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Myles Allen
1. Agricultural emissions on a path to Net Zero
Myles Allen, Ed Hornsby, John Lynch & Michelle Cain
Environmental Change Institute, School of
Geography and the Environment & Department of
Physics, University of Oxford
3. What will it take to โend our contribution to global
warmingโ?
Annual emissions 1900-2100 and their impact on global
temperature in an ambitious mitigation scenario
Annual emissions Global warming impact
4. For CO2, the answer is simple: just stop emitting
Dotted red line: CO2 emissions added up over time
Annual emissions Global warming impact
5. The same goes for nitrous oxide (more or less)
Annual emissions Global warming impact
Dotted green line: N2O emissions added up over time
6. But methane emissions donโt need to reach zero
to stop and reverse methane-induced warming
Dotted blue line: CH4 emissions added up over time
Annual emissions Global warming impact
7. But methane emissions donโt need to reach zero
to stop and reverse methane-induced warming
Dotted blue line: CH4 emissions added up over time
Annual emissions Global warming impact
Methane does not accumulate
โ
10. Nominally โequivalentโ emissions of CO2 and methane
have very different impacts on temperature
From Climate metrics for ruminant livestock, Oxford Martin Programme on Climate
Pollutants briefing: https://www.oxfordmartin.ox.ac.uk/publications/view/2714
WARMING
STABLE
COOLING
11. From Climate metrics for ruminant livestock, Oxford Martin Programme on Climate
Pollutants briefing: https://www.oxfordmartin.ox.ac.uk/publications/view/2714
WARMING
STABLE
COOLING
WARMING
WARMING
WARMING
Nominally โequivalentโ emissions of CO2 and methane
have very different impacts on temperature
12. Redefining equivalence between methane and
CO2
From Climate metrics for ruminant livestock, Oxford Martin Programme on Climate
Pollutants briefing: https://www.oxfordmartin.ox.ac.uk/publications/view/2714
WARMING
WARMING
STABLE
COOLING
COOLING
STABLE
13. What does this mean for UK agriculture?
*Taken from PRIMAP, โIPCMAGโ data:
http://doi.org/10.5880/PIK.2019.001
*
19. Implications for net zero
โข Reducing power sector CO2 emissions to zero will
stop that sector contributing to global warming.
โข Reducing agricultural sector emissions to zero will
also cause global cooling, taking warming caused by
past agricultural emissions back to the 1960s.
โข Is this a good thing?
โข It depends if youโre a livestock farmer.
โข And whether farmers are going to get any credit for
helping offset the impact of other emissions on
global temperatures.
20. Equivalent drivers of climate change
A closed power station
A gently declining (10% over
30 years) herd of cattle
21. A physics professorโs explanation of the impact of
methane emissions on global temperature
22. Assume a spherical (and immortal) cow...
โข Creating one new cow increases methane emission
rate by 100kg methane per year, which has the
equivalent impact on global temperature as:
โ A one-off release of 210 (28x75x0.1) tonnes CO2 plus
โ Sustained emission of 0.7 (28x0.25) tCO2/year from now on
ECO2 -e*
= GWP100
ร 0.25ร ECH4
+75ร
ฮECH4
ฮt
โ
โ
โ
โ
โ
โ
โ
โ
23. Assume a spherical (and immortal) cow...
โข Creating one new cow increases methane emission
rate by 100kg methane per year, which has the
equivalent impact on global temperature as:
โ A one-off release of 210 (28x75x0.1) tonnes CO2 plus
โ Sustained emission of 0.7 (28x0.25) tCO2/year from now on
ECO2 -e*
= GWP100
ร 0.25ร ECH4
+75ร
ฮECH4
ฮt
โ
โ
โ
โ
โ
โ
โ
โ
24. Assume a spherical (and immortal) cow...
โข Creating one new cow increases methane emission
rate by 100kg methane per year, which has the
equivalent impact on global temperature as:
โ A one-off release of 210 (28x75x0.1) tonnes CO2 plus
โ Sustained emission of 0.7 (28x0.25) tCO2/year from now on
ECO2 -e*
= GWP100
ร 0.25ร ECH4
+75ร
ฮECH4
ฮt
โ
โ
โ
โ
โ
โ
โ
โ
25. Assume a spherical (and immortal) cow...
โข Creating one new cow increases methane emission
rate by 100kg methane per year, which has the
equivalent impact on global temperature as:
โ A one-off release of 210 (28x75x0.1) tonnes CO2 plus
โ Sustained emission of 0.7 (28x0.25) tCO2/year from now on
ECO2 -e*
= GWP100
ร 0.25ร ECH4
+75ร
ฮECH4
ฮt
โ
โ
โ
โ
โ
โ
โ
โ
26. Assume a spherical (and immortal) cow...
โข Creating one new cow increases methane emission
rate by 100kg methane per year, which has the
equivalent impact on global temperature as:
โ A one-off release of 210 (28x75x0.1) tonnes CO2 plus
โ Sustained emission of 0.7 (28x0.25) tCO2/year from now on
ECO2 -e*
= GWP100
ร 0.25ร ECH4
+75ร
ฮECH4
ฮt
โ
โ
โ
โ
โ
โ
โ
โ
27. Assume a spherical (and immortal) cow...
โข Creating one new cow increases methane emission
rate by 100kg methane per year, which has the
equivalent impact on global temperature as:
โ A one-off release of 210 (28x75x0.1) tonnes CO2 plus
โ Sustained emission of 0.7 (28x0.25) tCO2/year from now on
ECO2 -e*
= GWP100
ร 0.25ร ECH4
+75ร
ฮECH4
ฮt
โ
โ
โ
โ
โ
โ
โ
โ
28. Assume a spherical (and immortal) cow...
โข Creating one new cow increases methane emission
rate by 100kg methane per year, which has the
equivalent impact on global temperature as:
โ A one-off release of 210 (28x75x0.1) tonnes CO2 plus
โ Sustained emission of 0.7 (28x0.25) tCO2/year from now on
โข Destroying one old cow decreases methane emission
rate by 100kg methane per year, equivalent to:
โ A one-off removal of 210 tonnes CO2 plus
โ Sustained removal of 0.7 tonnes CO2 per year from now on
ECO2 -e*
= GWP100
ร 0.25ร ECH4
+75ร
ฮECH4
ฮt
โ
โ
โ
โ
โ
โ
โ
โ
29. Assume a spherical (and immortal) cow...
โข Creating one new cow increases methane emission
rate by 100kg methane per year, which has the
equivalent impact on global temperature as:
โ A one-off release of 210 (28x75x0.1) tonnes CO2 plus
โ Sustained emission of 0.7 (28x0.25) tCO2/year from now on
โข Under a European-style emission trading scheme,
100kg methane per year is considered equivalent to:
โ Sustained emission of 2.8 tonnes CO2 per year
โ No consideration of changing methane emission rates
ECO2 -e*
= GWP100
ร 0.25ร ECH4
+75ร
ฮECH4
ฮt
โ
โ
โ
โ
โ
โ
โ
โ
30. If methane were included in a traditional emission
trading system @ ยฃ25/tCO2
โข Farmers increasing their methane emissions pay
exactly the same rate for โnewโ vs. โoldโ cows, even
though the impact of every new cow is equivalent to
a one-off release of ยฃ5000 worth of CO2.
โข Farmers managing to reduce their methane
emissions by -0.3% per year would still pay ยฃ70 per
year per cow even though these emissions are not
causing global warming.
โข Farmers reducing their methane emissions faster
than 0.3% per year get no credit for helping offset
the warming impact of other emissions.