Most of Europe’s biggest airports plan to expand to accommodate more passengers in the coming years. Transport & Environment (T&E), a European NGO focused on sustainable transportation, assessed the expansion plans and traffic forecasts of twenty of Europe’s largest airports in ten countries against a Paris Agreement-compliant 1,7°C carbon budget.

And guess what? By 2050, they will be emitting two to three times more CO2 than they are allowed to under the Paris Climate Agreement, and clean aviation technology cannot close that gap.

Twist on the facts

According to T&E, airlines and airports in Europe are telling governments that they can expand and carry more passengers while still meeting European climate targets, promising that environmentally friendly jet fuel and more efficient aircraft will reduce emissions sufficiently.

The NGO’s most recent study – in which it reversed its approach and started from the premise, “How much CO2 can a country still afford within its climate budget, and how much airport traffic actually fits within that?”, shows that this is not the case. Even when technological advances, such as less polluting aircraft and Sustainable Aviation Fuels (SAFs), are considered, every airports exceeds its climate budget.

Expansion leads to more CO2

For its calculations, T&E uses a so-called “fair share budget.” “Fair share” refers to the distribution of the global remaining carbon budget among countries, sectors, or activities according to a chosen allocation principle. Under the “grandfathering” approach, this allocation is based on existing emission quotas: those who emit a lot today receive a larger share of the remaining budget. This method is simple, but it favors high emitters and is therefore controversial from the perspective of climate justice.

Four countries stand out, according to these calculations: the UK, Ireland, Spain, and Portugal. The UK has the largest absolute increase: a third runway at Heathrow will result in cumulative additional emissions between 2035 and 2050 equivalent to a full year’s emissions from the entire Croatian economy.

Ireland has the largest relative increase (more than 65% per year in Dublin), even as the country is abolishing its statutory cap and incorporating a clause to prevent its reinstatement.

Spain is carrying out the largest expansion program, with construction projects at twelve airports, while the four largest airports already emit twice their fair share – and locals are increasingly fed up with mass tourism.

Portugal has seen the largest increase relative to its own economy: an additional 18 million metric tons of CO2 from a single new airport in Lisbon, equivalent to half a year’s worth of emissions from the entire Portuguese economy. Lisbon and Porto have the highest excess emissions (2,8x), followed by Dublin (2,6x). What’s more, Lisbon and Porto would have to reduce their emissions by about 12% per year – rather than expanding – to stay within the budget.

In fact, most airports will have already used up their entire budget by the 2030s. The planned expansions combined will add 225 million metric tons of CO2 on top of current emissions. And alongside the current growth trajectory, the European aviation sector will exhaust its 1,5°C budget this year and its 1,7°C budget in 2033.

Zaventem and Charleroi will also exceed climate budget

Belgian airports – including Zaventem and Charleroi, which are among the twenty airports surveyed – would also easily exceed that climate budget.

Brussels Airport expects to grow to 32 million passengers by 2032 (up from 24,4 million in 2025) and is preparing for this by working on a new transportation hub, an expanded terminal, and major runway construction projects. But according to T&E, the airport is marketing a planned expansion as “road maintenance,” while those plans “also include changes to intersections and other adjustments that will increase capacity”, T&E says.

According to the calculation, that extra capacity will result in approximately three million metric tons of additional CO2 emissions over the next two decades – the same order of magnitude as the airport’s annual emissions. In total, Brussels Airport is projected to reach 73 Mt of CO2 by 2050, or 2,3 times the budget of 32 Mt.

According to the T&E methodology, Brussels should not grow but, starting now, rather shrink by an average of about 10% per year to stay within its climate budget.

At Charleroi Airport, Ryanair’s main operational base in Belgium, a proposed new environmental permit would increase the maximum number of flights from 77,000 to 83,000 per year, and the number of passengers from ten million to sixteen million by 2045. However, according to the report, the airport is already approaching the limit of approximately 120,000 flight movements per year.

If it comes to that, Charleroi Airport’s annual emissions will rise by about 50%, amounting to an additional three million metric tons of CO2 over 25 years – roughly double what a member state like Malta emits in a single year. If the new environmental permit is fully implemented – the Council of State has yet to rule on it – Charleroi’s annual emissions would nearly double by 2050, according to T&E. The airport would exceed its allocated carbon budget by about 2,3 to 2,4 times.

Conflict of interest

“Both the federal government and the regional governments must ensure that capacity at the Zaventem and Charleroi airports remains within their climate budget,” states T&E. “In practice, this means they must reject the environmental permit for Charleroi as it currently stands, and they must also treat the runway work at Zaventem as an expansion rather than maintenance.”

In addition, there is the local argument: Zaventem is in a densely populated area, and aircraft noise over the capital has been a contentious political and legal issue between the federal government and the Brussels and Flemish Regions for years. T&E’s point here is that capacity limits protect residents from noise and air pollution while also addressing the climate crisis.

Whether the report will make a difference remains to be seen: if you look specifically at Belgium, the same government that is supposed to assess compliance with climate goals at both Brussels Airport and Charleroi Airport also has a financial stake in growth and a shareholder interest in returns.

Through the Federal Participation and Investment Company (FPIM), the federal government directly owns 25% of the shares in Brussels Airport Company. Furthermore, since the end of 2025, the Flemish Region has become the largest shareholder indirectly (39%, through the BAISA consortium) via the investment company PMV.

The situation is similar in Charleroi: the operator, BSCA, is majority-owned by SOWAER, the Walloon government holding company for airports—so the Walloon Region also has a seat at the table there.

The conflict of interest is therefore very real: the same government that is supposed to assess compliance with climate goals also has a financial stake in growth and a shareholder interest in returns.

More public funds for environmentally friendly alternatives

T&E is therefore calling on governments, among other things, not to automatically approve airport expansions and to direct more public funds toward more environmentally friendly alternatives. “Rail should be given priority on every route where it can realistically replace a flight,” the organization states, for example.

Furthermore, the study also points out that air connectivity drives economic growth in only 37% of European regions and air tourism growth transfers wealth to property and capital owners. It pushes up rents for low-income households and diverts investment away from productive economic sectors, the ones that create jobs and economic growth.

The argument that people want to fly and that the industry is therefore responding to demand is also less neutral than it seems. This is because demand is also actively stimulated by tax exemptions, such as untaxed jet fuel, VAT-free tickets, and only partial ETS coverage.