What are the potential environmental risks of atmospheric geoengineering?

1. The two different risk profiles: cooling the sky versus removing CO2

Solar radiation modification (SRM or SAI) and CDR are distinct: SRM aims to reflect sunlight quickly and can cool temperatures fast but leaves CO2 and ocean acidification largely unaddressed; CDR targets the root cause by removing CO2 but typically requires massive land, ocean, or industrial interventions with slow timescales and different ecological pressures ^{[3] [6]}. Analysts stress both approaches have unique trade-offs that cannot be conflated ^{[3] [6]}.

2. Ozone depletion, air pollution and acid deposition from aerosols

Government summaries and technical accounts flag that injecting particles into the stratosphere could damage the stratospheric ozone layer and change ground-level ozone and air pollution patterns; adding sulfur also raises the risk of acid rain and surface deposition that can harm soils and crops ^[1]. University modeling and policy pieces note sulfate aerosols are specifically dangerous because sulfate air pollution already contributes substantially to mortality and ecosystem harm ^{[7] [1]}.

3. Biodiversity, nutrient cycles and land-use pressures from CDR

Large-scale CDR approaches such as bioenergy with carbon capture and storage (BECCS) or land conversion for biomass can transgress other environmental limits: they threaten biodiversity, strain nutrient and water cycles, and create major land-use competition with food production ^{[2] [8]}. Carbon Brief and related analyses warn that depending on the scale modelled, BECCS could produce “large risks for the natural world” and undermine planetary boundaries ^{[2] [8]}.

4. Ocean interventions carry special marine risks and legal scrutiny

Proposals like ocean fertilization or marine CDR raise concerns about phytoplankton community shifts, altered food webs, oxygen and nutrient dynamics, and unintended transboundary impacts; international bodies have urged careful assessment and cautious governance because marine techniques could “pose serious environmental risks” ^{[9] [10]}. The literature also notes that SRM would not resolve ocean acidification—CDR is required to address that problem—so SRM can leave marine ecosystems vulnerable despite cooler temperatures ^[6].

5. Unpredictability, scale-up limits and the impossibility of full testing

Several environmental advocates and legal scholars argue it is effectively impossible to test geoengineering at the scale needed to know its planetary effects without actually deploying at large scale; that creates a “slippery slope” where small experiments could normalize deployment and lock in long-term harms ^{[5] [4]}. The Carnegie analysis cautions that technical readiness does not equal advisability, because scaling up poses environmental, social, and institutional risks not captured in biophysical assessments ^[3].

6. Termination shock and intergenerational commitments

Policy and advocacy sources warn that some SRM scenarios create dependence: if a long-running aerosol program were abruptly stopped, the climate could rebound rapidly (“termination shock”), causing severe stress to ecosystems and human systems unprepared for sudden change ^{[4] [2]}. Legal commentators frame this as a rights issue for future generations and a governance challenge ^[4].

7. Distributional and geopolitical environmental harms

Analyses emphasize that environmental effects would be uneven: regional precipitation, monsoon patterns, and ecological responses could differ across hemispheres and nations, producing winners and losers. That unevenness can convert environmental risks into geopolitical and social conflict—an argument raised in both academic and journalistic accounts ^{[10] [11] [3]}.

8. Where sources agree, and where they diverge

Most scientific and policy sources agree geoengineering could change climate and environmental variables in significant, sometimes harmful ways and that governance and further study are needed ^{[1] [3] [6]}. They diverge on whether careful research and limited fieldwork should proceed: advocates of research stress reduced uncertainty and potential benefits ^{[6] [7]}, while environmental NGOs warn that research risks normalization and that deployment would likely cause large-scale harms ^{[5] [4]}.

9. What reporting leaves unaddressed

Available sources do not provide definitive, empirically observed global-scale outcomes from long-term deployment because such deployments have not occurred; therefore many hazard estimates rely on models and scenario analysis rather than real-world experiments ^{[1] [3]}. They also underscore that governance frameworks and robust environmental impact assessments are only now being developed ^{[3] [9]}.

Conclusion: The environmental risks of geoengineering are real, varied, and strongly dependent on method, scale, governance, and duration. Policy-makers and researchers face a choice between accelerated emissions cuts and exploring high-uncertainty planetary interventions that could trade one set of environmental harms for another—an exchange repeatedly flagged by scientists, governments, and advocacy groups in the current reporting ^{[3] [1] [4]}.