As the world weighs how to deal with warming, the idea of human manipulation of climate systems is gaining attention.  Yet beyond the environmental and technical questions looms a more practical issue: How could governments really commit to supervising geoengineering schemes for centuries?

In the summer of 2006, geoengineering — the radical proposal to offset one human intervention into planetary systems with another — came roaring out of the scientific closet. Deliberate climate modification, as climate scientist Wally Broecker once noted, had long been “one of the few subjects considered taboo in the realm of scientific inquiry.”
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Amid a growing call for reducing atmospheric concentrations of CO2 to 350 parts per million, a group of economists maintains that striving to meet that target is a smart investment — and the best insurance policy humanity could buy.

The climate change news from Washington is cautiously encouraging. No one in power is listening to the climate skeptics any more; the economic stimulus package included real money for clean energy; a bill capping U.S. carbon emissions emerged, battered but still standing, from the House of Representatives, and might even survive the Senate. This, along with stricter emission standards in Europe and a big push for clean energy and efficiency standards in China, provides grounds for hope for genuine progress on emissions reduction.

But while climate policy is finally moving forward, climate science is moving faster. One discovery after another suggests the world is warming faster, and climate damages are appearing sooner, than anyone had expected. Much of the policy discussion so far has been aimed at keeping the atmospheric concentration of CO2 below 450 parts per million (ppm) — which was until recently thought to be low enough to prevent dangerous levels of warming. But last year, James Hansen, NASA’s top climate scientist, argued that paleoclimatic evidence shows 450 ppm is the threshold for transition to an ice-free earth. This would imply a catastrophic rise in sea levels, eventually flooding all coastal cities and regions.

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