In search of better models for explaining atmospheric methane accumulation
A new study examines methane (CH₄), the most significant greenhouse gas with water vapour and carbon dioxide, highlighting that its role in climate change is not yet fully understood. Its warming impact is still debated, particularly when using different measurement methods (like GWP100 vs. GWP*). Since 1750, methane levels have nearly tripled. To address this, the Global Methane Pledge (GMP) was launched at COP26 in 2021, aiming for a 30% reduction in global methane emissions by 2030. However, countries like China, India, and Russia, major emitters, have not joined, so the goal would require signatories to cut their emissions by 60% instead.
Reducing emissions may not lead to reduction in methane levels
A significant portion of methane emissions comes from ruminant livestock, which is responsible for approximately 20% of global emissions. In countries such as New Zealand, Ireland, and Brazil, livestock is the primary source, making it a key area for finding mitigation solutions. However, scientific tools for tracking and modelling methane are still in development. While satellite data and advanced models have become more available in recent years, current in situ data cannot fully pinpoint methane sources and sinks. Models also show significant discrepancies, suggesting that reducing emissions may not lead to a simple reduction in methane levels. Some researchers propose that methane dynamics are non-linear, influenced by complex atmospheric processes. This means that future mitigation strategies may need to move beyond basic emission models to understand better and influence these complex systems.
The mysteries surrounding methane concentrations in the atmosphere
This research discusses ongoing mysteries surrounding methane concentrations in the atmosphere that remain unexplained by current scientific models. For example, methane levels slowed down in the mid-1980s and even paused between 2000 and 2006. After 2006, however, methane levels surged at an unprecedented rate despite stable emissions. One of the key puzzles is why the carbon isotope ratio of methane (C13/C12) shifted after 2000, reversing a 100-year trend. Another unresolved issue is the robust 7-year cycle in methane concentrations, observed in both modern data and ice cores, which suggests an unknown geological driver.
Current models can explain broad seasonal methane patterns, like higher emissions in the Northern Hemisphere during summer, but they struggle to capture the finer fluctuations in methane levels. These minute-by-minute changes might indicate multiple stable states in the atmosphere, each driven by subtle factors that current models don’t account for. Understanding these unexplained cycles and fluctuations is crucial, as it could fundamentally alter our understanding of how methane behaves in the atmosphere.
Additionally, the Palaeolithic methane patterns remain puzzling and are not well understood by current science. For example, during the Younger Dryas (12,800 years ago), methane levels dropped sharply and then rose rapidly despite little change in global temperatures. This dramatic shift is unexplained. Another mystery is the 8% higher methane concentration in the Northern Hemisphere compared to the Southern Hemisphere, a pattern that has persisted since the end of the Ice Age. Additionally, around 5,000 years ago, methane concentrations began rising steadily, defyingthe usual pattern of gradual decline after interglacial periods.
Calling for methane emission reductions may be premature
Since pre-industrial times, atmospheric methane levels have nearly tripled, reaching levels not seen in the last 800,000 years, possibly since the age of the dinosaurs. While human activities, such as fossil fuel emissions, are often blamed, this doesn’t fully explain the rise. Before industrialization, natural sources, such as wetlands and methane-emitting animals, played a significant role. One possibility is that methane’s atmospheric lifetime was shorter in the past, meaning that similar emission levels would have resulted in lower concentrations.
These unexplained shifts suggest that important factors, such as methane’s lifespan and regional influences, are still not well understood. Despite extensive research and data collection, current methane models still face significant challenges and uncertainties. While many call for methane emission reductions, this may be premature, given our limited understanding of the full dynamics of methane in the atmosphere.
Current models fail to capture that methane could behave in a non-linear way
The search for better models is not just about gathering more data but also about improving the conceptual and mathematical frameworks used to understand methane’s behaviour. Many existing models attribute the recent rise in methane and changes in isotopic patterns to increased emissions from tropical wetlands. However, this theory is based more on fitting models to data than on direct evidence, as tropical wetland emissions are difficult to measure due to the presence of cloud cover. These models also don’t account for the possibility that methane is being destroyed at a slower rate rather than being emitted more. Moreover, the models struggle to explain why methane behaviour would be so different today compared to the past when methane levels were more stable.
Current models rely on two main approaches: bottom-up, which estimates emissions, and top-down, which uses satellite data to infer emissions. However, both methods have uncertainties. They also miss short-term or seasonal variations and cannot capture complex dynamics, such as those observed in the past. This is because the models often treat the atmosphere as a linear system, which may not be accurate. A new approach suggests that methane could behave in a non-linear way, with chaotic patterns or sudden shifts, which current models fail to capture. This could explain some of the unexpected changes in methane concentrations. As we struggle to explain both small-scale fluctuations and large anomalies, it may be time to rethink our approach and consider atmospheric methane as part of a more complex, non-linear system that requires new models and tools. As a result, the quest to develop more accurate methane models that can explain all these observations continues.