Neil O’Brien is Chairman of the Conservative Party’s Policy Board, and is MP for Harborough.

“The future is already here – it’s just not evenly distributed” – William Gibson

Over the last year, I’ve been around a lot to put our baby son to bed. Just before he’s finally tucked into his cot, he likes to go look at his little orange night light. We sit around for a bit in the dark, like cavemen around a campfire, with the warm glow reflected on our faces.

Sometimes I think about what the world will be like when he is old. Born in 2019, he has a decent chance of seeing the century’s end. What will the world be like?

Prediction is hard even in the short term. Decca records refused to sign the Beatles, believing that “guitar music is on the way out”. United Artists turned down Ronald Reagan to play the President in their 1964 movie “The Best Man”, insisting that he “just doesn’t have that presidential look.”

In 1996 a publisher rebuffed JK Rowling’s draft of Harry Potter, insisting “children just aren’t interested in witches and wizards anymore”. But there’s one bit of crystal ball gazing that isn’t completely balls: demographics.

Other things being equal, 43 year olds turn into 44 year olds.  While trends in migration, health and birthrates can swing the supertanker in different directions, we can see roughly where we are heading.

When my father was born, there were fewer than 2.5 billion people in the world.  When I was born there were 4.3 billion. When our younger one was born, there were 7.7 billion.

While for the world as a whole, the population is still rising, the pace of growth has slowed dramatically. Global population growth fell from two per cent a year during the late 1960s to one per cent now, and falling fast.

The UN suggests the world will arrive at peak population of about 11 billion by the century’s end. We’re already arriving at what Hans Rosling called “peak child”: while the global population is still rising, the number of children is topping out.  Over the last decade the total population grew 12 per cent but the number of under of five year olds by only five per cent, with growth slowing fast.

Of course, these numbers conceal massive shifts around the world. In the rich world, populations have levelled off – or would have done so if it weren’t for migration.

But in poorer countries, the population is still zooming up, fastest of all in Africa. In 2010 there were a billion people across the continent. Now there’s more than 1.3 billion.  The UN expects it to hit two billion by 2038.

The implications are massive.  Today, southern European states are struggling to control and deal with the movement of people north across the Med in search of a better life. Unless things can change for the better in Africa, the issues could soon be doubled in magnitude.

In the rich world, it’s the opposite story. Japan is the oldest country.  The population peaked in 2010 and has fallen since. The Japanese are rolling out robots in nursing homes, offices and schools to cope.

China is teetering at the point where the population will stop growing and start shrinking.  India will overtake it to have the world’s largest population in the middle of this decade, and by mid-century there will be 300 million more people in India than China.

Around the west countries face very different futures.  The UN’s central prediction sees the US population growing another 15 per cent by 2050. But in Europe it’s a mixed picture.  The UK population is expected to grow by nine per cent and France by four per cent.  But Germany is expected to shrink by four per cent, Spain by seven per cent, Italy by ten per cent and Poland by 15 per cent.  That’s one reason the French Institute for International Affairs warned the continent faces the “exit ramp of history” without change.

And the total growth is only part of the story.  Broadly speaking, when the share of the population of working age is increasing, countries get an economic tailwind, which turns into a headwind and slows them down when the share of working age starts falling. On average, and unsurprisingly, countries where the working age share is growing see GDP per head growing faster.

That’s something that we don’t take into account enough when we try and work out which economic policies work.

In Japan, in 1995 two thirds of the population were working age.  In about 20 years time, it will be less than half.  Japan’s had a rough couple of decades, but then again, it’s tough to grow your economy when fewer and fewer people can work.

While the share of the population who are working age will fall three per cent in the UK and US over the next 20 years (causing big challenges) in China the decline will be steeper – eight per cent.

One of the reasons Beijing are trying to grab for dominance in every industry now is that they are in a demographic race against time. Meanwhile, neighbouring India will see a growing share in the working age, and Africa massively so.  The tailwinds will be with them.

Similar tailwinds and headwinds are facing different parts of Britain too. Local authorities which had larger proportions of pensioners 20 years ago saw their proportion of pensioners grow faster: we are diverging by age, with the young clustering in cities and older people heading for the coast. Today, there’s just one local authority where more than a third of people are pensioners. By the 2040s there will be 53, with big implications.

One influence will be migration. Polls in the U.K. suggest few people want more migration, and more want reduced migration.

Many countries have some kind of population policy.  China has unwound its famous ‘one child’ policy, but it’s now making little difference. Getting richer has reduced the birthrate more than formal rules did.

Countries in Eastern Europe facing depopulation such as Hungary and Poland have launched a raft of pro-natal policies, while Greece last year launched a 2,000 euro ‘baby bonus’, described as a measure for “national preservation” by one minister. France has introduced some measures to help larger families while In the US, there is a lively discussion about the falling birth rate.

After a bump up in the late noughties, the U.K. birth rate here has fallen back over the last couple of years to near record lows – so perhaps some of the same debates will come here as we try to cope with our ageing society. In England, about 29 per cent of births are to mothers born overseas, and higher fertility rates among those born abroad have propped up the birth rate till now – but in recent years the gap has been shrinking.

British people are currently having fewer kids than they say they would like to, and policy can make a difference to how many children people have.  And for many decades policies in the UK have not been particularly child-friendly.  We used to recognise children in the tax system until the 70s.  Perhaps by the time my son has grown up we’ll have gone back to the future.

Some say the ageing of the global population will lead to a “geriatric peace” with less conflict. Others worry about global population decline in the longer term. Though we can’t be sure what impacts all these demographic trends will have, we can see in them a bit of what tomorrow’s world will look like.