This video segment from 'Earth: The Operators' Manual' explores how we know that today's increased levels of CO2 are caused by humans burning fossil fuels and not by some natural process, such as volcanic out-gassing. Climate scientist Richard Alley provides a detailed step-by-step explanation that examines the physics and chemistry of different "flavors," or isotopes, of carbon in Earth's atmosphere.

This static graph of changes in CO2 concentrations goes back 400,000 years, showing the dramatic spike in recent years.

This video succinctly explains the mechanism of the natural greenhouse effect and the cause of global climate change (anthropogenic global warming). It is short, basic, and to the point. It's also available in 12 languages!