Methane is probably familiar to most of us. It is the prime constituent of natural gas, the most popular fossil fuel. It is burnt and used for electricity generation, heating buildings and cooking round the world.

However it also has a sinister side. In its own right it is a very powerful greenhouse gas. Unburnt methane in the atmosphere is many times more damaging than carbon dioxide. While it is true that it has a limited lifetime in the atmosphere, when it is present it can do a great deal more warming. Calculated over a 20-year window, it is 80 times more damaging than the same mass of carbon dioxide and when calculated over a 100-year window it is 28 times more damaging than the same mass as carbon dioxide [1]. It is the second most abundant greenhouse gas in our atmosphere and gives us a large second place in the overall greenhouse warming effect. As of the latest observations, carbon dioxide is present at 420 ppm (parts per million, so in a million molecules of atmosphere, 420 are carbon dioxide molecules) and methane is present at nearly 2 ppm (see here).

The concentration of methane in our atmosphere has increased with human activity. Some methane is from leaks of fossil methane (also called fugitive emissions) and a lot is recently formed methane (such as from livestock farming). Simplistically methane is produced from anaerobic decay processes – those that happen without oxygen present. Decay processes in the presence of oxygen tend to release carbon dioxide instead. Now if that carbon dioxide released recently came from plant matter then the carbon dioxide is simply playing its part in the natural carbon cycle and no additional greenhouse gases are released when viewed over time and there is no additional warming effect from that. The same can’t generally be said for recently produced methane.

Let’s focus for a moment on anaerobic decay processes that create methane. Human activity has created at scale quite a number of these and it is arguably these processes that could be quite easy wins if we are looking for strong reductions in greenhouse gases that cause warming today.

Instead of food waste decay in landfill (anaerobic processes leading to methane formation) we could be composting our food waste (aerobic processes leading to carbon dioxide formation). Almost all food grown has absorbed carbon dioxide from the air so when it is released there is no net change in atmospheric carbon dioxide.

Instead of flooded paddy fields for growing rice (where anaerobic decay processes lead to methane release), we can explore drier growing options including intermittently flooded paddy fields (where oxygen can easily reach the ground and aerobic decay processes are more likely leading to more carbon dioxide release and less methane release).

The anaerobic digestion processes of livestock can produce large quantities of methane, popularly satirised as cow burps. Decomposition of manure also contributes. Modification of the composition of cattle feed (to make it more easily digestible) is being studied to reduce the quantity of methane produced. Vegetarians and Vegans may argue that a reduction in the livestock population will have a stronger effect on methane reduction. However, a reduction in the quantity released per animal is an important goal.

Have a look at the NASA visualisation of methane emissions here

In numbers [2],

• 30% is from fossil fuel extraction [human activity]
• 30% is from natural wetlands [natural]
• 20% is from agriculture (livestock, rice, waste etc) [human activity]
• 20% is all other sources with differing levels of human-related influence (wildfires, biomass, permafrost, dams and oceans) [both].

It is perhaps worth noting that some sources in the other category are affected by climate change too: as our climate warms from human causes, the frequency, intensity and area affected by wildfires increases; and the release of methane from the permafrost is affected by a warming polar region. So somewhere between 50 to 70% of methane release is potentially within our control and influence. This equates to around 11% to 16% of climate change is from methane release that we can influence [2].

References:

[1] IPCC AR6 WG1 Ch7 2021, https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter07.pdf

[2] Sources of Methane, NASA, July 2020, https://svs.gsfc.nasa.gov/4799