The whole world, in other words, must act.
"These numbers strengthen our conviction that industrialized countries will have to take the lead in reducing their emissions, but that the fight to prevent dangerous climate change can only be won if all countries act together," said Ottmar Edenhofer, a professor at the Technical University Berlin and co-chair of the Intergovernmental Panel on Climate Change Working Group III. He was not affiliated with the research.
Other experts praise the framework's potential to cut through 17 years of climate stalemate. One particular strength, several said, is its embrace of the entire spectrum of emitters - the abject poor, the broad middle, the high emitters.
"It's ingenious," said Larry Susskind, a professor of environmental planning at Massachusetts Institute of Technology who was not involved in the study. "It's a great way to shift the conversation."
The study assumes world leaders can agree to a global carbon emission reduction target. Once that's set, the big question is how to divide responsibility for meeting that target among different countries.
The new framework assigns that responsibility to individuals, not nations. The authors looked first at national income distributions based on World Bank data, then converted those distributions to carbon footprints based on emissions data from the Energy Information Agency.
The result is a series of projections showing the distribution of individual emissions for different regions. Each country worldwide would be assigned an emissions target based on the number of "high-emitter" individuals within their borders and their aggregate emissions. While all emissions contribute to global warming, the authors found that targeting the highest billion or so emitters gives the rest of the world room to continue to grow and develop.
"In principle," the authors wrote, "no country gets a pass, because even in the poorest countries some individuals have CO2 emissions above the universal emissions cap."
The idea was born, in part, from travels to India and other developing countries, Socolow said, where thriving cities support a middle and upper class enjoying a decidedly high-carbon lifestyle.
"Lack of attention to sustainable objectives in the developing world among people who live like us means they're going to replicate the same wastefulness," he said. "If those countries are given a free pass for the next decade or two, they're going to use that time to do the same foolish things we did."
Scientists have long held that to prevent the most dire effects predicted under a disrupted climate, society must slash emissions from today's levels and drastically alter growth projections.
At a minimum, scientists agree, the world needs a 30 percent cut by 2030 with respect to business-as-usual projections - a daunting challenge. But this is not the biggest problem confronting the world's governments on the climate change front.
That problem would be the vast disparity—generally linked to wealth—in per-capita emissions across the globe.
Americans, on average, pump 20 tons of climate-warming carbon dioxide into the atmosphere a year. Europeans average between 10 and 12 tons. Chinese are closer to four tons. And some three billion people worldwide emit less than one ton per year.
How to close that gap has been a major stumbling block in climate negotiations since 1992, when 172 countries—including the United States—agreed to divide responsibilities for emissions cuts based on economics.
The idea was simple: Rich nations would take the lead on cuts, with developing nations following at some unspecified later date.