GW, methane and vegetarianism: http://www.earthsave.org/globalwarming.htm

A reader would love to see http://www.earthsave.org/globalwarming.htm dissected. Hmm. Well, speaking as a vegetarian I'm all in favour of it, but for moral / animal welfare issues. The "vegetarian footprint" is smaller than a meat eaters, but is it really enough to be a factor in GW? Lets read on...

Global warming poses one of the most serious threats to the global environment ever faced in human history. Yet by focusing entirely on carbon dioxide emissions, major environmental organizations have failed to account for published data showing that other gases are the main culprits behind the global warming we see today. As a result, they are neglecting what might be the most effective strategy for reducing global warming in our lifetimes: advocating a vegetarian diet.

Hmm, hyperbolic, and as a first guess they are just using GW to push their pet idea, but I guess they have two points they are asserting:

1. Methane is more important than CO2
   
2. Meat eating is a major source of methane
   

Both of those sound dodgy, so how do they back them up?

Firstly, the radiative stuff. The IPCC fig 3 shows methane as about 0.5 w/m2, ie about 1/5 of the well-mixed GHG forcing and therefore about 1/3 the size of CO2. Earthsave are relying on Hansen, PNAS to bump the methane up from 0.5 to 0.7 by adding in some of the tropospheric ozone and (it looks like) all the stratospheric water vapour forcing, so making methane about 1/2 of CO2. Hansen then attributes sulphate aerosol, etc, to fossil fuel combustion (fair enough) and then offsets this against CO2 (hmmm) and then asserts that "the processes producing the non-CO2 GHGs have been the primary drive for climate change in the past century". Not very sure about that, but probably not much use even if true in predicting the future forcing, because sulphate to CO2 ratio is predicted to decline. Also, Hansens version of aerosol forcing seems to be rather larger than other peoples, which is why (I think) he gets them offsetting CO2. Compare the IPCC (aerosol indirect effect) with Hansens equivalent (forced cloud changes) and the range is similar, but the IPCC writes "very low" for the confidence; the range includes zero; and (AFAIK) the effect is entirely absent from the GCM studies that end up reproducing the cliamte change of the past century. On Hansens figure the range no longer includes zero; the confidence is unqualified; and there is a nice blue bar drawn down to -1 to guide your eye to the obvious conclusion.

Now its possible that Hansen is right, but I don't think its fair to represent his views as mainstream (earthsave tells me that Hansens results are generally accepted by global warming experts, including bigwigs but I'm not a bigwig, so I wouldn't know; they also reference the UCS review in their favour, but earthsave's version "the Union of Concerned Scientists had the data reviewed by other climate experts, who affirmed Hansens conclusions" is a misrepresentation of the UCS's far more tentative position), although this is a bit out of my area so I'm unsure. And even he doesn't think the CO2/aerosol balancing (as he would put it) can continue. Comments from the lurking Schtick welcome.

So... methane bigger forcing than CO2, dodgy (and then they totally lose my sympathy with "Whereas human sources of CO2 amount to just 3% of natural emissions..." which is septic garbage). What about the second point: "the number one source of methane worldwide is animal agriculture."? They reference the US EPA for this (which is odd, because they say *worldwide*, then ref the EPA US-only figures), who say "Methane is produced primarily through anaerobic decomposition of organic matter in biological systems. Specifically, methane is emitted as a result of the decomposition of organic wastes in municipal solid waste landfills and from agricultural and biological processes related to wetland rice cultivation, livestock digestion, and waste production. Methane emissions also occur during the production and distribution of fossil fuels such as coal, natural gas, and petroleum". But under the "agriculture" heading they say "The normal digestive processes in ruminant livestock (known as enteric fermentation [known as cows farting - WMC]) account for the largest portion of methane emissions.". So from this I guess that most of the *US* agricultural methane comes from cows, but probably not most of the total methane; and the global picture is likely to be different (and remember, Hansens figures were all global, so I don't think going back to a pure-US view is defensible). In fact, the table lower down resolves the uncertainty: the largest (in the US) is landfills, at 131 (Tg CO2 equiv in 2003); natural gas systems at 131; and cows farting at 125. And the total is 545. And globally? I don't know. wiki says 17% from cows, but cunningly doesn't venture whether this is global or not; the implication should be that it is. Ah... but http://cdiac.esd.ornl.gov/trends/meth/ch4.htm says "For flaring and venting of natural gas, estimated methane emissions rose from 0.0 in 1860 to a maximum of 29.3 million metric tons in 1973, then declined. For oil and gas supply systems, excluding flaring, estimated methane emissions rose from 0.0 in 1860 to a maximum of 18.0 million metric tons in 1994. For coal mining, estimated methane emissions rose from 2.2 million metric tons in 1860 to 49.5 million metric tons in 1989, then dropped slightly. For biomass burning, estimated methane emissions rose from 9.8 million metric tons in 1860 to 38.0 million metric tons in 1988 and subsequently declined slightly. For livestock farming, estimated methane emissions rose from 25.6 million metric tons in 1860 to 113.1 million metric tons in 1994; this appears to now be the largest individual anthropogenic source of methane emissions, having overtaken rice farming in the early 1980s. For rice farming and related activities, estimated methane emissions rose from 40.1 million metric tons in 1860 to 100.8 million metric tons in 1994. For landfills, estimated methane emissions rose from 1.6 million metric tons in 1860 to 40.3 million metric tons in 1994. Total estimated anthropogenic methane emissions rose from 79.3 million metric tons in 1860 to 371.0 million metric tons in 1994. During the period 1860-1994, the relative importance of the various component sources changed, with fossil fuels increasing and agriculture - although still dominant - declining in dominance. Within the agricultural sector, livestock replaced rice as the leading component."

To summarise that lot: yes they are probably right: livestock probably is the major source of methane, but is only about 1/4 of it. Then they continue: "Simply by going vegetarian (or, strictly speaking, vegan), we can eliminate one of the major sources of emissions of methane..." errrrmmm yes, good point there folks, and probably a good idea not to put it at the top: you need to be vegan to get rid of the cows, not just veggie; and not many can cope with becoming vegan (I couldn't). More: "there is no limit to reductions in this source of greenhouse gas that can be achieved through vegetarian diet. In principle, even 100% reduction could be achieved with little negative impact". Well no, this is wrong: since cows are only about 1/4 of the methane sources, you can only cut out 25% even with the whole world vegan. More: "efforts to cut carbon dioxide involve fighting powerful and wealthy business interests... vegetarian foods are readily available, and cuts in agricultural methane emissions are achievable at every meal" sounds like wishful thinking to me.

Conclusion: they probably have a reasonable point but they push it too far.