Global carbon dioxide emissions reached a record high of 31.6 trillion metric tons in 2011, according to a preliminary estimate released yesterday by the International Energy Agency.
It's an increase of 3.2 percent from 2010 emissions.
Worldwide, coal accounted for 45 percent of the emissions, oil 35 percent and natural gas 20 percent, the agency said in a media release.
Emissions increased more than 6 percent in developing countries, while those in developed countries decreased 0.6 percent.
China, the world's largest source of CO2, increased its emissions 9.3 percent, according to the agency, primarily through increased coal consumption. India increased emissions 8.7 percent.
China's efforts to improve carbon intensity -- the amount of carbon emitted per unit of output -- showed. Due to energy efficiency and clean-energy measures, the nation's carbon intensity fell 15 percent from 2005 to 2011. Without that, its 2011 emissions would have been 1.5 trillion metric tons higher rather than 720 million metric tons.
U.S. CO2 emissions fell by 1.7 percent, largely due to the switch from coal to natural gas for the production of electricity and to the mild winter. U.S. emissions have fallen 7.7 percent since 2006 due to those factors and, more generally, to the economic downturn.
The IEA published a "450 Scenario" in its World Energy Outlook 2011, "450" being a reference to the concentration of carbon dioxide and other climate-warming emissions in the atmosphere.
Many concerned about climate effects of emissions have called for measures that would stabilize the concentration at 450 parts per million, "consistent with a 50 percent chance of limiting the increase in the average global temperature to 2 degrees Centigrade," the agency wrote.
The current level is 396 parts per million.