News Excerpt: 

An intensive modelling study has found methane emissions from fossil fuels declined between 1990 and the 2000s and have been stable since, whereas microbes have been producing more methane of late.

Evolving understanding

• Methane is the second most abundant anthropogenic greenhouse gas after carbon dioxide (CO2) but it warms the planet more. 
• Over a century, methane has a global warming potential 28 times greater than CO2, and even higher over shorter periods like two decades.
• At the U.N. climate talks in 2021, member countries launched the ‘Global Methane Pledge’ to cut gas emissions and slow the planet’s warming.
• Yet our understanding of methane also continues to evolve.

The sources of methane

• Scientists are increasingly recognising various sources of methane, most of which fit into two categories: 
• Biogenic: Biogenic methane comes from microbial action.
• Thermogenic: When fossil fuels such as natural gas or oil are extracted from deep within the earth’s crust, thermogenic methane is released
• The microbes that produce methane are archaea single-celled microorganisms distinct from bacteria and eukaryotes — and are called methanogens. 
• They thrive in oxygen-deficient environments, such as the digestive tracts of animals, wetlands, rice paddies, landfills, and the sediments of lakes and oceans.
• Methanogens play a crucial role in the global carbon cycle by converting organic matter into methane. 
• While methane is a potent greenhouse gas, its production by methanogens is an essential part of natural ecosystems. 
• But human activities like agriculture, dairy farming, and fossil fuel production have further increased methane emissions.
• Both biogenic and thermogenic activities produce different isotopes of methane. 
• Tracking the isotopes is a way to track which sources are the most active.

Modelling with a supercomputer:

• According to scientists Carbon-13 isotope is key to determining the source of methane - biological sources have fewer carbon-13 atoms per 1000 methane molecules compared to thermogenic (fossil fuel) sources.
• Scientists collected data from 12 monitoring sites worldwide tracking atmospheric parameters since the 1990s.
•  Then they sorted the methane isotope data by year and ran it through a program they had developed to recreate the atmosphere from 1980 to 2020 on a supercomputer.

Data mismatch: 

• Their findings disagreed with  two emissions inventories,(EDGAR and GAINS)
• EDGAR had reported that methane emissions from oil and natural gas exploration had increased between 1990 and 2020. 
• GAINS had recorded a large “unconventional” rise in emissions since 2006 
• In fact, the models said methane emissions from fossil fuels declined between 1990 and the 2000s and that they’ve been stable since. 
• They also found microbes were producing more methane than fossil fuels.

Need for local data

• A study suggests an increase in cattle-rearing in Latin America and more emissions from waste in South and Southeast Asia. 
• Latin America, and Africa could be potential reasons for the rise in methane levels.
• The study also mentions that the number of wetlands worldwide had increased, which could contribute to the rise in methane levels.
• Studies in the past have pointed to microbes like anaerobic archaea as potentially top contributors of atmospheric methane using satellite data. 
• But according to Scientist “
• Most studies which use satellites cannot measure the actual [changes over time] of methane.” 
• Satellite data is interpreted using models “and thus are prone to uncertainties.” 
• Scientists state that ground models are required to confirm the interpretations from satellite data, and their atmospheric model, 
• while a beginning, needs more targeted measurement and localized measurements to determine the specific sources of methane emissions.
• Emphasizes that to reduce methane levels, anthropogenic activities need to be controlled first.
• waste and landfills, rice fields, enteric fermentation (from cattle), and emissions from oil, gas, and coal.