While CarbonTracker applies bottom-up estimates of fossil fuel and
wildfire emissions directly, it attempts to estimate optimal fluxes
from the ocean and land biosphere. This optimization starts with a
first guess of the flux component and its uncertainty (left panel).
The one standard-deviation level of uncertainty for the land flux is
shown with a thin green vertical line, and the uncertainty for oceanic
exchange is shown with a thin blue vertical line. These first-guess
fluxes are subsequently evaluated against atmospheric CO2 observations and modified to be consistent with
those measurements. The optimized results (right panel) have
different mean fluxes and reduced uncertainty ranges, indicating the
influence of information brought by the observations. The uncertainty
on the net flux (black vertical line) is the RMS sum of land biosphere
and oceanic flux uncertainties.
Note that fossil fuel emissions can occur over regions characterized
as ocean or non-optimized regions such as ice, polar deserts, and
inland seas. 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 1° x 1°
division scheme. Similarly, land regions may have a small
contribution from air-sea gas exchange, and vice versa.
Fossil fuel flux (bottom panel). As in the top panel, but for fossil fuel emissions. Note that fossil fuel emissions are not optimized in CarbonTracker.