Accuray of Emission Estimates of Greenhouse Gases

Quantitative estimates of the uncertainties in the greenhouse gas emissions were calculated using direct simulation, a technique similar to Monte Carlo Simulation. This corresponds to the IPCC Tier 2 approach. This work is described in detail by Eggleston et al (1998) though the estimates reported here have been revised to reflect changes in the 1999 Inventory. (Salway et al, 1991)

Table 2.10 Uncertainty of the Emission Inventories

Pollutant

Estimated Uncertainty %

Carbon Dioxide

± 2

Methane

± 20

Nitrous Oxide a

-76% to +285%

HFCs

± 25

PFCs

± 19

SF6

± 13

a - Skewed uncertainty distribution.

It should be noted that these uncertainties primarily arise from emission factor uncertainties. Activity data is considered to be more reliable and better characterised. As a result it can be assumed that the trends identified from time series plots are considerably more reliable than an absolute emission total.