At the start of the twenty-first century,
cities emerged as the source of the
greatest challenges that the planet
has faced since humans became social.
Although they have proven to be humanity’s
engines of creativity, wealth creation
and economic growth, cities have also been
the source of much pollution and disease.
Rapid urbanization and accelerating socioeconomic
development have generated
global problems from climate change and
its environmental impacts to incipient
crises in food, energy and water availability,
public health, financial markets and the
global economy1,2.