Edie: The scale of the popular movement and the force with which activists and agitators deliver their arguments is key to the success of any future international agreement to tackle climate change. These were the somewhat surprising words of the new Secretary of State for Climate Change and Energy, Ed Miliband, when he spoke at the Environment Agency’s conference this week. “We need the utopians and we need the agitators,” he said. “We need the people who say that people like …