One of a suite of online climate interactive simulations, this Greenhouse Gas Simulator uses the bathtub model to demonstrate how atmospheric concentrations of CO2 will continue to rise unless they are lowered to match the amount of CO2 that can be removed through natural processes.

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 simulation allows the user to project CO2 sources and sinks by adjusting the points on a graph and then running the simulation to see projections for the impact on atmospheric CO2 and global temperatures.