Guardian: The world now understands that climate change is not just an environmental problem. It’s also a security, economic, political and migration problem. What are we going to do when people begin fighting not about politics, but about water? What will we do when people start arriving on our shores fleeing not political persecution, but environmental catastrophe? And what will we do when the countries to which we sell goods can’t buy them any more because they are having to deal with rising sea …