OSLO - The world has emitted extra greenhouse gases this century equivalent to the annual totals of China and the United States above a maximum for avoiding the worst of climate change, a study estimated Tuesday.

Global accounting firm PriceWaterhouseCoopers said in the report that almost all major nations, including European Union countries that pride themselves on climate policies, were lagging since 2000 in a push for low-carbon growth.

It said the world was already far above a budget of total emissions of 1,300 billion tonnes of carbon dioxide from 2000-50 which it estimated as the maximum permissible while avoiding the worst of climate change.

For 2000-08, the cumulative global budget overshoot, or 'carbon debt', is estimated at around 13 billion tonnes of carbon dioxide -- roughly equivalent to the annual carbon emissions of China and the United States combined in 2008, it said.

China and the United States are the top world emitters of greenhouse gases, mainly carbon dioxide from burning fossil fuels. A conference in Copenhagen from December 7 to 18 will try to work out a new U.N. pact to curb rising emissions.

If you stay on this path the entire carbon budget will be used by about 2034, about 16 years early, John Hawksworth, head of macroeconomics at PwC, told Reuters of the report, based on a new PwC Low Carbon Economy Index.

CARBON INTENSITY

The index is a nation-by-nation tracker of efforts to improve carbon intensity -- the amount of carbon dioxide emitted per dollar of economic output -- rather than the usual yardstick of changes in overall national emissions.

So far this century, the world had improved carbon intensity by only about 0.8 percent a year, it said.

To get back on track, world carbon intensity would have to fall by about 3 percent a year, four times the speed at the moment, said Richard Gledhill, global leader of climate change at PwC. That shows the policy challenges.

China's rate of cutting carbon intensity was 0.7 percent a year from 2000-08, the United States 2.2 percent, the European Union 1.8 percent and India 2.1 percent. All were lagging the rates set by PwC for their carbon budgets.

It estimated a budget of 1,300 billion tonnes would give a fair chance of limiting global warming to a 2 degrees Celsius (3.6 Fahrenheit) rise over pre-industrial levels, widely seen as a threshold for dangerous change.

PwC calculated the world would have to cut carbon intensity by about 85 percent between 2008 and 2050 to avoid the worst of climate change such as more powerful cyclones, desertification, wildfires and rising sea levels.

China last week set itself a goal of cutting its carbon intensity by between 40 and 45 percent by 2020, compared with 2005 levels. Hawksworth estimated that would still allow China's overall emissions to rise by 65 percent in the period.

Former U.S. President George W. Bush also once set a carbon intensity goal that let U.S. emissions rise.

(Editing by Andrew Dobbie)

China Climate change