Scottish greenhouse gas emissions annual target report: 2016

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 2016 (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 2016 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 2015	Net Scottish emissions 2016	Change in net Scottish emissions 2015 - 2016
Carbon dioxide CO2	1990	57,366,238	31,522,487	27,338,048	-4,184,439
Methane CH4		13,455,418	6,597,838	6,451,438	-146,401
Nitrous oxide N2O		4,587,469	3,438,346	3,382,074	-56,272
Hydrofluorocarbons HFCs	1995	126,416	1,295,165	1,234,038	-61,128
Perfluorocarbons PFCs		115,777	119,549	132,211	+12,662
Sulphur hexafluoride SF6		36,032	32,123	36,112	+3,989
Nitrogen trifluoride NF3[10]		501	307	338	+31
Aggregate net greenhouse gas emissions		75,687,849	43,005,816	38,574,259	-4,431,557

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

The basket of greenhouse gases consists of carbon dioxide, methane, nitrous oxide, and hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulphur hexafluoride (SF₆) and nitrogen trifluoride (NF₃). 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 and Aether 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, 2016^[12], which is based on data published at the same time in Greenhouse Gas Inventories for England, Scotland, Wales and Northern Ireland: 1990-2016^[13].

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)^[14]. 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 (1990-2016) 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 1990-2016 Scottish and UK inventories were for one of the reasons above.

Revisions for the 1990-2016 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 1990-2016 inventories. Baseline emissions in the 1990-2016 inventory are 5.5 MtCO2e (7.8 per cent) higher than the 1990-2008 inventory.

Detailed information on revisions for the 1990-2016 inventory are published in the Official Statistics release Scottish Greenhouse Gas Emissions 2016 (Section D)^[15]. The most notable revisions are:

1. Forestry.

Methodological change to series has increased the sink. The area reported as forest remaining forest has been revised upwards. There are also changes in the model for calculating forest carbon stock. This has resulted in an increase in the magnitude of the sink from forest land across the time series.

2. Shipping

Improvements to the methodology for estimating shipping emissions has resulted in an increase in the estimates for gas oil and fuel oil used in Scotland. This has caused recalculations for emissions from domestic navigation and fishing vessels.

3. Agriculture and Related Land Use

Lower estimated nitrous oxide emissions from agricultural soils and the use of a new emission factor model for enteric fermentation incorporating UK-specific parameters are the largest contributors to recalculations from the agriculture sector in Scotland.

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 1990-2015 inventory estimates published in the Annual Target Report for 2015. Revisions arising from previous inventory reports are available in previous annual target reports^[16].

Table 3: Revisions to net Scottish emissions for earlier target years

Target year	Net Scottish emissions reported in the 2015 Annual Target Report (tCO2e)	Revision required (tCO2e)	Revised amount (tCO2e)
For the 1990-2016 Inventory
2010	61,798,157	-5,974,961	55,823,196
2011	55,497,246	-6,334,324	49,162,922
2012	56,284,564	-4,827,696	51,456,868
2013	53,727,580	-5,333,301	48,394,279
2014	49,515,198	-5,155,721	44,359,477
2015	48,051,092	-5,045,276	43,005,816
Reasons for Revisions. These are described above and in more detail in the Official Statistics Release Scottish Greenhouse Gas Emissions 2016