The world is blessed with a brilliant and industrious UN secretary-general, and it was certainly worth tuning in last week to watch António Guterres deliver his New Year message to the planet. As season’s greetings go, it was not exactly festive.

Intercut with shots of attack choppers and bombed-out cities, the UN secretary-general discharged a one-and-a-half minute jeremiad in which we learned that inequality was deepening; global warming was out of control; xenophobia and nationalism were on the march, not to mention war, famine, pestilence and other afflictions, as though 2018 were beginning with a positive cavalry charge of apocalyptic horsemen.

He was putting out an alert, he said, a ‘red alert’ on the state of humanity. One diplomatic friend told me it was the UN’s most bloodcurdling New Year message in 30 years.

António is of course right, in that the world faces a series of interconnected challenges that require us to unite, and also to get behind the UN, to back António Guterres and his teams in every unfolding crisis: Yemen, Libya, Burma, South Sudan, north-east Nigeria, Somalia and in many other places. The UN secretary-general is bringing a much-needed drive and focus to the job. He deserves our collective support, and will get it from the UK.

It would be a shame, however, if anyone were to be so downcast by his words as to believe that the world is indeed teetering on the lip of some new dark ages. I am conscious that some people are now so hungry for bad news they might misconstrue the secretary-general’s message. They might conclude that things are genuinely going backwards. Are you inclined to that kind of pessimism? If so (and even if you aren’t), allow me to put a contrary point of view. Yes, as António Guterres says, the world has problems — largely caused by the inordinate triumphs of the human race over some of the things that made our ancestors most miserable and afraid. There is also a respectable case for saying that this is the best moment — ever — to be alive.

Wherever you look, the armies of disease are being driven in headlong rout. Never mind the victories over smallpox, or leprosy. We have virtually wiped out polio, we are zapping tuberculosis, and as for HIV patients, they now live almost as long as someone without the virus. We are making enormous progress — notably in this country — in using the body’s own immune system to fight cancer; and thousands of patients are staging recoveries that would have been thought miraculous when I was a child.

Across the world, life expectancy is increasing so fast that we are all gaining, on average, an extra five hours every 24 (I know it sounds a bit like Zeno’s paradox, as though we are fated never to make the grave, but it’s true). It is estimated that in the next 12 years the average South Korean woman will live to be 90 — the average. And our quality of life is improving: poverty, malnutrition, child mortality — they are all falling.

It can never be repeated too often that 28 years ago, in 1990, there were 1.8 billion living in absolute poverty. Today that figure has been reduced by a billion to fewer than 800,000 in poverty, and is falling — in spite of the extra billions the world has acquired in the interim. I venture to say that we are living through the most spectacular reduction in inequality — and the greatest improvement in the overall condition of mankind — since Olduvai.

Our lives are spiced, our taste buds piqued with pleasures undreamt of by our grandparents; and not only is our food much better, but we have the continuous ocular stimulation of machines enabled by an internet whose pace and convenience accelerates everywhere, even in rural England.

As a species we seem less engaged in fighting each other than ever before. It is an astonishing reflection on our international relations that in 2016 and 2017 there was not a single British soldier killed on active service anywhere in the world — for the first time in 50 years. And for the first time in 60 years there was not a single worldwide fatality involving a commercial passenger jet — a fact for which President Trump was swift to take credit.

Even the world’s potholes are disappearing. Compared with only ten years ago, the proportion of tarmac roads across the planet has risen from 53 per cent to 64 per cent — a fact that surely deserves a presidential tweet. The overall result is that our ride is literally as well as metaphorically smoother.

We (i.e. the human race) are living longer, in better health, and with higher levels of comfort, education and all-round entertainment; and that is why all the data suggests that, in so far as the concept makes any sense, people are also happier. And it is that very triumph — especially of mankind over disease — that has created and exacerbated the problems we must address.

Think about the UN secretary-general’s list. We have an arc of instability from South Asia to the Middle East to North Africa, a horrible poxy belt of civil wars and proxy wars. We have governments and societies that are struggling to provide leadership, struggling to provide unity. But, above all, they are struggling to provide a credible economic programme in the face of unprecedented large numbers of young people. That is the root problem.

It is precisely because we beat infant typhoid and diphtheria that we now have a population explosion, again, in Africa, the Middle East and South Asia; and everywhere that you find insecurity and instability you will also find huge numbers of young people with not enough by way of gainful employment. Look at Yemen, whose gun-wielding Houthi rulers are mainly under 30. Look at Egypt, or Pakistan, both of which are set to see their populations top 200 million in the next 30 years. These countries will have to create tens of millions of new jobs every year if they are to meet the needs of their young.

Of all the apocalyptic horsemen, over-population — by which I mean the growth of restless and surplus labour — is once again the hardest-charging of the lot. As a global phenomenon, it is by no means universal. Things are going the other way in Japan (where they have the highest living standards in the world) and in much of the West. And that gives us the clue about the solution.

Look at those countries where population is growing the fastest, where unemployment is highest, and where the tensions are greatest, and without exception you will find a common factor: female illiteracy.

The correlation is astonishing. Look at the high birth rate countries of sub-Saharan Africa and you will find female illiteracy running at 50, 60, sometimes 70 per cent plus. In Pakistan it is 66 per cent among adult women; 34 per cent even in India. Small wonder that India’s population is set to overtake that of China, where female illiteracy has been all but eliminated.

Yes, it really is that simple. It is not only a moral outrage. It is directly contrary to the interests of world peace, prosperity, health and happiness that such a huge proportion of our population — so many women and girls — should be unable to participate, alongside their brothers, in the economic life of their country. Female education is the universal spanner, the Swiss army knife that helps tackle so many of the problems that António Guterres describes. Societies where women can read, write and do maths as efficiently as their male counterparts will be healthier, happier, more prosperous, with stabler populations and therefore with fewer alienated and maladjusted young men whose egos require them to think of women as childbearing chattels.

A few years ago I met Malala, shot by the Taleban for daring to equip herself with an education. She is a person of extraordinary intensity and persuasiveness. I have come to believe that she is basically right: that the single best and biggest thing we can do for the world is to make sure that every girl gets 12 years of full-time education.

That ambition is at the heart of UK overseas policy — shared by Penny Mordaunt’s DfID and the FCO — and will be at the heart of the Commonwealth summit in April. It is not just a campaign for fairness and freedom, but in its essential contraceptive impact it will help to fix so many other problems: not just overpopulation and poverty, but the threat of war, disorder, terrorism, climate change and the loss of habitat and species.

The lesson of the past few decades is that homo sapiens have seen off the doomsters with consummate style. Man keeps conquering the challenges, from famine to disease. But if we are to solve the problems of today, Man the wise needs to stop being such a damn fool about the education of girls.

Twelve years of full-time education is not the only answer to the world’s problems. It is not a panacea. But it is not far short.