Global emissions of greenhouse gases jumped 2.3 percent in 2013 to record levels, scientists reported Sunday, in the latest indication that the world remains far off track in its efforts to control global warming.
The emissions growth last year was a bit slower than the average growth rate of 2.5 percent over the past decade, and much of the dip was caused by an economic slowdown in China, which is the world's single largest source of emissions. It may take an additional year or two to know if China has turned a corner toward slower emissions growth, or if the runaway pace of recent years will resume.
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In the United States, emissions rose 2.9 percent, after declining in recent years.
The new numbers, reported by a tracking initiative called the Global Carbon Project and published in the journal Nature Geoscience, came on the eve of a United Nations summit meeting meant to harness fresh political ambition in tackling climate change. Scientists said the figures showed that vastly greater efforts would be needed to get long-term global warming within tolerable limits.
"You can no longer have some countries go first and others come in later, because there is no more time," said Glen P. Peters, a scientist at the Center for International Climate and Environmental Research in Oslo, who helped compile the new numbers. "It needs to be all hands on deck now."
Yet expectations for the summit meeting on Tuesday are low, with no sign of any political breakthrough that would lead to more ambitious efforts. Scientists say emissions must peak within the next few years, and then begin to decline, if the world is to have any hope of keeping global warming to an upper limit that countries agreed on five years ago. So far, no plans are in place that would come close to achieving that.
Emissions have been falling gradually in recent years in most of the developed countries, in part because of economic weakness but also because of strengthening climate policies. Emissions in the 28-nation European Union fell 1.8 percent in 2013, despite increases in coal consumption in a few countries, including Germany and Poland. Emissions decreased sharply in Britain, Italy and Spain.
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United States emissions had been declining because of increased burning of natural gas in power generation, which emits less carbon dioxide for each unit of energy than does coal. But the nation reported an increase in 2013 as coal regained some market share. If that trend continues, it could prove to be a challenge for the Obama administration as it seeks to institute tighter policies on greenhouse gases.
For years, slow emissions declines in the West have been swamped by rising emissions in the East, and the trend continued in 2013. China's emissions grew 4.2 percent and India's 5.1 percent. Both countries have been constructing coal-burning power plants at a breakneck pace.
China is spending heavily on renewable and nuclear energy as it tries to slow the growth of coal, but despite those efforts it has become by far the largest emitter of greenhouse gases. Its emissions of 10 billion tons a year of carbon dioxide from the burning of fossil fuels and cement manufacturing are almost twice those of the United States, though emissions per person are still far higher in the United States.
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"China is really in a tough position," Dr. Peters said. "Emissions have grown so much in the last 10 years or so that no matter how you look at China, it has an immense task."
In a separate report in early September, the World Meteorological Organization said the level of carbon dioxide in the air in 2013 was 42 percent above the level that prevailed before the Industrial Revolution. Other important greenhouse gases have gone up as well, with methane increasing 153 percent from the preindustrial level and nitrous oxide by 21 percent.
The increase of these and other gases from human activity has caused the planet to warm by about 1.5 degrees Fahrenheit since the preindustrial era, which is causing land ice to melt all over the world. The oceans are rising at what appears to be an accelerating pace, and heat waves and torrential rains are intensifying.
The nations of the world have agreed to try to limit the warming to 3.6 degrees Fahrenheit, which would require that emissions slow down and then largely stop in the next 30 years or so. If they continue on their present course through the century, scientists say, the earth could warm by as much as 10 degrees Fahrenheit above the preindustrial level, which would likely be incompatible with human civilization in its current form.