Revisiting the Global Methane Cycle Through Expert Opinion

• Published in: Earth's future 2024-06, Vol.12 (6), p.n/a
• Main Authors: Rosentreter, Judith A., Alcott, Lewis, Maavara, Taylor, Sun, Xin, Zhou, Yong, Planavsky, Noah J., Raymond, Peter A.
• Format: Article
• Language: English
• Subjects: Anthropogenic factors; Budgets; Climate change; Climate change mitigation; Confidence intervals; Emissions; expert opinion; Fossil fuels; Global warming; greenhouse gas; Greenhouse gases; Human impact; Methane; Methane budget; Methane cycle; methane sinks; Methane sources; methane uncertainty; Parameter uncertainty; Permafrost; Public policy; Questionnaires; Vegetation; Wetlands
• ISSN: 2328-4277; 2328-4277
• DOI: 10.1029/2023EF004234

An accurate quantification of global methane sources and sinks is imperative for assessing realistic pathways to mitigate climate change. A key challenge of quantifying the Global Methane Budget (Saunois et al., 2020, https://doi.org/10.5194/essd‐12‐1561‐2020) is the lack of consistency in uncertainties between sectors. Here we provide a new perspective on bottom‐up (BU) and top‐down (TD) methane uncertainties by using an expert opinion analysis based on a questionnaire conducted in 2021. Expectedly, experts rank highest uncertainty and lowest confidence levels in the Global Methane Budget related to natural sources in BU budgets. Here, we further reveal specific uncertainty types and introduce a ranking system for uncertainties in each sector. We find that natural source uncertainty is related particularly to driver data uncertainty in freshwater, vegetation, and coastal/ocean sources, as well as parameter uncertainty in wetland models. Reducing uncertainties, most notably in aquatic and wetland sources will help balance future BU and TD global methane budgets. We suggest a new methane source partitioning over gradients of human disturbance and demonstrate that 76.3% (75.8%–79.4%) or 561 (443–700) Tg CH4 yr−1 of global emissions can be attributed to moderately impacted, man‐made, artificial, or fully anthropogenic sources and 23.7% (20.6%–24.2%) or 174 (115–223) Tg CH4 yr−1 to natural and low impacted methane sources. Finally, we identify current research gaps and provide a plan of action to reduce current uncertainties in the Global Methane Budget. Plain Language Summary To effectively address climate change, it's crucial to gain a better understanding of the difficulties involved in estimating global methane sources and sinks. One of the key challenges in this process are the varying levels of uncertainty associated with different sectors responsible for methane emissions and methane uptake. In this study, we conducted a survey to gather expert opinions regarding the uncertainty of methane data. The experts highlighted that the Global Methane Budget has the highest uncertainty and lowest confidence levels when it comes to natural sources in the bottom‐up budgets. This uncertainty primarily stems from uncertain data related to natural sources like freshwater, vegetation, and coastal/ocean areas, as well as the parameters used in wetland models. We show that 76.3% of all global methane emissions are related to human‐impact or fully man‐made. Additionally,