Urban areas are home to more than 54% of the global population in 2017, and this proportion is expected to reach 66% in 2050. While urban areas only cover a small proportion of the Earth's land surface (<1%), they account for 67-76% of global energy consumption and 71-76% of fossil fuel-related CO2 emissions, approximately 60% of all residential water use, and 80% of the wood used for industrial purposes. More importantly, the impacts of cities are well beyond their physical boundaries. With the rapid urbanization, cities have been the centers of major environmental problems. Meanwhile, urban areas are increasingly the engines of innovation and socioeconomic development to mitigate and adapt to local, regional and global social and environmental challenges. With more and more people living in cities, urban areas are increasingly key to regional and global sustainability, and urbanization can, and shall be part of the solution of sustainability, from local and global scale.
Ecological knowledge about urban areas has been expanding since the 1990s with the growing scientific investments in the study of cities as urban ecological systems. This knowledge progression lays the foundation for better practices on urban ecosystem management, in response to the increasing need of urban areas to develop and implement plans to increase their sustainability and resilience, and ultimately, the human wellbeing of urban dwellers.