According to a recent study, cities have the potential to mitigate climate change by addressing energy consumption. However, the extent of that potential currently is “insufficiently understood.”

Researchers from the United States and Germany published their findings in a paper titled Global typology of urban energy use and potentials for an urbanization mitigation wedge, in the Proceedings of the National Academy of Sciences of the United States of America. Authors Felix Creutzig, Giovanni Baiocchic, Robert Bierkandt, Peter-Paul Pichler, and Karen C. Seto analysed data from 274 cities worldwide, and addressed three questions for the study:

  • How can cities contribute to climate change mitigation?
  • What urban strategies are effective for different types of cities?
  • What is the magnitude of the total mitigation potential of future urbanization?

As the world urbanises rapidly, urban areas consume between 67 and 76 per cent of global energy and generate about three quarters of global carbon emissions according to the most recent report from the Intergovernmental Panel on Climate Change (IPCC). Emissions of greenhouse gasses are likely to increase as urban populations grow by two to three billion people over the course of this century.

The study notes that “economic activity, transport costs, geographic factors, and urban form explain 37% of urban direct energy use and 88% of urban transport energy use.”

Current trends are leading to urban energy use more than tripling in the span from 2005 to 2050, growing from 240 EJ (exajoules) to 730 EJ. However, planning and transportation strategies can make a substantial difference, potentially limiting the future increase in urban energy use to 540 EJ in 2050.

A number of factors influence greenhouse gas emissions, with economic activity, gasoline price, and population density ranking highest. Also important are urbanisation level, household size, population size, and “an index of commercial centrality”, according the the authors.

A confounding factor in determining the potential for climate change mitigation is the realisation that “effective policies for reducing urban greenhouse gas emissions differ with city type,” the study notes. In mature, affluent cities with well-developed infrastructure, raising gasoline prices “can result in savings in both residential and transport energy use.”

However, the potential is small compared to developing nations, because cities in developed nations are “mature, built-up environments with established infrastructure and associated locked-in behavior and energy consumption patterns.”

Cities in developing countries, by contrast, can adopt compact urban forms and transport planning to avoid committing to high-carbon patterns of travel, and to achieve higher population densities. The ways in which “the cities of tomorrow develop spatially, especially their urban form, will lock in patterns of energy consumption for decades to come,” the report states. Cities in Asia, Africa, and the Middle East provide the bulk of the potential for GHG emissions reductions. In addition, in countries with low-cost fuel, the authors advocate raising fuel prices.

If countries with fuel prices below 1.2 USD/L increased this price to 1.6 USD/L, they would enable a market-based transition toward more energy-efficient cities,” the report states.

Urban planning also offers potential for cutting GHG emissions, using strategies such as “mixed-use design and high connectivity and accessibility, which are themselves closely related to population density, could be supportive in establishing long-term energy savings.”

As for the overall effectiveness of these strategies, the authors noted, “Currently thousands of cities worldwide are developing local climate action plans, but their aggregate impact on emissions is uncertain.”