Interview with Professor Callum Thomas

August 7, 2023

“Being involved with Airport Carbon Accreditation has been a fantastic experience, in part because we have seen a massive growth in awareness of the carbon consequences of running airports and the need to manage CO₂.”
– Professor Callum Thomas

It is time to bid farewell to Professor Callum Thomas from the Manchester Metropolitan University, who has decided to step down from the Airport Carbon Accreditation Advisory Board, having participated in it from its very beginning. He has followed the development of the programme over the span of the last (almost) 10 years and had a hand in its success through the invaluable input that he brought to the Advisory Board. As he retires, we invited him to share his perspective with us in a unique interview.

Airports are caught up in a bit of a double bind. On one side, they are expected to provide the regions they serve and their local communities with the maximum connectivity & economic benefits, on the other, their growth is constrained by environmental concerns. According to you, how can airports strike a balance between the two responsibilities?

I don’t think there is a choice. If the air transport industry does not strive to control and reduce all its environmental impacts (not just CO₂) in the context of growth, then growth will slow, falter and eventually stop. We see this trend already starting to emerge at some of the largest airports in the most developed parts of the world, so this is not a fantasy. This is what has driven my research over the past 20 years into the concept of Environmental Capacity Constraints at Airports.

Airports need to put an economic value on the environment in the same way that they put a price on other commodities, and incorporate this into their long term strategic and business planning processes. E.g. when Manchester Airport sought planning permission for a new runway in the ‘green belt’ an ecologically sensitive area on the edge of the city, it spent almost 15% of its expenditure on biodiversity and habitat protection work. This was necessary to secure ‘permission to grow’, as well as being an example of Corporate responsibility. For some airports today, the costs of mitigating environmental impacts such as noise, local air quality and climate change can be as great as the cost of actually constructing a new runway!

With regard to carbon emissions, there are some very challenging trade-offs that have to be made between the financial cost of flying and therefore the ability of more and more people to travel and the resulting carbon impacts of airports. For example, in order to facilitate low cost airline operations, airports are forced to develop new sources of commercial income, the two most obvious being airport retail and car parking. The presence of airport retail however results in increased energy use in terminals which can conflict with carbon reduction objectives. Equally, whilst airports would wish to encourage greater use of public transport and less car use to cut carbon, this results in less income from car parking.

Airports are also more and more constrained by the lack of capacity. Do you think that the London capacity conundrum is a harbinger of what’s going to happen in the most populated regions of the world?

I am convinced that over the next 10 years environment will emerge as the most significant capacity constraint at many airports. The debate around a new runway at Heathrow has been going on for 20 years, in the main for environmental reasons. When other airports in Europe are asking for major infrastructure, the main constraint they come across is the environmental impact of the construction, or the aircraft growth that would result from it.

Up until now, it has been very difficult to put an economic value on environmental impacts. But now, there is a need for airports to put into the business case just how big the threat is from climate change, noise and local air quality to their long term growth and invest accordingly.

But is it really quantifiable?

The answer is: at present, no, because our economic system does not properly incorporate these environmental impacts. And this is why the economist, Lord Nicholas Stern many years ago said that climate change represents the biggest failure of the market system, because we’ve never included the cost of climate change into the costs of products and services. As a result, it has been cheaper rather than manufacture in Europe, to make things in China and then carry those products all the way across the world to the consumer. This is a problem for society, economics, and now increasingly, the environment. As we begin to internalize the environmental cost of products and services, the high intensity products in terms of carbon emissions will become very expensive. This is where aviation faces a problem, because the physics of flight means lifting 400 tonnes of metal into the sky and flying at high speed across, say 2000km, needs lots of (carbon based) energy.

I’ve got aviation fuel running through my blood stream. I love the industry, I have a granddaughter in Thailand, I fly abroad all the time. I’m totally pro-aviation, but we’ve got a big environmental problem.

For so many years we’ve said: “The aviation industry is too important to the economy to prevent its growth”. And so the action to curb CO₂ emissions was delayed and we’re now beginning to pick up the damage. And this is why the Airport Carbon Accreditation programme is so important. Because we have to demonstrate that airports are doing absolutely everything that they can to reduce their carbon emissions and engage their business partners to do the same, even though we cannot make airplanes fly on fresh air.



Results of many surveys conducted across Europe, especially in the Northern countries, such as Sweden, Norway and Finland, show that people are willing to pay more for their tickets, if that would help to mitigate the negative impact on the environment of their flight.

We did a similar survey in Manchester and the majority of respondents said they would be willing to pay for carbon offsets to compensate for their flights. But as soon as we said: “OK, so get your wallets out, get your credit card out and pay”, they replied: “Ah! Ah! Well next week!”. (laughter) In the surveys, we would be embarrassed to answer no. We all know that we should be paying more.

However, you have two distinctive audiences here. We’ve got the great mass of the public, who might be inclined to compensate for their flights, if the cost is not too great, and then you’ve got the freight community, that understandably will not wish to pay more than it needs to, for simple commercial reasons.

If you think about it, every activity associated with the operation of an airport has implications for carbon emissions and therefore climate change, the most obvious being the:

  •  energy used to run the airport – the terminals, apron areas and vehicles.
  •  the emissions from aircraft using the airport – landing, on the ground and taking off.
  •  the emissions from passengers travelling to and from the airport

But it is much more than this. What about emissions associated with the handling of wastes, or use of water, provision of catering services and so on.

The airport cannot solve the problem on its own. It needs to take its service partners and the travelling public with it. Airports need to educate and then ask their passengers to participate in carbon reduction initiatives. For instance, at Dallas Fort Worth (the first & only carbon neutral airport in North America), they’ve got water fountains that say: “This is iced water. If you fill up a bottle at this water fountain, rather than buying a new plastic bottle, you will save CO₂”. This may seem small, in comparison to aircraft emissions, but if you think of the millions of people going through that airport every year, just getting them to drink water out of that cool tap has an impact on climate change.

It might be a tiny one, but it illustrates how every single activity has consequences quantifiable in carbon. As I often say, Mother Earth doesn’t care if it’s the activities of an airline or an airport operator, an air traffic controller, or a freight carrier that gives rise to CO₂ emissions, those emissions remain in the atmosphere for over a hundred years so everyone needs to engage with every possible carbon reduction opportunity.

Every action counts. There is also this popular saying regarding plastic waste: “One plastic straw cannot hurt anybody, said 7 billion people”.

That’s the logic, exactly.

You can get to a situation in which you say: “OMG, it’s so complicated, I give up. There is no way I will be able to manage all these sources of emissions.” This is where I come back to the fact that the Airport Carbon Accreditation programme is great, because it provides a workable framework for climate action. By creating it, ACI took stock of the need for climate action in the aviation industry early on. And the first thing they could do, was to raise awareness and to get people to measure what the carbon impacts of their operations were, because then you begin to create a management who are what we call “carbon-literate”. 15-20 years ago people could just about spell the word, and they just thought it was energy use. Now, there are senior managements at airports across the world who know that it means everything, not just the energy and the buildings, but also passenger transportation, managing wastes, airside vehicles, LTO of aircraft, and so on.

The public need to be encouraged also to play their part and they can do this in a variety of ways such as travelling to the airport by public transport. In this context, I would love the Airport Carbon Accreditation programme to produce infographics or a seatback leaflet, that says: this is the reality of the choices we all make when we fly, and this is what you can do to compensate for it, or to make sure that your personal footprint is as small as possible.

But then, wouldn’t the leaflet just read: “Fly less”?

No, because people want to fly and the benefits, economically, culturally and socially, of global mobility are so great. I’ve often said, if you went into a bar in Brussels, and a guy came up and he nudged you and said: do you want to buy this really cheap smart phone for 5 euros? You would think: “There is something not right here.” On the other hand, when some low cost operators come along and say: hey guys, do you want to buy a flight for 5 euros? The answer is “yes”, because people like to fly and they want to fly cheap. We’ve got used to having what is one of the most wonderful products available on the market place – the ability to fly across the world – way too cheap. There is, in fact, an irony here because ‘low frills’ airlines are often the most eco-efficient. They operate the most modern fuel efficient aircraft, carry the lowest weight per passenger and have the highest load factors.

In addition, as I said earlier, low cost flying, which has brought air travel within reach of so many (not just the rich) has forced airports to raise money from other sources, such as retail, that causes conflict with their carbon reduction objectives. And there is an additional irony here because airport retail means greater fuel burn and emissions from airlines (resulting from products sold in airport shops being carried onto aircraft). We have studied this, funded by a major airport retailer, and the answer that there is a small, but significant increase in emissions from this source, so new retail business models will probably be necessary in the future.

I don’t think people really recognise the incredible value of air travel I want people to start saying: “Yeah, I’m willing to pay more, because it’s such a good product”. And eventually they will need to do so, when CORSIA, the rising cost of fuel and fleet replacement for airlines pushes the price of flying up.

There is a very interesting paradox here. If we don’t pay to invest in new technologies to reduce the emissions from the industry, then climate change will restrict its growth in the longer term. If on the other hand we do pay more, then the increased cost of flying might reduce demand. Either way, we have a challenge and we need to take the travelling public with us.

What do you think is the most important factor weighing in on the aviation industry achieving carbon neutral growth?

For airlines, that are responsible for 95% of CO₂ emissions arising from the industry, it is a matter of the aerospace industry delivering step changes in technology that release the dependency of air transport upon carbon fuels.

For airports, its being able to build the correct business case to invest in low/zero carbon technologies and operating practices.

For the general public, it’s being willing to pay the right price (a higher price) for the fantastic service that the industry provides: the ability to fly across the world in a matter of hours. Never in history have we been so privileged to enjoy such global mobility.

You have been involved in the Airport Carbon Accreditation‘s independent Advisory Board since its very first meeting. Did you enjoy working on the programme? What do you consider your legacy as you retire?

Being involved with Airport Carbon Accreditation has been a fantastic experience, in part because we have seen a massive growth in awareness of the carbon consequences of running airports and the need to manage CO₂.

Working with such talented colleagues has been a great learning experience, particularly where we have had to debate apparent conflicts between commercial and environmental objectives. But in general, whilst being pragmatic and seeing the need to get as many airports to buy into carbon management as possible, members of the Advisory Board have recognised the importance of pushing for change to ensure that the programme retains its credibility, for without this credibility, the programme would be seen simply as an industry green-wash exercise.

Legacy – I hope that I can claim to have supported other members of the Board to push for radical change and I hope also that to a degree I have, through my work with Airport Carbon Accreditation and more broadly with ACI, helped the airports community understand that environmental issues (such as noise, local air quality and carbon), are real business threats to the growth of the industry and need to be viewed in commercial terms and properly invested in.

It has almost been a decade since the programme started. What is your assessment of Airport Carbon Accreditation’s evolution? Did it meet the expectations it had raised in its outset?

Are you a climate change optimist?

Probably not. I am an optimist by nature but there are a number of factors which I believe, means that we are unlikely to take the necessary action to prevent dangerous climate change:

  • I don’t think people are able, yet, to comprehend the fact that we are changing the climate and weather of the whole of Planet Earth. It’s rather like coming to terms with the fact that we will die one day, it’s just too big to comprehend.
  • The worst consequences of climate change will occur after we are dead so persuading people to make sacrifices now is difficult, even though our children and grandchildren will be the ones that suffer.
  •  From an aviation point of view its quite simple, we love the services offered by air transport and do not want to give them up. I have a granddaughter called Mya who lives in Bangkok. There is no way that I would give up the possibility of hugging her, simply because of the climate implications of flying.

Over the past 50 years, air transport has changed the world in which we live and brought so many massive social and economic benefits. If we are not able to address the climate consequences of flying, through the development of low carbon/carbon free flight, then I fear that we will not be as globally mobile in 50 years’ time as we are today and that would be a very sad thing.

If you were to give one piece of advice to an Environment Manager of an airport who sets out on a carbon management journey, what would it be?

Take a system wide view (the climate system does not differentiate between the source of emissions) and work with every service partner and your passengers to reduce carbon across every aspect of the business. We have no choice to do so if the industry is to continue to grow.


Prof Callum Thomas is, by training, an environmental biologist, having established the Environment and Bird Hazard Departments at Manchester Airport, he led the environmental programme for the Airport’s Second Runway project that played a major role in ensuring its success. For the past 20 years he has been Professor of Sustainable Aviation at the Manchester Metropolitan University in the UK. Callum will retire from the University at the end of the year but will continue his work as Director of the consultancy company Callum Thomas Limited which offers expertise on alleviating environmental business risks to aviation, thereby supporting its sustainable growth in an increasingly environmentally constrained world. He can be contacted on

I think the programme has expanded more rapidly than anyone could have expected, not just in numerical terms but also in terms of the size of airports that have signed up to the programme and in terms of the geographical spread.

I get a real buzz when I travel through an airport which advertises the fact that it is part of the Airport Carbon Accreditation programme.

Where do you see the programme in 10 years?

Government efforts to prevent dangerous climate change are resulting in tightening constraints upon all industries, including within the air transport sector (witness new ICAO CO₂ standard for aircraft and the CORSIA scheme for airlines). Airports will not be immune from this trend so I predict that in the next decade we are likely to see carbon limits or caps, imposed upon more airports, broadly similar to that found at Stockholm Arlanda Airport.

The principle of such caps is an intellectually logical response to the threat of climate change, after all why should airports be considered a special case when other industries face cap and trade schemes? The problem will be what operations are included within the boundary of such caps and where the base emissions limits are set.

This raises a question of whether an airport would be able to grow in response to demand and so maximize the role it plays in supporting sustainable development within the City/Region its serving within a carbon cap. And if not, would those benefits be driven elsewhere or would other modes of ground transport (High Speed Rail) take business away from the aviation industry.