At the same time that global biodiversity loss has accelerated, humanity has become an urbanised species. And the trend towards urban living is set to continue: 80% of the world’s population will live in cities by 2050—by then, the equivalent to 9 billion people. Urban development has often progressed without regard to the ecosystems of which they are a part. Now the mass of human-made things, from pavements to apartments to phones, outweighs all natural biomass, such as our oceans, trees and animals.

Building with, as opposed to over, nature has long been perceived as more of a burden than an opportunity, but this is rapidly changing. Examples of Nature-Based Solutions (NBS) in cities span from simple concepts—permeable pavements to reduce flood risks or green roofs to improve biodiversity and energy efficiency—to practical actions, such a city manager installing trees and grass along steep slopes to prevent landslides, or an urban planner protecting or restoring a nearby forest or wetland that is crucial to the city’s water supply and quality. NBS can also be seen as an effective element to prevent the heat island effect and consequently reducing energy demand. NBS that follow the circularity concept, for example by recycling nutrients, are enablers of the circular transition and can be used as tools to build new resilient, circular urban ecosystems. Conversely, the circular economy creates favourable conditions to attract more investments for NBS scaling up.

Cities can promote these solutions by developing heat-deflecting green infrastructure on buildings and in public spaces, prioritising their development on top of existing or new grey infrastructure, such as a park on top of a parking garage, or an urban garden on top of a school. Cities can also subsidise projects and technologies at both a commercial and household level, including nature-based solutions in their climate and energy plans, as well as increasing awareness of the issue and the available solutions.