Page 246 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

Chapter 11. Integration and outlook
Figure 1. CH4 climate feedback schematic showing the feedback mechanisms and interactions discussed in the review of Dean et al. (2018). Each feedback mechanism (within the central circle) is forced by climate change, altering CH4 emissions to the atmosphere. Direct CH4 feedbacks are indicated by the bottom arrows, and indirect feedbacks are within the circle. After production, CH4 is exposed to oxidation before being emitted to the atmosphere, where it is then consumed by the atmospheric CH4 sink (tropospheric OH radicals). The amount of CH4 in the atmosphere is known as the atmospheric CH4 burden. Prior to its oxidation in the atmosphere, CH4 causes radiative forcing (the greenhouse effect) that feeds back to the overall climate forcing (completing the positive CH4 climate feedback loop shown in the top loop).
Our increased knowledge on CH4 dynamics in the atmosphere over the last decades has led to the conclusion that the radiative forcing of CH4 equals roughly 60% of the contribution of CO2 (Myhre et al. 2013; Etminan et al. 2016). The major difference is found in its short atmospheric half-life of 9.1 years versus 27-100 years for CO2, although it is hardly feasible to estimate a single lifetime of CO2 due to the many variable components involved (Stocker et al. 2013). An important message of the atmospheric GHG lifetimes is that decreases in CH4 sources can have rapid, positive effects on the global climate. Therefore, CH4 is considered as an important target
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