Agence France-Presse: The crucial Copenhagen climate change summit could end without a deal, the US special envoy for climate change warned Saturday, while urging big developing economies to boost their efforts. Todd Stern spoke before the Major Economies Forum featuring politicians from 17 countries met in London on Sunday. 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 …