Introduction to Methane Emissions
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.
It wasn’t until recently that policymakers began to focus on methane vis-a-vis addressing global warming. At the U.N. climate talks in 2021, member countries launched the ‘Global Methane Pledge’ to cut the gas’s emissions and slow the planet’s warming. Yet our understanding of methane also continues to evolve.
The research team recently reported that microbes have been the biggest sources of methane in the atmosphere, not the burning of fossil fuels.
They conducts simulations at the Research Institute for Global Change in Japan using a supercomputer and aims to recreate the Earth's atmosphere over the past 50 years. Also, they examines methane concentration in the atmosphere during 2019-2020.
Historically, methane concentration increased until the 1990s, stabilized briefly, then began rising again around 2007. Current atmospheric methane levels are three times higher than they were 300 years ago.
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.
Modeling Methane Emissions
Description of the modeling approach using a supercomputer to simulate atmospheric changes over the last 50 years.
According to the study, carbon-13 is key. (Atoms of this carbon isotope have 13 nucleons: 6 protons + 7 neutrons.)
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.
The collected methane isotope data was sorted by year and fed into a program developed by the researchers. This program simulated the atmosphere from 1980 to 2020 using a supercomputer, enabling detailed analysis of methane trends over time.
The team compared their simulation results with two emissions inventories, EDGAR and GAINS, and found discrepancies. These inventories reported conflicting trends in methane emissions from oil and natural gas exploration, leading to questions about the accuracy of existing data.
To reconcile discrepancies, the researchers estimated methane emissions from various
sources, including rice fields, wetlands, dairy farms, and biomass burning. However, when they ran their atmosphere models using this additional data, they found that total methane emissions exceeded production estimates.
Contrary to expectations, the models indicated a decline in methane emissions from fossil fuels between 1990 and the 2000s, with stability thereafter. Additionally, microbial methane production surpassed emissions from fossil fuels, challenging previous assumptions about methane sources.
Reasons for Discrepancies: The study suggests that increased cattle-rearing in Latin America and
elevated waste emissions in South and Southeast Asia, Latin America, and Africa could contribute to discrepancies in methane emissions - The proliferation of wetlands worldwide is also cited as a potential factor - Limitations of Satellite Data
Way forward
Call for Local Observations: researcher underscores the importance of local measurements to accurately assess methane sources, particularly from specific locations such as wetlands and rice fields. Ground-based observations are essential for refining global emission estimates and guiding targeted mitigation efforts.
Anthropogenic Control: The study emphasizes the role of anthropogenic activities, such as waste and landfill management, agricultural practices, and fossil fuel extraction, in methane emissions. Controlling these activities is crucial for mitigating methane emissions and addressing climate change concerns.
COMMENTS