The concentration of methane in the atmosphere has been increasing for more than a decade and now appears to be accelerating. The rising concentration is worldwide, but is more pronounced in the tropics and northern mid-latitudes. What has caused this increase is not yet well understood. It is almost certainly due to rising emissions of the gas, but a decline in the ability of atmospheric oxidative mechanisms to breakdown methane is also possible.
What is alarming is that this increase in emissions was not anticipated in the preparation of the greenhouse gas emissions scenarios that are compliant with the targets of the Paris Agreement.
A research article just published by the American Geophysical Union paints a disturbing picture of the impact on global warming if atmospheric concentrations of methane continue to rise. At present rates, the additional global warming impact of the methane may significantly negate or even reverse progress in reducing global CO2 emissions. This effect may fatally undermine efforts to meet the target of the 2015 UN Paris Agreement on climate change to limit warming to no more than 2°C.
But strangely, the source of the rising levels of this powerful greenhouse gas is something of a mystery.
Where’s it coming from?
Methane is emitted from both anthropogenic sources (primarily the oil and gas industry and large-scale cattle production) and from natural sources such as wetlands. The table below shows the range of annual emissions from both groups of sources.
By far the largest source of emissions of methane is from wetlands. Emissions from the oil and gas industries and from livestock are about equal in second place.
The article in the American Geophysical Union offers three possible explanations for the global increase in atmospheric levels of methane:
1. An increase in biogenic emissions—either from wetlands, ruminants, or waste or a combination of all three. The AGU article memorably adds that “a cow is a walking wetland at 37°C”.
2. A rise in emissions from the use of natural gas and oil—although this would have had to have taken place with a concurrent reduction in emissions from biomass burning: the only way to explain the change in the isotopic signature of the increase in methane concentrations.
3. The oxidative capacity of the atmosphere (meaning its ability to oxidise methane into carbon dioxide) has declined.
The third hypothesis, although possible, is thankfully reckoned to be unlikely.
Since it is well documented that fossil fuel emissions of methane have been rising, a first response might be to assume that the increase in methane emissions is primarily due to increased production from the oil and gas sector, but the report disputes this assessment. The increase in emissions seems to be centered in the lower latitudes—which doesn’t align with the location of the major fossil fuel operations. This also rules out the methane released from warming permafrost in the Arctic regions.
The report notes that although fossil fuel emissions are rising, they are actually falling as a proportion of total methane emissions. The inference is that emissions from ruminants and wetlands have been increasing faster than emissions from fossil fuels.
It is well known that the number of cattle being grown for beef production has increased significantly over last several decades  This rise in the number of cattle raised for beef is likely to be a contributing factor. But what about the wetlands? Here there is the worrying possibility of a previously unrecognised positive feedback loop.
Tropical wetlands emissions respond quickly to warmth and increased precipitation. Flooding can be significant in expanding their surface area and hence emissions of methane, and this may partly explain global methane growth in 2014 – 2018. Methane emissions rise exponentially with increasing temperatures and linearly with increasing wetland area.
The extensive wetlands in Bolivia had extreme flood events in early 2014, filling wetlands before the onset of intense heat in 2014. Growth in 2015 took place in the powerful 2015-206 El Nino, one of the strongest on record. Methane emissions may have grown as biogenic sources responded to both warmth and flooding. Similarly 2016 was again a year of record warmth and the sustained methane rise in 2016, while not as strong as in the preceding two years may also be primarily a biogenic response to the third successive increase in global temperatures.
The article notes that the data are inadequate to reach a firm conclusion about the sources of the increased emissions. However, the observations are compatible with an increase in overall fossil fuel emissions if this increase has coincided with a shift from coal to natural gas, and/or a synchronous strong increase in emissions from sources such as wetlands, and/or a decrease in emissions from biomass burning, or all these factors together.
The fact that the origin of these increasing emissions of methane is uncertain only heightens the concern. There is an urgent need to determine the factors behind the rise in levels of atmospheric methane if global warming is to be limited to the target set in Paris in 2015. If the main causes are anthropogenic, they need to be substantially reduced. If the principal cause is the rise in emissions from wetlands, and if this is due to increasing global temperatures, there is once again an urgent need to reduce anthropogenic emissions of all the greenhouse gases.
Campaigns to persuade people to eat less meat are becoming more widespread in North America and Europe, but it is not evident that, globally, much progress will be made. However, reducing emissions from landfill sites should definitely be a priority for municipalities .
To substantially reduce emissions of methane the principal focus has to be on the oil and gas industry–where fugitive emissions of methane from hydraulic fracturing, the gathering pipeline network, gas processing and delivery, are known to be substantial.
Once again, as we consider the urgency of keeping global warming to within 2°C, the need to substantially and permanently reduce the production and consumption of oil and natural gas becomes ever more pressing.
The transition to renewable sources of energy, increased energy efficiency, and the electrification of the transport sector are an absolute priority. The USA and Canada should be taking the lead on this transition—showing the world how clean energy technology, smart demand management, megawatt-scale energy storage systems, and the internet of everything can produce a revolutionary shift in the way developed and developing countries produce and use energy. Instead, the oil and gas industry pours millions of dollars into propping up polluting fossil fuel technologies that poison the air, contaminate groundwater, and hold back the enormous employment opportunities offered by renewable energy and energy efficiency technologies.
For more on the catastrophic impacts of coal, oil and natural gas, follow this link: //climatezone.org/fossil-fuels/
For more background check these sources:
 IPCC 5th Assessment Report p474 Carbon and Other Biogeochemical Cycles. The units in the table are million tonnes of carbon dioxide equivalent per year (MtCO2e/yr)
 It’s a compelling image. I’ll never look at a cow in quite the same way again.
 The AGU paper is by Euan Nisbet et al. Very strong atmospheric methane growth in the 4 years 2014-2017: implications for the Paris Agreement. Accessed at: //agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018GB006009 . See also Methane in the atmosphere is surging and that’s got scientists worried. //www.latimes.com/science/sciencenow/la-sci-sn-methane-atmosphere-accelerating-20190301-story.html
 See the FAO report at : //www.fao.org/3/y4252e/y4252e07.htm
 See the AGU research article cited above
 For example in the book Drawdown: The most comprehensive plan ever propopsed to reverse global warming (ed. Paul Hawken), the management of municipal landfills is one of the top priority actions. See also the post: //climatezone.org/cities-muscle-up/
See also: Sharp rise in methane levels threatens world climate targets: //www.theguardian.com/environment/2019/feb/17/methane-levels-sharp-rise-threaten-paris-climate-agreement
The chart of atmospheric methane concentrations is from NOAA, and be accessed here: //esrl.noaa.gov/gmd/ccgg/trends_ch4/#global_data