Region Averaging
One-degree fluxes (Left). The pattern of air-sea exchange of CO2 averaged over the time period indicated, as estimated by CarbonTracker. This exchange represents ocean-to-atmosphere carbon exchange including the physical process of equilibration driving the mean ocean sink and a biological contribution due to photosynthesis and respiration in marine ecosystems. It does not include fossil fuel emissions. Negative fluxes (blue colors) represent CO2 uptake by the ocean, whereas positive fluxes (red colors) indicate regions in which the ocean is a net source of CO2 to the atmosphere. Units are gC m-2 yr-1.

The fluxes in this graphic have a nominal spatial resolution of 1° longitude by 1° latitude, but with a strong influence of air-sea gas transfer velocity modeled at 3° x 2°. Optimization of air-sea flux in CarbonTracker is actually performed on the scale of 30 large regions representing areas of similar physical and biological processes (see thumbnail map on the left side of this page and ecoregion documentation). CarbonTracker estimates only the total weekly flux from each ocean region. The distribution of that total flux onto finer spatial and temporal scales such as those shown here depends on an underlying model of air-sea CO2 exchange. These finer scales are driven primarily by variability of sea-surface wind speed from the 3° x 2° atmospheric transport model. Fluxes on the ocean region scale, without this presumed finer-scale distribution, are shown in the figure at the bottom of this page.

Ocean region uncertainties (Right). Uncertainty of the CarbonTracker estimate of air-sea exchange of CO2, averaged over the time period indicated. The quantity displayed is the one standard deviation uncertainty on estimated fluxes assuming Gaussian errors, in units of gC m-2 yr-1. Darker colors represent areas where the CarbonTracker flux estimate is less certain.

The uncertainties are originally available with weekly time resolution due to the inversion methodology. For monthly and annual averages, we show RMS averages from the weekly information. This scheme neglects temporal covariances. Uncertainties reported here are formal estimates from the inversion technique and do not include all sources of error. Flux uncertainties are among the most difficult quantities to compute, and care should be taken in their interpretation. Formal errors like these generally underestimate the true uncertainty, since they do not take into account all sources of error, like biases in simulated atmospheric transport.

The uncertainties in this graphic are uniformly distributed within each ecoregion (see thumbnail map on the left side of this page and ecoregion documentation). There is no assumed patterning of the uncertainty within ocean regions.

Summary Fluxes for 2001-2018 mean (all units PgC yr-1)
RegionFirst GuessFinal EstimateFire EmissionFossil EmissionTotal Flux
Global-4.88 ± 3.41 -6.62 ± 2.68 2.31 8.84 ± 0.01 4.53 ± 2.68
Global Land-2.26 ± 2.02 -3.62 ± 1.61 2.29 8.19 ± 0.16 6.86 ± 1.61
Global Ocean-2.62 ± 1.60 -3.00 ± 1.33 0.03 0.65 ± 0.17 -2.33 ± 1.33
Summary fluxes. This table shows first-guess, final estimate, and imposed fluxes and associated uncertainties, integrated over the region of interest and averaged over the relevant time period. The "first guess" and "final estimate" fluxes are the sum of land and ocean fluxes over the region of interest, excluding fossil and fire emissions. They represent the prior and posterior, optimized fluxes respectively. Fossil and fire emissions are prescribed in CarbonTracker. The "total flux" is the sum of the final estimate, fossil fuel emissions, and fire fluxes.

Note that fossil fuel emissions can occur over regions characterized as ocean. This is partly due to real emissions from international shipping, and partly due to emissions occurring in coastal land regions that are assigned to the ocean in our coarse 1x1 degree division scheme. The same is true for fossil fuel emissions over non-optimized regions such as ice, polar deserts, and inland seas.

Fluxes at different scales. Left: air-sea exchange of CO2 at 1° x 1°. This is a copy of the figure at the top left of this page. Right: Air-sea flux at the ocean region scale, as natively estimated by CarbonTracker. The fluxes in this graphic are uniformly distributed within each ocean region (see thumbnail map on the left side of this page and ecoregion documentation). The difference between these two figures is that the one on the left uses a model-based estimate of the within-region patterning of flux, whereas the one on the right has even distribution of flux throughout each ocean region. They have the same total flux integrated across each ocean region. Within-region gradients at 3° x 2° (and 1° x 1°) seen on the left are entirely due to the underlying model of air-sea exchange that we use to generate first-guess fluxes, driven in major part by 10m wind speeds in the TM5 model. The two figures share the same color scale and have units of gC m-2 yr-1.