Fossil CO2 Emissions Mapped Globally

Gridded fossil CO2 emissions and related O2 combustion consistent with national inventories

Matthew W. Jones, Robbie M. Andrew, Glen P. Peters, Greet Janssens-Maenhout, Anthony J. De-Gol, Philippe Ciais, Prabir K. Patra, Frederic Chevallier & Corinne Le Quéré

Read our article about the
Gridded Fossil Emissions Dataset (GridFED)
in Scientific Data (2021)

Intro: ‘Top-down’ Assessment of the Global Carbon Budget

A number of methods are available for monitoring carbon sources and sinks, and they are principally classed into ‘bottom-up’ and ‘top-down approaches’.

‘Bottom-up’ approaches are based on emission inventories and process-based models of the land and ocean sinks. The process-based models use physical and biogeochemical laws to estimate fluxes of CO2 at the surface.

‘Top-down’ methods, including inversion models, use statistical approaches to solve for the combination of sources and sinks that best explain observed changes in atmospheric CO2 concentrations.

The inter-comparison of ‘top-down’ and ‘bottom-up’ estimates is key to quantifying uncertainties in the global carbon cycle, and to identifying the regions and processes from which these uncertainties derive.

Bottom-up (black) and top-down (pink) estimates of the land, ocean and total sinks of CO2 are shown for the tropics, northern and southern hemispheres. Figure from Friedlingstein et al. (2020).

The Need to Map Fossil CO2 Emissions

To work as they do, top-down methods requires two key pieces of information:

  • some prior information about the CO2 fluxes that are occurring at the Earth’s surface.
  • a physical model of atmospheric transport and mixing of CO2

Fossil CO2 emissions are the largest flux in the global carbon budget, and so it is particularly important to map surface fluxes of fossil CO2.

New Fossil CO2 fluxes from ‘GridFED’

The Gridded Fossil Emissions Dataset (GridFED) provides monthly estimates of the surface fluxes of fossil CO2 at a resolution of ~10 km resolution. The latest version (v2020.1) covers the period 1959-2019.

GridFED’s fluxes are consistent at national scales with the emissions estimates of the Global Carbon Project (GCP).

As a result, top-down estimates of fossil CO2 emission can be directly matched with bottom-up inventories, and their estimates of other fluxes – such as the land and ocean sinks – become directly comparable with those from bottom-up estimates.

In the GCP’s 2020 assessment of the global carbon project, the majority of models used GridFED to constrain their estimates of fossil CO2 fluxes. This avoided the need to apply significant corrections to top-down estimates of fossil CO2 emissions estimates and the land CO2 sink.

Key Benefits to Carbon Cycle Science

By better constraining the global emissions of CO2 in top-down models, GridFED has aided the inter-comparison of top-down and bottom-up estimates of the land and ocean sinks.

This enhances compatibility of ‘top-down’ and ‘bottom-up’ estimates, and ultimately improves our ability to quantify and identify uncertainties in the global carbon cycle.

Separation by Fuel Type

GridFED includes estimates of emissions for specific fossil sources, including coal, oil, gas, cement, and international bunker fuels from shipping and aviation.

The emissions estimates for all fuel types are consistent at national scales with the emissions estimates of the Global Carbon Project (GCP).

Seasonality of Emissions

GridFED includes seasonality that is adjusted for weather impacts on fossil CO2 fluxes.

The impacts of summer and winter temperatures on fuel use are included for the power, buildings, manufacturing and transport sectors.

For example, fossil emissions rise during winter due to increased heating requirements in the northern hemisphere. The effects of particularly harsh winter temperatures are also included in GridFED.

Oxygen Uptake

Fossil fuel combustion not only leads to CO2 emission, but also the uptake of O2. This information can be used to enhance top-down methods. Different fuels consume O2 and emit CO2 at different rates, and hence the combination atmospheric measurements with surface fluxes of both O2 and CO2 provides additional information to top-down models. Also, natural uptake through photosynthesis on land has a countering effect: plants release O2 as they trap CO2, also at different ratios to fuel combustion.

All this extra information can be used to help top-down models to disentangle the sources and sinks of CO2 at the land surface.

GridFED provides estimates of oxygen uptake to aid with the top-down quantification of fluxes in the global carbon cycle, and it will also support the construction of a global oxygen budget.