11th December 2024 In the second article in this series – last week’s described how the priority transport strategies of the new Labour government have so far ignored those modes responsible for the vast majority of the sector’s carbon emissions – Anthony Rae describes how past and present failure to achieve emissions reduction – the issue underlying the Will Labour fail its transport decarbonisation test?  report – can be explained by the dynamic within a simple little fraction.

I first encountered how a numerator/denominator analysis – hereafter abbreviated as N/D Analysis or N/DA – could be applied to the problem of transport decarbonisation 20 years ago when Friends of the Earth commissioned (then Dr) Kevin Anderson et al to assess the climate implications of Labour’s 2003 hugely expansionary Aviation White Paper (I was the ‘expert volunteer’ on the FOE team). Although the formal title of the Tyndall Centre 2005 paper is Growth scenarios for EU and UK aviation: contradictions with climate policy, the nickname we applied to the project was ‘aviation will eat the climate’, and on page 12 you can find a table of ‘the proportion of UK emissions from aviation relative to 2030 and 2050 targets’, with aviation’s percentage share of the total available carbon budget soaring ever upwards each decade to 2050. Remember that this is before FOE proposed that the overarching policy framework the UK needed was a climate change act (CCA) which only became law in November 2008

Applying a numerator/denominator analysis to the UK carbon budget (UKCB) is entirely straightforward, and is also central to the working of the CCA. Whilst that legislation acts upon the entire UKCB  (the denominator in our fraction) – rather than at the level of individual emissions sectors such as transport (which are the numerators in the fraction) – the role of the Climate Change Committee (CCC) is also to model and recommend future policy change such that the carbon emissions of every sector reduce year by year as their contribution to the progressive, inevitable and urgent reduction of the UKCB pathway as a whole.

If, in the illustration above, the CO2e tonnage in the UKCB denominator was 100 units at the start of a pathway and has to reduce to 50 units over a time-limited period, then as long as the parallel reduction in such as a transport emissions sector numerator keeps to that same approximate pace  – so reducing from 40 to 20 units –  then the N/D fraction, expressed as a percentage (40% in this example), will remain the same. But if the numerator policy/decisionmakers fails to deliver that full reduction, say only to 30 units, then the N/D fraction would rise to 60%. Thus the N/D fraction becomes a critical monitoring indicator for decarbonisation progress, and a reminder or even warning to central government civil servants and ministers responsible for each emissions sector numerator to understand and respect their N/D obligation: to propose and then deliver a continuous pipeline of incremental carbon reduction measures so as to keep the N/DA fraction and the absolute emissions tonnages it represents moving consistently downwards.

But what if the department responsible for just one emissions sector numerator refuses to reduce, and indeed started to ‘game the system’, essentially by persistently maintaining ‘everyone else can decarbonise but we’re not going to, and the other sectors can make up the shortfall’? As indeed the Department for Transport lawyers have most determinedly argued when challenged by judicial review:

‘The CBs [carbon budgets] are not sector specific. It is axiomatic that the UK can seek to meet its CBs overall by a strategy which balances emissions generated or removed across the whole economy in all sorts of different sectors. … As stated by (Justice) Holgate “… there is no sectoral target for transport or any other sector, and that emissions in one sector, or in part of one sector, may be balanced against better performance in others. A net increase in emissions from a particular policy or project is managed within the government’s overall strategy for meeting carbon budgets and the net zero target as part of an “economy wide transition. … It is not a duty that fell upon the [Transport Secretary of State] and it is not engaged by the preparation and publication of the Jet Zero Strategy’.” DfT response to judicial review of the JZS brought by ngo Possible, paragraphs 23-25, 2022. We’ll come back to such legal stratagems in article 4, 28th December

By the mid-2010s I was becoming increasingly concerned about progress with both the UKCB denominator and transport emissions numerator. Climate campaigners (even FOE) had not understood that the CCA and delivery of its UKCB pathway required public advocacy by an external ‘cheerleader’ so, in 2017 and as a member of the Network for Social Change funder’s organisation, I proposed the creation of its ‘Cutting Carbon Now’ project – advocating future policy change in support of the CCC’s  ever reducing  UKCB pathway – for which I was the funders’ strategy ‘lead’ up to September 2024 when the project ended.

But as a transport campaigner – working in the areas of both roads and aviation modes, responsible for generating 89% of transport emissions – I knew that you couldn’t fight their carbon consequences one road scheme, or airport expansion, at a time. What was necessary instead was to try and attach a carbon ‘collar’ around both of those expansionist policy frameworks in order to collapse them. In April 2019 – just as Theresa May’s government and the CCC were making the decisive move to shift the target of the UKCB denominator to Net Zero – I published my briefing The threat of rising transport emissions to the UK Climate Change Act process, the narrative of which reapplied an ‘aviation will eat the climate’ analysis but now to total transport emissions within the UK carbon budget.

It had two findings: that a quantified numerator/denominator analysis of transport emissions demonstrated that, as in 2005 for an aviation numerator, the larger transport numerator’s percentage share of the UKCB had and would continue to push upwards decade after decade, to the extent that the CCA process might be destabilised;  and that the DfT had deployed a series of ‘distraction tricks’ in order to easily divert campaigners attention away from the cumulative erosion of the UKCB that the roads and aviation policy frameworks were driving.  Both of those conclusions were and still are extremely alarming.

Thus the 2019 briefing did indeed demonstrate that ‘transport is eating the UK carbon budget’! Its quantification of the N/D fraction (table, page 3) is now outdated – remember the data is pre the shift to Net Zero, and policy ‘off’ in relation to such measures such as 2020s ‘ICE vehicles phase-out by 2030’ – so, 5 years on, what are the tonnage and percentage share numbers for the transport numerator/UKCB denominator analysis, past present and future?. This was the starting point for the quantified analysis in Questions 1-5 of May’s Labour transport decarbonisation test report, and here are the latest figures.

Let’s start by summarising what these numbers are telling us. (A detailed exploration of the methodology, terminology and data sources in this table can be downloaded here). This is CCC data and properly counts ‘total transport emissions (TTE); the download describes the circumstance whereby transport emissions are sometimes misleadingly underestimated. The reduction of the UK Carbon Budget denominator tonnage – currently down by 49% below the 1990 baseline and projected to reach -77% by 2035, the extent of the current policy horizon – is on track.

The transport numerator on the other hand essentially hasn’t reduced below the CCA baseline at all: a reduction in the 33 years between 1990-2023 from 153MtCO2e to 152MtCO2e, just -1%. The tension between the completely different transport and UKCB emissions trend lines is immediately revealed as the transport numerator’s share in the N/DA fraction doubles, to 36%. The transport numerator is drastically off track.

An N/DA analysis can then zoom in further, both spatially and temporally. Question 2 in the report noted that the transport emissions pathway has flatlined, at both national and regional/local levels, over the  decade from 2009 to the 2019 pre-Covid peak, which means that ‘there is no established long-term momentum to the process and practice of transport decarbonisation, available to be accelerated into the future’. Consequently, from a standing start, it will require the DfT to pull a 64 megatonne ‘rabbit’ out of a hat in just 10 years (-42% reduction, the difference between 152MtCO2e in 2025 and 88Mt in 2035) in order for transport emissions to stay on pathway.

The strongest hypothesis to explain the magnitude of this numerator reduction shortfall would be that it could only have come about because of an extraordinary DfT policy failure over the 15 years since the 2008 CCA but which probably had its origins in the decade beforehand. The priority issue, however, is what this tell us about what should be the DfT’s future policy stance. All this has been revealed by a quite ordinary analysis of the dynamic trend within the N/D fraction: from an 18% manageable share at baseline 1990, transport emissions have currently doubled their take of the UKCB (to ‘36% and rising’) and are on course to reach 45% and rising’ in just 10 years.

If you want a comparator – an emissions sector where departmental policymakers did meet their obligation to bring forward carbon reductions to contribute to that N/D pathway – here are the numbers for electricity supply: the largest emissions numerator in 1990 (24% of annual emissions and 204MtCO2e), this is currently down to 9% and 38MtCO2e and heading towards just 1.5% and 3MtCO2e in 2035 (see the equivalent table in the data download).

We’ll come back to the critical interrogation – ‘how did this extraordinary DfT policy failure occur?’ – in just a moment but the preliminary question would be: ‘Did no one notice what was happening to the transport N/DA numbers?’ Were all the transport and climate policymakers (civil servants across government), decision-makers (politicians), campaigners and commentators just ‘asleep at the wheel’? My 2019 briefing suggested that they’d become maybe naive victims of DfT distraction tricks, but that’s no excuse.

In order to test the N/DA hypothesis, let’s consider this possible response: ‘OK, transport’s N/DA’s share of the UKCB has been ever rising and could exceed 50% and beyond. But does that really matter?’  Once again this question can be addressed by some further exploration of the dynamics within the N/D fraction.

A first answer would be that: ‘time is running out!’ When you reach 2025, which is Year -25 in the time-bounded 60 year UKCB denominator period (1990-2050) – and with no decarbonisation against baseline achieved in the first 35 years – the mechanics of the N/D fraction now start to penalise the stewards of the numerator who chose to ignore its workings. As the year countdown continues remorselessly towards the 2050 ‘year zero’  -25, -24, -23, -22, -21, -20 …  then the numerator reduction gradient becomes ever steeper as it struggles and fails to keep up, and ever more difficult to deliver: technically, politically and mathematically.

So the DfT policy/decision makers are now being punished for their, it turns out, foolish judgement not to decarbonise progressively in the first half of the 60 year NZ period but instead to double down with policy frameworks that promote the opposite – transport demand and emissions growth – pushing the N/DA fraction in absolutely the wrong direction. Certainly contrary to what the spirit of the CCA law requires and – it’s now being argued – its letter as well (see article 4 ‘Legal showdown: the DfT versus the Climate Change Act’, to be published on 28th December).

But, it’s worse! We don’t actually have 25 years left to the end of the UKCB denominator timeline;  in fact it’s immeasurably closer, effectively right now. Because the policy horizon up to Year-15 (2035) has already been set or should have been, and the denominator pathway to Year-8 is about to be when CCC’s proposed 7th Carbon Budget for the years  2038-42 is published on 25th February. Therefore Labour would have to make a decisive policy pivot towards transport decarbonisation in the next few months.

Except that the regulatory mechanisms needed to make that sudden pivot have already been ripped out within the existing roads and aviation policy frameworks that Labour has indicated it intends  to continue with. As Question 14 in the report points out ‘The government has so far refused to examine even the possibility of road pricing as a tool to constrain emissions’, and  Question 37: ‘the Jet Zero Strategy removes all regulatory controls over airport capacity, passenger demand and emissions growth’. Labour have communicated an almost ‘in principle’ intention not to constrain transport demand so would ideologically not be able to act quickly on decarbonisation even if it suddenly woke up to the N/DA perils confronting it.

A second answer is because the N/DA analysis is acting as a powerful diagnostic tool for spotlighting structural policy failure within the Department for Transport. The main part of the Labour’s transport decarbonisation test report is given over to a multipronged critique of the DfT roads (Questions 6-22) and then aviation (Qs23-40) policy frameworks; Q 55 concludes ‘if policy frameworks have failed, change them!’; and in the executive summary on page 6 is a list of those policy frameworks (mostly DfT but some elsewhere in government such as NPPF) that will ‘need to be revised urgently as essential early prerequisites for successfully implementing transport decarbonisation across the next Parliament’.

The N/D analysis also spotlights the consequences of the DfT policy frameworks choosing to disregard the cumulative impact of excessive numerator emissions. Every CO2e tonne or megatonne emitted above a notional emissions sector pathway (such as transport’s) in the early years after 2008 is eroding the total cumulative UK carbon budget – which CCC has quantified as just short of 13 gigatonnes for the period of carbon budgets 1-6 between 2008/37 – and would have to be clawed back in later years if the UKCB is not to be exceeded. But only if the policymakers had allowed sufficient time to attempt that clawback (as per the first answer above). In the DfT they haven’t.

Q27 in the report notes: ‘As Carbon Brief has commented ‘it is cumulative CO2 that matters in calculating the true climate impact of aviation emissions rather than a single year’s emissions’. However consideration of this cumulative impact has been omitted from the Jet Zero Strategy analysis in the same way that the cumulative impact of all transport emissions has been omitted from the Transport Decarbonisation Plan’.[174]   Footnote 174 then comments that ‘A search of the two documents shows that the ‘cumulative impact’ term [and concept] is entirely missing from both.‘

How is it possible that the DfT decarbonisation policy framework contrived to ‘make disappear’ the  critical cumulative emissions component, essential for protecting the UKCB as a whole? And – to point a particular finger – that the DfT science advisory council, stuffed with more than 10 learned professors, didn’t notice this analytical omission either?

A third answer would be that this is an illustration of precisely why our May report focused almost exclusively on explaining the complex intricacies of the transport decarbonisation problem – how to analyse it, and prepare the policy ground for tackling it – and very deliberately did not propose its own bespoke list of ’solutions’. The task of campaigners, it’s arguing, should be to identify that problem – for example as revealed by an N/D analysis – and then present it to the DfT policymakers for them to confront and take responsibility for the situation they themselves created.

Conclusions: The numerator/denominator fraction analysis is a critical directional tool – the algorithm inside the DfT policy satnav – and monitoring indicator for decarbonisation progress, which policymakers ignore at their peril. For the UK’s largest emissions sector, what the N/DA reveals is that: transport has been eating the UK carbon budget since before the CCA came into force; will continue to do so into the future; and then why that’s happened. It’s the unchanged DfT policy frameworks – and Labour’s apparent intention to keep them in place – which are driving the N/DA emissions trend upwards. The mathematical certainty about the future of that trend now is the strongest predictor that the new Labour government is running, or has already run out of time – both up to 2030 and 2035 NDC targets, and then the ultimate NZ 2050 target – to fix this problem.

If – like a set of Russian dolls, one inside the other – we see that ‘transport is eating UK carbon budget’, and potentially even the Climate Change Act itself, then it should be no surprise to find out, if we unpack the doll set a little further, that ‘aviation is eating the transport carbon budget’. That’s the subject of the next article …

Comments/questions about this article to info@transportnorth.org.uk

Precautionary caveat: The analysis of this article – that transport’s uniquely large and rising share of the UK carbon budget is such that it will be difficult if not impossible for the government to propose a lawful climate plan in 2025- is a hypothesis which can only be proven by quantified modelling. This would need to be undertaken i) by the government itself in the form of a scenario demonstrating the opposite, and/or ii) by CCC within the modelling it is now undertaking for CB7.

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The subsequent three articles in this series will be: ‘The Climate Change Committee needs to revise the aviation emissions pathway downwards’ – 18th December; ‘Legal showdown: the DfT versus the Climate Change Act’ – 28th December; and ‘Six months in: The answer to our question is … ??’, returning to the ‘test’ established by the title of our original report – 4th January 2025.