Fossil Gas is extracted directly as a gas or as a bi-product of extraction of other fossil fuels. It was named ‘Natural gas’ in a sublime moment that has seemingly labeled it forever as a benign product. As marketed, this fuel contains some 90% methane, and thereby lies the problem as discussed below.
Fossil fuels have different efficiencies in terms of the carbon dioxide produced per unit of energy generated. For example, from the U.S. Energy Information Administration, the number of pounds of CO2 emitted per million British thermal units (Btu) of energy for various fuels is identified below:
Coal (Anthracite) 228.6
Coal (bituminous) 205.7
Coal (lignite) 215.4
Coal (sub-bituminous) 214.3
Diesel fuel and heating oil 161.3
Gasoline (without ethanol) 157.2
Natural gas 117
But note that particulates are a major concern with diesel combustion.
The date explain why the combustion of fossil gas seems to confer benefits in terms of greenhouse gas emissions.
The catch, however is that 90% methane content. We have long understood that other greenhouse gases are more potent as warming agents that carbon dioxide. This understanding has led to the designation of other gases in terms of their Global Warming Potential (GWP) or Carbon dioxide Equivalent (CO2e). This defines the warming potential of other gases in comparison to carbon dioxide, with that gas designated as 1. Since other gases are stronger warming agents, they all have a higher GWP (or CO2e) than carbon dioxide. Thus, nitrous oxide has a GWP or 298, and Methane, which has a longevity in the atmosphere of about a decade compared to the longevity of carbon dioxide of between centuries and millennia, is designated by both its 100-year GWP of 34 and its 20-year GWP of 86.
For many years, fossil (natural) gas was considered to be cleaner than coal and oil. However, that bubble was burst earlier this decade (around 2014) when studies were reported of the full life cycle (cradle to grave/combustion) of the fuel. While previous estimates of the leakage (fugitive emissions) of the gas during extraction and processing had placed the value down in the 1% range, Robert Howarth reported a much higher percentage. The critical issue is the cut-off point at which the fugitive emissions of methane during extraction and processing negate the combustion benefits. Howarth and colleagues calculated this to be between 2.4 and 3.2%, mean 2.8%. On calculating this value, they reasonable used the 20-year GWP value for methane based on the argument, known at the time, that we do not have centuries to solve the global warming problem but mere decades. If leakages exceeds this value, fossil gas is worse as a global warming energy source than coal.
Not surprisingly, Howarth1 and his team also further assessed the actual fugitive emissions from fossil gas extraction and processing. They reported the value for conventional fossil gas extraction as between 1.7% and 6.0% (mean 3.8%), while emissions from shale-fracked fossil gas ranged between 3.6 and 7.9%, (mean of 5.8%). These data indicate that fossil gas is never better than coal; it is profoundly not “the clean fossil fuel.” Meanwhile, Schneissing2 reported 9.1% as the value for fugitive emissions and Howarth3 in a 2015 literature review, indicated the value was probably closer to 12%. Many subsequent studies have endorsed these findings. The concern was echoed by Powell4 in 2019. The notion that fossil (natural) gas is ‘the clean fossil fuel’ has been completely debunked in the research literature.
1 – A bridge to nowhere: methane emissions and the greenhouse gas footprint of natural gas 2014 by Robert Howarth in Energy, Science and Engineering. http://www.eeb.cornell.edu/howarth/publications/Howarth_2014_ESE_methane_emissions.pdf
2 – Remote sensing of fugitive methane emissions from oil and gas production in North American tight geologic formations: Remote sensing of fugitive methane emissions from oil and gas production, 2014 by Oliver Schneising, John P. Burrows, and Heinrich Bovensmann in Semantic Scholar. https://www.semanticscholar.org/paper/Remote-sensing-of-fugitive-methane-emissions-from-Schneising-Burrows/ebb006c04b06ebdad36f967bcc9cb291d33743e1
3 – Methane emissions and climatic warming risk from hydraulic fracturing and shale gas development: implications for policy, 2015 by Robert Howarth in Energy Emissions Control technologies 2015:3 45–54. http://www.eeb.cornell.edu/howarth/publications/f_EECT-61539-perspectives-on-air-emissions-of-methane-and-climatic-warmin_100815_27470.pdf
4 – Studying Full methane Life Cycle Critical to PNW Climate Policy 2019 by Tarika Powell in Sightline Institute Newsletter. https://www.sightline.org/2019/02/12/study-methane-life-cycle-critical-pacific-northwest/