Giant engineering schemes to reflect sunlight or suck carbon dioxide from the air could be the only way to save the Earth from runaway global warming, according to a group of leading scientists. But they say that these schemes could have their own catastrophic consequences, such as disrupting rainfall patterns, and should be deployed only as a last resort if attempts to reduce greenhouse gas emissions fail.

The Royal Society, a fellowship of 1,400 of the world’s most eminent scientists, published a report yesterday on the feasibility and possible dangers of technologies for cooling down the Earth, known as geoengineering. The ideas include artificial trees that draw CO2 from the air and mimicking volcanoes by spraying sulphate particles a few miles above the Earth to deflect the Sun’s rays. The most far-fetched would would be to launch trillions of small mirrors into space to act as a sunshield.

A far cheaper solution would be a fleet of 1,500 ships that would suck up seawater and spray it out of tall funnels to create sun-reflecting clouds. However, the report said that these clouds could disrupt rainfall patterns and result in mass starvation in countries dependent on the monsoon.

The panel of 12 scientists who produced the report concluded that all these approaches were theoretically possible and, despite the potential side-effects, should be explored with a view to holding trials.

They called for a £100 million annual global research fund to study geoengineering technologies and said that Britain should contribute £10 million a year, ten times the amount being spent now on such research.

Professor John Shepherd, who chaired the panel, said: “It is an unpalatable truth that unless we can succeed in greatly reducing carbon dioxide emissions we are heading for a very uncomfortable and challenging climate future, and geoengineering will be the only option left to limit further temperature increases.

“Our research found that some geoengineering techniques could have serious unintended and detrimental effects on many people and eco-systems — yet we are still failing to take the only action that will prevent us from having to rely on them. Geo- engineering and its consequences are the price we have to pay for failure to act on climate change.”

Professor Shepherd, Fellow in Earth System Science at the University of Southampton, admitted that there was a risk that the report would be exploited by fossil fuel companies, which might use it to argue that there was an alternative to cutting CO2 emissions.

But he said that it was better to start a thorough research programme now rather than wait until the start of rapid climate change, when the world would have no time to test solutions before deploying them.

Professor Shepherd added that he had no firm opinion on how likely it was that the world would need some form of geoengineering. “My opinion ranges from maybe to possibly to probably, depending on what I had for breakfast.”

Ken Caldeira, a climate scientist at the Carnegie Institution in the United States and a member of the panel, said: “We should spend 99 per cent of our effort on reducing greenhouse gas emissions and 1 per cent on this insurance policy \. We need to understand what our options are.”

The report said that an international body, possibly the United Nations, would need to oversee geoengineering projects because they would have impacts far beyond national boundaries. An international compensation scheme would also be needed to help those adversely affected by any project.

Professor John Beddington, the Government’s chief scientific adviser, endorsed the report’s call for more research into geoengineering. He said: “These are part of the armoury of dealing with what is an enormously difficult global problem.” But he added that it was “too early to say” whether trials should be approved.

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