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: pete.smith@abdn.ac.uk

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

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e

Res

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tivat

eor

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ils

Res

tore

deg

rade

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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

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anag

e

Live

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Seta

side,

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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