The Court of Appeal’s ruling on Heathrow raises an immediate political challenge for Boris Johnson’s Government over whether it will attempt to salvage the expansion plans for the UK’s largest airport.

But it also raises a wider economic and environmental question for the UK.

Is any UK airport expansion compatible with the Government’s goals of reaching net zero carbon emissions by 2050?

Despite ruling that the Government had failed to take account of this legislated objective when giving the green light to a third runway in West London – hence making decision was unlawful –  the appeal court judges did say that, in future, a third runway could go ahead, so as long as it fits with the UK’s climate policy.

So can it fit? Or should all UK airport expansions plans be scrapped?

Just how significant are emissions from aviation?

Total UK greenhouse gas emissions in 2017 were estimated at 460 million tonnes.

Emissions from aviation accounted for 36 million tonnes of that, or around 7 per cent.

That’s a lower share of emissions of residential housing (14 per cent) or energy generation (23 per cent).

Yet while carbon emissions from energy have been falling fast, those from aviation have been going the other way.

They have doubled since 1990.

And the vast majority of those emissions are from long haul international flights.

Domestic flights made up only 4 per cent of aviation emissions.

Can’t aviation be decarbonised?

Flying can certainly be made less polluting, by making planes more fuel efficient. And experts see a lot of scope for this over the coming decades.

But the technology that would allow zero carbon aviation is not on the horizon.

So how can we have zero emissions and yet have flying?

We can’t. But the Government’s target is for zero “net” emissions, not zero emissions.

This means that it can still produce some greenhouse gasses so long as these are offset by other activities that suck emissions out of the atmosphere such as planting trees.

The Committee on Climate Change, the independent body of experts set up by the Government to advise it on decarbonisation policies, says the economy overall can reach net zero by 2050 while still allowing flying to continue.

Indeed, the CCC says we can have net zero while UK aviation still produces 30 million tonnes of green house gasses a year by 2050, which would make it the largest emitting sector of the economy.

But that’s lower than the 36 million tonnes aviation produces today isn’t it?

Yes and the CCC said this reduction would rely on planes becoming more fuel efficient and using more sustainable biofuels.

But the CCC also, crucially, says that demand for flying would need to curbed.

Its scenario where the Government achieves its overall net zero target is based on an assumption of a 25 per cent growth in demand for flying by 2050 compared to today.

The Government’s existing projections are for up to an almost 50 per cent increase in demand over the same period.

That means many people will need to be somehow incentivised to fly less than they would otherwise choose to. 

Expanding current airport capacity does not sit easily with that.  

So what’s the bottom line? Is airport expansion compatible with meeting our climate targets or not?

The view of the CCC seems to be that the Government essentially has to choose between allowing Heathrow to expand and preventing any other UK airport from growing.

“Current planned additional airport capacity in London, including the third runway at Heathrow, is likely to leave at most very limited room for growth at non-London airports,” the CCC’s chair, Lord Deben, wrote to the Transport Secretary in September 2019.

The CCC told The Independent that its view has not changed since then.

And, of course, climate activists disagree with the view of the CCC that the UK can decarbonise while still allowing some expansion of the aviation sector.

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