Page 29 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

the layer above the troposphere that stretches between 7-20 and 50-60 km altitude, CH4 oxidation produces water vapor (H2O). The corresponding increase in stratospheric H2O contributes to radiative forcing. Finally, after oxidation, the C atom from the original CH4 molecule ends up in CO2 (Myhre et al. 2013). Taking these feedbacks into account, the GWP of CH4 rises to 34 over a 100-year timeframe and 86 over a 20-year timeframe.
Atmospheric methane sources
There is a wide variety of both natural and anthropogenic sources that contribute to the global CH4 budget. Natural CH4 sources include wetlands, freshwater bodies, coastal sediments and oceans, methane hydrates, geological sources, and fauna, each of which may respond differently to a warming climate (Fig. 5).
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30 (22-36)
109
(79-186) 178
219 (175-239)
(155-200)
37 (21-50)
Natural wetlands
Other natural sources Agriculture & waste
Fossil fuels
Biomass & biofuel burning
Figure 5. Overview of the main sources of CH4 emission to the atmosphere based on the top-down budget for the period 2008-2017 from Saunois et al. (2019); these are atmospheric observations within an atmospheric inverse-modeling framework providing averages and ranges (brackets). The CH4 emission numbers are in Tg CH4 yr-1. The natural environments other than wetlands (e.g. freshwaters, oceanic sources, wild animals, wildfires, permafrost) are counted as “Other natural sources”.
The main anthropogenic sources are agriculture and waste, biomass burning, and fossil fuels. These include both methanogenic processes and infrastructural leakage of fossil CH4. Methane from fossil fuel sources has recently been suggested to be a much larger component of the anthropogenic CH4 budget, as much as 60% greater than previous estimates (Schwietzke et al. 2016). These anthropogenic sources are primarily influenced by human population dynamics
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