CarbonTracker CT-NRT.v2021-3

CarbonTracker Near-Real Time (CT-NRT) is an extension of the formal CarbonTracker CO2 analysis system, designed to bridge the gap between annual updates of the formal CarbonTracker product. It extends model results past the end of the current CarbonTracker release up until the most recent date we can simulate. Usually this is limited by the availability of ERA-interim meteorology to drive the TM5 transport model. CT-NRT uses real-time meteorology, different flux priors, and assimilates only a fraction of the CO2 observations assimilated by the formal CarbonTracker product. These are provisional, near-real time CO2 observations from the small set of sites able to provide them.

CT-NRT was created with sponsorship from NASA, for use in the OCO-2 and ACT-America projects.

CT-NRT.v2021-3 is the current release. It provides results from 2019-Jan-01 to 2020-Jul-31. CT-NRT.v2021-3 starts from a CT2019B initial condition on 2018-Jan-06 using the CT2019B p1c2l1 suite member. CT-NRT.v2021-3 results are actually available starting on 2018-April-1, but for dates before 2019-Jan-1 we recommend use of the standard CarbonTracker release (CT2019B) These "early" results are provided so that interested parties can see the effects of the transition from one reanalysis product to the other (see below).

CT-NRT.v2021-3 was computed using ERA5 reanalysis meteorology, instead of the ERA-interim reanalysis used in CT2019B. While we find that these two sets of meteorology are statistically consistent, they do differ in their estimate of the instantaneous state of the atmosphere. This includes the locations of weather systems and fronts, which can affect the distribution of CO2 near the Earth surface. As a result, a simple transition from one reanalysis to another can cause significant transient diffrences in CO2 concentration. These discrepancies take a few weeks to integrate out, as they affect the short-term distribution of CO2 in the lower atmosphere. To mitigate this issue, CT-NRT.v2021-3 starts from a CT2019B initial condition on 2018-Jan-06, which is long before CT2019B actually ends. We recommend using CT-NRT.v2021-3 starting on 2019-Jan-01.

CT-NRT.v2021-3 results can be downloaded from /aftp/products/carbontracker/co2/CT-NRT.v2021-3/.

CT-NRT.v2021-3 differs from our standard CarbonTracker product in the following ways:

  • Assimilation of provisional CO2 observations. CT-NRT.v2021-3 uses CO2 observational data a Near-Real Time (NRT) ObsPack. The NRT data are made available through special arrangement with data providers and have two significant limitations. First, there are fewer data available in each day. This is due to unavoidable delays such as shipping of physical samples, analysis, data processing, and quality-control procedures for the measurements are still underway. Second, these observations generally have not undergone full quality-control procedures. Many of these procedures require a full year's worth of measurements to account for large seasonal variations. For more information, please see the NRT ObsPack release notes.

  • Assimilation of provisional CO2 observations. CT-NRT.v2021-3 uses CO2 observational data a Near-Real Time (NRT) ObsPack. The NRT data are made available through special arrangement with data providers and have two significant limitations. First, there are fewer data available in each day. This is due to unavoidable delays such as shipping of physical samples, analysis, data processing, and quality-control procedures for the measurements are still underway. Second, these observations generally have not undergone full quality-control procedures. Many of these procedures require a full year's worth of measurements to account for large seasonal variations. For more information, please see the NRT ObsPack release notes.

    CT-NRT.v2021-3 uses data from the obspack_co2_1_NRT_v6.1_2021-02-02 ObsPack. Decisions about which observations to assimilate, and with which level of model-data mismatch follow the CT2019B methodology.



  • Use of a different prior flux model. Our standard land biosphere flux prior is not available in near-real time, so we had to develop an alternative first-guess flux estimate. For this, we take the climatology of optimized land, wildfire, and ocean fluxes from the latest standard CarbonTracker release (for this release, that is CT2019B). Since the majority of flux variability comes from the land biosphere, a land flux anomaly model also has been developed. This is a simple regression of CT2019B land flux anomalies as a function of anomalies of precipitation, shortwave radiation, and temperature. The statistical flux anomaly model was developed for each CarbonTracker ecoregion, and provides daily estimates of NEE anomaly. The radiation and temperature data for this model come from the ERA-interim meteorology used by TM5; the precipitation anomaly comes from the Global Precipitation Climatology Project. Although this flux prior does not reliably reproduce interannual variability, it is arguably a more statistically optimal prior than that for our standard release since it already represents the long-term mean CO2 sinks that we know exist. Since the priors for our standard release do not represent these sinks, the standard CarbonTracker requires that CO2 observations correct these biased priors.


  • Fossil-fuel emissions CT-NRT.v2021-3 does not yet apply the TIMES scaling factors to fossil fuel emissions, and therefore does not have diurnal and day-of-week variability in those emissions. Impacts of the COVID-19 reduction in fossil-fuel combustion during 2020 are still being assessed and have not been applied in CT-NRT.v2021-3.

Previous releases of CT-NRT are available here.