Evaluating the Impact of the Atmospheric “Chemical Pump” on

CO2 Inverse Analyses

P. Suntharalingam

GEOS-CHEM Meeting, April 4-6, 2005

Acknowledgements

J. Randerson, N. Krakauer (UCI/CalTech); D. J. Jacob, J. A. Logan, Y. Xiao, R. M. Yantosca (Harvard); A. Fiore (GFDL)

Suntharalingam et al. [2005], Global Biogeochemical Cycles, submitted.

APPLICATION OF GEOS-CHEM TO EVALUATE CHEMICAL PUMP EFFECT

QUESTION :

What is impact of accounting for realistic representation of

reduced carbon oxidation

1) on modeled CO2 distributions

2) on inverse flux estimates

APPROACH :

Use GEOS-CHEM simulations to estimate magnitude of effect

ATMOSPHERIC CARBON BUDGET

An outstanding question on global CO2 budget :

What is magnitude and distribution of net terrestrial biospheric flux ? (“missing sink”)

The “Top-down” approach uses Inverse Analyses of Atmospheric CO2

? Net Terrestrial Flux ?

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

•Model prior distributions for fossil, seasonal biosphere, ocean ymod

•76 Surface CO2 observation stations (GLOBALVIEW-CO2) yobs

•Estimate “RESIDUAL” CO2 fluxes for 22 regions

Inference of Northern Hemispheric Carbon Uptake from Annual Mean Concentration Residuals

THE TRANSCOM 3 INVERSE ANALYSES (Gurney et al. 2002)

Residuals = ymod – y obsModel simulations (prior fluxes)

CO2 Observations

N. Hem. carbon uptake

OXIDATION OF REDUCED C SPECIES PROVIDES A TROPOSPHERIC SOURCE OF CO2

Fossil Biomass Burning, Agriculture, Biosphere Ocean

ATMOSPHERIC CO2

CO

0.9-1.3 Pg C/yr Non- CO pathways

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 REDUCED CARBON CONTRIBUTION AT SURFACE PRODUCES BIASED INVERSION 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.

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 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 Fossil and

Biosphere sources

CO2SURF Simulation : ySURFCO23D Simulation : y3D

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

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

•Global 3-D model of atmospheric chemistry (v. 5.07)

•2ox2.5o horizontal resolution; 30 vertical levels

•Assimilated meteorology (GMAO); GEOS-3 (year 2001)

•CO oxidation distribution from tagged CO simulation using archived monthly OH fields

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

SOURCE DISTRIBUTIONS : ANNUAL MEAN

Zonal Integral of Emissions

Latitude

CO23D: Column Integral of

CO2 from CO OxidationCO2SURF :CO2 Emissions from

Reduced C Sources

CO23D :Maximum in tropics, diffuse

CO2SURF : Localized, corresponding to regions of high CO, CH4 and biogenic NMHC emissions

CO23D

CO2SURF

gC/(cm2 yr)

-50 50

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

ymodel : Zonal average

at surface

CO

2 (p

pm

)

CHEMICAL PUMP EFFECT : N/S DIFFERENCES

Mean Interhemispheric

difference = - 0.21 ppm

0.21 ppm

Latitude

Impact on TRANSCOM3 Systematic decrease in Northern Hemisphere

Residuals

50-50

IMPACT ON SURFACE FLUX ESTIMATESInverse analyses by Nir Krakauer

•Estimate effect by modifying concentration error vector as :

(y – (K xa + ymodel))

Then, ‘adjusted’ state estimate is:

xadj = xa + G(y – (K xa + ymodel))

• Evaluate with 3 transport models (MATCH, GISS-UCI, LSCE-TM2)

Q : What are the changes in estimates of ‘residual’ fluxes when we account for chemical pump adjustment ymodel

Evaluate impact using TransCom annual mean analysis (Gurney et al. 2002)

Relative impact of chemical pump adjustment on CO2 uptake varies across models.

0.22 0.25 0.26

Original Uptake

-19%-27%-9%

2.5 0.9 1.4

% Change

REDUCTION IN LAND UPTAKE (Northern extratropics) Systematic Reduction (0.22-0.26 Pg C/year)

Pg

C/y

r

SUMMARY

•Neglecting the 3D representation of the CO2 source from reduced C oxidation produces biased 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 (equivalent to a reduction of 0.2-0.3 Pg C/yr in Northern Hemispheric land uptake in an annual mean inversion.)

•Regional changes are larger; up to 0.6 ppm concentration adjustment in regions of high reduced C emissions.

•Impacts on seasonal inverse estimates may be significant and will be examined in future work (N/S y variation: –0.32 ppm (January) to –0.15 ppm (July)).

EXTRA SLIDES

SOURCE ESTIMATES FROM INVERSE ANALYSIS

Minimize cost function:

J(x) = (x – xa)T Sa –1 (x - xa) + (y – K x)T S –1 (y –K x)

Solution:

x = xa + G (y - K xa)

where, G = Sa KT (K Sa KT + S) -1

A posteriori errors : S = (KT S –1 K + Sa –1) -1

Observed concentrations

Modeled concentrations

x = state vector (sources)

xa = a priori source estimate

K = Jacobian matrix (model transport)

Sa = Error covariance matrix on sources

Se = Error covariance matrix on

concentration error

IMPACT ON SURFACE FLUX ESTIMATES Relative Reduction in N.Hemisphere Land Uptake Varies with Model

Reduction in Land Uptake : LSCE-TM2

Reduction in Land Uptake : MATCH

CHEMICAL PUMP FLUX ADJUSTMENTSZONALLY AGGREGATED LAND REGIONS

Relative impact of chemical pump adjustment varies across models, though magnitude of zonally aggregated flux adjustment relatively invariant

Sum N. extratrop. Land net flux (PgC/yr)

- 2.5

- 0.9

-1.4