1. Lecture 4. GFDL Terrestrial Carbon Cycling Model Elena Shevliakova & Chip Levy

2. Ocean Biogeochemical and Dynamic Land Carbon Cycle Modeling (the GFDL Earth System Model) John DunneGFDL/NOAA (John.Dunne@noaa.gov)John.Dunne@noaa.gov Ron StoufferGFDL/NOAA Elena ShevliakovaPrinceton University (Elena.Shevliakova@noaa.gov)Elena.Shevliakova@noaa.gov Sergey MalyshevPrinceton University Chris MillyUSGS Steve PacalaPrinceton University Hiram levyGFDL/NOAA

3. GFDL’s earth system model (ESM) for coupled carbon-climate Land physics and hydrology Ocean circulation Atmospheric circulation and radiation Land physics and hydrology Ocean ecology and Biogeochemistry Atmospheric circulation and radiation Chemistry – CO 2, NO x, SO 4, aerosols, etc Ocean circulation Plant ecology and land use Climate Model Earth System Model Sea IceLand Ice Sea IceLand Ice

4. The Zero Order View of the Carbon Cycle (Integrated Assessment Models - IAMs for example) Atmosphere CO 2 = 280 ppmv (560 PgC) + FF Ocean Circ. + BGC Biophysics + BGC 37,400 Pg C + FF 2000 Pg C 90 ± 60± 10 0 -10 3 yr 10 0 -10 2 yr Fossil Fuels 4 yr …equilibrium takes 10 3 -10 4 yrs

5. Resolution Cubed sphere, Lat x Lon – 2 ° x 2.5 ° [atm.] – 1° x 1 ° [land] Time step: ~30 Minutes Simulation: centuries

6. Current land processes represented in GFDL’s current ESM Plant growth –Photosynthesis and respiration – f(CO 2, H 2 O, light, temperature) –Carbon allocation to leaves, soft/hard wood, coarse/fine roots, storage Plant functional diversity –Tropical evergreen/coniferous/deciduous trees, warm/cold grasses Dynamic vegetation distribution –Competition between plant functional types –Natural fire disturbance – f(drought, biomass) Land use –Cropland, pastures, natural and secondary lands –Conversion of natural and secondary lands and abandonment –Agricultural and wood harvesting and resultant fluxes in collaboration with Princeton U., U. New Hampshire and USGS (Schevliakova et al., 2009)

7. Land Model Forcings Lands use changes Climate

8. Canopy and canopy air Soil/snow Atmosphere Photosynthesis Plant and soil respiration Energy and moisture balance C & N uptake and release t~ 30 min fine roots Land energy, water, carbon and nitrogen exchange leaves sapwood labile wood C & N allocation and growth, t ~ 1 day Phenology, t~ 1 month Mortality, natural and fire t ~ 1 year Biogeography, t ~ 1 year { Land-use management, t ~ 1 year Climate statistics Carbon gain Plant type LAI, height, roots Vegetation dynamics Dynamic Land Model LM3 leaching Humans

9. LM3 structure: sub-grid heterogeneity

10. 5 vegetation types C3 and C4 grasses temperate deciduous evergreen coniferous tropical 5 vegetation C pools 2 or 4 soil C pools Sub-grid land use 4 land-use types up to 15 tiles for different ages Natural mortality and fire Land and atmosphere are on the same grid 2°x 2.5° in ESMs Cube-sphere in CM3 Vegetation structure in LM3

11. Hydrology

12. Now For Some Detail

13. Biosphere-atmosphere exchange: photosynthesis and respiration Photosynthesis: 6 CO2 + 12 H2O + light → C6H12O6 + 6 O2 + 6 H2O Carbon Dioxide + Water + Light energy → Glucose + Oxygen + Water Respiration: C6H12O6 + 6O2 → 6CO2 + 6H2O

14. Response to drying, lower CO 2 : C4 photosynthesis evolves in plants Advantages of C4 photosynthesis Higher CO 2 /O 2 ratio where Rubisco catalyzes photosynthesis, less CH 2 O oxidation Plants can take up CO 2 at night, when humidity is high, and not lose water Consequence: C4 plants do better at low CO 2, dry climates C3 plants - trees and some grasses C4 plants - other grasses, grains (corn, sorghum, millet) CO 2 CO 2 +H 2 O --> CH 2 O (C3) +O 2 or CH 2 O+O 2 --> CO 2 +H 2 O The enzyme Rubisco catalyzes both reactions. Oxidation increases at lower CO 2. CO 2 C4 --> C3+CO 2 CO 2 +H 2 O --> CH 2 O+O 2 or CH 2 O+O 2 --> CO 2 +H 2 O C3+CO 2 --> C4 (CO 2 molecule is loosely bound to C3 compound C4 C3 C3 photosynthesis C4 photosynthesis

15. C3, C4 and CAM plants Carbon fixation

16. Carbon Engine – Photosynthesis Model (Farquhar et al. 1980, Collatz et al. 1992, Leuning 1990) A system of three equations with three unknowns, the stomatal conductance; g s,the intercellular concentration of CO 2, C i (mol/mol); and the net photosynthesis, A n (mol CO 2 /m 2 s), defines the plant uptake of CO 2 and the rate of non-water-stressed transpiration for a thin canopy layer dLAI’ at a temperature T l (K)receiving an incident photosynthetically active radiation flux Q(LAI’) (Einstein/m 2 s) and surrounded by canopy air with vertically uniform specific humidity q ca (kg/kg) and CO 2 concentration C ca (mol/mol):

17. a is the leaf absorptance of photosynthetically active radiation, α 3 and α 4 are the intrinsic quantum efficiencies, V m is the maximum velocity of carboxylase in molCO 2 /m 2 s, Γ * = α co2 [O 2 ] K C /(2K O ) is the compensation point, K C and K O are the Michaelis-Menten constants for CO 2 and O 2, [O 2 ] is the atmospheric oxygen concentration, p ref =10 5 Pa is the reference pressure and p is an atmospheric pressure. The temperature dependence of the Michaelis-Menten constants, the maximum velocity of carboxylase, and the compensation point are described by Arrhenius function where T is the temperature (˚K) and E 0 is a temperature sensitivity factor (Foley et al. 1996) Parameters

18. Equation 13 gives the leaf stomatal conductance for vegetation if the soil water is not limiting. It links the rate of stomatal conductance for water g s to the net photosynthesis (A n ), intercellular concentration of CO 2 (C i ), and humidity deficit between intercellular space and external environment (q sat (T l ) - q ca ). This equation is a simplification of Leuning’s (1985) empirical relationship assuming that contribution of cuticular conductance is negligible. Equation 14 is a one-dimensional gas diffusion law The factor of 1.6 is the ratio of diffusivities for water vapor and CO 2. We assume that the diffusion of CO 2 is mostly limited by stomatal conductance and not by leaf boundary layer conductance. Equations 15 C3 and 15 C4 are based on the mechanistic model of photosynthesis by Farquhar et al. (1980) and its extensions by Collatz et al. (1991, 1992). The net photosynthesis is the difference between the gross photosynthesis and leaf respiration. The gross photosynthesis for C 3 plants is the minimum of three limited rates: the light limited rate J E, the Rubisco limited rate J C, and the export limited rate of carboxylation J j. Similarly, in Collatz et al. (1992) the gross photosynthesis rate for C 4 plants is the minimum of the light limited rate J E, the Rubisco limited rate J C, and the CO 2 limited rate J CO2. Leaf respiration is computed as R leaf = γV m (T l ). Although the formulation of Collatz et al (1991) is widely used in dynamic vegetation and land surface models, it requires computationally expensive iterative solutions. The simplifying assumption made in equation 13 that cuticular conductance is negligible, allows an analytical solution for the three unknowns.

19. Present Day Simulated Vegetation and Soil C pools model potential veg, current climate observation-based estimates LM3 generates present-day spatial distribution of vegetation and soil carbon Veg CSoil C

20. LM3 is designed to diagnose and predict the land use sink

21. Total carbon loss: 228 Gt Current crop area: 1.4 billion ha Current pasture area: 3.1 billion ha Ecosystem carbon, kg kg /m 2 Carbon Loss from 1700 to 2000 Current Crop FractionCurrent Pasture Fraction natural total natural secondary pasture crops LM3 Predicted Carbon Loss Due To Land Use Change

22. Why secondary vegetation is important ? Stand alone LM3V forced by the atmospheric data from the GFDL AM2 model, CO 2 =350 ppm C flux, GT C/yr No wood harvesting Land-use scenarios from Hurtt et al. 2006 HYDE SAGE/HYDE HYDE SAGE/HYDE Shevliakova et al. 2009

23. Why do we need a model of vegetation dynamics and C cycle?

24. 2050 Current Models Predict a Big Sink From CO 2 Fertilization

25. Uncertainty about the magnitude of CO 2 fertilization is the key factor determining whether vegetation is a net carbon source or sink No CO 2 fertilizationCO 2 Fertilization at 700 ppm Shevliakova et al. 2006 -460Pg GFDL Slab-Ocean Climate Model SM2.1coupled to Dynamic Land model LM3V Atmospheric CO 2 concentration: 700 ppm Change in Vegetation Biomass, kgC/m2 +200 Pg

26. Transient land C flux and storage, Historic and A1B Future (ESM2.1) GtC A1B_phot_fert A1B_phot_286 phot_hist phot_286 Even under assumption of CO 2 fertilization, C storage declines after 2100 Under assumption of “no CO2 fertilization ” land biosphere will undergo a catastrophic loss of C

27. Solving the carbon problem is twice as hard if the missing sink is caused by land use instead of CO 2 fertilization. Hypotheses for the terrestrial sink: 1. CO 2 Fertilization 2. Climate Change 3. Land Use Terrestrial Sink

28. Ocean processes represented in GFDL’s current ESM Coupled C, N, P, Fe, Si, Alkalinity, O 2 and clay cycles Variable Chl:C:N:P:Si:Fe stoichiometry Phytoplankton functional groups –Small (cyanobacteria) / Large (diatoms/eukaryotes) –Calcifiers and N 2 fixers Herbivory - microbial loop / mesozooplankton (filter feeders) Carbon chemistry/ocean acidification Atmospheric gas exchange/deposition and river fluxes Water column denitrification Sediment N, Fe, CaCO 3, clay interactions

29. Coupled elemental cycles in the GFDL global biogeochemical model Carbon Oxygen Phosphorus Nitrogen Iron Alkalinity/CaCO 3 DOM cycling Particle sinking Gas exchange Solubility pump Loss from system Atm. Deposition River Input Sediment Input Scavenging CaCO 3 only Lithogenic Silicon

30. Ocean ecology in the GFDL global biogeochemical model Small phyto. Large phyto. Protists Filter feeder DOM Detritus New nutrients Recycled nutrients N 2 -fixers

31. Observations (present) Model (pre-industrial) CO 2 Flux

32. 20 Yr Time Series of Southern Hemisphere CO 2 Flux (total and oceanic)

33. Where are we in the ESM model development process? Plan to use ESMs for next IPCC (AR5) –Thousands of years to spin-up and 300-yr runs into the future –4 new future scenarios of GHGs and land-use change –~40 experiments planned Atm CO 2 anomaly in a control integration

34. CO 2 Anomaly Time Series

35. Scientific Questions For The Land Model How did recent changes in climate, CO 2 and land use shape the present day distribution of land carbon and nitrogen sources and sinks? What are the influences of land cover changes on continental precipitation and runoff? What are the implications of climate change for the distribution and functioning of terrestrial vegetation? This is particularly important for agriculture. (Why?) What are the terrestrial biosphere feedbacks on climate? What is the role of plant diversity in the global biogeochemical cycles and climate system?

36. Scientific Questions For The Earth System Model How will climate interactions with the Land Model influence CO 2 levels in the atmosphere over the short term? How will land use interactions with the Land Model influence CO 2 levels in the atmosphere over the short term? What role will CO 2 fertilization play in controlling CO 2 levels? Will ocean biogeochemistry control the long-tem level of CO 2 in the atmosphere and what will it be? Two longer-term land wild cards: soil C release in a warmer Arctic; CH 4 release in a warmer Arctic

37. The End

38. Summary The GFDL land model: –represents a range of biosphere-climate interactions and feedbacks; –captures effects of both climate change and land use on vegetation dynamics and structure; –simulates historic and future distribution of Carbon sources and sinks; –Will characterize coupled Carbon-Nitrogen dynamics in plants and soils. Upcoming improvements include increased biodiversity, seasonal fire, N and P cycles, and ecological data assimilation for formal parameter estimation. Currently there is considerable uncertainty about the magnitude of climate effects on biosphere and its feedbacks.

39. GFDL LM3 Functionality Land surface parameterization: –energy, water, and momentum exchange Hydrological processes: –River flow, water resource development and use, extreme events Ecological processes: –vegetation functioning, structure, distribution, disturbance* (natural and anthropogenic), and succession* Carbon cycling – CO 2 fluxes, vegetation and soil carbon pool Land use and management* * These are relatively unique features

40. A Computer Model is: a theoretical/numerical construct that represent a set of particular processes and phenomena –a set of variables – input, output, state, parameters – a set of logical and quantitative relationships between them –a set of assumptions Idealized logical framework to test hypotheses and to ask scientific questions

41. Historic C emissions from anthropogenic pools simulated by LM3 Malyshev et al., 2009

42. Lichstein et al. in prep (2009) Above Ground Biomass (AGM) vs Annual mean Temperature

43. AR5 RCPs (van Vuuren et al. 2008) New scenarios are developed for the next IPCC assessment (pre-ind. to present day +2.3 W/m 2, IPCC AR4)