The most important number on Earth

In the most recent issue of Mother Jones, author and environmentalist Bill McKinney draws a line in the sand for carbon concentration in our atmosphere:

For most of the period we call human civilization, the amount of carbon dioxide in the atmosphere hovered at about 275 parts per million. ... Then, in the late 18th century, we started burning fossil fuel in appreciable quantities, and that number started to rise. The first time we actually measured it, in the late 1950s, it was already about 315. Now it's at 385, and growing by more than 2 parts per million annually.

...

And so we're now in the land of tipping points. We know that we've passed some of them—Arctic sea ice is melting, and so is the permafrost that guards those carbon stores. But the logic of Hansen's paper was clear. Above 350, we are at constant risk of crossing other, even worse, thresholds, the ones that govern the reliability of monsoons, the availability of water from alpine glaciers, the acidification of the ocean, and, perhaps most spectacularly, the very level of the seas. It is at least conceivable that instead of a slow, steady rise in the height of the oceans, we could see rapid melt in Greenland and the West Antarctic, where much of the world's frozen water resides. We can't rule out, warns Hansen, a sea level rise of up to 20 feet this century.

After drawing the line at 350 ppm, he discusses ways to combat the problem--not just through personal conservation like switching to energy-efficient light bulbs and buying more fuel-efficient vehicles, but undertaking the kind of political action and investment that needs to happen; a kind of Marshall Plan for carbon.

Read the full article or find out more at 350.org.