The Renewable Energy Industry Institute (IWR) said that the total amounted to 800 million tonnes more than in 2010, with China accounting for 8.9 billion tonnes -- far more than the US tally of 6.0 billion tonnes.

The study found that after a brief dip in 2009 due to the global economic crisis, the upward trajectory had resumed.

"If the current trend continues then global CO2 emissions will rise another 20 percent by the year 2020 to reach 40 billion tonnes of CO2," IWR director Norbert Allnoch said in a statement.

In 1990, the figure was 22.7 billion tonnes.

After China and the United States, India came in third with 1.8 billion tonnes followed by Russia with 1.7 billion, Japan with 1.3 billion and Germany with 804 million.

Among the top 10 countries, only the United States, Russia and Germany reduced emissions in 2011 compared to the previous year.

It said the figures were based on global consumption of fossil fuels made available by British energy giant BP.

The report comes ahead of annual negotiations under the UN Framework Convention on Climate Change (UNFCCC), which this year take place in Doha, Qatar, from November 26 to December 7.

The big issue is renewing commitments under the Kyoto Protocol after the first round of cuts in CO2 emissions expires on December 31, although agreement on a new globally binding deal is not expected until 2015 and will not come into force until 2020.