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. Soil bacteria known as methanotrophs are the sole biologicalsink for atmospheric methane (CH 4) , a potent greenhouse gas that isresponsible for ∼  20 % of the human-driven increase in radiativeforcing since pre-industrial times. Soil methanotrophy is controlled by aplethora of factors, including temperature, soil texture, moisture andnitrogen content, resulting in spatially and temporally heterogeneous ratesof soil methanotrophy. As a consequence, the exact magnitude of the globalsoil sink, as well as its temporal and spatial variability, remains poorlyconstrained. We developed a process-based model (Methanotrophy Model; MeMov1.0) to simulate and quantify the uptake of atmospheric CH4 by soils atthe global scale. MeMo builds on previous models by Ridgwell et al. (1999)and Curry (2007) by introducing several advances, including (1) a generalanalytical solution of the one-dimensional diffusion–reaction equation inporous media, (2) a refined representation of nitrogen inhibition on soilmethanotrophy, (3) updated factors governing the influence of soil moistureand temperature on CH4 oxidation rates and (4) the ability to evaluatethe impact of autochthonous soil CH4 sources on uptake of atmospheric CH4 . We show that the improved structural and parametric representationof key drivers of soil methanotrophy in MeMo results in a better fit toobservational data. A global simulation of soil methanotrophy for the period1990–2009 using MeMo yielded an average annual sink of33.5  ±  0.6 Tg  CH4  yr −1 . Warm and semi-arid regions(tropical deciduous forest and open shrubland) had the highest CH4 uptake rates of 602 and 518 mg  CH4  m −2  yr −1 , respectively.In these regions, favourable annual soil moisture content ( ∼  20 %saturation) and low seasonal temperature variations(variations  ∼  6  ∘ C) provided optimal conditions for soilmethanotrophy and soil–atmosphere gas exchange. In contrast to previous modelanalyses, but in agreement with recent observational data, MeMo predicted lowfluxes in wet tropical regions because of refinements in formulation of theinfluence of excess soil moisture on methanotrophy. Tundra and mixed foresthad the lowest simulated CH4 uptake rates of 176 and182 mg  CH4  m −2  yr −1 , respectively, due to their markedseasonality driven by temperature. Global soil uptake of atmospheric CH4 was decreased by 4 % by the effect of nitrogen inputs to the system;however, the direct addition of fertilizers attenuated the flux by 72 % inregions with high agricultural intensity (i.e. China, India and Europe) andby 4–10 % in agriculture areas receiving low rates of N input (e.g.South America). Globally, nitrogen inputs reduced soil uptake of atmospheric CH4 by 1.38 Tg yr −1 , which is 2–5 times smaller thanreported previously. In addition to improved characterization of thecontemporary soil sink for atmospheric CH4 , MeMo provides an opportunityto quantify more accurately the relative importance of soil methanotrophy inthe global CH4 cycle in the past and its capacity to contribute toreduction of atmospheric CH4 levels under future global changescenarios.

Soil Methanotrophy Model (MeMo v1.0): a process-based model to quantify global uptake of atmospheric methane by soil