What Science tells us:
What are the emissions & how can they
be reduced?
Harry Clark Director
New Zealand Agricultural GHG
Research Centre
Co-chair GRA Livestock Research
Group
Carolyn Imede Opio, Livestock Policy
Officer
Livestock Information, Sector
Analysis and Policy Branch (AGAL)

Global estimates of agricultural GHG emissions
from livestock
• Global consensus is that 12-14% of all anthropogenic non-CO2-e emissions (CH4
and N2O) arise directly from agriculture. Approximately 70% of these arise
directly from livestock (IPCC 2014).
• Country estimates obtained from global databases do not necessarily correspond
well with more complex in-country estimates or with supply chain approaches.
Estimated that livestock supply chains account for 7.1 GT CO2e (14.5% of all global
anthropogenic greenhouse gas emissions).
• Sector highly diverse, livestock serve multiple purposes, utilise a variety of
resources and vary widely in their emissions per unit of food produced.
• Emissions from livestock forecast to increase (20-30%?).

GHG emissions from the livestock sector
Relative contribution of life-cycle
phases – global livestock sector
• Total GHG emissions: 7.1 Gt
CO2-eq.
FAO, 2013

Livestock contribution to historical warming
0.81°C in 2010
- 0.11°C (14%)
- 0.16°C (19%)
- 0.27°C (34%)

Short vs long lived GHGs

How shall I compare thee to CO2?
• CO2 equivalents are a way of expressing different gases using a
common currency.
• A number of different methods are available and there is no ‘correct’
method – the best method depends upon the question being asked.
• The current IPCC/UNFCCC method (GWP100) used for international
accounting has some limitations with respect to setting reduction
targets for different gases.

CH4 and CO2 have very different effects on
the climate

CH4 concentration
0 50 100 150 200
Disappearance vs warming
methane

0 50 100 150 200
CO2 concentration
Disappearance vs warming
carbon dioxide

Concentration vs warming
(continuous pulse of emission)

Implications
• Constant carbon dioxide (and nitrous oxide) emissions result in linearly
increasing warming.
• Constant methane emissions result in warming that levels off; but it takes >
hundred years to do so.
• Carbon dioxide is the main driver of peak warming. To keep below 2oC net
CO2 emissions must go to zero.
• Methane emissions affect the trajectory towards peak warming and
reductions can help reduce peak warming. They do not have to go to zero to
limit warming to below 2OC.

Mitigation options for livestock agriculture
1. Further increases in animal productivity and farm efficiency
2. Technologies that directly seek to reduce emissions
3. Soil carbon sinks
4. Demand side measures – reducing meat consumption

Mitigation via increasing efficiency (20-30% reduction
potential)
• Increases in efficiency has resulted in consistent decreases in emissions intensity i.e. the
quantity of GHG emitted per unit of animal product - in Asia fell from 12.9kg CO2e to 4kg CO2e
between 1961 and 2012.
• The routes for increasing efficiency are known and based on technologies that improve
efficiency at both the individual animal and herd level. Relevant to all systems of production.
• Decreasing emissions via productivity increases is strongly synergistic with increased food
security, rising incomes and system resilience.
• Where livestock production is relatively static, increasing efficiency can reduce emissions per
unit of product and absolute emissions. Where the sector is expanding, it will, at a minimum,
reduce emissions below ‘business as usual’.

(Gerber et al., 2011)
Emissions intensity vs milk yield

Direct mitigation technologies e.g. enteric fermentation
(reduction potential ??)
• No shortage of potential mitigation approaches - concentrate feeding, lipids,
nitrate supplementation, garlic, essential oils, tannins, yeasts, statins, biogas etc.
• Uncertainty and variability of the mitigation impact, practicality, and costs pose
significant barriers which limit the extent to which the mitigation potential can
currently be realised in practice.
• Number of ‘new’ technologies under development – chemical inhibitors (2-3
years from market); anti-methanogen vaccines (still at POC stage); selective
breeding for low methane (industry implementation in sheep).

Hristov et al 2015
‘Clean cow’ – on the market in 2 years?

Soil carbon sequestration (reduction potential ??)
• Many soils have the potential to physically sequester more carbon than they do
currently. Increasing soil C stocks has multiple benefits –ecosystem resilience.
• Large gaps in knowledge on how management practices can be manipulated to
increase soil carbon sequestration, particularly in grasslands (pasture restoration,
grazing management, integration with trees promising but poorly quantified).
16/07/2018
1
8

Grassland management impacts on soil carbon
stocks: a new synthesis
Grassland management impacts on soil carbon stocks: a new synthesis, Volume: 27, Issue: 2, Pages: 662-668, First published: 07 March 2017, DOI: (10.1002/eap.1473)

Soil carbon sequestration (reduction potential ??)
• Many soils have the potential to physically sequester more carbon than they do
currently. Increasing soil C stocks has multiple benefits –ecosystem resilience.
• Large gaps in knowledge on how management practices can be manipulated to
increase soil carbon sequestration, particularly in grasslands (pasture restoration,
grazing management, integration with trees promising but poorly quantified).
• Quantification of soil carbon sequestration challenging; small changes & large stocks,
spatial variability, environmental influences; short vs. long term etc.
• Soil carbon stock increases are reversible and sequestration rate declines over time.
• General statements about soil carbon sequestration are potentially misleading –
context specific with good potential in some places at some times.
16/07/2018
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0

Demand-Side Mitigation Measures (reduction
potential 20-30% ??)
• Changing the demand for specific foods (for example via changes in
consumption patterns) could make a contribution to mitigation efforts.
• Livestock products, while varying considerably in their emissions per unit of
energy and protein, generally have higher emissions compared with plant
based products. Health benefits of lower meat consumption in some regions.
16/07/2018 21

Demand-Side Mitigation Measures (reduction
potential 20-30% ??)
• Changing the demand for specific foods (for example via changes in
consumption patterns) could make a contribution to mitigation efforts.
• Livestock products, while varying considerably in their emissions per unit of
energy and protein, generally have higher emissions compared with plant
based products. Health benefits of lower meat consumption in some regions.
• There is a lack of systematic analysis on whether the identified technical
mitigation potential is feasible in economic, social and political terms,
particularly in developing countries.
16/07/2018 23

Summary
• Livestock are important in context of
climate change
• When setting reduction targets the
properties of different gases need to be
considered
• Mitigation options exist
• Concerted action needed and a ‘basket’
approach likely to bring best results