The amount of heat-trapping carbon dioxide in the air jumped dramatically in 2012, making it very unlikely that global warming can be limited to another two degrees as many global leaders have hoped, new figures show.
Scientists said the rise in CO2 reflects the world's economy revving up and burning more fossil fuels, especially in China.
Carbon dioxide levels jumped by 2.67 parts per million since 2011 to total just under 395 parts per million, said Pieter Tans, who led the greenhouse gas measurement team for the National Oceanic and Atmospheric Administration.
That's the second highest rise in carbon emissions since record-keeping began in 1959.
The measurements are taken from air samples captured away from civilisation near a volcano in Mauna Loa, Hawaii.
More coal-burning power plants, especially in the developing world, are the main reason emissions keep going up - even as they have declined in the US and other places, in part through conservation and cleaner energy.
At the same time, plants and the world's oceans, which normally absorb some carbon dioxide, last year took in less than they do on average, said John Reilly, co-director of Joint Program on the Science and Policy of Global Change. Plant and ocean absorption of carbon varies naturally year to year.
But, Tans said the major factor was ever-rising fossil fuel burning: "It's just a testament to human influence being dominant."
Only 1998 had a bigger annual increase in carbon dioxide, the primary greenhouse gas from human activity. That year, 2.93 parts per million of CO2 was added.
From 2000 to 2010, the world averaged a yearly rise of just under two parts per million. Levels rose by less than one part per million in the 1960s.
In 2009, the world's nations agreed on a voluntary goal of limiting global warming to 3.6 degrees Fahrenheit over pre-industrial temperature levels.
Since the mid-1800s temperatures haven already risen about 1.5 degrees. Current pollution trends translate to another 2.5 to 4.5 degrees of warming within the next several decades, Reilly said.
"The prospects of keeping climate change below that (2-degree goal) are fading away," Tans said.
Scientists track carbon pollution both by monitoring what comes out of factories and what winds up in the atmosphere. Both are rising at rates faster than worst-case scenarios that climate scientists used in their most recent international projections, according to Pennsylvania State University climate scientist Michael Mann.
That means harmful effects of climate change will happen sooner, Mann said.
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