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You can’t always get what you want: a reflection on Climate Assembly UK’s deliberations on decarbonising passenger transport

23 September, 2020

Jillian Anable

Reading time: 16 minutes

Given where we are now and the short timescales required to decarbonise, only difficult decisions and very few win-win options remain. Jillian Anable shares her thoughts on the Climate Assembly outcomes.

The recommendations of the UK’s first Climate Assembly (CAUK) were published on 10 September 2020. This was the culmination of a very lengthy and rigorous deliberative process with over 100 members of the UK public selected using a robust scientific sampling methodology.

The assembly had been commissioned by six UK parliamentary committees to focus on the UK’s 2050 Net Zero carbon target in recognition of the need to both shape and be shaped by public opinion on how to navigate our way there.

Given where we are now and the short timescales required to decarbonise, there are only difficult decisions and very few win-win options remaining. Honest dialogue and conversations which acknowledge this are rare at all levels of policy making. CAUK was a very good start but, as I caution in this blog, only if the results are both interpreted correctly and used appropriately.

My role was somewhere between an Expert Lead and an Academic Advisor to the process. I closely supported one of the Expert Leads, Professor Jim Watson, in the design and execution of the ‘How We Travel’ strand of the Assembly. This was one of the ‘demand side’ topics (split into personal ‘land’ and ‘air’ transport) alongside ‘what we eat, how we use the land and what we buy’ and ‘how we heat and use energy in the home’. A third of the assembly members were allocated to each topic and immersed in two weekends of presentations, debate, deliberation and secret ballot voting on both individual policy options and policy packages/scenarios.

Just a few days after the launch of the final report, I feel compelled to help ensure that the findings of the “how we travel” deliberations are portrayed accurately in relation to established and developing UK government policy in this area. When outlined in brief, assembly members are summarised to have endorsed a ban on the sale of new petrol, diesel and hybrid cars by 2030–35, grants to buy lower carbon cars, investment in low carbon, better and cheaper bus services and cycling and scootering facilities. That is all accurate. But put like this, it does not appear to be recommending anything very different from current government thinking despite the numerous evidence-based calls for a need to go very much further. The government is already consulting on how much earlier than 2040 new ICE car sales should be phased out and is committed to investment in lower carbon buses and cycling. Job done, then? Nothing to see here for those responsible for implementing policies on transport decarbonisation in the UK?

No. It would be a gross injustice to the considerable depth of understanding and passion shown by the CAUK members to portray the results as being simply aligned with current government policy. Given that I designed the land transport scenarios and was there to explain them and witness the debates, I’d like to show here that the results are much more radical and important than such a summary would have you believe, albeit arguably nowhere near as radical as they actually need to be – as I discuss below.

The transport sector, with the notable exception of aviation, is expected to reach absolute zero carbon emissions, not net zero by 2050 (or 2045 in Scotland). Net zero is the economy-wide legislated target that allows for certain activities, such as aviation, to overshoot the 2050 goal but to have any excess emissions removed elsewhere through carbon capture or carbon sinks. But the rest of the transport sector is expected to go the whole way to zero. Carbon budgets are set that determine the total allowable accumulated emissions between now and 2050 to be compatible with holding global warming to less than 2 degrees C in line with the Paris Agreement. This is why so much focus has to be placed on progress over the next decade to avoid blowing all the budget by 2030 or at least leaving an impossibly small remaining allowance to be eked out over the final two decades.

Although these carbon budgets are set at the whole-economy level, not for each sector, the scale of the challenge means that other sectors can no longer compensate for transport’s failure to contribute to UK-wide carbon reductions so far. Analysis that has apportioned the UK-wide carbon budget (opens in new tab) down to sectoral level suggests that if the car-transport sector keeps emitting at the same rate as in recent years, it will have used up its total allocation by 2030. Whilst CAUK was focusing on the 2050 Net Zero target, the importance of the speed of getting there was made clear to participants and punctuated the discussion throughout.

The three land transport scenarios put to the vote in the assembly were designed to test the main trade-off involved in achieving the required speed and scale of carbon reduction for surface passenger transport in line with these budgets – the quicker we remove the most carbon intensive cars from our roads, the less people will have to have their car use constrained through pricing or physical restrictions. However, there are no future ‘Paris compliant’ pathways for surface transport that do not include at least some degree of reduction in car use (see Table 1) and this was the same in the scenarios voted on by the assembly members. The proposed reductions included in the scenarios are from today’s total traffic levels – not relative to a growing baseline or on a per capita basis.

the quicker we remove the most carbon intensive cars from our roads, the less people will have to have their car use constrained through pricing or physical restrictions

This means that all three scenarios require a halt to road building until at least the mid-2040s in order to remove the upward pressure on car use that adding new road capacity brings, as well as to avoid ‘white elephant’ expenditure – something very explicit in these scenarios but nowhere near accepted in policy circles. At one extreme was the scenario with the immediate phase out of the most polluting cars (eg most SUVs) plus the earliest phase out of conventional fossil-fuelled vehicles (ICEs), Hybrid Electric Vehicles (HEVs) as well as Plug-in HEVs (PHEVs)) alongside the lowest absolute cuts in car use (2% per decade = –6% by 2050). On the other end was a later ICE/HEV/PHEV phase out but requiring 10% car use reduction per decade (–30% by 2050) and including road pricing to achieve this. Improvements to public transport and active travel were in all three scenarios.

Scales showing the difference between sale of high polluting cars and not selling any after 2022.
Figure 1: The quicker we remove the most carbon intensive cars from our roads, the less people will have to have their car use constrained through pricing or physical restrictions.

The result of the assembly members’ deliberations was not a surprise – they chose to have the types of cars they could drive restricted to secure only a modest limit on future car use for everyone (Figure 1). Consequently, they came to see that in order to achieve this and reach Net Zero, it will be necessary to stop the sale straight away of the most polluting cars such as most SUVs, go for an earlier target than currently proposed for the phase out of ICEs and HEVs as well as PHEVs (although there was push back and confusion as to why PHEVs would be included in this), and accept there will not be any new road capacity until well into the 2040s once most vehicles on the road are electric [1]. This is already well beyond current government thinking including the advice set out in the Committee on Climate Change’s (CCC) Net Zero report and the framework set out in the Department for Transport’s Decarbonisation Plan (TDP) (opens in new tab). The TDP makes ambitious claims with respect to ‘mode shift’ but talks only about what will be improved with no mention of a car reduction target. Indeed, it would be very difficult to do so as it was published almost simultaneously with the current Road Investment Strategy (RIS2) which commits £27.4 billion to the “the largest ever road investment package”. A recent evaluation of this investment (opens in new tab) estimates it will lead to an additional 20Mt of carbon emissions by 2032 due to induced traffic demand, higher speeds and embodied carbon.

We drive found people most people prefer the option to change the cars they drive.
Figure 2: CAUK results of the ranking of surface passenger travel scenario options. Source: CAUK 2020 (Main report) p76.

To facilitate the rapid car market transformation/lowest car use reduction scenario, assembly members recommended fifteen policies aimed at accelerating the low carbon vehicle transition, discouraging car ownership and use and increasing public and active transport. Of these policies, three quarters of the assembly members supported the need to bring public transport under public control in order to meet their call for better services and their universal criteria of a fair and affordable transition. Again, this is a radical and important outcome of the assembly and deserves wide recognition.

The lesson here is of crucial importance – that communication of the key trade-offs between the kinds of cars and quantity of their usage leads to breakthrough understanding and acceptance of the hard choices that are required for the decarbonisation of personal travel. We cannot have it all ways. Taken one by one, restrictive policies are clearly unpopular even when they are acknowledged as potentially leading to deep carbon cuts. It is only when placed together in a bundle of measures showing the combination of carrots and sticks that their acceptability or otherwise can be examined. Designing a meaningful and effective decarbonisation agenda is not about the acceptance of individual policies – it is about which particular combination of hard choices is acceptable.

As CAUK’s findings are scrutinised parliamentary committees, MPs need to understand that CAUK were not presented with a linked set of policies that – if applied together – would be sure to achieve net-zero. The sets of policies across all the domains discussed in the assembly, were not derived from fully integrated, economy-wide modelled scenarios and the timing of the introduction of constituent measures and their impact on interim carbon budgets were not discussed in detail. Although we used the best available evidence, these policies could only ever be indicative of the kind of actions required across society to achieve deep carbon reductions. Even so, they still may not be sufficient.

Indeed, compared to a number of recent carbon pathways modelling exercises that have examined ‘Paris compliant’ trajectories for the UK transport sector, all of the surface passenger transport scenarios presented to the assembly look to be extremely conservative. In particular, the proposed cuts in car use are nowhere near the scale discovered as necessary in these other modelling exercises, even when these have assumed an extremely rapid transformation of the UK car market.

Table 1 presents the Department for Transport’s (DfT) car traffic growth forecasts for the most relevant scenario they modelled (Scenario 7 that includes an uptake of EVs conducive to a ban on ICE sales from 2040 but no other policies), the CAUK scenarios, the CCC Net Zero report and four recent UK-based transport and carbon pathway modelling exercises.

Although the proposed 2%, 5% and 10% absolute reductions per decade (–6%, –15% and –30% between 2020 and 2050) in the CAUK scenarios are low in comparison to the recent modelling studies, they need to be set against the DfT’s growth forecast of +35% between 2020 and 2050. In this context, they represent relative reductions in car use of up to around 65% by comparison. The scale of car use reductions in the CAUK scenarios are also much deeper than appear to have been proposed so far by the CCC. The CCC modelling approach for its net zero scenarios is not quite as clear, but it is assumed, especially as they have not ruled out future road building, that they have taken some form of DfT growth forecast and that their 10% mode shift from car use to other modes is relative to this growth baseline rather than absolute reductions from now.

Table 1: Proposed new ICE sales phase-out date and indicative car distance changes implied by various UK modelling exercises.
Author Scenario Date ICEs will be phased out in UK new car market % change in car miles (absolute reduction from specified year) Notes
By 2030 By 2050
CAUK (1) 1 “Fast action to change the cars we drive” 2030 (incl. HEV+ PHEV + phase out of ‘SUVs’ straight away) –2% –6%
  • From 2020
  • Assumes no new road building until at least 2045 but there will be upward pressure on car traffic requiring counteracting policies due to population and GDP growth and lower cost of ‘EV’ motoring
2 “Changing the cars we drive and how much we use them” 2032 –35 (incl. HEV + PHEV) –5% –15%
3 “Reducing amount travelled” Up to market with chance to review –10% –30%
DfT’s forecast traffic scenarios (2) Scenario 7 2040 (incl. HEV but not PHEV) +12% +35%
  • Calculated from 2020 using DfT spreadsheet
  • Applies to cars in England and Wales
  • The forecasts factor in induced traffic from reduced cost of motoring
CCC Net Zero Report (3) Core scenario 2040 (incl. HEV but not PHEV) +12% +35%
  • Start year unclear
  • Use of DfT forecast assumed although this is not stated in the CCC report
  • This scenario does NOT achieve absolute zero by 2050: – 79% by 2050, compared to a 1990 baseline for whole transport sector including domestic aviation
  • Aligned with carbon budgets set for whole economy
Further ambition 2035 (incl. HEV + PHEV)   +25%
  • Start year unclear
  • Based on 10% shift from car use expected in this scenario netted off the +35% DfT forecast
  • This scenario almost achieves absolute zero by 2050: –98% by 2050, compared to a 1990 baseline for whole transport sector including domestic aviation
  • Aligned with carbon budgets set for whole economy
Brand/Anable CREDS Low Energy Demand Lifestyle Scenarios (4) High ambition 2035 (incl. HEV + PHEV) –31% –51%
  • From 2020
  • This scenario achieves absolute zero by 2050 for cars and vans (but not for transport as a whole): direct/tailpipe CO2 reductions for cars and vans –50% by 2030, –100% by 2050 compared to 2020
Transformative 2030 (incl. HEV + PHEV) –53% –69%
  • From 2020
  • This scenario achieves absolute zero by 2050 for cars and vans (but not for transport as a whole): direct/tailpipe CO2 reductions for cars and vans –70% by 2030, –100% by 2050 compared to 2020
Brand/Anable UKERC/CREDS submission to OLEV consultation (5) Technology change only’ car market transformation scenario 2030 (incl. HEV but not PHEV + phase out of ‘SUVs’ from 2022) +3% +12%
  • From 2020
  • This scenario does NOT achieve absolute zero by 2050 for either the car/van sector or for transport as a whole: direct/tailpipe CO2 reductions for cars and vans –40% by 2030, –95% by 2050 compared to 2020
Transport for Quality of Life (6) 1a 2030 (incl. HEV but not PHEV) –17% n/a
  • From 2018 to 2030 only
  • The two scenarios shown here are the ones using lowest (50g/kWh) grid carbon intensity
  • Modelled to fit to a Paris Agreement compliant pathway with apportioned budget to the UK car sector
3a 2040 (incl. HEV but not PHEV) –46% n/a
Element Energy (7) 2030 (incl. PHEVs + phase out of ‘SUVs’ straight away) –45%
  • Modelling from 2015 to 2030 only for Royal Borough of Greenwich
  • Net Zero pathway not quite achieved
  1. Climate Assembly UK (2020) The path to net zero. Climate Assembly UK Full Report. September 2020.
  2. DfT (2018) Road Traffic Forecasts 2018. The Department for Transport.
  3. CCC (2019) Net Zero. The UK’s contribution to stopping global warming. Committee on Climate Change. May 2019.
  4. Brand, C., Anable, J. and Marsden, G. (2020) Low energy demand scenarios for mobility. CREDS Working Paper. Available upon request from authors.
  5. Brand, C., Anable, J. and Dixon, J. (2020) Response to DfT and OLEV Consultation: Ending the sale of new petrol, diesel and hybrid cars and vans. Joint UK Energy Research Centre and Centre for Research on Energy Demand Solutions Response. July 2020. This builds on Brand, C., Anable, J., Watson, J. and Ketsopoulou, I. (2020) Road to Zero or Road to Nowhere? Disrupting transport and energy in a zero carbon world. Energy Policy. 139, Article 111334.
  6. Hopkinson, L. and Sloman, L. (2018) More than electric cars. Why we need to reduce traffic to reach carbon targets. Transport for Quality of Life and Friends of the Earth. December 2018. A range of assumptions were tested of which two are presented here, with updated figures supplied by personal correspondence with Lisa Hopkinson in September 2020.
  7. Element Energy (2020) Development of the Greenwich Carbon Neutral Plan: The Evidence Base. Report for Royal Borough of Greenwich. November 2019.

In conclusion, CAUK should be regarded as an excellent foundation for the participatory processes that will be needed all along our path to Net Zero. The assembly members have sent a strong signal to policy makers that when a full suite of options is set out, and the end-objectives and trade-offs are made clear, tough measures can be accepted. As with previous research [2], and as with other thematic areas explored in the assembly, regulation (including regulating to accelerate technology transitions) is more acceptable than fiscal measures that restrict activity and lifestyles. In the case of surface passenger transport, the regulation of car technology is only acceptable alongside re-regulation and lowering the cost of public transport to ensure that the underpinning fairness principle is met and to allow car use reductions to take place. The policies debated cannot be selectively highlighted and cherry-picked – they only work as whole packages. Even then, they are unlikely to be enough.


[1] It is worth noting that the Assembly did not cover freight and heavy goods vehicles. Some members queried this and were keen to know whether the passenger travel sector was being expected to do more in order to make up for any lack of policy ambition or progress in freight. They were told not to assume this. It is true to say, however, that many modelling exercises referred to in this note do look at the whole transport sector and the resulting cuts in car use partially result from this compensatory effect.

[2] This is not the first time these propositions have been tested in robust deliberative research exercises with members of the UK public. In 2008, for instance, participants preferred regulation – through restricting access to high CO2 options – to taxation, seeing this as less regressive and as having more impact. See: ITS (2009) Exploring public attitudes to climate change and travel choices: deliberative research (opens in new tab), Final report for Department for Transport. London and Leeds: PSP and ITS Leeds.


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