Johann Hari: A turning-point we miss at our peril

We have the choice of burning all the oil left and hacking down all the remaining rainforests - or saving humanity

Sometimes, there are hinge-points in human history – moments when we have to choose between an exuberant descent into lunacy, and a still, sober voice offering us a sane way out. Usually, we can only see them when we look back from a distance. In 1793, the great democrat Thomas Paine said the French Revolution shouldn't betray its principles by killing the King, because it would trigger an orgy of blood-letting that would eventually drown them all. They threw him in jail. In 1919, the great economist John Maynard Keynes said the European powers shouldn't humiliate Germany, because it would catalyse extreme nationalism and produce another world war. They ignored him. In 1953, a handful of US President Dwight Eisenhower's advisers urged him not to destroy Iranian democracy and kidnap its Prime Minister, because it would have a reactionary ripple effect that lasted decades. He refused to listen.

Another of those seemingly small moments with a long echo is happening now. A marginalised voice is offering us a warning, and an inspiring way to save ourselves – yet this alternative seems to be passing unheard in the night. It is coming from the people of Ecuador, led by their President, Rafael Correa, and it would begin to deal with two converging crises.

In the four billion years since life on Earth began, there have been five times when there was a sudden mass extinction of life-forms. The last time was 65 million years ago, when the dinosaurs were killed, probably by a meteor. But now the world's scientists agree that the sixth mass extinction is at hand. Humans have accelerated the rate of species extinction by a factor of at least 100, and the great Harvard biologist EO Wilson warns that it could reach a factor of 10,000 within the next 20 years. We are doing this largely by stripping species of their habitats. We are destroying the planet's biodiversity, and so we are making the natural chains that keep us alive much more vulnerable to collapse. This time, we are the meteor.

At the same time, we are dramatically warming the atmosphere. I know it has become terribly passé to listen to virtually all the world's scientists, but I remember the collapsing glaciers I saw in the Arctic, the drying-out I saw in Darfur, and the rising salt water I saw in Bangladesh. 2010 was the joint-hottest year ever recorded, according to Nasa. The best scientific prediction is that we are now on course for a 3ft rise in global sea levels this century. That means goodbye London, Cairo, Bangkok, Venice and Shanghai. Doubt it if you want, but the US National Academy of Sciences – the most distinguished scientific body in the world – just found that 97 per cent of scientific experts agree with the evidence.

So where does Ecuador come in? At the tip of this South American country there lies 4,000 lush square miles of rainforest where the Amazon basin, the Andes mountains and the equator come together. It is the most biodiverse place on Earth. When scientists studied a single hectare of it, they found it had more different species of tree than the whole of North America put together. It holds the world records for different species of amphibians, reptiles and bats. And – more important still – this rainforest is a crucial part of the planet's lungs, inhaling huge amounts of heat-trapping gases and keeping them out of the atmosphere.

Yet almost all the pressure from the outside world today is to saw it down. Why? Because underneath that rainforest there are almost a billion barrels of untapped oil, containing 400 million tones of planet-cooking gases. We crave it. We howl for it. Unlike biodiversity and a safe climate, it's tradable for cash.

Here is a textbook example of what is driving both the sixth great extinction and global warming. We have been putting short-term profits for a few ahead of the long-term needs of our species. Every rainforest on Earth is being reduced to the money that can be stripped from it: yesterday, Brazil's Chamber of Deputies voted to slash the amount of the Amazon that must be preserved by landowners. Except this time, for the first time, the people of Ecuador have offered us an alternative – a way to break this pattern. Alberto Acosta, the former energy minister who drew up the plan, calls it a punto de ruptura – a turning point, one that "questions the logic of extractive development" that drilled us into this species-swallowing hole.

Here's the offer. The oil beneath the rainforest is worth about $7bn. Everybody knows that a stable climate, biodiversity and functioning lungs are worth far more than that. But until now, nobody has been willing to pay. Ecuador's democratic government says that, if the rest of the world offers just half of what the oil is worth – $3.5bn – they will keep the rainforest standing and alive and working for us all. In a country where 38 per cent live in poverty and 13 per cent are on the brink of starvation, it's an incredibly generous offer, and one that is popular in the rainforest itself. As one of its residents, Julia Cerda, 45, told New Internationalist magazine: "With oil, the government just sells it to richer countries and we're left with nothing, no birds or animals or trees."

No country with oil has ever considered leaving it in the ground because the consequences of digging it up are too disastrous. This is a startling attempt to reverse one of the greatest dysfunctions in the global economic system. The market considers things like species diversity, the climate, and the rainforests to be "externalities" – factors not affected by the price and profit mechanisms, so irrelevant, and dispensable. It's a system that, as Oscar Wilde put it, "knows the price of everything and the value of nothing". The people of Ecuador are trying to find a way to get us to see the value of some of the most important things on Earth.

They first made this offer in 2006. So how has the world responded? Chile has offered $100,000. Spain has offered $1.4m. Germany initially offered $50m, then pulled out. Now President Correa is warning that they can't wait forever in a country where 13 per cent are close to starving. If they don't have $100m in the pot by the end of this year, he says, they will have no choice but to pursue Plan B – the digging and destruction of the rainforest.

If one rainforest seems a small matter to you, remember that the head of one deposed French king, the punishment of one broken country and the deposing of one Iranian prime minister seemed fairly minor once.

This, too, could be a moment where history branches into two directions. On the path to the right, we turn down the chance to restrain ourselves, and decide with a shrug to burn all the oil left in the world's soils, and hack down all the remaining rainforests. Professor James Hansen, the Nasa climatologist, explains where this ends: "We would set the planet on a course to the ice-free state, with a sea level 75 metres higher. Coastal disasters would occur continually. The only uncertainty is the time it would take for complete ice sheet disintegration."

But there is another path, where we choose to protect humanity's habitat – and are prepared to pay for it. If our governments won't accept this offer, at this late moment in these ecological crises, what are they saying about themselves – and about us?

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j.hari@independent.co.uk