from: http://www.straightdope.com/classics/a4_176.html
“Each cow emits 200 to 400 quarts of methane gas per day, or 50 million metric tons per year.”
This doesn’t make sense.
Using 300 quarts (about 0.2839 cubic meters), and .68 kg/cubic meter (the density of methane at 15C and 1atm), that gives us .07 metric tons per year per cow.
Multiply by the number of cows.
Now, the carbon that comes out of cows came from the plants they eat, so it all was in the atmosphere originally (not dug out of the ground like fossil fuels). So, I’d think the cows are really carbon neutral – except that we’re getting methane back, instead of the original carbon dioxide, so I guess it makes for a net increase in greenhouse effect. Am I right about that?
I thought of that. Multiplying by the number of cows later in the article gives the right order of magnitude, but not 50 million.
What I think happened is that the author of the quoted study did include the number of cows, which was probably different than 1.2 billion.
I guess the reason I asked in the first place is that
“Each cow emits 200 to 400 quarts of methane gas per day, or 50 million metric tons per year.”
is simply not right. This sentence says that each cow emits 50 million tons per year.
According to the EPA, methane is 20 times more effective at trapping heat.
It’s been decades since I was rooting through the libraries over methane related things, so I don’t remember if it has anything to do with the Donald Johnson mentioned in Cecil’s article, but the early research into methane production by cows, and possible ways to decrease same, was done with an eye to feed efficiency, not to global warming. The math goes that any carbon atom from the feed that goes into the production of methane is a carbon atom that is not going into the production of beef.
Then came an awareness of global warming and grants available for studying global warming. Researchers spend about 1/3 of their time writing grants to get money for next year’s research and here was a new source of grant money. Presto! Suddenly the past research for feed efficiency is base data for global warming research and people studying cow burps get bigger budgets and more respect at parties.
I tried to look up the original study but didn’t have access. The 1.2 billion in the study referred to “ruminants”, which Cecil listed as types of animal in the column. I believe that cows are a subset of ruminants which are likely around 700m or so. If we could find the original study it might be more clear…
Well, the sentence could be read both ways. I think you’re most correct, however, that it could be written better.
Cecil claims that the methane in the atmosphere has been increasing at about 1% per year, which is wrong, wrong, and also wrong. Atmospheric methane has stabilized in the last decade, and is not increasing at all.
w.
But was it true in 1989, when the column was written?
Good point.
From: http://www.agu.org/pubs/crossref/2006/2006GL026199.shtml
“Over the past century, atmospheric methane (CH4) rose dramatically before leveling off in the late 1990s.”
Ah, yes, I didn’t notice that this was a “fly-in-amber” piece … :smack:
I will now go to work, suitably chastened …
w.