Rajendra Pachauri endorses 350 ppm, not as IPCC chair but “as a human being”

I’m delighted to have the great environmental writer and founder of, Bill McKibben, as the guest blogger for this big story. Note that Pachauri was the guy handpicked by Bush to replace the “alarmist” Bob Watson. But it’s the facts that make people alarmists, not their politics or professional background (see “Desperate times, desperate scientists”).

This blog was the very first place to take note of an oped I wrote for the Washington Post in late December of 2007, which in turn was the first public notice of a talk Jim Hansen had given a few days earlier at the AGU conference in San Francisco. That was where Hansen announced his finding: 350 ppm CO2 represented the bottom line for the planet.

In the 18 months since, as we’ve built, we’ve found lots of support — from Al Gore, from 94 of the world’s smallest and poorest nations, and so on. But today may have been the biggest breakthrough of all: Rajendra Pachauri, head of the IPCC, said clearly and unequivocally that 350 is the number. Here’s a few lines from his interview with Agence France Presse:

“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.

It’s not going to be stated any more clearly than that, at least until 2014 when the next IPCC report is due. There’s now no convenient gray area for national governments (or environmental groups) to hide in. The Obama administration, among others, has made 450 ppm its target, but that target is now clearly exposed as too little too late.


We’re now working towards our October 24 day of action at with redoubled energy. We’ve already got 1300 actions scheduled around the globe — it’s going to be the most widespread day of environmental action ever. It’s a day for the world to say what its leading climate scientists have now unequivocally declared: 350 is the most important number in the world.

— Bill McKibben, Middlebury College

JR: For the science behind 350 ppm, see “Stabilize at 350 ppm or risk ice-free planet, warn NASA, Yale, Sheffield, Versailles, Boston et al.” Since the science is preliminary and it is not not yet politically possible to get to 450 ppm, let alone 350, my basic view, as expressed in that post, is Let’s start working now toward stabilizing below 450 ppm, while climate scientists figure out if in fact we need to ultimately get below 350. Either way, this is what needs to be done technology-wise: “How the world can (and will) stabilize at 350 to 450 ppm: The full global warming solution (updated).” The difference between the two targets is that for 450 ppm, you need to do the 12–14 wedges in four decades. For 350 ppm, you (roughly) need 8 wedges in about two decades plus another 10 wedges over the next three decades (and then have the world go carbon negative as soon as possible after that), which requires a global WWII-style and WWII-scale strategy (see “An open letter to James Hansen on the real truth about stabilizing at 350 ppm”).