Cities account for more than 70% of global energy-related CO₂ emissions and an estimated 50% of global waste, and are home to nearly half of the world’s population. With a rising share of the global population expected to live in urban areas in the coming decades, the impact of cities on the environment – and their vulnerability to increasingly common extreme weather – will continue to grow unless significant action is scaled up.

Cities also provide concrete solutions to addressing climate change and to minimising wider impacts on the environment. Cities demonstrate strong leadership in many fields, setting sustainability and CO₂ reduction targets that are often bolder than those of national governments. They are in close contact with citizens and businesses, are knowledgeable of local conditions and are well positioned to pilot ambitious measures in key environmental areas such as spatial planning, transport, buildings, and waste and water services. In the OECD, 60% of public investment occurs at the subnational level, of which nearly a third is channelled in to transport systems, underlying the key role of cities to invest in green and resilient urban infrastructure – especially vital in the recovery from COVID-19.