Nitrous oxide (N2O) is a major greenhouse gas with a global warming potential of approximately 300 in a 100 year time horizon [Forster et al., 2007]. N2O is also involved in stratospheric ozone depletion [Crutzen, 1970], and its emissions weighted by ozone‒depletion potential currently dominate those of ozone‒depleting substances following the decline of the chlorofluorocarbon emissions [Ravishankara et al., 2009]. Microbial production in soils is considered to be the largest producer of N2O [Davidson, 2009], contributing nearly 60% to the total [Werner et al., 2007]. Measurements of atmospheric N2O mole fractions collected at various stations in the world since the late 1970s show an increase (with a drop in 1992–1993) at a rate of 0.2%–0.3% per year [Weiss, 1981; Prinn et al., 1990; Nevison et al., 1996; Khalil et al., 2002], and the recent increase in the atmospheric mole fractions has led to an estimation of the anthropogenic source (including agricultural soil) to be approximately 1/3 of the total N2O source [Khalil et al., 2002; Hirsch et al., 2006; Nevison et al., 2007]. Despite a large number of studies in the last several decades examining the cause of this increase as well as estimating the magnitude and the source of N2O emissions, large uncertainties still remain [Nevison et al., 1996; Forster et al., 2007; Huang et al., 2008]. Understanding and quantifying N2O fluxes from global soil in long time series is therefore an urgent task for predicting the future climate change and stratospheric ozone depletion [Forster et al., 2007].
 The bacterial processes of nitrification and denitrification are considered to be the most important source of N2O emissions from soil [Davidson et al., 2000]. Microbial biomass decomposes in soil and creates ammonium ion (), which is converted to nitrate () by the nitrification process in aerobic conditions. In this process, N2O is produced and a part of it is emitted to the atmosphere. During multistage redox reactions of denitrificaiton from to N2, N2O is also generated and a small fraction of that can escape from the soil before further reduction to N2[Goreau et al., 1980; Bremner and Blackmer, 1981; Poth and Focht, 1985; Nevison et al., 1996]. These nitrification and denitrification processes have been stimulated further by the increasing use of synthetic nitrogen fertilizers for food production [Davidson, 2009; Park et al., 2012].
 The mechanism of N2O emissions from soil has been studied in several process models [e.g., Li et al., 1992, 2000; Bouwman et al., 1993; Potter et al., 1996; Xu et al., 2003; Werner et al., 2007], but so far, no model has been able to capture both the long‒term variability of soil N2O emissions as well as the details of seasonality and interannual variability at the global grid level. In this paper we present and evaluate an N2O emissions module added to the Community Land Model with coupled Carbon and Nitrogen cycles version 3.5 (CLM‒CN v3.5), in order to better understand the seasonality and interannual variability of global natural soil N2O emissions.
 CLM v3.5 is the land component of the Community Earth System Model, which is designed to study interannual and interdecadal variability, paleoclimate regimes, and projections of future climate change [Collins et al., 2006; Oleson et al., 2008]. With a coupled carbon‒nitrogen (CN) biogeochemical model [Thornton et al., 2007; Randerson et al., 2009; Thornton et al., 2009] based on the terrestrial biogeochemistry Biome‒biogeochemical cycle model [Thornton et al., 2002; Thornton and Rosenbloom, 2005], the CLM‒CN v3.5 model represents land terrestrial water and carbon (C) and nitrogen (N) balances, and it is nominally run at an hourly time scale [Lawrence et al., 2011].
 Here we add a new N2O emissions flux module within CLM‒CN v3.5 to create CLMCN‒N2O. CLMCN‒N2O includes all of the Denitrification‒Decomposition (DNDC) Biogeochemistry Model [Li et al., 1992] components to capture both the nitrification and denitrification processes that are important producers of N2O. CLMCN‒N2O estimates produced by decomposition and calculates N2O production through nitrification and denitrification depending on soil temperature and moisture, utilizing the soil C and N concentrations in soil as calculated by CLM‒CN v3.5.
 The main objectives of this study were (1) to build and validate the soil N2O emissions module in CLM‒CN v3.5, (2) to quantify global natural soil N2O emissions between 1975 and 2008, and (3) to understand the effects of meteorology on seasonal and interannual natural soil N2O emissions. In this paper, the term “natural” soil N2O emissions refers to those from soil where we assume no application of artificial nitrogen fertilizers on the land. We therefore do not exclude any land areas from our model, but our emissions do not include agricultural emissions that are due to fertilizers. We first estimate the global natural N2O emissions from 1975 to 2008 and analyze the variability in annual and seasonal emissions in different regions. We use four separate forcing data sets (described in section 2.2) to compare our N2O emissions estimates due to given meteorological conditions. Next, we evaluate CLMCN‒N2O by comparing our estimated N2O emissions with observations from field measurements in the Amazon, the USA, Costa Rica, Indonesia, Australia, Kenya, and China. Finally, we analyze the impact of meteorology on regional emissions by paying special attention to the role of El Niño–Southern Oscillation (ENSO).
 The paper is organized as follows. Section 2 describes the methodologies we use, including the model development and the observational data for this study. Section 3 explains the model simulation and the comparison with existing emissions inventories. Section 4 provides the comparison of our model results with observations at 25 sites. Section 5 discusses the interannual variability of our modeled soil N2O emissions in relation to ENSO and some accounts on uncertainties in our model estimates. We present a summary of results and conclude in section 6.