LONDON — Opening a third runway at Heathrow Airport could result in pollution equivalent to an additional 2.4 million tons of carbon dioxide being released into the atmosphere each year by 2050, according to government estimates seen by POLITICO.

The data, obtained through a Freedom of Information request, sets out for the first time Whitehall’s forecasts for the additional environmental damage caused if a controversial third runway is opened at Heathrow in 2039.

The figure, from analysis conducted in January this year, is based on modeling applying ministers’ current “policy ambition” to cut aviation emissions.

Chancellor Rachel Reeves announced in January that the government would back a third runway at Heathrow, the U.K.’s biggest airport. Her support is part of the Treasury’s bid to boost sluggish economic growth and generate jobs. 

But the government has come under pressure from green groups and MPs concerned that airport expansion would make it harder for the U.K. to hit its climate goals.

Energy Secretary Ed Miliband, who voted against Heathrow expansion in 2018, said it would take place only if legally-binding carbon budget targets can still be met, which in practice means emissions from the third runway would need to be offset by reducing pollution elsewhere in the economy.

Miliband’s Department for Energy Security and Net Zero declined to answer how it would achieve these offsets, referring the query to the Department for Transport.

It is now up to Heathrow bosses to submit expansion plans by the summer. The airport is aiming to get a green light before the end of this parliament.

Jet zero

The data, released by the Department for Transport (DfT), is based on a scenario where a third runway at Heathrow becomes fully operational in 2039. Under that scenario, sustainable aviation fuel (SAF) — a lower-carbon jet fuel still in the initial stages of development — would make up 22 percent of fuels by 2050. 

New legislation requiring airlines to ensure two percent of the jet fuel they use is sustainable, known as a SAF mandate, was laid before parliament this week. Ministers hope the industry could hit 22 percent as early as 2040, where the requirement will be fixed “until there is greater certainty regarding SAF supply.”

Separate government calculations released by the DfT, based on a “high ambition” scenario where SAF makes up 50 percent of jet fuel by 2050, found additional emissions from Heathrow would be equivalent to 1.4 million tons of CO2.

That scenario, modeled on a “jet zero” strategy published by the previous government, would also see the roll out of zero-emissions flights and greater fuel efficiency.

Some emissions created from a third runway could be offset by passengers opting to fly from Heathrow who could otherwise have flown from a different U.K. airport, according to an accompanying DfT document.

“A third runway at Heathrow doesn’t make sense for the economy or the environment. It would undermine regional growth and the U.K.’s domestic tourism industry,” said Nick Davies, head of climate policy at the Green Alliance think tank. “We’ve got a long way to go to zero-emissions flights — so the reality is that allowing airport expansion to go ahead will fly in the face of the U.K.’s climate targets.”

Experts warned that overall emissions could still be higher than the DfT estimate, since government modeling looked at expansion at other airports and excluded any additional emissions produced in the construction of new infrastructure and other airport operations. 

“The environmental damage created by an expanded Heathrow is a danger to us all, especially when factors missing from this calculation are considered. Counting other greenhouse gases and inbound flights could quadruple the DfT’s estimate,” warned Alex Chapman, a senior economist at the New Economics Foundation think tank. 

The government risks “tarnishing the U.K.’s climate credentials” for “minimal economic benefit,” Chapman added. “We estimate around two-thirds of new flights created are taken by a tiny minority of wealthy, U.K.-based, frequent flyers travelling for leisure.”

A DfT spokesperson said: “Expanding Heathrow could drive growth, trade and tourism and unlock over 100,000 jobs, cementing our position as a world leader in aviation. We are committed to reaching net zero by 2050 and any expansion plans would be assessed against the government’s legal, carbon and environmental obligations.”