The pledge from 21 carriers will oblige them to clarify that the emissions of a specific flight cannot be "neutralised, offset, or directly reduced" by contributing to climate protection projects or alternative fuels -- claims the EU says amount to greenwashing.

"To avoid misleading consumers, airlines must refrain from using vague environmental language and ensure that any claims about future environmental performance are substantiated," the commission said in a statement.

The announcement made in the run-up to next week's COP30 UN climate summit in Brazil stems from a consultation between airlines, the EU executive and consumer protection groups.

Airlines also pledged to present carbon emission calculations in a clear and transparent manner and provide robust scientific evidence when claiming environmental improvements.

The carriers concerned are Air Baltic, Air Dolomiti, Air France, Austrian Airlines, Brussels Airlines, Eurowings, EasyJet, Finnair, KLM, Lufthansa, Luxair, Norwegian, Ryanair, SAS, SWISS, TAP, Transavia France, Transavia CV, Volotea, Vueling and Wizz Air.

The commitments follow a formal complaint lodged with the European Commission in June 2023 by consumer groups, which accused the aviation sector of misleading advertising practices.

The industry has begun to shift its messaging after a series of legal setbacks.

In March 2024, a Dutch court ruled against KLM in a greenwashing case, saying the airline misled consumers with vague claims about the sustainability of its flights.

A year later, a German court barred Lufthansa from advertising carbon offsetting in a way deemed deceptive.

Air France no longer offers carbon offsets for flights. Instead, it suggests passengers contribute to the purchase of sustainable aviation fuel (SAF).

"There is room to change" in the way airlines communicate, said Diane Vitry, who heads up the aviation section of the NGO Transport & Environment.

She said the ideal would be for flight ads to mention their climate impact, similar to the health warnings included on tobacco and alcohol labels.

Aviation accounts for around three percent of global carbon emissions, but its overall contribution to climate change is higher because of the release of other greenhouse gases and condensation trails at high altitudes.

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