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)
Introductory remarks (1)
The inverse of the usual view: how the climate impacts agriculture ?
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…
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..)
Manure / Slurry
OM fluxes
Dissolved organic C
Herbivore
Vegetation
Soil
Atmosphere
CH4
CO2
CO2
CH4
CO2
N2O
At field scale : first level of interactions
But also surface biophysical variables:albedo, roughness, surface temp.. etc !!!
At field scale (~100m)
also the basic scale for physical assessment by measure and modelling
N2O: automated static chambers and TDL
SF6 pill
SF6CH4
CH4 , SF6
CH4: in-situ SF6 tracer method
CO2: eddy-correlation system
Carbon Loss since Ploughing
0
0.05
0.1
0.15
0.2
0.25
0.3
J un-02 J ul-02 Aug-02 Sep-02 Oct-02
Cu
mu
lati
ve C
arb
on
Loss
(kg
C m-2
)
Carbon loss: 0.25 t C ha-1 within 5 monthsOr 1.9% of total carbon in the top 15 cm
of soil CEH
-1500
-1000
-500
0
500
1000
1500
24/04 24/05 23/06 23/07 22/08 21/09
Cum
ulat
ed G
WP
(equ
ival
ent C
/CO
2 h
a-1
) the effect of management mode
CH4 Int
CH4 Ext
CO2 Ext
CO2 Int
N2O IntN2O Ext
Cumulative fluxes in C equivalentfor each gas (Laqueuille, 2002)
Intensive Extensive Extensive
the effect of management mode
( 2002)
-600
-500
-400
-300
-200
-100
0
100
200
300
400
a m j j a s o o
Cum
ula
ted
GW
P (e
qu
ival
ent C
/CO
2 h
a-1
)
Extensive
Intensive
Greenhouse gas balance (Laqueuille, 2002)
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
CH4 N2O CO2
tC e
q. h
a-1 yr
-1
-0.6
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Stockage et traitement déjections animalesExhalé/Respiré par les animauxGrasslandCulturesCombustion energie fossileStockage aliment
(Salètes et al., GHG Conference, Leipzig, 2004)
Bilan de GES d’une ferme d’élevage bovin mixte (100 ha SAU)
Mitigation options at livestock farm level Nitrogen Carbon Water
Management
Technology
Structural Change
FertilizationSoil cultivationStocking rate
Manure storageSoil cultivation
Grazing
IrrigationDrainage
Groundwater level
Fertilizer type Manure processing
Housing system
Manure digestionSoil cultivation
Farm typeAnimal number
Other crops
Farm typeAnimal number
Other crops
FloodingWater buffers
(after Oenema, WUR, NL)
Farm scale budgets and mitigation
Account for all emissions from the barn to the pastures
(J Olesen, DIAS, DK)
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
Average organic C stocks in French soils vs. land useLand use and average soil organic C stocks (0-30 cm) in France
0
10
20
30
40
50
60
70
80
90
100
Vin
e/O
rch
ard
Ara
ble
lan
d
Ran
gela
nd
Con
ifero
us
Dec
idu
ous
.
Com
ple
x
Gra
ssla
nd
Gra
ssla
nd
Mix
ed fo
rest
Mo
un
tain
Mo
un
tain
gra
ssla
nd
gra
ssla
nd
Wet
land
Stocks (t C ha-1)
(Arrouays et al. 2002)
(0-30 cm)
Effect of land-use changes on carbone storage for France (computed)
Arrouays, J. Balesdent, 08/06/01
-2
-1
0
1
2
3
4
5
6
7
8
-2
-1
0
1
2
3
4
5
6
7
8S
tock
age
annu
el d
eca
rbon
el(M
t a
n-1)
Abandon de la jachère triennale ou quadriennale
Mise en prairies
Afforestation
Artificialisation et bâtiment
Retournements de prairies
Jachère Européenne
1850 20001900 19501850 20001900 19501850 20001900 19501850 20001900 1950
Land use change effects on soil carbon stocks
-40
-30
-20
-10
0
10
20
30
40
0 20 40 60 80 100 120Years after start of policy measure
Carb
on s
tock
s(tC
/ha)
arable -> forest
arable -> grassland forest -> arable grassland -> arable
Land use change: carbon storage is slower than carbon relase(After INRA, 2002)
GWP (Eq tC-CO2 ha-1 yr-1 ) over Europe for grassland vegetation with cutting management
GWP (Eq tC-CO2 ha-1 yr-1 ) over Europe for grassland vegetation with a grazed management
The effect of land-use on surface radiative balance
Snow 0.7 300 20 420 20 280Desert 0.40 600 50 618 218 382Bare soil 0.25 750 45 580 180 570Dry pasture 0.25 750 40 544 144 607Irr. pasture 0.20 800 32 490 90 710forest 0.10 900 28 460 60 840
a (1-a) Rg Ts Rs Rs - Ra Rn
Rn = (1-a) Rg – (Rs - Ra)
Computed values of Rn (W/m2) near midday for different land uses
with Rg = 1000, Ra = 400 and Ta = 27 °
The effect of land-use on local climateLand-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
Forests 10 4 10 20.1 20.3
from Courault et al (1998)
20.
19
18
17.
16
450
300
200
50
LE latent heat flux Ta air temp
Land use change => feedback on the climateForested 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)
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 dfrom Seguin (1973)
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
Implementation of agriculture within LPJ – how?
Sowing date estimation:for 4 temperate CFTs = f(T), for 4 tropical CFTs = f(P)Adaptation of heat sum and vernalization requirement
Oct Jul
LAI, ~ 6
Total biomass, ~ 20 tDM/haGrain harvested, ~ 6 tDM/ha
Daily coupled growth and development simulation:Phenology, LAI change, carbon allocation to leaves, roots, storage organs, ... Estimation of the harvesting period
No water stress for irrigated crops, computation of the water requirement and of the effective irrigation
For grasses, several cuts (f(LAI)), or regular grazing
Winter wheat
Harvested biomass removed, residues sent to the litter pool or removed (fodder, biofuel, ...)
Possibility of multiple cropping (e.g. rice)Grass during the intercrop season otherwise
each CFT on a distinct stand with access to a
separate soil water pool
Two examples of implementation of agriculture within GCM in european projects : how?
LPJ
LPJ-crops - global results 20th century trends
LPJ-crops - global results 20th century trends
Initial Conditions State of atmosphere and ocean
At a given time
Boundary conditionsSolar radiation
GHG concentrationsVEGETATION COVER
ModelVariables describing
the state of climate
Reference simulation (potential vegetation = mainly forests)Perturbated simulation (vegetation = agriculture)
Numerical experiment with the IPSL model
Land-use by agriculture
Results for Europe..Differences: (agriculture – potential vegetation)
Brovkin et al., GEB, 1999
But….
Crops are not adequately represented by vegetation models inside climate models …
Blé d’hiver
ORCHIDEE
50 100 150 200 250 300 3500
1
2
3
4
5
6
50 100 150 200 250 300 3500
1
2
3
4
5
6LAI :
Corn
LAI
daysdays
Winter wheat
measures
C3 ~ 35% C4 ~ 2.5 %
Agriculture ~ 37.5% of the Europe surface
Resolution = 1°*1° ( combining the CORINE land-ues map with FAO data to partition C3 & C4)
distribution of surfaces occupied by agriculture in Europe
Figure 8
NOCROP
CROP
Figure 8
The influence of crop/ no crop on water balance at the european scale
The influence of C3 crop (wheat/soybean)
Evapotranspiration(mm/jour)
Flux de chaleur sensible(W/m2)
ORCHIDEE
ORCHIDEE-STICS / C3 =wheat
ORCHIDEE-STICS / C3 = soybean
4
-5
Photosynthesis and carbon fluxes at the european scale
LAI NEP (gC/m2/day)
ORCHIDEE
ORCHIDEE-STICS / C3 = wheat
ORCHIDEE-STICS / C3 = soybean
NPP (gC/m2/day)
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
Conclusions (1/2)
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