World climate: 6 irreversible tipping points and other good news

The World at 350: A Last Chance for Civilization

By Bill McKibben
Sunday 11 May 2008

Even for Americans, constitutionally convinced that there will always be a second act, and a third, and a do-over after that, and, if necessary, a little public repentance and forgiveness and a Brand New Start — even for us, the world looks a little Terminal right now.

It's not just the economy. We've gone through swoons before. It's that gas at $4 a gallon means we're running out, at least of the cheap stuff that built our sprawling society. It's that when we try to turn corn into gas, it sends the price of a loaf of bread shooting upwards and starts food riots on three continents. It's that everything is so inextricably tied together. It's that, all of a sudden, those grim Club of Rome types who, way back in the 1970s, went on and on about the "limits to growth" suddenly seem... how best to put it, right.

All of a sudden it isn't morning in America, it's dusk on planet Earth.

There's a number — a new number — that makes this point most powerfully. It may now be the most important number on Earth: 350. As in parts per million (ppm) of carbon dioxide in the atmosphere.

A few weeks ago, our foremost climatologist, NASA's Jim Hansen, submitted a paper to Science magazine with several co-authors. The abstract attached to it argued — and I have never read stronger language in a scientific paper — "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 CO2 will need to be reduced from its current 385 ppm to at most 350 ppm." Hansen cites six irreversible tipping points — massive sea level rise and huge changes in rainfall patterns, among them — that we'll pass if we don't get back down to 350 soon; and the first of them, judging by last summer's insane melt of Arctic ice, may already be behind us.

(Scary? You bet. The rest is here.)