Chapter 2: Historical emissions analysis
The emissions data presented in this chapter are from the 'Greenhouse Gas Inventory for England, Scotland, Wales and Northern Ireland: 1990-2010'9 (GHGI) unless stated referenced. The GHGI is compiled on an annual basis and the full time series of all greenhouse gases is updated in each publication to take account of improved data and any advances in calculation methodology. The greenhouse gases associated with transport and recorded by GHGI are Carbon Dioxide (CO2), Nitrous Oxide (N2O) and Methane (CH4)10.
The transport category within the GHGI covers emissions from road, aviation, rail and maritime transport. While domestic aviation and shipping emissions are reported in the GHGI, emissions associated with international aviation and shipping were not originally reported. However, using existing data sources, an indicative assessment of the emissions from international aviation and shipping from each country in the United Kingdom was first published in 2009 and continues to be published as an appendix within the annual GHGI publications, including a breakdown for the four home countries. Consequently, in line with the Scottish Government commitment to include emissions from international aviation and international shipping within the targets set by the Climate Change (Scotland) Act, references to aviation and maritime emissions in this document refer to both domestic and international, unless otherwise stated.
The transport emissions reported in this section only cover emissions at the point of use (tailpipe emissions). Consequently, no lifecycle impacts within the transport infrastructure and no displaced impacts, such as the emissions generated by the electricity used on electrified railways, are included.
2.2 Total Emissions Trends
Transport in Scotland produced 13.2 mega-tonnes of carbon dioxide equivalent (MtCO2e) emissions in 2010. This total represents a 0.4 MtCO2e or 2.9% fall from the equivalent 2009 figure, and is the third consecutive year of annual reduction in transport emissions. 2010 emissions are though still some 1.3% above the 1990 base year emissions total of 13.0 MtCO2e. The uncertain economic conditions clearly continue to play a significant part in the reported transport emissions but movements in transport emissions are in addition affected by car ownership levels, global oil prices, household income, population, land planning and use, public transport provision, culture and lifestyles.
While the uncertainty has also impacted on emissions from all other sectors the 2010 emissions estimate for Scotland shows an increase of 3.1 MtCO2e between 2009 and 2010.11 This rise is largely due to an increase in fossil fuels burnt in domestic heating (gas) and in power generation (coal)12. Total Scottish emissions are though still 23% below their 1990 level.
The rise in total Scottish emissions coupled with the further decline in transport emissions means that, for the first time since 2006, transport's share of all Scottish emissions has fallen. The transport sector now accounts for 20.1 % of total emissions if International Aviation and Shipping (IAS) emissions are excluded from both transport and the aggregate figure, and 23.7% with the inclusion of IAS emissions. These 2010 proportions are though still considerably above the equivalent 1990 percentages of 15.1% and 18.0% respectively.
Figure 1: Total emissions from transport and transport emissions as a percentage of total Scottish emissions, 1990-2010
Source: Greenhouse Gas Inventory, NAEI, 2012, Transport Scotland. Total emissions calculation excludes the impact of the EU Emissions Trading System
Emissions by mode
The fall in aggregate transport emissions between 2009 and 2010 is largely a result of reduced emissions from international aviation and shipping. Road emissions are broadly unchanged as the significant reduction in emissions from cars is offset by an almost equivalent increase in emissions from lorries and vans. In more detail:
- Emissions from cars and motorbikes fell by 3.6% from 5.6 to 5.4 MtCO2e;
- Emissions from lorries and vans increased by 6.5% from 3.2 to 3.4 MtCO2e;
- Emissions from IAS fell by 12.1% from 2.8 to 2.5 MtCO2e; and
- Combined, the other sectors13 saw emissions fall by 3.3% from 1.9 to 1.8 MtCO2e.
Figure 2: Transport emissions 1990-2010 broken down by broad transport sector
2.3 Emissions analysis by transport sector
Road transport emissions cover emissions from all private, public and commercial road vehicles. Together, this category accounts for over 71% of all transport's emissions, with cars alone accounting for 57% of road transport emissions and 41% of all transport emissions.
Emissions from road transport in 2010 saw a marginal increase over the equivalent 2009 figure, but remain at 9.4 MtCO2e. This total is more than 6% below the 2007 road emissions peak of 10.1 MtCO2e. Overall road emissions in 2010 were 3.8% higher than their equivalent 1990 figure. Road emissions as a percentage of total transport emissions rose marginally in 2010.
Figure 3: Road transport emissions 1990-2009 and as a share of total transport emissions
Further detailed analysis of road transport emissions by vehicle type is undertaken in section 2.4.
Maritime emissions14 in 2010 are estimated to be 1.9 MtCO2e or 14% of total transport emissions. As international shipping accounts for between 75% and 85% of the sector's total emissions, so the performance of the maritime category is principally driven by changes in this one activity. Historically, maritime emissions, and international emissions in particular, have been very volatile. Between 1995 and 2002 shipping emissions fell by almost a third to 1.7 MtCO2e before rising again by a third to 2.3 MtCO2e by 2008. International shipping emissions fell by almost 16% between 2009 and 2010. Emissions in 2010 are now over 0.7 MtCO2e below the equivalent 1990 figure.
Figure 4: Maritime emissions 1990-2010 and as a share of transport emissions
Aviation emissions have fallen by 7% continuing a trend begun in 2008. Between 2009 and 2010 emissions fell from 1.8 MtCO2e to 1.7 MtCO2e, and are now some 0.5 MtCO2e below the 2007 peak of 2.2 MtCO2e. Current aviation emissions account for 13% of total transport emissions, down from 15% of all transport emissions in 2007. International aviation emissions make up around 60% of total emissions from the sector.
Overall aviation emissions are still over 0.5 MtCO2e above their equivalent 1990 figure, driven almost exclusively by the increase in international emissions over the period.
Figure 5: Aviation emissions 1990-2010 and as a share of total transport emissions
Rail emissions rose by 1.6% between 2009 and 2010 and the 2010 emissions total of 0.2 MtCO2e is 35% above the equivalent 1990 figure. Despite these shorter and longer term increases in rail emissions the sector still accounts for less that 2% of all Scottish transport emissions.
Figure 6: Rail emissions 1990-2010 and as a share of total transport emissions
2.4 Road Emissions by vehicle type
Cars: At 5.4 MtCO2e in 2010, emissions from cars account for both the greatest proportion of road emissions as well as all transport emissions; just over 57% and 41% respectively. Emissions from cars have fallen slowly from a peak of 6.1 MtCO2e in 2002 to their current level. The 2010 emissions level is 11% below that 2002 peak figure and also 0.4 MtCO2e below the 1990 level.
HGVs: Emissions from HGVs make up the second largest proportion of road emissions. HGV emissions in 2010 were just under 2.1 MtCO2e, a 10% increase over the 2009 figure of 1.9 MtCO2e. This increase marks the end of a short run of declining emissions from HGVs and takes the total marginally above the 1990 baseline figure.
LGVs: LGV emissions increased by 1.1 % between 2009 and 2010 but remain at 1.3 MtCO2e, having previously fallen for 2 years. The latest emissions figure for LGVs is almost 70% above the base year total of just under 0.8 MtCO2e.
Buses and motorcycles: Emissions from buses rose marginally between 2009 and 2010 but remain under 0.6 MtCO2e, while motorcycle emissions fell slightly and now account for less than 0.04 MtCO2e of total transport emissions.
Figure 7 shows the changes in emissions for road vehicles, broken down by vehicle type while Figure 8 shows the year on year percentage change in emissions in the three largest road emitting categories (Car, HGV and LGV). While the downward trend in emissions from cars continues there has been a return to increasing emissions in both goods vehicle categories after two years of reductions.
Figure 7: Breakdown of Road Emissions by Vehicle Type 1990-2010
Figure 8: Year on year change in car, HGV and LGV emissions 1995-2010
Emissions by road type
The GHGI database also differentiates road transport emissions across three road types: rural, urban and motorway. All three road categories saw virtually no change in emissions between 2009 and 2010. Just over half of Scottish road emissions arose from rural driving in 2010, a small reduction in percentage terms from the position in 1990. Urban emissions have fallen from just over one third of road emissions to just below one third with the increase in emissions from motorway driving causing these gradual declines on other parts of the road network. Emissions from motorway driving in 2010 are 40% higher than in 1990.
Figure 9: Breakdown of road emissions by road type 1990-2010
2.5 Comparison of key Scottish and UK Transport emission figures and trends
Table 1: Comparison of Scottish and UK GHG emissions
|| Scottish emissions
| Scottish emissions as a % of UK emissions
| Change in Scottish emissions
| Change in UK emissions
| Change in Scottish emissions
| Change in UK emissions
| All Transport
|| - 1.9%
| All Transport (excl. IAS)
| Road Transport
| of which : Cars
Scottish transport emissions including IAS currently account for 8.1% of total UK transport emissions and 8.8% of emissions if IAS is excluded. Emissions from road transport in Scotland are in proportion to the overall UK figure although emissions on rural roads are above the UK equivalent percentage with the reverse holding for motorway emissions. The aviation (4.7%) and maritime (15.3%) sectors show the greatest variation from a proportional share.
Historically, all sub categories of Scottish transport emissions have moved broadly in line with the equivalent UK level series. This is to be expected given the similarities in economies, transport networks and levels of interconnectivity.
It is the difference in size and relative importance of the aviation and maritime sectors in the UK and Scotland that have largely driven the change in overall transport emission performance between Scotland and the UK, particularly in respect of the changes seen between 1990 and 2010. Excluding IAS UK emissions in 2010 are only marginally above the 1990 level, with Scotland seeing a greater increase, albeit still below 2%. However, once emissions from IAS are included the position changes significantly. UK emissions in 2010 are just over 11% above their equivalent 1990 figure while in Scotland the rise is just over 1%.
More specifically, while international aviation emissions have increased by almost 70% at the UK level the figure for Scotland is significantly lower at 46%. For the maritime sector emissions have fallen by 3% at the UK level but by 29% in Scotland. This sub-UK level change in maritime emissions is due in significant part to a methodological change and reallocation of emissions between the countries of the UK. With international maritime emissions making up just under 25% of total UK IAS emissions but almost 60% of Scottish IAS emissions the drivers behind the changes in overall transport emissions including IAS are more obvious.
2.6 Efficiency of passenger vehicles
Different modes of transport have the capacity to transport different numbers of passengers. For example the average number of passengers on a bus is higher than the average number of passengers in a car. As such the efficiency of transport modes, in terms of the CO2 per passenger kilometre transported, varies. Defra's Company Reporting Guidelines15 allow comparisons to be made between the emissions per passenger kilometre16 of different modes of travel.
Table 2: CO2e emissions per passenger kilometre by mode
|| Average petrol car
|| Average diesel car
|| Average petrol hybrid car
|| Average petrol motorbike
|| Average bus
|| Average coach
|| National rail
|| Light rail and tram
| Ferry (Large RoPax)
|| Average foot and car passengers
|| Domestic flights
|| Short haul international
|| Long haul international
Source: 2012 Guidelines to Defra/DECC's GHG Conversion Factors for Company Reporting: Methodology Paper for Emission Factors May 2012
All values shown in Table 2 are estimated using data for Great Britain so do not specifically relate to Scotland. In general, public passenger transport (rail, coach, and tram) is more efficient in terms of CO2e/pkm because they transport more people at one time.
2.7 Leading indicators
Data on greenhouse gas emissions tends to lag approximately a year behind other transport data. Consequently, in order to keep the information in the CAT as relevant as possible, the following indicators provide some insight into likely future trends in GHG emissions:
- Road vehicle kilometres travelled: Emissions are directly related to the kilometres travelled. This indicator tracks vehicle kilometres travelled by all vehicle types on all roads.
- Road transport fuel consumption per vehicle kilometre: Fuel efficiency in this context relates to reducing fuel consumption in road transport without impinging on our ability to transport ourselves. Holding all else constant, the more fuel efficient we are as we travel the fewer emissions we emit. Improving fuel efficiency can be achieved through a combination of measures to improve the fuel efficiency of vehicles and decreasing the volume of fuel consumed through widening travel choices. This indicator tracks the fuel consumption per vehicle kilometre and per 1000 of population.
- Proportion of new road vehicles that are alternatively fuelled: Improving the average efficiency of new vehicles is crucial to reducing emissions from the transport sector. Alternatively fuelled vehicles18, including electric and hybrid vehicles, have the potential to emit very low levels of tailpipe emissions. This indicator tracks the proportion of vehicles newly registered that are alternatively fuelled.
- Modal share of public transport and active travel: Promoting the use of public transport or active travel as an alternative to the private car is an important element of reducing transport emissions. This indicator tracks the proportion of average distance travelled per person per annum by public transport, walking or cycling.
- Aviation passengers: Emissions from aviation have grown rapidly over the past 20 years. This indicator tracks the total number of aviation passengers, both terminal and transit.
- Waterborne freight lifted in Scotland and moved: Commercial shipping constitutes the greatest element of maritime emissions. This indicator tracks the total level of waterborne freight lifted in Scotland and moved, measured in million tonne-kilometres.
Table 3: Trends in leading transport indicators19 Awaiting an update of the table from STS when published for first half of table
|| 2011 level
|| Average growth p.a.
| Road vehicle kilometres travelled
(million vehicle kilometres)
| Proportion of new road vehicles that are alternatively fuelled (%)20
| Modal share of public transport and active travel (distance travelled) (%)21
| Aviation passengers
| Waterborne freight lifted in Scotland and moved (million tonne-kilometres)22
|| 2010 level
|| Average growth p.a.
| Road transport fuel consumption23
(a) tonnes per 1000 vehicle kilometres;
(b) tonnes per 1000 population.24
| (a) 0.07
|| (a) -1.1%
|| (a) -1.4%