Click to edit Master title style Click to edit Master text styles –Second level Third level –Fourth level »Fifth level 1 List of Nominations Closing in on the Missing Carbon Sink: Implications for Climate Research and Mitigation Dr. Britton Stephens National Center for Atmospheric Research

Click to edit Master title style Click to edit Master text styles –Second level Third level –Fourth level »Fifth level 2 List of Nominations Outline: 1.Current state of scientific knowledge concerning global carbon cycling 2.Climate change mitigation challenges associated with knowledge gaps 3.New northern and tropical land uptake estimates from airborne CO 2 measurements 4.Implications of new results for strategies to address climate change

Click to edit Master title style Click to edit Master text styles –Second level Third level –Fourth level »Fifth level 3 List of Nominations Careful atmospheric CO 2 measurements since the 1950s show that about half of fossil fuel emissions remain in the atmosphere FF Atm [IPCC, 2007]

Click to edit Master title style Click to edit Master text styles –Second level Third level –Fourth level »Fifth level 4 List of Nominations How can we separate the natural uptake between land and ocean? [Sabine et al, Science, 2004]

Click to edit Master title style Click to edit Master text styles –Second level Third level –Fourth level »Fifth level 5 List of Nominations 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

Click to edit Master title style Click to edit Master text styles –Second level Third level –Fourth level »Fifth level 6 List of Nominations Carbon Units 1 Petagram C (PgC) = 1 Gigaton C (GtC) = “1 Billon Tons C” = 3.7 Gigaton CO 2 (GtCO 2 ) C CO 2 CH 4 C2H6OC2H6O CaCO 3 H 2 CO 3

Click to edit Master title style Click to edit Master text styles –Second level Third level –Fourth level »Fifth level 7 List of Nominations Uncertainties on natural ocean and land fluxes are +/- 25 to 75 % [IPCC, 2007 and *Canadell et al., PNAS 2007] 1990s Atmospheric Increase 3.2 ± ± 0.1 Fossil Fuel Emissions6.4 ± ± 0.3 Ocean-to- Atmosphere–2.2 ± 0.4–2.2 ± 0.5 Land-to- Atmosphere–1.0 ± 0.6–0.9 ± 0.6 Land-use Change1.6 (0.5 to 2.7)1.5* Residual Land Sink-2.6 (–4.3 to –0.9)-2.4* Land-Based Sink Net Oceanic Sink

Click to edit Master title style Click to edit Master text styles –Second level Third level –Fourth level »Fifth level 8 List of Nominations 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

Click to edit Master title style Click to edit Master text styles –Second level Third level –Fourth level »Fifth level 9 List of Nominations 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

Click to edit Master title style Click to edit Master text styles –Second level Third level –Fourth level »Fifth level 10 List of Nominations 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 At $30/ton of CO 2 : ± 1.5 PgCyr -1 = ± $165 Billion

Click to edit Master title style Click to edit Master text styles –Second level Third level –Fourth level »Fifth level 11 List of Nominations Challenges associated with flux uncertainty 1) Verification

Click to edit Master title style Click to edit Master text styles –Second level Third level –Fourth level »Fifth level 12 List of Nominations Challenges associated with flux uncertainty 2) Prediction [IPCC, 2007] How much can we burn?

Click to edit Master title style Click to edit Master text styles –Second level Third level –Fourth level »Fifth level 13 List of Nominations Challenges associated with flux uncertainty 3) Detection Melting permafrost Thermohaline circulation

Click to edit Master title style Click to edit Master text styles –Second level Third level –Fourth level »Fifth level 14 List of Nominations All model average and standard deviations: Northern Land = -2.4 ± 1.1 PgCyr -1 Tropical Land = +1.8 ± 1.7 PgCyr -1

Click to edit Master title style Click to edit Master text styles –Second level Third level –Fourth level »Fifth level 15 List of Nominations Bottom-up estimates have generally failed to find large uptake in northern ecosystems and large net sources in the tropics

Click to edit Master title style Click to edit Master text styles –Second level Third level –Fourth level »Fifth level 16 List of Nominations An 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

Click to edit Master title style Click to edit Master text styles –Second level Third level –Fourth level »Fifth level 17 List of Nominations 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).

Click to edit Master title style Click to edit Master text styles –Second level Third level –Fourth level »Fifth level 18 List of Nominations 12 Airborne Sampling Programs from 6 International Laboratories

Click to edit Master title style Click to edit Master text styles –Second level Third level –Fourth level »Fifth level 19 List of Nominations Vertical CO 2 profiles for different seasonal intervals

Click to edit Master title style Click to edit Master text styles –Second level Third level –Fourth level »Fifth level 20 List of Nominations 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

Click to edit Master title style Click to edit Master text styles –Second level Third level –Fourth level »Fifth level 21 List of Nominations [Stephens et al., Science, 2007] 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 Outcomes of this work: Helps to resolve a major environmental mystery of the past two decades  Northern “missing carbon sink” may not have 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

Click to edit Master title style Click to edit Master text styles –Second level Third level –Fourth level »Fifth level 22 List of Nominations Implications for Climate Mitigation Strategies 1) National emission estimates Temperate North America Tropical America Fan et al, ± 0.5NA Transcom 3, ± ± 1.1 U.S. SOCCR-0.5 ± 0.25NA NOAA CarbonTracker-0.5 ± ± 0.7 [PgCyr -1 ] Models 4, 5, and C still estimate a strong sink in Temperate North America (-0.9) and a strong source in Tropical America (+0.8) but with large compensating flux revisions in other regions. Zonal partitioning by these models is highly uncertain.

Click to edit Master title style Click to edit Master text styles –Second level Third level –Fourth level »Fifth level 23 List of Nominations Implications for Climate Mitigation Strategies 2) Processes and prediction a.Northern uptake will slow as forests mature b.A tropical fertilization sink will continue as long as CO 2 continues to increase c.A tropical climate change sink may decrease or even reverse depending on feedbacks

Click to edit Master title style Click to edit Master text styles –Second level Third level –Fourth level »Fifth level 24 List of Nominations Implications for Climate Mitigation Strategies 3) Deforestation releases C pool and removes C sink Nominal C Pool (tC/hectare) Sink spread evenly over all forest (tC/hectare/year) Boreal Forest35 1 Temperate Forest60 Tropical Forest120 (~ 200 w/peat) 2 A palm oil plantation can only offset fossil CO 2 emissions at ~ 3 tC/hectare/year

Click to edit Master title style Click to edit Master text styles –Second level Third level –Fourth level »Fifth level 25 List of Nominations Implications for Climate Mitigation Strategies 4) Caveat concerning short-term nature of afforestation and reforestation offsets [IPCC, 2007] On century time-scale oceanic and geologic sequestration will be required

Click to edit Master title style Click to edit Master text styles –Second level Third level –Fourth level »Fifth level 26 List of Nominations Conclusions 1)Large uncertainties exist in estimates of regional carbon fluxes and limit our ability to make optimal mitigation decisions 2)There is a strong need for expanded atmospheric and oceanic observational networks related to carbon cycling 3)Airborne CO 2 data suggest that tropical forests are taking up a lot more and northern much less carbon than previously believed 4)Preventing tropical deforestation is important for preserving existing carbon pools and the capacity to absorb future CO 2 emissions