Humanity facing the challenges of the twenty-first century

The whole Earth, round and blue, with swirling white clouds, the brown African continent in the centre and the white Antarctic ice cap at the bottom. — The Earth photographed by the Apollo 17 crew on the way to the Moon, 7 December 1972: Africa, Antarctica and the Arabian Peninsula can be seen. NASA, Apollo 17 crew, Public domain (NASA), source

⚠ This page is reviewed every year.

The world’s population passed eight billion on 15 November 2022. The forecast for what comes next has been revised three times in five years.

This page will age faster than any other on this site. Better to say so from the outset.

The other pages deal with what has happened. This one deals with what is happening now, and with what might come about. These are not the same kind of claims, and they are not checked in the same way.

So let us begin with exactly that.

A number, revised three times in five years

On 15 November 2022, the world’s population passed eight billion people. In 2024, it stood at about eight billion two hundred million.¹

We now need to look at what the United Nations demographers have projected for what comes next, and at how their projection has changed.

In 2024, they announced a peak of about ten billion three hundred million in the mid-2080s, followed by a slow decline to ten billion two hundred million by the end of the century.²

That is not what they said before. For the year 2100, this is six per cent fewer — about seven hundred million people — than was anticipated ten years earlier.³

That leaves the most striking change. About ten years ago, the same demographers put the probability that world population growth would end during this century at 30%. In 2024, they put it at 80%.⁴

Did they get it wrong?

No. Understanding why is the last tool this encyclopaedia provides.

Two closely related notions must be told apart.

A measurement says what is. We count, we weigh, we take a census. Eight billion two hundred million inhabitants in 2024 is a measurement — and it rests, moreover, on nearly two thousand censuses.

A projection says what would happen if current trends were to continue. It is not a prediction: it is a calculation under a condition.

The condition has shifted. In several very large countries, the number of children per woman has fallen faster than expected. In 2024, a woman gives birth, on average worldwide, to one child fewer than in 1990. The projection has therefore changed — not because the calculation was wrong, but because the world that was fed into it has changed.⁵

A projection that is revised is not a wrong projection. It is a calculation whose data have been updated.

Another point deserves attention. The authors do not just say 80%: they specify that the peak would come between the mid-2060s and the year 2100. A range of thirty-five years.⁶

They state their uncertainty. This is the third time in this domain: the three hundred and fifteen thousand years “give or take thirty-four thousand”, the “about” of the historians who count the crossings, and now this eighty per cent.

Those who state their margin deserve trust.

One last detail helps to explain why the population keeps growing even though births are falling. The number of women of childbearing age, for its part, is still rising — because they were born when families were larger. Today’s population drives tomorrow’s, even if everyone has fewer children. Demographers call this population momentum.⁷

Present-day figures, and what they count

A few numbers that appear elsewhere on this site are gathered here. Each comes with what it counts, because a figure without its definition means nothing.

Hunger. Of the order of six hundred and fifty million people, or a little under eight per cent of humanity. This figure is revised every year, sometimes by several tens of millions, and it is often given as a range.
Fish. According to a fixed list of stocks monitored since the 1970s: 62.3% are fished at a sustainable level. But if one counts not the stocks but the fish actually caught: 76.9%. Two figures, two ways of counting, and neither is wrong.
Languages. About 42% of living languages are classed as endangered.
Child labour. Of the order of one hundred and forty million — but this figure rests on an economic definition of work, and therefore leaves out a large part of household chores, which fall mainly on girls.
Indigenous peoples. About 6.2% of the world’s population, and a far higher share of the people living in extreme poverty: 18.2% according to the World Bank, nearly 19% according to the International Labour Organization.⁸

These five lines have one thing in common: none of them can be understood without knowing what it counts. It is the lesson this site has been repeating since the beginning, and here it appears all at once.

Climate and resources: measuring the transformations

Dealing with the twenty-first century requires measuring how humanity transforms its immediate environment and how it depends on its physical limits.

Climate

The climate system is measured mainly by the average temperature at the Earth’s surface relative to the pre-industrial era (1850-1900).⁹

The measurement: The 2015-2024 decade shows an average warming of 1.24 °C (it was 1.19 °C for 2014-2023: the average rises by about 0.05 °C for each year the window moves forward).
The projection: According to the Intergovernmental Panel on Climate Change (IPCC), crossing the +1.5 °C threshold is estimated to occur in the near term (2030-2035) on current emissions pathways.
What this counts: These figures measure global averages. They do not show the local intensity of extreme events (droughts, floods), which varies greatly from region to region.¹⁰

Freshwater

The measurement: of the order of two billion people lack access to safely managed drinking water services, according to joint monitoring that is updated regularly.
The constraint: Water on Earth is abundant, but accessible freshwater accounts for less than 1% of the world total. Its distribution is very uneven and subject to seasonal variations.¹¹

Metals and minerals

The energy and technological transition relies on physical elements extracted from the ground (lithium, copper, cobalt, rare earths).

Measurement vs reserve: One must distinguish identified reserves (what is known and can be exploited under current economic conditions) from total resources (what technically exists in the Earth’s crust).
The constraint: Pressure on metals does not generally come from the definitive exhaustion of the material in the Earth, but from the time needed to open new mines, the energy cost of extraction and local environmental impacts.¹²

What works

This page must end with something other than problems — not to reassure, but because it is a measured result.

Back to fish. The global average is not good. But the situation differs from region to region.

The best-managed areas reach more than three quarters of sustainable stocks, while those in the worst shape fall to one third. Moreover, 86% of major tuna stocks are in good health.¹³

Why there and not elsewhere? Because rules exist there, based on scientists’ advice, and those rules are enforced. The FAO itself draws the conclusion: effective management leads to stock recovery and increased catches.¹⁴

This success must nevertheless be examined in full, because it has an instructive limit. Highly migratory sharks are caught largely as bycatch in these same tuna fisheries, and a much smaller share of their stocks is in good health. We have learned to manage what we wanted to catch, not what we were catching at the same time (see Entry 5.4).

The same holds for the ozone layer: thanks to the Montreal Protocol, signed in 1987 and applied internationally, the gradual elimination of harmful chemical substances is allowing a measured recovery of the ozone layer, expected by the middle of the twenty-first century.¹⁵

So this is neither a matter of fate nor a matter of individual goodwill. It is a matter of management, agreements and suitable rules, and we know what works. That is far more useful information than encouragement.

Note 1

up from 8.2 billion in 2024

Nations unies, Département des affaires économiques et sociales, World Population Prospects 2024 — Summary of Results, New York, 2024