The United Nations’ 2030 Agenda for Sustainable Development is a “blueprint for peace and prosperity for people and the planet, now and into the future” (THE 17 GOALS). It is a call to action that consists of seventeen goals. The eleventh goal is to “Make cities and human settlements inclusive, safe, resilient and sustainable” (THE 17 GOALS). Essentially, we must create a harmonious relationship between the ecological environment and urbanization. This includes areas such as sustainable transport, sustainable cities, and human settlements.
Urban areas are and will be very important in the realm of sustainability. In 2050, it is projected that 68% of the world’s population will live in urban areas, according to scientists from the Chinese Academy of Sciences (Yu-Sheng 1). However, urban areas produce more than 70% of the global carbon emissions, according to authors from the Department of Civil Engineering, Construction, Infrastructure, and Transportation at Polytechnic University of Madrid’s Higher Technical School of Civil Engineering (Pacheco-Torres 1). Urban areas across the globe are reliant on carbon emitting fossil fuels and are a major contributor to the rising global temperatures (EPA). In effect, with urban areas experiencing rising populations, this relationship is not sustainable. In order for the world to adhere to the Paris Climate Change Conference’s limit of the increase in global temperatures to 2 ◦ C by the year 2100, urban areas will need to become more sustainable and less reliant on fossil fuels.
So, because climate change is a threat and cities are at the front of this, can city planning lead to a decrease in carbon emissions? According to Spanish researchers from the Polytechnic University of Madrid, “Urban planning is usually regarded as a third carbon reduction pathway beyond technological and market methods” (Pacheco-Torres 2). So, if urban planning can reduce carbon emissions, how can cities reduce emissions? This investigation will look into the effect of population and commercial density in cities, analyzing density’s effects in the areas of housing and transportation.
Transportation Systems
Density in cities is important in the realm of the transportation system because the transportation system produces 23% of carbon emissions, according to the Technical University of Civil Engineering in Romania (Popescu & Luca 9). Because of transportation’s high carbon emissions, how can they be decreased? Transportation modes such as biking, walking, and public transportation are considered sustainable and are more energy efficient (Wang 1). These modes of transportation allow for a much more sustainable and efficient city, especially with high density. Hence, a denser city means less emissions. According to authors from the Chinese Culture University, “A negative correlation was found between the population density and the per-capita carbon dioxide emissions in the transportation sector” (Wang 1). Increasing density allows for a decrease in carbon emissions and provides a pathway for cities to decrease carbon emissions.
A large part of this can be done with reducing car usage. An author from the Resilient and Sustainable Cities Project in Boulder Colorado stated that in a neighborhood with 1000 fewer living units per square mile, a household drives 1200 more miles and consumes 65 more gallons of fuel per year than they would in a high density neighborhood (Romero-Lankao 12). Gasoline powered vehicles contribute to carbon emissions, so reducing car use is an appealing idea in a pathway to decrease carbon emissions.
So how does this relate to planning? An easy to understand concept in urban and transportation planning is the model of a “15 minute city” (15-Minute City). 15 minute cities prioritize all amenities within a 15 minute walk. Amenities should include—but are not limited to—a bus stop, post office, pharmacy, park, primary and secondary schools, nursery, convenience store, supermarket, bank, restaurant, barber shop, and shopping center. Advocates for 15 minute cities believe neighborhoods in cities should be built in this way, prioritizing walking and biking. This model of a city would densify cities, decreasing carbon emissions in the transportation system from a focus on walking.
Another way for cities to promote sustainable transportation and density is the use of transit-oriented development. Transit-oriented development is compact, walkable, mixed-use, and pedestrian-oriented. It has residential, business, and leisure spaces within walking distance of public transportation. It prioritizes public transit and reduces private vehicles. For example, building apartments near or on train stations is an example of transit-oriented development. This method of building cities, with prioritization of public transit, is useful in reducing carbon emissions in cities because it promotes density (Shen 2). It also promotes smart planning and lays the foundation for multimodal transport (walking, biking, buses, trains), which uses less carbon emissions (Kim and Thioye, 238). Transit-oriented development is important for building sustainable cities because it prioritizes sustainable transportation and density.
In sum, highly dense cities have the lowest carbon emissions of any scale of density. This is because dense cities decrease car dependency, which decreases emissions. Models such as 15 minute cities and transit-oriented development are pathways for decreasing carbon emissions. These are traits of a sustainable urban system that will use little carbon emissions.
Buildings and Housing
Another way to decrease carbon emissions is to change our buildings and housing. Buildings and housing account for 37% of global carbon emissions (Kim and Thioye 230). This includes offices, shops, hotels, schools, and residential buildings. In essence, densifying buildings and housing allows for mixed use development and more efficient heating and cooling systems. This decreases the final carbon emissions that buildings and housing emits and allows for less carbon to be emitted.
Buildings must use energy. For example, buildings need heating and cooling. These systems can be made to be more efficient and sustainable. Scientists found that in Spain, heating and cooling systems account for 50% of the total energy consumption per housing unit (Pacheco-Torres 4). Large apartment buildings that centralize heating and cooling systems also centralize electricity systems. Because these units share walls, their walls are not exposed to the outside elements, but rather exposed to the room temperatures of every other wall, so this leads to a simpler and more efficient use of energy, which decreases the need for more energy, decreasing carbon emissions.
Additionally, dense housing leads to less carbon emissions through waste management, water management, and electrical infrastructure. This is important because “water and wastewater sectors can represent up to 16% of the total of city electricity-related emissions” (Pacheco-Torres 3). The city has a role of providing water and waste management. With increasing frequency of climate change induced drought, as seen in the Western portion of America, sustainable water infrastructure is in high demand (Bates 2021). In fast growing cities, sustainable water infrastructure is a huge challenge (Pacheco-Torres 3). Densifying housing would mean cities would not need to build as much infrastructure for water and waste transport, saving money and decreasing emissions (Strong Towns 2023). Furthermore, waste collection routes would be decreased, decreasing carbon emissions in the transportation of waste (Pacheco-Torres 8). These methods all provide pathways for decreased carbon emissions.
Green infrastructure on the tops of buildings is an additional way to decrease carbon emissions through buildings. A green roof features plants, trees, or gardens on the top of buildings. This can be seen below in Figure 1. According to the book “Planning Climate Smart and Wise Cities,” “green roofs can reduce the heat penetration by up to 80%, reducing energy consumption by 2–17%, while green walls’ energy demand reduction potential is estimated in the range 10–30%” (Kim & Thioye 164). This establishes the importance and effectiveness of green roofs for reducing energy consumption, and furthermore, carbon emissions. Additionally, green roofs can be used for farming. This saves food transport distance and decreases emissions.
Figure 1: View of Beirut and green roof buildings
Source: TheCityFix
Another way for building development to be a pathway for decreased carbon emissions is the use of mixed-use development. Mixed-use development establishes energy efficiency and resource wise planning. It incorporates all buildings, whether it be commercial, residential, or industrial (Kim 71). The importance of mixed-use development is that residents of an area can have all their needs met in a short area around them. It is similar to the idea of a ‘15 minute city.’ Mixed-use development is an example of how ‘15 minute cities’ can be planned and built. Features of mixed-use development usually are multistoried buildings, with retail and/or entertainment on the lowest levels, and office or residential space on the highest levels. It is organized this way to allow customers that walk along to be able to shop and play, but has additional function as space for offices and living areas. An example of this is shown below in Figure 2.
Figure 2: View of mixed use development 
Source: Complete Communities
Another value of mixed-use development is that it is more efficient financially for a city. The Urban 3 research group argues for the use of measuring value in property development with value per acre. In a video by Strong Towns, they ask, “Will it be an effective use of valuable land?” (Strong Towns, 2023). An example they use is a mixed-use building valued at 11 million dollars and a Walmart valued at 20 million dollars. In value-per-acre, the mixed-use building has $634,000 total property taxes per acre, whereas Walmart has $6,500 total property taxes per acre. In residents per acre, the mixed-use building has 90, and the Walmart has zero. In jobs per acre, the mixed-use building has 74 and the Walmart has 6 (Strong Towns, 2023). As one can notice, the mixed-use development building is more valuable per acre in each measurement. This is important because of the financial angle. City land is valuable, and using it efficiently is in the best interest of the city.
However, a large reason mixed-use development is hindered in its development is zoning laws. Exclusionary single family housing zoning prevents mixed-use development in neighborhoods (Knaap, 2007). For example, in the US city of San Francisco, residents try to preserve low density suburbs from pre-World war II developments because changing it would “threaten the California lifestyle” of low density. The authors establish this as a reason for housing shortages and, therefore, high housing prices (Sullivan and Tarlock, 18-19). Cities trying to build mixed-use development will find challenges in zoning policies and in social and cultural norms. However, cities and residents will see the possibilities of the financial savings and environmental savings they could have with the implementation of mixed-use development.
In most North American cities, the central business district, or downtown, is a cluster of tall and dense office and residential buildings surrounded by miles of single family homes and large wide roads with commerce. There is a lack of mixed-use development. This lack of mixed-use development in cities is called the “missing middle” (MissingMiddleHousing). It is referred to as the “middle” because it is not tall imposing buildings, but usually buildings of 5-6 stories. This mixed-used development offers a perfect combination of the residential quality of neighborhoods with enough density to be sustainable and walkable.
Building efficient structures with dense and mixed-use development will save energy expenditures, and therefore carbon expenditures, saving money for city investments. This demonstrates the effectiveness of density in city planning in order to decrease carbon emissions.
Concluding Statements
Urban city planning that encourages and requires for higher densification is a pathway to reduce per-capita carbon emissions, and therefore can be used to create a sustainable urban future. This was seen in the transportation system through encouraging public modes of transportation, walking, biking, transit-oriented development, all of which can be encouraged through densification. This was seen in the building and housing system since dense housing allows for more efficient heating and cooling, efficient waste management, green infrastructure, “15 Minute Cities,” mixed-use development, and efficient costs-per acre. Therefore, as explained and analyzed above, high density urban areas that promote safe and affordable micro-mobility and transit have lower carbon emissions per capita— a way we can build sustainable cities for the future.
Works Cited
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