Solar Radiation Management (SRM)
Solar radiation management is a form of climate engineering that aims to reduce global warming by reflecting some of the sun's energy back into space before it can heat up the Earth.
Methods used for SRM
Stratospheric Aerosol Injection (SAI):
This involves injecting reflective particles, such as sulfate aerosols, into the upper atmosphere (stratosphere), where they would scatter some of the incoming solar radiation back into space.
This would mimic the cooling effect of volcanic eruptions, which also release aerosols into the stratosphere.
Marine Cloud Brightening (MCB):
This involves spraying fine droplets of seawater or other substances into low-level clouds (marine stratocumulus) over the oceans, where they would act as cloud condensation nuclei and increase the reflectivity and persistence of the clouds.
This would enhance the cooling effect of clouds, which already reflect about 20% of the incoming solar radiation.
MCB is considered to be more localized and reversible than SAI, but also more technically challenging and dependent on weather conditions.
Space Sunshades:
This involves placing large mirrors or screens in orbit around the Earth or at a stable point between the Earth and the sun (Lagrange point 1), where they would block or deflect some of the incoming solar radiation.
This would reduce the amount of solar energy reaching the Earth’s surface.
Space sunshades are considered to be more controllable and adjustable than SAI or MCB, but also more expensive and complex to deploy and maintain.
Advantages of SRM
When implemented properly it will mitigate the effect of climate change very rapidly, within months of enactment
Some of the SR methods proposed are cost-effective when it comes to implementing them.
SRM has certain advantages relative to emissions cuts, carbon dioxide removal.
The provision of emissions reduction and carbon dioxide removal present collective action problems (because ensuring a lower atmospheric CO2 concentration is a public good).
A single country or a handful of countries could implement solar radiation management.
The direct climatic effects of solar radiation management are reversible on short timescales.
Challenges, Limitations and Risks associated with SRM
Actual results may differ from the predicted effect:
There are no real-world simulations done so far regarding the effects of SRM.
Most of the information available is from models and computer simulations.
The actual results may differ from the predicted effect.
It may be difficult to predict the ultimate effects of projects, with models presently giving varying results.
In the cases of systems which involve tipping points, effects may be irreversible.
Termination Shock:
If solar radiation management were masking a significant amount of warming and then were to abruptly stop, the climate would rapidly warm.
This would cause a sudden rise in global temperatures towards levels which would have existed without the use of the climate engineering technique.
Could not address all aspects of climate change:
SRM could not address all aspects of climate change, such as ocean acidification, biodiversity loss, or sea level rise due to thermal expansion.
Effect on sunlight, sky and clouds:
Managing solar radiation using aerosols or cloud cover would involve changing the ratio between direct and indirect solar radiation.
This would affect plant life and solar energy.
It is also believed that additional effects would include the difference in the appearance of the sky notably a hazing of blue skies.
Side effects:
It could have negative or unintended side effects on regional or global climate systems, such as altering precipitation patterns, affecting monsoons, droughts, storms, or crop yields.
Ozone depletion is a risk of techniques involving sulfur delivery into the stratosphere.
Not all side effects are negative, and an increase in agricultural productivity has been predicted by some studies due to the combination of more diffuse light and elevated carbon dioxide concentration.
Ethical or geopolitical challenges:
Climate engineering techniques could theoretically be used by militaries or militants to cause droughts or famines.
For example, if an SRM experiment by one country leads to more rain over the Horn of Africa than expected, it could trigger a locust swarm that eventually destroys crops in Pakistan and India.
There is currently no mechanism that holds a geoengineering government accountable to consequences beyond its borders nor through which affected countries can appeal for restitution.
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