Annual total emissions. The bars in this figure represent carbon dioxide emissions for each year in PgC yr-1 from the specified region. The final bar, labeled 'Mean', represents the 2001-2012 average. CarbonTracker models four types of surface-to-amosphere exchange of CO2, each of which is shown in a different color: fossil fuel emissions (tan), terrestrial biosphere flux excluding fires (green), direct emissions from fires (red), and air-sea gas exchange (blue). Negative emissions indicate that the flux removes CO2 from the atmosphere, and such sinks have bars that extend below zero. The net surface exchange, computed as the sum of these four components, is shown as a thick black line.

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. The total uncertainty, extending to the end of the vertical bar, incorporates within-model and across-model uncertainties. This is due to the use of the 8 prior flux models used in CT2013B; within-model error is the average posterior uncertainty from these 8 simulations, and across-model error is the additional uncertainty from the scatter of the 8 inversions. As shown in the legend, the within-model error, which usually dominates the total error, is indicated by the small horizontal cross bar in each vertical error bar. Fossil fuel uncertainty is shown by the darker tan bar inset into the main fossil bar. The two fossil fuel emissions estimates used in CT2013B are at the ends of the darker inset bar.

The 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.

Results Summary (all units PgC yr-1)
YearFirst GuessFinal EstimateFire EmissionFossil EmissionTotal Flux
2000-3.37 ± 6.29 -6.21 ± 6.52 1.66 6.74 ± 0.00 2.19 ± 6.52
2001-3.55 ± 6.32 -5.33 ± 6.59 1.56 6.91 ± 0.00 3.14 ± 6.59
2002-3.98 ± 6.51 -4.44 ± 6.63 2.06 6.97 ± 0.00 4.59 ± 6.63
2003-3.72 ± 6.23 -4.43 ± 6.07 2.11 7.39 ± 0.00 5.06 ± 6.07
2004-3.85 ± 6.36 -6.41 ± 6.60 1.96 7.77 ± 0.00 3.33 ± 6.60
2005-3.54 ± 6.27 -4.77 ± 6.47 2.10 8.08 ± 0.00 5.40 ± 6.47
2006-3.66 ± 6.37 -6.34 ± 6.59 2.05 8.34 ± 0.00 4.05 ± 6.59
2007-4.01 ± 6.35 -6.18 ± 6.18 2.04 8.53 ± 0.00 4.39 ± 6.18
2008-4.25 ± 6.60 -6.76 ± 7.50 1.68 8.74 ± 0.00 3.66 ± 7.50
2009-4.22 ± 6.33 -6.79 ± 6.86 1.52 8.65 ± 0.04 3.38 ± 6.86
2010-4.42 ± 6.49 -5.96 ± 7.20 2.18 9.13 ± 0.01 5.35 ± 7.20
2011-4.54 ± 6.43 -7.18 ± 7.07 1.63 9.42 ± 0.03 3.87 ± 7.07
2012-4.51 ± 6.33 -6.67 ± 7.98 1.99 9.65 ± 0.01 4.98 ± 7.98
Mean-4.02 ± 6.38 -5.94 ± 6.83 1.91 8.30 ± 0.00 4.27 ± 6.83

Results Summary. Annual and long-term mean (2001-2012) fluxes for the specified region, by component. "First-guess" and "Final" are the land biosphere (excluding fires) and ocean exchange fluxes before and after optimization, respectively. The uncertainties listed for these fluxes are one standard deviation confidence intervals. Fire and fossil fuel emissions do not list uncertainties since they are imposed without optimization in CarbonTracker. The "Total Flux" is the sum of the final estimate, fire emission, and fossil emission columns.

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.

Monthly natural fluxes (top panel). The annual cycle of optimized natural fluxes from the specified region, resolved by month and plotted for each year. "Natural flux" is the sum of land biosphere, fire, and air-sea CO2 emissions to the atmosphere. It does not include fossil fuel emissions. Units are PgC yr-1.

Cumulative flux anomalies (bottom panel). Cumulative anomalies of the natural flux for each year, resolved by month. Flux anomalies are defined as the optimized flux for a given year and month minus the climatological mean flux for that same month. These anomalies are accumulated from January to the current month of each year in order to show the impact of unusual seasons on the total annual flux.

Natural flux (top panel). First guess (red) and final (black) natural fluxes from the specified region, resolved by week. "Natural flux" is the sum of land biosphere, fire, and air-sea CO2 emissions to the atmosphere. It does not include fossil fuel emissions. Units are PgC yr-1. Faint background lines are the raw, weekly fluxes integrated over the specified region. The dark black and red lines in the foreground have been smoothed using a low pass filter. The filter used is an eight-week Hanning window, which has a similar frequency response to a four-week boxcar filter, but superior performance in attenuating high frequencies.

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.