Carbon dioxide (CO2) is an end product created by the combustion of carbon-based fuel. It is usually released to the atmosphere, and most scientists believe these emissions are a major contributing factor to climate change. Under both international law and U.S. domestic law, CO2 is a pollutant, but it cannot be controlled with the techniques used to control traditional air pollution. One option for preventing CO2 emissions from being released to the atmosphere is to require combustion sources to utilize carbon capture and storage (sequestration) (CCS). This involves capturing CO2, compressing it to a supercritical state, injecting it into an underground geological depository, and managing the site to assure permanent sequestration. Because the electric power industry emits over 40% of U.S. CO2 emissions, it is a primary target for government efforts aimed at developing and using CCS.