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Myles Allen

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Presentation from Fir Farm 2019

Published in: Environment
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Myles Allen

  1. 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
  2. 2. “The defining decision of this generation”
  3. 3. What will it take to “end our contribution to global warming”? Annual emissions 1900-2100 and their impact on global temperature in an ambitious mitigation scenario Annual emissions Global warming impact
  4. 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. 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. 6. But methane emissions don’t 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. 7. But methane emissions don’t 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 ✗
  8. 8. Combining cumulative methane emissions & annual methane emission rates predicts warming response Annual emissions Global warming impact ✓
  9. 9. Combining cumulative methane emissions & annual methane emission rates predicts warming response Annual emissions Global warming impact ✓ ECO2 -e* = GWP100 × 0.25× ECH4 +75× ΔECH4 Δt ⎛ ⎝ ⎜ ⎜ ⎞ ⎠ ⎟ ⎟
  10. 10. Nominally “equivalent” 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. 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 “equivalent” emissions of CO2 and methane have very different impacts on temperature
  12. 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. 13. What does this mean for UK agriculture? *Taken from PRIMAP, ”IPCMAG” data: http://doi.org/10.5880/PIK.2019.001 *
  14. 14. Emissions combined using DEFRA’s preferred method of representing them
  15. 15. Emissions combined using DEFRA’s preferred method of representing them
  16. 16. Emissions combined in a way that reflects their impact on global warming
  17. 17. An alternate scenario for future methane emissions *- 20% Methane & Net-Zero CO2, N2O *
  18. 18. Alternate emissions combined in a way that reflects their impact on global warming
  19. 19. Implications for net zero • Reducing power sector CO2 emissions to zero will stop that sector contributing to global warming. • Reducing agricultural sector emissions to zero will also cause global cooling, taking warming caused by past agricultural emissions back to the 1960s. • Is this a good thing? • It depends if you’re a livestock farmer. • And whether farmers are going to get any credit for helping offset the impact of other emissions on global temperatures.
  20. 20. Equivalent drivers of climate change A closed power station A gently declining (10% over 30 years) herd of cattle
  21. 21. A physics professor’s explanation of the impact of methane emissions on global temperature
  22. 22. Assume a spherical (and immortal) cow... • Creating one new cow increases methane emission rate by 100kg methane per year, which has the equivalent impact on global temperature as: – A one-off release of 210 (28x75x0.1) tonnes CO2 plus – Sustained emission of 0.7 (28x0.25) tCO2/year from now on ECO2 -e* = GWP100 × 0.25× ECH4 +75× ΔECH4 Δt ⎛ ⎝ ⎜ ⎜ ⎞ ⎠ ⎟ ⎟
  23. 23. Assume a spherical (and immortal) cow... • Creating one new cow increases methane emission rate by 100kg methane per year, which has the equivalent impact on global temperature as: – A one-off release of 210 (28x75x0.1) tonnes CO2 plus – Sustained emission of 0.7 (28x0.25) tCO2/year from now on ECO2 -e* = GWP100 × 0.25× ECH4 +75× ΔECH4 Δt ⎛ ⎝ ⎜ ⎜ ⎞ ⎠ ⎟ ⎟
  24. 24. Assume a spherical (and immortal) cow... • Creating one new cow increases methane emission rate by 100kg methane per year, which has the equivalent impact on global temperature as: – A one-off release of 210 (28x75x0.1) tonnes CO2 plus – Sustained emission of 0.7 (28x0.25) tCO2/year from now on ECO2 -e* = GWP100 × 0.25× ECH4 +75× ΔECH4 Δt ⎛ ⎝ ⎜ ⎜ ⎞ ⎠ ⎟ ⎟
  25. 25. Assume a spherical (and immortal) cow... • Creating one new cow increases methane emission rate by 100kg methane per year, which has the equivalent impact on global temperature as: – A one-off release of 210 (28x75x0.1) tonnes CO2 plus – Sustained emission of 0.7 (28x0.25) tCO2/year from now on ECO2 -e* = GWP100 × 0.25× ECH4 +75× ΔECH4 Δt ⎛ ⎝ ⎜ ⎜ ⎞ ⎠ ⎟ ⎟
  26. 26. Assume a spherical (and immortal) cow... • Creating one new cow increases methane emission rate by 100kg methane per year, which has the equivalent impact on global temperature as: – A one-off release of 210 (28x75x0.1) tonnes CO2 plus – Sustained emission of 0.7 (28x0.25) tCO2/year from now on ECO2 -e* = GWP100 × 0.25× ECH4 +75× ΔECH4 Δt ⎛ ⎝ ⎜ ⎜ ⎞ ⎠ ⎟ ⎟
  27. 27. Assume a spherical (and immortal) cow... • Creating one new cow increases methane emission rate by 100kg methane per year, which has the equivalent impact on global temperature as: – A one-off release of 210 (28x75x0.1) tonnes CO2 plus – Sustained emission of 0.7 (28x0.25) tCO2/year from now on ECO2 -e* = GWP100 × 0.25× ECH4 +75× ΔECH4 Δt ⎛ ⎝ ⎜ ⎜ ⎞ ⎠ ⎟ ⎟
  28. 28. Assume a spherical (and immortal) cow... • Creating one new cow increases methane emission rate by 100kg methane per year, which has the equivalent impact on global temperature as: – A one-off release of 210 (28x75x0.1) tonnes CO2 plus – Sustained emission of 0.7 (28x0.25) tCO2/year from now on • Destroying one old cow decreases methane emission rate by 100kg methane per year, equivalent to: – A one-off removal of 210 tonnes CO2 plus – Sustained removal of 0.7 tonnes CO2 per year from now on ECO2 -e* = GWP100 × 0.25× ECH4 +75× ΔECH4 Δt ⎛ ⎝ ⎜ ⎜ ⎞ ⎠ ⎟ ⎟
  29. 29. Assume a spherical (and immortal) cow... • Creating one new cow increases methane emission rate by 100kg methane per year, which has the equivalent impact on global temperature as: – A one-off release of 210 (28x75x0.1) tonnes CO2 plus – Sustained emission of 0.7 (28x0.25) tCO2/year from now on • Under a European-style emission trading scheme, 100kg methane per year is considered equivalent to: – Sustained emission of 2.8 tonnes CO2 per year – No consideration of changing methane emission rates ECO2 -e* = GWP100 × 0.25× ECH4 +75× ΔECH4 Δt ⎛ ⎝ ⎜ ⎜ ⎞ ⎠ ⎟ ⎟
  30. 30. If methane were included in a traditional emission trading system @ £25/tCO2 • Farmers increasing their methane emissions pay exactly the same rate for “new” vs. “old” cows, even though the impact of every new cow is equivalent to a one-off release of £5000 worth of CO2. • Farmers managing to reduce their methane emissions by -0.3% per year would still pay £70 per year per cow even though these emissions are not causing global warming. • Farmers reducing their methane emissions faster than 0.3% per year get no credit for helping offset the warming impact of other emissions.

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