Heathrow's third runway cannot be approved without changes to current climate policies, the government's advisers have said.
The Climate Change Committee, external said expansion can still go ahead but only if the aviation industry funds cleaner fuels and pays for machines that suck carbon dioxide out of the air.
Making the industry pay could push up the cost of flying with a return trip to Alicante costing around £150 more by 2050, and a return to New York up £400 in today's prices, it said.
Once built, the expanded airport would produce more carbon dioxide than any other single sector of the economy by 2050. Heathrow said expansion and climate goals were "not a choice" and it would deliver both.
The government would "carefully consider" the advice alongside other responses to its consultation according to the Department for Transport (DfT).
The £33bn project would raise Heathrow's capacity to 150 million passengers a year - up from 85 million.
A DfT spokesperson said any expansion would need to align with the country's climate targets, but added it "could deliver around £40bn to the economy and support up to 60,000 local jobs".
The CCC has said carbon-removal machines must be deployed to cut more than a third of the emissions by 2050.
Phased across 25 years, the cost of a flight to Alicante would rise by a few pounds a year - "less than a cup of coffee each way", Topping said.
Tim Alderslade, chief executive of Airlines UK, said carriers backed the government's target of net zero by 2050 but added that the transition "has to be affordable".