Five geoengineering proposals for reversing global warming, presented through the scientists and engineers who designed them. Arizona professor Roger Angel, who built the world's largest telescope, wants to launch a glass sunshade into space to deflect a fraction of the sun's rays. Nobel laureate Paul Crutzen proposes firing sulphur-loaded rockets into the stratosphere to build a thin reflective haze. British physicist John Latham and engineer Stephen Salter have designed remote-controlled yachts that spray seawater into clouds to thicken them and bounce back more sunlight. The other two proposals target carbon dioxide directly: Sydney engineer Ian Jones wants to fertilize plankton blooms so they absorb more CO2, while New York's Klaus Lackner has built machines that pull carbon dioxide from the air, convert it to powder, and bury it in spent oil and gas fields. Most of the scientists interviewed are reluctant about their own ideas, insisting that cutting fossil fuel use should come first, but each argues time may run out before conventional solutions work.