How to moderate the impact of agriculture on climate

1. How to moderate the impact of agriculture on climate B.Seguin, D.Arrouays, J.F Soussana INRA (France), A.Bondeau, S.Zaehle PIK Potsdam (Germany) N.de Noblet, P.Smith, N.Viovy, N.Vuichard LSCE (France)

2. Introductory remarks (1) The inverse of the usual view: how the climate impacts agriculture ?

3. Introductory remarks (2) • ‘ moderate’ implies: . an a priori of negative impact (to be discussed) . impact well understood (not totally the case !!) • the impact of agriculture on climate may combine : . indirect effects on GHG net emissions (CO2,CH4,N20.. and H2O ) . direct effects on SEB components , water cycle and local/global climate to be considered concurrently( regional climate change potential as defined by Pielke et al 2002) at different spatial scales…

4. I. At field scale (~100m) • basically action by management practices as : . conservation tillage,fertilization/ irrigation scheduling, residues, animal feed,.. for GHG emissions . mainly irrigation for biophysical SEB, but also timing of crop cycles (winter/summer) • scale corresponding to practical outputs of farmer tactical decisions within the strategic options • first level of interactions (tillage CO2/N20, irrigation for SEB/ N20, pasture management for CH4/N20..)

5. Atmosphere At field scale : first level of interactions CH4 OM fluxes CO2 Herbivore CO2 Manure / Slurry Vegetation CH4 But also surface biophysical variables: albedo, roughness, surface temp.. etc !!! CO2 N2O Dissolved organic C Soil

6. CH4 SF6 CH4 , SF6 SF6 pill CH4: in-situ SF6 tracer method At field scale (~100m) also the basic scale for physical assessment by measure and modelling N2O: automated static chambers and TDL CO2: eddy-correlation system

7. Carbon Loss since Ploughing Carbon loss: 0.25 t C ha-1 within 5 months Or 1.9% of total carbon in the top 15 cm of soil CEH

8. Intensive Extensive the effect of management mode CH4 Int CH4 Ext N2O Int N2O Ext CO2 Int CO2 Ext Cumulative fluxes in C equivalentfor each gas (Laqueuille, 2002)

9. the effect of management mode Greenhouse gas balance (Laqueuille, 2002) ( 2002)

10. II .At farm scale (~1 to 10 km) • the basic scale for strategic options (choice of agricultural productions and resulting crop/livestock systems) • mainly driven by economical constraints • includes alternative solutions as energy cropping (biomass for heat and power, biofuels) and biogas • second level of interactions (annual crops/livestock, conventional/organic farming..) including the fuel energy use (fertilizers, machinery..) • accessible with farm-scale models

11. Bilan de GES d’une ferme d’élevage bovin mixte (100 ha SAU) (Salètes et al., GHG Conference, Leipzig, 2004)

12. Mitigation options at livestock farm level Nitrogen Carbon Water Fertilization Soil cultivation Stocking rate Manure storage Soil cultivation Grazing Irrigation Drainage Groundwater level Management Fertilizer type Manure processing Housing system Manure digestion Soil cultivation Technology Structural Change Farm type Animal number Other crops Flooding Water buffers Farm type Animal number Other crops (after Oenema, WUR, NL)

13. Farm scale budgets and mitigation (J Olesen, DIAS, DK) Account for all emissions from the barn to the pastures

14. III. At large scales (~ 10 to 1000 km) • mainly land-use (crops, pastures,forests,urban areas.. with/without irrigation) and landscape components (trees, hedges) • only accessible with atmospheric models: . local features (detailed land-use, irrigation, landscape components like trees, hedges) in mesoscale models . regional features (main land-use classes) in global models

15. Average organic C stocks in French soils vs. land use (0-30 cm) (Arrouays et al. 2002)

16. Arrouays , J. Balesdent , 08/06/01 Effect of land-use changes on carbone storage for France (computed)

17. Land use change effects on soil carbon stocks 40 30 20 (tC/ha) arable -> forest 10 arable -> grassland 0 forest -> arable Carbon stocks grassland -> arable -10 -20 -30 -40 0 20 40 60 80 100 120 Years after start of policy measure Land use change: carbon storage is slower than carbon relase (After INRA, 2002)

18. GWP (Eq tC-CO2 ha-1 yr-1 ) over Europe for grassland vegetation with cutting management

19. GWP (Eq tC-CO2 ha-1 yr-1 ) over Europe for grassland vegetation with a grazed management

20. The effect of land-use on surface radiative balance Rn = (1-a) Rg – (Rs - Ra) a (1-a) RgTsRsRs - Ra Rn Snow 0.7 300 20 420 20 280 Desert 0.40 600 50 618 218 382 Bare soil 0.25 750 45 580 180 570 Dry pasture 0.25 750 40 544 144 607 Irr. pasture 0.20 800 32 490 90 710 forest 0.10 900 28 460 60 840 Computed values of Rn(W/m2) near midday for different land uses with Rg = 1000, Ra = 400 and Ta = 27 °

21. Land-use classes % surface (1987) LAI(15/4/87) ZOm(15/4/87) Ts(15/4/87) Ta(15/4/87) Dry meadow 23 0.5 0.5 25.2 21 Irr. meadow 12 2 2 22.7 19.3 Rice 9 0.5 1 24.2 21.9 Wheat 9.5 2 4 21.5 21.5 Swamp 7 2 2 22.9 21 Vegetable 3.5 3 3 22.3 20.9 20. 19 18 17. 16 Forests 10 4 10 20.1 20.3 450 300 200 50 The effect of land-use on local climate from Courault et al (1998) LE latent heat flux Ta air temp

22. Land use change => feedback on the climate Forested Deforested: cropland or pasture (Foley et al. 2003) irrigation may induce a global warming of 0.03 to 0.1 W/m2 and a local cooling of 0.8 °K on large irrigated areas (Boucher et al 2004)

23. The effect of landscape components on surface parameters computed influence of relative spacing of tree hedges on albedo (for a surface base value of 0.2) from Guyot and Seguin 1976 Schematic influence of relative spacing of tree hedges on surface aerodynamic roughness z0 and displacement height d from Seguin (1973)

24. Two examples of implementation of agriculture within GCM in european projects : why? to determine the changes of energy and matter (esp. water and carbon) fluxes at the soil-vegetation-atmosphere interface, and the changes in carbon stocks and runoff that occur when agriculture takes place instead of natural vegetation => feedback on the climate LPJ

25. LAI, ~ 6 Jul Oct Total biomass, ~ 20 tDM/ha Grain harvested, ~ 6 tDM/ha Two examples of implementation of agriculture within GCM in european projects : how? each CFT on a distinct stand with access to a separate soil water pool Sowing date estimation: for 4 temperate CFTs = f(T), for 4 tropical CFTs = f(P) Adaptation of heat sum and vernalization requirement Daily coupled growth and development simulation: Phenology, LAI change, carbon allocation to leaves, roots, storage organs, ... Estimation of the harvesting period Implementation of agriculture within LPJ – how? LPJ Winter wheat For grasses, several cuts (f(LAI)), or regular grazing No water stress for irrigated crops, computation of the water requirement and of the effective irrigation Possibility of multiple cropping (e.g. rice) Grass during the intercrop season otherwise Harvested biomass removed, residues sent to the litter pool or removed (fodder, biofuel, ...)

26. LPJ-crops - global results 20th century trends

27. LPJ-crops - global results 20th century trends

28. Initial Conditions State of atmosphere and ocean At a given time Variables describing the state of climate Model Boundary conditions Solar radiation GHG concentrations VEGETATION COVER Numerical experiment with the IPSL model Reference simulation (potential vegetation = mainly forests) Perturbated simulation (vegetation = agriculture)

29. Land-use by agriculture

30. Results for Europe.. Differences: (agriculture – potential vegetation) Brovkin et al., GEB, 1999 But….

31. Corn LAI : LAI 6 6 Blé d’hiver 5 5 4 4 3 3 2 2 1 1 0 0 50 100 150 200 250 300 350 50 100 150 200 250 300 350 days days ORCHIDEE Crops are not adequately represented by vegetation models inside climate models … Winter wheat measures

32. C3 ~ 35% C4 ~ 2.5 % distribution of surfaces occupied by agriculture in Europe Agriculture ~ 37.5% of the Europe surface Resolution = 1°*1° ( combining the CORINE land-ues map with FAO data to partition C3 & C4)

33. NOCROP CROP The influence of crop/ no crop on water balance at the european scale Figure 8 Figure 8

34. ORCHIDEE Evapotranspiration (mm/jour) ORCHIDEE-STICS / C3 =wheat ORCHIDEE-STICS / C3 = soybean Flux de chaleur sensible (W/m2) The influence of C3 crop (wheat/soybean)

35. NPP (gC/m2/day) ORCHIDEE ORCHIDEE-STICS / C3 = wheat ORCHIDEE-STICS / C3 = soybean NEP (gC/m2/day) LAI Photosynthesis and carbon fluxes at the european scale 4 -5

36. Conclusions (1/2) • technical bases for mitigation of GHG emissions by agriculture exist at the field scale • their advantages may be limited (or possibly inversed) by technical aspects at the field scale when considering trade-offs with other GHG or longer term scales. • consistent inventories at the plot scale are lacking in current IPCC methodology • strategical orientations at the farm level (organic/conventional, extensive/intensive management for grassland, etc..) may lead to farm use efficiency as the best tool

37. Conclusions (2/2) • At the larger scales, land-use also induce significant trade-offs, so that biophysical variables need to be considered to fully evaluate the effect of GHG mitigation procedures • Only more comprehensive studies allowing to assess the overall aspects at the various scales (from local to global) will give the significant inputs • If GHG emissions may be considered as aggregative along spatial scales, actions on micro or local climates may significantly locally affect the global climate