700 Cities, One Warming Planet

What can city governments do to fight climate change? In an influential 2018 paper, renowned climate scientists Daniel Kammen, Chris Jones, and Stephen Wheeler analyzed the emissions reduction potential of 717 California cities and all 58 counties. 

What they found: For most coastal cities, the number one opportunity for reducing carbon pollution is through “infill” housing development — also known as “making it legal to build more multi-family housing in our cities.”

The study has important findings that should be central to land use, climate, public health, and environmental policy in the Golden State.

Key takeaways:

  1. Local governments have policy levers they can use right now to reduce statewide emissions by up to 35%.
  2. Infill housing is the most powerful local policy tool for climate action in urban areas. While the urban core of the San Francisco Bay Area has some of the lowest per capita emissions in the state, and lowest emissions overall, the area also has some of the highest carbon footprint neighborhoods in California, indicating major decarbonization potential. 
  3. “Urban infill reduces all aspects of carbon footprints, including 2.5 MtCO2e from transportation, 1.3 MtCO2e from energy, 1.8 MtCO2e from food, and 1.7 MtCO2e from goods and services statewide.” 

By analyzing 23,000 census tracts across the state of California, Jones, Wheeler, and Kammen were able to model consumption-based emissions patterns to study how local governments could help to reduce them. This led to the creation of the Cool Climate Calculator, a powerful analytical tool for quantifying the emission reduction potential of local policy.

Developing a consumption-based inventory of greenhouse gas emissions is critical to this field of study, because many of the goods we buy produce emissions across their “lifecycle” that may not otherwise show up in a local inventory. The goal of public policy is not just to decarbonize our immediate surroundings, but our lifestyles, too. 

“Household carbon footprints are calculated with the assumption that all global economic activity is at the service of households and, therefore, all life cycle emissions associated with the production, use and disposal of goods and services are included in household carbon footprints,” they write. “For example, if a factory in China produces a computer that is purchased by a California household, then all emissions related to the mining, refining, manufacturing, shipping and trade of the computer are allocated to the California household, not the Chinese company.” 

When analyzed this way, our carbon footprints appear much larger than traditional methods show, because “lifecycle” emissions come from outside our borders. Remarkably, an inventory based on household consumption shows 25% more emissions than a “territorial” one: “550 MMTCO2e from a consumption based approach vs. 445 MMTCO2e from the state’s 2010 GHG inventory.”

From these inventories, the scientists then model future emissions in a “deep carbon abatement policy scenario,” which assumes these four policy tools are maximized: 

  1. “Urban infill policies adjust the population of each block group by putting more new development in lower carbon footprint locations and adjusting the size of homes in those locations.”
  2. “Conservation strategies reduce the amount of consumption for each household (e.g., driving less or turning down thermostats in summer).”
  3. “Efficiency strategies involve the purchase of highly efficient technology to use less energy or fuel.”
  4. Last but not least, “renewable energy strategies” are self-explanatory.

Jones et al find that local governments have significant power to reduce their constituents’ carbon emissions. This is in spite of major policy areas that are mostly not under local control, such as energy efficiency and agriculture. The importance of urban infill as a crucial policy lever is made more apparent by pockets of very high carbon footprints in urban centers with some of the lowest carbon neighborhoods. “Income largely accounts for the discrepancy.” More concretely, wealthier people tend to have much larger carbon footprints. 

But regardless of income, it’s better for more residents to be living in a low-carbon urban core: “While these neighborhoods have higher than average carbon footprints, they have lower than average carbon footprints for their income level,” they add. “Low carbon footprint cities that make housing available at all income levels help share the burden of meeting housing demand, while lessening the impact on the climate across the population.”

With the transportation sector accounting for half of all emissions reductions in this optimistic scenario, urban infill emerges as the single most powerful tool for local governments to fight climate change, particularly in higher-income localities in the urban core (the paper uses Berkeley as a prime example). “Mixed income urban core cities (e.g., Berkeley) hold the most potential for urban infill, with statewide GHG benefits,” the authors conclude.

Even though lower-income areas and rural communities may see more potential for decarbonization from other policies, they still stand to benefit from cities like Berkeley building more infill housing. “Those who are least responsible for emissions are frequently the most exposed to harmful effects of pollution,” Jones et al observe. However: “If California meets its climate targets, large disparities in carbon footprints will essentially disappear with important co-benefits of reduced pollution in vulnerable communities.”