By UW Net Impact Consulting Experience (NICE) Consultants: Uma Drinan, Britney Ikemura, Olin Blycker
UW Net Impact Consultancy Experience (NICE) was asked to quantify the social cost of carbon in the cities of Shoreline and Sammamish to better understand the climate-related costs of urban sprawl. We were challenged to identify the primary drivers of the variation and examine how these differences impact the cities.
NICE is a program that partners with mission-driven businesses and organizations to strengthen their impact. With a goal to leverage student excellence, academic research, and professional mentorship, we encourage students to deliver actionable insights and creative strategies that help partners grow and thrive.
What we studied:
We identified land use, utilities, and transportation as key variables to estimate the social cost of carbon. We researched and calculated the carbon produced within each variable for both Sammamish and Shoreline and then converted it to the social cost of carbon to get the total cost for each city. Utilities and transportation both proved to have a significant impact on the total carbon output while the land use, with a focus on the canopy cover, absorbed carbon and thus decreased the total amount.
What we learned:
One of the biggest takeaways from this project was seeing how differences in urban form influence carbon emissions in ways that aren’t always obvious. By comparing Shoreline and Sammamish, we examined how land use, transportation, and utilities each contribute to the social cost of carbon, and how planning decisions can shape long-term environmental and community outcomes.
As we explored the land assessments for both cities, we found notable differences in how the land is structured and managed. Shoreline’s assessment was a comprehensive 24-page report with a wide range of datasets, while Sammamish’s was a much shorter summary. Even with the more limited information available, Sammamish showed a 2.2% increase in tree canopy, about 150 acres, compared to Shoreline’s 0.1% increase. Using i-Tree data also helped us understand that urban tree canopies provide measurable benefits beyond aesthetics, including carbon sequestration, carbon dioxide uptake, air pollution removal, and stormwater mitigation. These findings reinforced the importance of preserving and expanding tree canopy as communities continue to grow.
Looking into transportation highlighted another important piece. We found that the relationship between urban form and emissions is more nuanced than we initially expected. While Sammamish had a lower share of residents driving alone than anticipated, its longer average commute times, lower public transit usage, and lack of direct light rail access still resulted in higher transportation-related social carbon costs. This showed us that transportation emissions aren’t driven by a single statistic, but rather by the combined effects of land use, transportation infrastructure, and access to alternatives like public transit. We also saw how seemingly small differences, just a few extra minutes spent commuting each day, can add up to hundreds of additional miles traveled annually per commuter and, across thousands of residents, translate into meaningful increases in emissions and long-term social costs.
Our utility analysis highlighted a similar relationship between development patterns and emissions. Electricity consumption was relatively similar in both cities and produced comparatively low emissions because Seattle City Light’s electricity comes from approximately 99% renewable sources. The largest difference came from natural gas consumption used for heating homes. Despite having similar populations, Sammamish produced more than 100,000 additional metric tons of CO₂ emissions from natural gas than Shoreline. Much of this difference can be explained by housing type: Shoreline has a larger share of apartments and attached housing, where shared walls improve heating efficiency, while Sammamish is primarily composed of larger single-family homes that require more energy to heat on a per-person basis.
We would say one of the biggest lessons from the project was that the social cost of carbon provides a meaningful way to connect climate impacts to everyday planning decisions. Whether it’s preserving tree canopy, expanding transportation options, or encouraging more efficient housing patterns, decisions about how communities grow have measurable environmental, economic, and social consequences. Looking at these systems together helped us better understand that the effects of urban sprawl extend well beyond carbon emissions, they influence the long-term resilience, affordability, and quality of life of our communities.
Why it matters:
The findings from this research reinforce an important idea during this era of city planning: how we choose to grow our communities has lasting consequences for both people and the environment. Decisions about where housing is built, how transportation networks are designed, and how growth is managed influence commuting patterns, infrastructure needs, greenhouse gas emissions, and quality of life for decades to come.
This research helps demonstrate that preserving open space and encouraging more connected development can provide benefits that extend beyond conservation alone. Communities with better access to transportation options and existing infrastructure may reduce long-term social and environmental costs while supporting healthier, more resilient neighborhoods. At the same time, tools like Transfer of Development Rights (TDRs) and the Landscape Conservation Local Infrastructure Program (LCLIP) create opportunities to protect working lands and natural areas while directing growth toward places that are better equipped to accommodate it.
For local governments, incorporating the social cost of carbon into planning decisions offers another way to evaluate the long-term impacts of development. Rather than considering only the upfront financial costs of growth, policymakers can also account for the broader economic effects of transportation emissions, infrastructure demands, and climate-related impacts. As communities across the greater Seattle region continue to grow, understanding these connections will be increasingly important for making informed, sustainable planning decisions.
Reflections from the team:
Working with Forterra gave us the chance to take the research and critical thinking skills we had built in the classroom and apply them to a problem that actually mattered outside of it. This was not a hypothetical case study built for a grade. The findings we produced were meant to inform how a real organization thinks about growth, conservation, and planning in the communities we studied, which gave the work a weight that classroom projects rarely carry. Knowing that our research could genuinely shape how Forterra approaches land use and climate policy made us more careful, more thorough, and more invested in getting it right.
Looking ahead:
Looking ahead, communities in the Pacific Northwest will continue to grow, the question is how. Our research shows that not only can two cities with different urban plans output different levels of carbon, but that this carbon output has a monetary penalty reflected onto the population. The future of our city planning depends on whether people are aware of, grasp, and believe the monetary penalty of greater urban sprawl.
Awareness and understanding can come from intercommunity conversations, and various online resources. However, belief from the general population about the true cost of urban sprawl will require further research.
Ultimately the choices we make about how and where we live will shape the future of our planet. We can’t force people to make sustainable choices, but through education and spreading awareness people can learn to make those sustainable choices for themselves.
