In each sector, up to four trajectories were developed for the types of changes that might be seen. These are designed to cover a broad range of possibilities and to test the boundaries of what might be possible. They are intended to reflect the whole range of potential futures that might be experienced in that sector. They are illustrative and are not based on assumptions about future policy and its impacts, and should not be interpreted as such.
The trajectories developed have drawn on existing work as well as input from a large number of experts in businesses, NGOs, technical fields, and academics, through workshops and other discussions. Several hundred stakeholders have so far been involved in the analysis, and about 100 of those experts took part in detailed discussions about the trajectories. We are keen to refine this analysis in the light of new evidence. The section below describes how the trajectories were defined and developed.
The work aimed to achieve a level of consistency across the different sectors in terms of ‘level of change’, so that a ‘level 2’ effort in one sector would be broadly comparable to a ‘level 2’ effort elsewhere. Although by necessity this is something of a subjective judgement – particularly when comparing very different sectors, for example offshore wind power and thermal comfort levels in buildings.
The energy supply sectors
The energy supply trajectories examine different energy generation sectors. These trajectories have been presented as four levels of potential roll-out of energy supply infrastructure (levels 1–4), representing increasing levels of effort. The levels depend on the lead time and build rate of new energy infrastructure, and different assumptions about how quickly and on what scale the infrastructure can be rolled out. The higher levels also depend on improvements in technology, such as floating wind turbines and carbon capture and storage. The build rates will in practice depend not only on the physical possibilities, but also on investment decisions by the companies involved, as well as wider international developments and public acceptance.
- Level 1: assumes little or no attempt to decarbonise or change or only short run efforts; and that unproven low carbon technologies are not developed or deployed.
- Level 2: describes what might be achieved by applying a level of effort that is likely to be viewed as ambitious but reasonable by most or all experts. For some sectors this would be similar to the build rate expected with the successful implementation of the programmes or projects currently in progress.
- Level 3: describes what might be achieved by applying a very ambitious level of effort that is unlikely to happen without significant change from the current system; it assumes significant technological breakthroughs.
- Level 4: describes a level of change that could be achieved with effort at the extreme upper end of what is thought to be physically plausible by the most optimistic observer. This level pushes towards the physical or technical limits of what can be achieved.
It should be recognised that even at level 2, the consequences of pursuing this effort across several different sectors in parallel will place a high demand on supply chains and skills, especially given that other countries are likely to be undertaking concurrent infrastructure changes. In addition to the domestic supply sectors, the analysis also sets out some international dimensions, including four levels of potential bioenergy imports and four levels of electricity imports.
The energy demand and non-energy sectors
The demand sectors explore several different drivers of change. The primary drivers of change are summarised below. Where these factors can be considered as changing levels of effort or ambition, these are described in the analysis as levels 1–4 on a similar basis to the supply side sectors. Where the changes described reflect a choice rather than a scale (for example choices of fuel or technology), they are described as trajectories A, B, C, D; these choices cannot be compared between sectors.
The demand trajectories have been developed to be consistent with two key input assumptions: 0.5% per year growth in population, based on the central scenario of the Office of National Statistics; and 2.5% growth in the UK GDP to reflect HM Treasury’s assumption for long term growth. Different actual rates of population and GDP growth would have potentially significant impacts on the level of effort required to reach 80% emissions reductions.
In determining the trajectories, several factors are considered:
- Levels of behavioural and lifestyle change: reductions in energy demand and emissions through changes such as wasting less food; accepting lower average room temperatures in winter; and transport mode shifts, such as from private to public transport.
- Levels of technological improvement and change: the development and penetration of less carbon intensive technologies, such as LED lighting or ground source heat pumps; technological advance such as new industrial processes; and improvements in the efficiency of existing technologies. More ambitious trajectories may be dependent on the successful deployment of technologies still in development.
- Different technological or fuel choices: technological and fuel choices that are not directly related to ambition levels; examples include choices between district heating or ground source heat pumps, or between fuel cells and batteries for cars.
- Structural change: reflects possible changes in the structure of the economy, for example a decline or resurgence in manufacturing.