I don’t like to be constantly complaining about things, so let’s start with the good stuff from Wednesday’s budget announcement that air passenger duty (APD) is going to be halved on domestic flights. It won’t take long.

The best thing about it is that the cut in domestic APD will now apply only to those in the cheapest seats – “reduced rate” passengers. The Treasury had consulted on a change that would have cut GBP39 from the cost of an internal private jet flight, and GBP13 for a first-class traveller – but this didn’t happen, thankfully. It is also true that the overall direct impact on carbon emissions of this new tax incentive to domestic air travel is likely to be small; domestic flights account for just 4% of UK aviation emissions, and this cut in the tax rates won’t do much to change that.

And yet I am still banging my head on the table over this news. Why? First, it’s the symbolism of cutting taxes on the most environmentally damaging form of transport just as the UK hosts an existentially important international climate conference, Cop26. The government’s own figures show that travelling to Cop26 in Glasgow from London by plane would emit 154kg CO₂e – five and a half times more than the same journey by train. The plane here isn’t even any faster than the train; colleagues from Campaign for Better Transport recently raced this route, arriving within two minutes of one another. Per passenger kilometre, domestic flights are substantially worse for the climate than long haul, as so much of the fuel burn takes place during takeoff and landing.

Our own research at Possible shows that most people would prefer to travel by climate-friendly train than polluting plane, but cost is the main barrier. Which? recently found that domestic flights to popular UK holiday destinations are on average 50% cheaper than the rail alternative. Making these flights even cheaper with yet more tax breaks seems deeply perverse – especially as British domestic flight passengers generally have income of around double the national average.

The Treasury shtick on the domestic APD cut is that it’s about “union connectivity” – the subject of a recent government commission that concluded that regions across the UK need help to establish better transport links. But that review specifically said that its key concerns included “the appropriate rate of air passenger duty for journeys not realistic by rail”. There is only one part of the UK that this really applies to: Northern Ireland (airports in Scotland’s Highlands and Islands are already exempt from APD; regular visitors to Jersey and Guernsey may not need any further help avoiding tax). By far the most popular domestic air route in the UK is London to Edinburgh, also served by 41 trains every day. People moaning about the schlep down to Cornwall would do better to ask the government what has happened to its Integrated Rail Plan, now around nine months late. Electrification of the Cornish main line up to London, as recommended over a year ago by Network Rail in its own decarbonisation plan, would improve reliability and slash journey times through increased speed and acceleration. What journeys are “realistic by rail” depends on investment in the British rail network, and the budget has done nothing to provide clarity on this.

The real reason for the domestic APD cut is political: it is something the UK’s pandemic-struck aviation industry has been badgering the Treasury about for years, and the government wanted to be seen to throw it a bone at a difficult time for the sector. Everyone knows it won’t really do much to help. But the fact that the government ranks the symbolism of helping the aviation industry higher than the climate symbolism – incentivising people to travel short distances by the most climate-damaging mode available when the fate of the planet hangs in the balance at Cop26 – signals something disturbing about its priorities.

It also adds to the emerging picture around the troubling ideological limits to this government’s climate action. This is the thing that bothers me most about the APD tax cut. The transport decarbonisation plan published in the summer contained a foreword stressing that it was: “not about stopping people doing things: it’s about doing the same things differently. We will still fly on holiday, but in more efficient aircraft, using sustainable fuel.” But “sustainable aviation fuels” comprised less than 0.1% of jet fuel consumed in 2019, and no credible analysis expects all future jet fuel to come from sustainable sources by 2050, when the UK has committed to achieving “net zero” carbon emissions. The government’s grand net zero strategy published last week reiterated this magical thinking around aviation, and consequently its statutory advisers, the Climate Change Committee, have picked out the absence of any plan to manage growth in demand for air travel as one of the strategy’s key failings. It’s not just air travel; the UK’s climate plans have no targets for reducing fossil-fuelled vehicle miles driven on the UK’s roads either, and are perplexingly weak even on measures to reduce energy demand from buildings, despite both these things being central to any viable pathway to deep decarbonisation.

Fundamentally, the climate action challenge for government is straightforward: decarbonise everything we can, and do less of the things that we can’t. But the second half of this very basic and obvious formula is one Boris Johnson’s administration refuses to even talk about in public. Witness the farcical publication and immediate depublication of the research it commissioned on behavioural change initiatives to help people fly less and eat less meat – two insolubly high-carbon activities that meeting climate goals requires us to collectively do less of.

Domestic flights in a small island nation such as Britain should be among the easiest of the things to give up to meet the challenge of the unfolding climate crisis (indeed, France is already showing us how). But until the government has grown out of the pretence that this challenge can be met without anyone forgoing anything, we will remain locked on a course to catastrophe.

• Leo Murray is co-founder and director of innovation at climate charity Possible