The overwhelming scientific consensus predicts that human emissions of carbon dioxide will warm the planet over the coming decades and centuries. By how much and how quickly is still up for dispute, but most agree it’s time to take action. Reducing carbon dioxide emissions is the key, but what if it’s already too late, and the temperature tipping point has already been reached? Dr. Roger Angel from the University of Arizona takes a page from the book of C. Mongomery Burns and suggests a gigantic sunshade placed in space above the Earth might help keep us cool.
Humans are pumping mountains of carbon dioxide into the atmosphere, from our cars, powerplants, and manufacturing. The carbon dioxide acts as a greenhouse gas, trapping heat inside the atmosphere, and warming the planet globally. The economic consequences of rising sea levels, expanding deserts, and failing crops could be measured in the trillions of dollars.
With large potential losses, there are incentives to find big solutions.
Instead of trying to reduce the greenhouse gasses, what if you could block out the light from the Sun? Dr. Roger Angel from the University of Arizona has calculated that a solar shade 2000 km (1,250 miles) across would block enough radiation from reaching the Earth to reduce the warming effects of carbon dioxide emissions back to industrial levels.
The best place to build this structure would be at the Earth-Sun L1 Lagrange point – a stable spot in space where the gravity from the Earth and the Sun cancel each other out. Spacecraft located at this point require very little fuel to maintain their position.
Instead of a single large shade, Dr. Angel is proposing to build a fleet of free flying spacecraft that look something like spiderwebs. Each mini-shade would be approximately 200 metres (650 feet) across, and be covered with a gossamer thin layer of solar radiation absorbing glass. To stop them from drifting away from the L1 point, each shade would be equipped with 6 steerable solar sails that would use the light from the Sun to maintain position.
As amazingly enormous an undertaking this might be, Dr. Angel thinks there could be two ways to construct the fleet of shades. They could be manufactured here on Earth, and then launched en masse into orbit by rockets. Manufacturing facilities could also be set up on the Moon, where there are ample supplies of all the raw materials required, and plenty of free energy from the Sun. With less gravity, it would require less energy to get the shades into position if they were launched from the Moon.
All in all, it would be a mind-bogglingly large undertaking, requiring launch technology and space-based manufacturing light-years beyond anything we’ve done to date. It would cost trillions of dollars to implement, and the dangers of interfering with the global climate could be catastrophic. But then, it seems we’re already interfering with the global climate.
Dr. Angel’s proposal was one of 11 proposals that received Phase 1 awards from the NASA Institute for Advanced Concepts (NIAC). The agency today announced its awards for the six months beginning September 2006. NIAC was created in 1998 to solicit ideas that push the limits of science and space exploration.