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Reactive halogens increase the global methane lifetime and radiative forcing in the 21st century
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Methane (CH4) is a greenhouse gas with the second-largest contribution to global warming after CO2. Unlike the inert gas CO2, CH4 actively participates in atmospheric chemistry. A better understanding of the global CH4 budget (i.e., sources and sinks) is vital to constrain its atmospheric levels and radiative forcing in the 21st century, as well as to guide climate mitigation efforts, e.g., policies to fulfil the Paris agreement. Previous studies focus on CH4 sources with less attention on its losses, which have been reported to be the direct reactions with the OH radical (the dominant sink) and Chlorine atoms (Cl). Current chemistry-climate models tend to underestimate the lifetime of CH4, suggesting uncertainties in its sources and sinks.
Over the past decades, a large and growing body of observational evidence has demonstrated the ubiquitous existence of…