Guardian: The leaders of the world’s two biggest greenhouse gas emitters – Barack Obama and Hu Jintao – are to meet on Tuesday in Beijing, in one of the most significant moments leading up to the world summit on climate change in Copenhagen next month. Agreement between the US and China on key issues would breathe new life into the moribund negotiations towards a global climate deal. But sources are downplaying the chances of a breakthrough, suggesting another blow to the talks. Instead, …