Scottish greenhouse gas emissions annual target report: 2017

Part 2 – Net Scottish emissions

Requirements of the Act

Section 34 of the Act requires that, in respect of each greenhouse gas, the report must:

• state the amount of net Scottish emissions for the baseline year (subsection (1)(a)).
• state the amount of net Scottish emissions for the target year (subsection (1)(b)).
• state whether the amount of net Scottish emissions represents an increase or decrease compared to the equivalent amount for the previous target year (subsection (1)(c)).
• identify the methods used to measure or calculate the amount of net Scottish emissions (including in particular any change to those methods) (subsection (1)(d)).

The report must also set out the aggregate amount for the target year of net Scottish emissions (subsection (2)).

If the method of measuring or calculating net Scottish emissions changes and that change is such as to require adjustment of an amount for an earlier target year, the report must specify the adjustment required and state the adjusted amount (subsection (6)). An adjustment must, in so far as reasonably practicable, be made in accordance with international carbon reporting practice (subsection (7)).

Net Scottish emissions of each greenhouse gas

Table 2 provides data for each of the seven greenhouse gases covered by the Act. This includes details of:

• The amount of net Scottish emissions for the baseline year, and for 2017 (the target year);
• Whether any of those amounts represent an increase or decrease compared to the equivalent amount for the previous year; and
• The aggregate amount for 2017 of net Scottish emissions.

Table 2: Net Scottish emissions for each greenhouse gas (tCO2e)[9]
Greenhouse gas	Base year	Net base year emissions	Net Scottish emissions 2016	Net Scottish emissions 2017	Change in net Scottish emissions 2016 - 2017
Carbon dioxide CO2	1990	58,183,631	30,874,638	29,579,034	-1,295,604
Methane CH4		13,383,452	6,395,469	6,396,263	+794
Nitrous oxide N2O		4,416,078	3,231,428	3,219,798	-11,629
Hydrofluorocarbons HFCs	1995	126,416	1,227,518	1,146,951	-80,567
Perfluorocarbons PFCs		115,777	132,211	143,524	+11,313
Sulphur hexafluoride SF6		37,096	35,048	35,651	+603
Nitrogen trifluoride NF3[10]		501	338	371	+34
Aggregate net greenhouse gas emissions		76,262,950	41,896,650	40,521,593	-1,375,057

Methods used to measure or calculate the amount of net Scottish emissions

The basket of greenhouse gases consists of carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, sulphur hexafluoride and nitrogen trifluoride. Greenhouse gases are weighted by Global Warming Potential (GWP) and presented in carbon dioxide equivalent units. The GWP for each gas is defined as its warming influence relative to that of carbon dioxide, as specified by the Intergovernmental Panel on Climate Change (IPCC).

Greenhouse gas emissions estimates are provided by Ricardo Energy and Environment under contract to the UK Government and the devolved administrations. Reports are published on the National Atmospheric Emissions Inventory (NAEI) website^[11] and the latest figures for Scotland are published in the official statistics publication Scottish Greenhouse Gas Emissions, which is based on data published at the same time in Greenhouse Gas Inventories for England, Scotland, Wales and Northern Ireland.

The greenhouse gas inventory covers anthropogenic sources of greenhouse gas emissions from 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 IPCC.

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 related 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 UK Department for Business, Energy and Industrial Strategy publication Digest of UK Energy Statistics (DUKES)^[12]. This approach is prompted by data availability on emissions being more limited at the sub-UK level.

Changes to methods used to measure or calculate the amount of net Scottish emissions

Scottish greenhouse gas emissions are reviewed every year, and the whole historical data series is revised to incorporate methodological improvements and new data. As a result, both net Scottish emissions and the net Scottish emissions account for each target year are revised every year. The latest published Scottish greenhouse gas inventory (1990-2017) represents the best available data and supersede any previous data, which should be disregarded.

The Scottish greenhouse gas inventory is a subset of the UK inventory, which is assembled using international guidelines that require countries to keep it under review and take account of amongst other things:

• new data and revisions to data;
• international developments in inventory methods;
• the need for the inventory to take account of policy needs as they evolve;
• results of research.

All of the revisions to the 1990-2017 Scottish and UK inventories were for one of the reasons above.

Revisions for the 1990-2017 inventory

Due to methodological improvements and new data, as described above, there has been a cumulative upwards revision to emissions across the entire time series between the 1990-2008 and 1990-2017 inventories. Baseline emissions in the 1990-2017 inventory are 6.1 MtCO2e (8.6 per cent) higher than the 1990-2008 inventory which was used to set the statutory fixed annual targets for 2010-2027.

Detailed information on revisions for the 1990-2017 inventory are published in the official statistics release Scottish Greenhouse Gas Emissions 2017 (Section D)^[13]. The most notable revisions are:

1. Forestry

Technical revisions were made to historic forestry data across the UK, including improvements in models of carbon stock in trees and soils. The Scottish inventory was disproportionately affected by these changes given its relatively large forestry sink. These revisions acted to increase estimates of net emissions across the time series, making statutory targets relatively harder to meet.

2. Energy Supply

Some relatively modest revisions were made to the energy supply sector due to updated assumptions around the carbon content of waste materials subsequently used for energy production.

3. Transport

A revision to trends provided in the UK Sea Annual Fisheries publication meant that there were recalculations to emissions from fishing vessels throughout the UK. These recalculations were driven by changes to the UK national inventory.

4. Agriculture and Related Land Use

The UK inventory estimates for dairy and non-dairy cattle emissions were revised following a recalculation to correct an error in breed breakdown.

Adjustment of an amount for earlier target years

Revisions to estimates of net Scottish emissions for earlier target years are detailed in Table 3. These represent revisions to 1990-2016 inventory estimates published in the Annual Target Report for 2016. Revisions arising from previous inventory reports are available in previous annual target reports^[14].

Table 3: Revisions to net Scottish emissions for earlier target years
Target year	Net Scottish emissions reported in the 2016 Annual Target Report (tCO2e)	Revision (tCO2e)	Revised amount (tCO2e)
For The 1990-2017 Inventory
2010	55,823,196	3,009,060	58,832,256
2011	49,162,922	3,054,931	52,217,853
2012	51,456,868	1,354,761	52,811,629
2013	48,394,279	2,506,470	50,900,749
2014	44,359,477	2,890,439	47,249,916
2015	43,005,816	3,179,593	46,185,409
2016	38,574,259	3,322,391	41,896,650

Reasons For Revisions. These are described above and in more detail in the official statistics release Scottish Greenhouse Gas Emissions 2017