OPINION: Cities can Drive Net-Zero Carbon Goals and Create Vibrant Urban Communities

The Fifth and Sixth Intergovernmental Panel on Climate Change Assessment Reports make clear that urban areas are central to solving climate change because they contribute to 65–75 percent of greenhouse gas emissions.

The challenges that cities face today are innumerable and well-documented. Whether it is their role in driving global environmental change or their vulnerability to economic, social, and ecological crises, cities are at the confluence of risks and threats from local to planetary scales.

The Fifth and Sixth Intergovernmental Panel on Climate Change Assessment Reports make clear that urban areas are central to solving climate change because they contribute to 65–75 percent of greenhouse gas emissions. In order to limit global warming to 2°C or below, there needs to be a transformational change in urban systems and their infrastructure.

For cities that have already been built, the challenge will be how to redesign, transform, and renovate existing infrastructures so that they are low- or net-zero carbon. For new and developing cities with nascent infrastructure, their energy use and associated behaviors have not been locked in. Therefore, it is essential that the design of their urban infrastructure fosters low-carbon lifestyles.

However, it is not only operational energy use of cities with which we need to be concerned about. Urban emissions are driven by many factors, including a growing urban population, the increased ownership of private vehicles, heating and cooling, and the growing use of steel, cement, and other building materials. Thus, cities need to consider the energy and embodied emissions of their built environment.

Some studies show that the embodied emissions from building, not even operating, the urban infrastructure for the Global South will exceed the remaining carbon budget. With urban areas expanding at a rate equivalent to 20,000 American football fields per day, the infrastructure challenge is enormous. With disorienting speed, older towns and metros all around the world are building up and spreading out. Agrarian towns and villages are being absorbed by or transformed into larger urban megapolitans. Rapid urban development will continue through the middle of this century at least, and in many regions of the Global South, such as India and Nigeria, it will accelerate.

According to the latest United Nations projections, the urban population is growing by approximately 1 million every five days. Although the long-term effects of COVID-19 on urbanization and birth rates are unknown, the current trends of city and infrastructure building and urban population growth are unprecedented in history. The global infrastructure gap is estimated to be $94 billion between 2016 and 2040. This is to develop the road, power, transport, water, and telecommunications infrastructure, and notably does not include the cost to build housing, schools, hospitals, and other built-up elements of cities.

How cities grow will affect not only global climate; it will also affect local climate. The urban heat island has been well documented, showing that cities are warmer—especially at night—than surrounding regions, due to urban materials, land cover, and activities. Urban expansion also drives changes in local temperature because of changes in land cover, evapotranspiration, and surface albedo—the ability of surfaces to reflect heat from the sun.

Research from my group shows that in many regions of Sub-Saharan Africa and Southeast Asia, urban expansion-driven changes in local temperature will be much greater than climate change-driven changes in local temperatures. Given this, cities need to consider their use of building and infrastructure materials.

Cities must therefore achieve four goals: minimize greenhouse gas emissions, foster low and net-zero carbon behaviors, minimize changes in land cover that increase local temperatures and exacerbate the urban heat island effect, and create livable and vibrant communities. How can they possibly do this with limited human and financial resources and given the need for urgent action?

Nature-based solutions through natural infrastructure can help cities achieve all of these aims simultaneously. Numerous studies have shown that nature-based solutions can provide cost-effective solutions that have multiple benefits for people and the environment, such as reducing urban heat, providing shade to buildings and thus reducing demand for air conditioning, and absorbing storm surges. Furthermore, there are myriad economic, health, and social benefits of neighborhoods with green spaces and tree cover. Therefore, it is not surprising that nature-based solutions have garnered much attention from the science and practice communities in the past decade.

This hardhatOPINION was written by Karen C. Seto the Frederick C. Hixon Professor of Geography and Urbanization Science, and Director of the Hixon Center for Urban Sustainability at Yale University for Public Seminar