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Stratospheric Aerosol

Promises

Solar radiation management methods (SRM) modify the rate at which the Earth absorbs solar radiation to lower global temperatures directly, but do not reduce the volume of CO2 in the Earth’s atmosphere. The modification of the biosphere interaction with solar radiation could potentially be achieved at a global scale (e.g., stratospheric aerosol scattering) or locally (e.g., heat reflection to protect and restore snow or glaciers).

  • Stratospheric Aerosol Injection (SAI) techniques involve the injection of gas in the stratosphere, which converts into aerosols that block some incoming solar radiation. SAI is a fast-acting method to immediately mask climate impacts during a period of emissions “overshoot”, which would increase the time available for mitigation to lower atmospheric CO2 concentrations.
  • SAI is considered to be very cost-effective, with estimates between $US 1-10 billion per year to mask the climate effects of approximately half a degree of temperature overshoot (i.e., rendering climate impacts of 2C into 1.5).
  • The masking of some climate impacts via SAI would decrease heat-related mortality.

Opportunities

  • Several molecules for SAI are being explored, the most common involving various sulphur compounds, but also titanium dioxide and diamond are under consideration.
  • CASE The SCoPEX (Stratospheric Controlled Perturbation Experiment) project is a scientific experiment looking to improve the fidelity of computer simulations and broaden the knowledge about aerosol and nanoparticle interaction with the background stratospheric air, and with solar and infrared radiation. The SCoPEX project aims to use aerosol suspended in the air to reflect incoming solar radiation back into space and thus contrast the global increase in temperature. In addition to computer simulations, the project plans to launch a high-altitude balloon to lift an instrument package approximately 20 km into the atmosphere. Once it is in place, a very small amount of material (100 g to 2 kg) will be released to create a perturbed air mass roughly one kilometre long and one hundred meters in diameter. The test is aimed to enrich data and confirm simulations about changes in the perturbed air mass, aerosol density, atmospheric chemistry, and light scattering.
  • The infrastructure for the delivery of the aerosols to the top layer of the stratosphere (tropopause) 11km from the Earth’s surface already exists: civilian or military aircraft, modified artillery or high altitude balloons.

Concerns

  • SAI technology allows a single actor to modify global weather patterns with long-lasting effects. The geopolitical consequences of one actor holding the “global thermostat” may lead to political and economic power imbalance and generate conflicts.
  • SAI allows humans to intentionally modify global temperature. This “playing God” attitude places them in a position of control and dominance over nature. This overconfidence is often not supported by sufficient knowledge and leads to the promotion of risky techniques that might not work.
  • Would the implementation of this measure that has an immediate effect dissuade people from making the harder, long-term changes that are necessary to slow climate change?
  • Who gets to decide where and when SAI is implemented? Given that investing in SAI research makes its implementation more likely, and given the very large set of potential stakeholders likely to be affected by any decision to implement it, the question of justice needs to be raised already at the research and development stage.

Boundaries

  • Risks include changing precipitation patterns and air circulation, with adverse impacts on monsoon areas in particular, harming agriculture and many ecosystem types.
  • For sulfate-based SAI, risks include disrupting the chemistry of the stratosphere, affecting the length of time of methane storage, the formation of ice, and the microphysics of clouds.
  • Sulfate-based SAI would also deplete stratospheric ozone, leading to adverse health impacts.
  • The effect of SAI as an intervention is temporary. As soon as it would be stopped, the global temperatures would rapidly rebound again, with impacts that would have developed over decades hitting all at once. This “termination shock” could have catastrophic side-effects.
SCoPEx

Individual technologies

Stratospheric aerosol
Ocean fertilization
Bio energy with carbon
Ground based Albedo
Afforestation & reforestation
Direct Air C02