Man-made volcanoes may cool Earth

Jonathan Leake, Environment Editor
THE Royal Society is backing research into simulated volcanic eruptions, spraying millions of tons of dust into the air, in an attempt to stave off climate change.
The society will this week call for a global programme of studies into geo-engineering — the manipulation of the Earth’s climate to counteract global warming — as the world struggles to cut greenhouse gas emissions.
It will suggest in a report that pouring sulphur-based particles into the upper atmosphere could be one of the few options available to humanity to keep the world cool.
The intervention by the Royal Society comes amid tension ahead of the United Nations-sponsored climate talks in Copenhagen in December to agree global cuts in carbon dioxide emissions. Preliminary discussions have gone so badly that many scientists believe geo-engineering will be needed as a “plan B”.
Ken Caldeira, an earth scientist at Stanford University, California, and a member of a Royal Society working group on geo-engineering, said dust sprayed into the stratosphere in volcanic eruptions was known to cool the Earth by reflecting light back into space.
“If I had a dollar for geo-engineering research I would put 90 cents of it into stratospheric aerosols and 10 cents into everything else,” said Caldeira.
The interest in so-called aerosols is linked to the eruption of Mount Pinatubo in the Philippines in 1991, the second largest volcanic eruption of the 20th century. The explosion blasted up to 20m tons of tiny sulphur particles into the air, cooling the planet by about 0.5C before they fell back to earth.
The Royal Society is Britain’s premier science institution and its decision to take geo-engineering seriously is a measure of the desperation felt by scientists about climate change.
Brian Launder, a professor at Manchester University, who is also on the working group, recently said that without CO2 reductions or geo-engineering “civilisation as we know it will end within our grandchildren’s lifetime”. “The only rational scheme is to reduce the sunlight reaching Earth and to reflect back more of it,” he said.
The world’s population generates the equivalent of 50 billion tons of CO2 a year, a figure which is projected to reach 60-70 billion tons by 2030 on current trends.
Scientists warn that the planet could warm by 5C by 2100 and say emissions must fall to 20 billion tons a year by 2050 if a disaster is to be averted.
However, many researchers and policymakers regard this target as impossible.
The Royal Society report is expected to draw partly on research by Tim Lenton, professor of earth sciences at the University of East Anglia, who has just completed the first big comparison of different forms of geo-engineering.
“We estimate that 1.5-5m tons of sulphate particles could be released [artificially] into the stratosphere each year on a recurring basis,” said Lenton.
“This is quite a small amount, which makes it potentially economically viable, but it could reduce global temperature rise by up to 2C.”
The study investigates several other proposals for geo-engineering, dividing them into two broad approaches. One approach involves reducing the sunlight reaching the Earth’s surface — a premise that lies behind both aerosol release and the construction of mirrors in space.
Lenton regards the latter idea as “science fiction”, pointing out that any space sunshade would need a surface area of 1.8m square miles to be effective.
Another suggestion for cutting the light reaching the Earth is cloud-whitening, where salt water is sprayed into the air from thousands of ships, producing brighter clouds.
However, the Met Office has attacked this idea in its submission to the Royal Society, warning that it could cut rainfall in areas such as the Amazon and Africa.
Vicky Pope, head of climate change advice at the Met Office, said: “If humanity starts messing with the world’s cloud systems it is bound to have major side effects, some of which will be dangerous.”
The other main approach to geo-engineering is to try to accelerate the rate at which CO2 is removed from the air by plants and ocean plankton, or through chemicals.
This is the basis of ideas such as ocean fertilisation, where nutrients such as iron are added to water to promote plankton growth. Plankton absorb CO2 as they grow and carry it down to the seabed when they die.
Such techniques would have relatively few adverse side effects but the disadvantage, the report will say, is that they would take far too long to make significant cuts in atmospheric CO2.
The same criticism applies to the idea of using giant artificial filters driven by nuclear power that chemically strip CO2 from the air.
John Shepherd, professor of earth system science at the National Oceanography Centre in Southampton, who chaired the Royal Society working party, is expected to warn of other problems. Any measures that are taken may have to be kept going for decades or even centuries.
Met Office research has suggested that if techniques such as sulphate aerosols were to be suddenly discontinued the Earth could experience a disastrous warming surge.