Scottish Greenhouse Gas Statistics 2023

This section examines key revisions in estimated source emissions between the latest inventory (1990-2023) and the previous inventory (1990-2022). 

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.

Impact of Revisions

Revisions between the 1990-2022 and 1990-2023 inventories

Charts 14 to 16 illustrate the impacts of revisions between the 1990-2022 and 1990-2023 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 1990-2022 and 1990-2023 Inventories.

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

Chart 15.  Revisions to emissions in 1990, from the 1990-2022 inventory to the 1990-2023 inventory, by Territorial Emissions Statistics Sector.

Chart 16 shows revisions to the data for the year 2022, between the two most recent inventories.

Chart 16.  Revisions to emissions in 2022, from the 1990-2022 inventory to the 1990-2023 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 1990-2023) 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 - 2023.  Details of the most notable revisions are listed below:

• Agriculture
  • Recalculations early in the timeseries to agricultural stationary combustion are driven by an improvement to redistribute burning oil DUKES values to pre-1998 using the 2016-2019 DUKES reported totals for burning oil.
  • There are recalculations to agricultural non-road mobile machinery (NRMM) later in the timeseries due to changes to the gas oil reconciliation including the bottom up NRMM recalculations to incorporate revisions to the Defra agricultural statistics.
  • In both agricultural stationary combustion and NRMM there are revisions to DUKES allocations to end users back to 2009. Changes in the earlier years are due to sector splits in later years now used in earlier years to maintain timeseries consistency.
  • There are also DA level recalculations due to the incorporation of new agricultural offroad fuel use mapping from 2005-2023. Pre-2005 values were also updated to use the 2005 mapping grid resulting in reallocations of data across all the DAs. This results in a decrease for Scotland early in the timeseries and a slight increase throughout the rest of the timeseries.
• Buildings and product uses
  • "There have been Digest of UK Energy Statistics (DUKES) revisions at the UK level back to 2009 as well as an improvement to redistribute burning oil DUKES values to pre-1998 using the 2016-2019 DUKES reported totals for burning oil. This redistribution pre-1998 increases the timeseries consistency and is driving the recalculations to the base year. Following the DUKES revision, the wood data are used fully and plant and animal biomass are now reported separately in the inventory. Furthermore, waste is now split into renewable (biomass) and non-renewable (non-biomass) fractions and into municipal solid waste and non-municipal solid waste.
  • mapping grid updates for the non-domestic sector. There were also minor changes due to the incorporation of modelled estimated subnational gas use data from 2005-2014 using a DA specific heating degree day analysis. This was used to extrapolate the 2015 non-domestic gas use mapping grids before 2015. "
  • Revision to stove data. Furthermore, there was an inclusion of new activity for coffee logs from the 2019 and 2022 domestic burning surveys.
  • At the DA level, there were changes due to heating degree day analysis.
  • The Inter-Departmental Business Register (IDBR) analysis was used estimate f-gas emissions from commercial refrigeration in supermarkets and other stores. This is an improvement from the previous methodology using GDP.
• Domestic Transport
  • Recalculations to the road transport model within the UK inventory from revisions to the cold start methodology to apply emissions factors related to Euro 2 to 5 petrol vehicles. This impacts non-CO2 emissions. Higher DERV consumption was estimated in cars in the last few years of the timeseries.
• Industry
  • improvement to redistribute burning oil DUKES values to pre-1998 using the 2016-2019 breakdown average.
  • Changes to the residual fuel dataset.
  • The UK sub-national residual fuel dataset revisions are driven by a improvement to the distribution of non-domestic energy use. Energy Performance Certificates (EPCs) and Display Energy Certificates (DECs) have been incorporated into the modelling to give a better indication of where oil and solid fuels are used.
  • mapping grid updates for chemical industry oil and solid fuel use. These recalculations affect the entire timeseries and drive the recalculations seen in 2022 in Scotland.
• LULUCF
  • "There were revisions to the Forest Land emissions across the timeseries due to a number of updates to the CARBINE model:
  • Improved early growth estimates.
  • Incorporate carbon from branches on dead trees into the soil.
  • Change the dead branch decay rate from 4% to 14% to match the model description.
  • Fix to the calculation of the anaerobic conditions of soil water availability in Scotland.
  • Update to latest data from 2024 preliminary Forestry Statistics.
  • Interpolation of Scotland data for 2022 where no cropland area data are available.
  • Recalculations to soil emissions for organic soil drainage and mineral soils as cropland management is calculated for mineral soils only and mineral soil area is assumed as total area minus organic area so there are small changes to the mineral soil.
    Small changes for forest land converted to cropland over the timeseries as biomass losses, dead organic matter losses and controlled burning emissions are all dependent on average forest biomass as calculated by the CARBINE model which had updates to activity data and methodology."
  • Peatland restoration areas for 2013-2023 updated from Peatland Action including changes in which year hectarage is reported due to overlapping projects.
  • For wetlands there are recalculations to the areas of Forest land converted to Wetland to include new Forest to Wetland areas for Scotland (from 2013).
• Waste
  • "Recalculations are driven by changes to landfill emissions at the UK level. There was an emission factor revision to the delay time for the decay reaction in MELmod. This results in decreases in emissions earlier in the timeseries and an increase in later years.

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[1].

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.