The Do the Math campaign spurred a resurgence of climate advocacy in America that includes a divestment movement, sponsored by 350.org. Students at 252 universities in North America have asked their schools to divest their endowments of fossil fuel companies, and a few have agreed. Several faith-based organizations are also considering divestment, as are some municipal governments, including the City of Seattle.
The group says its #ForwardOnClimate rally on February 17 at the White House against the Keystone XL oil pipeline could be the biggest climate change rally ever in the United States.
President Obama vowed in his State of the Union speech Tuesday night "to reduce pollution" and "prepare our communities for the consequences of climate change." But it's unclear what action he might take.
He faces difficult decisions in his second term that could change the national energy landscape for decades and increase global temperatures, including on Keystone XL, Arctic oil drilling and natural gas fracking. McKibben said he is using the science and the math to urge supporters to force Obama to draw a line in the sand on those mega-projects and plans.
What's been surprising, McKibben said, is "the fossil fuel industry and skeptics haven't done the slightest thing to say the math isn't true."
Roger Pielke Jr., an environmental studies professor at the Center for Science and Technology Policy Research at the University of Colorado Boulder, said any criticism about the campaign "has nothing really to do with the science," but more "about the campaign as an incomplete set of policy arguments."
John Felmy, the chief economist for the American Petroleum Institute, the oil industry's main trade group, agreed.
"Oil, gas and coal are going to be used for the foreseeable future. It's inevitable. Instead of talking about an improbable fossil fuel scenario, we need to have a rational discussion about energy policy ... focusing on things like improving efficiency."
Meinshausen said it's common for non-scientists to misuse or exaggerate scientific results, so there's always concern among researchers when their findings are used for advocacy. But, he said, he and his colleagues have been pleased with how McKibben and 350.org have used the numbers to incite action.
"I wouldn't agree necessarily with every wording [the campaign uses]," Meinshausen said. "But the basic message—that we have a finite carbon budget, that we have much more in the ground than we can afford to burn if we want to avoid dangerous climate change—I think all this is uncontroversial."
Leaton of the Carbon Tracker Initiative said he isn't surprised by the popularity of McKibben's efforts.
"The way the campaign has framed these issues makes it easy for anyone who has ever balanced a budget to understand the problem ... When you run out of money, that's it, you’re out. When we've burned through the carbon budget, that's it, we can't afford for the sake of our planet to use more."
Correction: An earlier version of this article said that Meinshausen's paper didn't account for short-lived gases like methane, and that the omission had raised discussion among scientists. The model does account for short-lived gases, and the discussion has been about whether the emission levels of such gases and their impact on the climate system will change over time.