Great news via Grist. Rajendra Pachauri, the chairman of the Intergovernmental Panel on Climate Change has just endorsed what many scientists have been saying for a long time – to avoid a climate catastrophe we need to aim for 350 parts per million (ppm) of carbon dioxide in the atmosphere, not 450 as earlier determined in the IPCC report.

From AFP, “Top U.N. climate scientist backs big CO2 cuts, 350-ppm goal“:

“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 AFP in an interview.

The article goes on to note:

Even at current CO2 levels of 385-to-390 ppm, severe impacts from climate change—rising sea levels, drought, violent storms—have started and are likely to get worse, experts say.

Many scientists also worry that carbon pollution has damaged Earth’s capacity to absorb CO2 and triggered events—the shrinking Arctic ice cap, the decay of the Greenland ice sheet, methane release from permafrost—that will drive global warming on their own.

This is very important, and it further supports the goal of 350 ppm, and while challenging, it is still (hopefully) reachable, at least from a scientific / technical standpoint, if not necessarily from a political standpoint.

Bill McKibbon at Grist notes:

When Jim Hansen and other scientists looked at phenomena like the Arctic ice melt of the last two summers, they produced new data demonstrating that 350 ppm is the bottom line. But it’s been hard to get that news out to the powers that be. So today it comes as enormous and welcome news that Pachauri, from his New Delhi office, said that 350 was the number.

For more on this see 350.org.