Science writer and author Matt Ridley discusses climate change with EconTalk host Russ Roberts. Based on his reading of the scientific evidence, Ridley describes himself as a "lukewarmer." While Ridley agrees that humans have made the climate warmer, he argues that the impact is small or positive over some temperature ranges and regions. He rejects the catastrophic scenarios that some say are sufficiently likely to justify dramatic policy responses, and he reflects on the challenges of staking out an unpopular position on a contentious policy issue.