Refugee crisis: Is climate change affecting mass migration?

John Kerry painted an apocalyptic vision of climate change last week as he addressed a global warming conference in Alaska. "You think migration is a challenge in Europe today because of extremism, wait until you see what happens when there's an absence of water, an absence of food, or one tribe fighting against another for mere survival," the US secretary of state warned. Few experts would argue with Kerry's analysis of the future, but some would argue his vision is already upon us.