EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Top-down Atmospheric Inventories of CO2 and CH4 to Support the Global Stocktakes

David Crisp1, Mark Dowell2, and the CEOS/CGMS WGClimate Greenhouse Gas Task Team*
David Crisp and Mark Dowell and the CEOS/CGMS WGClimate Greenhouse Gas Task Team
  • 1Jet Propulsion Laboratory, California Institute of Technology, Earth and Space Sciences Division, Pasadena, United States of America (
  • 22European Commission, Joint Research Centre, Directorate Natural Resources, Ispra, Italy
  • *A full list of authors appears at the end of the abstract

Parties to the Paris Agreement agreed to report GHG emissions and removals to the United Nations Framework Convention on Climate Change (UNFCCC), which will evaluate progress toward the NDCs through Global Stocktakes (GSTs) conducted at five-year intervals, the first of which is scheduled in 2023. National emission reports are based on “bottom-up” inventories of emissions or removals, derived from statistics such as the number tons of coal or barrels of oil delivered to the commercial, residential, industrial or transportation sectors or the number of acres of forest converted to agriculture. These methods can provide accurate estimates for fossil fuel emissions, but are somewhat less reliable for tracking changes in emissions from agriculture, forestry and other land use (AFOLU) or rapid changes in emissions due to disturbance events, such as hurricanes, drought, wildfires, or climate change.

CO2 and CH4  emissions and removals can also be estimated using high resolution, time-resolved measurements of their concentrations in the atmosphere. These data are analyzed with atmospheric inverse models to derive the flux distribution needed to match the observed atmospheric concentrations in the presence of the winds. These top-down atmospheric inventories complement bottom-up inventories by providing an integrated constraint on emissions from all sources and removals by all sinks. They are less source specific than bottom-up inventories, but are ideal for tracking rapid changes in large emitters or changes in emissions or uptake by forests, crops or the ocean associated with human activities, severe weather or climate change.

The GHG Task Team of the Joint CEOS/CGMS Working Group on Climate has embarked on an ambitious effort to use available ground-based and space based atmospheric measurements of CO2 and CH4 to develop a pilot, top-down atmospheric inventory to support the 2023 GST. CO2 estimates derived from Orbiting Carbon Observatory-2 (OCO-2) data will be combined with surface CO2 measurements from the World Meteorological Organization (WMO) Global Atmospheric Watch (GAW) and its partners to construct a CO2 inventory. CH4 estimates derived from Greenhouse gases Observing SATellite (GOSAT) and the Copernicus Sentinel 5 Precursor (S5P) data will be combined with ground based GHG data to construct a CH4 inventory. These inventories will be compared with results from a parallel effort within CEOS to produce space-based bottom-up inventories for emissions and removals by AFOLU to provide more source specific constraints on emissions and removals.

With the current measurement and modeling capabilities, these pilot inventories may not improve the results delivered by developed nations, where high-quality bottom-up inventories have been produced for decades. They should have greater value in the developing world, where countries have much less experience and resources for developing inventories and/or a much larger fraction of their emissions come from AFOLU. They are also expected to yield much greater insight into the evolution of the natural carbon cycle as it responds to human activities, extreme weather and climate change. The pilot products prepared for the 2023 Global Stocktake will provide the basis for iterative improvements in the products and their delivery to users for future GSTs.

CEOS/CGMS WGClimate Greenhouse Gas Task Team:

Albrecht von Bargen, Akihiko Kuze (JAXA, CEOS WGCV), Frederic Chevallier (LSCE/IPSL), Carole Deniel (CNES), Richard Engelen (ECMWF), Hiroshi Suto (JAXA), Rüdiger Lang (EUMETSAT), Yasjka Meijer (ESA), Paul Palmer (UKSA) Hiroshi Tanimoto (NIES), Alisa Young (NOAA)

How to cite: Crisp, D. and Dowell, M. and the CEOS/CGMS WGClimate Greenhouse Gas Task Team: Top-down Atmospheric Inventories of CO2 and CH4 to Support the Global Stocktakes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13535,, 2021.

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