Climate Change: The Greatest Challenge for American Planning

Introduction to American Planning and Climate Change

Planning — also called American planning or city and regional planning — is a dynamic profession dedicated to improving the well-being of people and their communities by creating more equitable, healthful, efficient, and attractive places for current and future generations. Good planning enables civic leaders, businesses, and citizens to play a meaningful role in shaping communities that enrich people's lives. It helps communities envision how they want their future to look, discover the right balance between new growth and vital services, protect the environment, and manage change responsibly.

Planning ahead is more necessary now than at almost any previous point in history. With that reality in mind, climate change will in all likelihood be the greatest challenge facing American planning over the next 20 years, for a variety of interconnected reasons explored in the sections below.

Urban Heat Islands

One major reason climate change will challenge American planning is the growing problem of urban heat islands. According to the U.S. Environmental Protection Agency (EPA), heat islands are an increasingly serious concern for millions of Americans living in and around cities. The urban heat island effect is a positive temperature anomaly that occurs over urban areas relative to surrounding non-urban areas. The air over cities becomes warmer because of the high concentrations of paved surfaces, dense building stock, and large populations (Ahrens 2006). Over time, the heat island effect can drive urban temperatures 2 to 10 degrees Fahrenheit (1 to 6 degrees Celsius) higher than those in surrounding non-urban locations.

Elevated temperatures affect communities in multiple ways: they increase peak energy demand, raise air-conditioning costs, worsen air pollution levels, and contribute to heat-related illness and mortality. Warmer air hovering over cities also influences local wind and precipitation patterns. Fortunately, growing vegetation in cities — by creating or expanding parks and open space networks — can reduce these effects. Urban parks and green space cool the air through shading and evapotranspiration, the process by which moisture evaporates from plant leaf surfaces.

Through the EPA's Urban Heat Island Pilot Project (1998–2003), cities across the United States, including Salt Lake City and Chicago, developed strategies to expand green space and tree cover in order to moderate their local climates. Since 1996, Chicago Public Schools have collaborated with the Chicago Park District and the Public Building Commission to create 80 new campus parks adjacent to public schools, designed to provide students and the surrounding community with recreational opportunities and cooling benefits.

One of Salt Lake City's most notable projects is a three-acre alpine meadow on the roof of a 1.5-million-square-foot conference center that occupies an entire city block. A waterfall cascades down the front of the structure, and a restored creek runs along its length on North Temple Street. The roof meadow — a recreation of Utah mountain scenery featuring 21 varieties of native grasses and 350 types of wildflowers — demonstrates how constructive green space can alleviate urban heat.

Wind Patterns and the Park Cool Island Effect

Another climate challenge American planning will face involves changes to wind patterns — a lesser-known consequence of the urban heat island effect. Urban areas warm faster and reach higher daytime temperatures than adjacent non-urban areas (Ahrens 2006). Because warmer air is lighter and less dense than cooler air, it rises, creating lower atmospheric pressure over urban zones. As warm urban air ascends and spreads outward, it cools, becomes denser, and sinks over non-urban areas, generating higher pressure there. The pressure difference between urban and non-urban areas drives winds from the non-urban high-pressure zones toward the urban low-pressure core. The return of cool non-urban air to replace the rising warm urban air completes what is called the urban draft cycle (Spronken-Smith and Oke 1999).

Parks can function as micro-scale "non-urban areas" within a city, generating a smaller version of this circulation known as the "park draft." Daytime cooling from the evapotranspiration of park vegetation, combined with evening cooling because vegetative cover retains less heat than asphalt and buildings, produces what researchers call the "park cool island" (PCI) effect (Spronken-Smith and Oke 1999). The temperature difference between park interiors — especially in larger parks — and the surrounding city creates a pressure gradient similar to that found between non-urban and urban areas. This pressure difference generates a breeze flowing from park interiors into surrounding city neighborhoods, partially counteracting the urban heat island.

In recent years, New York State has directed a significant share of its parks funding toward two large waterside parks designed to improve urban and park wind circulation within New York City. The state contributed half of the $300 million needed to construct Hudson River Park (150 acres of land and 400 acres of open water), with annual operating assumptions of approximately $20 to $25 million. Sustaining this level of investment against anticipated climate change will present a genuine long-term challenge.

Conclusion

Increasing the amount and size of well-vegetated parks can help reduce the level of pollutants in the atmosphere. In addition to the obvious health benefits for humans, the pollutant-reducing capabilities of vegetation also bode well for climate change management, particularly with respect to the greenhouse effect. Across all four dimensions examined — urban heat, wind patterns, precipitation, and tree mortality — climate change poses an urgent and multifaceted challenge for American planning. Green infrastructure, especially well-designed urban parks, represents one of the most promising and cost-effective strategies available to planners as they work to build more resilient communities for the decades ahead.