Methane (Natural Gas): A Bridge to Nowhere

Alan Journet, Cofacilitator, Southern Oregon Climate Action Now

Methane (Natural 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
Propane  139
Natural gas 117

But note that particulates are an additional major concern with diesel combustion.

The data above explain why the combustion of methane seems to confer benefits in terms of greenhouse gas emissions.  What the fossil gas companies consistently fail to acknowledge, however, is the full life cycle assessment (LCA) of emissions.

The catch is that 90% methane content. We have long understood that other greenhouse gases are more potent as warming agents than 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 CO2  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, methane (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 reasonably 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 maybe a decade.  If leakages exceeds 2.8%, fossil gas is worse as a global warming energy source than coal.

The following chart indicates the leakage estimates for methane reported in several studies.

For documentation of the cited values, visit the Carbon Brief  link.

Note how many of the studies report results hovering around or exceeding that critical threshold level of 2.8%.  A more recent study by Alvarez et al in 2018 reported a leakage value of 2.3%.

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 methane ranged between 3.6 and 7.9%, (mean of 5.8%). These data indicate that fossil gas is probably 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 subsequent 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.

Regrettably, methane producers seem unable to prevent the emissions of methane – particularly as infrastructure ages.

It is for this reason that methane is now described as “the bridge to nowhere.”

The bottom line is that even if fossil gas is slightly better than coal or oil, it still emits a considerable amount of carbon dioxide when combusted, and results in substantial leakage of methane during extraction, processing, and transmission.  Fossil gas may be slightly better than coal or oil, but not by much, and might actually be worse.  It makes little sense for us to continue to promote vehicles, appliances and industrial processes that use methane or install infrastructure – having a life span of decades, that collectively require the ongoing use of methane.  It is far better to promote the electrification of all aspects of our energy economy.  This is because (a)  electric motors are far more efficient than internal combustion engines for transportation and even if that electricity is now generated by a fossil fuel-powered utility it will result in reduced emissions compared to oil,  and (b) in the very near future we will have converted fossil fuel electricity generators to renewable sources.

It is worth noting that Assessment Report 6, the Intergovernmental Panel on Climate Change (IPCC 2021) Working Group 1⁵ on the physical science basis reports that fully 25% of global warming is currently a function of methane emissions. We cannot afford an energy source with such a high and apparently inevitable methane loss.

Citations:

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/

5 – IPCC. Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Intergovernmental Panel on Climate Change; 2013. https://www.ipcc.ch/report/ar5/wg1/.