Scottish Greenhouse Gas Statistics 2022

This section examines key revisions in estimated source emissions between the latest inventory (1990-2022) and the previous inventory (1990-2021). 

Compilation of the Greenhouse Gas Inventory

The greenhouse gas inventory covers a wide variety of anthropogenic sources of greenhouse gas emissions.   There is therefore a wide variety of emissions sources which require different approaches to their estimation. There are a large number of data sources used in its compilation, obtained from Government statistics, regulatory agencies, trade associations, individual companies, surveys and censuses. The methods used to compile the greenhouse gas inventory are consistent with international guidance on national inventory reporting from the Intergovernmental Panel on Climate Change.

Most emission estimates are compiled by combining activity data (such as fuel use) with a suitable emission factor (such as amount of CO2 emitted per unit of fuel used). Estimates of emissions from the industrial sector are often compiled based on plant-specific emissions data. Emissions from some sectors are based on more complicated models - such as the model used to estimate emissions from landfill, and the model used to estimate the carbon dynamics in soils when trees are planted. Much of the data on net emissions from ‘agriculture’ and  ‘land use, land use change and forestry emissions’ are based on modelled data for Scotland, which are consistent with, but not constrained to, the UK totals and thus are known as “bottom up” estimates.

Many of the remaining emissions sources within the inventory have been collated on a “top down” approach where estimates of emissions have been apportioned to Scotland using proportions of energy use in the Department of Business, Energy and Industrial Strategy (BEIS) Publication “Digest of UK Energy Statistics (DUKES)”. This approach is prompted by data availability on emissions being more limited at the sub-UK level.

Revisions between the 1990-2021 and 1990-2022 inventories

Charts 14 to 16 illustrate the impacts of revisions between the 1990-2021 and 1990-2022 inventories.  This is followed by a discussion of the reasons for the key revisions.

Chart 14.  Scottish Greenhouse Gas Emissions.  Comparison of the net greenhouse gas emissions for the 1990-2021 and 1990-2022 Inventories.

Chart 15 shows revisions to the baseline period, between the two most recent inventories.

Chart 15.  Revisions to emissions in 1990, from the 1990-2021 inventory to the 1990-2022 inventory, by Territorial Emissions Statistics Sector.

Chart 16 shows revisions to the data for the year 2021, between the two most recent inventories.

Chart 16.  Revisions to emissions in 2021, from the 1990-2021 inventory to the 1990-2022 inventory, by Territorial Emissions Statistics Sector.

Details of Main Revisions and Interpretation of Revisions to the Inventory

Revisions to emission inventory estimates reflect the continuous development of scientific understanding of emissive processes, and the improvement to underlying data and methods to generate accurate emission estimates; few revisions to the Greenhouse Gas Inventories arise as a result of 'errors' in the popular sense of the word. The compilation of the inventory is governed by a rigorous quality assurance process and is subject to a great deal of third party scrutiny, such as annual reviews by the UNFCCC of the UK inventory.

The latest published Scotland greenhouse gas inventory (currently 1990-2022) represents the best available data at the time and these supersede any previous data, which should be disregarded.

A complete list of the revisions between the previous and latest inventories can be found in the National Atmospheric Emissions Inventory report Greenhouse Gas Inventories for England, Scotland, Wales and Northern Ireland: 1990 - 2022.  Details of the most notable revisions are listed below:

• Agriculture
  • The most significant recalculations for stationary combustion in agriculture are from burning oil combustion which are due to revisions in the UK inventory. This relates to an improvement in the resolution of oil combustion data which now differentiate the sector using these fuels.
• Buildings and product uses
  • Revisions to natural gas combustion due to:
    • Revisions due to the incorporation of the new data which relate to actual gas consumption rather than weather corrected data.
    • Revisions to the Digest of UK Energy Statistics (DUKES) for the later portion of the timeseries and to incorporate point source data into methodology.
  • The most significant recalculations are from the combustion of burning oil, gas oil and coal, with the latter two only impacting the later portion of the timeseries and mainly affect commercial combustion.
• Domestic Transport
  • Recalculations to road transport from revisions to the activity data and a more appropriate fuel consumption split between hot and cold-start emissions. In addition there have been revisions to the Non-Road Mobile Machinery data which now differentiate between vehicle types.
• Electricity supply
  • Recalculations are primarily due to revisions to DUKES data in 2020 and 2021.
• Fuel supply
  • Recalculations are primarily due to revisions to DUKES data in later years and also small recalculations across the timeseries due to a revision to the model used to split emissions from abandoned coal mines to UK Nations.
• Industry
  • Revisions to Non-Road Mobile Machinery which now differentiate between vehicle types.
  • Most significant recalculations from gas combustion in industry.
    • Recalculations between 2016-2021 from a revision to DUKES.
    • Revisions due to the incorporation of the new data which relate to actual gas consumption rather than weather corrected data.
  • The most significant recalculations are from the combustion of burning oil, gas oil and coal, with the latter two only impacting the later portion of the timeseries.
• LULUCF
  • The largest recalculations for forest land were the inclusion of new data to the forest land carbon stock change soil model and inclusion of urban trees across the whole timeseries.
  • For grassland, there were minor changes to peatland restoration areas in Scotland from Peatland Action including the addition of restoration areas for domestic peat extraction.
• Waste
  • Recalculation to landfill emissions in 2021 in Scotland due to adjustment in landfill gas data regional statistics.
  • For composting there was a revision to the compositing data timeline provided by UK Centre for Ecology & Hydrology affecting the national inventory.

Interpretation of uncertainties in the inventory

All estimates, by definition, are subject to a degree of statistical 'error' but in this context it relates to the uncertainty inherent in any process or calculation that uses sampling, estimation or modelling.

Estimates of greenhouse gases are compiled by a consortium of contractors.  The source emissions are based upon a range of data sources, ranging from model based estimates to point source emission data.  As a result, the estimates are subject to a degree of uncertainty.  Full analyses of these uncertainties are provided on the National Atmospheric Emissions Inventory website.

The Scottish Government previously commissioned research to overhaul and update the uncertainties model used for the Scottish greenhouse gas inventory.  A detailed study was carried out in parallel with the compilation with the 1990-2014 Scottish greenhouse gas inventory to review and improve the uncertainty calculations.  A link to this project and to the full report can be found in the Scottish Greenhouse Gas Inventory Uncertainties Project.