What’s the big idea?
Aerosols reduce the amount of sunlight reaching the earth’s surface by reflecting some of the sun’s rays back into space. Injecting sulphur into the stratosphere could create artificial aerosols, which would cool the earth quickly and cheaply, say proponents of the scheme.
How would it work?
Shooting so-called “precursor gases” into the stratosphere with balloons, aircraft or even artillery would create sulphur dioxide, which would in turn combine with water and attach to particles of solid matter, forming an aerosol.
This is supposed to replicate a process that occurs naturally when a volcano erupts. In 1991, the eruption of Mount Pinatubo, in the Philippines, pumped 10 million tonnes of sulphur into the atmosphere. Over the following two years, say scientists, global temperatures dropped 0.6° Celsius. The Nobel Prize winning ozone scientist Paul Crutzen is a major proponent of this idea, and suggests using rockets to inject sulphur into the atmosphere.
What are the risks?
As with most geoengineering proposals, there are a lot of unanswered questions. “Uncertainties relating to aerosol radiative forcings remain large” said the Intergovernmental Panel on Climate Change in its last report. In the past, an increase of sulphur in the lower atmosphere has caused an increase in acid rain and respiratory diseases, while the side-effects of injecting sulphur higher into the upper atmosphere may include ozone depletion.
There is also the possibility that such a scheme would increase unpredictable weather: some scientists have speculated that large-scale aerosol formation in the upper atmosphere could cause the failure of seasonal monsoons in Asia and Africa, which would have devastating consequences for people’s livelihoods on the two continents.
Our verdict
Saving the earth with giant guns may sound implausible, but aerosol formation is actually one of the more credible and less costly geoengineering schemes. However, the risks involved are still huge. Clearly, the climate situation would need to be very urgent if we were to seriously contemplate reducing the amount of sunlight that reaches the earth.
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