Abstract
Surface observations have recorded large and incompletely understood changes to atmospheric methane (CH4) this century. However, their ability to reveal the responsible surface sources and sinks is limited by their geographical distribution, which is biased towards the northern midlatitudes. Data from Earth-orbiting satellites designed specifically to measure atmospheric CH4 have been available since 2009 with the launch of the Japanese Greenhouse gases Observing SATellite (GOSAT). We assess the added value of GOSAT to data collected by the US National Oceanic and Atmospheric Administration (NOAA), which have been the lynchpin for knowledge about atmospheric CH4 since the 1980s. To achieve that we use the GEOS-Chem atmospheric chemistry transport model and an inverse method to infer a posteriori flux estimates from the NOAA and GOSAT data using common a priori emission inventories. We find the main benefit of GOSAT data is from its additional coverage over the tropics where we report large increases since the 2014/2016 El Niño, driven by biomass burning, biogenic emissions and energy production. We use data from the European TROPOspheric Monitoring Instrument to show how better spatial coverage and resolution measurements allow us to quantify previously unattainable diffuse sources of CH4, thereby opening up a new research frontier.This article is part of a discussion meeting issue ‘Rising methane: is warming feeding warming? (part 1)’.
Highlights
Atmospheric methane (CH4) absorbs and emits radiation at infrared wavelengths and plays a role in determining Earth’s radiative balance
We take advantage of the decadal record of CH4 column data from gases Observing SATellite (GOSAT) to explore the value of these data over and above the information provided by the National Oceanic and Atmospheric Administration (NOAA) in situ network, described in §2, to understand CH4 emissions on global to subcontinental spatial scales
We find broad geographical agreement between a posteriori fluxes inferred from NOAA and GOSAT data, there are differences in the magnitude of trends (e.g. India) and there is widespread discrepancy across tropical South America and Australia
Summary
Atmospheric methane (CH4) absorbs and emits radiation at infrared wavelengths and plays a role in determining Earth’s radiative balance It has a higher global warming potential than CO2; after carbon monoxide it is the principal sink of the hydroxyl radical (OH), which is the major oxidant in the global troposphere, and contributes to the production of tropospheric ozone, another important greenhouse gas. The original purpose of these measurements was to observe large-scale changes driven by natural and anthropogenic emissions, the network has grown with time and a growing body of work (including this study) have used these data to infer continental-scale emission estimates The preponderance of these measurement sites, taking advantage of sites established to collect CO2 measurements, are over North America and Europe and that has implications (a) surface flask-air surface continuous
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