While levels of atmospheric carbon dioxide (CO2) are at their highest, an estimated 2.5 billion more individuals are anticipated to move into urban environments globally by 2050, emphasizing the need to lower urban CO2 emissions. A team of researchers examined how urban structure, especially regarding buildings and streets, impacts CO2 emissions in detail across three cities in the U.S.
Research indicates that cities might lower their carbon dioxide (CO2) emissions by refining their urban design. However, the connection between urban layout and emissions varies significantly based on specific circumstances, making broad conclusions difficult.
As CO2 levels soar, it is projected that 2.5 billion additional people will populate urban areas worldwide by 2050. This rise is closely linked to energy use and its role in climate change, fueling interest in designing cities that conserve energy.
Unfortunately, there is a shortage of scientific studies focusing on energy-efficient urban designs, with many existing studies only evaluating urban form at a macro level, lacking standardization and generally considering only a few urban design elements. To tackle this gap, researchers from Hiroshima University, Shiraz University, and Northern Arizona University launched a study to explore the impact of urban structure on carbon emissions using more in-depth assessment techniques across three U.S. cities.
The findings of their research were published in the November 2024 edition of the Journal of Environmental Management.
“While the link between urban design and CO2 emissions is well established, prior studies have predominantly focused on broader urban forms, lacking a nuanced understanding of this relationship. In contrast, our research utilizes the Local Climate Zones (LCZ) framework to examine urban form and its connection to CO2 emissions at a more localized scale,” explained Ayyoob Sharifi, a professor at the IDEC Institute at Hiroshima University and one of the paper’s authors.
The LCZ framework categorizes urban forms into ten built types (like low-rise and high-rise buildings, as well as heavy industry) and seven natural types. It has been effectively implemented to analyze urban heat island effects. In this research, the team applied the framework to classify the urban structures in Baltimore, Maryland; Indianapolis, Indiana; and Los Angeles, California through remote sensing techniques, including satellite imagery.
These three cities were selected due to their varying climates and population densities. Los Angeles has a warm, dry climate with minor temperature fluctuations; Indianapolis experiences a cold, humid climate; while Baltimore has a mixed, humid climate. Among these, Baltimore has the highest population density, whereas Los Angeles and Indianapolis have comparable densities, with Los Angeles covering a significantly larger geographic area.
The differences in climate and population density among these cities were deliberately chosen to assess whether variations in LCZ could influence CO2 emissions throughout the year or during specific seasons, given different per capita densities and climate types. CO2 emissions were quantified using data from the Hestia Project, which determines the amount of fossil-fuel CO2 emitted on a street and building scale each hour in these cities.
The study shed light on how LCZ type impacts CO2 emissions, yet few universal conclusions could be made across the cities. “The findings highlight that the connection between urban design and CO2 emissions is intricate and ever-changing. Emission patterns vary based on multiple factors, including climate, city size, and function. Observations from one city cannot automatically be applied to others, suggesting that standardized solutions for urban design are inappropriate,” Sharifi noted.
What emerged as crucial from the research is the importance of urban open and green spaces. “[W]ithout intelligent and sufficient allocation of open and green areas, densely packed urban expansion may not effectively reduce urban CO2 emissions,” remarked Sharifi.
The research group plans to continue exploring the correlation between LCZ and urban CO2 emissions to lessen the impacts of city-based fossil fuel consumption. The authors propose that enhancing the resolution of LCZ categorization in urban environments and investigating specific sources of fossil fuel use in cities—like transportation and residential or commercial sectors—could help clarify the relationship between LCZ and CO2 emissions.
“We intend to expand our research by including data from more cities across various regions worldwide to [better] comprehend the links between LCZ types and CO2 emissions in diverse climatic and socioeconomic contexts,” concluded Sharifi.
