The planet of cities: peak population and urbanisation in the next 100 years

Greg Clark, Urbanist
Borane Gille, Head of Cities Innovation, The Business of Cities

As discussed in the first column of this series, when considering the future of cities, it is important to observe the increasing urbanisation of our people and planet. Headlines on this topic often focus on the growing importance of cities, with the world already majority urban. In this column, we will examine the whole cycle of our journey towards our human population peak, the evolution of our settlement patterns, the planetary effects, and crucially what comes after? If we observe the whole cycle, rather than just portions of it, what fresh insights might it produce about our world and its built environment?

When will the global human population start to decline?

In the summer of 2024, both the New York Times and the Financial Times provided detailed commentary on new uncertainties surrounding global population projections. In summary, demographers have, for several years, been predicting human population will numerically peak at about 10.4 billion by 2100. After that, human population would stabilise, and then begin a process of slow, predictable decline into the 2100s. There are a vast range of demographic skills and data involved in such projections, including fertility rates, life expectancy, nutrition, the observed patterns of family sizes that change with prosperity (demographic transition) and much more.

However, new analysis suggests that we may now reach human population peak sooner, with a smaller population and with a consequently more rapid decline thereafter. The latest edition of the World Population Prospects, a report published by the UN every two years, said the global population would grow from 8.2bn in 2024 to a new maximum of around 10.3bn in 2080, before declining to around 10.2bn by the end of the century.  Two additional studies (cited below) show more marked lower population projections.

The population scientists agree that the world’s population:

• will peak within this century (80% likelihood) and
• by 2100 will be smaller than what was expected ten years ago.
   

Why? According to the UN:

• People are having less children than initially expected in some of the world’s largest countries, particularly China.
• One in four people live in a country where the population has already peaked in size.
• Some countries are already starting to see their population decrease, and in the 24 countries with ultra-low fertility (less than 1.4 births per woman), returning to 2.1 births (the number of children born to women needed for population to replace itself in a given area) is very unlikely (0.1%).
• By 2080, there will be more people over the age of 65 years than under the age of 18 years.
• Immigration is projected to be the main driver of population growth in 62 countries through 2100.
• China is projected to lose over half its current population by 2100 – and return to its population size in the late 1950s (50% likelihood).
   

What does this mean for our cities and built environment?

Let’s first look at what the whole cycle might now be. Figure 2 shows the whole population cycle in a single chart revealing the multiple future scenarios between more rapid and more gentle decline.

If we map on this population curve the projections on urbanisation levels, we might see something like Figure 3 below. We can see the whole of human population up to its newly anticipated peak. We can observe the share of people living in cities within it and we can also observe the shifting distribution of urban populations across regions. We do not attempt to project much beyond the new peak in about 2080.

Planning for a post-peak population world

For those of us concerned with cities, sustainability and the built environment, several important issues arise from Figure 3.

1. Peak human population (numerical) and peak urbanisation (percentage) will be closely associated. That means the process of managing the journey to peak population will be one that is essentially about the natural environment and the built environment.
2. We will need to speed up our transition to resilient, adaptable and sustainable buildings and infrastructure. With the population peak predicted to come sooner than expected – just 56 years away – there is greater urgency and more uncertainty about what comes next. Given that much of the built environment is constructed for a 100+ year or longer life cycle, those life cycles now extend beyond the peak. Embedding flexibility in our buildings and infrastructure will be essential to plan for a sustainable peak urbanisation now, and adaptability post-peak.
3. While we can expect cities to grow and evolve in various ways in all regions of the world, Africa, Asia, and India will see the most intense urban development. The quest for sustainable urbanisation will be most keen in these regions.
4. Just as urbanisation accelerates towards 80% by 2080, and given the 50 years of rapid urban growth we are all now expecting, we need to consider two things. Not only how to build sustainable cities for population growth now, but also how to make cities that can adjust resiliently to population decline in the future. The experience of shrinking cities over the past 50 years in some regions of the world will become relevant to many others.
5. Addressing climate, biodiversity, and planetary boundaries will require understanding what the optimum distribution of population will be post peak. Lower population and changing demographics will produce multiple population decline scenarios. There will be complex issues concerning which regions of the world can sustain populations and which will manage to attract population from outside. How will population be decided in the future? Will nations compete on their immigration policies, or are alternative models possible?
    

These new projections raise many questions on how we plan cities today and how we prepare for the world beyond the peak. In this context, looking at the next 100 years helps to see the challenge of managing growth and decline sustainably within a single century.