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Comment by sampo | Hacker News Reader

> your comment suggests a misunderstanding. Cows convert inert carbon from feed into methane, a much more potent greenhouse gas. Not all carbon is created equal from the perspective of climate.

Your comment also suggests a misunderstanding. Methane has an atmospheric lifetime of only ca. 10 years. A constant source of methane will not lead to increasing atmospheric methane levels, nor to continuous warming. Whereas a constant source of CO2 will.

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Methane traps about 80 times more heat than CO2 over the first 20 years, before it degrades into CO2 and then overall ends up trapping about 25 times more over the first 100 years.

https://climate.mit.edu/ask-mit/why-do-we-compare-methane-ca...

Sure, but that methane + CO2 has been in a steady cycle (cow -> air -> grass -> cow) and fairly constant quantity (before mass agriculture there were e.g. numerous bisons in the US), so they’re not contributing to “global warming” (i.e. a rise in temperature).

All of that warming is caused by fossil fuels.

This is a very interesting discussion, and I feel like I'm learning a lot.

One thing I figured was worth checking was how many bison there were pre-industrialization, and how many cows there are now.

Some quick googling seems to say:

~60,000,000 Bison in North America in 1600

~1,000,967,000 Livestock Cattle worldwide in 2021

https://allaboutbison.com/bison-in-history/bison-timeline/ https://beef2live.com/story-world-cattle-inventory-1960-2014...

> ~60,000,000 Bison in North America in 1600

94,400,000 cattle and calves in USA in 2017.

https://www.aphis.usda.gov/animal_health/nahms/downloads/Dem...

I think the overall question is whether the decrease in bison is offset by the increase in cattle. Bison primarily decreased in NA, but cattle increased worldwide.

> Whereas a constant source of CO2 will.

Which Methane is. It decomposes into CO2 and Water.

Yeah, but that is mostly beside the point. In pure carbon, anthropogenic CO2 emissions are about 12 GtC/year, and CH4 emissions (from fossil fuel, agriculture, waste) about 0.27 GtC/year. So CO2 from methane emissions is only 2% of all CO2 emissions.

Assuming these numbers are correct - given that CH4 traps 80x more heat than CO2 over the first 20 years[1], it would be the equivalent of adding another 21.6 GtC per year for those first 20 years. Over the span of 100 years, that CH4 degrades into CO2 but still ends up trapping 25x more heat than the same amount of CO2 emitted at the outset, resulting in the same impact as releasing another 6.75 GtC/year over the next century.

Nothing to dismiss, especially because that extra boost to heating in those first 20 years could be the difference between us hitting various tipping points, like melting permafrost and releasing yet another 185 GtC[2] into the atmosphere, and not.

[1]https://climate.mit.edu/ask-mit/why-do-we-compare-methane-ca...

[2]https://www.carbonbrief.org/imminent-tipping-point-threateni...

Methane is like 80x worse than CO2 in terms of greenhouse effect. So that 0.27Gt of CH4 has the GHG effect of 22Gt of CO2. When it decomposes to CO2 it then still has the greenhouse effect of gigs tons of CO2.

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