Here's a simple solution to global warming: vacuum carbon dioxide out of the air.
Klaus Lackner, a physicist at Columbia University, said placing enough carbon filters around the planet could reel the world's atmosphere back toward the 18th century, like a climatic time machine.
After a decade of work, his shower-sized prototype whirs away inside a Tucson warehouse, each day capturing about 10 pounds of the heat-trapping greenhouse gas as air wafts through it.
Only a few billion tons to go.
In the battle against global warming, technology has long been seen as the ultimate savior, but Lackner's machine is a clunky reminder of how distant that dream is.
He estimates that sucking up the current stream of emissions would require about 67 million boxcar-sized filters at a cost of trillions of dollars a year.
The orchards of filters would have to be powered by complexes of new nuclear plants, dams, solar farms or other clean-energy sources to avoid adding more pollution to the atmosphere.
Despite the scope of the proposal, the allure of high technology is irresistible for modern humans. Salvation has arrived again and again over the last century: the automobile, the jet, the Internet, the iPod.
That dream has pushed scattered groups of scientists to work on massive schemes to reengineer the planet.
One idea is to block sunlight, either by constructing artificial volcanoes to blast sulfur particles into the atmosphere or by launching millions of tiny satellites into space and arranging them into a giant mirror.
Another concept is sprinkling iron over the oceans to nurture plankton colonies that would absorb carbon dioxide from the air and transfer it to the depths.
But while the science of dialing back the planet's thermostat is straightforward, the execution is fabulously expensive, complex and grandiose on a scale that boggles the mind.
"Nobody doubts it is possible to take CO2 out of the air," said David Keith, a professor of engineering and economics at the University of Calgary in Canada and one of several scientists around the world working on the problem. "The issue is, 'What does it cost?' "
Some policy experts argue that blind faith in technology is a harmful distraction from the hard sacrifices needed to control global warming.
"The temptation is to say, 'Let's get John Wayne on horseback or Bill Gates . . . and solve this problem,' " said Dale Jamieson, director of environmental studies at New York University.
