cricketo said:
https://timeforchange.org/are-cows-cause-of-global-warming-meat-methane-CO2
You can't compare carbon in the active carbon cycle to the release of sequestered carbon. This is the mistake that people make all the time.
If the cow didn't eat the grass the carbon in the grass doesn't DISAPPEAR. It's not like burning 1000 liters of gas. The carbon in the gas was locked in a complex molecule, stored underground for millions of years.
What are the sources of methane (Figure 10)? The 1992 Report of the Intergorvernmental Panel on Climate Change (IPCC) lists the largest natural source of methane to be wetlands, which produce 115 teragrams (1012 grams) of carbon annually. The uncertainty in these numbers, however, is very large. Termites are very significant producers of methane in that they eat wood and release methane in the digestion process. The ocean produces about 10 teragrams per year of methane, and fresh water and methane hydrate contribute smaller amounts.
Anthropogenic sources include the coal mining, natural gas, and petroleum industries at about 100 teragrams, which is almost as much as natural wetlands. Rice paddies produce on the order of 60 teragrams by means of a process where methane produced in the soil is able to travel up to the hollow stem of the rice plant and be released into the atmosphere without passing through the water, which would tend to suppress the evolution of methane gas (Figure 11).
Enteric fermentation, the digestion process in ruminant animals such as cattle, sheep and goats, produces very large amounts of methane. Animal wastes produce about 25 teragrams; domestic sewage, 25 teragrams; landfills about 30 teragrams; and biomass burning, about 40 teragrams. Some landfills are now being tapped for their methane as a source of power production. This makes good sense on the basis of global warming in addition to getting a "free" source of combustion gas. Burning one methane molecule produces one CO2 molecule, but the global warming potential is reduced by a factor of 20 because the carbon dioxide molecule is only about one-twentieth as effective as the methane molecule in absorbing infrared radiation.
Increases in animal populations are contributing to the increase in atmospheric methane. Figure 12 shows recent increases in several different classes of livestock. If humans continue to have an appetite for meat, the upward trend in animal production and resulting production of methane will likely continue. A particular situation to watch is the development and possible dietary changes in China. If we examine the eating habits of Japan, South Korea, and other Asian nations that have developed very rapidly, one of the significant changes that occurs during economic development is that people's eating habits change from eating primarily grains, mainly rice in these cases, to substantial increases in meat. The big question on the horizon right now is what's going to happen in China? China has an enormous population and it is developing extremely rapidly. If China follows the pattern of other Asian nations, the demand for meat will increase dramatically. I have estimated that if every person in China at a MacDonald's Quarter Pounder every 10 days, raising the beef to meet this demand would consume all the corn grown in Iowa.
The most common way of comparing the greenhouse gas effect of different gases is to express them as carbon dioxide equivalents, i.e. how much carbon dioxide corresponds to a pulse (a one-time) emission of the gas in question. The most common way of expressing this is by the unit GWP-100, which express the cumulative forcing over hundred years. For methane (CH4) the GWP-100 value is 28, i.e. a pulse of methane emission of 1 kg corresponds to a pulse of 28 kg carbon dioxide emission. But we could equally use other figures as shown in the table below (from the IPCC Synthesis report 2014). For example the GTP-100 measures the actual temperature change after 100 years. With that measurement a pulse of 1 kg methane corresponds only to 4 kg of carbon dioxide. The actual effect on the temperature is probably more in line with what most people expect of the comparisons between greenhouse gases.
https://www.resilience.org/stories/2017-10-20/false-methane-math/
But neither the GWP nor the GTP can properly reflect the difference between short lived greenhouse gases such as methane and long-lived carbon dioxide. In the article New use of global warming potentials to compare cumulative and short-lived climate pollutants in Nature Climate Change Myles Allen and colleagues demonstrate how the calculations for expressing methane in carbon dioxide equivalents hides a lot of information. For short-lived greenhouse gases the comparison with carbon dioxide based on a pulse of emissions of both gases gives a reasonably correct result only in a time span of a few decades. In the longer term, the more correct comparison is between a pulse of carbon dioxide and an constant rate of methane emissions. [ed. note: the preceding sentence was corrected 14/12/17.] Or as expressed in the article
It goes on. I would urge you, if you have any interest in coming to a conclusion, and not validating your own preconceptions, read as much as you can. Never stick to any single source or ideology.
