Once dismissed as daft or dangerous, some of these “geo-engineering” projects can be of use in fending off the juggernaut of climate change, but only if they go hand-in-hand with cuts in carbon emissions, they warned.

“Geo-engineering” describes large-scale schemes such as erecting sunshades or mirrors in space, sowing the stratosphere with white particles or whitewashing building roofs to reflect sunlight, or scattering iron filings in the ocean to promote carbon-gobbling algae. None of these projects has been launched on any significant scale.

In a paper published on Wednesday in the journal Atmospheric Chemistry and Physics Discussions, researchers at Britain's University of East Anglia make the first attempt at calculating the effectiveness of these schemes. They do not analyse environmental impact, nor do they estimate the cost.

“We found that some geo-engineering options could usefully complement mitigation (of emissions), and together they could cool the climate,” said Tim Lenton, a professor of environmental sciences. “But geo-engineering alone cannot solve the problem.”