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.
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)
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)
CARBON FLUX FRAMEWORK UNDERLYING RECENT ATMOSPHERIC CO 2 INVERSIONS FossilSeasonal Biosphere “ Residual Biosphere ” Land use change, Fires, Regrowth, CO 2 Fertilization Ocean Units = Pg C/yr Atmospheric CO NET LAND UPTAKE ?? ( 0-2 ) All surface fluxes y mod - y obs Concentration residual
REDUCED C OXIDATION PROVIDES TROPOSPHERIC CO 2 SOURCE The “ Atmospheric Chemical Pump ” FossilBiomass Burning, Agriculture, Biosphere Ocean ATMOSPHERIC CO 2 CO Pg C/yr Non- CO pathways (< 6%) CH 4 NMHCs Distribution of this CO 2 source can be far downstream of C emission location
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
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
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
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
GEOS-CHEM Model Global 3-D model of atmospheric chemistry (v ) 2 o x2.5 o horizontal resolution; 30 vertical levels Assimilated meteorology (GMAO); GEOS-3 (year 2001) CO chemistry of Duncan et al 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)
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
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%
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)
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
Largest changes in regions in and downstream of high reduced C emissions TAP : ; ITN : ; BAL : (ppm) REGIONAL VARIATION OF CHEMICAL PUMP EFFECT y model = CO2 3D – CO2 SURF ppm
y model : Zonal average at surface CO 2 (ppm) ANNUAL MEAN CHEMICAL PUMP EFFECT Mean Interhemispheric difference y = ppm 0.21 ppm Latitude Impact on TransCom3 residuals (Level 1) Systematic decrease in Northern Hemisphere 50-50
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) ppm (July) LATITUDE JAN JUL Surface y (ppm )
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)
Largest regional impact in Temperate Asia (reductions of 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 ( Pg C/year) Pg C/yr Original Uptake (a posteriori uncertainty) -19% -27%-9% % Change MATCH-CCMTM2-LSCE -1.4 (0.5) -2.5 (0.4) -0.9 (0.5)
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) Flux adjustment (Level 1) MATCH-NCEP
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.