Context: A 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.
One reason could be an increase in cattle-rearing in Latin America and more emissions from waste in South and Southeast Asia.
Study on Methane Emissions
- Naveen Chandra has been conducting simulations at the Research Institute for Global Change in Japan for the past three years, focusing on recreating the earth's atmosphere over the last 50 years on a supercomputer.
- The concentration of methane in the atmosphere has been a subject of their research. Methane concentration increased until the 1990s, stabilized briefly, then started increasing again around 2007. Current estimates suggest methane levels are three times higher than 300 years ago.
- 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 (GWP is around 80 over 20-year time period).
- Policymakers began focusing on methane recently, leading to initiatives like the 'Global Methane Pledge' at the U.N. climate talks in 2021.
- Recent research by Mr. Chandra's team suggests microbes, particularly archaea called methanogens, are the primary sources of atmospheric methane, not fossil fuel burning.
Sources of methane
- Scientists are increasingly recognising various sources of methane, most of which fit in two categories: biogenic and thermogenic.
- When fossil fuels such as natural gas or oil are extracted from deep within the earth’s crust, thermogenic methane is released.
- Biogenic methane comes from microbial action.
- 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. include biogenic (microbial action) and thermogenic (fossil fuel extraction) activities.
Measuring methane
- If there are fewer carbon-13 atoms than a certain level in a group of 1,000 methane molecules, the methane is from a biological source. If the methane is from thermogenic sources, such as trapped fossil fuels or geological activities, there will be more carbon-13 atoms in 1,000 molecules.
- Mr. Chandra and Mr. Patra, along with international scientists, collected data from 12 monitoring sites worldwide since the 1990s to recreate the atmosphere from 1980 to 2020 on a supercomputer.
- Finally, the team compared their own results with two emissions inventories, called EDGAR and GAINS, and found some discrepancies.
- 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. Their findings disagreed with both inventories.
- Possible reasons for discrepancies include increased cattle-rearing in Latin America and more waste emissions in South and Southeast Asia, Latin America, and Africa, as well as an increase in global wetlands.
- The team's models indicated that methane emissions from fossil fuels declined between 1990 and the 2000s and have been stable since, with microbes producing more methane than fossil fuels.
- Ground models are needed to confirm interpretations of satellite data on methane emissions, as satellites rely on models and are prone to uncertainties.
- Anthropogenic activities such as waste and landfills, rice fields, enteric fermentation, and fossil fuel extraction contribute significantly to methane emissions and should be controlled to reduce methane levels.