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Written - Revised Greenhouse Gas Emission Inventory Statistics for 2005

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Jane Davidson, Minister for Environment, Sustainability and Housing

On 19 September, I made a Written Statement to Plenary highlighting the publication of the ‘Greenhouse Gas Inventories for England, Scotland, Wales and Northern Ireland 1990 -2005’.

AEA Energy and Environment produce the ‘Greenhouse Gas Inventories for England, Scotland, Wales and Northern Ireland’ each year.

Following the publication of the inventories report an error in the data processing relating power station emissions data for Wales for 2005 has been identified. Although the error only relates to one installation it does have a discernable impact on emissions and revised greenhouse gas emission statistics have been produced to correct the error.

The error meant that Wales’ greenhouse gas emissions and CO2 emissions were overestimated for 2005 (and those for England, Scotland and Northern Ireland were slightly underestimated). Table 1 (see attachment below) shows the differences between the original inventory and the corrected inventory for emissions of CO2 and total greenhouse gases in Wales.

The change in the Welsh Inventory, also affects the data for England, Scotland and Northern Ireland. Table 2  (see attachment below) shows the impact on the differences in original and corrected 2005 inventories for England, Scotland and Northern Ireland (compared to the base year of 1990 or 1995 for f-gases).

The overall UK trend is unaffected.

The error was made in the allocation of power station gas use, due to a misinterpretation of the EU Emissions Trading Scheme (EU ETS) data for one site. This data was used for the first time in producing the 1990 – 2005 report.

The EU ETS fuel use data for Connah’s Quay power station contained both positive and negative gas consumptions. The negative consumption was unique in the England and Wales EU ETS dataset. It was assumed that the negative values were erroneous and they were treated as being positive values which led to an overestimate of the gas use at this site.

In reality it turned out that the negative values entered were part of an accounting system that allows imports and exports of gas to the power station to be recorded. The gas terminal, BHP Billiton, provides most of the fuel used by Connah’s Quay. Any surplus fuel that is not used for power generation is treated further and exported back out of the Connah’s Quay site and into the National Transmission System (NTS) for natural gas. A single meter records the imports and exports of gas to the Connah’s Quay site, as positive and negative values respectively.

The incorrect assumption that the negative values were erroneous therefore led to a significant over-allocation of gas use (and consequently CO2 emissions) to Connah’s Quay power station.

AEA is introducing additional checking procedures to avoid similar errors occurring again. These include:

  • Automated checks of year-to-year emission trends, to help to identify any outliers in the emission trends, which will then be investigated to find out whether these reflect the real emissions trend, or if there has been an error.
  • Automated cross-checking of different point source data, where data for the same site are available from more than one source.
  • In addition, for the power generation sector, the emission trends will be compared with the electricity generation data published in BERR’s Energy Trends.

Further details are available in the ‘Corrigendum to the Greenhouse Gas Inventories for England, Scotland, Wales and Northern Ireland: 1990 to 2005’ which is available on the National Atmospheric Emissions Inventory website. All greenhouse gas emissions data available for download from this site will now incorporate this amendment.

The Greenhouse Gas Inventories for England, Scotland, Wales and Northern Ireland 1990 – 2006 will be published later this year.