Bill McKibben is on a crusade. He wants to pound the number 350 into the heads of everyone on the planet, including yours.

Three fifty is the amount of carbon in parts per million that the atmosphere can handle safely without warming up and melting glaciers, raising the sea level, bringing on killer storms, destroying wildlife habitat, and all the other horrors that pop like mushrooms from your morning paper nearly every day.

Three fifty. Remember it.

So what’s the current CO2 level? About 375 and rising quickly.

Dozens, scores, probably hundreds of organizations (including this one) are working hard to reverse the trend and bring us back under this safe upper limit. McKibben’s thought is to get everyone aware of the 350 limit to spur them to take action.

What sort of action? On a recent radio appearance a caller asked what she, as a citizen, can do about the problem. After you’ve changed your light bulbs and bought a hybrid car, Bill said, the three most important things you can do are organize politically, organize politically, and organize politically. The problem is too huge, and the economic power and inertia of the present system are too great, to be challenged by scattered consumers. Collective action is needed to force government to act quickly and decisively.

(As a footnote, Greenwire carries a sobering story about how Big Energy is pouring loads of cash into the campaign coffers of conservative Democrats to ensure that they don’t do anything too radical.)

Anyhow, Bill has got a new campaign just starting. Visit www.350.org and be one of the first to sign up.