Impact of Reduced Carbon Oxidation on Atmospheric CO2 : 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 CO2 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 CO2 INVERSIONS

Fossil Seasonal Biosphere

“Residual Biosphere”

Land use change, Fires, Regrowth, CO2 Fertilization

Ocean

6 120 120

Units = Pg C/yr

Atmospheric CO2

9092

NET LAND UPTAKE

??

( 0-2 )

All surface fluxes

ymod - yobsConcentration residual

REDUCED C OXIDATION PROVIDES TROPOSPHERIC CO2 SOURCE The “Atmospheric Chemical Pump”

Fossil Biomass Burning, Agriculture, Biosphere Ocean

ATMOSPHERIC CO2

CO

0.9-1.3 Pg C/yr Non- CO pathways

(< 6%)

CH4NMHCs

Distribution of this CO2 source can be far downstream of C

emission location

HOW IS REDUCED CARBON ACCOUNTED FOR IN CURRENT INVERSIONS ?

A : Emitted as CO2 in surface inventories

Fossil fuel : CO2 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 (CO2) and emissions of reduced C gases (biogenic hydrocarbons, CH4,etc)

(Randerson et al. , 2002; Randerson et al. 1997)

Seasonal Biosphere : CASA

Fossil Fuel

Modeling CO2 release at surface rather than in troposphere leads to systematic error in inversion flux estimates

Surface release of CO2 from reduced C

gases

Tropospheric CO2 source from reduced C oxidation

CO, CH4, NMHCs

VS.

Observation network detects tropospheric CO2 source from

reduced C oxidation

ymodsurf ymod3D yobs

VS.

ymod = modeled concentrations

CALCULATION OF CHEMICAL PUMP EFFECT

• Flux Estimate: x = xa + G (y - K xa)

• STEP 1 : Impact on modeled concentrations

Adjust ymodel to account for redistribution of reduced C from surface inventories to oxidation location in troposphere

ymodelyobs

• Adjustmentymodel = y3D – ySURF

ADD effect of CO2 source from tropospheric reduced C

oxidation

SUBTRACT effect of reduced C from surface inventories

EVALUATION OF THE CHEMICAL PUMP EFFECTGEOS-CHEM SIMULATIONS (v. 5.07)

Standard Simulation

CO2 Source from Reduced C Oxidation = 1.1 Pg C/yr

Distribute source according to seasonal 3-D

variation of CO2 production from CO

Oxidation

Distribute source according to seasonal SURFACE

variations of reduced C emissions from Combustion

and Biosphere sources

CO2SURF Simulation : ySURFCO23D Simulation : y3D

Simulations spun up for 3 years. Results from 4th year of simulation

GEOS-CHEM Model http://www-as.harvard.edu/chemistry/trop/geos/index.html

•Global 3-D model of atmospheric chemistry (v. 5-07-08)

•2ox2.5o 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]

CH4 : A priori distributions from Wang et al. [2004] (monthly)

REDUCED CARBON SOURCES BY SECTOR STANDARD SIMULATION : CO2 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,CH4,NMHCs) 0.27

Biomass Burning (CO,CH4,NMHCs) 0.26

Biofuels (CO,CH4) 0.09

Biogenic Hydrocarbons 0.16

Other Methane Sources* 0.31

TOTAL 1.1

CH4 EMISSIONS AND BUDGET PROPORTIONS

Rice

Livestock

Wetlands

Termites

BiomassBurn

Fossil

Landfills

Biofuel

Standard Simulation :CH4 Oxidation to CO = 0.39 Pg C/yr

CH4 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

CO2COox: Column Integral of

CO2 from CO OxidationCO2RedC :CO2 Emissions from

Reduced C Sources

CO2COox :Maximum in tropics, diffuse

CO2RedC : Localized, corresponding to regions of high CO, CH4 and biogenic NMHC emissions

CO2COox

CO2RedC

gC/(m2 yr)

MODELED SURFACE CONCENTRATIONS : Annual Mean

CO2SURFCO23D

Surface concentrations reflect source distributions:

Diffuse with tropical maximum for CO23D and localized to regions of high reduced C emissions for CO2SURF

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 ymodel = CO23D – CO2SURF

ppm

ymodel : Zonal average

at surface

CO

2 (

pp

m)

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

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

Surfa

ce

y (p

pm)

-50 +50

-0.3

-0.1

0.1

IMPACT ON SURFACE FLUX ESTIMATESInverse analyses by Nir Krakauer

•Estimate effect by modifying concentration error vector as :

(y – (K xa + ymodel))

Then, ‘adjusted’ flux estimate is:

xadj = xa + G(y – (K xa + ymodel))

• 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 ymodel

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 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/y

r

0.22 0.25 0.26

Original Uptake

(a posteriori uncertainty)

-19%-27%-9% % Change

MATCH-CCM TM2-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-UCI TM2-LSCE

Original estimate

With Chemical pump

FLUX ADJUSTMENT (Level 2)

-0.99 +0.34 -0.06 +0.29

-0.64 0.26

0.35 0.32

Flux adjustment (Level 1) 0.26 0.25

MATCH-NCEP

-4.02 +0.27

-3.80

0.22

SUMMARY

•Neglecting the 3D representation of the CO2 source from reduced C oxidation produces systematic errors in inverse CO2 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 CO2 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.