Aircraft CO 2 Observations and the Missing Carbon Sink 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

Science paper coming out June 22 draft graphic from NCAR communications Airborne CO 2 measurements indicate: Northern forests, including U.S. and Europe, are taking up much less CO 2 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

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, IGY started 50 years ago next month

Expected from fossil fuel emissions Motivation: Atmospheric CO 2 increase Climate change

Annual-mean CO 2 exchange (PgCyr -1 ) from atmospheric O 2 Surface Observations TransCom1 fossil-fuel gradients Global and hemispheric constraints on the carbon cycle 1.8 ± ± ± ± ± ± 0.6 IPCC, 2007

[courtesy of Scott Denning]

[figure courtesy of Scott Denning] Seasonal vertical mixing

Transcom3 neutral biosphere flux response 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

ModelModel Name Northern Total Flux (1  ) Tropical Total Flux (1  ) Northern Land Flux (1  ) Tropical Land Flux (1  ) 1CSU-4.4 (0.2)3.7 (0.6)-3.6 (0.3)3.3 (0.7) 2GCTM-3.4 (0.2)2.3 (0.7)-2.0 (0.3)2.7 (0.8) 3UCB-4.4 (0.3)3.7 (0.6)-3.1 (0.3)4.0 (0.7) 4UCI-2.6 (0.3)0.5 (0.7)-1.5 (0.3)-0.1 (0.8) 5JMA-1.4 (0.3)-0.5 (0.8)-0.9 (0.4)-0.5 (0.9) 6MATCH.CCM3-3.0 (0.2)2.2 (0.6)-2.1 (0.3)2.3 (0.7) 7MATCH.NCEP-4.0 (0.2)3.2 (0.5)-4.0 (0.3)3.4 (0.7) 8MATCH.MACCM2-3.7 (0.3)3.1 (0.8)-3.0 (0.3)2.5 (0.9) 9NIES-4.0 (0.3)2.2 (0.6)-3.5 (0.3)2.7 (0.8) ANIRE-4.5 (0.3)1.6 (0.7)-2.8 (0.3)1.2 (0.8) BTM2-1.6 (0.3)-1.4 (0.7)-0.5 (0.3)-1.0 (0.8) CTM3-2.4 (0.2)1.4 (0.6)-2.2 (0.3)1.0 (0.8) TransCom 3 Level 2 annual-mean model fluxes (PgCyr -1 ) StudyN. TotalT. TotalN. LandT. Land Jacobson et al., 2006 ('92-'96) Baker et al., 2006 ('91-'00) Gurney et al., 2004 ('92-'96) CarbonTracker, 2007 ('01-'05) Rödenbeck et al., 2003 ('92-'96) Rödenbeck et al., 2003 ('96-'99) Comparison to other studies fluxes in PgCyr -1 = GtCyr -1 = “billions of tons of C per $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 ModelModel Name 1CSU 2GCTM 3UCB 4UCI 5JMA 6MATCH.CCM3 7MATCH.NCEP 8MATCH.MACCM2 9NIES ANIRE BTM2 CTM3

ppm pressure NSNSNSNS 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 CO 2 contour plots for all sampling locations

Model-predicted NH Average CO 2 Contour Plots Observed NH Average CO 2 Contour Plot

Vertical CO 2 profiles for different seasonal intervals

Observed and predicted NH average profiles

3 models that most closely reproduce the observed annual-mean vertical CO 2 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 ModelModel Name 1CSU 2GCTM 3UCB 4UCI 5JMA 6MATCH.CCM3 7MATCH.NCEP 8MATCH.MACCM2 9NIES ANIRE BTM2 CTM3

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, ] WLEF Diurnal Cycle Observations

Estimated fluxes versus predicted 1 km – 4 km gradients for different seasonal intervals Observed values ModelModel Name 1CSU 2GCTM 3UCB 4UCI 5JMA 6MATCH.CCM3 7MATCH.NCEP 8MATCH.MACCM2 9NIES ANIRE BTM2 CTM3

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 13 C and O 2 constraints. 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:

HIPPO (PIs: Harvard, NCAR, Scripps, and NOAA): A global and seasonal survey of CO 2, O 2, CH 4, CO, N 2 O, H 2, SF 6, COS, CFCs, HCFCs, O 3, H 2 O, and hydrocarbons HIAPER Pole-to-Pole Observations of Atmospheric Tracers Fossil fuel CO 2 gradients over the Pacific UCIUCIs JMAMATCH.CCM3 ppm pressure SNSNSN NS NS NS NS

Science paper coming out June 22 draft graphic from NCAR communications Airborne CO 2 measurements indicate: Northern forests, including U.S. and Europe, are taking up much less CO 2 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

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