Uncertainties in the Norwegian greenhouse gas emission inventory

The national greenhouse gas (GHG) emission inventory is compiled from estimates based on emission factors and activity data and from direct measurements by plants. All these data and parameters will contribute to the overall inventory uncertainty. The uncertainties and probability distributions of the inventory input parameters have been assessed based on available data and expert judgements. Finally, the level and trend uncertainties of the national GHG emission inventory have been estimated using Monte Carlo simulation. The methods used in the analysis correspond to an IPCC tier 2 method, as described in the IPCC Good Practice Guidance (IPCC 2000) (IPCC 2000). Analyses have been made both excluding and including the sector LULUCF (land use, land-use change and forestry).

The uncertainty analysis performed in 2011 is an update of the uncertainty analyses performed for the greenhouse gas inventory in 2006 and 2000.

During the project we have been in contact with experts, and have collected information about uncertainty from them. Main focus has been on the source categories where changes have occured since the last uncertainty analysis was performed in 2006. This includes new methodology for several source categories (for example for solvents and road traffic) as well as revised uncertainty estimates. For the installations included in the emission trading system, new information from the annual ETS reports about uncertainty in activity data and CO2 emission factor (and N2O emission factor for nitric acid production) has been used. This has improved the quality of the uncertainty estimates for the energy and manufacturing sectors.

The results show that the uncertainty level in the total calculated greenhouse gas emissions for 2009 is ±4 per cent. When including the LULUCF sector, the total uncertainty is ±17 per cent in 2009. The uncertainty estimate is lower now than previous analyses have shown. This is partly due to a considerable work made to improve the calculation methodology. It is also partly the uncertainty estimates themselves that have been improved.

The results also show that the increase in the total GHG emissions from 1990 to 2009 is 3 per cent, with an uncertainty in the trend of ±3 percentage points. With the sector LULUCF included in the calculations there has been a decrease in the total emissions figures of -37 per cent, with a trend uncertainty of ±7 percentage points.