The NPR show Justice Talking had an excellent show last month on "Greenhouse Gases and Global Warming."
Issues discussed include cap and trade policies and legislation, Massachusetts v. EPA (does Clean Air Act regulate carbon, and must EPA regulate carbon?); and a discussion about whether the United States must take a leading role in order for the world to take effective action on global warming. The show is an accessible primer on the both the environmental and legal challenges of global warming.
The show can be heard by stream or MP3 download, and a transcript is available.