Chris Vernon has a look at the impact on global warming of natural gas extraction - Climate Danger from Natural Gas.
A couple of years ago I wrote a piece (Natural gas, the green choice?) for The Oil Drum looking at the climate change implications of using gas rather than coal. Burning gas to produce electricity produces only around 40% the CO2 emissions of burning coal. However, since methane (CH4) is itself a potent greenhouse gas, its release to the atmosphere without being burnt can quickly compensate for this CO2 advantage against coal. I included this chart to illustrate the point:
On the left, CO2 emissions per kWh for coal and natural gas. On the right, the global warming potential of leaked CH4 expressed as CO2
The key take-away was that if the natural gas leak rate is 3%, the global warming potential of a kilowatt-hour of electricity from gas is equivalent to coal. The details behind the chart are in the original article.
This week the journal Nature has an article (Air sampling reveals high emissions from gas field) presenting measurements from a gas field and suggesting that “Methane leaks during production may offset climate benefits of natural gas.”Led by researchers at the National Oceanic and Atmospheric Administration (NOAA) and the University of Colorado, Boulder, the study estimates that natural-gas producers in an area known as the Denver-Julesburg Basin are losing about 4% of their gas to the atmosphere — not including additional losses in the pipeline and distribution system. ...
Gas is often described as the ‘cleaner’ choice, as a transitional energy source between coal and low-carbon renewables. Gas does burn without emitting the oxides of sulphur (SOx) and nitrogen (NOx), traces of mercury, selenium and arsenic, as well as the particulates associated with coal and doesn’t leave the non-combustible slag. Despite this it is increasingly unclear that gas has a significantly lower climate impact and the fracking process itself is not as clean as conventional gas extraction.
This figure of 4%, their range is 2.3–7.7% loss, with a best guess of 4%, is well inside the danger zone suggesting gas has similar, if not higher, climate impact as coal.