Methanogenesis: Part 5: Methane Budgeting and Determining Source Contributions

     The multiple new discoveries about methanogenesis and its variability mean that methane budgeting and the determination of source contributions are more complex than previously thought. The main conclusion is that more methane is being naturally produced than previously thought, and this is reflected in previous studies that ruled out oil & gas systems as responsible for the increase in atmospheric methane. While oil & gas may not be responsible, several other anthropogenic activities contribute to the increase. These include increased amounts of landfill gas and agricultural methane sources, increased nutrient availability in coastal zones due to fertilizer runoff, spreading of coastal and possibly deep-sea methanogens via ocean currents. Below is a graph of global atmospheric methane increase since 1983.

     Last year, I wrote about research that confirmed that the increase in atmospheric methane was mainly biogenic rather than thermogenic, strongly suggesting that leaks from oil & gas systems were not driving the increase. The authors and I concluded that the main sources were landfills, cows, and wetlands, including rice paddies. The first two are anthropogenic, and while wetlands are mostly natural, they can be anthropogenic as well. However, more recent research suggests that other coastal and oceanic sources could be important factors as well, which need to be better quantified.   

     In the first parts of this multiple-part post, I explored several possible explanations or contributors to the increased atmospheric biogenic methane. These include a new understanding of coastal processes involving seaweed and seagrasses, coastal fertilization, a better understanding of the proliferation and mobility of deep-sea methanogens, growth and spread of methanogens via ocean currents, warmer oceans, glacial meltwater, and seafloor disturbance, and environmental fluxes of component availability for methanogenesis. There are also other sources to quantify, such as methane released from melting permafrost, tropical wetlands, and other anthropogenic and non-anthropogenic sources. We still don’t know what processes have contributed in what percentages to the increase in atmospheric biogenic methane. That will require further research and monitoring. We can measure global atmospheric methane much like we measure atmospheric CO2. Thus, we know by how much biogenic methane is increasing, but now we have to work backwards and determine the source attributions of each possible mechanism of increase.

     While the accelerated increase since around 2015 is concerning, I am unaware of any explanation for the lack of increase from about 1995 to about 2005. Knowing why there was no increase during that time period might shed more light on source attributions. According to the graph, there was also an acceleration in the 1980s comparable to the acceleration now. The reason for those changes is not explained either. We simply need to know more in order to make those determinations.

     The Global Carbon Project does global methane budgeting. However, with all this new information about methanogenesis, their numbers, as shown below, may be due for re-analysis.

 

  

References:

 

Global atmospheric methane concentrations. Our World in Data. Global atmospheric methane concentrations

Global Carbon Project: Briefing on key messages for Global Methane Budget 2024. Global CarboN Project. September 10, 2024. Key Highlights_CH4 Budget_2024

Methanogenesis: Part 1: Discovery of New Oxygen-Tolerant Methanogens May Partially Explain Recent Increase in Biogenic Atmospheric Methane: Coastal Methanogenesis is More Abundant Than Thought and Implications for Methane Budgeting. September 3, 2025. Blue Dragon Energy & Environmental Blog 2.0: Methanogenesis: Part 1: Discovery of New Oxygen-Tolerant Methanogens May Partially Explain Recent Increase in Biogenic Atmospheric Methane: Coastal Methanogenesis is More Abundant Than Thought and Implications for Methane Budgeting

Methanogenesis: Part 2: Deep-Sea Methanogens and Chemosynthesis: Quantifying Its Contribution. September 4, 2025. Blue Dragon Energy & Environmental Blog 2.0: Methanogenesis: Part 2: Deep-Sea Methanogens and Chemosynthesis: Quantifying Its Contribution

Methanogenesis: Part 3: Fingerprinting Methane by Isotopes Reveals Sources and CRISPR Gives Insights into Enzyme Mechanisms for Methanogenesis. September 4, 2025. Blue Dragon Energy & Environmental Blog 2.0: Methanogenesis: Part 3: Fingerprinting Methane by Isotopes Reveals Sources and CRISPR Gives Insights into Enzyme Mechanisms for Methanogenesis

Methanogenesis: Part 4: Growth and Spread of Methanogens Due to Fertilization, Ocean Currents, Warmer Oceans, Melting Glaciers, and Deep-Sea Mining. September 4, 2025. Blue Dragon Energy & Environmental Blog 2.0: Methanogenesis: Part 4: Growth and Spread of Methanogens Due to Fertilization, Ocean Currents, Warmer Oceans, Melting Glaciers, and Deep-Sea Mining