What is geoengineering, and why is it so controversial?
Geoengineering refers to large-scale, deliberate interventions in the Earth's climate system to counteract global warming. The two main categories are solar radiation management (SRM), which reflects a small fraction of sunlight back into space, and carbon dioxide removal (CDR), which pulls CO2 out of the atmosphere. The controversy stems from the fact that these technologies are unproven at scale, carry unknown risks, and could create a 'moral hazard' by reducing the urgency to cut emissions [5][9]. One review of the literature found that the term 'moral hazard' is used in at least eight different ways in geoengineering debates, ranging from the fear that research itself will distract from mitigation to the worry that deployment will encourage continued fossil fuel use [9].
The precautionary principle, a key concept in EU law, actually cuts both ways: it can be used to argue against geoengineering research because of its unknown risks, but also to argue *for* geoengineering as a precaution against the worst impacts of climate change [1]. This creates a complex decision-making landscape where there is no simple 'safe' or 'unsafe' answer.
Geoengineering's effects are not uniform—they vary wildly by region and method
One of the most critical findings is that geoengineering does not simply reverse climate change. Instead, it creates a new, different climate with its own winners and losers. For example, a study on stratospheric aerosol injection (SAI) in South Asia found that while it would reduce malaria transmission across most of the region, it would *increase* malaria risk in specific areas like southeastern Pakistan and western Afghanistan due to changes in temperature and precipitation that favor mosquitoes [3]. This means that a global intervention could require highly localized public health responses.
Similarly, a 2023 review of the hydrological consequences of solar geoengineering concluded that while most approaches would weaken the global water cycle, regional effects would vary based on the specific method and strategy used [4]. The authors stress that whether these changes are 'harmful' or 'beneficial' depends entirely on the social and economic context of the affected region. Another study on extreme climate events in South Asia found that SAI would actually make some types of extremes *worse* than they would be without it, even as it mitigated others [8].
Even a seemingly targeted intervention like building underwater barriers to slow glacier melt in Greenland would have severe unintended consequences. Research shows that such barriers would likely reduce marine productivity and harm regional fisheries, which are socially and economically vital for Greenland [2]. This highlights that technical viability does not equal social or ecological safety.
Are there any clear benefits that make geoengineering worth considering?
Despite the risks, some studies do show potential benefits, particularly for food production and disaster risk reduction. A 2021 study using an advanced crop model found that three different solar geoengineering technologies could increase global yields of six major crops by about 10% by the late 21st century, compared to a business-as-usual scenario [7]. This was largely due to cooling that reduced heat stress on plants. However, the same study found that emissions reductions alone would decrease yields by about 5% over the same period, primarily because of reduced CO2 fertilization—a reminder that geoengineering's benefits are relative to a very damaging baseline.
Another study on dam safety in India found that both SAI and solar dimming could offset the increased flood risk (Probable Maximum Flood) expected under a high-emissions scenario [10]. The peak flood from a dam failure under the high-emissions scenario was significantly greater than the current design flood, but under the geoengineering scenarios, the increase was only marginal, suggesting these methods could reduce hydrological risk for critical infrastructure. However, the same study notes that this is only a partial solution and does not address the root cause of climate change.
Finally, a modeling study on marine cloud brightening (MCB) in the Pacific suggests it could be used to weaken El Niño events, potentially reducing economic losses and coral reef bleaching [6]. This is a very targeted application, but it also demonstrates that even regional geoengineering can have far-reaching climate 'teleconnections' that are difficult to predict.
Sources used in this answer
Geoengineering, the Precautionary Principle, and the Search For Climate Safety
The precautionary principle in EU law can be used both for and against geoengineering, creating a complex decision-making framework that requires comprehensive scientific review before action.
Glacier Geoengineering May Have Unintended Consequences for Marine Ecosystems and Fisheries
Installing underwater barriers to slow glacier melt in Greenland would likely reduce marine productivity and harm regional fisheries, making the intervention socially unacceptable.
Malaria transmission dynamics under climate change and solar geoengineering in South Asia: a GLENS-based assessment.
Stratospheric aerosol injection (SAI) would reduce malaria transmission across most of South Asia but increase it in specific areas like southeastern Pakistan and western Afghanistan.
Hydrological Consequences of Solar Geoengineering
Solar geoengineering would likely weaken the global hydrologic cycle, but regional effects are highly uncertain and depend on the specific method and social context.
Reckless or righteous? Reviewing the sociotechnical benefits and risks of climate change geoengineering
Geoengineering options like carbon removal and solar radiation management are controversial but increasingly discussed as complements to emissions reduction, though they carry moral hazard risks.
Modeling the far-reaching climate responses of regional geoengineering proposals
Targeted marine cloud brightening in the Pacific could weaken El Niño events, potentially reducing economic losses and coral reef bleaching, but with uncertain side effects.
Solar geoengineering can alleviate climate change pressures on crop yields
Solar geoengineering could increase global crop yields by about 10% by 2100 compared to business-as-usual, while emissions reductions alone would decrease yields by about 5%.
Responses of Extreme Climates in South Asia under a G6sulfur Scenario of Climate Engineering
Stratospheric aerosol injection would not effectively mitigate all climate extremes in South Asia; some extremes would become worse than without the intervention.
What do we mean when we talk about the moral hazard of geoengineering?
The term 'moral hazard' is used in at least eight different ways in geoengineering debates, creating ambiguity that could impede policy and public debate.
Impact of Geoengineering in Offsetting Climate Change-Induced Dam Break Risk
Geoengineering methods like stratospheric aerosol injection and solar dimming could offset the increased flood risk to dams under high-emissions climate scenarios.