Agence France-Presse: A British official said Thursday that “negative forces” in the United States are holding up a climate change policy, while praising China’s efforts in adopting a low-carbon economy. John Ashton, special representative for climate change at the Foreign and Commonwealth Office, said a tug-of-war between “positive forces” and “some very negative forces” was delaying a US plan on curbing the carbon emissions blamed for global warming. “There are plenty of positive forces (in the US), but there…