CO2 simulation

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This page contains information about the carbon dioxide (CO2) simulation in GEOS-Chem.


The original GEOS-Chem CO2 simulation was developed by Parv Suntharalingam (Suntharalingam et al., 2003; 2004), now at the University of East Anglia. A major update to the CO2 simulation was completed in 2010 by Ray Nassar and Dylan B.A. Jones of the University of Toronto (Nassar et al., 2010). The latest update to the CO2 simulation was developed by Ray Nassar (now at Environment Canada) and appears in GEOS-Chem v10-01, which was released on 2015 May 1.

v8-03-02 update (April 2010)

The 2010 update retained the original six CO2 fluxes: fossil fuel, ocean exchange, biomass burning, biofuel burning, balanced terrestrial exchange (CASA) and net annual terrestrial exchange. Other inventories are available as options for some of these fluxes and other new fluxes were added such as CO2 emissions from international shipping and aviation. There is also an optional feature to include CO2 production from the oxidation of CO, CH4 and NMVOCs. This chemical source concept was first highlighted by Enting and Mansbridge (1991). Although a few attempts have been made by other groups in the past, this implementation made GEOS-Chem the only 3-D global model to account for the chemical production of CO2. The GEOS-Chem implementation uses an approach similar to that described in Suntharalingam et al. (2005), with some updated year-specific numbers and some other modifications described in Nassar et al. (2010). The full GEOS-Chem CO2 update was applied to and tested with v8-02-01 (along with some patches). It has been publicly available in GEOS-Chem release v8-03-02 and later versions, along with an update to the GEOS-Chem online manual. The references below are cited in the updated code's comments and online manual, and include the new CO2 simulation description paper Nassar et al. (2010).

v10-01 update (May 2015)

GEOS-Chem v10-01 includes a substantial update to the CO2 simulation. A number of new or updated inventories have now been added at the same time as emissions are now handled by HEMCO. HEMCO reads emissions from netCDF files at any specified resolution and regrids the data, along with applying scaling factors where applicable. Major changes in this update include new options for fossil fuel emissions, biospheric fluxes and ocean fluxes and a modified treatment of the chemical source surface correction.

The CO2 emission updates are the following:

  1. Carbon Dioxide Information Analysis Center (CDIAC) gridded data has been updated to include additional years [Andres et al. 2011] – CDIAC v2014 now extends to 2011 and RN has applied BP scaling for 2012 and 2013 with a projection for 2014 based on the Global Carbon Project values.

  2. Open-source Data Inventory for Atmospheric CO2 emissions (ODIAC version 2013) fossil fuel option s now added [Oda and Maksyutov, 2011], which is known to have a more reliable spatial distribution for large countries but is consistent with an earlier version of CDIAC version for national emission totals.

  3. Temporal Improvements for Monitoring Emissions by Scaling (TIMES) is now added [Nassar et al., 2013], which introduces weekly and diurnal variations to national fossil fuel emissions

  4. The Takahashi et al. (2009) ocean fluxes in the model were included as a 1-year climatology corresponding to the year 2000 with a sink of 1.4 PgC. The same paper also describes a method for scaling the Takahashi et al. (2009) fluxes with year-specific atmospheric CO2 to yield year specific fluxes with an increasing global sink. This approach has been applied to scale the fluxes for 2000-2013 inclusive with an ocean sink ranging from (1.4 to 2.6 PgC/yr).

  5. Balanced biospheric CO2 uptake and emission from the Simple Biospheric Model version 3 (SiB3) for the years 2006-2010 from Nick Parazoo [Messerschmidt et al. 2012]

  6. Aviation emissions spatial and temporal distributions now come from AEIC. Updates to the scaling factors for the global annual emission amount from the International Energy Agency [Olsen et al., 2013] are now used for 1990-2008. A new system for aviation surface correction factors is now implemented which scales national fossil fuel emissions by a factor slightly less than 1 in order to remove the estimated contribution from domestic aviation emission, which is counted in the air instead of at the surface.

  7. The chemical source of CO2 now spans a larger time period 2000-2009. The 2008 chemical source was recalculated with GFED for 2008, which was unavailable at the time of the previous update. A 2009 chemical source is now added. The surface correction approach has been revised such that the magnitude of the fossil fuel surface correction is now year specific for 1980-2014. In v8-03-02, the percentage of fossil fuel carbon emissions released as CO (and other carbon species like CH4 and non-methane hydrocarbons) was assumed to be 4.89% based on the work of Suntharalingam et al. [2005], with no temporal dependence. However, studies have demonstrated that even as fossil fuel CO2 emissions have continually risen for decades, fossil fuel CO emissions have held essentially constant since about 1980 at 500-600 Tg CO/year [Granier et al., 2011]. Fossil fuel CH4 is also found to be roughly constant at 80 TgCH4/yr in CarbonTracker-CH4. In GEOS-Chem v10-01, the fossil fuel emission surface correction for the chemical source from Nassar et al. [2010] has been modified based on the decreasing CO/CO2 and CH4/CO2 emission ratios, attributed to improved technology in both developed and developing countries, demonstrated by roughly constant CO and CH4 emissions despite increasing CO2 emissions. The surface correction goes from 5.28% in 1980 and decreases to 2.84% in 2013, replacing the constant value of 4.89% prior to v10-01. This new approach assumes a negligible percentage of fossil fuel carbon from sources other than CO2, CO, and CH4 (such as non-methane hydrocarbons) and assumes that the combustion completeness is globally-uniform. The assumption of global uniformity, though not a good assumption for the past, is becoming more reasonable as the developed countries adopt cleaner combustion technology releasing less non-CO2 carbon species. Note that for the 3D emission sources, both aviation CO2 emissions and CO2 chemical production, there has been a change in emission units to molecules/cm2/s instead of molecules/cm3/s, for consistency with HEMCO implementation in other parts of GEOS-Chem.

Note: The new HEMCO netCDF file for CDIAC national fossil fuel CO2 emissions is not ready due to a delay from CDIAC, but is expected to be available by mid-May.

Note: Nassar et al. (2010) remains the recommended reference for the GEOS-Chem CO2 simulation from v8-03-02 to the present version.


  1. Andres. R.J., J.S Gregg, L. Losey, G. Marland, T.A. Boden (2011), Monthly, global emissions of carbon dioxide from fossil fuel consumption, Tellus 63B, 309-327.
  2. Granier, C., et al. (2011), Evolution of anthropogenic and biomass burning emissions of air pollutants at global and regional scales during the 1980-2010 period, Climatic Change, 109:163-190, doi:10.1007/s10584-011-0154-1.
  3. Keller, C.A., M.S. Long, R.M. Yantosca, A.M. DaSilva, S. Pawson, D.J. Jacob (2014), HEMCO v1.0: a versatile, ESMF-compliant component for calculating emissions in atmospheric models, Geosci., Model Dev., 7, 1409–1417, doi:10.5194/gmd-7-1409-2014.
  4. Messerschmidt, J., N. Parazoo, N.M. Deutscher, C. Roehl, T. Warneke, P.O. Wennberg, and D. Wunch (2012), Evaluation of atmosphere-biosphere exchange estimations with TCCON measurements, Atmos. Chem. Phys. Discussions, 12, 12759-12800, doi:10.5194/acpd-12-12759-2012.
  5. Nassar, R., D.B.A. Jones, P. Suntharalingam, J.M. Chen, R.J. Andres, K.J. Wecht, R.M. Yantosca, S.S. Kulawik, K.W. Bowman, J.R. Worden, T. Machida and H. Matsueda (2010), Modeling global atmospheric CO2 with improved emission inventories and CO2 production from the oxidation of other carbon species, Geoscientific Model Development, 3, 689-716.
  6. Nassar, R., L. Napier-Linton, K.R. Gurney, R.J. Andres, T. Oda, F.R. Vogel, F. Deng (2013), Improving the temporal and spatial distribution of CO2 emissions from global fossil fuel emission datasets, Journal of Geophysical Research: Atmospheres, 118, 917-933, doi:10.1029/2012JD018196.
  7. Oda, T. and S. Maksyutov (2011), A very high-resolution (1 km x 1 km) global fossil fuel CO2 emission inventory derived using a point source database and satellite observations of nighttime lights, Atmos. Chem. Phys., 11, 543–556, doi:10.5194/acp-11-543-2011.
  8. Olsen, S.C., D.J. Weubbles, B. Owen (2013), Comparison of global 3-D aviation datasets, Atmos. Chem. Phys., 13, 429–441, doi:10.5194/acp-13-429-2013.
  9. Simone, N., M. Stettler, S. Eastham, S. Barrett, Aviation Emissions Inventory Code (AEIC) User Manual (R1), Laboratory for Aviation and the Environment, Massachusetts Institute of Technology, January 2013, Report No: LAE-2013-001-N,
  10. Takahashi, T., Sutherland, S. C., Wanninkhof, R., Sweeney, C., Feely, R. A., Chipman, D. W., Hales, B., Friederich, G., Chavez, F., Sabine, C., Watson, A., Bakker, D. C. E., Schuster, U., Metzl, N., Yoshikawa-Inoue, H., Ishii, M., Midorikawa, T., Nojiri, Y., K¨ortzinger, A., Steinhoff, T., Hoppema, M., Olafsson, J., Arnarson, T. S., Tilbrook, B., Johannessen, T., Olsen, A., Bellerby, R., Wong, C. S., Delille, B., Bates, N. R., and de Baar, H. J. W (2009), Climatological mean and decadal change in surface ocean pCO2, and net sea-air CO2 flux over the global oceans, Deep-Sea Res. II, 56(8–10), 554–577, doi:10.1016/j.dsr2.2008.12.009.

--Ray Nassar, 2015 May 12

Additional Update and Bug Fix

These updates were included in the 1-month benchmark simulation v11-01c and approved on 14 Sept 2015.

1) The new HEMCO netCDF file for CDIAC national fossil fuel CO2 emissions is now available (as of September 4, 2015). The file contains data for 1980-2014. For 1980-2011 the data come directly from the Carbon Dioxide Information Analysis Center (CDIAC) 1x1 gridded dataset (Andres et al., 2011) version 2014. For 2012-2014, the CDIAC year 2011 spatial and seasonal distribution has been scaled using the BP Statistical Review of World Energy 2015. The ratio of emissions from each year (2012-2014) against 2011 emissions for the 20 highest CO2 emitting countries and for the remainder of the world from the BP data, were used to scale the spatial-temporal CDIAC distributions for 2011. Note: there are differences in the component CO2 emissions in the CDIAC and BP methodologies, but this should not be a major factor such that this approach is considered better than the simple alternative approach of simply using 2011 for subsequent years.

2) A new file is now available for CASA balanced biosphere fluxes. This file has been reprocessed to replace an error in the earlier available version, which was based on CASA bpch files from back in 2005. For some reason, the file for day of year 189 was renamed to “nep.geos.2x25.189.orig” and the file for day 188 was copied and renamed to “nep.geos.2x25.189” so there was a resulting anomaly in the date-times in the netCDF file since actual date-times for day 189 were missing, and day 188 appeared twice. This has now been corrected using day 189.orig to create a new netCDF file so that there are no oddities with dates in the file.

--Ray Nassar, 2015 September 4

Authors and collaborators

CO2 simulation user groups

User Group Personnel Projects
University of Toronto Dylan Jones Model updates and application to inverse modeling
Korea Environment Institute (KEI) Changsub Shim
University of Colorado Boulder Daven Henze CO2 adjoint
UEA Chen Inverse modeling of CO2 using satellite
Tsinghua University Yuxuan Wang ; Mingwei Li
Environment Canada Ray Nassar CO2 modeling and source sink estimation using satellite and in situ data
Caltech CO2 source/sink estimation using ground-based FTS data
University of Wollongong Nicholas Deutscher CO2 source/sink estimation using ground-based FTS (TCCON) data and co-located surface measurements. Focus on Australia
Florida State University] Chris Holmes

Kelly Graham

Evaluation and improvement of Arctic CO2 simulation with O-Buoys
Add yours here!


In Nassar et al. (2010) model comparisons are made with GLOBALVEIW-CO2 ( and CONTRAIL (Comprehensive Observation Network for TRace gases by AIrLiner) measurements. In other work, the CO2 simulation has also been compared with aircraft observations from the HIAPER Pole-to-Pole Observations (HIPPO) campaigns of 2009 (Wofsy et al., 2010).

Nested-grid CO2 simulation

This update was tested in the 1-month benchmark simulation v9-01-03h and approved on 09 Mar 2012.

Yuxuan Wang wrote:

The nested-grid CO2 simulation is developed and tested based on v8-02-01. Except for code changes for nested-grid simulation in general, specific changes are made to read the CO2 fluxes at 0.5x0.667 resolution . These fluxes are regridded to 0.5x0.667 either from 1x1 input files on the fly when running GEOS-Chem or from 2x2.5 data files off-line using IDL.

--Melissa Payer 16:00, 2 December 2011 (EST)


  1. Andres, R. J., G. Marland, I. Fung, and E. Matthews, A 1°x1° distribution of carbon dioxide emissions from fossil fuel consumption and cement manufacture, Global Biogeochem. Cycles, 10, 419–429, 1996.
  2. Andres, R. J., Gregg, J. S., Losey, L., Marland, G., and Boden, T. A.: Monthly, global emissions of carbon dioxide from fossil fuel consumption, Tellus B, 63B, 2011.
  3. Baker, D. F., et al., TransCom 3 inversion intercomparison: Impact of transport model errors on the interannual variability of regional CO2 fluxes, 1988-2003, Global Biogeochem. Cycles, 20, GB1002, doi:10.1029/2004GB002439, 2006.
  4. Boden, T.A., G. Marland, and R.J. Andres, Global, Regional, and National Fossil-Fuel CO2 Emissions. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tenn., U.S.A. doi 10.3334/CDIAC/00001, 2009.
  5. Corbett & Koehler, Updated emissions from ocean shipping, J. Geophys. Res., 108, D20, 4650, 2003.
  6. Corbett, J. J., and H. W. Koehler, Considering alternative input parameters in an activity-based ship fuel consumption and emissions model: Reply to comment by Øyvind Endresen et al. on Updated emissions from ocean shipping, J. Geophys. Res., 109, 2004.
  7. Duncan, B. N., R. V. Martin, A. C. Staudt, R. Yevich, and J. A. Logan, Interannual and seasonal variability of biomass burning emissions constrained by satellite observations, J. Geophys. Res., 108(D2), 4100, doi:10.1029/2002JD002378, 2003.
  8. Endresen, O, et al., A historical reconstruction of ships fuel consumption and emissions, J. Geophys. Res, 112, D12301, 2007.
  9. Enting, I. G. and Mansbridge, J. V.: Latitudinal distribution of sources and sinks of CO2: results of and inversion study, Tellus B, 43, 156–170, 1991.
  10. Kim, B. Y., et al., System for assessing Aviation's Global Emissions (SAGE) Version 1.5 global Aviation Emissions Inventories for 2000-2004, 2005.
  11. Kim, B. Y., et al., System for assessing Aviation’s Global Emissions (SAGE), Part 1: Model description and inventory results, Transportation Research, Part D 12, 325–346, 2007.
  12. Le Quere, C. et al., Trends in the sources and sinks of carbon dioxide, Nature Geoscience, doi:10.1038/ngeo689, 2009.
  13. Nassar, R., D. B. A. Jones, P. Suntharalingam, J. M. Chen, R. J. Andres, K. J. Wecht, R. M. Yantosca, S. S. Kualwik, K. W. Bowman, J. R. Worden, T. Machida, H. Matsueda, Modeling global atmospheric CO2 with improved emission inventories and CO2 production from the oxidation of other carbon species, Geoscientific Model Development, 3, 689-716, 2010.
  14. Olsen, S. C., and J. T. Randerson, Differences between surface and column atmospheric CO2 and implications for carbon cycle research, J. Geophys. Res., 109, D02301, doi:10.1029/2003JD003968, 2004.
  15. Potter, C. S., J. T. Randerson, C. B. Field, P. A. Matson, P. M. Vitousek, H. A. Mooney, and S. A. Klooster, Terrestrial ecosystem production: A process model based on global satellite and surface data, Global Biogeochem. Cycles, 7, 811–841, 1993.
  16. Sausen, R. and U. Schumann, Estimates of the Climate Response to Aircraft CO2 and NOx Emissions Scenarios, Climate Change, 44: 27-58, 2000.
  17. Suntharalingam, P., C. M. Spivakovsky, J. A. Logan, and M. B. McElroy, Estimating the distribution of terrestrial CO2 sources and sinks from atmospheric measurements: Sensitivity to configuration of the observation network, J. Geophys. Res., 108(D15), 4452, doi:10.1029/2002JD002207, 2003.
  18. Suntharalingam, P., D. J. Jacob, P. I. Palmer, J. A. Logan, R. M. Yantosca, Y. Xiao, M. J. Evans, D. G. Streets, S. L. Vay, and G. W. Sachse, Improved quantification of Chinese carbon fluxes using CO2/CO correlations in Asian outflow, J. Geophys. Res., 109, D18S18, doi:10.1029/2003JD004362, 2004.
  19. Suntharalingam, P., J. T. Randerson, N. Krakauer, J. A. Logan, and D. J. Jacob, Influence of reduced carbon emissions and oxidation on the distribution of atmospheric CO2: Implications for inversion analyses, Global Biogeochem. Cycles, 19, GB4003, doi:10.1029/2005GB002466, 2005.
  20. Takahashi, T., R. A. Feely, R. Weiss, R. H. Wanninkhof, D. W. Chipman, S. C. Sutherland, T. T. Takahashi, Global air-sea flux of CO2: an estimate based on measurements of sea-air pCO2 difference, Proc. Natl. Acad. Sci., 94, 8292–8299, 1997.
  21. Takahashi, T., et al., Climatological mean and decadal change in surface ocean pCO2, and net sea–air CO2 flux over the global oceans, Deep-Sea Res. II, doi:10.1016/j.dsr2.2008.12.009, 2009.
  22. Wang, C., J.J. Corbett, J. Firestone, Modeling Energy Use and Emissions from North American Shipping: Application of the Ship Traffic, Energy, and Environment Model, Environ. Sci. Technol., 41, 3226-3232, 2008.
  23. Wilkersen, J.T. et al., Analysis of emission data from global commercial Aviation: 2004 and 2006, Atmos. Chem. Phys. Disc., 10, 2945-2983, 2010.
  24. Wofsy, S.C., et al., HIAPER Pole-to-Pole Observations (HIPPO): Fine grained, global scale measurements of climatically important atmospheric gases and aerosols, Proceedings of the Royal Society A, 369, 2073-2086, 2011.
  25. Yevich, R., and J. A. Logan, An assessment of biofuel use and burning of agricultural waste in the developing world, Global Biogeochem. Cycles, 17(4), 1095, doi:10.1029/2002GB001952, 2003. PDF

--Bob Yantosca (talk) 21:45, 10 January 2017 (UTC)

Previous issues that are now resolved

Prevent double-counting in CO2 chemical source

This update was included in GEOS-Chem 12.2.1, which was released on 28 Feb 2019.

Beata Bukosa (U. Wollongong) wrote:

I tested the new 2x25 CO2 chemical source field file, and modified the CO2 code, and the results look good now. Below is a plot with the final results.

CO2 Bugfix Comparison.png

Top plots show the integrated column values of different source types as a reference (e.g. biofuel and chemical source surface correction) + the chemical source without and with the fix, and the bottom plots are the surface concentrations. I would say that scientifically speaking the values make sense now.

I would also like to suggest to modify the public CO2 HEMCO_Config file and set the chemical surface correction (line 259) from "E" to "C". With "E" the chemical source surface correction won't be applied after year 2014, and the chemical source will be double counted.

--Bob Yantosca (talk) 16:42, 28 February 2019 (UTC)

CO2 emissions are double counted

This update (Git ID: 8320e73d ) was included in GEOS-Chem 12.0.2, which was released on 10 Oct 2018.

Jenny Fisher wrote:

Bea Bukosa (CC’d) has discovered what appears to be a pretty serious bug in the CO2 simulation, at least in v11-01. We haven’t seen any mention of it on the wiki for v11-02, so assume it is still there.

Bea has provided some slides. Basically, it appears the CO2 emissions were all being double-counted by being added directly by HEMCO and added again in co2_mod.F. This is causing a massive long-term accumulation of CO2 in the tracers.

She found this by running a simulation where she removed the addition of E_CO2 to the Spc array in co2_mod.F [e.g. line 470 Spc(I,J,1,2) = Spc(I,J,1,2) + E_CO2 –-> Spc(I,J,1,2) = Spc(I,J,1,2)]. Despite all tracers starting with initial values of ~0, the tracers still show signatures from the sources (for example BB elevated over Africa, ocean source elevated over the ocean, etc.). In other words, this is not noise and the species accumulate even when emissions are not added in co2_mod.F.

If she ALSO prevents HEMCO from providing emissions during the run (by commenting out some lines in hco_interface_mod.F90, see attached) then we can get the near-zero values we would expect. Note that there is a bit of noise for the bi-directional tracers because we first add then later subtract a constant to avoid negative species amounts.

Obviously, what we have done to find the bug isn’t an appropriate long-term solution. Can you please let us know the best way to fix this in our code (and in v11-02 going forward)? One thing to note is that some of the sources have negative values – is that something HEMCO can handle? Or is it better to keep the CO2 sources in co2_mod.F and just prevent HEMCO from providing emissions when running CO2 simulations?

--Bob Yantosca (talk) 18:07, 24 September 2018 (UTC)