What do we actually know?

Ruminants, such as cows, are a main contributor to methane emissions

Today I came across this article in the Guardian and which illustrates how little we actually know about the relative strength of different methane sources.

The article refers to publication by Wolf, et al. (2017) and discusses that global methane emissions from livestock in 2011 were 11% higher than estimated by the IPCC (2006). To blame is the increased use of anaerobic lagoons, where manure is stored, and larger livestock as a result of selective breeding. Wolf, et al. suggest that the new estimates could explain the surge of atmospheric methane levels between 2000 and 2010.

To me this article shows how sensitive the carbon cycle is to small variations in source factors, such as changes in livestock management.

This is not the only article that questions the relative methane emissions. In October 2016, Schwietzke et al. published a study in Nature about the uncertain effect of fossil fuel exploitation on the global methane budget. They found, based on isotopic records, that the fossil fuel industry emits 20 - 60% more methane than previously thought.

It is important to note that there is a general consensus about the total methane emissions. This means that if fossil fuels and livestock emissions are indeed greater than thought, other sources should be smaller globally.

The point to take away is that there is still ambiguity in measurements and it is important to keep a critical eye on error bars. In the case of methane emissions, the uncertainty which remains around the proportionate impact of the various sources on global methane concentrations makes it difficult to project future emissions. It is therefore difficult to gauge the impact of investing in reduction of emissions from a particular source, such as livestock.