Climate mitigation by agriculture in Europe Pete Smith School of Biological Sciences, University of...

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

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CB

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missing fluxes

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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)

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Manure Sludge Straw No-till Extensification Woodland Bioenergy

Land Management Change

Max

imum

Yea

rly

C M

itig

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oten

tial

(T

g C

y-1)

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% O

ffse

t of

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0 E

uro

pean

CO

2 car

bon

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sion

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Combined land-management options

Smith et al. (2000)

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B+NTB+S

B+O

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E+O

E+O+NTOpt

Scenario

Max

imum

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rly

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itig

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tial

(T

g C

y-1)

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% O

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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

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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

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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

)

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% 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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Years after 1900

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an

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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