So, if coal is the problem, is natural gas the solution? Natural gas already plays a major role as a backup power supply for peak demand at coal-fired power plants. The Rawhide Energy Station, for example, has five gas turbines that can provide 388 MWe on a hot summer day to provide electricity for air conditioning (yes, we do need air conditioning in Colorado—at least we think we do! We can thank global warming for that.). Natural gas provides 27% of the energy production for the United States and contributes 24% to electricity production (Chapter 2). In principle, burning natural gas produces about half as much CO2 as an equivalent amount of coal, so a greater reliance on natural gas would at least reduce the prob­lem of CO2 production. But even if all coal-fired power plants in the United States were replaced by plants burning natural gas, they would release about one billion tons of CO2 yearly, which is still a major problem.

Natural gas was produced in geological times by anaerobic decay of organic matter that was then compressed and heated over eons. Slightly different condi­tions created coal, oil, and natural gas. Conventional natural gas rises through pores in permeable rock strata to form domes above oil reservoirs, usually one or two miles deep in the earth, and pure methane can be found even deeper (28). To form a dome containing natural gas, the permeable reservoir rock has to be sealed by an impermeable rock layer that traps the natural gas. In recent years, the tech­nology to develop unconventional sources of natural gas from layers of shale has greatly increased the availability of natural gas. Gas-rich shales are thick layers of rock that are buried deep in the earth. Shale is a type of rock with very small pores, so it serves both as a source and reservoir of natural gas. However, the gas cannot be released from the shale without fracturing the shale. This has led to one of the controversies about natural gas—hydraulic fracturing, or fracking.

Natural gas from wells consists of about 75% methane, a potent greenhouse gas in its own right (see Appendix A), but also contains higher order hydrocar­bons such as ethane, butane, and propane. The natural gas supplied to homes for heating and cooking and to power plants for electricity production is pro­cessed to greater than 93% methane. Methane is also produced from landfills as methanogenic bacteria decompose the organic material, and this is increasingly being collected to power small electrical plants. The other major source of meth­ane is from food digestion in livestock (don’t smoke around farting or belching cattle!). And, yes, we humans generate it too!