Carbon sequestration in agricultural soils a global ... · against reliance on carbon sequestration...
Transcript of Carbon sequestration in agricultural soils a global ... · against reliance on carbon sequestration...
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Carbon sequestration in agriculturalCarbon sequestration in agricultural soils – a global perspectiveg p p
Pete SmithRoyal Society-Wolfson Professor of Soils & Global Change, FSB, FRSE &Science Director of Scotland’s ClimateXChangeI i f Bi l i l & E i l S iInstitute of Biological & Environmental Sciences,School of Biological Sciences, University of Aberdeen, S tl d UKScotland, UKE-mail: [email protected]
Carbon Credits for Sustainable Land Use Systems (CaLas). Scientific basis and practical implications – reality and visions. Frick, Switzerland, 15 December 2010
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Outline• The challengeg• How can carbon be sequestered in
agricultural soilsagricultural soils• Global mitigation potential for soil C
sequestrationsequestration• Comparison with other GHG mitigation
measures• Limitations of soil C sequestrationq• Conclusions
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What are our emission reduction targets?What are our emission reduction targets?The UK as an example
UK Cli Ch A (2008)• UK Climate Change Act (2008)– Targets of 34% (or 42%) reduction in UK g ( )
emissions by 2020, and 80% by 2050
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UK emissions now and in 2050
Source: UK Committee on Climate Change
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What will it cost?What will it cost?
• 80% cut in GHG emission by 2050 relative to 1990: all GHGs, aviation and shipping , pp gincluded
• 42% cut in GHGs by 2020 relative to 1990• 42% cut in GHGs by 2020 relative to 1990 (31% relative to 2005)
• 2020 cost less than 1% of GDP
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How does soil C sequestration k?work?
Increase C inputs or reduce C lossesOrganic e.g. residue management,
Increase C inputs…e.g. restore & rewet farmed
...or reduce C lossesOrganic carbon source
organic amendments, increased plant C input…
rewet farmedorganic soils
Add to soilCO2
C in soil Some C is stabilisedSoilin the soil
il lSoil C cycle
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How does soil C sequestration work? – reduced disturbance
No-till Tillage
Tillage breaks
CC
C
CTillage breaksopen aggregates
CC
C
CC Organic material (C)more exposed to microbial attack and
K
microbial attack and weathering
= microbe C = C inside aggregate
= weatheringKey:
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A ti it P ti S ifi t h I D R d
Mechanisms for soil C sequestration in agriculture
Activity Practice Specific management change Increase C inputs
Decrease C losses
Reduce disturbance
Cropland management Agronomy Increased productivity XRotations XCatch crops X
g
Catch crops XLess fallow XMore legumes XDeintensification XImproved cultivars XImproved cultivars X
Nutrient management Fertilizer placement XFertilizer timing X
Tillage / residue management Reduced tillage XZero tillage XgReduced residue removal X XReduced residue burning X X
Upland water management Irrigation XDrainage X
Set-aside and land use change Set aside X XWetlands X X
Agroforestry Tree crops inc. Shelterbelts etc. X XGrazing land management Livestock grazing intensity Livestock grazing intensity X
Fertilization Fertilization XFire management Fire management XSpecies introduction Species introduction XMore legumes More legumes XI d d ti it I d d ti it XIncreased productivity Increased productivity X
Organic soils Restoration Rewetting / abandonment X XDegraded lands Restoration Restoration X X X
Smith et al. (2008)
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Manure – large & long-lasting ff teffects100
Organic C in Soil Farmyard manure annually
80
(t ha-1)
60
Farmyard manure 1852-1871
40
Farmyard manure 1852 1871 nothing thereafter
20 Unmanured
01850 1890 1930 1970
Rothamsted Hoosfield – Jenkinson 1998
1850 1890 1930 1970Year
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Global mitigation potential in i lagriculture
16001 )
1200
1400M
t CO 2-e
q. y
r-1
N2OCH4
800
1000
on p
oten
tial (
M CO2
400
600
sical
miti
gatio
0
200
ent
ent
ent
& nd ent
ed ed oils ck entloba
l bio
phys
-200
plan
d m
anag
eme
Wat
er m
anag
eme
Ric
e m
anag
eme
Seta
side,
LU
C
agro
fore
stry
Gra
zing
lan
man
agem
e
Res
tore
cul
tivat
eor
gani
c so
ils
Res
tore
deg
rade
land
s
Bio
ener
gy (s
oco
mpo
nent
)
Live
stoc
anur
e m
anag
emeG
Cro
p W Ma
Mitigation measure
Smith et al. (2008)
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High and low estimates of the
1800
mitigation potential in each region
1400
1600
1000
1200
q. y
r-1
400
600
800
Mt C
O2-
eq
0
200
400
a a n a a a a
-200
Sout
heas
t Asia
Sout
h A
mer
ica
East
Asia
Sout
h A
sia
Easte
rn A
fric a
sian
Fede
ratio
n
Nor
th A
mer
ica
Wes
tern
Eur
ope
Wes
tern
Afri
ca
Cen
tral A
sia
orth
ern
Euro
pe
Mid
dle
Afri
ca
Easte
rn E
urop
e
Oce
ania
outh
ern
Euro
pe
Cen
tral A
mer
ica
Nor
ther
n A
frica
Wes
tern
Asia
Sout
hern
Afri
ca
Car
ribea
n
Japa
n
Poly
nesia
Rus
N W W
No E So C N S
Region Smith et al. (2007)
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Effect of C price on implementation
1400
1000
1200
1400up to 20 USD t CO2-eq.-1up to 50 USD t CO2-eq.-1up to 100 USD t CO2-eq.-1
600
800
1000
CO
2-eq.
yr-1
400
600
Mt C
0
200
vate
dils an
dm
ent
g la
ndm
ent
aded
emen
t
stock
UC
&ry ure men
t
Res
tore
cul
tivor
gani
c so
i
Cro
pla
man
agem
Gra
zing
man
agem
Res
tore
deg
rala
nds
Ric
e m
anag
e
Live
s
Seta
side,
LU
agro
fore
str
Man
um
anag
em
Smith et al. (2007)Measure
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Global mitigation potential in agriculture (Mt CO2-eq. yr-1)
Price range (USD t CO2-eq. -1)0->>100 (technical
Scenario 0-20 0-50 0-100 potential)
B1 1925 2384 3149 5480B1 1925 2384 3149 5480
A1b 1982 2439 3254 5670
B2 2047 2495 3330 5844
A2 2119 2549 3330 5957
Smith et al. (2007)
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Global economic mitigation potential for g pdifferent sectors at different carbon prices
7GtCO 2-eq
4
5
6
2
3
4
Non-OECD/EI T
0
1
<20
<50
<100 <2
0
<50
<100
EITOECDWorld total
US$/tCO 2-eqEnergy supply
< <
Transport Buildings Industry Agriculture Forestry WasteUS$/tCO 2 eq
IPCC WGIII (2007)
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How do we cut GHG emissions d h h ill it t?and how much will it cost?
From: McKinsey (2009) - Pathways to a low-carbon economy Version 2 of the Global Greenhouse Gas Abatement Cost Curve
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How do we cut GHG emissions and how much will it cost?and how much will it cost?
From: McKinsey (2009) - Pathways to a low-carbon economy Version 2 of the Global Greenhouse Gas Abatement Cost Curve
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Smith (2008) International Journal of Agricultural Sustainability 6(3),169–170
“There are a number of well rehearsed arguments• “There are a number of well rehearsed arguments against reliance on carbon sequestration for tackling climate change, involving saturation of the carbon sink (th b i l d f th t h hil(the carbon is only removed from the atmosphere while the tree is growing or until the soil reaches a new equilibrium soil carbon level; Smith, 2005), permanence( b i k b d t t b(carbon sinks can be reversed at any stage by deforestation or poor soil management; Smith, 2005), leakage/displacement (e.g. planting trees in one area l d d f i i h I lleads to deforestation in another; Intergovernmental Panel on Climate Change (IPCC), 2000), verificationissues (can the sinks be measured; Smith, 2004), and ( )total effectiveness relative to emission reduction targets (only a fraction of the reduction can be achieved through sinks; IPCC, 2007)”.; , )
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Saturation – the time course of C sequestration
stoc
k
Soil C
C s
Vegetation C
Time since management changeManagement change
• Sink saturation ~ 20-100 yearsSink saturation 20 100 years• Sink strength declines towards new equilibrium
Smith (2004a)
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Permanencee a e ce
75
85C
ha-1
) Conversion to low-input cropland
65
cm
(t C
Management change
45
55
OC
to 2
3
35
45
Tota
l SO
251844 1894 1944 1994 2044 2094
T
YearManure treatment in red, Woodland in blue Smith (2005)
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Leakage / displacement: are we actually g p ysequestering carbon or just moving it about?
Manure Manure Mineral NMore manure here….but……..less manure here
Farm with more manure Farm with less manureEffect over the whole cropland area = zero
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VerificationVerification
Cost
Zero return
Value of C sequestered
Cost
No. of samples required to demonstrateincrease in soil C
Smith (2004b)
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“Trying to sequester the geosphere in the biosphere”
The C we release through fossil fuel burning has been• The C we release through fossil fuel burning has been locked up for ~300 Million years and was accumulated over many millions of years – we are trying to lock that
/ d d it d t dd !up over years / decades – it does not add up!• “It is easier to leave the marbles in the jar than to tip
them out and try to pick them all up again” W.H. (Bill) y p p g ( )Schlesinger
• Soil C sequestration is time limited, non-permanent, difficult to verify and is no substitute for GHG emissiondifficult to verify and is no substitute for GHG emission reduction
• Soil C sequestration may have a role in reducing the h t t t h i CO t ti d b ishort term atmospheric CO2 concentration, and buying
us time to develop longer term solutions, largely in the energy sector
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ConclusionsConclusions
S il C t ti l b ll h l• Soil C sequestration globally has a large, cost-competitive mitigation potential
• Useful to meet short / medium term targets – especially if these are high (e.g. in UK)p y g ( g )
• Many co-benefits – soil fertility, workability, water-holding capacity etc (see other talk)water-holding capacity etc. (see other talk)
• Don’t forget the limitations: time limited, not permanent doesn’t replace gen inenot permanent, doesn’t replace genuine emission reduction
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Thank you for your attentionThank you for your attention