2. Historical Emissions Analysis

Carbon Account For Transport Volume 9, 2017

2. Historical Emissions Analysis

2.1 Background data and sources

All historical emissions data presented were originally published in Greenhouse Gas Inventories for England, Scotland, Wales & Northern Ireland: 1990-2015 by the National Atmospheric Emissions Inventory[3]. Some information presented is from alternative sources where stated.

The inventory is compiled annually and consists of a time series of emissions back to 1990[4]. It is updated in full in every publication to take account of on-going improvements in estimation techniques and methodology. 

Emissions levels are presented in either mega-tonnes or kilo-tonnes[5] of carbon dioxide equivalent[6] (Mt CO2e, Kt CO2e). 

Emissions from international aviation and shipping were not originally reported in the inventory, but have been included since 2009 under a separate category titled Exports. The Scottish Government has committed to including them in the emissions targets, hence references to maritime and aviation emissions refer to both domestic and international combined, unless otherwise stated.

In line with the methodology used to report against the Climate Change (Scotland) Act, emissions from transport reported only include those at the point of use, also known as tailpipe emissions. As a result, lifecycle and displaced impacts, such as the emissions from generating the electricity powering electric trains, are not included.

2.2 Emissions trends for Scotland

In 2015 emissions from all sectors amounted to 48.1 Mt CO2e, down -3.0% from 49.5 Mt CO2e in 2014. Source adjusted emissions[7]  were 45.5 Mt CO2e[8] in 2015, -41.0% below the 1990 baseline.

Measured at source, transport emissions including International Aviation and Shipping (IAS)[9] accounted for 13.1 Mt CO2e in 2015, an increase of 0.4% on the previous year. The inventory states that transport emissions have now risen for two years[10]. Furthermore, in 2015 transport was the largest contributing sector to greenhouse gas emissions in Scotland, overtaking energy production for the first time.

The factors affecting transport emissions are numerous and complex. The 2008 recession was a contributing factor to the fall in emissions from that time, alongside investments in transport infrastructure, efficiency improvements and fluctuations in the price of oil. The significant fall in oil prices since 2014 is likely to have contributed to the increase in demand for fuel and travel in the period since.

Excluding IAS, transport accounted for 23.6% of Scottish greenhouse gas emissions in 2015. This proportion is 27.4% when including IAS. Figure 1 shows the growing prominence of transport as a source of greenhouse gas emissions since 1990.

Figure 1: Historical emissions from transport and its share of total emissions in Scotland

Figure 1: Historical emissions from transport and its share of total emissions in Scotland

Source: National Atmospheric Emissions Inventory

2.3 Emissions analysis by transport sector

2.3.1 Road Transport

Road transport accounted for 9.6 Mt CO2e in 2015. This is 72.7% of total transport emissions; a proportion which has generally risen since 2008. Figure 2 shows road emissions since 1990 with the proportion of transport emissions it accounts for. 

Figure 2: Historical road emissions in Scotland

Figure 2: Historical road emissions in Scotland

Source: National Atmospheric Emissions Inventory

Figure 3 shows the proportion of road emissions for each vehicle type for selected years. Since 1990, there has been a slow shift towards goods vehicle emissions relative to cars. 

Figure 3: Emissions from vehicles as a proportion of road emissions for selected years

Figure 3: Emissions from vehicles as a proportion of road emissions for selected years

Source: National Atmospheric Emissions Inventory

Changing consumer preferences on fuel are a contributing factor to the falling proportion of road emissions from cars. Diesel cars tend to be more fuel efficient, and hence have lower greenhouse gas emissions. Figure 4 shows the increasing proportion of new vehicles powered by diesel relative to petrol. New registrations of diesel vehicles overtook those of petrol in 2013.

Figure 4: Distribution of new Scottish vehicle registrations over time

Figure 4: Distribution of new Scottish vehicle registrations over time

Source: Scottish Transport Statistics 2016 Table 1.1

2.3.2 Shipping

Shipping emissions were 1.4 Mt CO2e in 2015. This is 10.5% of total transport emissions, an all-time low. Figure 5 shows a generally downward trend in total shipping emissions from their all-time peak in 1998.

Figure 5: Historical shipping emissions 

Figure 5: Historical shipping emissions

Source: National Atmospheric Emissions Inventory

Figure 6 shows shipping emissions disaggregated into domestic and international. International shipping emissions are much more volatile than domestic emissions, which have seen a steady decrease overall. A potential reason for the volatility in international emissions is economic activity, which drives demand for imports and exports.

Figure 6: Historical domestic and international shipping emissions

Figure 6: Historical domestic and international shipping emissions

Source: National Atmospheric Emissions Inventory


2.3.3 Aviation

In 2015 total aviation emissions, including aircraft support vehicles and military aircraft, were 2.0 Mt CO2e, an increase of 6.0% on 2014 and 46.1% above 1990. Aviation accounted for 15.5% of transport emissions in 2015. Total aircraft movements fell -11.8 % between 2005 and 2015[11]. Contrasting with rising emissions this suggests the use of larger aircraft and / or higher load factors on planes. Figure 7 shows the trend in total aviation emissions since 1990.

Figure 7: Historical aviation emissions and share of total transport emissions

Figure 7: Historical aviation emissions and share of total transport emissions

Source: National Atmospheric Emissions Inventory

Figure 8 disaggregates the data in figure 7 to show domestic and international aviation emissions. In recent years, emissions from domestic aviation have fallen while international emissions have risen to a new high in 2015. Domestic aircraft movements fell -18.8% between 2005 and 2015, while international aircraft movements increased 10.9%[12]

Figure 8: Domestic and international aviation emissions over time

Figure 8: Domestic and international aviation emissions over time

Source: National Atmospheric Emissions Inventory

2.3.4 International aviation and shipping

Emissions from international aviation and shipping were 2.4 Mt CO2e in 2015, a drop of -3.9% on the previous year, and -7.6% below the 1990 baseline. Figure 9 shows the pattern of international emissions over time, disaggregated by aviation and shipping. It is characterised by the general falling pattern of shipping emissions and the rising pattern of aviation emissions. In 2015 international aviation generated more emissions than international shipping for the first time since the emissions inventory was compiled.

Figure 9: International shipping and aviation emissions over time

Figure 9: International shipping and aviation emissions over time

Source: National Atmospheric Emissions Inventory

2.3.5 Rail

Rail accounted for 0.17 Mt CO2e in 2015; -4.5% below the previous year, but 33.7% above the 1990 level. In the ten years to 2015/16, passenger kilometres on Scotrail services increased by 32.9%, and scheduled train route kilometres increased 20.2%[13]. Figure 10 shows the trend of rail emissions since 1990.

Figure 10: Rail emissions and its share of total transport emissions over time

Figure 10: Rail emissions and its share of total transport emissions over time

Source: National Atmospheric Emissions Inventory

2.4 Road emissions by vehicle type

2.4.1 Cars

Emissions from cars rose in both 2014 and 2015, having generally fallen since 2007. Between 2005 and 2015, car kilometres in Scotland rose from 22.1 million to 34.7 million[14], while emissions fell from 6.2 Mt CO2e to 5.7 Mt CO2e. Despite this improved fuel efficiency, in 2015 cars still accounted for 59.3% of road emissions and 43.2% of total transport emissions in Scotland. These are the highest proportions of any mode of transport.

2.4.2 Heavy Goods Vehicles

At 18.1%, HGVs accounted for the second largest proportion of road emissions in 2015. This is 12.3% of total transport emissions. At 1.7 Mt CO2e, HGV emissions were 2.2% higher than the previous year, but -3.5% below the 1990 figure. Between 2005 and 2015 HGV kilometres in Scotland fell by -5.0%.

2.4.3 Light Goods Vehicles

LGV emissions were 69.2% higher in 2015 than in 1990. In 2015 they accounted for 1.6 Mt CO2e, 4.6% more than the previous year. This is 16.9% of road emissions and 12.3% of total transport emissions. In the decade to 2015, light goods vehicle kilometres in Scotland rose 27.8%, from 5.5 million to 7.0 million.

2.4.4 Buses and coaches

Buses and coaches accounted for under 0.5 Mt CO2e in 2015, a drop of -3.0% on the previous year. Bus emissions have gently declined since 1990, and in 2015 stand -21.7% below this 1990 figure. Between 2005 and 2015, published public service vehicle kilometres fell -12.3%[15].

2.4.5 Motorcycles

Motorcycles emitted 0.033 Mt CO2e in 2015. This is only 0.3% of road emissions and 0.1% of transport emissions. Motorcycle emissions have been low since 1990, and as such have never significantly impacted Scotland’s transport emissions in the time the emissions inventory has been collated.

Figures 11, 12 and 13 illustrate changes in road emissions by vehicle type, the changing share of road emissions attributable to different vehicle types and year on year changes in emissions of different vehicle types respectively. 

Figure 11: Road emissions by vehicle type, selected years

Figure 11: Road emissions by vehicle type, selected years

Source: National Atmospheric Emissions Inventory

Figure 12: Share of road emissions by vehicle type, 1990 and 2015

Figure 12: Share of road emissions by vehicle type, 1990 and 2015

Source: National Atmospheric Emissions Inventory

Figure 13: Year on year change in emissions by vehicle type, 1999-2015

Figure 13: Year on year change in emissions by vehicle type, 1999-2015

Source: National Atmospheric Emissions Inventory

2.5 Road emissions by type of road

2.5.1 Rural

At 4.8 Mt CO2e in 2015, rural road emissions were 2.7% above the previous year, and 2.5% above 1990. Rural emissions accounted for 50.0% of road emissions.

2.5.2 Urban

At 3.0 Mt CO2e in 2015, urban road emissions are 0.1% above the previous year, but -12.8% below 1990. Urban emissions accounted for 31.2% of road emissions in 2015, down from 37.1% in 1990.

2.5.3 Motorways

At 1.8 Mt CO2e in 2015, motorways emissions are at their highest level on record, 59.8% higher than 1990.  Motorways contribute the smallest proportion of road emissions, at 18.8%, up from 12.2% in 1990.

Figure 14 shows an index of emissions from different types of road since 1990.

Figure 14: Emissions by road type (1990=100)[16]

Figure 14: Emissions by road type (1990=100)

Source: National Atmospheric Emissions Inventory

Figure 15: Share of road emissions by road type

Figure 15: Share of road emissions by road type

Source: National Atmospheric Emissions Inventory