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TRUE: methane is a powerful greenhouse gas, with 25 times the global warming potential as carbon dioxide.
ALSO TRUE: cows produce methane as part of digesting the plants that they eat - which goes into the atmosphere.

So if we want to stop global warming, then lets get rid of the cows (and sheep and goats). Right? RIGHT?

Well, not so fast.....there are a couple of problems with that logic.

Firstly, it doesn't take into account the fact that the methane (and hence carbon) cycle is just that - a cycle - and it is a relatively short one at that. Here's how it all works....

  1. Start with carbon dioxide (CO2) in the atmosphere
  2. Plants take CO2 out of the atmosphere and combine it with water (H2O) and energy (sunlight) during the process of photosynthesis to produce Oxygen (O2) and carbohydrates (C6H12O6 and other molecules) which make up the structure of the plant.
  3. Ruminants eat the plants, and as part of the digestion process they produce methane (CH4) in their rumen and burp it out.
  4. Once in the atmosphere, the methane combines with water vapour (H2O) and sunlight in a number of chain reactions to produce CO2 and water vapour along with a number other important things (like ozone).

Added to that, some of the methane from the manure doesn't make it up into the atmosphere because it is converted to other components by the methanotrophic bacteria in the soil.

So, we're back where we started. The important thing about this process is that it has a relatively short timeframe - methane in the atmosphere has a lifetime of approximately 9.6 years - and because it is a cycle, it means that we aren't generating new sources of carbon in the atmosphere, just cycling the existing carbon.

The struggle to save the global environment is in one way much more difficult than the struggle to vanquish Hitler, for this time the war is with ourselves. We are the enemy, just as we have only ourselves as allies.

Al Gore

So where does that leave us? If we want to solve the problem of climate change, then we should put our focus on the major culprit which is our profligate use of fossil fuels. The issue here is that, unlike the methane cycle discussed above, these stores of carbon have taken BILLIONS of years to be converted from atmospheric carbon into stable carbon in the ground. By extracting them (in the form of coal, oil and gas) and then burning them (which creates the atmospheric pollutants such as carbon dioxide), we are overloading the ecosystems ability to deal with those pollutants.

And that is why we think farmers (and their cows, sheep and goats) are getting the bum rap. There is a plethora of information out on the interweb, so just go hunting. On the topic of methane and cows, you might like to check out David Mason-Jones' mythbusting views.