If global warming is the biggest problem humans have ever caused and the sole civilization-a challenging trial the modern world has ever faced, what do most of us do- just watch the slow-motion horror unfold . So far, the planet’s temperature has gone up little more than 1 degree F. But Earth is more finely balanced than we’d realized and that 1 degree has been enough to knock it off-kilter. Hydrological cycles have been destabilized—we see massive increases in both droughts and flooding because warm air holds more water vapor than cold. We see increase in intense storms. And in the last 2 years we’ve seen a jaw-dropping sight: the runaway melt of Arctic sea ice. This is a sign that the global warming human beings kick-started has begun to take on a life of its own; the open Northwest Passage not only proves that the planet is heating up but, because blue water absorbs sunlight that the white ice once reflected, amps up the warming
1 degree so far, but the consensus suggests that, without truly dramatic action very soon, Earth’s temperature will rise by something on the order of an additional 5 degrees within this century. And if anything like that happens? Picture this: monsoons shifted off their historic paths. Sea levels will rise so high and so fast that you can pretty much forget the coastlines where civilization developed. In fact, we may well end up losing much of civilization. That strikes you as overblown, right? Yet the US National Aeronautics and Space Administration’s James Hansen, our foremost climatologist, wrote in 2008 that “if humanity wishes to preserve a planet similar to that on which civilization developed and to which life on Earth is adapted, paleoclimate evidence and ongoing climate change suggest that carbon dioxide will need to be reduced” 2 to no more than 350 parts per million.
The key word in that sentence is the last one: reduced. Almost all climate policy work has focused on the idea that we’ll eventually need to cap the amount of carbon in the atmosphere, at 550 parts per million, say, or 450 parts per million. But the melt of the Arctic should kill those cozy plans. We’re at 385 parts per million of carbon dioxide right now, up from 275 before the Industrial Revolution. Hansen says that any number above 350 parts per million will push us past all the tipping points
The world comes together in Copenhagen, in December 2009, to strike a new climate deal, a successor to the Kyoto treaty. We have just one last chance to get it right.