In December 2024, the European Commission’s Scientific Advice Mechanism published an opinion recommending a ban on the deployment of Solar Radiation Modification (SRM) techniques in the Union, while at the same time supporting the expansion of the Carbon Removal Certification Framework for the removal of CO₂ from the atmosphere. Two conflicting recommendations, in the same document, for two technologies that are commonly grouped under the same term. In its Sixth Assessment Report, the IPCC has largely abandoned the term “geoengineering,” preferring instead to use two distinct subcategories. The public debate has not yet followed suit.
Solar Radiation Management encompasses techniques that reduce the amount of sunlight reaching the Earth’s surface. The most widely studied approach is stratospheric aerosol injection (SAI): injecting reflective particles into the upper atmosphere, as occurs naturally during major volcanic eruptions. The 1991 eruption of Mount Pinatubo lowered the global average temperature by about 0.5 °C for one year. Artificially replicating this effect reduces global warming but does not remove CO₂ from the atmosphere: concentrations remain unchanged, the ocean continues to acidify, and if the intervention is halted, the temperature quickly rises back toward the levels it would have reached anyway. This effect is known as termination shock.
Carbon Dioxide Removal involves techniques based on the opposite principle: removing CO₂ from the atmosphere and storing it permanently. The methods range from managing peatlands and forests (slow biological removal) to Direct Air Capture, which filters the air using chemical processes, to BECCS (Bioenergy with Carbon Capture and Storage). CDR reduces CO₂ concentrations and can slowly reverse the cause of global warming. It does not alter the amount of light reaching the Earth. The two approaches differ in every respect: physical mechanism, timescale, reversibility, side effects, and governance framework.
The analogy is with two cardiovascular medications: an anticoagulant that prevents blood clots from forming and a defibrillator that restarts a heart that has stopped. Both are “cardiovascular.” The clinical protocol for one does not apply to the other, and a patient who must choose between the two cannot use the same criteria for both.
The European regulatory framework has already incorporated this distinction. The Carbon Removal Certification Framework Regulation (2024/3012), which entered into force in 2024, standardizes the measurement, verification, and reporting of carbon removals, including agricultural, forestry, and technological methods. Regarding SRM, the approach is one of precaution: the ban on deployment recommended in December 2024 reflects the “significant uncertainties and knowledge gaps” that the IPCC itself attributes to this category. The European Parliament had already adopted a resolution in 2023 calling for an international “do-not-use” mechanism for SRM techniques. In May 2026, a group of countries—including several EU member states—issued a joint statement on the governance of solar radiation management, committing to develop an international framework and apply the precautionary principle. The African group of countries has called for a non-use agreement three times since 2023, citing the risks of altered regional precipitation for populations already vulnerable to climate change.
There is a legitimate position in the field of research that argues for the value of keeping the two categories under the same umbrella: to compare risk profiles, allocate governance resources, and prevent one category from being developed without considering the alternatives. The Center for Future Generations and other research institutions focused on climate governance argue that the debate on SRM and CDR should proceed in parallel, not separately, to prevent one from diverting resources away from the other. The terminological distinction is important not because comparison is forbidden, but because conflating them under a single term makes it difficult to form a position on each.
This column explores climate-related terms whose technical meanings differ from common perceptions. “Geoengineering” introduces a new mechanism: an umbrella term that groups together two interventions with opposing physics, risks, and logic, creating the impression that those who are for or against it are evaluating a single issue. The Commission’s scientific opinion from December 2024 took different positions on the two subsets within the same document. The public debate often treats the two as one and the same.
The next time you see the term “geoengineering” in a policy document or press release, there’s one question to ask: SRM or CDR? The two are not evaluated by the same standard.
