HIPPO: Global Carbon Cycle Britton Stephens, NCAR EOL and TIIMES

Careful atmospheric CO 2 measurements since the 1950s show that about half of fossil fuel emissions remain in the atmosphere FF Atm [IPCC, 2007]

Annual fluxes are small relative to balanced seasonal exchanges and to standing pools The global carbon cycle for the 1990s, showing the main annual fluxes in GtC yr –1. [IPCC, 2007] Annual residuals Land-Based Sink Net Oceanic Sink Pools and flows Uncertainties on natural annual-mean ocean and land fluxes are +/- 25 to 75 %

Global atmospheric inverse models and surface data have been used to make regional flux estimates Forward: Flux + Transport = [CO 2 ] Inverse: [CO 2 ] – Transport = Flux

12 Model Results from the TransCom 3 Study ModelModel Name 1CSU 2GCTM 3UCB 4UCI 5JMA 6MATCH.CCM3 7MATCH.NCEP 8MATCH.MACCM2 9NIES ANIRE BTM2 CTM3 Systematic trade off between northern and tropical land fluxes

Regional land flux uncertainties are very large All model average and standard deviations: Northern Land = -2.4 ± 1.1 PgCyr -1 Tropical Land = +1.8 ± 1.7 PgCyr -1

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

A helpful discovery about the nature of the model disagreements ModelModel Name 1CSU 2GCTM 3UCB 4UCI 5JMA 6MATCH.CCM3 7MATCH.NCEP 8MATCH.MACCM2 9NIES ANIRE BTM2 CTM3 Systematic trade off is related to vertical mixing biases in the models Tropical Land and Northern Land fluxes plotted versus vertical CO 2 gradient

12 Airborne Sampling Programs from 6 International Laboratories 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).

12 Airborne Sampling Programs from 6 International Laboratories

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

Comparing the Observed and Modeled Gradients ModelModel Name 1CSU 2GCTM 3UCB 4UCI 5JMA 6MATCH.CCM3 7MATCH.NCEP 8MATCH.MACCM2 9NIES ANIRE BTM2 CTM3 Most of the models overestimate the annual-mean vertical CO 2 gradient Observed value 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 Northern Land Tropical Land

[figure courtesy of Scott Denning] Seasonal vertical mixing

[Stephens et al., Science, 2007] Airborne measurements suggest: 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 However, large (O ~ 2 PgCyr -1 ) flux uncertainties associated with modeling atmospheric CO 2 transport remain

ppm pressure NSNSNSNS Transcom3 Tropical Asia Response ppm latitude

ppm pressure NSNSNSNS Transcom3 Southern Ocean Response ppm latitude

Air-Sea Flux Comparison Contemporary Fluxes [courtesy A. Jacobsen]

ppm pressure NSNSNSNS Transcom3 Fossil Fuel Response ppm latitude

TransCom Seasonal APO Amplitude T. Blaine, SIO Dissertation, 2005

START: Gravitational Fractionation [Ishidoya et al., O 2 /N 2 in the Stratosphere, GRL, 2006]

Ishidoya et al., O 2 /N 2 in the Stratosphere, GRL, 2006 Stratospheric O 2 and N 2 Observations Observations Corrected for Gravitational Fractionation This study: 12 samples per balloon flight, ± 40 per meg precision in O 2 /N 2 START-08 AO2: 5-second sampling at ~ ± 5 per meg precision in O 2 /N 2 START-08 MEDUSA: 16 samples per flight, ± 2 per meg precision in O 2 /N 2 and ± 10 per meg precision in Ar/N 2 Gravitational fractionation 3 X greater for Ar/N 2

[NOAA ESRL] Many other relevant species will be measured, including: SF 6