What is geoengineering and its main techniques?
Executive summary
Geoengineering is the deliberate, large-scale intervention in Earth’s climate system to counteract human-caused climate change, generally grouped into Carbon Dioxide Removal (CDR) and Solar Radiation Management (SRM) approaches [1] [2]. Proposals range from planting forests and sucking CO2 from the air to spraying reflective particles into the stratosphere, but all carry major scientific uncertainties, environmental risks and governance challenges [3] [4].
1. What geoengineering means in plain terms
Geoengineering — also called climate engineering or climate intervention — describes a set of human-planned measures to intervene in the oceans, soils and atmosphere at large scale with the explicit aim of reducing global warming or its impacts; the term has been in technical and policy discourse since mid-20th century and various definitions emphasize intentional alteration of climate-controlling processes such as albedo, clouds and greenhouse-gas concentrations [5] [1] [2].
2. The two big buckets: CDR and SRM
Practitioners and reviews divide proposals into two broad categories: Carbon Dioxide Removal (CDR), which seeks to remove CO2 from the air and address a root cause of warming, and Solar Radiation Management (SRM), which aims to cool the planet quickly by reflecting more sunlight back to space — a symptomatic approach that does not reduce atmospheric CO2 [2] [1] [6].
3. Carbon dioxide removal — methods and practical trade-offs
CDR techniques include biological approaches such as reforestation and enhanced soil sinks, engineered systems like direct air capture and storage, and ocean-based options including iron fertilization and alkalinity enhancement; CDR is slow and often costly but directly reduces CO2, and is therefore considered by many reviews to be preferable in principle to SRM [3] [7] [2] [6].
4. Solar radiation management — fast cooling, uncertain side‑effects
SRM schemes range from stratospheric aerosol injection — releasing reflective particles into the upper atmosphere to mimic volcanic cooling — to marine cloud brightening, cirrus cloud thinning, and more speculative space-based sunshades; SRM could lower temperatures relatively quickly but would not stop ocean acidification, carries risks of regional harms and “termination shock” if halted abruptly, and remains highly uncertain scientifically and politically [1] [8] [9] [10].
5. Marine and glacial proposals sit at the frontier
Ocean-focused CDR and SRM ideas — such as ocean iron fertilization to stimulate plankton carbon uptake, ocean alkalinity enhancement, and regional proposals to stabilize ice sheets or thin clouds above glaciers — have been singled out for priority assessment by treaty bodies because of potential marine impacts and limited evidence about effectiveness and side effects [3] [11] [1].
6. Uncertainties, governance and geopolitical risks
Major scientific uncertainties about climate responses and ecological side‑effects combine with unresolved governance: there is no comprehensive international agreement for solar geoengineering, and analysts warn of risks from unilateral state or nonstate deployment, unequal regional impacts, and political incentives to treat geoengineering as a “technofix” that could weaken emissions reductions [4] [8] [2].
7. Where the evidence and debate stand today
Scholarly and policy reviews conclude CDR and SRM are fundamentally different tools — CDR addresses the cause but is slow and costly, SRM is fast but risky and incomplete — and most experts urge more research, careful governance frameworks, and that geoengineering not substitute for deep emissions cuts; many techniques remain unproven at scale, and some activist sources argue claims of feasibility are speculative or risky [2] [6] [3].