MPs look set to approve a third runway at Heathrow airport (Photo by Peter Macdiarmid/Getty Images)

This piece has been updated to correct an error

Carbon emissions from the aviation industry must not rise if the UK is to meet its legally-binding climate change targets, according to the government’s independent climate advisers.

In a letter to Transport Secretary Chris Grayling following his statement on the government’s airport policy, the chair and deputy chair of the Committee on Climate Change (CCC) wrote:

“Aviation emissions at 2005 levels in 2050 means other sectors must reduce emissions by more than 80%, and in many cases will likely need to reach zero.

Higher levels of aviation emissions in 2050 must not be planned for, since this would place an unreasonably large burden on other sectors.”

The government’s latest figures foresee aviation emissions rising by 4.9 million tonnes CO2 by 2030 if a third runway is developed at Heathrow airport.

A previous edition of this article said that the government expects aviation CO2 emissions to increase by 7.3m tonnes by 2030 if a new runway is built at Heathrow. That number is actually how much Heathrow’s emissions would rise, not the UK’s total aviation emissions — which are projected to rise by 4.9m.

That’s because, according to the government’s figures, aviation emissions at the UK’s other airports (Gatwick, Stansted and regional airports) would fall, in part covering for the significant increase out of Heathrow.

The sums were calculated using the numbers in tables 69 (nice) and 70 in the Excel spreadsheet underpinning the Department for Transport’s aviation forecast.

The Davies Commission report from 2015 that recommended expanding Heathrow instead of Gatwick said a mammoth CO2 price of £330 per tonnes by 2050, in addition to unspecific biofuels wizardry, would be required for the UK to stay within its carbon budget.

It has been calculated that a carbon price at this level would add over £130 to a return trip from London to New York.

Cait Hewitt, Deputy Director of the Aviation Environment Federation, said: “The Government’s own forecasts show Heathrow expansion sending UK aviation CO2 emissions well beyond the limit that the CCC recommends.

“There are no measures set out in the NPS to tackle this, and no climate change condition linked to the expansion.”

“The Government has never been able to show how it can square a new runway with the Climate Change Act, even based – as it is – on a target of limiting the risk of 2 degrees of global warming.

“It’s impossible to see how any increase in airport capacity could be compatible with the more ambitious target set by the Paris Agreement.”

In April, climate minister Claire Perry announced that the CCC will review the country’s 2050 targets in light of the new 1.5 degrees warming ambition outlined in the Paris Agreement, but the group has yet to receive official instructions and would not comment as to whether increased airport capacity could be compatible with the net zero goal.

Of course it stands to reason that if Heathrow expansion jeopardises the UK’s existing climate targets, it would make more dramatic carbon cuts even more difficult.

‘All domestic flights will need to end pretty much immediately’

If the UK does put in place a 2050 net-zero emissions target then that could be especially costly for the country’s domestic air routes.

Leo Murray, director of campaigning group Fellow Travelers, explained: “International air travel emissions have a uniquely ambiguous status under UK carbon budgets, in which they are not quite in and not quite out.

This means politicians have a lot of wriggle room to express vague aspirations about global deals to tackle these greenhouse gases.”

Emissions from domestic air travel, by contrast, are very much part of our national inventory and the legal framework for the UK Climate Change Act.”

“And if Britain moves to a net zero 2050 target to honour the Paris Agreement, all domestic flights will need to end pretty much immediately.”