Proc. Natl Acad. Sci. USA doi:10.1073/pnas.0700609104 (2007)

Credit: PUNCHSTOCK

Worldwide emissions of man-made carbon dioxide are rising faster than even the worst case predictions made by scientists. The increase in CO2 levels, which averaged 1.1% per year from 1990 to 1999, leaped to over 3% per year from 2000 to 2004, according to a new study by Michael Raupach of the Commonwealth Scientific and Industrial Research Organisation, Australia, and international colleagues.

The researchers divided the world into nine regions and analysed population trends, economic factors and energy-related data for each region. They found that developed nations, representing 20% of the world's population, accounted for 59% of global human CO2 emissions in 2004. Developing nations, including those with rapidly expanding economies, were responsible for just 41% of total emissions in 2004, but contributed 73% of emissions growth that year.

Even the most fossil fuel-intensive scenarios developed by the Intergovernmental Panel on Climate Change underestimated the rapid increase in CO2 levels since 2000. Raupach and colleagues attribute the observed trends to the increasing energy intensity of economic activity and the carbon intensity of energy sources. The study shows that no region is decarbonizing its energy supply and that CO2 emissions are accelerating worldwide, with China in the lead.