The announcement comes a day after the United States, the world's second-biggest emitter, for the first time announced plans to rein in carbon emissions from its power sector, a move the Obama administration hopes can inject ambition into the slow-moving international climate negotiations.
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"The China-US one is a key trust relationship (in climate talks) and if they are rising above that it sends a very powerful signal to the rest of the world to get serious," said John Connor, CEO of Melbourne-based The Climate Institute.
Focus will now turn to Bonn in Germany, where negotiators from over 190 nations meet from Wednesday for the latest 10-day round of talks in a process meant to lead to a new global climate treaty in Paris in December 2015.
"Interesting hint from Beijing, although the key point will be where (the cap) is set. If ambitious and announced well in advance of Paris, it could be a game changer," said a spokesman for EU Climate Action Commissioner Connie Hedegaard.
China, often blamed by rich countries for holding back progress in U.N. talks on emissions due to its reluctance to take on a binding target, is stepping up efforts to clean up or shut down carbon-emitting sources such as coal-fired power plants, factories and vehicles, because they have also created a much-publicised pollution crisis that ends hundreds of thousands lives prematurely every year.
Despite the absolute cap on CO2, adviser He said China's greenhouse gas emissions would only peak in 2030, at around 11 billion tonnes of CO2-equivalent. Its emissions currently stand at around 7-9.5 billion tonnes.
But He said that would depend on China achieving a real reduction in coal consumption from sometime around 2020 or 2025, and on the nation meeting its target of having 150-200 gigawatts of nuclear power capacity by 2030. The share of non-fossil fuels in China's energy mix would reach 20 to 25 percent in 2030, He added.