Mr President, your excellencies, ladies and gentlemen,

An inspection of the fossil record over the last 178m years – since mammals first appeared – reveals that the average mammalian species exists for about a million years before it evolves into something else or vanishes into extinction.

Of our allotted lifespan of a million, humanity has been around for about 200,000.

In other words, we are still, collectively, a youngster.

If you imagine that million years as the lifespan of an individual human being – about 80 years – then we are now sweet 16.

We have come to that fateful age when we know roughly how to drive and we know how to unlock the drinks cabinet and to engage in all sorts of activity that is not only potentially embarrassing but also terminal.

Johnson begins his speech conventionally, if dully, by stretching back to the dawn of humanity, as many have done before to stress the momentous nature of the climate crisis, which as the Intergovernmental Panel on Climate Change noted in August is bringing about changes “unprecedented” in hundreds of thousands, and in some cases millions, of years.

But he quickly swerves into far different territory, revealing far more perhaps of the preoccupations and psyche of the prime minister himself than of the aims of Cop26 and the task the world faces.

In the words of the Oxford philosopher Toby Ord, ‘We are just old enough to get ourselves into serious trouble.’

We still cling with part of our minds to the infantile belief that the world was made for our gratification and pleasure and we combine this narcissism with an assumption of our own immortality.

We believe that someone else will clear up the mess we make, because that is what someone else has always done.

We trash our habitats again and again with the inductive reasoning that we have got away with it so far, and therefore we will get away with it again.

My friends, the adolescence of humanity is coming to an end.

We are approaching that critical turning point – in less than two months – when we must show that we are capable of learning, and maturing, and finally taking responsibility for the destruction we are inflicting, not just upon our planet but ourselves.

It is time for humanity to grow up.

Name-checking a moral philosopher is a shortcut to signalling high seriousness, and Ord is noted for his work on existential risk at the Future of Humanity Institute in Oxford. But perhaps a psychologist rather than a philosopher might have been more appropriate – Johnson has frequently been accused of narcissism, and what better way to deflect the charge than extend it to the whole of humanity?

With its extensive references to mistakes made in the name of gratification and pleasure, and a new willingness to reform, this is definitely the speech of a man on his third marriage.

It is time for us to listen to the warnings of the scientists – and look at Covid, if you want an example of gloomy scientists being proved right – and to understand who we are and what we are doing.

The world – this precious blue sphere with its eggshell crust and wisp of an atmosphere – is not some indestructible toy, some bouncy plastic romper room against which we can hurl ourselves to our heart’s content.

Daily, weekly, we are doing such irreversible damage that long before a million years are up, we will have made this beautiful planet effectively uninhabitable – not just for us but for many other species.

Good that Johnson is now listening to the warnings of scientists – as recently as December 2015, just after the landmark Paris climate agreement was signed, he was writing in the Daily Telegraph that he didn’t believe the science. He wrote then: “Global leaders [at Paris] were driven by a primitive fear that the present ambient warm weather is somehow caused by humanity; and that fear – as far as I understand the science – is equally without foundation.”

Yet by that stage, decades of repeated warnings by the world’s leading scientists were so clear that only hardcore conspiracy theorists, deceitful fossil fuel interests and highly paid newspaper columnists could pretend to disagree. Speaking to the Guardian and others on the way to New York for the UN general assembly, Johnson obliquely acknowledged his past writings, in which he trashed climate science and renewable energy repeatedly, though characteristically tried to say it was much longer ago than it really was. He said: “If you were to excavate some of my articles from 20 years ago you might find comments I made, obiter dicta, about climate change that weren’t entirely supportive of the current struggle, but the facts change and people change their minds and change their views and that’s very important too.”

The facts, though, have not changed: the IPCC was set up in 1988, to investigate the clear likelihood that human actions were causing changes to the climate. The scientific evidence was forceful enough even then to bring Johnson’s predecessor, Margaret Thatcher, to the UN the following year to call for urgent action. Quoting Charles Darwin and Paradise Lost as well as the latest science, her speech – read it here, for a contrast with Johnson’s effort – helped lead to the signing of the UN Framework Convention on Climate Change, parent treaty to the Paris accord, in 1992. Successive IPCC reports made the science clearer still, and by 2007, the last major IPCC report before Paris, the fourth IPCC report recorded more than 90% certainty of our fossil-fuelled damage to the climate.

The obfuscation and delay fomented by fossil fuel interests, and amplified by their media helpers, after the UNFCCC was signed are the major reasons we are facing calamity today.

And that is why the Glasgow Cop26 summit is the turning point for humanity.

We must limit the rise in temperatures – whose appalling effects were visible even this summer – to 1.5C.

We must come together in a collective coming of age. We must show we have the maturity and wisdom to act. And we can.

Even in this feckless youth we have harnessed clean energy from wind and wave and sun. We have released energy from within the atom itself and from hydrogen, and we have found ways to store that energy in increasingly capacious batteries and even in molten salt.

We have the tools for a green industrial revolution but time is desperately short.

Two days ago, in New York we had a session in which we heard from the leaders of the nations most threatened by climate change: the Marshall Islands, the Maldives, Bangladesh and many others. And they spoke of the hurricanes and the flooding and the fires caused by the extreme meteorological conditions the world is already seeing.

And the tragedy is that because of our past inaction, there are further rises in temperature that are already baked in – baked is the word. And if we keep on the current track then the temperatures will go up by 2.7C or more by the end of the century.

And never mind what that will do to the ice floes: we will see desertification, drought, crop failure, and mass movements of humanity on a scale not seen before, not because of some unforeseen natural event or disaster, but because of us, because of what we are doing now.

And our grandchildren will know that we are the culprits and that we were warned and they will know that it was this generation that came centre stage to speak and act on behalf of posterity and that we missed our cue and they will ask what kind of people we were to be so selfish and so shortsighted.

In just 40 days time we need the world to come to Glasgow to make the commitments necessary.

Johnson’s invocation of some of the poorest and most vulnerable countries is key here. The UNFCCC process is unlike the cabals of the powerful, like the G7 or the recent Aukus pact, where Johnson likes to perform. At the UNFCCC Cops – conference of the parties – every country, even the smallest, has an equal say, and consensus is required for agreement. That means the UK will have to form the broadest coalition possible of developing countries to have any hope of success. As Mary Robinson, the former UN climate envoy and chair of the Elders group, said earlier this year: “The poorest countries are the moral authority at the Cop, they drive the urgency, they drive the credibility. You need them fully behind the UK presidency to get the good ambition needed.”

And we are not talking about stopping the rise in temperatures – it is alas too late for that – but to restrain that growth, as I say, to 1.5C.

And that means we need to pledge collectively to achieve carbon neutrality – net zero – by the middle of the century.

And that will be an amazing moment if we can do it because it will mean that for the first time in centuries humanity is no longer adding to the budget of carbon in the atmosphere, no longer thickening that invisible quilt that is warming the planet, and it is fantastic that we now have countries representing 70% of the world’s GDP committed to this objective.

But if we are to stave off these hikes in temperature we must go further and faster – we need all countries to step up and commit to very substantial reductions by 2030 – and I passionately believe that we can do it by making commitments in four areas – coal, cars, cash and trees.

I am not one of those environmentalists who takes a moral pleasure in excoriating humanity for its excess. I don’t see the green movement as a pretext for a wholesale assault on capitalism. Far from it.

The whole experience of the Covid pandemic is that the way to fix the problem is through science and innovation, the breakthroughs and the investment that are made possible by capitalism and by free markets, and it is through our Promethean faith in new green technology that we are cutting emissions in the UK.

When I was a kid we produced almost 80% of our electricity from coal; that is now down to 2% or less and will be gone altogether by 2024.

We have put in great forests of beautiful wind turbines on the drowned prairies of Doggerland beneath the North Sea.

In fact we produce so much offshore wind that I am thinking of changing my name to Boreas Johnson in honour of the North Wind.

And I know that we are ambitious in asking the developing world to end the use of coal power by 2040 and for the developed world to do so by 2030, but the experience of the UK shows that it can be done and I thank President Xi for what he has done to end China’s international financing of coal and I hope China will now go further and phase out the domestic use of coal as well, because the experience of the UK shows it can be done.

No mention of the fact that Johnson’s government is also hoping to exploit more of what lies under the North Sea, with a new round of licensing for oil and gas fields, and legal battles in attempts to open the vast Cambo oilfield near Shetland. The International Energy Agency has said all new prospecting and development of oil, gas and coal must cease from this year to stay within 1.5C, but the UK is arguing developments can go ahead subject to hazy promises of a “climate checkpoint”. And the potential for a new coal mine in Cumbria is still live, even while the prime minister is urging China to close its mines.

And when I was elected mayor of London only 13 years ago, I was desperate to encourage more electric vehicles and we put in charging points around the city.

And I am afraid that in those days they were not greatly patronised.

But the market in EVs in the UK is now growing at an extraordinary pace – maybe two thirds every year – and Nissan is sufficiently confident to invest GBP1bn in a new EV factory and a gigafactory for the batteries.

And that is because we have set a hard deadline for the sale of new hydrocarbon ICEs of 2030 and again we call on the world to come together to drive this market so that by 2040 there are only zero-emission vehicles on sale anywhere in the world.

And you can make these cuts in pollution while driving jobs and growth: we have cut our greenhouse gas emissions by 44% in the last 30 years while expanding our GDP by 78%.

And we will now go further by implementing one of the biggest nationally determined contributions – the NDC is the pledge we ask every country to make in cutting carbon – going down by 68% by 2030, compared to where we were in 1990.

We are making a huge bet on hydrogen, we are expanding nuclear, we are helping people to reduce their own household CO2.

We are working towards Jet Zero – the first large carbon-free passenger plane.

Political leaders love talking about whizzy new technology, and Johnson’s favourites are hydrogen and nuclear. But we should not forget that most of the technology we need to get to net zero by 2050 is already available, and according to the International Energy Agency we can get to a 45% cut in global emissions by 2030 – the key number for staying within 1.5C – with technologies such as renewable energy, energy efficiency and electric vehicles, that are already available and in widespread use today.

Politicians may find shiny new things more exciting to talk about, but it’s the hard graft of rolling out unsexy equipment such as home insulation and heat pumps that is needed to cut the UK’s emissions in line with Johnson’s targets. Unfortunately, that has stalled with the Treasury’s scrapping of the green homes grant, and there is currently no real plan for the UK to cut the 14% of its emissions that come from home heating.

And we also recognise that this is not just about using technical fixes for CO2: we need to restore the natural balance, we need to halt and reverse the loss of trees and biodiversity by 2030, and that is why we in the UK are committed to beautifying the landscape, strengthening our protection against flooding, by planting millions more trees.

We must also work towards the crucial Kunming summit in China and I call on all nations to follow the example of Imran Khan, who has pledged to plant 10bn trees in Pakistan alone. And we in the developed world must recognise our obligation to help.

We started this industrial revolution in Britain: we were the first to send the great puffs of acrid smoke to the heavens on a scale to derange the natural order.

And though we were setting in train a new era of technology that was itself to lead to a massive global reduction in poverty, emancipating billions around the world, we were also unwittingly beginning to quilt the great tea cosy of CO₂ and so we understand when the developing world looks to us to help them and we take our responsibilities.

And that’s why two years ago I committed that the UK would provide GBP11.6bn to help the rest of the world to tackle climate change and in spite of all the pressures on finances caused by Covid, we have kept that promise to the letter.

And I am so pleased and encouraged by some of the pledges we have heard here at UNGA, including from Denmark, and now a very substantial commitment from the US that brings us within touching distance of the $100bn pledge.

Johnson says the UK’s climate finance pledge has been fulfilled “to the letter” – what he doesn’t mention is that this has come while dismantling the UK’s broader pledges of overseas aid to developing countries. The UK’s spending on overseas development aid, set at 0.7% of GDP under Johnson’s predecessor David Cameron, was slashed to 0.5% of GDP, wiping billions a year off and causing projects around the world to be scrapped.

That Johnson, preparing for the UK’s hosting of Cop26, would preside over such a cut, at a time when poor countries are also suffering the impacts of the Covid-19 pandemic, and the accompanying recessions in many countries, has astounded observers around the world. Alok Sharma, the UK cabinet minister who will preside over Cop26, said in August that the cut “comes up from time to time, but generally it is not raised by governments. It is raised by civil society groups.” But developing countries have raised it frequently in conversations with the Guardian and are clear that it has cast a pall over the talks, the prospects for a satisfactory outcome on climate finance, and the trust that developing countries place in the UK as president of the talks.

But we must go further, and we must be clear that government alone will not be able to do enough. We must work together so that the international financial institutions – the IMF, the World Bank – are working with governments around the world to leverage in the private sector, because it is the trillions of dollars of private sector cash that will enable developing nations – and the whole world – to make the changes necessary.

It was the UK government that set the strike price for the private sector to come in and transform our country into the Saudi Arabia of wind, and only yesterday the UK’s first sovereign green bond raised GBP10bn on the markets, from hardheaded investors who want to make money.

And these investments will not only help the countries of the world to tackle climate change: they will produce millions and millions of high wage, high skill jobs, and today’s workforce and the next generation will have the extra satisfaction of knowing that they are not only doing something useful – such as providing clean energy – but helping to save the planet at the same time.

And every day green startups are producing new ideas, from feeding seaweed to cows to restrain their traditional signs of digestive approval, to using AI and robotics to enhance food production.

And it is these technological breakthroughs that will cut the cost for consumers, so that we have nothing to fear and everything to gain from this green industrial revolution.

And when Kermit the frog sang It’s Not Easy Being Green, I want you to know he was wrong – and he was also unnecessarily rude to Miss Piggy. We have the technology: we have the choice before us.

Sophocles is often quoted as saying that there are many terrifying things in the world, but none is more terrifying than man, and it is certainly true that we are uniquely capable of our own destruction, and the destruction of everything around us.

But what Sophocles actually said was that man is deinos and that means not just scary but awesome – and he was right.

We are awesome in our power to change things and awesome in our power to save ourselves, and in the next 40 days we must choose what kind of awesome we are going to be.

I hope that Cop26 will be a 16th birthday for humanity in which we choose to grow up, to recognise the scale of the challenge we face, to do what posterity demands we must, and I invite you in November to celebrate what I hope will be a coming of age and to blow out the candles of a world on fire.

See you in Glasgow.

Johnson ends in typical fashion, invoking Kermit the Frog and Sophocles in almost the same breath. Political leaders around the world, and their advisers, are less used to such Johnsonian flights of fancy than the British public, so it is safe to say they will be looking harder at what the UK does than what the prime minister says.

The rhetoric may soar between Greek tragedy and the Muppets, but the decisions the government has taken – cutting overseas aid; continuing the expansion of oil and gas, and perhaps a new coalmine, in the UK; dropping references to the Paris temperature goals from the Australian trade deal; forming the Aukus defence pact with climate rogue Australia, and so offending ally France and the pivotal player at the Cop26 talks, China, in doing so – will do far more than any words of the prime minister at UNGA to set the diplomatic tone for Cop26.