Urban biodiversity also delivers important health benefits. [File photo]

"More than half the global population already resides in cities. This number is projected to increase, with 60 percent of the population living in urban areas by 2030,"said Achim Steiner, UN Under-Secretary General and Executive Director of the United Nations Environment Programme. "This report makes a strong argument for greater attention to be paid by urban planners and managers to the nature-based assets within city boundaries. Sustainable urban development that supports valuable ecosystems presents a major opportunity for improving lives and livelihoods, and accelerating the transition to an inclusive green economy,"he added.

Cities are also increasingly recognized for their role in supporting plant and animal species and diverse ecosystems. For example, over 50 percent of Belgium's floral species can be found in Brussels, while 65 percent of Poland's bird species occur in Warsaw.

Urban green spaces perform important ecosystem services, such as filtering dust, absorbing carbon dioxide from the air and improving air quality. Data from the United Kingdom shows that a 10 percent increase in tree canopy cover in cities may result in a 3-4°C decrease in ambient temperature, thus reducing energy used in air conditioning.

Urban biodiversity also delivers important health benefits. Studies have shown that proximity to trees can reduce the prevalence of childhood asthma and allergies. Sustainable urban planning, which addresses biodiversity issues along with other priorities such as poverty alleviation, employment, and housing, can bring positive effects for health and the environment.