Plan to avert global warming by cooling planet artificially 'could cause climate chaos'

Proposal to inject tiny reflective particles into the upper atmosphere to block out sunlight could lead to droughts, warn scientists

A giant cloud of volcanic debris rises some 20km above Mount Pinatubo in the Philippines in June 1991 (Getty Images)

A controversial proposal to cool the planet artificially by injecting tiny reflective particles into the upper atmosphere which block out sunlight would cause droughts and climate chaos in the poorest countries of the world, a study has found.

One of the more serious plans to “geoengineer” the global climate would in effect create another climate catastrophe that would result in misery for millions of people, according to a computer model of the plan.

Some climate researchers have suggested that mimicking the cooling effects of volcanic eruptions with massive injections of sulphate particles into the atmosphere may be necessary in an emergency if global temperatures and carbon dioxide levels continue to rise unabated.

It is known that the sulphate particles produced by volcanoes, which are relatively quickly washed out of the atmosphere, can reduce incoming solar radiation significantly, and so cause average global temperatures to dip.

However, a study by scientists at Reading University has found that the effect of a massive and continuous injection of sulphates into the air would be to alter the rainfall patterns over vast regions of the world, notably Africa, South America and Asia which could as a result be devastated by drought.

“We have shown that one of the leading candidates for geo-engineering could cause a new unintended side-effect over a large part of the planet,” said Andrew Charlton-Perez of the University of Reading, a co-author of the study published in the journal Environmental Research Letters.

“The risks from this kind of geo-engineering are huge. A reduction in tropical rainfall of 30 per cent would, for example, quickly dry out Indonesia so much that even the wettest years after a man-made intervention would be equal to drought conditions now,” Dr Charlton-Perez said.

“The ecosystems of the tropics are among the most fragile on Earth. We would see changes happening so quickly that there would be little time for people to adapt.

“Discussion of geo-engineering often prompts heated debate, but very often there is a lack of understanding of what putting large amounts of aerosol in the stratosphere will do to the complex climate system. Our findings should help to fill in some of the gaps about one of the leading candidates,” he said.

Volcanoes, such as the Mount Pinatubo eruption in 1991, can cool average global temperatures significantly for short periods, but to reverse the expected 4C rise in global temperatures as a result of global warming would need large quantities of sulphate aerosols to be injected into the upper atmosphere over the course of several years.

“To reduce global temperatures enough to counter effects of global warming would require a massive injection of aerosol – the small particles that reflect sunlight back into space. This would be equivalent to a volcanic eruption five times the size of that of Mount Pinatubo every year,” said Angus Ferraro of Exeter University.

“Previous predictions of how stratospheric aerosol injection would affect climate were based on a number of assumptions. By actually modelling what would happen if aerosol were to be pumped into the atmosphere around the equator, we have revealed a new impact of geo-engineering on tropical climate,” Dr Ferraro said.

“As well as reflecting some of the incoming energy from the sun and cooling surface temperature, the aerosol also absorbs some of the heat energy coming from the surface which warms the stratosphere. We have shown for the first time that warming the stratosphere makes the troposphere below more stable, weakening upward motion and reducing the amount of rainfall at the surface,” he said.

Professor Ellie Highwood of University of Reading, a co-author of the study said that there is an understandable desire to explore alternatives to deep-cuts in carbon dioxide emissions, which do not seem to be materialising as a result of the failure of countries to reach a binding international agreement.

“Climate scientists agree that cutting carbon emissions is still necessary to curb the damaging effects of future climate change. However, since such cuts are far from certain to materialise, proponents of geo-engineering research argue that whatever the world decides on its carbon emissions, it would be prudent to explore alternatives that might help us in the decades ahead,” Professor Highwood said.

“On the evidence of this research, stratospheric aerosol geo-engineering is not providing world leaders with any easy answers to the problem of climate change,” she said.