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Scotland's National Transport Strategy

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Annex B - Climate Change Data

Carbon Emissions Data

The emissions data quoted here are taken from the Inventory of Greenhouse Gases which is compiled by the National Environmental Technology Centre (Netcen). This is published annually for the UK overall and a separate disaggregated inventory is published covering each country within the UK. The Netcen inventories allocate emissions to each sector by source (eg emissions from a power station are allocated to the energy sector). The reporting methodology is in line with international requirements under the UNFCCC.

Carbon Dioxide Emissions from Road Transport

There are two different methods of estimating carbon emissions from road transport:

  • Constrained emissions - the current method is based on UK fuel sales data with emissions apportioned to countries on the basis of vehicle kilometre travelled data.
  • Unconstrained emissions - road transport emissions have also been estimated using vehicle kilometre and vehicle-type data, unconstrained to the UK total derived from fuel sales data.

For the purposes of UK reporting on greenhouse gas emissions under the Kyoto Protocol, the UK is required to use estimation and reporting methodologies for estimation of CO 2 emissions that comply with IPCC guidance. The recommended methodology for road transport is to estimate emissions on the basis of fuel sales data. This avoids the risk of double counting road transport CO 2 emissions across a group of countries, though the results using this method are inconsistent with trends revealed by the vehicle kilometre data.

The UK Climate Change Programme ( UKCCP, 2006) and Scotland's Climate Change Programme ( SCCP, 2006) report the constrained figures, as these follow the internationally recognised methodology. For consistency, the figures reported in the National Transport Strategy are also for constrained emissions.

However, the difference in estimated carbon emissions for Scotland using these two methods is significant. Information provided with the 2004 disaggregated inventory indicated that between 1990 and 2004, while constrained estimates of road transport emissions increased by 11%, unconstrained emissions increased by 21%. The inventories are subject to ongoing improvements in data collection and estimation techniques and work will continue with the aim of improving road transport emission estimates.