Air Departure Tax: consultations and environmental report
Consultations relating to our policy for an overall 50% Air Departure Tax (ADT) reduction by the end of the current session of Parliament. Includes a Strategic Environmental Assessment (SEA).
3 Climatic Factors
3.1 Environmental Objectives
3.1.1 The 2009 Act [42] created the statutory framework for GHG emissions reductions in Scotland and set targets for reductions in emissions of the basket of seven Kyoto Protocol greenhouse gases [43] of 80% by 2050, with an interim 2020 target of 42%, compared to the 1990/1995 baseline level. The 2009 Act sets out Scotland's ambition on tackling climate change and, through this legislation, Scotland's contribution to international ( EU and UN) efforts on climate change mitigation and adaptation. Under the 2009 Act, both domestic aviation emissions and Scotland's share of international aviation emissions are included when measuring progress towards meeting statutory emission reduction targets.
3.1.2 The 2009 Act also requires that annual GHG emissions targets are set, by Order, for each year in the period 2010-2050. When setting each batch of targets, Scottish Ministers are required to have regard to advice received from the Committee on Climate Change. Following the initial phase of target-setting, the annual targets are set in five year batches, at least twelve years in advance. The third and most recent batch of annual targets, covering the years 2028-2032, was agreed by the Scottish Parliament in October 2016.
3.1.3 Official statistics published in June 2016 show that Scottish emissions, for the purpose of reporting against statutory targets, were 45.8% below the 1990 baseline level in 2014 [44] . This means that the level of the statutory interim 2020 target has been exceeded six years early [45] . Having made strong progress towards the targets set out in the 2009 Act, the Scottish Government has committed to keeping Scotland at the forefront of global climate action by responding to the United Nations Framework Convention on Climate Change (" UNFCCC") Paris Agreement with a Climate Change Bill that sets new, evidence-based, statutory emission reduction targets [46] .
3.1.4 Section 35 of the Act requires that Scottish Ministers lay a report in Parliament setting out proposals and policies for meeting emission reduction targets, as soon as reasonably practicable after each batch of annual targets has been set. These have become the series of Reports of Proposals and Policies. In January 2017, the draft Climate Change Plan: the draft Third Report on Policies and Proposals 2017-2032 [47] was published for parliamentary scrutiny. The draft Climate Change Plan builds on the work of the previous RPP reports, taking forward these ambitions and exploring opportunities to further reduce Scotland's GHG emission between now and 2032. The draft Climate Change Plan sets out Scotland's ambitious approach to mitigating the effects of climate change across a range of sectors including transport.
3.1.5 The Scottish Climate Change Adaptation Programme ("the Programme") [48] was developed in 2014 to address the impacts identified for Scotland in the 2012 UK Climate Change Risk Assessment [49] . The Programme set out Scottish Ministers' objectives in relation to adapting to climate change, their proposals and policies for meeting these objectives, the period within which these proposals and policies would be introduced, and arrangements for wider engagement in meeting these objectives. The impacts identified for Scotland by the 2017 UK Climate Change Risk Assessment [50] are expected to be addressed by the second iteration of the Programme which is due in 2019 [51] .
Paris Climate Agreement
3.1.6 In November 2016 the UNFCCC Paris Agreement came into force [52] after being adopted by 195 countries. The Agreement is the first ever universal, legally binding global climate deal and sets out goals to limit global warming to well below 2°C, and to pursue further efforts to limit it to 1.5°C [53] . The Agreement also covers a range of other issues such as mitigation through reducing emissions, adaptation, and loss and damage [54] .
EU Emissions Trading System
3.1.7 The EU Emissions Trading System (" EU ETS") is a key component of the EU's policy to combat climate change, with a 20% emission reduction target for 2020 on 2005 levels. In operation since 2005, it introduced a cap for GHG emissions from energy intensive industries. Companies are required to obtain allowances, the availability of which decreases over time, to cover their emissions. The EU ETS operates in 31 countries (all 28 EU countries plus Iceland, Liechtenstein and Norway) [55] and covers 45% of the EU's emissions.
3.1.8 The EU ETS was amended to include emissions from international aviation in 2012, with the target of reducing emissions 5% below the 2004-6 average. Under the EU ETS CO 2 emissions from both domestic and international aviation, are capped at 95% of historic levels from 2013 to 2020 [56] . A subsequent decision was taken to exclude flights outwith the European Economic Area (" EEA") between 2013 and 2016 (known as the "Stop the Clock" decision) [57] . This decision was taken to avoid jeopardising talks by ICAO on the development of a global market-based measure.
3.1.9 In February 2017 the European Commission proposed to permanently fix the scope of the aviation EU ETS to flights within the EEA from the 2017 compliance year onwards (effectively meaning a continuation of the Stop the Clock decision beyond 2016 with no break) [58] . The proposal recognises that an agreement was reached to develop a global market based measure for international aviation emissions at the ICAO assembly in October 2016 (discussed further in Section 3.3). It therefore includes the future review of the aviation EU ETS once the detail of the global market based measure is known.
3.2 Environmental Context
3.2.1 Over the last 50 years, it has become increasingly apparent that the world's climate is changing at an unprecedented rate. Evidence of an increase in average global temperatures, along with an increase in GHG in the atmosphere, has led to the conclusion that human activities such as the use of carbon based fuels is the main reason for this increase [59] . In addition, many of the activities that contribute to climate change ( e.g. transport and energy generation) are often also responsible for generating air pollution.
3.2.2 Climate change is considered to be one of the most serious environmental threats to sustainable development, with adverse impacts expected on human health, food security, economic activity, natural resources and physical infrastructure [60] [61]. Adaptation to the effects of climate change is now acknowledged as necessary for responding effectively and equitably to the impacts of climate change.
3.2.3 Within Scotland, higher temperatures and changes in rainfall patterns have been exhibited since 1961. For example, some parts of northwest Scotland have become up to 45% drier over the summer months, while increases in winter rainfall of as much as 60% have been observed in northern and western regions [62] . As discussed above, climate change has the potential to have a wide range of direct, secondary or indirect effects on the natural environment, and has been identified as a primary pressure on many of the SEA topic areas ( i.e. soil, water, biodiversity, cultural heritage and the historic environment). The predicted impacts from a changing climate have been discussed further under the relevant SEA topics in this Report.
3.2.4 In 2014, Scotland's emissions of the basket of seven Kyoto GHGs were estimated to be 46.7 million tonnes of carbon dioxide equivalent ( MtCO 2e). This is 8.6% lower than the 2013 figure of 51.1 MtCO 2e, a 4.4 MtCO 2e decrease in absolute terms [63] . In 2014, Scotland's emissions from transport (including international aviation and shipping) were 12.9 MtCO 2e. This is the second largest source of GHG emissions in 2014, after the energy supply sector (13.8 MtCO 2e) [64] . Between 1990 and 2014, there was an overall 0.4 MtCO 2e (2.8 per cent) fall in emissions from the transport sector (including international aviation and shipping). Emissions in this sector rose from 1990 to a peak in 2007, before falling slightly since then [65] .
3.2.5 GHG emissions from transport tend to correlate with Gross Domestic Product. Hence the 2008 recessions is widely thought to be a contributing factor for the fall in transport emissions in Scotland after 2007. For example, when the economy grows, the demand for goods rises. The demand for these increases the volume of goods in transit, and the volume of passengers traveling to purchase them, and the reverse is true when the economy contracts.
3.2.6 At a Scotland level, the latest GHG inventory shows that aviation accounted for around 4% of total Scottish GHG emissions in 2014 [66] . The share of aviation emissions which arise from domestic flights is much higher for Scotland than for the UK as a whole, at approximately 30% of aviation emissions. The table below sets out the proportion of emissions between domestic and international aviation in 2014 [67] .
| Proportion of Total Aviation Emissions, 2014 | Scotland | UK |
|---|---|---|
| Domestic | 34.07% | 8.37% |
| International | 65.93% | 91.63% |
| Total | 100.00% | 100.00% |
3.2.7 The nature of flights undertaken can be varied and complex. Some can be point to point flights; others, whilst considered domestic, can be connecting flights to onward journeys. For example, a domestic flight starting in Scotland can often be part of a long-haul route via airports such as London Heathrow, as this serves as a major airport hub for Scotland's main airports.
3.2.8 Approximately 25.5 million air terminal passengers utilised Scottish airports in 2015, an increase of 5.9%, or 1.4 million passengers from the previous year [68] . Of this number, three quarters travelled to or from Edinburgh or Glasgow [69] . In 2015, four airports, Edinburgh, Glasgow, Aberdeen and Inverness, accounted for 94% of total passenger numbers at Scottish airports. Passenger numbers increased by 39% between 2001 and 2007, reaching a peak of 25,132 before falling 17% to 20,907 in 2010 [70] . Since then they have risen 22% [71] .
3.2.9 At the UK level, the Civil Aviation Authority (" CAA") reports that direct emissions from flights equalled approximately 34 million tonnes (Mt) in 2012 [72] . It is also stated that the average house produces 4.5t of CO 2 per annum so aviation's contribution to GHG emissions is approximately equivalent to the CO 2 generated from 7.7 million homes [73] . In 2011, it was reported that in the UK aviation accounted for approximately 6% of total UK CO 2 emissions in 2011 [74] . Of these emissions, around 90% arise from international flights, and 10% from domestic flights [75] .
3.2.10 Aircraft emit a range of GHG throughout the different stages of flight and are fairly unique in that they emit gases directly into the higher levels of the atmosphere. The GHG created by aviation are: CO 2; oxides of nitrogen; ozone (created by the reaction of sunlight and nitrogen oxides); soot; aerosols; and water vapour (causing contrail or man-made cirrus clouds) [76] . CO 2 is generally viewed as the most problematic GHG and in aviation it is primarily generated by burning carbon-rich fossil fuels in engines. Aircraft emit CO 2 in direct proportion to the quantity of the fuel burned [77] . In approximate terms, every tonne of aviation fuel burned produces between 3.15 and 3.18 tonnes of CO 2 [78] .
3.2.11 There are many factors that affect the amount of CO 2 emissions emitted from a flight. Some of these are within the capacity of airlines to manage, such as operational features; some can be controlled or influenced by airports and regulators; and some are to do with weather. The main factors are aircraft type, flight profile and distance, weight of the aircraft, operational procedures, use of next-generation biofuels, weather, and efficiency improvements [79] .
3.2.12 One approach to reducing aviation emissions growth in the future is the development and use of sustainable alternative fuels. These have a reduced carbon footprint compared to conventional jet fuel and could therefore reduce GHG emissions. It is predicted that sustainable fuels could contribute to an 18% reduction in the UK's aviation CO 2 emissions by 2050 [80] . Some alternative fuels are clean burning and can provide air quality benefits as the fuels emit low levels of particulates [81] .
3.2.13 Closer to the ground, airport related operations also contribute to climate change. For example aircraft taxiing, passengers and workers travelling to and from the airport, airfield ground transport, airport buildings and airfield systems all produce GHG emissions [82] . It should also be noted that below 1,000 feet, aviation related emissions also affect air quality [83] . This has been assessed under the topics of population and human health and air quality.
Other non- CO 2 GHG
3.2.14 Aviation contributes to climate change through a range of "non- CO 2" impacts which occur at altitude. Certain emissions, though not direct GHG themselves, can act to modify, produce or destroy GHGs. The interaction between nitrogen oxides and methane and ozone concentrations are of primary concern [84] . Furthermore, the magnitude of the impact these emissions can have on climate change is a function of the height at which the emissions are realised. For example, compounds such as nitrogen oxides and water vapour have a greater effect at higher altitudes.
3.2.15 The scenario that arises as a result of this greater effect is expressed by scientists as a multiplier [85] . Less is known about the effect of non- CO 2 GHG emissions and scientific uncertainty remains [86] .
3.3 Assessment Findings
3.3.1 In order to assess the impacts likely to arise from the proposal to reduce the overall burden of ADT by 50% by the end of the current session of the Scottish Parliament, consideration needs to be given to the potential impact this could have on current passenger and flight numbers. It has been estimated [87] that passenger numbers (without the introduction of the preferred policy option) could reach 28.0 million by 2021(an increase of 10% from 2015) and 33.3 million by 2032 (a rise of 30% over the period from 2015) [88] .
3.3.2 Research by Transport Scotland in 2017 ("the 2017 research") reported that reducing the overall burden of ADT by 50% was likely to lead to increased aviation activity over current levels [89] . This activity is likely to comprise both international and domestic flights. Consideration was also given to the implications that might arise from passengers "switching" airports as a result of changes in the tax rate amounts. For example, passengers choosing to fly from Scottish airports instead of northern English airports, such as Manchester and Newcastle, in response to lower tax rates.
3.3.3 It is recognised that there are a number of different ways in which a 50% reduction in the overall ADT burden could be delivered. For example, the tax charged across all flights types could be reduced equally by 50%. Alternatively, the policy could also be delivered by applying a zero tax charge to all short-haul flights and maintaining the tax charged on long-haul flights at current UK APD levels, or vice versa. It is considered that these illustrative scenarios would meet the preferred policy option of a 50% reduction in the overall tax burden as it is estimated that approximately 48% of APD revenues currently generated in Scotland is accrued from short-haul flights, and approximately 52% of revenue is from long-haul flights.
3.3.4 In terms of passenger numbers, applying a zero tax rate amount only to short-haul flights has the potential to lead to a greater number of passengers than cutting both short and long-haul flights by an equal proportion. Conversely, if a zero tax rate amount were to be applied only to long-haul flights, it is likely that the increase in passenger numbers could be lower than cutting both equally or applying a tax reduction only to short-haul flights.
3.3.5 The above view has been based on the Transport Scotland research which included the current understanding of price elasticity on passenger demand for air travel. For example, short-haul leisure travel - both domestic and international - tends to be the most elastic ( i.e. most price sensitive), with long-haul business and leisure trips considered as the most inelastic ( i.e. least price sensitive) [90] . Additionally, there are fewer long-haul flights operating from Scottish airports and, therefore, fewer passengers. Currently less than 5% of passengers fall within this these types of long-haul flights.
3.3.6 A reasonable alternative to the preferred policy option is that there is no reduction in the overall burden of ADT. It is considered that this represents a "like for like" approach as the tax rate amount would remain the same as that currently set under UK APD. Under this approach there would be no reduction under ADT (compared to UK APD) in the tax charged on flights from Scottish airports and, as such, it is considered that there would be no additional impact on passenger and flight numbers. Activity in the sector would likely continue on the current predicted trajectory.
What are the likely implications of increased passenger and flight numbers on climatic factors?
3.3.7 The 2017 research has estimated that the introduction of a 50% reduction in the overall burden of ADT (applied proportionally equally across all flight types) could lead to increased emissions of between 0.087 MtCO 2e and 0.101 MtCO 2e in the year of introduction (assumed to be 2018), relative to where they would be in the absence of the policy [91] . This is an increase greater than the estimated figures of between 0.05 MtCO 2e and 0.06 MtCO 2e set out in the 2014 research [92] . Furthermore, the 2017 research estimates (assuming the growth in baseline passenger numbers used in the research continues) that by 2021, the carbon emissions will increase by between 0.090 MtCO 2e and 0.105 MtCO 2e. Aviation currently accounts for less than 4% of total Scottish emissions and the increase in aviation emissions forecast as a result of the 50% reduction in ADT is estimated to represent less than 0.3% of the Scottish total [93] .
3.3.8 Applying a zero tax rate amount only to short-haul flights has the potential to lead to a greater increase in passenger numbers over current levels, compared to either reducing the tax equally across all flight types or only on long-haul flights. Conversely, the impact on passenger numbers of applying a zero tax rate amount only to long-haul flights is likely to be lower than either applying a proportionally equal tax reduction to all flight types or only applying a tax reduction to short-haul flights. This will have the potential to influence GHG emissions.
3.3.9 As the reasonable alternative is not considered likely to have an impact on passenger and flight numbers due to there being no change in the tax rate amount, it would therefore be reasonable to assume that no additional impact on GHG emissions, over that which is expected, would occur.
3.3.10 There are a number of challenges in predicting with any certainty the likely increase in GHG emissions arising from the preferred policy option and the illustrative pathways that could be considered in order to meet a 50% reduction in the overall ADT burden. Whilst growth in the sector has steadily increased, there have also been substantial improvements in efficiency measures, such as engine and air frame technologies and air traffic management, leading to reductions in GHG emissions. The potential impact of aviation emissions at altitude is also a key variable. These and other relevant considerations are discussed below in greater detail.
Passenger switching
3.3.11 As part of the 2014 and 2017 research undertaken by Transport Scotland, consideration was given to passengers "switching" from northern English airports to Scottish airports in response to lower tax rates. This consideration was based on separately published research by HMRC [94] that concluded that a 50% cut in tax in Scotland could lead to an estimated increase in passengers/trips being undertaken from passengers switching to Scottish airports from airports in northern England, principally Manchester and Newcastle [95] [96].
3.3.12 The consideration of passenger "switching" and the implications of this on GHG emissions is complex as it has the potential to lead to a number of outcomes. For example, longer surface journeys being undertaken to capitalise on lower flight rates could lead to further emissions. Conversely, emissions may also be impacted though increased opportunities for more direct flights, thus eliminating the need to undertake multiple journeys to reach a given destination. The potential creation of new routes and destinations brought about by a reduced tax rate amount could also incentivise Scottish passengers who may have previously travelled to airports in northern England, such as Manchester, to use Scottish airports.
3.3.13 Passenger switching could also be further influenced if a zero tax rate were to be applied only to short-haul flights. For example, it would be reasonable to assume that flying would provide a feasible alternative mode of transport for journeys of this distance within the UK mainland, whilst alternative modes of transport are more restricted when considering longer journeys.
3.3.14 Another factor that will influence the extent of passenger "switching", and the estimated additional impact on Scottish emissions as considered in the Transport Scotland research, is price differentials. It is noted that any passenger switching occurring as a result of a 50% reduction of tax would be dependent on the price differential between the airports. Were the price difference to be eroded (either through the cutting of ticket prices or a similar reduction in UK APD being applied for flights from northern English airports), then the additional emissions impact from passenger switching as estimated would not materialise [97] . The extent to which passenger switching will arise, and the time period in which this effect will be realised, is unknown.
Additional destinations
3.3.15 A key assumption of this assessment has been that the preferred policy option will boost Scotland's air connectivity and economic competitiveness, encouraging the establishment of new routes which would enhance business connectivity and inbound tourism and help generate sustainable growth. The impact of additional destinations from Scotland as a result of a reduction in APD/ ADT in Scotland has not been considered as part of the 2014 and 2017 research. It was however noted in the 2014 research that, should there be an extension of the route network which included long-haul destinations, this would add to the total impact on emissions [98] . It would be reasonable to assume that applying a zero tax rate amount only to long-haul flights has the potential to increase the start-up opportunities for new long-haul routes to a greater extent than if a tax reduction was applied either only to short-haul flights or proportionally equally to all flight types.
3.3.16 As new routes are business decisions which are market-led, it would not be possible to predict with any degree of certainty how many and what type of new routes would be established as a result of a 50% reduction in the overall ADT burden.
Non- CO 2 climate impacts of aviation
3.3.17 Another important factor to consider is the effect of aviation emissions at altitude. In order to estimate the full effect of aviation on climate change it is necessary to account for CO 2 as well as for all other non- CO 2 warming effects [99] . As discussed previously, the scenario that arises as a result of the greater effect these non- CO 2 gases have at altitude is expressed by scientists as a multiplier [100] .
3.3.18 Whilst there is no straightforward answer to what the overall impact of aviation on climate change is, there is high scientific confidence that the total climate warming effect of aviation is more than that from CO 2 emissions alone [101] .
What wider context and potential mitigation measures (both current and future) should be taken into account?
3.3.19 Current and future mitigation, including efficiency measures such as technological improvements, can provide relevant context when assessing the potential implications arising from the preferred policy option.
3.3.20 The following paragraphs set out further discussion on some of these under relevant headings.
Mitigation measures within the aviation industry
3.3.21 As discussed earlier ( Section 1.3), collaborative efforts are being made within the aviation industry to reduce climate impacts. Common aspirational goals have been agreed that include stabilising net emissions from 2020 through carbon-neutral growth (subject to a concerted effort from industry and government initiatives), and reducing net aviation carbon emissions 50% by 2050, relative to 2005 levels [102] .
3.3.22 To achieve these aspirational goals, a comprehensive set of mitigation action has been rolled out, based on a basket of measures which includes technological and operational improvements and better use of infrastructure, particularly air traffic management. The development of an effective, global market-based measure for international aviation is also part of this work (discussed further under the development of future international mitigation measures in paragraphs 3.3.31 to 3.3.36).
Technical and operational improvements
3.3.23 The most direct way for an airline to improve its fuel efficiency is to modernise its fleet with new aircraft incorporating the latest available technology [103] . For example, fleet replacement programmes can help achieve fuel efficiencies with newer, more modern planes. Boeing states that the 737 MAX aircrafts utilise a new type of engine that results in 9-14% reduction in carbon emissions and fuel consumption per seat [104] . Carrying capacity can also be improved through technological improvements alongside increased fuel efficiency. For example, some of the newer more modern planes can carry 48% more passengers 119% further with a 67% increase in payload, while burning 23% less fuel - or 48% less fuel on a per-seat basis [105] . However, there can be a long lead in time between the acquisition and roll out of new fleets, meaning that the investments made in new fuel efficient aircraft can take some time to make a difference to emissions performance [106] .
3.3.24 More recently, airlines have undertaken a range of operational, maintenance and planning procedures to ensure that their current technology aircraft are flying to their optimal levels of efficiency [107] . Air traffic management affects when, how far, how high, how fast and how efficiently aircraft fly. These parameters in turn influence how much fuel an aircraft burns, the release of GHG and other gases from the engine and how much noise an aircraft makes. Fuel savings of up to 40% during the approach phase through continuous descent operations have been demonstrated, with potential secondary benefits arising through reduced noise footprints [108] .
3.3.25 A number of publications are available promoting procedures such as the above to improve fuel efficiency, including Sustainable Aviation's Continuous Descent Campaign [109] . Additionally, the Single European Sky Air Traffic Management Research is the technical pillar of the Single European Sky and it aims to improve air traffic management. Specific objectives include a target of a 10% reduction of CO 2 emissions per flight through introducing new technologies and procedures to decrease fuel burn [110] .
3.3.26 Whilst aircraft have become substantially more energy efficient through improvements in engine and airframe technology, projections show that aviation will increase its relative share of UK emissions if greater improvements are not made [111] . This is supported by the findings of a trends assessment performed by the ICAO Committee on Aviation Environmental Protection, which forecasts that even with the anticipated gain in efficiency from technological and operational measures, aviation CO 2 emissions will increase in the next decade due to the continuous growth in air traffic [112] .
3.3.27 The assessment also notes the role of sustainable alternative fuels in reducing GHG emissions, with some potential additional benefits with regard air quality. However, there are long-term challenges associated with the development and deployment of alternative fuels, including feedstock availability and sustainability [113] . These challenges are also noted in the Committee on Climate Change 2009 report "Meeting the UK Aviation target - options for reducing emissions to 2050" [114] . The report states that that the use of biofuels in aviation is likely to be technically and economically viable but that concerns around land availability and sustainability mean that it is not prudent to assume that biofuels in 2050 could account for more than 10% of global aviation fuel [115] .
Efficiency and distance
3.3.28 As discussed in previous sections of this report, aviation emissions are directly related to fuel burn and there are many factors that can affect the amount of CO 2 emissions emitted from a flight. Flight distance is an essential factor in determining fuel consumption [116] and is therefore a key consideration when assessing the potential GHG implications that may arise from applying a zero tax rate amount to either only short-haul flights or only long-haul flights in order to meet the 50% reduction in the overall tax burden set out in the preferred policy option.
3.3.29 Generally speaking, the farther the route, the more fuel burned [117] . However, since take-off and landing demand higher fuel burn rates than level flights, shorter routes tend to be the least efficient as they spend a greater proportion of their total journey in the high emissions phase of take-off and landing [118] . Long-haul flights are, broadly speaking, the next most inefficient type of flight [119] . Although the aircraft spend a long time at its most efficient cruise altitude, over very long distances the fuel use per mile increases because of the greater amount of fuel that has to be carried during the early stages of the flight [120] . Medium range routes are considered to be generally more efficient, as smaller proportions of the flight are spent in the take-off or landing phase [121] .
3.3.30 For any given aircraft flying the same route, emissions will vary because of factors such as climatic conditions, aircraft may be kept in holding patterns and the mass load may vary between flights [122] . Improving efficiency also means reducing the level of emissions per passenger or tonne of freight carried [123] . Whilst passengers make up a relatively small proportion of the total weight of an aircraft, an aircraft is more 'efficient' when more passengers are carried as the total emissions are shared between larger numbers of people [124] . Passenger load factors are the percentage of actual passengers carried relative to the number of seats available and this is considered a good indicator of efficiency [125] . Operational and technical developments also need to be taken into account, for example, some of the newer, more modern planes can carry more passengers whilst burning less fuel [126] .
International mitigation measures
3.3.31 Currently, the main international mitigation measure for Scottish aviation emissions is through participation in the EU ETS (see Section 3.1.7). The EU ETS is currently limited to flights within the EEA, which the European Commission proposes to maintain indefinitely, but with a future review when a truly global mitigation measure emerges [127] .
3.3.32 Global efforts to address emissions from aviation are being led by industry through ICAO. In 2013 ICAO agreed to develop a "basket of measures" to address international aviation emissions including technological improvements, biofuels and operational improvements to air traffic management. Most significant was the proposal for a global market-based measure (" GMBM") to deliver ICAO's goal of carbon neutral growth in aviation from 2020. Agreement on a GMBM, the Carbon Offsetting and Reduction Scheme for International Aviation (" CORSIA") was reached at the ICAO Assembly in October 2016 [128] . Unlike the EU ETS, which reduces emissions against 2005 levels, CORSIA aims to achieve carbon neutral growth in aviation above 2020 levels but will not seek to reduce emissions below 2020 levels.
3.3.33 To date 50 countries have opted-in to the first two voluntary phases of CORSIA (2021-2023 and 2024-2026) [129] . Airline operators flying between these countries will have to purchase certified offsets to cover their emissions above 2020 levels. From 2027 participation will be mandatory for all countries in ICAO [130] .
3.3.34 Work is on-going to develop the detail of CORSIA including the necessary operational rules for monitoring, reporting and verification and the Standards and Recommended Practices. The effective implementation of CORSIA will depend on national measures to be developed and enforced at a domestic level [131] . Once the legal instruments to implement CORSIA are adopted by ICAO, the EU will consider how to implement them. There will be a review of the operation of the EU ETS for aviation post-2020 once CORSIA comes into effect [132] . It is not yet known therefore whether the EU ETS will continue to be the means by which emissions from aviation within the EEA continues to be accounted for [133] .
3.3.35 The future of international mitigation measures is not yet clear - neither how CORSIA will be implemented nor the future of the EU ETS for aviation. Furthermore, following the UK's vote to leave the EU, its continued participation in the EU ETS is uncertain. The future of international mitigation measures will be influenced by future changes in the wider political landscape.
3.3.36 It is anticipated that a new global emissions standard proposed by ICAO will be applicable to new aircraft from 2020 and new aircraft in production from 2023 [134] . A cut-off date of 2028 for aircraft that do not comply with the Standard was also recommended [135] . The new Standard is reported to be especially stringent where it will have the greatest impact, such as specific rules for larger aircraft that weigh over 60 tonnes [136] . However, care has been taken to ensure that the proposed Standard covers a full range of sizes and types of aircraft used in international aviation, encompassing all technological feasibility, emissions reduction potentials, and cost considerations [137] .
National mitigation measures
3.3.37 Scotland's emissions are adjusted to take into account trading in the EU ETS for the purpose of reporting progress towards statutory targets under the 2009 Act. In March 2017, the Committee on Climate Change provided advice to the Scottish Government on the new Scottish Climate Change Bill [138] . Advice was provided on a range of issues and included a recommendation that the overall accounting framework shift to one based on actual emissions, which would involve removing the accounting adjustment to reflect the operation of the EU ETS. It was further recommended that Scotland's shares of international aviation emissions should continue to be included in Scottish targets
3.3.38 The Committee on Climate Change's UK-level report "Meeting the UK Aviation target - options for reducing emissions to 2050" states a current expectation that improvement in fleet fuel efficiency of 0.8% per annum in the period to 2050 is achievable, through evolutionary airframe and engine technology innovation, and improved efficiency of air traffic management and operations [139] . The Report also highlights that, whilst faster technological improvements are possible, unless and until they are achieved aviation policy should be based on the assumption that demand growth between now and 2050 cannot exceed 60% if aviation emissions in 2050 are to be no higher than 2005 levels (37.5 MtCO 2e) [140] .
3.3.39 The predicted increase in passenger and flight numbers that is considered likely to arise through the introduction of the preferred policy option, as well as the likely environmental implications of this on climate change, also need to be considered within the context of the range of relevant policies and strategies in which it sits. For example, NPF3 sets out a long-term vision for development and investment across Scotland over the next 20 to 30 years. Strategic Airport Enhancements were discussed within the "A Connected Place" section which considered maintaining and developing good internal and global connections.
3.3.40 It is a requirement of the 2009 Act that Scottish Ministers lay a report in Parliament setting out proposals and policies for meeting annual GHG emissions reduction targets. The Climate Change Plan: the draft Third Report on Policies and Proposals was submitted for parliamentary scrutiny in January 2017. The report sets out how the Scottish Government intends to meet its statutory climate change targets for the period of 2017-2032.
3.3.41 Having made strong progress towards the statutory emission reduction targets set out in the 2009 Act, the Scottish Government has committed to keeping Scotland at the forefront of global climate action by responding to the UNFCCC Paris Agreement with a Climate Change Bill that sets new, evidence-based, statutory emission reduction targets [141] .
What is the likely significance of the predicted impacts?
3.3.42 The 2017 research has estimated that the introduction of a 50% reduction in ADT (applied proportionally equally across all flight types) could lead to increased emissions from aviation in the first year (assumed to be 2018), relative to where they would be in the absence of the policy [142] . The latest analysis estimates an increase in carbon emissions by between 0.087 MtCO 2e and 0.101 MtCO 2e [143] , an increase on the previous analysis of between 0.05 MtCO 2e and 0.06 MtCO 2e set out in the 2014 research [144] . Furthermore, it is estimated in the 2017 research, that assuming the growth in baseline passengers numbers continues, by 2021 carbon emissions will increase by between 0.090 MtCO 2e and 0.105 MtCO 2e.
3.3.43 Aviation currently accounts for less than 4% of total Scottish emissions and the increase in aviation emissions forecast as a result of the 50% reduction in ADT is estimated to represent less than 0.3% of the Scottish total [145] .
3.3.44 The 2014 and 2017 Transport Scotland research estimated that a 50% reduction in APD/ ADT in Scotland could lead to additional flight and passenger numbers over current levels, and included the consideration of passenger switching. The estimated impact of CO 2 emissions as a result of this has been included within the overall impact assessment.
3.3.45 The degree to which passenger switching takes place, alongside changing prices, will be key drivers behind any emissions profile. There is the potential that if a zero tax rate amount was applied only to short-haul flights, this could have a greater influence on passenger switching than if a tax reduction were applied either only to long-haul flights or to all flight types.
3.3.46 Technological developments and operational improvements will play a key role in seeking to reduce emissions arising from activity in the sector. Collaborative agreements and objectives agreed across industry will also continue to play an important part in effort undertaken in the sector to improve sustainability. Future mitigation measures, such as the development of a GMBM, are considered as key to achieving ICAO's goal of carbon neutral growth of international aviation from 2020 [146] . Agreement on the form this should take has since been reached and a pilot phase of implementation will begin from 2021 through to 2023.
3.3.47 The introduction of the preferred policy option of a 50% reduction in the overall ADT burden by the end of the current session of the Scottish Parliament represents one of many challenges that will need to be considered to Scotland's ambitious climate change targets. The implications of climate change are far reaching and can have adverse effects across a range of environmental receptors. The implications of this have been discussed in this assessment under relevant topic headings.
3.3.48 It is considered that the preferred policy option, in the short-term, will lead to increases in GHG emissions even with efficiency measures in place, relative to where they would be in the absence of the preferred policy option. If the preferred policy option were to be reached through a pathway of applying a zero tax rate amount only to short-haul flights, there is the potential that this could lead to higher passenger numbers than if tax reduction was applied only to long-haul flights or proportionally equally to all flight types. In turn, this could have an influencing effect on overall GHG emissions.
3.3.49 Medium to long-term, it is more challenging to predict the magnitude of future increases in GHG emissions. There are a number of key drivers, such as changing ticket prices and the degree of passenger switching that require consideration when projecting emissions beyond the short-term. Technological developments and the aspirational goals agreed by the aviation industry, alongside international measures such as the development and introduction of a GMBM, will also play a key role in the wider mitigation of emissions once implemented.
3.3.50 A number of uncertainties also exist that could influence significance, such as the creation of new routes, the multiplier effect and price differentials, and it has not been possible to consider these in this SEA.
3.3.51 The assessment considers that as the reasonable alternative represents a "like for like" approach, no additional impact on GHG emissions over that which is currently projected would occur.
Box 3.1 Climatic Factors: Summary of impacts and key points
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