The important thing about any agenda isn’t so much what’s on it, but what is missing. And so it is with the 21st UN climate change conference (Cop26), in Glasgow. There are some crucial issues up for discussion and negotiation: the $100bn finance promise, the 1.5C target and how to raise global mitigation ambition to meet it. But I have a proposal for something that is still firmly off the agenda, even though it would arguably do more than anything else to address the climate emergency.

The problem with Cops – and I’ve been to a few – is that activity tends to substitute for action. The atmosphere is frenetic: people rush to and fro, from meeting to meeting, negotiation to negotiation, clutching bundles of paper, phones, laptops, and (if they are lucky) a hastily grabbed, limp sandwich. Some negotiators trundle everywhere with wheeled suitcases, stuffed with printed materials from every previous Cop – so they never have to miss an opportunity to refer directly to the Bali declaration or the Berlin mandate.

It’s heaven for lawyers – but hell for everyone else. Everything hinges on wording: whether the square brackets contain “shall” or “should”, “may” or “must” becomes an all-consuming obsession. The details are so tiny they are almost fractal: dive in and you find yourself in a parallel universe of ever-expanding detail, with passionate arguments about incomprehensibly arcane sub-clauses which run for weeks, or sometimes even years. Former Maldives president Mohamed Nasheed, who I advise on climate issues, has a joke about Cop babies – that negotiators have been doing this so long that some of them have even got married and had children. It’s funny because it’s true.

The one thing that tends to get lost is the bigger picture – actually solving the climate emergency. It’s on the agenda, of course, because it’s what the meeting is meant to be about, but at the same time it’s not actually on the agenda. We might get an agreement on financing, on loss and damage, on carbon markets, on “nationally determined contributions” – the Paris pledges that are meant to deliver on the 1.5C goal – which would all be great. I’ll be the first to celebrate, and to dance on the Cop tables at five in the morning on the final weekend.

But even 1.5C is a slippery target: it is not something anyone can actually deliver, even collectively. Whether the planet’s temperature will cross the threshold of 1.5C above pre-industrial temperatures is a product of the Earth system’s response to cumulative emissions of greenhouse gases, which cannot be known precisely except in hindsight. That’s why it is framed probabilistically by scientists; for example there is a one-in-six chance that we have already exceeded the 1.5C budget as I write today.

So what might be a Glasgow climate emergency target that we actually could meet? My suggestion is extremely simple: we set a date for the worldwide exit from fossil fuels, a sort of independence day from carbon. Like all ideas that eventually become mainstream, at first sight this looks preposterous. You mean, we actually have to stop burning oil? No more petrol? No more LNG tankers plying the world’s oceans? No more giant coal machines scraping up carboniferous forests from underneath medieval villages in eastern Germany?

Yes, that’s exactly what I mean. A fossil fuels exit date forces us to confront what net zero doesn’t – that we have to actually entirely stop combusting carbon. (We also have to figure out ways to remove the excess carbon already in the atmosphere and to get everyone on largely plant-based diets, but one thing at a time.) It means there must be no more exploration for fossil fuels well before that date, because all that would be doing would be creating unwanted hydrocarbon reservoirs. It means there must be no more building of fossil infrastructure – coal-burning power stations, LNG terminals, oil refineries and so on – at least 30 years before that date, because doing so would merely be creating stranded assets.

There will, of course, be objections from carbon addicts, citing the “methadone” option of carbon capture and storage. This – which is as physically and thermodynamically implausible as the endlessly receding fantasy of nuclear fusion – has been touted for decades as a way to carry on burning our carbon cake and eating it. Yet it is still nowhere near to at-scale deployment anywhere in the world, and never will be. I’m sorry my friends, but fossil fuel freedom day means we have to leave the unburned stuff in the ground, right where the dinosaurs left it.

Of course, the date is crucial. If we set it at 2150, as Saudi Arabia would no doubt immediately volunteer, we will be well on our way to turning Earth into Venus by then. I propose 2047, far enough away for a rapid transition to zero-carbon economies to be feasible worldwide with minimal economic damage, but close enough to still give us a decent – probably 50:50 – chance of keeping the Earth from heating up beyond 1.5C. Fittingly, 2047 is also exactly a century on from the year of Indian independence in 1947, when the world’s largest democracy came into being after more than a century of British colonial exploitation. As Jawaharlal Nehru said then in his tryst with destiny speech: “At the stroke of the midnight hour, when the world sleeps, India will awake to life and freedom.”

At Glasgow we could make our own tryst with destiny, one that could save our civilisation from the carbon catastrophe that looms over us all. Imagine that evening, in August 2047, as the clock ticks towards midnight: we could all awake, as the sun breaks through the smoky ruins of the industrial revolution, to the life and freedom of independence from fossil fuels.

• Mark Lynas is a freelance writer working full-time on climate change