GLOBAL WARMING: COWS OR CARS? - MEAT: A Benign Extravagance - page 203

are farmed. Sheep are normally kept indoors overnight in France, and anyone who has ever
slept the night in a bergerie containing a 500 strong flock will be familiar with the music
of ovine flatulence. The soothing cadence of mastication, farts, belches and showers of piss
never ceases from dusk till dawn; only when there is cause for alarm - usually a lamb lost
from its mother - will an animal resort to using its vocal chords. Digestion, in the world
of the ruminant, seems to serve as a form of peaceful communication. Methane is integral
to the metabolism of the ruminant, and indeed to the entire biological world. It is released
under anaerobic conditions, and most animals, insects, plants and trees emit some methane
at some point in their life or death cycle. Ruminant animals are reputed to be the second
largest source, after natural wetlands - 'marsh gas' being a traditional term for methane,
and the 'will o' the wisp' a manifestation.
Methane also happens to be a potent greenhouse gas whose levels in the atmosphere have
risen by about 150 per cent since pre-industrial times. After carbon dioxide it is second
highest element in the GHG budget, and you will often read that 'methane is a potent
greenhouse gas, 25 times as powerful as carbon dioxide'. While, gram for gram, this is an
agreed exchange rate, in most contexts this is about as useful as saying that a tonne of iron
weighs more than a tonne of hay. The value of the two gases is measured on a common
scale, known as Global Warming Potential (GWP) using units known as CO 2 equivalents
(CO 2 eq). Currently every gram of methane is viewed as having a GWP of 25 - ie it has the
same effect as 25 grams of CO 2 .
Human induced methane emissions are currently thought to be responsible for between
14 and 16 per cent of all man-made greenhouse gas emissions - a decline from a figure of
20 per cent three decades ago, but still quite a chunk. 33 However, there is considerable dis-
agreement amongst academics as to which human activities are responsible, and the IPCC,
the authority for climate statistics, unhelpfully doesn't commit itself on this matter. In the
1980s and 1990s, the majority of studies estimated that ruminants were responsible for
between 16 and 24 per cent of man-made methane emissions 34 but this estimate has gone
up, partly because methane emissions from other sources have gone down. The UK En-
vironmental Change Institute state that livestock are responsible for 23 per cent of global
human-made methane emissions, whereas the US Environmental Protection Agency reck-
ons the figure is 34 per cent. 35 The EPA's figure is the equivalent of 5.4 per cent of all
man-made emissions, which is similar to that given in Livestock's Long Shadow.
To eliminate the bulk of these animal-sourced methane emissions, the human race would
not need to eliminate all its livestock; just its cows, sheep, goats and other ruminants -
the fibre eaters - representing about half the nourishment derived from livestock. This is
because methane is a byproduct of digestive systems that have evolved to process protein
from high fibre diets. So whereas beef cattle produce anything from 18 to 66 kg of methane
per year, and dairy cattle up to 115 kg, pigs produce just 1 to 1.5 kg per year and humans