Overshoot: How expansion plans break European airports’ carbon limits

Executive summary

Europe's airports cannot expand as currently planned if countries are to stay inside their national climate limits. We tested the announced expansion plans and traffic forecasts at 20 of Europe's biggest airports across 10 countries against a Paris-aligned 1.7°C carbon budget. The results are clear: all of them are set to overshoot, and clean aviation technology cannot close the gap.

Airlines and airports tell governments they can expand and fly more passengers, and still meet Europe's climate targets, on the promise that cleaner fuel and more efficient aircraft will cut enough emissions. Policymakers rarely see that promise tested against a hard limit. This report therefore attempts to do so. We did not measure each expansion against a distant 2050 net-zero target, which can make an airport appear compliant while its emissions increase. Instead, we defined a clear carbon budget to keep global warming within 1.7°C. A budget achieves something an annual target cannot, as it converts a volume of emissions into a date, and tells us the year the sector runs out of room to emit.

Every airport we tested overshoots its fair-share 1.7°C carbon budget, even after SAF uptake and more efficient aircraft are accounted for - a sign that technological advancement is not a panacea.

On current plans, each of these airports will overshoot its budget by two to three times, by 2050. Lisbon and Porto have the biggest overshoots, at 2.8 times the budget, followed by Dublin at 2.6. Most airports will have used up their entire carbon budget by the 2030s, which is decades ahead of the 2050 target. Málaga runs out in just eight years. To stay within budget, the airports facing the steepest challenge, Lisbon and Porto, would have to cut emissions by around 12% every year from now on, rather than expanding.

Increasing traffic volume cancels out any benefits from more efficient aircraft and cleaner fuel. No plausible improvement in fuel or engines can close the gap in time. Overall, planned expansions would add 225 million tonnes of CO₂ to today's emissions.

Among the results are four particularly worth highlighting. The United Kingdom (UK) has the largest absolute increase: cumulative extra emissions from a third Heathrow runway between 2035 and 2050 would be equivalent to a full year of emissions from Croatia’s entire economy.

Ireland shows the biggest relative rise in emissions, at more than 65% a year in Dublin, as the country appears to be moving backwards on its decision about the expansion of the airport. It previously had a legal cap, but is now legislating to remove it while also writing in a clause to prevent it from ever returning.

Spain is carrying out the largest airport expansion programme, with work planned at 12 airports, with its four biggest airports already emitting twice their fair share.

Set against its own economy, Portugal shows the biggest increase: an extra 18 million tonnes of CO₂ from a single new airport in Lisbon, which is equal to half a year of emissions from the entire Portuguese economy.

This issue extends beyond aviation. Since emissions come from a shared national budget, if one sector overspends, another must save. Every additional tonne that an airport uses above its share demands extra efforts from other sectors, such as industry, farming or heating. There is a growing legal risk too. Courts across Europe are now holding governments accountable for their climate obligations, and a government that approves airport expansion beyond budget exposes itself to legal action.

The economic case for expansion no longer holds either. Our previous study with the New Economics Foundation found that air connectivity drives economic growth in only 37% of European regions, mostly in Eastern Europe, while in a majority of regions, air transport growth appears instead to be a response to increasing GDP per capita. Where air tourism grows, it is local renters and low-income households, rather than visitors, who bear the cost through higher rent prices. The case for expansion rests on benefits the evidence no longer supports, while the costs to the climate, health and housing keep mounting.

Aviation's tax exemptions are exacerbating aviation’s growth problem: untaxed fuel, VAT-exempt tickets and flights that are only marginally covered by the European carbon markets.

Governments do not need to invent a new methodology to fix this. Three of the countries in this report have already developed one. The United Kingdom and France show that a country can define a national aviation carbon budget or decarbonisation pathway that also covers international flights. The Netherlands goes even further, defining a national carbon ceiling for aviation with caps at the airport level. These decisions convert 2050 targets into binding, actionable limits that airports must comply with. The methodology is settled and there to be applied.

We recommend three actions:

Europe's airports cannot expand as currently planned if countries want to stay within their national climate limits. This report shows why, testing each expansion against a fixed carbon budget rather than a distant net-zero target. Each country with airport expansion plans overshoots, and clean aviation technology cannot close the gap. So one question remains: do policy makers have credible plans to reduce aviation and national emissions whilst continuing to expand airports?

Our Down to Earth analysis revealed that growth cancels out the sector's own decarbonisation plans. Aircraft leaving European airports will burn nearly 60% more fuel in 2050 than in 2019, because rising traffic outruns every efficiency gain. Even with the ReFuelEU sustainable aviation fuel (SAF) mandates, emissions in 2049 will be less than 3% below their 2019 level. On current growth plans, European aviation is set to exhaust its 1.5°C carbon budget this year and its 1.7°C budget by 2033.

These dates show that European aviation will exhaust its carbon budget within years, not decades. Sustainable fuels alone cannot reduce emissions fast enough, because genuinely sustainable feedstocks do not exist in the volumes the sector needs.

At the same time, the claim that more flights mean more prosperity no longer holds. The industry presents expansions as economic gains and plays down what it costs the climate. A recent New Economics Foundation (NEF) study, commissioned by T&E, found that air connectivity drives economic growth in only 37% of European regions, mostly in Eastern Europe. In a majority of regions, air transport growth appears instead to be a response to increasing GDP per capita. Across much of northern and western Europe, business travel has reached saturation, and rising incomes now drive travel growth rather than the other way round.

Our scope is 20 airports across 10 countries. Seven of those countries have live expansion projects. These include the United Kingdom, France, the Netherlands, Spain, Portugal, Belgium, Ireland. In the other three, no headline project is planned, yet sustained traffic growth alone is enough to exceed the budget. These are Germany, Switzerland and Austria. This contrast highlights the fact that the problem extends more broadly to projected capacity, not just the infrastructure.

We divide the aviation budget between countries using a 'grandfathering' approach, whereby each country receives a share based on how much it flew in the past. This system rewards the countries we study, all of which fly more than their corresponding share of population. We have chosen this methodology deliberately. If expansion exceeds this generous budget, the finding still holds under the industry's most favourable accounting. Alongside it we show a population-share split, which gives everyone an equal claim. The gap between the two reveals the question of fairness.

The idea that Europe can expand its airports while meeting its climate targets can be tested. The chapters that follow show where this promise falls short, by how much, and what governments can do instead.

Download the report to read about the expansion pipeline, airport by airport.

Every airport we tested overshoots its fair-share 1.7°C carbon budget, even after SAF uptake and more efficient aircraft are accounted for. On current expansion plans, airports are set to emit two to three times their budgets by 2050. Most airports exhaust their entire carbon budget in the 2030s, decades ahead of 2050. In total, expansion adds 225 million tonnes of CO₂ on top of today's capacity.

This section sets out the actions that governments should take to change course: rejecting expansion that exceeds the budget, using slots and taxation to limit air traffic, and supporting clean alternatives.

The timing is the most important part. The path to a 1.7°C reduction rewards early action: the sooner the sector starts cutting emissions, the easier the later cuts will be. Expansion does the reverse. Each additional flight increases the difference between the target and actual emissions, meaning that widening the gap now demands steeper, costlier cuts later on.

This issue extends beyond aviation. Since emissions come from a shared national budget, if one sector overspends, another must save more in order for the country to remain within its budget. Every additional tonne that an airport uses above its share demands extra efforts from other sectors, such as industry, farming or heating.

For countries, there is also a growing legal risk to consider. Courts across Europe are now holding governments accountable for their climate obligations. For example, the European Court of Human Rights ruled that Switzerland had violated its citizens' rights by failing to cut emissions enough, achieving only 11% against a 20% target. The court also singled out Switzerland's failure to set a carbon budget.

The Dutch Urgenda case established the same principle: a government's climate obligations can be enforced in court. In Ireland, legal advice on the Dublin cap-repeal Bill states that the government is bound to protect health, meet its climate targets and take responsibility for the emissions of projects it approves. Removing a cap to allow an airport to expand would contravene all three of these duties. A government that approves expansion beyond budget is not just missing a target. It is also exposing itself to legal action.

Our Tax Gap analysis showed the revenue side of the fix: by introducing a fuel tax on departing flights, applying VAT to tickets and ensuring that departing flights are fully covered by the EU Emissions Trading System. Aviation's tax exemptions are what make this growth possible in the first place.

Public money raised through these measures must stop funding the problem. Governments should redirect public money, including from the European Investment Bank and state aid, away from airport capacity and towards clean alternatives such as e-kerosene and zero-emission and hybrid aircraft technologies.

This must work hand in hand with cleaner transport alternatives. Rail must take priority on every route where it can realistically replace a flight. This highlights the need for a unified vision of European mobility that considers aviation, high-speed rail and other clean modes together, rather than expanding airports as if other options did not exist.