'Space umbrella' could stop global warming

It’s a radical idea, and it just might just work. Reducing the amount of light reaching our planet could cool the Earth quickly, even with rising carbon dioxide levels. While the asteroid which helped wipe out the dinosaurs blocked out 90% of the Sun’s rays, we would need to divert just 2-4%, it's believed, to take the Earth back to its pre-industrial climate.

Space sunshades have support in high places, from the Royal Society to Nasa, to the European Union. It’s even roused the interest of the most respected authority on global warming, the Intergovernmental Panel on Climate Change (IPCC).

By far the greatest challenge is getting the sunshade into outer space

The concept may be increasingly mainstream, but how we’d do it sounds more far-fetched. To uniformly cool the planet in a system that’s always on the move, the shade would be installed in an area of outer space that’s balanced between the gravity of the Earth and the Sun – the L1 point – about a million miles away.

First conceived by engineer James Early in 1989, the original design was a vast, 2,000 km-wide glass shield – a structure so heavy, it would need to be constructed on the Moon. More recent suggestions include clouds of Moon dust, 55,000 wire-mesh mirrors or a planet-girdling ring of tiny umbrellas. And just when you thought they couldn’t get more ambitious: how about moving the Earth further away from the sun, with an explosion equivalent to five thousand million million hydrogen bombs.