In 1800, less than two percent of the global population lived in cities. Today one out of every two people is a city dweller and by 2050 it’s likely that over 70% of people will live in a city. The growth of mega-cities in Africa, Asia and South America, and the rebirth of post-industrial cities in Europe and North America is creating a new wave of urbanisation. Such mass urbanisation requires a rethink about how we plan and design cities. If we want the cities of the future to be sustainable and healthy places for people to live, the city of 2025 will need to look radically different.

Cities are the engines of the global economy: just 600 urban centres generate 80% of global GDP. Today, the economic power of cities is primarily found in the developed world with 20 percent of global GDP contributed by North American cities alone. However, this is changing and the trend is likely to accelerate. By 2025 the centre of growth will move to the emerging economies with cities in China, India and Latin America forming the largest city economies supplanting cities in Europe and North America from the list.

Cities consume 75% of the world’s natural resources, and produce more than 60% of greenhouse gas emissions. As a result, while the economic power of cities continues to grow, they remain vulnerable to the by-products of their success.

Rapid urbanisation is placing strains on the economic, environmental and social fabrics of cities. Challenges caused by a growing population such as traffic congestion, pollution and social tensions as well as diseases such as cancer, obesity and depression represent a growing challenge to policy makers.

Climate change poses a new and worrying challenge for cities. Already 50% of cities are dealing with its effects, and nearly all are at risk. Over 90% of all urban areas are coastal, putting most cities on earth at risk of flooding from rising sea levels and powerful storms.

Our cities are also home to a sizeable and increasing older population. By 2050 there will be two billion people aged over 60 worldwide, a 250% increase on today’s figures. Many of these people will live in cities. In developed countries, 80% of older people are expected to live in cities by 2050, while cities in developing countries will house a quarter of the older population.

Japan has faced this population change earlier than many countries and faces an enormous challenge with extra pressure on public services and appropriate housing. With more than 30% of the Japanese population aged over 60 – far higher than any other country – Japanese architects and planners have taken a major role in adapting urban environments to support healthy ageing of populations. This experience will soon be of global interest – by 2050, there will be another 64 countries where over 60s represent over 30% of the population.

This combination of environmental pressures, changing economic patterns and demographic change means that the cities of the future will need to be designed to operate differently. These challenges also present with them huge opportunities. With the right focus and resources, cities can become more sustainable – urban planning, design, technological and governance models could all facilitate this.