Zero-carbon city

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. , 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 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. , 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.
* Sooner is better. Front-loading climate action, combined with long-term planning over years or decades, is the most cost-effective way to reach temperature targets, as well as the most flexible in the face of new information.
* Be comprehensive. Plans that tackle comprehensive rather than partial emissions reductions are becoming necessary as carbon levels reach critical tipping points. Harder-to-treat problem areas must be addressed as well as easier ones.
* Beware of over-reliance on early-stage carbon removal strategies. These are not yet well understood and may enable a "business as usual" attitude to climate change.
* Reassess and improve systems for carbon offsets. Such systems have been questioned in terms of their scientific and technical capabilities; environmental integrity; monitoring, reporting and verification structures; and social and environmental impact.
* Apply principles of sustainable development. Achieving net zero globally requires implementation of equitable and just transitions that balance social, economic and environmental objectives in areas with very different conditions.
* Focus on broad strategies for sustainability. Cities can potentially address multiple problems at once, through solutions that are nature-based, biodiversity-based and people-led. It is important to consider that parents with small children, the poor, the elderly and the disabled may experience a city differently from those who are affluent and more easily mobile.
* See opportunities. New net-zero solutions and innovation will drive economic shifts which will include opportunities for investment, renewal and growth.

There are strong similarities between zero carbon cities and eco-cities. Discussions of eco-cities tend to focus more broadly on social and environmental issues, with less emphasis on carbon monitoring and the necessity of reaching net zero energy balance.
Many of the principles proposed for developing eco-cities are also relevant to net zero cities, including revising land use priorities to create sustainable mixed-use communities; revising transportation priorities to favor foot, bicycle, cart and public transit over automobiles; increasing environmental awareness; supporting local agriculture and community gardens; and promoting recycling and resource conservation.

City infrastructure

Urban areas involve essential infrastructure for energy, transport, water, food, shelter, construction, public spaces, and waste management. Transforming cities to achieve net zero sustainability means rethinking both supply-side issues (power supplies and transportation) and demand-side issues (reducing use through better urban design and policy.) Key factors in city planning include density, land use mix, connectivity, and accessibility.

To achieve net zero, a city must collectively reduce emissions of greenhouse gases to zero and cease all practices that emit greenhouse gases. Achieving net zero sustainability also means considering sources and production of materials, and ensuring that what comes into the city travels via zero-emission transport. Appearing to reduce emissions in one location by shifting emissions-causing activities to a different location will not contribute to the global goal of a sustainable net zero environment.

Energy

To become a zero-carbon city, renewable energy must supersede other non-renewable energy sources and become the sole source of energy, so a zero-carbon city is a renewable-energy-economy city. Transitioning to a zero carbon city means examining the generation of power sources, such as renewable electricity and decarbonising electricity production.

Electricity needs are increasingly being met through the development of solar and wind power as energy sources, which are becoming the cheapest forms of power. The shift to solar power, in particular, means that energy can be produced close to its intended use. This is suited to a distributed energy infrastructure in which local areas are connected into a city-wide or region-wide electrical grid. The ability to provide a steady supply of electricity is also being supported by the development of more efficient and cost-effective battery storage technology.

Issues of equity, balance, and efficiency are all relevant to energy distribution and use. A net-zero carbon electricity grid is a necessary foundation for supply side strategies that aim to shift provisioning systems for buildings, energy use, mobility, and light industrial energy use to electric power. The development of a net-zero carbon electric grid can become the basis for transitioning key urban activities such as transportation, heating, and cooking from fossil fuels to zero-carbon electricity.

Transport

Transportation of people and goods is estimated to contribute 20% of global greenhouse gas emissions.
In terms of transport, approaches to low-carbon urban development often focus on reducing fossil-fuel based transportation, improving public transit, and creating areas of mixed use development so that people are more likely to work and shop near their homes, reducing transportation needs. A study of 274 cities worldwide suggests that compact urban development is important in both affluent mature cities and developing-country cities with emerging infrastructures, reducing urban emissions by up to 25%.

The transition from fossil-fuel-based cars and trucks to electric vehicles (EVs) is occurring globally. China has been a major center of technology growth for EVs. Vehicle-fuel technologies that can contribute to reductions in energy use include hybrid electric, plug-in electric, natural gas, and bioethanol-powered vehicles. The last diesel and gasoline cars are expected to be produced in the 2020s, with 25% or more of all vehicles worldwide being electric by 2040 as fossil fuel prices rise.

A narrow focus on electrifying vehicles can lead planners to overlook opportunities for increasing efficiency within existing systems. Good urban planning can develop an infrastructure that combines and supports initiatives in multiple areas. For example, the generation of solar power and the provision of recharge hubs near public transit can support the use of electric vehicles for both private and public transit. Another way to support use of electric vehicles might be to integrate EV charging points into lampposts.

Increasingly, city planners are looking to the use of digital technologies to create smarter and more sustainable cities. By gathering large diverse datasets and modelling the impact of possible interventions, planners hope to identify and target key aspects of energy use, air quality, and traffic for improvement. By incorporating smart measurement technology into buildings, lighting, appliances and transportation, systems can better adapt to changing conditions, reduce energy consumption, and improve city services.

Heating, cooling and cooking

Heating, cooling and cooking are also targets for improved energy efficiency and reduction of carbon emissions. Increasingly following Europe and Asia, North Americans are switching from gas or electrical resistance stoves to induction cooking. Consumers are also switching heating systems from coal, fuel oil, or natural gas to electricity-driven steam or hot water; and to air-source or ground-source heat pumps for both heating and cooling.

Food

Food production tends to be heavily dependent on fossil fuels, in the production of nitrogen fertilizer and to power agricultural machinery used in the planting, tending and harvesting of crops. The movement of food from producers to consumers also tends to involve major fossil-fuel costs, since many crops are grown far from their potential market and have a short shelf life. Many countries depend on international markets to obtain critical food supplies. Food production and supply chains are being increasingly destabilized by the effects of climate change on agriculture, the COVID-19 pandemic, and the Russian invasion of Ukraine. In the United States, at the same time that millions of Americans experience food insecurity, as much as 40 percent of food is wasted.

At the consumer level, steps towards achieving net zero include eating more local and plant-based foods, minimizing food waste, and composting remaining plant-based wastes. Consumers and investors may also choose to support companies based on their carbon footprint and transparency.

In terms of city infrastructure, initiatives to identify and redirect usable food (" food rescue"), to separate waste streams, and to improve handling of food waste are all important.
In low-income countries, small-scale and household-level biogas systems are being used to convert wastes into energy. Composting and anaerobic digestion (AD) are increasingly being used in countries at all income levels.

Farmers and farming communities need scientific, technical, and financial support to move to more climate-friendly farming practices and to support initiatives for climate change adaptation, regenerative agriculture">öller, V., R. van Diemen, J.B.R. Matthews, C. Méndez, S. Semenov, J.S. Fuglestvedt, A. Reisinger ...