Dear World—

This is an invitation to build a movement—to take one day and use it to stop the climate crisis.

We are a group of people from around the planet—young and old, scientists and writers and activists—who have one thing in common. We know the most important number on earth: 350. And we know how to use that number to finally get global action on the worst crisis humans have ever faced. But we can only do it if you help.

A year ago, our greatest climatologist—NASA’s James Hansen—and his team produced a landmark series of studies. They showed that if we let the amount of carbon in the atmosphere top 350 parts per million, we can’t have a planet “similar to the one on which civilization developed and to which life on earth is adapted.”

The bad news is we’re already past that number—we’re at 390 parts per million, which is why the Arctic is melting, why drought is spreading across the planet, why people are already dying from diseases like dengue fever and malaria occurring in places where they’ve never been seen before.

The good news: that number gives us a target to aim for. When the world’s leaders meet in Copenhagen in December to reach agreement on a new climate treaty, we need them to go farther than they’ve planned to go: we need to make sure they’ll pay attention to the latest science and put forward a plan that gets us back to safety.

So here’s the plan. On October 24, we need you to organize an action in the place where you live, something that will make that most important number visible to everyone. People in more than 1000 communities around the globe have already announced plans—they’ll be school children planting 350 trees in Bangledesh, scientists hanging banners saying 350 on the statues on Easter Island, 350 scuba divers diving underwater at the Great Barrier Reef, and a thousand more creative actions like these. At each event, people will gather for a big group photo that somehow depicts 350--and upload that photo to the web 350.org. As actions take place around the world, we'll link all the pictures together electronically via the web--by the end of the day, we'll have a powerful visual petition linking together the entire planet that we can deliver to the media and world leaders.

So far more than 100 nations are taking part—it's shaping up to be to be the biggest day of grassroots action on global warming ever. But we need it to be much larger—we need you, in your village or town or city, to take part. It’s not hard—we can help you with materials and ideas. But you need to take the first step, by registering an action and starting to let your friends and neighbors know about it.

Involve groups that you’re in—everything from your church, mosque or synagogue to your local bicycle group. People want to help, especially if they see the chance for something that might actually matter. This is even more important than changing your lightbulb—this is your chance to help change the way the whole world operates. October 24 comes six weeks before those crucial UN meetings in Copenhagen. It’s a great chance to take a stand—maybe the last great chance, given what the scientists tell us about the momentum of global warming.

But it can only happen with the help of a global movement—and it's starting to bubble up everywhere. Farmers in Cameroon, students in China, even World Cup skiers have already helped spread the word about 350. Churches have rung their bells 350 times; Buddhist monks have formed a huge 350 with their bodies against the backdrop of Himalayas. 350 translates across every boundary of language and culture. It's clear and direct, cutting through the static and laying down a firm scientific line.

This is like a final exam for human beings. Can we muster the courage, the commitment, and the creativity to set this earth on a steady course before it's too late? October 24 will be the joyful, powerful day when we prove it's possible.

Please join us and register your local action today.

Onwards,

Bill McKibben - Author and Activist- USA Vandana Shiva - Physicist, Activist, Author - India David Suzuki - Scientist, Author, Activist - Canada Bianca Jagger - Chair of the World Future Council - UK Tim Flannery - Scientist, Author, Explorer -Australia Bittu Sahgal - Editor of Sanctuary magazine - India Andrew Simmons - Environmental Advocate, St. Vincent & The Grenadines Christine Loh - Environmental Advocate and Legislator - Hong Kong

P.S.—We need you to do something else, right away, that's pretty easy. Please forward this message to anyone you know who is even remotely appropriate.

What does the number 350 mean?

350 is the most important number in the world--it's what scientists say is the safe upper limit for carbon dioxide in the atmosphere.

Two years ago, after leading climatologists observed rapid ice melt in the Arctic and other frightening signs of climate change, they issued a series of studies showing that the planet faced both human and natural disaster if atmospheric concentrations of CO2 remained above 350 parts per million.

Everyone from Al Gore to the U.N.’s top climate scientist has now embraced this goal as necessary for stabilizing the planet and preventing complete disaster. Now the trick is getting our leaders to pay attention and craft policies that will put the world on track to get to 350.

Is 350 scientifically possible?

Right now, mostly because we’ve burned so much fossil fuel, the atmospheric concentration of co2 is 390 ppm—that’s way too high, and it’s why ice is melting, drought is spreading, forests are dying. To bring that number down, the first task is to stop putting more carbon into the atmosphere. That means a very fast transition to sun and wind and other renewable forms of power. If we can stop pouring more carbon into the atmosphere, then forests and oceans will slowly suck some of it out of the air and return us to safe levels.

Is 350 politically possible?

It’s very hard. It means switching off fossil fuel much more quickly than governments and corporations have been planning. Our best chance to speed up that process will come in December in Copenhagen, when the world’s nations meet to agree on a new climate treaty. Right now, they’re not planning to do enough. But we can change that--if we mobilize the world to swift and bold climate action, which is what we're planning to do on October 24th

What is the day of action?

On October 24, the International Day of Climate Action will cover almost every country on earth, the most widespread day of environmental action in the planet’s history.

There will be big rallies in big cities, and incredible creative actions across the globe: mountain climbers on our highest peaks with banners, underwater demonstrations in island nations threatened by sea level rise, churches and mosques and synagogues and ashrams engaged in symbolic action, star athletes organizing mass bike rides--and hundreds upon hundreds of community events to raise awareness of the need for urgent action.

Every event will highlight the number 350--and people will gather at some point for a big group photo depicting that all important message. At 350.org, we'll assemble all the photos for a gigantic, global, visual petition.

The thousands of events on October 24 will drive 350 and all that it represents into the human imagination, and change the negotiating environment as we head towards the crucial UN Climate Negotiations in Copenhagen in December of 2009. Copenhagen may well be the pivotal moment that determines whether or not we get the planet out of the climate crisis, and your actions on October 24 will help our leaders realize we need a real solution that pays attention to the science