A growing number of experts say yes – and that radically altering our environment may be our last, best hope of avoiding disaster. From orbiting space mirrors to artificial trees to brighter clouds, here’s what’s under discussion.

 

 

Risks vs. rewards Like any untested technology, geoengineering harbours unknown risks. An artificial cooling of the earth could disrupt global weather patterns, bringing drought and famine to parts of North Africa, India, and China.

 

What it would cost Hoisting mirrors or sun shields into space could cost trillions of dollars, according to a September 2009 report by the United Kingdom’s Royal Society. Stratospheric aerosols, which could block solar radiation and cool the earth, could cost tens of billions of dollars a year; cloud brightening, which reflects sunlight away from the earth, $2 billion a year. Expensive, yes, but to some economists, geoengineering is worth pursuing. One well-regarded but controversial report projects that stratospheric aerosols could carry a benefit 27 times higher than their cost; it also suggests that marine cloud brightening could save $7.5 trillion by reducing the damage caused by global warming.

 

The “Greenfinger” scenario David Victor, a climate policy expert at the University of California, San Diego, worries about the prospect of a single nation taking matters into its own hands. “It could be a Hail Mary pass by a country getting hammered by global warming,” he says. A wealthy individual – Victor calls him a “lone Greenfinger” – could also choose to go it alone. To prevent unilateral action, experts need a framework for researching geoengineering and deciding, as Victor says, “who gets to put their hand on the thermostat.”

 

 

Contain the carbon Removing carbon from the air and storing it underground, or reusing it for fuel, would help slow and possibly reverse global warming. This solution, says David Keith, a physicist at the University of Calgary, would cost considerably less than what we might spend converting carbon-fed electrical to rooftop solar power. England’s Institution of Mechanical Engineers has even come up with a proposal to line highways with “artificial trees that would collect carbon dioxide at rates far exceeding those of lazy natural trees and convert it into a form that’s easily collected and stored.

 

Deflect, deflect, deflect National Center for Atmospheric Research climatologist John Latham, along with University of Edinburgh engineer Stephen Salter, has designed a novel way of “brightening” clouds: a fleet of remote-controlled, wind-powered ships that would spray a fine seawater mist into marine clouds. “It’s established that if you have a lot of little drops instead of a few big ones, then the clouds are more reflective,” says Latham. They hope to increase that reflectivity by ten percent, which, they say, would hold the earth’s temperature steady until at least 2050. Keith is devising a reflective metal particle that could levitate itself above the ozone layer to reflect heat from the sun back into space, although his main focus remains on reflective aerosols. Washington-based Intellectual Ventures Lab, owned by former Microsoft guru Nathan Myhrvold, has proposed a 30-km-long hose suspended from balloons that would pump liquefied sulphur dioxide (a gas emitted when volcanoes erupt) into the stratosphere.

 

Show them the money Last year, a US House of Representatives committee held its first hearing on climate engineering but shied away from funding any proposals. “We need a balanced, open, publicly funded research programme,” says Keith.