The crucial Copenhagen climate change summit could end without a deal, the US special envoy for climate change Todd Stern warned today. He urged big developing economies to boost their efforts. He was addressing the Major Economies Forum featuring politicians from 17 countries.<br/> This will help pave the way for a crunch summit in the Danish capital in December when nations will try to agree a new global climate treaty to replace the Kyoto Protocol which expires in 2012. Speaking at the forum Mr. Stern said that progress on the talks front is slow.