Writer Bill McKibben has built an international climate activism movement around a concentration: 350 ppm. Two years ago he launched 350.org  after NASA climate scientist Jim Hansen told him that was the carbon dioxide concentration needed to prevent dangerous man-made warming (pdf ). But the atmosphere already is around 390 ppm—and scientists expect the concentration to rise beyond 550 ppm if drastic measures aren't taken soon to reduce humanity's carbon emissions. So it's an understatement to say that McKibben's goal is a tough one.
But McKibben is undeterred, and his movement has gone viral. This weekend will see more than 4000 rallies around the world, including hundreds in the developing world, to drum up for a climate treaty in Copenhagen. ScienceInsider spoke to McKibben on the eve of the event.
Q: 350 a really hard goal. Do you wonder sometimes if you've chosen a goal that you'll always be falling short of?
B.M.: I wonder all the time whether we're going to get there. It's definitely a tough number. But the point is aiming for another number isn't useful. There’s the Tripati  study out of UCLA [University of California, Los Angeles]: 390 parts per million, the last time we were there, 15 million years ago, we had 100 foot rise in sea level. If 390 melts the Arctic, there's no point in doing our best to get to 450. Yes, we're probably going to hit 450, but we need to bounce off it as fast as we possibly can and get back down. There are whole countries that are going to disappear this century unless we bring things under control. Island nations that are going to go beneath the waves, and African nations that are going to be so drought ridden no one's going to live there. So this is incredibly pragmatic. It may not be easy, and it may not be at the moment politically realistic—but the negotiation that's going on right now is between human beings on the one hand and physics and chemistry on the other. … Physics and chemistry have stated their bottom line: 350 parts per million if you want the world to work at all the way you're used to it working. That's a pretty hard number. I'm pretty confident it's going to be easier to change the political reality than it is to change the laws of nature. One of the reasons this seems so difficult to do is that we've never built a political movement to demand that change happen. That’s what we’re doing now. The scientists have done their job—they've given us a robust number to work with.
Q: What are we doing right to get to 350 right now?
McKibben: We’ve got a awful lot of the technology that we need. It's proved itself more capable than we would've thought 10 years ago. Wind power and solar power are coming fast, they're becoming more reliable than we thought. ... It's becoming more possible to see the [renewable] future than we would've thought. But we're not doing it anywhere near fast enough. We've got the engineering; it's the political will that’s lacking.
Q: 350, since it's below the concentration we are at now, means actually removing carbon from the atmosphere at some point. That might require new stuff that we don't have on the shelf right now.
B.M.: The best analyses that people have done so far point to the real ability of the natural systems, of changes in agricultural practices to remove a lot of carbon from the atmosphere if we stop pouring more in. It won't happen immediately. Young people will be elderly before we get back to 350. But we’ve got to start that path incredibly aggressively right now.