1. Impact of Reduced Carbon Oxidation on Atmospheric CO 2 : Implications for Inversions P. Suntharalingam TransCom Meeting, June 13-16, 2005 N. Krakauer, J. Randerson (CalTech/UCI); D. J. Jacob, J. A. Logan (Harvard); A. Fiore (GFDL/NOAA) The TransCom3 Modelers Suntharalingam et al., Global Biogeochemical Cycles, in press.

2. MOTIVATION QUESTION : What is impact of accounting for realistic representation of reduced carbon oxidation 1)on modeled CO 2 distributions 2) on inverse flux estimates APPROACH : 1) Use 3-D atmospheric chemistry model (GEOS-CHEM) to estimate impact on concentrations. (Harvard) 2) Inverse analysis with MATCH and TransCom3 model basis functions (Caltech/UCI)

3. Previous Work on this Topic  Enting and Mansbridge (1991)  Enting et al. (1995)  Tans et al. (1995)  Baker (2001) Suntharalingam et al.Folberth et al. (2005)

4. CARBON FLUX FRAMEWORK UNDERLYING RECENT ATMOSPHERIC CO 2 INVERSIONS FossilSeasonal Biosphere “ Residual Biosphere ” Land use change, Fires, Regrowth, CO 2 Fertilization Ocean 6 120 Units = Pg C/yr Atmospheric CO 2 90 92 NET LAND UPTAKE ?? ( 0-2 ) All surface fluxes y mod - y obs Concentration residual

5. REDUCED C OXIDATION PROVIDES TROPOSPHERIC CO 2 SOURCE The “ Atmospheric Chemical Pump ” FossilBiomass Burning, Agriculture, Biosphere Ocean ATMOSPHERIC CO 2 CO 0.9-1.3 Pg C/yr Non- CO pathways (< 6%) CH 4 NMHCs Distribution of this CO 2 source can be far downstream of C emission location

6. HOW IS REDUCED CARBON ACCOUNTED FOR IN CURRENT INVERSIONS ? A : Emitted as CO 2 in surface inventories Fossil fuel : CO 2 emissions based on carbon content of fuel and assuming complete oxidation of CO and volatile hydrocarbons. (Marland and Rotty, 1984; Andres et al. 1996) Seasonal biosphere (CASA) : Biospheric C efflux represents respiration (CO 2 ) and emissions of reduced C gases (biogenic hydrocarbons, CH 4,etc) (Randerson et al., 2002; Randerson et al. 1997) Seasonal Biosphere : CASA Fossil Fuel

7. Modeling CO 2 release at surface rather than in troposphere leads to systematic error in inversion flux estimates Surface release of CO 2 from reduced C gases Tropospheric CO 2 source from reduced C oxidation CO, CH 4, NMHCs VS. Observation network detects tropospheric CO 2 source from reduced C oxidation y modsurf y mod3D y obs VS. y mod = modeled concentrations

8. CALCULATION OF CHEMICAL PUMP EFFECT Flux Estimate: x = x a + G (y - K x a ) STEP 1 : Impact on modeled concentrations Adjust y model to account for redistribution of reduced C from surface inventories to oxidation location in troposphere y model y obs Adjustment  y model = y 3D – y SURF ADD effect of CO 2 source from tropospheric reduced C oxidation SUBTRACT effect of reduced C from surface inventories

9. EVALUATION OF THE CHEMICAL PUMP EFFECT GEOS-CHEM SIMULATIONS (v. 5.07) Standard Simulation CO 2 Source from Reduced C Oxidation = 1.1 Pg C/yr Distribute source according to seasonal 3-D variation of CO 2 production from CO Oxidation Distribute source according to seasonal SURFACE variations of reduced C emissions from Combustion and Biosphere sources CO2 SURF Simulation : y SURF CO2 3D Simulation : y 3D Simulations spun up for 3 years. Results from 4 th year of simulation

10. GEOS-CHEM Model http://www-as.harvard.edu/chemistry/trop/geos/index.html Global 3-D model of atmospheric chemistry (v. 5-07-08) 2 o x2.5 o horizontal resolution; 30 vertical levels Assimilated meteorology (GMAO); GEOS-3 (year 2001) CO chemistry of Duncan et al. 2005 Reduced Carbon Emissions Distributions (spatial and temporal variability) Fossil : Duncan et al. [2005] (annual mean) Biomass Burning : Duncan et al. [2003] (monthly) Biofuels : Yevich and Logan [2003] NMVOCs : Duncan et al. [2005] ; Guenther et al. [1995]; Jacob et al. [2002] CH 4 : A priori distributions from Wang et al. [2004] (monthly)

11. REDUCED CARBON SOURCES BY SECTOR STANDARD SIMULATION : CO 2 Source from Reduced C Oxidation = 1.1 Pg C/yr Sector breakdown based on Duncan et al. [2005] *Methane sources distributed according to a priori fields from Wang et al. [2004] REDUCED CARBON SOURCES Pg C/yr Fossil (CO,CH 4,NMHCs)0.27 Biomass Burning (CO,CH 4,NMHCs)0.26 Biofuels (CO,CH 4 )0.09 Biogenic Hydrocarbons0.16 Other Methane Sources*0.31 TOTAL 1.1

12. CH 4 EMISSIONS AND BUDGET PROPORTIONS Standard Simulation :CH 4 Oxidation to CO = 0.39 Pg C/yr CH 4 emissions distributions and budget proportions from the a priori distribution of Wang et al. [2004] Rice 11% Wetlands 36% Termites 5% Biomass Burning 4% Fossil 16% Landfills 10% Biofuel 2% Livestock 11%

13. Source Distributions : Annual Mean Zonal Integral of Emissions Latitude CO2 COox : Column Integral of CO 2 from CO Oxidation CO2 RedC :CO 2 Emissions from Reduced C Sources CO2 COox :Maximum in tropics, diffuse CO2 RedC : Localized, corresponding to regions of high CO, CH 4 and biogenic NMHC emissions CO2 COox CO2 RedC gC/(m 2 yr)

14. MODELED SURFACE CONCENTRATIONS : Annual Mean CO2 SURF CO2 3D Surface concentrations reflect source distributions: Diffuse with tropical maximum for CO2 3D and localized to regions of high reduced C emissions for CO2 SURF

15. Largest changes in regions in and downstream of high reduced C emissions TAP : - 0.55; ITN : - 0.35; BAL : - 0.35 (ppm) REGIONAL VARIATION OF CHEMICAL PUMP EFFECT  y model = CO2 3D – CO2 SURF ppm

16.  y model : Zonal average at surface CO 2 (ppm) ANNUAL MEAN CHEMICAL PUMP EFFECT Mean Interhemispheric difference  y = - 0.21 ppm 0.21 ppm Latitude Impact on TransCom3 residuals (Level 1) Systematic decrease in Northern Hemisphere 50-50

17. SEASONALITY OF CONCENTRATION ADJUSTMENT  y  Greatest seasonal variation in northern mid-latitudes  Smallest impact of chemical pump in N. Hem. summer (shorter CO lifetime) Seasonal variation of interhemispheric  y: – 0.32 ppm (January) -0.15 ppm (July) LATITUDE JAN JUL Surface  y (ppm ) -50+50 -0.3 -0.1 0.1

18. IMPACT ON SURFACE FLUX ESTIMATES Inverse analyses by Nir Krakauer Estimate effect by modifying concentration error vector as : (y – (K x a +  y model )) Then, ‘ adjusted ’ flux estimate is: x adj = x a + G(y – (K x a +  y model )) Evaluate with 3 transport models (MATCH, GISS-UCI, TM2-LSCE) Q : What are the changes in estimates of ‘ residual ’ fluxes when we account for chemical pump adjustment  y model Evaluate impact on TransCom3 Inversions: 1) annual mean (Gurney et al. 2002) 2) seasonal (Gurney et al. 2004)

19.  Largest regional impact in Temperate Asia (reductions of 0.1- 0.15 PgC/yr)  Tropical efflux reduced (by 0.14 to 0.19 Pg C/year)  Relative impact varies across models. ANNUAL MEAN INVERSION (Level 1) REDUCTION IN UPTAKE : NORTHERN EXTRA-TROPICAL LAND Systematic Reduction (0.22-0.26 Pg C/year) Pg C/yr 0.220.250.26 Original Uptake (a posteriori uncertainty) -19% -27%-9% % Change MATCH-CCMTM2-LSCE -1.4 (0.5) -2.5 (0.4) -0.9 (0.5)

20. Annual Mean Estimates from Cyclostationary Analysis (Level 2) NORTHERN LAND UPTAKE (Pg C/year) Bias from seasonal analysis similar to Level 1 analysis (slightly larger) Bias comparable to a posteriori uncertainty ‘ Between model ’ uncertainty is 1.1 PgC/yr from Gurney et al. [2004] GISS-UCITM2-LSCE Original estimate With Chemical pump FLUX ADJUSTMENT (Level 2) -0.99 +0.34 -0.06 +0.29 -0.64 0.26 0.350.32 Flux adjustment (Level 1) 0.260.25 MATCH-NCEP -4.02 +0.27 -3.80 0.22

21. SUMMARY Neglecting the 3D representation of the CO 2 source from reduced C oxidation produces systematic errors in inverse CO 2 flux estimates Accounting for a reduced C oxidation source of 1.1 Pg C/yr gives a reduction in the modeled annual mean N-S CO 2 gradient of 0.2 ppm (Regional changes are larger; up to 0.6 ppm in regions of high reduced C emissions) Inverse estimates of N. extratropical land uptake reduce by about 0.25 Pg C/yr in Level 1 inversions; by up to 0.35 Pg C/yr in Level 2. We can provide chemical pump concentration adjustments (e.g. at GLOBALVIEW stations) or reduced C source distributions (3D and surface) to calculate the impacts in your own models.