City living is growing at an astonishing rate. In 1985, two billion people lived in cities; today the number is four billion, and by 2050 there will be some six billion urban dwellers.

Cities will have to adapt. Either they can expand horizontally so that they cover a greater area, or they can adapt by growing vertically—by building more skyscrapers. Indeed, that’s how many cities in places such as China and the Middle East have coped with growing populations.

And that raises an interesting question. If trends in skyscraper construction continue, what will cities look like in the future? How will the skyscraper evolve in the next 30 years?

Today, we get an answer thanks to the work of Jonathan Auerbach at Columbia University in New York and Phyllis Wan. They have studied the historical patterns of growth in skyscraper construction and used them to predict future patterns of growth. Their results suggest that skyscrapers are set to play an even more significant role in future cities and in the lives of city dwellers.

Auerbach and Wan’s method is straightforward. They begin with a database of skyscrapers compiled by the Council on Tall Buildings and Urban Habitat in Chicago, which sets building standards and arbitrates titles such as “world’s tallest building.” For this research, Auerbach and Wan consider buildings more than 150 meters “tall.” There are 3,251 such skyscrapers in 258 cities around the world.

The researchers first characterize historical patterns the height of skyscrapers and the numbers built. It turns out the number of skyscrapers built each year has followed a remarkably stable pattern. “The number of skyscrapers exceeding 150 meters and 40 floors has risen eight percent each year since 1950,” say Auerbach and Wan.

That leads to a clear prediction. If this trend continues, some 41,000 skyscrapers will be built by 2050. That dramatically outpaces the rate at which city populations are expected to grow.

For instance, today there are around 800 skyscrapers for every billion people on the planet. “By 2050, cities will have 6,800 skyscrapers per billion people,” say Auerbach and Wan.

The historical record shows that skyscrapers have increased in height over time as well. But this follows a different pattern, mainly because taller buildings are harder to make profitable. That’s because more room has to be given over to services such as elevators, and this reduces the usable area within a building.

Nevertheless, Auerbach and Wan predict that the tallest buildings in 2025 will be about 50 percent taller than today. “The probability a new building will exceed the current tallest building, the Burj Khalifa (828 meters), is estimated to be nearly 100 percent,” say the researchers. “The probability that a new building will exceed the Jeddah Tower (1,000 meters), scheduled to open in 2020, is 77 percent.”

There is even a possibility that a mile-high skyscraper will be built. That’s long been a dream of architects, many of whom have created mile-high designs. Most famous among these is Frank Lloyd Wright’s Illinois, conceived in the 1950s as a 1,600-meter-high building with 528 stories.

A building of this size has yet to be constructed. But this analysis suggest there is 9 percent chance that the world’s tallest building in 2050 will be a mile high.

That’s interesting work, but it rests on the assumption that current trends will continue for the next 30 years.

There are all kind of reasons why that might not happen. On the one hand, social instabilities caused by climate change, disease, or war could dramatically change the planet’s economic outlook and reduce investment in tall buildings. In that case, their numbers could be significantly lower.

On the other hand, technology breakthroughs could make it cheaper and easier to build tall buildings. In that case, the numbers could be significantly higher.

One way or the other, city living is set to look very different, with important implications for city planners, policymakers, and the public in general.

Ref: arxiv.org/abs/1808.01514 : An Extreme Value Analysis of the Urban Skyline

_{This article was originally published on techreview.com. on August 20, 2018.}