The world's cities need to transform to become places where societies can thrive in the face of significant challenges. Urban environments have always seen constant change, but the rapid shift toward remote office work and the increasing incidence of climate catastrophes are damaging cities' economies and creating a need to revamp infrastructures at a much faster rate. Implementing radical structural changes could help cities reduce their vulnerability to shocks and maintain their role as centers of innovation and opportunity. Conversely, delaying changes or making poor planning and construction choices could lock in worsening livability and high carbon emissions in cities for decades to come.

Cities are exploring a variety of ways to address their economic, social, and environmental challenges and to improve their long-term resilience. The following bullets highlight a few of these approaches.

• Remaking cities as centers of community and creativity. Cities are recovering from the shocks of the covid‑19 pandemic, but remote work has severely reduced the ranks of highly paid professional workers and hurt businesses in many urban centers. For example, occupancy levels in the premier office spaces in New York, New York, are still at less than 50% of prepandemic levels, according to Kastle Systems International's Back to Work Barometer. By contrast, mobile-phone data from SafeGraph show a more promising picture for individual visits to the city, which have experienced a far‑less-steep decline. Harvard University economist Edward L. Glaeser and Massachusetts Institute of Technology Senseable City Lab director Carlo Ratti believe that the world is "witnessing the dawn of a new kind of urban area: the Playground City" ("26 Empire State Buildings Could Fit Into New York's Empty Office Space. That's a Sign." New York Times, 10 May 2023; online). According to Drs. Glaeser and Ratti, the Playground City focuses on recreation rather than on vocation, making it a place where people with a broad range of talents want to spend their free time after they finish working remotely. Drs. Glaeser and Ratti have identified six lines of actions that are crucial to the creation of such cities: experimenting and learning from big data, eliminating regulations that inhibit urban innovation, reinventing the urban core, animating the street, leveling the playing field between e‑commerce and local businesses, and involving citizens in the process of creation. In a related approach, Melbourne, Australia, has a long-term urban plan that encourages the creation of compact neighborhoods in which shopping, education, jobs, and other opportunities are within a 20‑minute walk, bicycle ride, or public-transport trip of most residents' homes.
• Coping with rising sea levels and floods. Sea‑level rise is a major threat to at least two‑thirds of the world's largest cities, including New York; Shanghai, China; and Mumbai, India. Compounding the problem, many urban centers are slowly sinking under their own weight. Hundreds of millions of people are living on land that could be partially submerged by midcentury, and UN Secretary-General António Guterres has warned that a biblical-level mass exodus of populations could occur unless nations take effective action. Many cities are revising regulations to prevent building in flood-prone areas. For example, Rotterdam, Netherlands, is building and improving levees and seawalls, and Ho Chi Minh City, Vietnam, is focusing on improving drainage systems and relocating freshwater reserves. Elevating homes to accommodate higher water levels is another approach that cities are investigating. As cities face major land losses, a more extreme strategy of managed retreat may be necessary. For example, 40% of land in Jakarta, Indonesia, now lies below sea level, and the government is building a new capital city from scratch on higher ground. Radical approaches such as building floating cities may also become common. New types of planning tools and tracking systems could aid in efforts to move large numbers of people while preserving some sense of community.
• Adapting to hotter temperatures. Global temperatures are rising quickly and could exceed the critical average threshold of 1.5°C above preindustrial levels by as soon as 2024. Many cities will become increasingly uncomfortable and perhaps unlivable. Extreme heat waves are already making working outside during the day dangerous for people in hot regions such as India. Urban planners will need to redesign and retrofit indoor and outdoor spaces to make them more climate resilient and livable. For example, Madrid, Spain, is working on one of Europe's largest urban-renewal schemes: creation of a huge urban forest that can lower the city temperature by as much as 4°C. Urban forests can improve air quality as well.
• Accelerating sustainability. Urban areas are responsible for a majority of the world's carbon emissions. Cities have long taken a leading role in transforming fossil-fuel-dominated energy systems into more flexible and distributed systems that incorporate high shares of renewable energy. To achieve ambitious net-zero goals and help limit the scale of climate catastrophes, cities need to accelerate moves to displace fossil fuels. Urban electrification and implementation of strict building codes can further reduce carbon emissions by improving energy efficiency and thermal performance, which would also make buildings more comfortable for occupants and reduce energy bills. Decentralization of food and water supplies through the use of vertical farming and wastewater recycling at commercial buildings and homes could also support sustainability efforts.

The cities of tomorrow will offer many opportunities to implement smarter technologies and services. In addition to facing disruptions relating to climate, energy, food, water, commerce, health care, and security, many cities will face the need to integrate increasing numbers of people as the global trend toward urbanization continues. Other cities may face declining populations, which will present another set of challenges. Improvements in urban governance will be essential to tackle barriers such as excessive regulation and resistance to automation to accomplish large public projects efficiently. Poor governance could waste vast amounts of money and further entrench societal inequalities. City officials will have to determine what adjustments are most beneficial and affordable, but efforts must ramp up soon to avoid the most chaotic outcomes.