The current greenhouse gas inventory for agriculture in the UK
uses the methods from the IPCC guidelines published in 2000
(Penman et al., 2000; Brownet al., 2012). The calculations of CH4 from
enteric fermentation in dairy and beef cows, and the calculations of
CH4 from manure management use Tier 2 methods. All other calculations
used Tier 1 methods. Almost all of the activity data and
emission factors have some uncertainty associated with them. We
usedMonte Carlo simulation to quantify howthe uncertainties in the
model inputs propagate through themodel.We used @Risk software
(Palisade, 2010) to run our Monte Carlo simulation. Some initial
testing showed that running theMonte Carlo simulation for 300,000
iterations gave acceptable convergence.We assessed the convergence
of the simulation by considering the stability of the 95% percentile.
We chose a convergence tolerance of 1% on the 95% percentile.
In order to do our Monte Carlo simulation, we sought PDFs to
describe the uncertainties in the model inputs. This is detailed
below.