Carbon trading is a business arrangement in which someone who produces CO₂ pays a fee, which in turn is used to support a project that reduces CO₂. The carbon trading market is a measurable and deliverable means to offset emissions for which a person is responsible. If all airline passengers paid a "carbon tax", for example, it could have a broad impact on carbon reduction projects around the world.

"e²: the economies of being environmentally conscious" is an ongoing PBS documentary series about solutions to the world's most pervasive environmental challenges. The latest addition to the series - "e² transport" - examines transportation alternatives and urban planning in cities around the world. Check your local PBS listings for television broadcast dates in your area.

The "e²" series and its video podcasts are produced by kontentreal, and distributed within the United States by PBS. More information is available at pbs.org/e2/ and e2-series.com/