Reducing global meat consumption would

improve the climate, food security and

human health, so why is it not a no-brainer?

Pete Smith

Professor of Soils & Global Change, FSB, FRSE,

Institute of Biological & Environmental Sciences

University of Aberdeen,

Scotland, UK.

E-mail: pete.smith@abdn.ac.uk

What role for grazing livestock in a world of climate change and

diet-related disease? Bristol, 3rd February 2015

Delivering food security by 2050 will

be extremely challenging

~ 3 billion in 1960

~7 billion in October 2011

~6 billion 1997

7.218 billion in January 2015

http://www.csiro.au/Portals/Multimedia/On-the-record/Sustainable-Agriculture-Feeding-the-World.aspx

Reducing demand for livestock

products is essential

Demand- and supply-side measures need to be considered

• Supply-side measures in

the AFOLU sector are

large & cost-competitive

• Demand-side measures

such as dietary change and

waste reduction also have

large, but uncertain,

mitigation

• Demand-side measures

may be difficult to

implement, but are worthy

of further research

• Other options in the

AFOLU sector include

bioenergy

Smith et al. (2014) – IPCC WGIII AR5

Ripple et al.(2014)

GHG emissions per

unit of food product

– if indirect

emissions are

included, non-

ruminant meat

emissions also

increase

Changed consumption patterns

Land based GHG emissions:

Fewer animal

products in global diet

allows everyone to be

fed, and land is

available for energy

and nature

conservation

Stehfest et al. (2009)

Popp et al. (2011)

Reducing GHG emissions – dietary

change vs. technical mitigation

Increased meat Decreased meat

Without

technical

mitigation

With

technical

mitigation

Food demand must be managed because sustainable

intensification alone will not suffice

Bajželj et al. (2014) Nature CC

units 2009* CT1 CT2 CT3 YG1 YG2 YG3

Cropland Mkm2 15.6 22.5 (+44%) 18.7 (+20%) 17.6 (+12%) 18.2 (+16%) 16.0 (+2%) 14.6 (-6%)

Pasture Mkm2 32.8 35.2 (+7%) 32.6 (-1%) 26.8 (-18%) 36.0 (+10%) 33.1 (+1%) 27.1 (-17%)

Net Forest cover Mkm2 26.1 23.1 (-12%) 24.7(-6%) 26.1(+0%) 24.2 (-7%) 25.6(-2%) 27.1 (+4%)

Tropical Pristine Forests Mkm2 7.9 7.2 (-9%) 7.4 (-7%) 7.4 (-6%) 7.4 (-6%) 7.6 (-4%) 7.6 (-4%)

Total GHG emissions GtCO2/y 13.5 22.2 (+64%) 16.1 (+20%) 11.7 (-13%) 19.2 (+42%) 15.0 (+11%) 10.2 (-25%)

Carbon sink potential GtCO2/y 14.7 14.5 (-1%) 14.6 (-0%) 14.8 (+0%) 14.6 (-1%) 14.7 (+0%) 14.7 (+0%)

Fertiliser use Mt/y 103 166(+61%) 136(+32%) 125(+22%) 226(+120%) 196(+90%) 175(+70%)

Irrigation water use km3/y 2889 6496(+125%) 5328(+84%) 5075(+76%) 5051(+75%) 4413(+53%) 4157(+44%)

Current yield

trend

Yield gap

closure only

Yield gap closure +

demand options

How will food demand be met in future?

Smith (2014b)

Debunking the perpetual carbon

sequestration in grassland myth

Bellamy et al. (2005)

From gridded resampling of soils across the whole UK, no gain in

soil C over 25 (losses if anything)

Grasslands

No change measured in long term grassland plots in the UK

…flat dairy pastures lost 0.73±0.16 Mg C ha−1 y−1 and 57±16 kg N

ha−1 y−1 but we observed no significant change in soil C or N in flat

pasture grazed by “dry stock” (e.g., sheep, beef), or in grazed

tussock grasslands. [over 2-3 decades]

Smith (2014)

After establishment, soil C increases in grasslands, but after

about 100 years it reaches a new equilibrium

Increase in organic carbon (%C to 23 cm depth), calculated from total N

values presented in Johnson et al. (2009), assuming a C : N ratio of 10 : 1.

Total N values were from a number of silty clay loam soils sown to grass

from cropland at various times and for various periods at Rothamsted, UK.

What would grasslands be like if they were

continually sequestering C at these rates?

• If all grasslands where continually sequestering 1 t C ha-1

yr-1, from a zero baseline, grasslands would gain 2000 t C

ha-1 yr-1 over 2000 years – so many European grasslands

would have stocks as high as peatlands if this were the

case.

• Actual grassland SOC stocks in UK are around 160 t C ha-

1 to 1m depth (or 230 t C ha-1 in Scotland; Bradley et al.,

2005).

• So as well as being theoretically untenable, continual C

accumulation by grasslands is not supported by the

evidence

Potential for soil C sequestration by

IMPROVING MANAGEMENT

Smith et al. (2008)

0

200

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Mt

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q.

yr-1

up to 20 USD t CO2-eq.-1

up to 50 USD t CO2-eq.-1

up to 100 USD t CO2-eq.-1

Soil C increase of

0.22 t C ha-1 yr-1

possible under

improved (not

constant) management

Soil C

Vegetation C

Time since management change

C s

tock

Management change

Confusion over stocks vs. fluxes

• Sink saturation ~ 20-100 years

• Sink strength declines towards new equilibrium

Smith (2004a)

Summary of evidence on grassland

carbon sequestration• Grasslands under constant management do not

sequester carbon - apparent C sequestration could

result from legacy effects, perhaps many years ago

• High carbon stocks do not equate to high rates of C

sequestration - business as usual does not sequester

carbon

• Policy implications: Protect the high C stocks in

grasslands, and if management is suboptimal,

improve it to sequester carbon

Smith (2014)

Reducing meat consumption would

improve human health

Other papers arriving at similar conclusions……

The diet–environment–health trilemma

• “Alternative diets that offer substantial health benefits

could, if widely adopted, reduce global agricultural

greenhouse gas emissions, reduce land clearing and

resultant species extinctions, and help prevent such diet-

related chronic non-communicable diseases.

• The dietary choices that individuals make are influenced

by culture, nutritional knowledge, price, availability, taste

and convenience, all of which must be considered if the

dietary transition that is taking place is to be counteracted.

• The implementation of dietary solutions to the tightly

linked diet–environment– health trilemma is a global

challenge, and opportunity, of great environmental and

public health importance.” Tilman & Clark (2014)

Taxes on food by GHG emissions?

Wirsenius et al. (2011)

So why is it not a no-brainer?

So why is it not a no brainer?• Not all grassland is suitable for conversion to cropland

(too wet/dry) – best way to get human edible food from

this land is via ruminants. But concentrate feed must be

reduced

• Food is immensely socially and culturally important –

deeply embedded in all cultures and self-identities

• Resistance to interference in personal choice – could be

political suicide

• Resistance from the meat, livestock and dairy industries

• Food taxes are a blunt instrument and lead to a range of

other issues (e.g. food access / social justice / equity)

• Opportunity for high-quality, grass fed beef to fill a niche

as an occasional, luxury product (with high premium)

Conclusions• Reducing demand for livestock products (particularly

ruminants) would improve climate mitigation, improve future food security and improve human health

• We need to change consumption patterns (demand-side measures) – techno-fixes are not enough to make the necessary changes

• Grasslands under constant management do not sequester carbon – but they do contain high C stocks which should be protected

• Food is extremely important for people and it will be extremely difficult to incentivise behaviour change – some radical and probably extremely unpopular policies (e.g. meat taxes) would be needed – creating a range of other political / social issues (e.g. equity / social justice)

• It is not a no brainer for political, environmental, social and cultural reasons – but it does need to happen Smith (2014a)

Thank you for your attention