Two days before the UN Climate Summit in New York, three new studies paint the clearest picture yet of rising greenhouse gas emissions and the dwindling opportunity for staving off the worst impacts—and also of at least one way that huge undertaking might be shared fairly among the nations of the world.

“The overall outlook is rather bleak,” says Steven J. Davis, a climate scientist at the University of California, Irvine, who co-authored a paper published Sunday in the journal Nature Climate Change on how nations might share in reducing their carbon emissions.

Davis points to the “Global Carbon Budget 2014,” which was published Sunday in the journal Earth System Science Data Discussions. Produced by dozens of scientists from around the world, it’s the latest in a series of annual reports showing that “we're moving in the wrong direction,” says Davis.

“We're talking a lot about putting the brakes on emissions, but we’re actually accelerating.”

According to the new carbon budget, global greenhouse gas emissions rose by 2.3 percent in 2013 over 2012. The authors estimate that emissions will riseanother 2.5 percent in 2014, to a level that is 65 percent above emissions in 1990—the benchmark year established in the Kyoto Protocol.

Meanwhile the concentration of carbon dioxide in the atmosphere exceeded 395 parts per million (ppm) in 2013. That’s an increase of more than 40 percent from the 277 ppm concentration in 1750, before the Industrial Revolution. (See “Greenhouse Gases Hit Record High Amid Fears of CO2 Saturation Point.”)

Country Breakdowns

According to a review paper published Sunday in Nature Geoscience by an international team led by Pierre Friedlingstein of the University of Exeter in the United Kingdom, three countries accounted for more than 90 percent of the growth in emissions from 2012 to 2013: China (57 percent), the United States (20 percent), and India (17 percent).

The fourth major emitter, the European Union, actually cut its emissions in 2013, such that the global rise was 11 percent less than it otherwise would have been.

What’s particularly striking, says University of Wisconsin climate scientist Galen A. McKinley, is that China is now emitting more on a per capita basis than the European Union, for the first time in history.

“In 2007 China overtook the U.S. in overall carbon emissions, but on a per capita basis we always thought of them as much smaller,” says McKinley, who was not involved in the research published Sunday. “But since then their emissions have been rising rapidly.”

According to the Nature Geoscience review, the world’s emissions in 2013 were 5 metric tons per person. China’s were 7.2 metric tons per person, the U.S. produced 16.4, the EU produced 6.8, and India produced 1.9. In 1990, China produced 2.2 metric tons per person, and the United States produced 19.1.

Cumulative emissions from 1870 to 2013 total 1,430 gigatons for the world, including 161 gigatons from China, 370 from the U.S., 328 from the European Union, and 44 from India.

Another important conclusion from the data is the role the state of the economy plays in emissions, notes Davis. “A lot of people thought the reason the U.S. emissions were down [in recent years] was because of the natural gas boom, in that we have substituted gas for coal,” he says. Natural gas emits about half as much CO2 as coal to produce the same amount of electricity.

Switching coal-fired power plants to gas has indeed helped slow emissions, Davis says, “but if you dig in deeper you see that a lot of the reason why our emissions were down was because of the recession, and with the economy improving they are on the rise again.” Relatively cold winters have also required the use of more fuel for heating.

Still, Davis says, the Environmental Protection Agency’s proposed rules curtailing emissions from power plants are likely to have a significant impact if they go into effect next year.

Filling the World’s Carbon Quota?

In Nature Geoscience, Friedlingstein and his colleagues write that the world has already used up two thirds of the CO2 emissions quota that scientists say will keep the planet from warming more than 2°C (3.6°F). Beyond that temperature threshold, serious consequences are expected from sea-level rise and widespread disruption of weather patterns.

The remaining emissions quota “will likely be exhausted in a further 30 years at the 2014 emissions rates,” the scientists write.

Although President Barack Obama is expected to speak at the UN Climate Summit on Tuesday, the leaders of China, India, Australia, and several other major countries have signaled they will not attend. Signatories of the United Nations Framework Convention on Climate Change are scheduled to meet in Paris in December 2015.

Davis says the current political climate suggests there’s a good chance the international community “won't ever reach a binding agreement” on climate. Perhaps the best that can be hoped for is individual goals set by national and even state and city governments, he says.

The reports out Sunday show that the world “has wasted a lot of time,” Davis adds. “We're well on our way to some pretty scary global warming, and we can't afford to waste any more time. It's going to be a political shift that's necessary.”

A New Way to Divide Responsibility?

Part of the barrier to reaching a global agreement on climate change has been the perception by developing countries that they would be forced to bear an unfair amount of the burden. Why should they limit development based on fossil fuels, they ask, when it was that very process that allowed developed nations to rise to affluence?

The paper written by Davis and his colleagues attempts to outline one way the burden could be shared.

The researchers consider two basic principles for distributing the global emissions quota: “inertia,” under which countries would continue to emit the same share of global emissions as they do now, and “equity,” under which countries would be allowed to emit according to their population, with per capita emissions being the same everywhere.

The first principle would hamstring developing countries, while the second one would force developed countries to immediately scrap existing infrastructure, such as fossil fuel plants that were just built, says Davis. A practical approach to dividing up the emissions quota, his team suggests, will have to be a blend of the two principles.

Countries that have had high emissions in the past, such as the United States and Europe, would be able to emit a little more going forward, although they would be asked to taper emissions in the coming years. Developing countries with historically lower emissions would not be able to raise their emissions as much as developed countries did in the past, but they would still be allowed to power some of their economic growth with fossil fuels. The rest would be powered by an increasing investment in renewables.

McKinley calls the approach “a really nice way of dealing with the distribution of emissions.”

It’s a compromise approach, Davis admits, but it could allow the world to stay under the overall quota that would cap warming at 2°C—unlike the current trajectory, which will soon overshoot it.

“We can't burn all proven fossil reserves and stay even below 3°C of warming,” warns Davis, unless experimental carbon-capture technology pans out on a large scale. (See “Can Coal Ever Be Clean?”)

“I liken this to a cookie jar,” he says, referring to fossil fuels and the emissions they produce. “We and our descendants will have to walk past it.”