In Impact of Dairy: What if a Dairy Farm became a Hazelnut Orchard, we learned that a Wisconsin dairy farm with 600 milking cows generates
* 201,000 kg or 201 tons of methane (CH4) per year
Are 201 tons of methane a lot, or are these emissions nothing to be concerned about?
Even climate scientists have a tough time assessing the impact of methane emissions. In general, they think in terms of ‘carbon dioxide equivalence’ or ‘CO2 eq.’ So they tend to find conversion factors to express non-CO2 greenhouse gas (GHG) emissions in terms of CO2 emissions. For long-lived GHGs like N2O it’s as simple as multiplying N2O emissions by 298 and you’re done. But for methane, it’s not so simple. Sailesh Roa of Climate Healers puts it well:
It is important to point out that the IPCC has consistently undercounted the impact of our annual methane emissions by averaging its impact over a 100 year period. Even as it warns humanity that catastrophic climate change is imminent within the next 11 years, not 100 years! – Animal Agriculture is the Leading Cause of Climate Change – A White Paper
Sailesh Rao, Climate Healers
In other words, the reason for the CH4 to CO2 ‘equivalence’ complexity is simple: CO2 endures in the atmosphere more than ten times longer than CH4. Mismatched timescales make comparisons difficult. This table lays out various conversion factors one might legitimately use.
The first column expresses the point in time at which you measure the actual warming impact of methane after the greenhouse gasses are emitted. For this calculation, we assume the GHGs are emitted from 600 cows for one full year, emissions stop, and then the clock starts.
In the second column, we see that after 10 years, 201 tons of methane emissions have warmed the earth 104 times more than 201 tons of CO2 would have warmed the earth.
After 20 years, the warming impact is 87x, and after 100 years it is 100x.
| Warming impact of 1 yr of emissions measured after this many years | CH4 : CO2 warming factor (x)† |
| 10 years | 104 |
| 20 years | 87 |
| 100 years | 28 |
Again, as noted already, the variation is due to the fact that methane is a short-lived gas, and CO2 is long-lived. Here’s a brief video explanation:
Controversy swarms around choosing the right CH4:CO2 conversion factor. Since we humans continue to replace ‘spent’ cows, and since we are looking at climate catastrophe within a decade or two, AFA agrees with Climate Healers. We favor using a 10-year conversion factor. Consider too that as the emissions continue increasing as does the global methane concentration.
Let’s take that chart and see what 201 tons of our dairy farmer’s methane emissions translate to in terms of carbon dioxide equivalence or ‘CO2 eq.’:
| Warming impact of 1 yr of emissions measured after this # yrs | CH4:CO2 warming factor (x)† | CO2 equiv. emissions from 1 yr CH4 emissions from 600 US dairy cows (kg, kilotons) |
| 10 years | 104 | 20,904,000 kg (21 kilotons CO2 eq.) |
| 20 years | 87 | 17,487,000 kg (17.5 kilotons CO2 eq.) |
| 100 years | 28 | 5,628,000 kg (5.6 kilotons CO2 eq.) |
Hmm… even after converting to ‘CO2 eq.’ we’re left wondering, are 21 kilotons high? Low? Are they low? Unless you’re a climate scientist it’s difficult to form an opinion around whether these GHG emissions are acceptable or not.
In other words, ‘CO2 eq.’ is still just a number.
So how about we take the conversion one step further and express Dan’s 600 cow dairy farm emissions into something we can get our heads around? Let’s compare these emissions to something we all know: cars.
| Warming impact of 1 yr of emissions measured after this # yrs | CH4:CO2 warming factor (x)† | CO2 equiv. emissions from 1 yr CH4 emissions from 600 US dairy cows (kg, kilotons) | Number of equivalent cars |
| 10 years | 104 | 20,904,000 kg (21 kilotons CO2 eq.) | 4,544 cars |
| 20 years | 87 | 17,487,000 kg (17.5 kilotons CO2 eq.) | 3,802 cars |
| 100 years | 28 | 5,628,000 kg (5.6 kilotons CO2 eq.) | 1,223 cars |
In terms of the equivalent impact of cars, depending on what CH4 to CO2 conversion factor you use, those cows are heating the earth as much as thousands of cars. Measured after 100 years, the impact is 1,310 cars (1,223+87). But if you measure after ten years, the impact is like 4,631 cars (4,544+87).
No matter how you cut it, the environmental impact of dairy is enormous.
Do you still want further study? Here you go!
- This video reviews ten, twenty and hundred-year timeframes.
- This white paper from Climate Healers further explains CH4 vs CO2.
- https://www.agriculturefairnessalliance.org/news/how-bad-are-dairy-cows-for-the-environment/
Since we like Mr. Roa’s quotation so much, we’ll leave you with it once again:
It is important to point out that the IPCC has consistently undercounted the impact of our annual methane emissions by averaging its impact over a 100 year period. Even as it warns humanity that catastrophic climate change is imminent within the next 11 years, not 100 years!
– Sailish Rao, Climate Healers