1. Atmospheric inversion of CO 2 sources and sinks Northern Hemisphere sink Jay S. Gregg

2. Goal Inverse modeling identifies carbon sources and sinks, and coupled with a planetary transport model, generates predicted CO 2 concentrations. Ideally, the model is adjusted so that the predicted flux measurements best match those measured at various locations around the globe. Paraphrased from Gurney, 2006, http://www.purdue.edu/eas/carbon/inverse_modeling.html

3. Components Observed Atmospheric Concentrations of CO 2 Observed Atmospheric Concentrations of CO 2 Spatiotemporal concentrations (ppm) of CO 2 Spatiotemporal concentrations (ppm) of CO 2 Observed Sea Surface Concentrations of CO 2 Observed Sea Surface Concentrations of CO 2 Partial Pressure of CO 2 Partial Pressure of CO 2 General Circulation Model General Circulation Model

4. Sources and Sinks Involved Fossil-Fuel-Based Emissions (Confidence: High) Land Use Change (Confidence: Low) Terrestrial Ecosystem Response to Elevated CO 2 (Confidence: Low) Terrestrial Sink (Confidence: Low) Ocean Sink (Confidence: Low) *Confidence refers to amount, temporal pattern, and spatial location

5. Atmospheric CO 2 Observations Geophysical Monitoring for Climate Change (GMCC) Network Based on flask measurements 20 cites since 1980

6. Atmospheric CO 2 Sampling Sites Mountainous Sites (e.g., Mauna Loa) were not used due to difficulty in elevation for the transport models ppm +300 Tans et al., 1990

7. Atmospheric CO 2 Concentration predicted concentrations from known sources and sinks (b, c, d) Tans et al., 1990 observed concentrations Evidence for missing northern hemisphere sink

8. Oceanic Observations Observed pCO 2 difference between surface ocean and atmosphere Transect Sampling, some data gaps in Indian and Southern Ocean- extrapolation based on Sea Surface Temperatures Oceans divided into 2 o x 2 o grids, and mean  pCO 2 is calculated for the periods (January through April) and (July through October)

9. Oceanic CO 2 Calculations Working Formula for F (CO 2 flux across air-sea interface): E: gas transfer coefficient, depends on wind speed V p : gas transfer piston velocity, depends on turbulence, atmospheric and oceanic S: solubility of CO 2 in seawater  pCO 2 : Sea surface – Atmosphere (>0 is a ocean sink, 0 is a ocean sink, <0 is an ocean source) Tans et al., 1990

10. Oceanic CO 2 Calculations Transect Samples as of 1972 Tans et al., 1990

11. Oceanic CO 2 Fluxes Largest positive fluxes (sinks) are in the equatorial oceans Largest negative fluxes (sources) are in the Southern gyres Tans et al., 1990

12. Oceanic CO 2 Fluxes Jan-Apr Jul-Oct Tans et al., 1990

13. Transport Model 3-D General Circulation Model (GCM) from Goddard Space Flight Center, NASA 3-D General Circulation Model (GCM) from Goddard Space Flight Center, NASA Seasonal, diurnal Seasonal, diurnal

14. Transport Model (vs. Observed) ScandinaviaBass Strait Tans et al., 1990 observed modeled

15. Modeled Atmospheric CO 2 Concentrations Tans et al., 1990 Relative to Global Mean Concentration observed modeled

16. Modeled Fluxes (C. Roedenbeck et al., 2002)

17. Modeled Fluxes (C. Roedenbeck et al., 2002)

20. Modeled NPP (C. Roedenbeck et al., 2002) arbitrary units (linear)

21. Modeled CO 2 Sources and Sinks Atmospheric CO 2 increases about 3 Gt C/yr Atmospheric CO 2 increases about 3 Gt C/yr Sinks are larger in northern hemisphere than southern Sinks are larger in northern hemisphere than southern ocean sink is largest at equator ocean sink is largest at equator must be a larger northern terrestrial sink must be a larger northern terrestrial sink El Nino and La Nina cycles changes fluxes El Nino and La Nina cycles changes fluxes Still a lot of uncertainty in global carbon cycle Still a lot of uncertainty in global carbon cycle

22. Which Transport Model to Use? Many different transport models can give different results Many different transport models can give different results Underscores uncertainty in inverse model results Underscores uncertainty in inverse model results Transcom 3 Project (Gurney, 2002) seeks to compare the outcome from various models Transcom 3 Project (Gurney, 2002) seeks to compare the outcome from various models

23. Which Transport Model to Use? Comparison of two transport models, confidence range for all models are in boxes (Gurney et al., 2002)

24. Which Transport Model to Use? Confidence range for all models based on latitude (Gurney et al., 2002)

25. Factors in CO 2 Flux Variability El Nino and La Nina (increased biomass burning), changes in NPP El Nino and La Nina (increased biomass burning), changes in NPP Volcanic Eruptions (e.g., Pinatubo- changes in NPP from sunlight limitations) Volcanic Eruptions (e.g., Pinatubo- changes in NPP from sunlight limitations) Temperature and humidity affect microbial respiration (soil respiration increases at higher temperatures) Temperature and humidity affect microbial respiration (soil respiration increases at higher temperatures) (C. Roedenbeck et al., 2002)

26. References I.G. Enting, C.M. Trudinger, R..J.A. Francey (1995) A synthesis inversion of the concentration of  13 C of atmospheric CO 2. Tellus B 47, 35-52. S. Fan, et al., (1998) A large terrestrial carbon sink in North America implied by atmospheric and oceanic carbon dioxide data and models. Science 282, 442- 446. K. R. Gurney et al., Towards robust regional estimates of CO 2 sources and sinks using atmospheric transport models, Nature 415, 626 (2002). C. Roedenbeck, S. Houweling, M. Gloor, and M. Heimann (2003) CO 2 flux history 1982–2001 inferred from atmospheric data using a global inversion of atmospheric transport, Atmos. Chem. Phys., 3, 1919–1964. P. P. Tans, I. Y. Fung, T. Takahashi, (1990) Observational Constraints on the Global Atmospheric CO 2 Budget, Science 247, 1431-1438.