Oral evidence: Scrutiny of the draft Heathrow Expansion National Policy Statement, HC 482
Oral evidence, 13 October 2026.
Witnesses
Professor Piers Forster CBE and Dr James Richardson.
Chair
Good afternoon, could I ask you both to introduce yourselves?
Professor Forster
Good afternoon. I am a member of the Climate Change Committee. I have been on the Committee since 2018, and I am one of the two aviation champions. I am also a climate scientist who has done particular work on aviation.
Dr Richardson
I am the chief analyst of the Climate Change Committee.
Chair
Excellent. The first question is on the draft HENPS climate test. In order to pass the climate test, the Heathrow Expansion National Policy Statement states that any proposed scheme must not have a “material impact on the UK’s legally binding carbon emissions.” However, the draft NPS does not define the term “material impact.” How would you define it?
Dr Richardson
Inevitably the courts are going to end up defining the terms, but what we have said is that you have to look at the impact not just on the carbon budgets but on 2050 net zero, and the full impact when Heathrow is fully expanded. That could be after 2050, but you cannot just say the problem has gone away if it is later than 2050. You have to have a way of balancing any additional emissions from Heathrow within those targets. For 2050, if there is a plus from Heathrow expansion, there has to be an equivalent minus to get you back to net zero. On current policies that would not be achieved, but there are alternative policies that could be put in place before granting a DCO that would achieve that.
Chair
We will come to that. Would you expect material impact to be defined quantitatively or qualitatively?
Dr Richardson
It is bound to be a decision in the round to some extent because you have to look at what other parts of the economy could do, particularly engineered removals, because really you are not going to be able to deal with 2050 from other sectors such as buildings or surface transport. You have to be a little wary of putting a fixed number on it because that might encourage slightly heroic modelling assumptions to push you to one side or the other. However, if you say, “Look, actually, you have to show how this is compliant with the net zero target,” you are pushing people to really explain everything.
Alex Mayer
Your advice does not specify the volume of emissions caused by Heathrow expansion that would make it unviable. Do you think there should be a higher-end emissions threshold that means if it reached that, you would fail the climate test? If so, what should it be?
Dr Richardson
Again, the point really is that if Heathrow expansion leads to an increase in emissions, you have to have an offsetting equivalent amount to get you back to that net zero because it is a zero target. That could be from greater use of sustainable aviation fuels, it could be from engineered removals, but you have to get back to zero. You cannot rely on other parts of the economy to do the job for you because aviation is just too big.
Alex Mayer
Some witnesses have said to us that they do not feel there is a way that you can fail the climate test at the moment. Would you agree with that assessment?
Dr Richardson
If you made the amendments to it that we are proposing—to include the 2050 target, to include the full scope of full expansion—then there definitely would be a way of failing that. Indeed, we would say that under the current policy you would fail that test.
Alex Mayer
You have just spoken about your four recommended changes. What practical difference do you think those would make to the decision making?
Dr Richardson
The key thing here really is being clear on the face of the document that it is not just about the carbon budgets, which only run through to the early 2040s when the airport would not be fully open. It has to include that 2050 net zero target. It has to look beyond that as well so that the full scope of Heathrow expansion, which might come after 2050, is included. It must recognise that hitting net zero in 2050, you still have to do that or better in 2051, 2052 and so on. You cannot just say, “Well, the problem doesn’t arise if it’s after 2050.”
Alex Mayer
If those four changes that you suggest are not made, do you think that the whole document should be rejected?
Dr Richardson
You have to be clear about what the approach is. A test that does not include the net zero target is no test at all.
Dr Arthur
Thanks for coming, nice to meet you. You seem to be saying that we cannot rely on carbon savings elsewhere to offset the additional emissions from Heathrow Airport.
Professor Forster
That is correct to the first order. The point of the Climate Change Act 2008 and the carbon budget framework we have is that they give the Government flexibility about which parts of the economy ought to be decarbonising. If you look at the reality of the aviation industry at that 2045 to 2050 timeframe, there are not a lot of alternatives there, basically. If you are talking about other ways to compensate for carbon dioxide, you have the choice only between decarbonising aviation directly through sustainable aviation fuels and efficiencies, or potentially building up your removals. If there is a trade-off, it is a trade-off between those two components. It is a trade-off between direct action on the aviation industry and alternatively trying to build up a removal industry. If you look at our advice, we are quite clear that the aviation industry should be paying for the removals.
Dr Arthur
It is difficult to argue with the notion that the aviation industry .should pay for the removals, is it not? However, if the Government were to look elsewhere for emissions savings, you are saying that they cannot be found anywhere in the economy. It is not just the transport sector, you are saying anywhere in the economy. The Transport Secretary said that she thought the emissions could be offset holistically elsewhere.
Professor Forster
To give the Transport Secretary some credit, it is explicitly allowed for within the Act to do that, but it becomes quite difficult in the case of aviation. The other factor to consider is that if you look at the residual emissions we have in the 2050 timeframe, the others come from agriculture and waste, for example, but that is in methane emissions predominantly. That is a short-lived greenhouse gas, which cannot really compensate for the climate effect of carbon dioxide. Looking at it from a climate science point of view, you have to look for compensation in carbon dioxide. If you are looking at that, you actually cannot really take it from other bits of the economy. It is just the trade-off between aviation and the removals. Perhaps the Secretary of State could have been thinking of the Department for Transport, which has the responsibility for aviation, compared with DESNZ, which has the responsibility for the removals. Perhaps she is talking about a conversation between two Secretaries of State.
Dr Arthur
Okay. I do not want to put words in your mouth, but if the Government were to choose to focus more on agriculture to offset some emissions—the example you gave—while Heathrow is not going to use Government money, it is unlikely that the agricultural sector could accelerate reducing its emissions without Government support.
Professor Forster
Yes, absolutely. Those emissions from agriculture are very difficult to get rid of. You would almost have to get rid of our livestock animals completely.
Dr Arthur
Some of our vegetarian friends maybe would not feel bad, but yes, let us leave it for another day. Is there an ethical issue here where we are saying “Actually, Heathrow is so important that we are going to ringfence those emissions and allow them, while other sectors have to make that sacrifice”? I was speaking to people today about reducing carbon emissions from road transport and how challenging that is right now. It seems unfair to people in that sector if Heathrow has some kind of special status. That is another leading question for you.
Professor Forster
Yes. If you have a look at the sectors of the economy, practically all those other sectors will have completely decarbonised by that time. It is almost impossible to find any degree of compensation. You can look at one of our reports that outlines those compensations.
Dr Arthur
In terms of SAF and engineered removals, which have been mentioned, realistically, if you are investing your pension or your savings, are these products going to deliver over the time period required? Do we have confidence in that yet? SAF is nowhere near what we thought it was going to be two years ago. Can we have confidence that these things will come online at the time required?
Professor Forster
We certainly do not have confidence currently. If you look at our advice, we are very, very clear that the investment and the policies really need to come in today to be able to deliver the technology by this timeframe. We want to see the Government policy put in, and we want to see significant investment that goes into aircraft efficiency, sustainable aviation fuel for the next generation and removals.
Dr Arthur
I do not expect you to have watched it but we previously discussed HS2. One of the criticisms was that HS2 would have worked if technology had been invented to allow it to work. Is there not that danger here, actually? Should we be cautious about approving expanding the airport before we have more certainty about engineered removals and SAF?
Professor Forster
That is correct in some way, but the way out of it is to try to get airlines to pay for the cost of their carbon currently. It could then be up to the Government to decide what to do with that cost of carbon in some way. They could invest it in trying to scale up the technologies to make them more economical, for example. If they were to do that, that would also benefit other industries that also potentially rely on carbon capture and storage.
Dr Arthur
The challenge is affordability, which we will hear about tomorrow. What you are suggesting is just going to add to affordability, which just undermines further the business case. I am putting words in your mouth; maybe I should hand back to the Chair now.
Chair
We have moved on to SAF, which is fine, but I just want to go back to a clarification question on carbon budgets. Obviously, your overall regular reports cover aviation as a whole and in relationship to other sectors, but just in terms of this report on Heathrow, could you confirm which airport expansion projects are included within your Seventh Carbon Budget modelling? Does that include Gatwick, which only relatively recently passed its final hurdles? We have some other airport expansions that have growth in air traffic movements.
Dr Richardson
It includes all approved expansions within the modelling, including Gatwick.
Chair
Thank you, that is useful.
Jacob Collier
Just to pick up on Scott’s questions there about SAF and engineered removals, are there any implications for the wider sector of aviation on needing to rely very heavily on both SAF and engineered removals that you can foresee?
Professor Forster
When we talk about the timeframe we are considering, we are talking about the second and third generation type of SAF here, particularly power-to-liquid. This does not necessarily have the same restrictions to it as some competition in the current SAF that are being produced with bio energy and pre-production. Of course, the next generation will be more expensive, and they also require a lot of renewable energy to produce them. There are not necessarily material restrictions, but there are certainly these financial ones.
Jacob Collier
The Government are relying on more SAF and engineered removals if this expansion goes ahead. How much more do you think is going to be needed on top of what is already required for the industry to decarbonise overall?
Professor Forster
The estimate that we have is 4.5 million tonnes annually to compensate for the extra Heathrow expansion. The total removal in our net zero pathway is about 36 million tonnes, as far as I remember.
Chair
How much is being produced at the moment?
Professor Forster
Zero.
Jacob Collier
You are not confident at the moment?
Professor Forster
No.
Chair
Over to Chris, who will ask about polluter pays and carbon pricing. We have touched on that already.
Chris Hinchliff
I will try to go quickly, Chair. In your advice to the Government on Heathrow Airport expansion, you say that Government should legislate policies that require the aviation sector to abate 100% of its emissions before a development consent order for Heathrow. Can you provide a bit more detail about what timelines parliamentarians should be looking at for that legislation and what you would expect to see in that legislation, in order for us to feel comfortable that we have done our job scrutinising a DCO?
Dr Richardson
The key policy moment in this would be the revised jet zero strategy that the Government have committed to for next year. There are a number of mechanisms by which you could do this. We are not trying to specify exactly how you would do that. You could do it through the emissions trading scheme, through expanding the SAF mandate, or through creating an additional removals mandate. There are other ways. The key thing is it has to add up to 100% of removals by 2050. We would hope to see that through that jet zero strategy. That would then create enough time before the timescale—as we understand it, I know these things keep moving around—for a DCO at the end of 2029.
Chris Hinchliff
Thank you, that is very helpful. Picking up on that for my second question, following on from what my colleague was just getting to, there seems to be a fundamental issue that is difficult to reconcile at the heart of this. The DFT figures for carbon emissions associated with Heathrow expansion assume that—let me get this right—74% of Heathrow’s additional passengers come from other London airports. If you assume that the airport expansions that are cumulatively going on all want to see passenger increase, then the additional carbon emissions are enormous. I understand that you as a Committee say, “Well, that could be offset by additional investment in SAFs. Make the aviation sector pay for that.” Does that not bring us to the point where the cost becomes so high that the whole thing becomes self-defeating, and the demand would not exist to justify the expansion in the first place?
Dr Richardson
There are a lot of things there. Let me try to unpack our position. First, what we are saying is that the growth in demand would be lower; it is not lower relative to today’s demand. In our pathway, the growth in demand relative to today is about 21%. In the Government’s, including Heathrow, it would be 64%. There is a big difference there in terms of demand growth. It is the growth in demand rather than the level of demand. Then there is the question of how many airports do you want? Do you allow a competitive market? Do you centrally plan that? Those are issues for the Government, not for us. We assume in our modelling that there is displacement. If you expand Heathrow, there are fewer flights from other airports. I would not want to put any particular emphasis on which airports it would be. Airports would compete. The most successful would get them and others would not. We are clear that the risk in this expansion should sit with the developers. It should not sit with the taxpayers or the flying public. If you own an airport and you choose to expand it and there is no demand, that risk should sit with the developers. Therefore, it is really important that it is clear to the developers what the policy pathway is and that they are not working on an assumption that we will never solve emissions but think, “Actually, we have to do that,” so the developers know whether there is actually going to be the demand or not. That is another point about getting the Government to set out a viable pathway for the sector to net zero. Developers can then make their decisions. Obviously, those questions: is it one airport, two airports, or hubs are not for us. Those are for Government and the developers.
Chair
Does your demand modelling obviously include the carbon price?
Dr Richardson
Yes.
Chair
Does it include the construction cost: £35 billion divided by the passengers?
Dr Richardson
We have not specifically included that. There is obviously a question about how that would flow through, which is quite complicated.
Chair
That goes back to the point that was just being established earlier. Have you finished?
Dr Richardson
I have for now.
Chair
Let us get through this quickly and then there might be time for you to come back.
Daniel Francis
Your advice states that Government should be prepared to implement contingency measures if aviation emissions exceed the trajectory required for net zero. What specific measures do you have in mind to achieve that?
Professor Forster
The big thing is we need to see the industry begin to pay for the cost of the carbon basically. There are lots of different ways of potentially doing that. From our scenario, it will make the cost of taking flights a bit more expensive. By doing that investment, they can potentially invest in the technology. That is also a way to suppress the increase in demand. It is required to suppress that increase in demand until these technologies become widely available because we have to also hit the interim carbon budget. If you look at the trajectory currently, we are not on course to hit the sixth carbon budget because of the increase in emissions that come from aviation.
Daniel Francis
Do you think Heathrow should be subject to ongoing climate performance tests if consent is granted? What is your view on how that should be looked at?
Professor Forster
The key thing that James talked about before is that this revised jet zero strategy, when it comes out, will have to illustrate the way the Government plan to achieve this net zero aviation industry. That should be the key test to deciding whether expanding Heathrow Airport is compatible with our net zero policies. In terms of the ongoing checks on delivery, there ought to be ongoing checks of course that the jet zero strategy approach of the Government is delivering.
Alex Mayer
I would just like to follow on from what Daniel was saying. When Gatwick got the go-ahead to expand, some future growth is tied into meeting various environmental requirements but that is not in this Heathrow document. Would you be more comfortable if it was?
Dr Richardson
In a sense, it is the point we have made already in terms of being clear in the planning framework that any expansion has to be consistent with net zero.
Alex Mayer
Professor Forster, you mentioned earlier about the need for co-ordination between the DFT and DESNZ in relation to carbon budgets and the upcoming revision of the jet zero strategy. Where do you believe the ultimate accountability should lie if the expansion results in overshooting carbon budgets?
Professor Forster
It is not my job to run the Government, but if I was the Secretary of State taking the decision, I would want a very frank conversation with DESNZ. If you look at the jet zero strategy of the Government, that ought to be across the Government Departments to deliver on.
Alex Mayer
You said that the Secretary of State for DESNZ should play a defined role in Heathrow expansion. In what way? How would you define it? How would you envisage that that would work?
Professor Forster
The Secretary of State for DESNZ is responsible for the policies that will increase the removals, so they need to show that they can deliver these engineered removals. This is not just the 36 million tonnes; it is the extra that comes from the Heathrow expansion.
Chair
Let us move on to non-CO2 emissions. If the non-CO2 effects are not properly assessed, there is a level of risk that the overall climate impact of Heathrow will be underestimated or overestimated. The Committee appears to disagree with the Government as to whether the non-CO2 effects can be quantified robustly enough to inform decision-making. Where is the difference of opinion on this?
Professor Forster
This is my area of expertise. I am really pleased to talk about it.
Chair
Have you submitted on this basis?
Professor Forster
Yes. We are very pleased that the HENPS document talks about non-CO2 directly, but it could go a bit further than that. There is enough evidence to quantify the impact of non-CO2 despite its uncertainty. There is a different way to do it. It is not necessary to include it within the carbon budget calculation, but that does not mean it should not be accounted for quantitatively in some way.
Chair
Do you have a methodology or evidence base that you feel could be used to give confidence in the non-CO2 impacts?
Professor Forster
We have one proposal in our Seventh Carbon Budget work, which is to have no more warming from non-CO2 after 2050. That is what we proposed. That is the same sort of thing that could be considered with this.
Chair
Okay, we will dig that out from the Seventh Carbon Budget. I have just a final question on this issue. Is the risk sufficiently high that the decision whether to approve Heathrow expansion should be paused until an agreed method of quantifying non-CO2 emissions is arrived at between your Committee and the Department?
Professor Forster
There is still a lot more work that needs to be done to understand the exact role of non-CO2 components and to try to look at ways we can reduce the non-CO2 impacts. What we recommend is really that there are opportunities to put in trials and things, for example. If Heathrow were to get the go-ahead, it could do trials of reducing the non-CO2 effects over the north Atlantic corridor, for example, where we expect the effect to be particularly pronounced.
Chair
Sorry, which corridor?
Professor Forster
The north Atlantic corridor. There are a lot of contrails that develop when you fly between the UK and the States.
Chair
Is it possible for changes to the draft Heathrow Expansion NPS, as opposed to changes in other Government policy, to allay your concerns about the climate impact of Heathrow expansion?
Professor Forster
We need the two. James talked about how the most important document is the revised jet zero strategy. That is the one that will give our Committee confidence that net zero aviation is a serious commitment from the Government and that they can introduce the policies to deliver a net zero aviation industry. As a Committee, we would like to see two documents. We would like to see that revised jet zero strategy and a reinforced HENPS.
Chris Hinchliff
On my Committee we have discussed multiple times the need to have contingency measures if we get off track, as we have already discussed. We have reached the point where in your advice on Heathrow you say that even before Heathrow Airport expansion, we do not have enough policy in place to decarbonise aviation. In your 2026 progress report you said that only 32% of aviation emission reductions in the Sixth Carbon Budget are supported by credible plans. We have the World Meteorological Organisation now expecting global average temperatures to breach 1.5°C by 2029, which previously we had not expected to be passed until 2045 when the Paris Agreement was being signed. After the summer we have just had, my final question is, are we not in emergency time now? Is it not time to start applying the more stringent approach and firmer measures now, rather than continuing down a path of saying, “This is a risk, but we’ll have contingency to fall back to”?
Professor Forster
We absolutely agree as a Committee that aviation is not currently on track to deliver the reduction required for the Sixth Carbon Budget. We need to see additional policies from the Government. The Government should absolutely prepare these contingencies and should be prepared to introduce them. As we said before, the industry needs to start paying for the cost of its pollution and the cost of carbon.
Chair
I just want to pick up a question from earlier on carbon pricing and affordability. Airlines have said to us in open session that affordability—in fact it is a Government consideration as well—should be a key consideration in Heathrow expansion. A third runway should only be provided if the costs to airlines, and therefore passengers, are not excessive and do not result in demand dropping. Is there any way to square that with the polluter pays principle?
Dr Richardson
There is no getting away from the fact that emissions are a cost. At the moment we are all facing that cost through blisteringly hot summers, droughts and floods. We are saying that the cost of tackling that should be addressed by the aviation industry. That will have an effect on the cost of flying. We are quite clear about that. It is important to put that in context. We have said that a flight to Spain would add about £150 by 2050, but that should be phased in. You are looking at a few pounds a year. The impact of that will have an impact on overall demand. That is why our figures for overall demand are lower than the Government’s current policy figures, because of that cost. That is enough to address all this. It is still only a relatively small fraction of what is expected as the growth in household incomes over that period. I appreciate that right now, with households suffering from the cost of the second fossil fuel shock in five years, the idea that anything might become more expensive is pretty hard to accept. However, over that period with things phased in gradually, that is a pretty small percentage of the total increase in people’s income. It is enough to address the costs of tackling the emissions from aviation.
Professor Forster
It is more appropriate to put the cost on those people who take aeroplane flights, because it is still the majority who do not take flights at all.
Chair
Finally, unless anybody indicates, in terms of the draft NPS, does the climate test make sense to you as a test for the promoter to meet, rather than something for the Government as a whole to address?
Dr Richardson
It is a bit of both, but in many ways it is more about Government policy. That is why we have emphasised the actions we think the Government need to take before the Government could award a DCO. Clearly, it matters that the aviation industry is on board with that. There are things that any developer can do. Partly that is about airside emissions and smaller parts that are within their direct control; partly it is about supporting the development of SAF. It is predominantly a question for the Government because it has to address the whole of the aviation industry, not just the Heathrow expansion slice of it.
Chair
Thank you. That brings us to the end. The bell has not yet gone. Thank you very much for your written evidence, the time you spent preparing to talk to us today and for your time today. If there is anything you feel you did not have a chance to cover or cover adequately, feel free to email us ASAP. That concludes today’s meeting. We will continue our oral evidence on the draft Heathrow Expansion National Policy statement tomorrow morning.