Aircraft CO2 Observations and Global Carbon Budgeting

Britton Stephens, NCAR EOL and TIIMES

Collaborating Institutions:

USA: NOAA GMD, CSU, France: LSCE, Japan: Tohoku Univ., NIES, Nagoya Univ., Russia: CAO, SIF, England: Univ. of Leeds, Germany: MPIB, Australia: CSIRO MAR

Carbon cycle science as a field began with the careful observational work of Dave Keeling

Keeling, C.D., Rewards and penalties of monitoring the earth, Annu. Rev. Energy Environ., 23, 25-82, 1998.

IGY started 50 years ago this month

Annual-mean CO2 exchange (PgCyr-1) from atmospheric O2

Surface Observations

TransCom1 fossil-fuel gradients

Global and hemispheric constraints on the carbon cycle

1.8 ± 0.8

0.3 ± 0.9 5.4 ± 0.3

2.2 ± 0.4

6.4 ± 0.41.0 ± 0.6

IPCC, 2007

[courtesy of Scott Denning]

[figure courtesy of Scott Denning]

Seasonal vertical mixing

Transcom3 neutral biosphere flux response

349.5

350.0

350.5

351.0

351.5

352.0

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353.0

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354.0

-90 -70 -50 -30 -10 10 30 50 70 90

CSU.gurney

GISS.fung

GISS.prather

GISS.prather2

GISS.prather3

J MA-CDTM.maki

MATCH.bruhwiler

MATCH.chen

MATCH.law

NIES.maksyutov

NIRE.taguchi

RPN.yuen

SKYHI.fan

TM2.lsce

TM3.heimann

GCTM.baker

Latitude

ppm

“Rectifier Effect”

Gurney et al, Nature, 2002

TransCom3 model results based on surface data imply a large transfer of carbon from tropical to northern land regions.

Level 1 (annual mean)Level 2 (seasonal)

Gurney et al, GBC, 2004

Bottom-up estimates have generally failed to find large uptake in northern ecosystems and large net sources in the tropics

Model Model NameNorthern

Total Flux (1)Tropical

Total Flux (1)Northern

Land Flux (1)Tropical

Land Flux (1)

1 CSU -4.4 (0.2) 3.7 (0.6) -3.6 (0.3) 3.3 (0.7)

2 GCTM -3.4 (0.2) 2.3 (0.7) -2.0 (0.3) 2.7 (0.8)

3 UCB -4.4 (0.3) 3.7 (0.6) -3.1 (0.3) 4.0 (0.7)

4 UCI -2.6 (0.3) 0.5 (0.7) -1.5 (0.3) -0.1 (0.8)

5 JMA -1.4 (0.3) -0.5 (0.8) -0.9 (0.4) -0.5 (0.9)

6 MATCH.CCM3 -3.0 (0.2) 2.2 (0.6) -2.1 (0.3) 2.3 (0.7)

7 MATCH.NCEP -4.0 (0.2) 3.2 (0.5) -4.0 (0.3) 3.4 (0.7)

8 MATCH.MACCM2 -3.7 (0.3) 3.1 (0.8) -3.0 (0.3) 2.5 (0.9)

9 NIES -4.0 (0.3) 2.2 (0.6) -3.5 (0.3) 2.7 (0.8)

A NIRE -4.5 (0.3) 1.6 (0.7) -2.8 (0.3) 1.2 (0.8)

B TM2 -1.6 (0.3) -1.4 (0.7) -0.5 (0.3) -1.0 (0.8)

C TM3 -2.4 (0.2) 1.4 (0.6) -2.2 (0.3) 1.0 (0.8)

TransCom 3 Level 2 annual-mean model fluxes (PgCyr-1)

Study N. Total T. Total N. Land T. Land

Jacobson et al., 2006 ('92-'96) -3.9 5.0 -2.9 4.2

Baker et al., 2006 ('91-'00) -3.7 2.7 -2.6 1.9

Gurney et al., 2004 ('92-'96) -3.3 1.8 -2.4 1.8

CarbonTracker, 2007 ('01-'05) -2.8 1.1 -1.8 0.1

Rödenbeck et al., 2003 ('92-'96) -2.3 -0.1 -0.7 -1.0

Rödenbeck et al., 2003 ('96-'99) -2.1 0.3 -0.4 -0.8

Comparison to other studies

fluxes in PgCyr-1 = GtCyr-1 = “billions of tons of C per year”

@ $3 - $30 / ton, 3 PgCyr-1

~ $10 - $100 billion / year

TransCom3 predicted rectifier explains most of the variability in estimated fluxes

Impact on predicted fluxes

349.5

350.0

350.5

351.0

351.5

352.0

352.5

353.0

353.5

354.0

-90 -70 -50 -30 -10 10 30 50 70 90

CSU.gurney

GISS.fung

GISS.prather

GISS.prather2

GISS.prather3

J MA-CDTM.maki

MATCH.bruhwiler

MATCH.chen

MATCH.law

NIES.maksyutov

NIRE.taguchi

RPN.yuen

SKYHI.fan

TM2.lsce

TM3.heimann

GCTM.baker

Model Model Name

1 CSU

2 GCTM

3 UCB

4 UCI

5 JMA

6 MATCH.CCM3

7 MATCH.NCEP

8 MATCH.MACCM2

9 NIES

A NIRE

B TM2

C TM3

ppm

pres

sure

N S N S N S N S

Transcom3 neutral biosphere flux response

Northern Hemisphere sites include Briggsdale, Colorado, USA (CAR); Estevan Point, British Columbia, Canada (ESP); Molokai Island, Hawaii, USA (HAA); Harvard Forest, Massachusetts, USA (HFM); Park Falls, Wisconsin, USA (LEF); Poker Flat, Alaska, USA (PFA); Orleans, France (ORL); Sendai/Fukuoka, Japan (SEN); Surgut, Russia (SUR); and Zotino, Russia (ZOT). Southern Hemisphere sites include Rarotonga, Cook Islands (RTA) and Bass Strait/Cape Grim, Australia (AIA).

Map of airborne flask sampling locations

Airborne flask sampling data

Altitude-time CO2 contour plots for all sampling locations

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-15

10

-10

10

-10

0

-5

Model-predicted NH Average CO2 Contour Plots

Observed NH Average CO2 Contour Plot

Vertical CO2 profiles for different seasonal intervals

Observed and predicted NH average profiles

• 3 models that most closely reproduce the observed annual-mean vertical CO2 gradients (4, 5, and C):

Northern Land = -1.5 ± 0.6 PgCyr-1

Tropical Land = +0.1 ± 0.8 PgCyr-1

• All model average:

Northern Land = -2.4 ± 1.1 PgCyr-1

Tropical Land = +1.8 ± 1.7 PgCyr-1

Estimated fluxes versus predicted 1 km – 4 km gradients

Observed value

Model Model Name

1 CSU

2 GCTM

3 UCB

4 UCI

5 JMA

6 MATCH.CCM3

7 MATCH.NCEP

8 MATCH.MACCM2

9 NIES

A NIRE

B TM2

C TM3

• Interlaboratory calibration offsets and measurement errors

• Diurnal biases

• Interannual variations and long-term trends

• Flight-day weather bias

• Spatial and Temporal Representativeness

Observational and modeling biases evaluated:

All were found to be small or in the wrong direction to explain the observed annual-mean discrepancies

[Schulz et al., Environ. Sci. Technol. 2004, 38, 3683-3688]

WLEF Diurnal Cycle Observations

Estimated fluxes versus predicted 1 km – 4 km gradients for different seasonal intervals

Observed values

Model Model Name

1 CSU

2 GCTM

3 UCB

4 UCI

5 JMA

6 MATCH.CCM3

7 MATCH.NCEP

8 MATCH.MACCM2

9 NIES

A NIRE

B TM2

C TM3

• Models with large tropical sources and large northern uptake are inconsistent with observed annual-mean vertical gradients.

• A global budget with less tropical-to-north carbon transfer is more consistent with bottom-up estimates and does not conflict with independent global 13C and O2 constraints.

• The mean of systematically varying model results is meaningless.

• Simply adding airborne data into the inversions will not necessarily lead to more accurate flux estimates

• Models’ seasonal vertical mixing must be improved to produce flux estimates with high confidence

• There is value in leaving some data out of the inversions to look for systematic biases

Conclusions:

• Improved carbon flux estimates will come from models with improved transport, assimilation of discrete samples, and more comprehensive atmospheric observations.

HIPPO (PIs: Harvard, NCAR, Scripps, and NOAA): A global and seasonal survey of CO2, O2, CH4, CO, N2O, H2, SF6, COS, CFCs, HCFCs, O3, H2O, and hydrocarbons

HIAPER Pole-to-Pole Observations of Atmospheric Tracers

Fossil fuel CO2 gradients over the PacificUCI UCIs

JMA MATCH.CCM3

ppm

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sure

pres

sure

S N S N S N

N S

N S

N S

N S

Science, June 22, 2007

graphic from NCAR communications (Steve Deyo)

Airborne CO2 measurements indicate:

• Northern forests, including U.S. and Europe, are taking up much less CO2 than previously thought

• Intact tropical forests are strong carbon sinks and are playing a major role in offsetting carbon emissions

Implications of this work:

• Helps to resolve a major environmental mystery of the past two decades

Northern “missing carbon sink” has not been found because it is not there

• Improved understanding of processes responsible for carbon uptake will improve predictions of climate change and assessment of mitigation strategies

1

1Faraday, 1855

TransCom3 Modelers:Kevin R. Gurney, Rachel M. Law, Scott Denning, Peter J. Rayner, David Baker, Philippe Bousquet, Lori Bruhwiler, Yu-Han Chen, Philippe Ciais, Inez Y. Fung, Martin Heimann, Jasmin John, Takashi Maki, Shamil Maksyutov, Philippe Peylin, Michael Prather, Bernard C. Pak, Shoichi Taguchi

Aircraft Data Providers:Pieter P. Tans, Colm Sweeney, Philippe Ciais, Michel Ramonet, Takakiyo Nakazawa, Shuji Aoki, Toshinobu Machida, Gen Inoue, Nikolay Vinnichenko, Jon Lloyd, Armin Jordan, Martin Heimann, Olga Shibistova, Ray L. Langenfelds, L. Paul Steele, Roger J. Francey

Additional Modeling:Wouter Peters, Philippe Ciais, Philippe Bousquet, Lori Bruhwiler