By Joel Levin, Huffington Post.

Combustion of natural gas is responsible for a quarter of California's carbon emissions. If we are going to achieve the 80 percent reduction in emissions proposed by state legislators in S.B. 32, we will need to think clearly about the role that natural gas plays now and the role that we envision for it in the future.

Natural gas today is primarily -- but not exclusively -- a fossil fuel. It mainly comes from fossil carbon stored in the earth's crust, just like coal and petroleum. It is used for electricity generation and also for heating our homes and hot water, cooking our food, and to generate heat for various manufacturing processes. However, gas is different from other fossil fuels in three important ways.

First, gas is not just a fossil fuel. Natural gas can also come from biogas, created from the decay of organic waste products in landfills, and from waste water, animal manure, and agricultural waste.