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What are the main types of geoengineering techniques?
Executive summary
Geoengineering is commonly divided into two broad families: carbon dioxide removal (CDR) — techniques that extract CO2 from the atmosphere or ocean — and solar radiation management (SRM) — methods that aim to cool the planet by reflecting sunlight or altering heat distribution [1]. Examples cited in recent reporting include afforestation, direct air capture, ocean fertilization, stratospheric aerosol injection, marine cloud brightening, cirrus cloud thinning and space‑based reflectors; capacity and risks vary widely, and current CDR capacity is small at roughly 2.2 GtCO2/year according to one assessment [1].
1. Two big buckets: CDR and SRM — the organising frame
Most authoritative overviews split geoengineering into carbon dioxide removal (CDR) and solar radiation management (SRM). CDR seeks to reduce atmospheric CO2 by biological, chemical or technological means; SRM seeks to reduce incoming solar energy or change how the Earth redistributes heat [1]. This taxonomy is used by policy analysts and scientists because it separates approaches that address the root cause (greenhouse gases) from those that mask warming’s symptoms [1].
2. Carbon dioxide removal: pulling carbon out at many scales
CDR includes natural and engineered methods. Commonly mentioned techniques are afforestation and reforestation, regenerative agriculture, accelerated rock weathering, ocean‑based approaches such as enhanced plankton or seaweed growth, and engineered technologies like direct air capture (DAC) that literally suck CO2 from air or sea [1]. Policy analysis notes that current CDR capacity remains small relative to emissions — roughly 2.2 GtCO2/year in the cited assessment — and that CDR will likely have to play a role in mitigation even if it is not a silver bullet [1] [2].
3. Ocean options: fertilization, seaweed, and tricky trade‑offs
Ocean proposals are often grouped under CDR but have unique governance and ecological stakes. Proposals range from iron fertilization to promote algae blooms to large‑scale seaweed cultivation and sinking biomass into the deep ocean [1]. Some polar geoengineering assessments include ocean fertilization among proposed concepts but caution that such interventions carry serious environmental risks and governance gaps [3] [2].
4. Solar radiation management: ‘dimming the sun’ and rapid coolants
SRM techniques aim to cool the planet faster than CO2 reductions can. Leading proposals include stratospheric aerosol injection (SAI) — releasing reflective particles high in the atmosphere — marine cloud brightening (spraying sea salt to make low clouds more reflective), cirrus cloud thinning (changing high‑altitude clouds to let more heat escape), and even space‑based reflectors (mirrors or dust in orbit) [4] [5] [6]. Media and analysts characterise SRM as a “painkiller, not a cure,” because it can mask warming quickly but does not remove greenhouse gases [7].
5. Research, trials and governance: who’s experimenting and who’s watching
Small experimental trials and startup ventures have drawn scrutiny and regulatory attention. Examples in 2025 include field trials conceptually linked to marine cloud brightening and an instance of a startup reportedly releasing about 0.1 tons of SO2 into the stratosphere that the U.S. EPA flagged for review [8] [9]. Governments, research agencies and funders are actively debating how to regulate field experiments, with some national agencies investing in cautious research programs [10] [9].
6. Risks, feasibility and scientific debate
Peer assessments specifically warn that many proposed geoengineering ideas — especially for polar intervention or large‑scale manipulation — face prohibitive costs, decades of maintenance and significant environmental dangers, and some experts say further investment could distract from emission reductions [3] [2]. SRM carries concerns about regional weather disruption (for example impacts on monsoons), ozone alteration, and governance conflicts; even proponents stress it cannot replace cutting emissions [11] [4].
7. Misinformation and activist narratives: chemtrails vs. peer‑reviewed research
There are active public campaigns and websites asserting covert or ongoing global programs (“chemtrails”), which present a different narrative from mainstream science and policy sources [12] [13] [14]. Major research programmes and commentators instead frame geoengineering as a subject of cautious research, regulated experiments and heated ethical and governance debates [4] [10]. Available sources do not mention covert global programs being admitted by governments beyond reported startup activities and tracked trials [9] [8].
8. Bottom line for readers: options, limits and the political question
The principal techniques fall into CDR (pull CO2 out) and SRM (reflect or redistribute sunlight) with many variant methods under each heading — from tree planting and direct air capture to stratospheric aerosols and cloud brightening [1] [4]. Across the literature and reporting there is agreement that techniques differ dramatically in maturity, capacity and risk, and that SRM at scale is controversial because it masks rather than removes warming and could produce uneven regional effects [7] [3] [11]. Policymakers therefore face not only scientific and technical questions but also deep governance, ethical and geopolitical choices [10] [9].