A zero-carbon city is a goal of city planners that describes a significant reduction in carbon use by a city. The term describes a range of carbon reduction, ranging from a city that generates as much or more carbon-free sustainable energy as it uses, to a city that manages greenhouse gas emissions and reduces its carbon footprint to a minimum (ideally 0 or negative) by using renewable energy sources, by reducing 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. As of 2019, 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. As of 2022, 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 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. An established modern city attempting to achieve net-zero status needs to assess seven key provisioning systems, for energy, transportation-communications, food, construction materials, water, green infrastructure, and waste-management. Strategies for reaching net zero include developing renewable energy supplies, reducing energy and resource use through better urban design and lifestyle changes, reducing waste, and creating green spaces and carbon sinks to remove carbon from the atmosphere. Approaches to sustainable urban planning of zero carbon cities increasingly emphasize the use of locally sourced food, energy, and renewable resources. Some city planners have designed zero-carbon cities from scratch, instead of using and adapting established cities. This gives city planners greater control over all aspects of city design and how each city can contribute to being without carbon emissions. Such design enables the city to benefit from economies of scale and from construction options that might not be feasible in a city with existing structures. Such zero-carbon cities maintain optimal living conditions and economic development while eliminating environmental impact.
Guiding principles Net zero is a scientific concept that can be defined in terms of measurable targets. It can provide a frame of reference for understanding and assessing the impact of actions to address climate change. To be used as a framework for climate action, it must be operationalised and measured as part of the ongoing activities of social, political and economic systems. Time scale is an essential factor driving the urgency of net zero interventions. The impact of carbon emissions on surface warming of the planet is monotonic, near-linear (as of 2021) and long term. Attempts to achieve net zero must therefore be long term plans, maintained over multiple decades. The goal of net zero is to achieve a state of balance that can be maintained over multiple decades to centuries. Scientists can measure ongoing changes in the global atmosphere and estimate carbon budgets, but identifying and operationalising interventions occurs at multiple levels worldwide. As a frame of reference for decision-makers, global impact must be translated into definable targets for entities at national, subnational, corporate, organizational and individual levels. In practice, determination of net-zero targets has been self-regulated and voluntary. Entitles set and achieve goals, some participating in voluntary campaigns and initiatives such as the Paris Agreement, the United Nations Race to Zero campaign, Cities Race to Zero, the Net Zero Asset Owners Alliance, and the Science Based Targets initiative. Regular global progress assessments, including those of independent global initiatives such as CDP and the Transition Pathway Initiative (TPI), provide a form of feedback. As of 2022, over 1000 cities, including 25 megacities worldwide and 100 cities in the United States, are part of Cities Race to Zero. While the setting of targets is key, it must be followed up through effective mechanisms for governance, monitoring, accountability and reporting. Long-term goals must be translated into practical near-term actions, with detailed plans and methods for establishing baselines, measuring outcomes and assessing impacts. In many ways, cities are in a critical position to address climate issues effectively: they are large enough to benefit from economies of scale, and close enough to actual problems to focus on developing real implementable strategies. As demands on their infrastructures increase, they have a strong incentive to address issues and find and share solutions. Seven aspects of net zero have been identified as highly important to its successful use as a framework for climate action. These have relevance to the development of net zero cities.
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