A large portion of the work of climate policy people is to measure emissions. It is a tedious and nerdy labour but nonetheless important. We are talking about science, about predictions and models, so we need rigorous monitoring and measurement of the subject matter.
The numbers derived from measurement are then used by policy makers to determine priorities and strategies. You need good numbers for good policy.
One of the most significant causes of greenhouse gas emissions is the eating of meat and dairy products. This leads to emissions through the destruction of forest and degradation of land for grazing and for growing animal feed, through the digestive processes of animals, through the manufacture of fertiliser for their feed, through the use of energy in transporting, processing, chilling, cooking and disposing of meat and dairy, and through the decay of meat and dairy waste.
Strangely, although this is one of the largest categories of emissions, there is a bizarrely wide range of estimates. The lowest figure of 14.5% comes from the latest work by the FAO (http://www.fao.org/docrep/018/i3437e/i3437e.pdf) – down from its earlier estimate of 18% in its 2006 report (ftp://ftp.fao.org/docrep/fao/010/a0701e/a0701e.pdf). The highest is from the 2009 work of World Bank experts, the late Robert Goodland and Jeff Anhang (http://www.worldwatch.org/files/pdf/Livestock%20and%20Climate%20Change.pdf) who put the total impact at 51% of GHGs.
(The latter figure is so high not least because they use a global warming factor of 72 for methane reflecting the impact of this gas over a 20 year period. This is in contrast to the standard factor of 21 which is the impact over a 100 year period. Given that we are worried about climate change today and looking at policies up to 2050 (in 35 years’ time) it makes more sense to use the 20 year factor of 72.)
So the literature on one of the most significant causes of emissions has a highest figure which is 3.5 times greater than the lowest figure. This implies an extraordinary degree of uncertainty given the importance of tackling climate change with evidence-based policy. In contrast, policy makers would not accept the same latitude in measures of emissions from burning coal or refining oil.
As long as policy makers willingly tolerate such uncertainty over the environmental impact of eating meat and dairy, it is unlikely that the matter will be treated seriously in politics or by the general population. You need solid numbers to be credible. A solid number is sorely needed: without cutting meat and dairy from our diet we have little hope of getting emissions down to where they should be.