Atmospheric methane (CH4), like carbon dioxide (CO2), interferes with the upward infrared thermal radiation from Earth into space, as the planet cools itself.
For current concentrations of greenhouse gases, the potential warming effect of an added CH4 molecule, is about 30 times larger than an added
CO2 molecule.
This is due to the heavy saturation of the infrared (wavelength) absorption band of the abundant greenhouse gas, CO2.
“Saturation” means that adding more molecules causes very little change in Earth’s thermal (infrared energy) radiation to space.
The rate of increase of CO2 molecules, of about 2.3 ppm/year (ppm = part per million), is about 300 times larger than the rate of increase of CH4 molecules, which has been around 0.0076 ppm/year since the year 2008.
So the potential contribution of methane to global warming is one tenth ( 30 / 300 ) that of carbon dioxide, and the potential global warming is too small to measure.
Keep that real cience in mind as you continue reading:
The fossil-fuel industry is a big source of atmospheric methane, believed mainly due to to leaks from the production of oil and gas.
A new paper published in the Journal of Cleaner Production suggests that coal mining may be a bigger contributor of methane, and old coal mines continue to seep methane long after they have been abandoned.
Attempts to curb methane emissions from mines have been limited.
The authors of the new study say their results are based on extrapolations from the only nations for which sufficient information was available.
Methane is produced by natural sources, such as wetlands, as well as human activities, such as agriculture and fossil-fuel production.
The contribution from fossil fuels makes up around a fifth of the total, with oil-and-gas production believed to be the biggest contributor.
Coal releases 75% more CO2 than gas per unit of energy, but has been overlooked when it comes to methane, another greenhouse gas..
Methane gas escapes from coal seams and is often siphoned off through ventilation systems to ensure a safe environment for miners.
In its most recent World Energy Outlook (WEO), published in November 2019, the International Energy Agency (IEA) attempted to quantify the global total, settling on a figure of 40m tonnes (Mt) each year from operational coal mines.
The IEA says nations with deeper coal mines and less regulatory oversight have higher levels of these “indirect” methane emissions, with China by far the largest contributor.
The authors developed a methodology for estimating global methane emissions from old mining sites, suggesting a considerable role for abandoned mine methane (AMM), which in the past has been largely ignored.
The central calculation is straightforward – multiplying coal production, or tonnes of coal, by the emissions factor, which is how much methane is released (in cubic meters) for every tonne of coal mined.
The team based its emissions factor coefficient on relatively detailed datasets from US and Ukrainian coal mines, the only ones available.
All of this can vary a lot between countries, whereas this study relied on extrapolating globally from the US and Ukrainian data.
CMM emissions are tied with coal production, but emissions from abandoned sites will likely continue growing or at least stay constant, even if dramatic climate action is taken.
The methane from coal is not released in a pure form and can be expensive to capture.
Air passing through mine ventilation systems contains less than 1% methane, according to the IEA.