This is an important number.

Watch out for campaigning activity linked to this on October 24th. See www.350.org 

This article is based on a letter from Bill McKibben who's organising that campaign.

Rajendra Pachauri is the U.N.'s top climate scientist who leads the Intergovernmental Panel on Climate Change (IPCC), which every five years produces the authoritative assessment of climate science. Their last report, in 2007, helped set the target of 450 ppm (parts per million of CO2) that many environmental groups and national governments have adopted as their goal for Copenhagen.

We now know that number is out of date. James Hansen, climate scientist with the NASA/Goddard Institute for Space Studies, New York, has clearly stated the challenge and the threat of the "unknown natural forcing" mechanisms that include albedo change from polar ice melt and GHG release as polar oceans and tundra thaw:

He says: "If humanity wishes to preserve a planet similar to that on which civilization developed and to which life on Earth is adapted, paleoclimate evidence and ongoing climate change suggest that CO2 will need to be reduced from its current 385 ppm to at most 350 ppm, but likely less than that. The largest uncertainty in the target arises from possible changes of non-CO2 forcings."

But it's been hard to get that news out to the powers that be.
So it’s very welcome news that Dr. Pachauri, from his New Delhi office, has said that 350 is the number

"As chairman of the Intergovernmental Panel on Climate Change (IPCC) I cannot take a position because we do not make recommendations," said Rajendra Pachauri when asked if he supported calls to keep atmospheric carbon dioxide concentrations below 350 parts per million (ppm).

"But as a human being I am fully supportive of that goal. What is happening, and what is likely to happen, convinces me that the world must be really ambitious and very determined at moving toward a 350 target," he told Agence France Presse in an interview.

Pachauri specifically cited the last big piece of news for 350: the decision of 80+ small island nations and less developed countries to endorse the 350 target.

"I think this is a good development," said Pachauri. "Now people -- including some scientists -- see the seriousness of the impacts of climate change, and the fact that things are going to get substantially worse than what we had anticipated."

This news makes it much easier for all of us to push hard leading up to the International Day of Climate Action on the 24th of October (signup to start or attend an event at www.350.org) , and the UN Climate Conference in Copenhagen this December.

It's clear now that science is powerfully on the side of the 350 target. Now we need the political world to follow suit. You will make that happen in the next two months. Oct. 24 is officially 60 days away, and we're building just the momentum we need to make it count