Remember This: 350 Parts Per Million

Bill McKibben can be counted on to explain critical truths in simple ways, and in this case he had some help from his editors at the Washington Post, and from James Hansen, who took advantage of last year’s meeting of the American Geophysical Union to argue that we’re already over a key Earth-system tipping point.

There’s a lot of analysis behind this (check our Hansen’s web page if you want to see how much) but McKibben, a seasoned journalist, get’s just the right quote: “The evidence indicates we’ve aimed too high — that the safe upper limit for atmospheric CO2 is no more than 350 ppm.” And, of course, the current level of 383 ppm is well past 350. Does this mean that we’re doomed McKibben’s answer is “not quite,” and it’s the right one. But there’s no more time to waste.

“Hansen called for an immediate ban on new coal-fired power plants that don’t capture carbon, the phaseout of old coal-fired generators, and a tax on carbon high enough to make sure that we leave tar sands and oil shale in the ground. To use the medical analogy, we’re not talking statins to drop your cholesterol; we’re talking huge changes in every aspect of your daily life. ”

Maybe too huge. The problems of global equity alone may be too much — the Chinese aren’t going to stop burning coal unless we give them some other way to pull people out of poverty. And we simply may have waited too long.

But at least we’re homing in on the right number. Three hundred and fifty is the number every person needs to know. “