It would be 100 times cheaper to shield the Earth from sunlight with a man-made "sun block" than to cut emissions of greenhouse gases. This is one of the reasons why the world needs an international project to investigate ways of safely manipulating the global climate in addition to cutting greenhouse gases, scientists have said.
Simulating a volcanic eruption by putting man-made aerosol particles into the atmosphere to reflect the Sun's heat would rapidly lower global temperatures and could provide a vital respite from global warming until cuts in carbon dioxide emissions begin to have the desired effect, they added.
It is important to start tests in "geoengineering" now rather than leave it until a full-blown emergency, according to three environmental scientists who argue that governments should establish a multimillion-pound fund to pay for research into solar-radiation management – techniques for shielding the Earth against sunlight.
"The idea of deliberately manipulating Earth's energy balance to offset human-driven climate change strikes many as dangerous hubris," said David Keith of the University of Calgary in Canada, Edward Parson of the University of Michigan and Granger Morgan of Carnegie Mellon University, writing in the journal Nature.
"Many scientists have argued against research on solar radiation management, saying that developing the capability to perform such tasks will reduce the political will to lower greenhouse gas emissions. We think that the risks of not doing research outweigh the risks of doing it," they wrote.
Until recently, even discussing the idea of manipulating the global climate artificially to combat rising temperatures has been considered a taboo subject among scientists. However, last year a survey of 50 climate scientists by The Independent found there was a growing appetite to at least investigate the idea, an approach supported by a report into geoengineering last September by the Royal Society.
The latest call by David Keith and his colleagues emphasises that there are serious potential problems with building a solar shield, and that it should never be seen as an alternative to cuts in greenhouse gases. Nevertheless, they argue that it is better for an international research project to be established rather than leaving it until a "rogue state" decides to go it alone.
"It is plausible that, after exhausting other avenues to limit climate risks, such a nation might decide to begin a gradual, well-monitored programme of deployment, even without any international agreement on its regulation," the scientists said.
"In this case, one nation – which need not be a large and rich industrialised country – could seize the initiative on global climate, making it extremely difficult for other powers to restrain it."
An international research effort into such a project could begin with an annual budget of about $10m (£6.3m), rising to about $1bn by 2020. It could investigate the risks, such as altering weather patterns, as well as known drawbacks, such as it doing nothing to combat the increasing acidity of the oceans.
Scientists have suggested that generating sulphate aerosols in the upper atmosphere, which are naturally emitted during a volcanic eruption, could quickly lower global temperatures, which happened after the eruption of Mount Pinatubo in the Philippines in 1991. Another possibility is to spray fine droplets of seawater into the air to create low-level clouds that would lower daytime temperatures over the oceans.
"Opinions about solar radiation management are changing rapidly. Only a few years ago, many scientists opposed open discussion of the topic. Many now support model-based research, but field testing of the sort we advocate here is contentious and will probably grow more so," the three scientists wrote.
"The main argument against solar radiation management research is that it would undermine the already-inadequate resolve to cut emissions. We are keenly aware of this 'moral hazard'; but sceptical that suppressing research would in fact raise commitment to mitigation.
"Indeed, with the possibility of solar radiation management now widely recognised, failing to subject it to serious research and risk assessment may well pose the greater threat to mitigation efforts, by allowing implicit reliance on solar radiation management without scrutiny of its actual requirements, limitations and risks," they said.
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