We’ve had many breakthroughs in the 350 campaign in the last 18 months, but maybe none as important as today.

Rajendra Pachauri, the U.N’s top climate scientist, said in an interview today that 350 was the bottom line for the planet.

Here’s the background–the Intergovernmental Panel on Climate Change, which Pachauri heads, is responsible for advising the world’s governments on climate change. The IPCC’s last report, which came out in the winter of 2007, didn’t actually set a target for CO2, but it was widely interpreted as backing a goal of 450 ppm CO2.

It was a number that many environmental groups, and many governments including the Obama administration, seized on as the best science. But that finding came before the Arctic melted, and before the world’s leading climate scientists started producing reports showing that 350 ppm was in fact the planet’s real threshold. Now Pachauri has given his imprimatur to that message.

Here’s his remarks, from an interview with Agence France Presse reporter Marlowe Hood:

"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."

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