Scottish greenhouse gas emissions annual target report: 2015

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 2015 (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 2015 of net Scottish emissions.

Table 2: Net Scottish emissions for each greenhouse gas ( tCO ₂e) ^[9]

Greenhouse gas	Base year	Net base year emissions	Net Scottish emissions 2014	Net Scottish emissions 2015	Change in net Scottish emissions 2014 - 2015
Carbon dioxide CO 2	1990	58,520,749	37,500,226	36,234,616	-1,265,610
Methane CH 4		13,466,016	6,749,260	6,657,029	-92,232
Nitrous oxide N 2O		4,825,089	3,801,774	3,721,123	-80,651
Hydrofluorocarbons HFCs	1995	126,416	1,290,169	1,286,353	-3,816
Perfluorocarbons PFCs		115,777	142,008	119,549	-22,459
Sulphur hexafluoride SF 6		36,020	31,481	32,115	+634
Nitrogen trifluoride NF 3 [10]		501	279	307	+28
Aggregate net greenhouse gas emissions		77,090,568	49,515,198	48,051,092	-1,464,106

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 ( SF ₆) and nitrogen trifluoride ( NF ₃). 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, 2015 ^[12] , which is based on data published at the same time in Greenhouse Gas Inventories for England, Scotland, Wales and Northern Ireland: 1990-2015 ^[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 CO ₂ 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 (1990-2015) 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:

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

All of the revisions to the 1990-2015 Scottish and UK inventories were for one of the reasons above.

Revisions for the 1990-2015 inventory

Due to methodological improvements and new data, as described above, the baseline has been revised upwards in every successive inventory between
1990-2008 to 1990-2013, with a downwards revision to the baseline between
the 1990-2013 and 1990-2014 and 1990-2015 inventories.

Despite the recent downwards revision, there has been an overall upward revision to the baseline to 77.1 MtCO ₂e, which is 6.9 MtCO ₂e higher than estimated at the time annual targets for 2010 to 2027 were set based on the 1990-2008 Inventory.

Detailed information on revisions are published in the Official Statistics release Scottish Greenhouse Gas Emissions 2015 (Section D) ^[15] . The most notable revisions are:

Forestry

Forestry is a carbon sink which means that it removes emissions from the atmosphere. Methodological revisions to the forestry data show that the size of the forestry sink has reduced by approximately 30 per cent over the whole time series compared with previous estimates. Despite these revisions, the forestry sector remains a significant carbon sink in Scotland.

Waste Management

Methodological changes have reduced waste management emissions by approximately 40 per cent across the series. The reduction in emissions as a result of the methodological changes is greater at the start of the time series (early 1990s) than it is in later years which means that actual emissions reductions across the time series are less than previous estimates.

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 estimates reported in the 2014 Annual Target Report for the 1990-2014 inventory. Revisions to net Scottish emissions arising from previous inventory reports are available in previous annual target reports ^[16] .

Table 3: Revisions to net Scottish emissions for earlier target years ^[17]

Target year	Net Scottish emission estimate reported in 2014 Annual Target Report [18] ( tCO 2e)	Revision required ( tCO 2e)	Revised amount ( tCO 2e)
FOR THE 1990-2015 INVENTORY
2010	58,997,604	+2,800,554	61,798,157
2011	52,252,945	+3,244,301	55,497,246
2012	52,710,674	+3,573,890	56,284,564
2013	51,121,730	+2,605,850	53,727,580
2014	46,704,130	+2,811,068	49,515,198

REASONS FOR REVISIONS. These are described above and in more detail in the Official Statistics Release Scottish Greenhouse Gas Emissions 2015 ^[19]

Chart 1 shows the impact of successive revisions of the inventory on the reported source emissions for the baseline and the years from 2010 to 2014, as well as the source emissions for 2015.

Chart 1. Impact of successive revisions of the inventory on the reported source emissions for the baseline and the years from 2010 to 2014, and source emissions for 2015. Values in MtCO ₂e