Climate change is one of the most important public policy issues facing the world. But many elected officials, and even news organizations, still portray global warming as a controversial and disputed scientific theory, with arguments on both sides.For example, here’s the President of the United States. “Obama was talking about all of this global warming. And a lot of that is a hoax, it’s a hoax,” President Trump said at a rally. “I mean, it’s a money-making industry, okay? It’s a hoax.”But climate change is not a hoax, or even something that scientists with supercomputers have predicted for the future. The geological record of the Earth’s history shows that, whenever carbon dioxide concentrations in the atmosphere have gone up, temperatures have also risen – often with catastrophic consequences.