data with broadly-calibrated emissions factors (Crippa et al. 2020; Solazzo et al. 2021). Policy analysts can use spatial inventory data to identify emissions-intensive areas, trace the emissions to specific subsectors, and perform benefit-cost assessments of alternative technologies for emissions reduction.

Satellite-based methane measurements have the potential to inform priority-setting by supplementing “bottom-up” emissions estimates with direct observations. The value added by the satellite-based approach depends on the comparative accuracy of the estimated sectoral outputs and emissions intensities used by existing inventories. This paper initiates a round of empirical assessments with a comparative study for irrigated rice production. It combines atmospheric CH4 concentrations from our Sentinel-5P database with georeferenced data on paddy areas, production yield and planting seasons from IFPRI (2019) and RiceAtlas (Laborte et al. 2017). The results are compared with agricultural CH4 emissions estimates from the EDGAR database.

The remainder of the paper is organized as follows. Section 2 describes our global methane database, and Section 3 introduces the application to irrigated rice production. Section 4 describes the computation of CH4 concentrations over irrigated rice production areas. Section 5 incorporates IFPRI and RiceAtlas data to study the relationship between the scale of irrigated rice fields and local methane concentrations, and to identify outlier areas where methane concentrations deviate significantly from scale-based expectations. Section 6 incorporates EDGAR emissions estimates and analyzes their relationship to the scale of irrigated fields. Section 7 assesses the “value added” of S5P by identifying outlier areas where S5P methane concentrations deviate significantly from expectations based on field scale and EDGAR estimates. Section 8 integrates the S5P concentration data and IFPRI production data to develop an index of local methane intensity (methane emissions per ton of rice produced). Section 9 summarizes and concludes the paper.

# **2.  The Atmospheric Concentration of Methane**

# **2.1 Global Warming Potential**

The concentration<sup>2</sup> of atmospheric methane (CH4) was 1,857 ppb in 2018, about 2.6 times greater than its estimated level in 1750 (Saunois et al. 2020). The primary sources of the increase are emissions from agriculture, fossil fuel production and use, and waste disposal (Ciais et al. 2013). Atmospheric CH4 is a potent greenhouse gas, with a global warming potential 28 times the potential of CO2<sup>3</sup> (Myhre et al. 2013). Although current anthropogenic CH4 emissions are only 3% of anthropogenic CO2 emissions by volume, they are accountable for 23% of the radiative forcing in the lower atmosphere since 1750 (Etminan et al. 2016). CH4’s average 9-year duration in the atmosphere (Prather et al. 2012) is dwarfed by the multi-century duration of CO2. By implication, rapid CH4 emissions reduction should have high priority because it can reduce

> 2 Technically, the surface dry air mole fraction.

> 3 This ratio is calculated for a 100-year time horizon and without considering climate feedbacks.

2