THIS INTERNET THING – what’s it for? I mean, why now at this particular moment in human history did there arise this strange connection machine? For playing poker in your underwear? If you ask me, the web came about (just in time) so that we can spread – by year’s end – the most important number on our beleaguered planet to every corner of that beleaguered planet. When I say we, I mean a growing number of – mostly but not entirely – young people on every continent, and when I say the most important number, I mean 350. As in parts per million, carbon dioxide.

In the wake of the alarming ice melt in the Arctic ocean, James Hansen and his team at NASA published a paper showing that “if humanity wishes to preserve a planet similar to that on which civilisation developed and to which life on Earth is adapted” we can’t have more than 350 parts per million CO2 in the atmosphere.

Which is a problem, since we’re already at 387, and rising. That’s why the Arctic is melting, why rainfall patterns are suddenly shifting, why drought is breeding mega-fires. The number puts a whole new spin on global warming: no longer a problem for the future, but an Emergency for the Present. It’s not our grandchildren who need to deal with it – it’s us, right now, because if we don’t shut down the fossil-fuel system very soon, we’ll quickly reach the point where there will be no way for the forests and the oceans to scrub enough carbon from the atmosphere to get us back to 350. In other words, the global negotiations set to conclude in December in Copenhagen have become the last bite at the apple for heading off utter disaster.

And so we’ve formed an outfit – – that is attempting to spread that realisation across the planet prior to Copenhagen and we need your help. First, we’re using the web to organise real-world actions all across the globe for 24th October 2009. There will be climbers high in the Himalayas with banners, and 350 scuba divers on the Great Barrier Reef, and a rally on Easter Island – and there needs to be one in your town square, or at your church, or on the nearest beach.

It needn’t be enormous, but it does need to be creative enough to draw the media: 350 bike riders? Ten bike riders going 35 kilometres apiece? The bell of your church or town hall ringing 350 times? Roz Savage, the English distance athlete, will set off from London to Copenhagen on 24th October, and people around the world are pledging to walk 350 million steps with her – on and on.

If all goes well, those images will make a dent. We’ll take them and by day’s end have them up on the web, and in newspapers and on TV broadcasts, all over the world. We’ll connect the good-hearted people of the planet in a way that makes them more than the sum of their individual parts – and in a way that will put real pressure on the negotiations in Copenhagen. We want those delegates knowing that the question they’ll be asked is not “Did you reach an agreement?” but “Will that agreement actually get us back where we need to go?”

And so we need your help in another way too – we need you to use the address book of your email to spread the word about now, all over the planet. We have an arcane number to communicate to the whole planet, which is no easy task – and we have no money! But we do have the possibility represented by this newly wired world. If you go to our website, minds younger than mine have figured out a way you can dump your addresses into the ether and automatically send out the word, in the hopes that the whole six degrees of separation business turns out to be true. In hopes that your friends on every continent will join the quite brave young people who are leading this fight.

I can’t promise you it will work. But I’m certain it’s worth a try.

Bill McKibben is the author of Wandering Home: A Long Walk Across America’s Most Hopeful Landscape.