Heathrow Airport launched its public consultation on plans for a third runway barely a week after the government laid historic legislation to introduce a target for net-zero greenhouse gas emissions in the UK by 2050.

Common sense might suggest that massive expansion at the UK’s single largest source of carbon emissions cannot possibly be consistent with plans to eradicate Britain’s net contribution to climate change. But the consultation documents assure us that there will be no increase in carbon emissions from the airport’s operations after 2022 – although there will be a 50 per cent increase in flights. What kind of magic is being used to square this circle?

The basis for the Net Zero legislation is a detailed piece of analysis from the Government’s statutory advisors, the Committee on Climate Change (CCC), published in May this year. But the Net Zero legislation for this target departs from the CCC’s advice to the Government in two critical ways.

First, the Net Zero legislation opts to continue excluding shipping and aviation emissions from the UK’s formal carbon budgets, instead insisting that “there is a need for further analysis and international engagement”. Second, it leaves the door open for future governments to meet this target through offsetting.

Offsetting is problematic in principle – it actively defers structural change in high carbon sectors. It’s also demonstrably ineffective in practice. Less than 15 per cent of offsets under the United Nations’ flagship Clean Development Mechanism were found to have actually reduced emissions, for example. These shortcomings are why the CCC explicitly advised the Government against using offsets to meet the UK’s Net Zero target.

As a result of these loopholes, Heathrow is able to claim in the headlines that there will be no increase in emissions from its expansion plans – because the nearly 40 per cent extra emissions that will result from the additional flights (hidden in the consultation documents’ small print) will all be magically disappeared through international offsetting.

Heathrow’s summary of environmental impacts is also emphatic that “expansion at Heathrow is not considered to materially affect the ability of the Government to meet UK carbon reduction targets.” This is very important to them. Not because they are bothered about meeting the targets, but because the policy that gave the green light to Heathrow expansion last summer stipulated that this – a material risk to carbon budgets – is the only way in which it will be possible to challenge planning permission for the new runway on climate change grounds.

So although the British public are being nominally consulted on the airport’s plans to expand, the biggest, most obvious problem with these plans – the fact that they will greatly exacerbate the climate crisis – will not be considered a legitimate complaint, and any responses pointing this out will be disregarded. Aviation emissions aren’t included in carbon budgets, ergo increasing these emissions can’t threaten our ability to meet the budgets, ergo expansion cannot be challenged on climate grounds. Seen in context, it is clear that the UK’s core climate legislation has been doctored specifically so it doesn't represent an obstacle to the expansion plans of one of the most carbon intensive sectors of the economy.

In many ways, the official dissembling around Heathrow expansion and Net Zero is a perfect microcosm for the Conservative government’s response to climate change to date. They accept the science, sure; look, they will even legislate for ambitious targets 30 years in the future, when they will all be dead. What they cannot do is process the meaning of the science for society and the profound implications for government – much less implement any actual policies, inconvenience any corporations, or spend any money in response to what we have all agreed is definitely a crisis.

In fairness of course, Labour has its own problems when it comes to Heathrow’s third runway. Last summer, 119 Labour MPs voted with the tories for expansion, helped along by a friendly shove from Len McCluskey and Unite, who want more jobs for baggage handlers. Less than a year later, many of those same MPs confusedly rocked up to support Labour’s opposition day debate declaring a climate emergency.

A vast high carbon infrastructure project like Heathrow’s expansion is exactly the moment in confronting the climate crisis where reality bites, for politicians and wider society alike. Our collective ability to reflect on the wisdom of this project is a litmus test of our ability to rise to the epic challenge of environmental breakdown. If this runway is built, it will be a sure sign that we are incapable of mounting an effective response to the unfolding crisis. It will be a portent of doom.

But I still believe we can do it. As one caller to Five Live Breafkasts’ radio phone-in yesterday put it: “What I can’t see is why climate change means I have to get rid of my gas boiler, but rich folks down South get hundreds more planes to do all their flying?”

Leo Murray is director of innovation at 10:10 climate action, and advocates for a frequent flyer levy at afreeride.org