Regional trends and drivers of the global methane budget

Abstract

Methane (CH 4 ) has a large contribution to the global radiative budget and is responsible for about 0.5°C of present global warming over the period 1850 -1900(IPCC, 2021. Methane has a relatively short perturbation lifetime (12.4 years (Balcombe et al., 2018)) and high global warming potential (28-36 times that of CO 2 over a 100year period (IPCC, 2021)). As such, a decline in CH 4 emissions will rapidly reduce global CH 4 concentrations and mitigate the impact of climate change at decadal time scales (United Nations Environment Programme & Climate & Clean Air Coalition, 2021). However, any efforts to target CH 4 emissions reductions require a thorough understanding of the dominant CH 4 sources and sinks and their temporal and regional distribution and trends.Methane is produced in three ways-pyrogenically, thermogenically, or biogenically-from both anthropogenic and natural processes. Pyrogenic sources of CH 4 include biofuel combustion (e.g., wood burning for heating and cooking) and biomass burning (e.g., wildfires and peat fires). All pyrogenic sources produce CH 4 from the incomplete combustion of organic matter. Thermogenic CH 4 is produced from the breakdown of organic matter buried deep within the Earth's crust at high pressure and temperature. Although geological CH 4 is released naturally into the atmosphere through gas seeps, most is released through activities related to the exploration, mining, and transport of fossil fuels (Hmiel et al., 2020;Janssens-Maenhout et al., 2019;Petrenko et al., 2017). The majority of biogenic CH 4 is produced in anaerobic environments by the microbial mediated breakdown of organic matter. These environments include wetlands, inland waters, marine sediments, ruminants such as cattle, rice paddies, manure management and wastewater and landfill systems. Small quantities of CH4 are also produced from the aerobic bacterial metabolization of methylated compounds (e.g., Florez-Leiva et al., 2013) and even photochemically (Li et al., 2020). Counter-balancing these CH 4 sources are three chemically driven atmospheric sinks of CH 4 . The first two reactions with tropospheric OH radicals and tropospheric atomic chlorine account for ~88% (476 -677 Tg CH 4 yr −1 ) and ~2% (1-35 Tg CH 4 yr −1 ) of the total sink, respectively, with a third stratospheric sink (e.g., reaction with O('D), Cl and OH in the stratosphere) accounting for a further ~5% (12-37 Tg CH 4 yr −1 ) (Saunois et al., 2020). However, due to their highly reactive nature, the key reactants are inherently difficult to quantify, driving a significant level of uncertainty in the spatial and temporal distribution of atmospheric sink estimates (Zhao et al., 2019). Many fundamental aspects of the spatial distribution of OH are currently unresolved, for example, estimates of the interhemispheric gradient can vary from 0.85 to 1.4 (NH/SH) depending on the methodology

Global inventory of the stable isotopic composition of methane surface emissions, augmented by new measurements in Europe

“…Users need to define the dominant CH 4 sources impacting an area, as well as the relative source type emission rates. Emission inventories provide such estimates, but top-down approaches are essential to identify potential biases and evaluate the bottom-up approaches (Alvarez et al, 2018; Etiope and 300 Schwietzke, 2019;Rutherford et al, 2021;Stavert et al, 2021).…”

“…While emission estimates are reported at a country-level using statistical indicators, atmospheric inversions, based on observations, can be used to verify the inventories (Houweling et al, 2000;Zavala-Araiza et al, 2015;Henne et al, 2016;Maasakkers et al, 2019). But the results from two approaches, respectively called bottom-up and top-down, are not fully compatible, reflecting a lack in our understanding of the CH 4 cycle (Etiope and Schwietzke, 2019;Saunois et al, 2020;Stavert et al, 2021).…”

“…However, our averages are an indication of the general δ 13 C signatures from all measurements until now. Because of the high heterogeneity of the δ 13 C of CH 4 from fossil fuel related activities, and the temporal variations in the production from the different regions(Stavert et al, 2021; US Energy Information Administration, 2021;Lan et al, 2021), it is important to keep a relatively large uncertainty when estimating in the global signature of fossil fuel emissions.In section 2.4, we have shown the use of δ 13 C CH4 to distinguish fossil fuel emissions in western Europe, and the need for δ 2 H CH4 measurements in central and eastern Europe. In the global database, most fossil fuels records (83.5%) have δ 2 H CH4 values >-250 ‰.…”

Methanogenesis and Methane Oxidation in Paddy Fields under Organic Fertilization

“…Regionally, Mainland China and the Middle East saw a significant increase in methane emissions from 2000 to 2017, mainly due to coal mines, waste, and livestock. Europe, South Korea, and Japan decreased methane emissions due to reduced waste and fossil fuel use [39].…”

“…Studies related to methane production and emission [33,39,40] as well as methanogens and methanotrophic bacteria [41][42][43][44][45][46] and methane transformations in various environments such as wetlands are actively conducted [47][48][49][50][51]. To reduce greenhouse gas emissions, the carbon sequestration ability of the soil itself and CO 2 fixing and carbon sequestration in grassland or rice paddies have recently attracted attention [24,[52][53][54].…”