Region Averaging
One-degree fluxes (Left).The pattern of net ecosystem exchange (NEE) of CO2 of the land biosphere averaged over the time period indicated, as estimated by CarbonTracker. This NEE represents land-to-atmosphere carbon exchange from photosynthesis and respiration in terrestrial ecosystems, and a contribution from fires. It does not include fossil fuel emissions. Negative fluxes (blue colors) represent CO2 uptake by the land biosphere, whereas positive fluxes (red colors) indicate regions in which the land biosphere is a net source of CO2 to the atmosphere. Units are gC m-2 yr-1.

The fluxes in this graphic have a spatial resolution of 1° longitude by 1° latitude. Optimization in CarbonTracker is actually performed on the scale of "ecoregions", which are large areas of similar ecosystem type within a given continental-scale land region (see thumbnail map, top right of this page and ecoregion documentation). CarbonTracker estimates only the total weekly flux from each ecoregion. The distribution of that total flux onto finer spatial and temporal scales such as those shown here depends on an underlying terrestrial biosphere model. Fluxes on the ecoregion scale, without this presumed finer-scale distribution, are shown in the figure at the bottom of this page.

The pattern of net ecosystem exchange CO2 follows swings in temperature and sunlight. As a result, there are strong seasonal variations of NEE. It is common to see net uptake by land ecosystems during the Northern Hemisphere summer and net release during winter.

Ecoregion uncertainties (Right). Uncertainty of the CarbonTracker estimate of net ecosystem exchange (NEE) of CO2 from the land biosphere, averaged over the time period indicated. NEE is defined in the first caption on this page, above. The quantity displayed here 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, top right of this page and ecoregion documentation). There is no assumed patterning of the uncertainty within ecoregions.

Summary Fluxes for 2001-2012 mean (all units PgC yr-1)
RegionFirst GuessFinal EstimateFire EmissionFossil EmissionTotal Flux
All of North America-0.11 ± 2.18 -0.68 ± 1.14 0.07 1.78 ± 0.03 1.17 ± 1.14
Temperate North America-0.08 ± 1.54 -0.45 ± 0.81 0.02 1.75 ± 0.02 1.31 ± 0.81
Boreal North America-0.03 ± 1.27 -0.23 ± 0.80 0.06 0.03 ± 0.01 -0.14 ± 0.80
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: net ecosystem exchange (NEE) of CO2 of the land biosphere at 1° x 1°. This is a copy of the figure at the top left of this page. Right: NEE at the ecoregion scale, as natively estimated by CarbonTracker. The fluxes in this graphic are uniformly distributed within each ecoregion (see thumbnail map, top right 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 ecoregion. They have the same total flux integrated across each ecoregion. Within-region gradients seen on the left are entirely due to the underlying terrestrial biosphere model we use to generate first-guess fluxes. The two figures share the same color scale and have units of gC m-2 yr-1.