By Matt McGrath
Environment correspondent, BBC News
Attempts to reverse the impacts of global warming by injecting reflective particles into the stratosphere could make matters worse, say researchers.
A new study suggests the idea, seen as a last-ditch way to deal with runaway climate change, could cut rainfall in the tropics by 30%.
This would have devastating impacts on rainforests in South America and Asia
The research has been published in the journal Environmental Research Letters.
The concept of curbing rising temperatures by blocking sunlight has been discussed by scientists for many years now.
Some of the ideas have been dismissed as crazy notions, but others have been taken more seriously.
One of the most credible plans involves using reflective particles called aerosols to reflect solar radiation away from the Earth.
This happens naturally when volcanoes erupt, sending plumes of ash into the stratosphere, as with Mount Pinatubo in the Philippines in 1991.
Now a team at the University of Reading have modelled the impacts of a large-scale injection of sulphur dioxide particles at high altitudes around the equator.
Artist’s conception of space sunshield
Deployment of a giant sunshield in space to reflect solar energy is another geoengineering idea
“We have shown that one of the leading candidates for geoengineering could cause a new unintended side-effect over a large part of the planet,” said Dr Andrew Charlton-Perez, one of the co-authors of the paper.
The scientists found that as well as absorbing some of heat coming in from the Sun, the particles also absorb some of the heat energy that comes from the surface of the planet.
“The heating acts to stabilise the part of the atmosphere we live in, by making it more stable it reduces the upwelling of air,” said Dr Charlton-Perez.
“In the tropics much of the rainfall comes from air moving up rapidly, so this acts to reduce surface precipitation.”
Rainfall around the tropics could be cut by 30% with significant impacts on rainforests in South America and Asia and increasing drought in Africa.
The changes would happen so quickly there would be little time to adapt, say the researchers.
The scientists involved in the study believe that this is a new impact that others have missed until now.
“We modelled sulphate aerosols which is sort of an analogue for when you have a large volcanic eruption – but instead of putting aerosols into your model you can also just reduce the amount of solar radiation coming into your system,” said Dr Charlton-Perez.
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