climate mitigation by agriculture in europe pete smith school of biological sciences, university of...
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Climate mitigation by agriculture in Europe
Pete Smith
School of Biological Sciences, University of Aberdeen, Scotland, UK
Distribution of croplands globally
Distribution of croplands in Europe
Why croplands?
• European croplands (for Europe as far east as the Urals) lose 300 Mt C y-1 (Janssens et al., 2003)
• Mean figure for the European Union estimated to be 78 (SD: 37) Mt C y-1 (Vleeshouwers & Verhagen, 2002)
• Largest biospheric source of carbon lost to the atmosphere in Europe each year
• Highest uncertainty of all European fluxes• There is significant potential to decrease the flux of
carbon to the atmosphere from cropland, and for cropland management to sequester soil carbon.
Main figure from Janssens et al., Science 2003
Croplands in the overall carbon balance of Europe
Cropland flux
0
200
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600
D
CB
A
missing fluxes
?
land signal
atmospheric signal
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Carbon balance estimates
Eu
rop
ean
ter
rest
rial
C b
alan
ce (
Tg
C a
)-1)
Why croplands?
• European croplands (for Europe as far east as the Urals) lose 300 Mt C y-1 (Janssens et al., 2003)
• Mean figure for the European Union estimated to be 78 (SD: 37) Mt C y-1 (Vleeshouwers & Verhagen, 2002)
• Largest biospheric source of carbon lost to the atmosphere in Europe each year
• Highest uncertainty of all European fluxes• There is significant potential to decrease the flux of
carbon to the atmosphere from cropland, and for cropland management to sequester soil carbon.
a
b
c
d
e
f
Vleeshouwers & Verhagen (2002)
Carbon fluxes in SOC in Europe (t C ha-1 y-1) in the 1st commitment period (business as usual scenario)
Croplands Grasslands
Using mean soil organic carbon content
Using mean soil organic carbon content plus S.D.
Using mean soil organic carbon content minus S.D.
Why croplands?
• European croplands (for Europe as far east as the Urals) lose 300 Mt C y-1 (Janssens et al., 2003)
• Mean figure for the European Union estimated to be 78 (SD: 37) Mt C y-1 (Vleeshouwers & Verhagen, 2002)
• Largest biospheric source of carbon lost to the atmosphere in Europe each year
• Highest uncertainty of all European fluxes• There is significant potential to decrease the flux of
carbon to the atmosphere from cropland, and for cropland management to sequester soil carbon.
Can cropland GHG fluxes be reduced ?
Options for combating the greenhouse effect on European agricultural land• More efficient use of animal manure
• Application of sewage sludge
• Return surplus cereal straw to the soil
• Convert to no-till agriculture
• Use surplus arable land to de-intensify production (extensification)
• Use surplus arable land to plant woodland
• Use surplus arable land to grow biofuelsSmith et al. (2000)
C sequestration potential
over 1st commitment periodActivity t C ha-1 yr-1 Mt C yr-1
Conversion arable to grassland 1.92 178.49Zero till 0.29 26.69Straw 0.21 19.85Farmyard manure (10 ton ha-1) 1.47 136.38CO2 0.01 0.94Temperature -0.06 -5.80
Vleeshouwers & Verhagen (2002)
Carbon mitigation potential / CO2-C offsets
Smith et al. (2000)
0
10
20
30
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60
70
Manure Sludge Straw No-till Extensification Woodland Bioenergy
Land Management Change
Max
imum
Yea
rly
C M
itig
atio
n P
oten
tial
(T
g C
y-1)
-
0
1
2
3
4
5
6
% O
ffse
t of
199
0 E
uro
pean
CO
2 car
bon
emis
sion
s
Combined land-management options
Smith et al. (2000)
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10
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B+NTB+S
B+O
B+O+NT
W+NT
W+S
W+O
W+O+NT
E+NTE+S
E+O
E+O+NTOpt
Scenario
Max
imum
Yea
rly
C M
itig
atio
n P
oten
tial
(T
g C
y-1)
0
1
2
3
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8
9
% O
ffse
t of
199
0 E
uro
pean
CO
2 car
bon
emis
sion
s
Europe’s 8% Kyoto target
Carbon sequestration potential
Biological potential
Biologically / physically constrained potential (e.g. land suitability)
Maximum value Minimum value
Economically constrained potential
Socially / politicallyconstrained potential - estimatedrealistically achievablepotential (~10% of biological potential)
What is meant by C sequestration potential ?
EU-15 can sequester up to 16-19 Mt C y-1 during the first commitment < 1/5 of theoretical potential ~ 2% of European anthropogenic emissions (Freibauer et al., 2004).
Smith (2004)
Study
Study 1 Study 2 Study 3 Study 4
C s
eque
stra
tion
pote
ntia
l by
2010
(T
g C
y-1
)
-50
0
50
100
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200
Low estimateHigh estimate
Carbon sequestration potential (EU-15 cropland)
1 = Vleeshouwers & Verhagen (2002)
2 = Smith et al. (1997, 2000)
3 = Freibauer et al. (2004)
4 = Smith et al. (2004)
Is C sequestration important in the long term?
Why use C sequestration?
IPCC TAR WGIII (2001)
The energy / emission gap under different SRES scenarios
• Current yearly atmospheric C increase = 3.2 ± 0.1 Pg C y-1
• Maximum yearly global C sequestration potential = 0.9 ± 0.3 Pg C y-1
• Emission gaps here of up to 25 Pg C y-1 by 2100
So why use C sequestration?
Critical period determining trajectory IPCC (2001)
Importance of non-CO2 GHGs
Agricultural non-CO2 GHG emissions in Europe
GHG Yearly emission Mt CO2-C equivalents
Carbon dioxide (CO2) ~80
Methane (CH4) ~50
Nitrous oxide (N2O) ~60
C mitigation potential with and without trace gases
Smith et al. (2001)
= CO2 only= with trace gases
0
10
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70
Manure Sludge Straw No-till Extensification Woodland Bioenergy
Land Management Change
Max
imum
Yea
rly
C M
itig
atio
n P
oten
tial
(T
g C
y-1
)
0
1
2
3
4
5
6
% O
ffse
t of
1990
Eur
opea
n C
O2 E
mis
sion
s= CO2-C alone
= CO2-C plus N2O and CH4
Some land-management practices are influenced by including trace gases
Mean soil C stock to 30cm (t C ha-1) - excluding highly organic soils
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100
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12
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0
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Years after 1900
Me
an
so
il C
sto
ck
(t
C h
a-1
)
SRES climate only
SRES-B2 plus convertgrassland to arable in 2000
Loss (2001-2100) of 37.7 t C ha-1 compared to B2 loss of 9.5 t C ha-1 due to climate change alone
Land-use change – potential size of effect
Research Priority Areas• Soil process studies in agriculture
• Data / inventory collation and meta-analysis
• Development of future land-use and land management scenarios
• Coupling of the C & N cycles (with N-IP)
• Assessment of total GHG budget (with N-IP)
• Mitigation options
Overall aim: Quantify the carbon and GHG balance of European croplands for the 1990s, for the present, and in the future