The U.S., China and India led the world in pushing carbon pollution in the atmosphere to an all-time high last year, scientists announced in a series of articles published Sunday in the scientific journals Nature Geoscience and Nature Climate Change.

The news comes as leaders from around the world gather in New York this week to discuss how to reduce heat-trapping greenhouse gases like carbon dioxide, and begin the push toward a final global climate agreement next year.

The world pumped an estimated 39.8 billion tons of carbon dioxide into the air last year, the papers released Sunday note, primarily by burning coal, oil and gas. That is 778 million tons, or 2.3 percent more, than the previous year.

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"It's in the wrong direction," said Glen Peters, a Norwegian scientist who was part of the Global Carbon Project international team that tracks and calculates global emissions every year.

Laborers work in a coal chemical factory in Huaibei, in east China's Anhui province.

(STR/AFP/Getty Images)

The team projects that emissions of carbon dioxide, the main heat-trapping gas from human activity, are increasing by 2.5 percent this year.

The scientists forecast that emissions will continue to increase, adding that the world in about 30 years will warm by about 2 degrees Fahrenheit from now. In 2009, world leaders called that level dangerous and pledged not to reach it.

"Time is running short," said Pierre Friedlingstein of the University of Exeter in England, one of the studies' lead authors. "The more we do nothing, the more likely we are to be hitting this wall in 2040-something."

Chris Field, a Carnegie Institution ecologist who heads a U.N. panel on global warming, called the studies "a stark and sobering picture of the steps we need to take to address the challenge of climate change."

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More than 100 world leaders will meet Tuesday at the U.N. Climate Summit to discuss how to reverse the emissions trend.

The world's three biggest carbon polluting nations -- China, the U.S. and India -- all saw their emissions jump. No other country came close in additional emissions.

Indian emissions grew by 5.1 percent, Chinese emissions by 4.2 percent and the U.S. emissions by 2.9 percent, when the extra leap day in 2012 is accounted for.

China, the No. 1 carbon polluter, also had more than half the world's increases over 2012. China's increases are slowing because the Chinese economy isn't growing as fast as it had been, Peters said.

The U.S. had reduced its carbon emissions in four of the five previous years. Peters said it rose last year because of a recovering economy and more coal power.

Only two dozen of the about 200 countries cut their carbon emissions last year, led by mostly European countries. Spain had the biggest decrease.

The world emissions averaged to 6.3 million pounds of carbon dioxide put in the air every second.

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