Abstract
The global warming gasses, water vapour, carbon dioxide, methane, and nitrous oxide all cycle differently through the environment but are bundled into CO2 equivalents. This discussion paper explores aspects of methane’s cycling through the environment. The difficulty in establishing a valid CO2 equivalence begins at the molecular level, based on varying estimations for its persistence in the environment. CO2 equivalence calculations for methane range from 28 to 100 times. The difficulty of establish valid equivalence is compounded by the variety of ways that methane interacts in the soil, vegetation, in ruminants, and the troposphere, including climatic influences. Ruminants raised on diverse actively growing pastures, with practices that build soil fertility and structure might reduce methane levels significantly, or even be a methane sink. A more nuanced understanding of how soil, pasture and animal husbandry practices has potential to reveal how methane levels in any specific environment might vary. This is especially important when CO2 equivalence is used to determine policy. III-conceived policy could disadvantage some farmers, misguide investment decisions, and overlook opportunities to mitigate and adapt to climate change.
Generated Summary
This technical report explores the complexities of methane cycling in the environment, focusing on sources, sinks, and the challenges of establishing accurate CO2 equivalence. The paper examines the role of ruminants, soil, vegetation, and the troposphere in methane dynamics. It highlights the difficulties in determining valid CO2 equivalence due to varying estimations of methane’s persistence and the multiple ways methane interacts within the environment. The report aims to provide a nuanced understanding of methane levels in specific environments and emphasizes the potential for practices like diverse, actively growing pastures to reduce methane emissions. The paper also discusses the implications of policy decisions based on CO2 equivalence, the role of methane in climate change, and the need for better-informed policies that consider the complexities of methane sources and sinks.
Key Findings & Statistics
- The global warming potential (GWP) of methane over 100 years is estimated between 25 and 30 equivalents of one CO2 molecule (eq CO2). Over the shorter period of 20 years, methane’s global warming potential is much higher, between 72 and 85 eq CO2.
- Globally, atmospheric concentrations of methane have almost tripled since preindustrial times, rising from 719ppb in 1750 to 1,858ppb in 2018.
- Natural sources of methane emissions total approximately 238 Tg CH4/yr, while anthropogenic sources account for 562 Tg CH4/yr.
- Anthropogenic sources include: coal mining (36 Tg/yr), gas & oil industry emissions (61 Tg/yr), landfills and waste (54 Tg/yr), and agricultural emissions (ruminants 84Tg/yr., rice agriculture 54 Tg/yr., biomass burning 47 Tg/yr.).
- World Bank data calculates total global methane as 8.17 million kt CO2 equivalents, and agricultural emissions at 3.51 million kt CO2 equivalents for 2018.
- Global emissions increased by 54% between 1970 and 2018 while agricultural emissions increased 22%.
- Total CO2 equivalent emissions increased by 69% from 27.05 to 45.87 million kt.
- Animals including humans emit some 100-220 Tg of methane per year.
- Ruminants emit 66-90 Tg of this.
- Cattle emit some 64 Tg of this.
- The global population of cattle decreased slightly from 1,004.72 million in 2012 to 1,000.97 million in 2021.
- For the period 2008 to 2017, there is a variation of 156 Tg CH4 Yr¯¹ between top-down (215 Tg CH4 Yr¯¹) and bottom up (371 Tg CH4 Yr¯¹) sources of methane.
- Sinks vary by 88 Tg CH4 Yr¯¹ (514 to 602 Tg CH4 Yr¯¹).
- The role of oceanic methane hydrates, by far the largest reservoir of stored methane, remains mostly unknown.
- The study by the Climate Council stated that calculations of the carbon equivalence vary between 28 and 100 times.
Other Important Findings
- The report highlights the role of ruminants in methane emissions, noting that they are a significant source. However, it also suggests that good land management with grazing animals may open up an overlooked methane sink: healthy pastures.
- The document discusses the impact of different agricultural practices on methane fluxes, noting that soil and pasture management practices influence methane fluxes.
- The report emphasizes the importance of understanding methane sinks, with the largest being tropospheric hydroxyl radicals. The document notes the significant uncertainty in estimates of the sinks, highlighting the need for further research.
- The document references studies on the effects of land use changes and agricultural practices, such as monoculture feed production, on methane sinks.
- It emphasizes the need to better understand the underlying processes that affect methane, especially the sinks, and to address climate policies that consider the remaining uncertainty.
- The paper suggests that the role of vegetation plays in the OH cycles, the biggest sink for methane, and vegetation-driven OH directly removes methane emissions from grazing herds.
- The document notes that tannins reduce enteric methane and confer other benefits including improving nitrogen utilization, reducing nitrogen waste and improved animal, wool and milk production.
- The document also notes that the natural processes for cycling methane are breaking down.
Limitations Noted in the Document
- The document points out the difficulty in establishing a valid CO2 equivalence due to varying estimations for methane persistence in the environment and the diverse ways methane interacts within the soil, vegetation, and the troposphere.
- The report highlights the challenges in quantifying atmospheric methane because of multiple variables.
- The document acknowledges uncertainties in the estimation of methane sinks, specifically the tropospheric OH radicals, which remain highly uncertain.
- The paper indicates that the current estimates of methane emissions are not a solid basis for calculating levies or setting zero-carbon targets due to the unsettled nature of the science and the coarse calculations in national or global-level modeling.
- The report also notes that the association between the decline of green grasslands and the decrease in hydroxyl methane sink processes is not a proven direct causal effect.
Conclusion
The report concludes that policy development is significantly influenced by public discourse and that the complexity of methane cycling requires a shift in focus. The study highlights the instability of the CO2 equivalence as a foundation for modeling, and suggests caution to policymakers before taking action on methane emissions in ruminant agriculture. It emphasizes the need to improve land stewardship and animal husbandry practices to minimize methane emissions, optimize conditions for rapid recycling, and improve food quality. The report also suggests that there is more to know about the complex dynamic natural processes and academic uncertainty must not impede the action to reduce anthropogenic causes of climate change. The study emphasizes the need to look at the issue of climate change and agricultural practices. The report suggests that there needs to be a better understanding of the link between atmospheric processes. It recommends that the science provided should provide sufficient caution to policy makers before acting on any blanket approach to methane emissions in ruminant agriculture, cautioning that rushed policy changes could be counter-productive. Before even considering charging for emissions, it suggests there is a lot of scope for improving land stewardship and animal husbandry practices to minimize methane emissions, optimize conditions for rapid recycling, improving productivity and food quality.