One of the most dangerous threats to the human future in this, the Age of Perils, is … optimism.

Nowadays, if you tell the tested truth about climate science, weapons of mass destruction, global pollution, extinction or, indeed, any of the ten existential threats now closing in on humanity, you are likely to provoke one of two responses.

The first is a sober “I never knew it was that bad,” followed by “What can we do about it?”

The second ranges from “I don’t want to hear all that bad news”, to outright, hysterical abuse, in which you are labelled a ‘doomsayer’, a ‘Malthusian’, a spreader of “fake news”, a “tree hugger” or even a socialist, or a contemptible liberal!

Human society neatly divides into folk who can handle bad news – and those who can’t. People who put their hands over their ears and demand you shut up. Or, as Charles Darwin might have observed, those who are fit for survival – and those who ain’t.

How do I know this? Well, as a newspaper editor, I once decided to test the old theory that the media favours bad news over good. So, for three weeks I published nothing but good news in my paper – and watched the circulation drop by 15 per cent! When I restored the usual ratio of 60:40 bad news to good news, the circulation returned to normal. I concluded from this experiment that it was the public, not the editor, who preferred the bad news.

Why on Earth should humans, as a species, favour bad news over good? As a science writer who has closely followed human prehistory, a reasonable explanation wasn’t hard to find. We don’t prefer ‘bad’ news: we need to know about it in order to survive, to overcome looming threats or to exploit changing circumstances. Not reacting to bad news means more deaths from disease, conflict, famine, pollution, violence etc. It means the leopards will keep on eating the kids.

That’s what happened about 1.5 million years ago at a place called Sterkfontein, South Africa. Two child skulls were discovered in a bone pile of what was evidently the lair of a now-extinct form of leopard. Indentations in the rear exactly matched the leopard’s lower canine teeth, indicating it had dragged its prey around by the head.

Within almost the same archaeological layer appear lenses of ash and charcoal: pre-humans have discovered the use of fire.

It’s a safe bet they didn’t discover it in order to compete on Master Chef. Prehistorians generally accept that pre-humans overcame their own fear of fire because they observed that leopards and other predators were even more frightened of it than they were. After millions of years of being dinner it was finally: Prehumans 1, Predators nil.

However, to use fire you have to do several remarkable things: (i) look into the future and anticipate being eaten by leopards (ii) have the foresight and courage to collect fire after a lightning strike and bring it back to the home cave or shelter (iii) collect a supply of fuel and feed it constantly, 24/7/365, as you don’t have any matches.

Wisdom is defined as “the ability to think and act, using knowledge, understanding, common sense and insight”. That’s what our ancestors exercised in the case of fire – and it is clearly what we must do to overcome the far greater risks of climate change, nuclear holocaust, ecological collapse, a poisoned planet, and an exploding population with unconstrained demand for limited resources.

That little rocky hill in southern Africa marks the birthplace of wisdom. It is a solemn reminder of what we now need to do, as a species: be wise.

So how is it that humanity was able to assess and solve existential threats back then, when we were barely brighter than chimps – but seeks to demean, decry and punish those who warn us about the far greater threats which now surround us? How come our political leaders are promising ‘climate and environmental  action’ while authorising ever increasing volumes of greenhouse gases, toxic pollution and destruction of key resources like breathable air, forests, soil and water?

Some academics have argued that the public should be sheltered from the truth about the risks we now face, for fear they may become depressed and hopeless. But lying to people about the danger they are in is never a good idea. It merely spreads delusion.  Many self-described ‘optimists’, whose optimism is based on blind hope not on truth, are unable to handle bad news. They want just to simply block it out.

Optimism can be a useful attribute in a general, a politician or a business manager, providing it is based on tested fact, not on mere conjecture: it can nurture the resilience to endure tough times. Winston Churchill’s promise of “blood, toil, tears and sweat” was just such a realistic appraisal.

But remaining stubbornly ‘optimistic’ while ignoring imminent dangers to civilization and our species is a formula for disaster. It leads to procrastination, inaction and, inevitably, a vast increase in the actual risk. It decreases our fitness for survival. In short, optimism is extremely unwise and can be very dangerous.

Many ‘techno-optimists’ argue that humans are so smart we will find technical solutions to all the threats we face. And it is true that technical solutions exist to most of them. However, the real danger with unwarranted optimism is that defers the universal uptake of these technical solutions. Like Pollyanna, it insists everything is fine, so there is no need to do anything.

In this case it is the blind optimists, rather than the realistic pessimists – or doomers, as some now call themselves – who most imperil our future.

An important departure from traditional blind optimism is Pope Francis’s encyclical Laudato Si, which basically argues that if humans don’t take better care of the planet, it won’t be able to take care of us. It’s a case of one far-sighted, wise man, trying to move a conservative institution into taking the actions essential to survival. It has set a fresh example and possibly charted a new course for the world’s faiths, which are largely stumbling in the dark when it comes to existential threats. What the world needs most at this critical juncture are political and business leaders with similar wisdom.

A handful of Governments – Germany, Denmark, Sweden, Bhutan, Norway, France, possibly China – show signs of awareness of the tenfold risk we face, and the need for universal collaborative action to solve it. And likewise, a handful of corporates realise that future profits depend on business models which are sustainable, and which don’t wreck the resource or skills base they depend on. These are wise realists, not pessimists. They have a general grasp of what is coming down – though maybe not its size and speed. And they are willing to take action (though many scientists would argue it is far too little and far too slow).

Whether you self-define as an optimist, a pessimist or something in between, you, your children and grandchildren now face threats on a scale never before seen in human history. Inaction, or false optimism, will only increase the harm these threats do to us.

To overcome them humanity doesn’t need optimism or pessimism. It needs to exercise a singular attribute, that has stood us in good stead for over a million years.

We need wisdom.

• Julian Cribb