The Carbon footprint of livestock farming

Question 1

What percentage of human-made GHG emissions does livestock production contribute? Which emissions does this include and why is it hard to reduce these?

Answer 1

• Livestock contribute 14.5% of human-made GHG emissions
• Includes methane and nitrous oxides
• Hard to reduce as food demand rises (offsetting reductions)

Question 2

Within livestock, which type of organisms produce the greatest GHG emissions (think digestion)?

Answer 2

Ruminant animals (5.7 Gt vs 1.3 Gt)

Question 3

What is the largest “area” where CH4 emissions can be mitigated (think industry)?

Answer 3

Livestock

Question 4

Where globally are diets associated with significant land requirements found? Diets requiring minimal land are associated with what - where are these found?

Answer 4

North America, eastern South America and parts of Europe.
Diets with the lowest land use are those typically consuming less meat (and fewer ruminant animals), such as South-east Asia and Africa

Question 5

What is a ruminant?

Answer 5

An animal that contains a multi-chambered digestive system (essentially a fermentation chamber). for better nutrient acquisition e.g., cattle, sheep, deer etc.

Question 6

Why are ruminant animals significant sources of methane (CH4)?

Answer 6

Ruminants have a multi-chambered digestive system (a fermentation chamber) where microbes break down tough molecules (polysaccharides) in anaerobic conditions.
This anaerobic process produces methane (methanogenesis).

Question 7

Where is the majority of CH4 released from ruminants?

Answer 7

Burps (95%)

Question 8

Where do cattle gain the majority of their nutritional needs?

Answer 8

From forages (grasses) and roughages (high-fibre food sources)

Question 9

How could the formation of CH4 by ruminants be reduced?

Answer 9

• More digestively efficient feeds with supplements (more C to the animal; less CO2 as waste)
• The consumption of hydrogen by organisms in the gut to reduce methane production (although this requires adaptations to the microbiome)

Question 10

Other than the production of GHGs by the ruminant itself, what are other sources of GHGs in livestock production?

Answer 10

• Waste (slurry anaerobic tanks)
• Manure (high production of N2O)

Question 11

Can pastures be a sink for CO2? What about other gases?

Answer 11

Yes - CO2 can be taken up into soils
However -> N2O produced by these pastures, so need to find a balance

Question 12

Which GHG has the highest GWP over 100 years?

Answer 12

N₂O – ~273x more warming potential than CO₂.

Question 13

What is the GWP of methane (CH₄) compared to CO₂ over 100 years?

Answer 13

CH₄ ≈ 30x more than CO₂.

Question 14

What is the GWP of carbon dioxide (CO₂)?

Answer 14

1 (baseline for comparison).

Question 15

List CO2, CH4 and N2O in order of greatest GWP (from lowest to highest).

Answer 15

CO2, CH4 and N2O

Question 16

Which GHG stays in the atmosphere the longest?

Answer 16

CO₂ – hundreds to thousands of years.

Question 17

What is the approximate lifetime of methane (CH₄)?

Answer 17

~12 years.

Question 18

What is the approximate lifetime of nitrous oxide (N₂O)?

Answer 18

~120 years.

Question 19

List CO2, CH4 and N2O in order of greatest atmospheric lifetime (from lowest to highest).

Answer 19

CH4, N2O and CO2

Question 20

What happens after a pulse emission of CH₄?

Answer 20

Causes a quick temperature spike, but effect declines rapidly (as has an atmospheric lifetime of only 12 years)

Question 21

What is the effect of a CO₂ pulse?

Answer 21

Small initial warming, but lasts much longer (less warming potential in the short-term but long lifetime)

Question 22

How does a pulse of N₂O behave?

Answer 22

Moderate initial warming that persists for centuries.

Question 23

What happens with continuous CH₄ emissions?

Answer 23

Rapid warming early, then plateaus as CH₄ breaks down.

Question 24

What is the pattern of warming for continuous CO₂ emissions?

Answer 24

Gradual, linear increase – keeps rising over time.

Question 25

What happens with continuous N₂O emissions?

Answer 25

Strong, growing warming – combines high GWP + long lifetime. Does sort of plateau as molecules do breakdown, but much less significant than that of methane.

Question 26

Why is reducing CH₄ emissions important for short-term climate benefits?

Answer 26

CH₄ causes fast warming, so reducing it leads to quick cooling.

Question 27

Why are CO₂ reductions crucial even if the effects are slow?

Answer 27

Because CO₂ accumulates and lasts for centuries, long-term reduction is vital.

Question 28

Why is N₂O a serious concern despite lower attention than CH₄?

Answer 28

It has very high GWP and long lifetime, contributing significantly to long-term warming.

Question 29

Within livestock GHG emissions, list the top five sources of GHGs within this production (from greatest to smallest).

Answer 29

1. Enteric fermentation in ruminants (40%) 2. Manure (25%) 3. Animal feed (13%) 4. Land-use change (10%) 5. Post-farm emissions e.g., transport (2.9%)

Question 30

What does a negative flux of CO2 during livestock production suggest (e.g., the UK)?

Answer 30

That pastures and grasslands for livestock is allowing an uptake of CO2 (becoming a sink), suggesting land-use change is not necessarily required.

Question 31

What is the main source of grain crop production? What is second to this?

Answer 31

To feed people (47%) 36% is produced to feed animals

Question 32

How many people could be fed by the grain that livestock eat in the US?

Answer 32

800 million people

Question 33

How much of livestock grain is unfit for human consumption?

Answer 33

86%

Question 34

Describe the life cycle of feedlot cattle in the US.

Answer 34

Spend first year on pasture. Moved to feedlots, where they are fed high-energy grain to fatten quickly Slaughtered at 14-18 months old at ~1350 lb.

Question 35

What are the disadvantages of feedlot systems for cattle?

Answer 35

- Use of antibiotics in feed - Environmental damage from grain production & transport - Animal welfare concerns - Resource use for concentrated feeding

Question 36

Describe the life cycle of grass-fed cattle in the US.

Answer 36

Spend their entire lives in pasture. Slaughtered when aged 18-24 months at ~1200 lb.

Question 37

What are the disadvantages of grass-fed systems for cattle?

Answer 37

- More land required (could involve deforestation) - Greater GHG emissions due to longer finishing times, conversion of grasses to methane and less efficient meat production as lower weights

Question 38

Which cattle system (feedlot or grass-fed) produces more GHG emissions overall? Why?

Answer 38

Grass-fed cattle, with about 37% higher emissions. Due to: - Longer lifespan = more total emissions - More enteric methane from grass fermentation - Lower slaughter weight means less efficient meat production

Question 39

Is grass-fed beef better for the environment than feedlot beef in the USA?

Answer 39

Not necessarily. While grass-fed systems seem more “natural,” they often result in higher GHG emissions and greater land use, especially if new pastures require deforestation.

Question 40

What are some new discoveries in terms of reducing CH4 and N2O emissions in livestock production?

Answer 40

- Carbon sequestration - Breeding to acquire livestock strains producing less GHGs

Question 41

What are some of the best current practices in terms of reducing CH4 and N2O emissions in livestock production?

Answer 41

- Manure management - Pasture management - Gas capturing

Question 42

Can livestock grazing of the soil enhance soil carbon? Is there a term associated with this?

Answer 42

Yes -> Overturns soil, promotes extensive roots and manure adds soil carbon Holistic Management (planned grazing to enhance plant growth and C accumulation in soils)

Question 43

What is Holistic Management (cattle)?

Answer 43

Planned grazing to enhance plant growth and C accumulation in soils

Question 44

Can holistic management balance the beef industry (in the long term)?

Answer 44

Although holistic grazing does increase C sequestration, this is not enough to offset. This extra sequestered carbon will also not permanently stay in the soil - some will be respired and end up back in the atmosphere – this means this is not a long-term strategy (especially under poor management).

Question 45

Where is the most soil carbon sequestration required globally to offset ruminant GHG emissions?

Answer 45

- South Asia - South America - South Europe