Zero-carbon city

A zero-carbon city is a goal of city planners that can be variously defined. In a narrower sense of energy production and use, a zero-carbon city is one that generates as much or more carbon-free sustainable energy as it uses. In a broader sense of managing greenhouse gas emissions, a zero-carbon city is one that reduces its carbon footprint to a minimum (ideally 0 or negative) by using renewable energy sources; reducing all types of carbon emissions through efficient urban design, technology use and lifestyle changes; and balancing any remaining emissions through carbon sequestration. Since the supply chains of a city stretch far beyond its borders, Princeton University's High Meadows Environmental Institute suggests using a transboundary definition of a net-zero carbon city as "one that has net-zero carbon infrastructure and food provisioning systems". Most cities throughout the world burn coal, oil or gas as a source of energy, resulting in the release of carbon dioxide into the atmosphere, a key greenhouse gas. The development of cities is therefore intimately linked to the causes and impacts of climate change. , cities accounted for two thirds of all energy consumption and generated 70% of energy-related greenhouse gas emissions. Over 50% of the people in the world currently live in cities, a proportion that is projected to rise to 70% by 2050, and almost 80% by 2080. Urban development focused on lowering carbon is seen as an inevitable trend for sustainability in urban spaces. Underlying goals include avoiding harm to the planet and countering the impacts of climate change. , over 1000 cities worldwide have undertaken steps to transition in response to climate change as part of the Cities Race to Zero campaign, one part of a larger United Nations Race to Zero campaign. Among them are 25 mega-cities including Rio de Janeiro, New York, Paris, Oslo, Mexico City, Melbourne, London, Milan, Cape Town, Buenos Aires, Caracas, Copenhagen, Vancouver and Hong Kong. In the United States, more than 100 cities have pledged to become carbon neutral.