Abstract
We employed a global high-resolution inverse model to optimize the CH4 emission using Greenhouse gas Observing Satellite (GOSAT) and surface observation data for a period from 2011–2017 for the two main source categories of anthropogenic and natural emissions. We used the Emission Database for Global Atmospheric Research (EDGAR v4.3.2) for anthropogenic methane emission and scaled them by country to match the national inventories reported to the United Nations Framework Convention on Climate Change (UNFCCC). Wetland and soil sink prior fluxes were simulated using the Vegetation Integrative Simulator of Trace gases (VISIT) model. Biomass burning prior fluxes were provided by the Global Fire Assimilation System (GFAS). We estimated a global total anthropogenic and natural methane emissions of 340.9 Tg CH4 yr−1 and 232.5 Tg CH4 yr−1, respectively. Country-scale analysis of the estimated anthropogenic emissions showed that all the top-emitting countries showed differences with their respective inventories to be within the uncertainty range of the inventories, confirming that the posterior anthropogenic emissions did not deviate from nationally reported values. Large countries, such as China, Russia, and the United States, had the mean estimated emission of 45.7 ± 8.6, 31.9 ± 7.8, and 29.8 ± 7.8 Tg CH4 yr−1, respectively. For natural wetland emissions, we estimated large emissions for Brazil (39.8 ± 12.4 Tg CH4 yr−1), the United States (25.9 ± 8.3 Tg CH4 yr−1), Russia (13.2 ± 9.3 Tg CH4 yr−1), India (12.3 ± 6.4 Tg CH4 yr−1), and Canada (12.2 ± 5.1 Tg CH4 yr−1). In both emission categories, the major emitting countries all had the model corrections to emissions within the uncertainty range of inventories. The advantages of the approach used in this study were: (1) use of high-resolution transport, useful for simulations near emission hotspots, (2) prior anthropogenic emissions adjusted to the UNFCCC reports, (3) combining surface and satellite observations, which improves the estimation of both natural and anthropogenic methane emissions over spatial scale of countries.
Highlights
Climate change, a matter of global concern, is driven by the increasing anthropogenic emissions of greenhouse gases (GHGs), currently, in particular, from developing countries
We carried out inversion of methane fluxes for seven years using gas Observing Satellite (GOSAT) satellite observations and surface observations using a high-resolution inverse model National Institute for Environmental Studies (NIES)-TM-FLEXPART-VAR (NTFVAR) that couples a Lagrangian particle dispersion model FLEXPART with a global Eulerian model NIES-TM
Optimization was applied to natural and anthropogenic emissions on a bi-weekly time step, and the results were analyzed on a global country scale
Summary
A matter of global concern, is driven by the increasing anthropogenic emissions of greenhouse gases (GHGs), currently, in particular, from developing countries. Methane (CH4), a major greenhouse gas, has the global warming potential of about 28 times (over a time span of 100 years) higher than carbon dioxide (CO2) [1] and a tropospheric lifetime of about 8–11 years. Methane is oxidized by photochemical reactions to carbon monoxide (CO), carbon dioxide (CO2), water (H2O), and formaldehyde (CH2O). These reactions consume the hydroxyl radical (OH) and are the biggest sink of methane in the atmosphere. Its oxidation produces other important greenhouse gases (such as CO2 and H2O), it contributes to global warming through its infrared absorption spectrum, and it controls the lifetime of many other climate-relevant gases, such as ozone. Due to a heterogeneous network of surface observations, missing in some key regions, satellite observations have been widely used in such studies (e.g., [7,8]), owing to the advantage of the global coverage high-frequency observation
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