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
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
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
UK emissions now and in 2050
Source: UK Committee on Climate Change
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
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
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:
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)
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
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)
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)
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
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)
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)
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
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
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)”.; , )
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)
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)
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
VerificationVerification
Cost
Zero return
Value of C sequestered
Cost
No. of samples required to demonstrateincrease in soil C
Smith (2004b)
“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
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
Thank you for your attentionThank you for your attention