 Chinese President Hu Jintao on Tuesday promised to put a "notable" brake on the country's rapidly rising carbon emissions, but dashed hopes he would unveil a hard target to kickstart stalled climate talks. The leader of the world's biggest emitter told a United Nations summit that China would pledge to cut "carbon intensity," or the amount of carbon dioxide produced for each dollar of economic output, over the decade to 2020. His promise is a landmark because China had previously rejected rich nations' demands for measurable curbs on its emissions, arguing that economic development must come first while millions of its citizens still live in deep poverty. "It's still a very significant step -- a Chinese leader standing on that platform and saying China will make a mid-term carbon intensity target," said Yang Ailun of Greenpeace China. "We should think of this as a clear signal that China wants to de-couple carbon emissions from economic growth," she said. But without a firm figure attached, the offer to reduce emissions intensity may not be enough to rekindle faltering talks on a new global deal to tackle climate change. Hu said only that carbon intensity would come down "by a notable margin by 2020 from the 2005 levels," which still leaves Beijing and other major powers room for manoeuvre before final negotiations in Copenhagen in December. "I didn't hear new initiatives so much," said Todd Stern, special envoy on climate change in the United States, one of the most vocal critics of China's emissions policy. "It depends on what the number is and he didn't indicate the extent to which those reductions would be made." But Xie Zhenhua, China's top environment official, later told reporters China would soon unveil a target, based on projections that by 2020 it will double its use of renewable energy and dramatically cut energy use per dollar of GDP. "After further study and discussion, we should be able to announce a target soon," he said in New York. Hu's choice of a global stage to answer rich nation demands that China take stronger, verifiable steps to control carbon dioxide output, was a sign of how rapidly climate change has risen up the agenda of leaders in Beijing. The country's geography has made it particularly vulnerable to the effects of a warming world, from droughts to flooding and rising sea levels, adding to their sense of urgency. "IMPRESSIVE LEADERSHIP" Nobel laureate Al Gore praised China for "impressive leadership" and said Hu's goals pointed to more action. "They are very important and we've had ... indications that in the event there is dramatic progress in this negotiation, that China will be prepared to do even more," he said. Hu also made clear, however, that China had high expectations from the rest of the world, repeating a long-standing request for more support in moving away from dirty growth. Backed by India and other developing nations, China argues that rich nations emit more per person and enjoyed an emissions-intensive industrialization, so they have no right to demand others do differently -- unless they are willing to pay for it. "Developed countries should take up their responsibility and provide new, additional, adequate and predictable financial support to developing countries," Hu said. Hu also repeated well-established targets including boosting the portion of renewables in China's energy mix, to 15 percent by 2020, as the country strives to move away from dirty coal. Beijing's worries about energy security and severe pollution have already prompted the introduction of an energy intensity target from 2006. A carbon target should speed up a planned boost in renewables like wind and hydropower. It will also appeal to those in the financial industry who hope to see China set up a carbon trading scheme, because Beijing will be forced to step up its ability to measure output of the gasses, which is key to any market in credits to emit. But while carbon intensity is a financially viable way to contain emissions growth, if economies expand too fast, even massive improvements in efficiency might not be enough to contain dangerously high output of greenhouse gasses.