Climate intervention

Research and a few outdoor trials. Not deployed planetary engineering, and not a substitute for cutting emissions.

The 1991 Pinatubo eruption plume: the natural aerosol pulse SAI papers analogise, not an SAI deployment

Research community (no operational national deployment) Research

Stratospheric aerosol injection

Discussed since the 1990s (and earlier volcanic analogies). IPCC AR6 treats solar radiation modification as researched, not recommended as a substitute for cuts. Harvard SCoPEx cancelled March 2024. Status: research.

Mimic a volcano, cool the planet. It exists as models, reviews and one cancelled balloon. It is not a deployed thermostat.

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NASA satellite view of a Southern Ocean phytoplankton bloom: a natural iron-rich bloom, not a named fertilization experiment

High seas / London Convention and Protocol parties Research

Ocean iron fertilization

IronEx I 1993; later Southern Ocean trials including SOIREE and LOHAFEX (2009). Haida Salmon Restoration Corporation dump 2012. LC/LP assessment framework 2010; LP amendment 2013. Status: research (commercial use not allowed).

Add iron, grow plankton, sink carbon. Small experiments grew green water. They did not prove a carbon vault, and a 2012 dump became a dumping case.

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MODIS image of ship tracks in Pacific stratocumulus: pollution brightening clouds, the analogue MCB studies, not an MCB fleet

Research groups (Australia reef trials; U.S. university programme) Research

Marine cloud brightening

Proposed by Latham (1990) and later reviews. Great Barrier Reef RRAP spray campaigns from 2020. University of Washington MCB Program ongoing; Alameda outdoor spray halted by the city in 2024. Status: research.

Spray sea salt into low ocean clouds so they reflect more sun. Ship tracks prove clouds notice pollution. That is not a planetary dimmer switch.

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MODIS true-color image of high cirrus clouds over the Pacific and central Chile: natural ice clouds, not a cirrus-thinning experiment

Research community (models; no operational national deployment) Research

Cirrus cloud thinning

Cirrus cloud thinning (CCT); assessed in IPCC AR6 WG I alongside other radiation-budget proposals; NOAA SRM State of the Science (July 2024) lists CCT separately from SAI and MCB. Status: research.

Seed high ice clouds so they thin and leak more heat to space. Models disagree; IPCC has low confidence in the cooling. It is not SAI with a different name.

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Whitewashed roofs and terraces in Santorini, Greece: Mediterranean light-surface tradition, not a planetary albedo programme

Cities, buildings, and land-cover proposals (no planetary programme) Research

Surface albedo modification

Surface albedo enhancement (cool roofs, reflective pavements, land-cover brightening); listed in NOAA SRM SoS (July 2024); cool roofs documented by U.S. EPA for urban heat; buildings chapter of IPCC AR6 WG III. Status: research / local practice.

Paint roofs and roads lighter so cities bounce more sun. That can cool streets and cut AC. It is not a global dimmer: cities are about one percent of Earth’s surface.

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NOAA MAP-CO2 ocean acidification research buoy at Cayo Enrique Reef, Puerto Rico: carbonate-chemistry monitoring, not an alkalinity-enhancement deployment

Research groups / NOAA-supported mCDR trials (no commercial planetary licence) Research

Ocean alkalinity enhancement

Ocean alkalinity enhancement (OAE); National Academies ocean CDR research strategy; NOAA Ocean Acidification Program CDR overview; NOPP marine CDR awards. Status: research.

Add alkalinity so seawater can hold more CO₂ as bicarbonate. Chemistry, not iron-fed plankton blooms. Still research: measurement and ecology are the hard parts.

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Calving front of Thwaites Ice Shelf, Amundsen Sea, photographed on a NASA IceBridge flight: the class of ice the 2024 research vision discusses, not a built seabed curtain

Research vision (glaciology / polar engineering proposals; no deployed ice-sheet programme) Research

Glacial climate intervention

Glacial Climate Intervention research vision (MacAyeal, Moore, Mankoff, Wolovick, Minchew et al., 2024); surveyed among high-latitude interventions in Climatic Change (2024). Status: research / speculative.

Slow ice-sheet collapse with seabed curtains, basal-water tricks, or winter ice thickening: on paper. A 2024 research vision asks whether any of it can work. Nothing here is a built sea wall for Antarctica.

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