Reuters: Joe Biden and Sarah Palin agreed that climate change is real, but differed on whether human activity was its root cause in Thursday’s U.S. vice presidential debate. Palin, the Republican governor of Alaska, acknowledged that human activities may play a role in heating up the planet, but also said natural cycles are part of the picture. “I don’t want to argue about the causes,” she said in St. Louis. “What I want to argue about is, how are we going to get there to positively …