6.3E Geoengineering (HL) Notes

1. Geoengineering is the deliberate, large-scale intervention in Earth’s climate system.
2. It aims to reduce the impacts of climate change, but treats the symptoms, not the root cause (GHG emissions)
3. Two major categories:
   1. Solar Radiation Management (SRM): reflects sunlight away from Earth
   2. Greenhouse Gas Removal (GGR): removes CO₂ from the atmosphere
4. Methods include space mirrors, stratospheric aerosols, cloud seeding, ocean fertilization, biochar, carbon capture and storage, and direct air capture.
5. All options involve high uncertainty, high cost, limited real-world trials, and strong geopolitical implications

Solar Radiation Management (SRM)

1. Stratospheric Aerosol Injection (SAI)

1. Releases reflective sulfate aerosols into the stratosphere, mimicking volcanic eruptions
2. Aerosols scatter sunlight back into space, lowering temperatures
3. Delivered via aircraft, balloons, or artillery
4. Cooling potential is high, but effects are temporary, lasting 1–3 years
5. Drawbacks include:
   1. Reduced rainfall, affecting agriculture
   2. Regional drought risks
   3. Uncertain effects on cloud formation, monsoons, and ozone chemistry

2. Space Mirrors / Solar Shields

1. Uses large mirrors in space to block or deflect sunlight
2. Could reduce solar input by a small percentage but create global cooling
3. Requires extreme precision, launch capacity, and energy
4. High costs, extremely difficult to maintain, and no real-world trials

3. Cloud Brightening (Marine Cloud Enhancement)

1. Sprays sea-salt particles into marine clouds to make them whiter and more reflective
2. Short-term, regional cooling effect, especially over oceans
3. Already used experimentally for drought and heat mitigation
4. Risks include unpredictable rain patterns, flooding, and regional atmospheric changes

Greenhouse Gas Removal (GGR)

1. Ocean Fertilization

1. Adding iron, nitrogen, or phosphorus to stimulate phytoplankton growth
2. Phytoplankton absorb CO₂ during photosynthesis; later sink to the ocean floor
3. Oceans store ~35,000 gigatonnes of carbon, making them a major long-term sink
4. Concerns:
   1. Algal blooms may disrupt ecosystems
   2. Possible dead zones, oxygen depletion
   3. Uncertain long-term stability of stored carbon

2. Direct Air Capture (DAC)

1. Machines capture CO₂ directly from ambient air
2. CO₂ is stored underground or used industrially
3. High energy demand and currently very expensive
4. Still promising because it can create negative emissions

3. Bioenergy with Carbon Capture and Storage (BECCS)

1. Biomass is grown, burned for energy, and the resulting CO₂ is captured and permanently stored
2. Produces energy while removing atmospheric CO₂
3. Requires large land areas, potentially competing with agriculture and biodiversity

4. Biochar

1. Biomass is partially burned (charred) and buried to lock carbon into soils
2. Soil fertility improves, but impact depends on scale and land availability

5. Enhancing Natural Carbon Sinks (Afforestation & Reforestation)

1. Involves planting or restoring forests and wetlands
2. Needs vast land areas to produce global-scale change
3. Risk of future re-emissions if forests burn or projects end

Advantages of Geoengineering

1. Some SRM methods offer rapid temperature reduction, useful in climate emergencies
2. Provides a backup plan if emissions reduction fails or is too slow
3. Could protect vulnerable ecosystems (e.g., slowing coral bleaching)
4. Stimulates technological innovation and new climate policies
5. GGR methods provide long-term CO₂ removal if deployed at global scale

Disadvantages & Risks

1. High scientific uncertainty about regional climate impacts
2. Potential for unintended consequences:
   1. disrupted monsoons
   2. agricultural failures
   3. drought/flood cycles
3. SRM does not reduce CO₂, so:
   1. ocean acidification continues
   2. warming rebounds rapidly if SRM stops
4. High economic cost for development, deployment, and maintenance
5. Political hesitancy, conflicting national interests
6. Potential for geopolitical conflict if one nation alters climate unilaterally
7. Risk that geoengineering reduces motivation to cut emissions (“moral hazard”)