BBC: Thousands of protesters have joined a mass rally in London to call on the government to combat climate change. The environmental campaigners marched from Grosvenor Square to Westminster as part of a global day of action. It coincides with the UN Framework Convention on Climate Change, currently taking place in Poznan, Poland. Protesters called for controversial plans for a third runway at Heathrow to be scrapped and an end to expansion plans for coal-burning …