Pete Smith's presentation from the Sustainable Food Trust's meeting: What role for grazing livestock in a world of climate change and diet-related disease?

1. 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

2. Delivering food security by 2050 will
be extremely challenging

3. ~ 3 billion in 1960
~7 billion in October 2011
~6 billion 1997
7.218 billion in January 2015

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

5. Reducing demand for livestock
products is essential

6. 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

7. Ripple et al.(2014)
GHG emissions per
unit of food product
– if indirect
emissions are
included, non-
ruminant meat
emissions also
increase

8. 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)

9. Popp et al. (2011)
Reducing GHG emissions – dietary
change vs. technical mitigation
Increased meat Decreased meat
Without
technical
mitigation
With
technical
mitigation

10. 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

11. How will food demand be met in future?
Smith (2014b)

12. Debunking the perpetual carbon
sequestration in grassland myth

13. Bellamy et al. (2005)
From gridded resampling of soils across the whole UK, no gain in
soil C over 25 (losses if anything)
Grasslands

14. No change measured in long term grassland plots in the UK

15. …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]

16. 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.

17. 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

18. Potential for soil C sequestration by
IMPROVING MANAGEMENT
Smith et al. (2008)
0
200
400
600
800
1000
1200
1400
Restorecultivated
organicsoils
Cropland
management
Grazingland
management
Restoredegraded
lands
Ricemanagement
Livestock
Setaside,LUC&
agroforestry
Manure
management
Measure
MtCO2-eq.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

19. Soil C
Vegetation C
Time since management change
Cstock
Management change
Confusion over stocks vs. fluxes
• Sink saturation ~ 20-100 years
• Sink strength declines towards new equilibrium
Smith (2004a)

20. 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)

21. Reducing meat consumption would
improve human health

22. Other papers arriving at similar conclusions……

23. 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)

24. Taxes on food by GHG emissions?
Wirsenius et al. (2011)

25. So why is it not a no-brainer?

26. 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)

27. 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)

28. Thank you for your attention