreement does not address it. The 2010 Convention on Biological Diversity imposed a moratorium on geoengineering, but it is non-binding and has no enforcement mechanism.

This governance vacuum is especially dangerous because SAI is cheap enough for a single nation — or even a wealthy individual — to deploy unilaterally. A country suffering disproportionately from climate change might conclude it has no choice but to cool the planet on its own, regardless of what other nations want. The results would be felt globally, potentially benefiting some regions while harming others. This raises profound questions of justice: who gets to set the global temperature, and who bears the consequences if the intervention goes wrong?

06The Moral Hazard Argument

Critics of geoengineering research raise a sharp moral hazard concern: even studying SAI might reduce the political pressure to cut emissions. If policymakers believe a technological escape hatch exists, the argument goes, they will be less willing to make the difficult economic and political choices needed to decarbonize. The very prospect of geoengineering could become an excuse for delay.

This concern is not hypothetical. Fossil fuel companies and allied political actors have occasionally promoted geoengineering as an alternative to emissions cuts, using it to frame the climate problem as solvable without restructuring the energy system. Climate scientists who support research into SAI, such as David Keith, have argued for a firewall: study the technology openly and rigorously, but never present it as a substitute for decarbonization. Whether that firewall can hold in the political arena remains an open question.

07Is Geoengineering Inevitable

The trajectory of global emissions does not inspire confidence. Despite decades of climate summits, atmospheric CO2 continues to rise, hitting record levels each year. The world is on track to exceed the 1.5°C Paris target within the decade, and current policies point toward 2.5°C to 3°C of warming — a level that scientists warn would trigger cascading climate impacts and potential tipping points.

In that context, geoengineering shifts from hypothetical to plausible. Not because it is a good idea, but because the alternative — allowing temperatures to rise unchecked past tipping points — may come to seem worse. The Kurzgesagt video frames the dilemma precisely: this is a horrible idea we might have to do. The choice is not between geoengineering and a stable climate. The choice may be between geoengineering and a world where large regions become uninhabitable. If emissions reductions continue to fall short, a future where the planet's thermostat is deliberately managed — imperfectly, riskily, under fraught governance — may become less a question of if than when.