A Hot Topic: Cities tackle rising temperatures
By Kurt Shickman, Executive Director, Global Cool Cities Alliance
This month, C40 will highlight Cool Cities: the cities working to address our overheated urban spaces. The Cool Cities Network is a city-driven partnership between C40 and the Global Cool Cities Alliance to share the successes, and challenges that cities experience as they strive to achieve a cooler, more resilient future.
Temperatures in the world’s cities are substantially higher than those of surrounding rural areas due to a phenomenon called the urban heat island effect. Urban heat islands form because many of our cities are made of dark, impermeable surfaces like asphalt that absorb heat, and lack enough green space. In addition, human activity and industry generate heat, and large cities block or slow down natural wind patterns. Taken together, these factors make our cities several degrees hotter, on average, than rural areas. During peak temperature periods, though, urban temperatures may spike significantly above the average urban/rural difference.
Not only are cities hotter, but they are heating up nearly twice the global average rate. Rising urban temperatures are occurring in the context of a massive global urbanization. Before the end of this century, two out of every three people will live in urban spaces where excess heat will play a critical role in their lives.
Extreme heat events are getting more frequent and more intense. Heat kills more people than any other natural disaster, and heat-related deaths tend to be underreported. Cities on dangerously hot days consistently experience spikes in mortality from all causes, sometimes as high as an additional 17 deaths per 100,000 people in US cities alone. Nine of the ten most deadly heat waves on record have occurred since 2000 (killing nearly 130,000 people in total).
Rising urban heat is an important factor in nearly every aspect of urban life including health, air quality, energy demand, and social equity.
The economic impact of unchecked urban overheating will be staggering. By 2100, urban heat and local climate change impacts will cost the average city 5.6% of their economic output. The most affected cities will lose 11% of their economic output as a result of urban heat and local climate change.
The good news is that there are proven strategies for mitigating urban heat that deliver huge potential benefits to cities and their residents. Research shows that reflective roofs and pavements and green infrastructure can deliver 12 times their cost in net benefits and cool cities by 0.5° Celsius. Cooling of that magnitude is equivalent to cancelling over a third of total global warming over the last century.
C40 cities in the Cool Cities Network have proven to be global leaders on addressing urban heat. New York City recently committed over $100 million to implement its Cool Neighborhoods program. Los Angeles is targeting a nearly 3°F reduction in their urban heat over 20 years by establishing strong cool roofing requirements. Durban has undertaken a comprehensive urban heat study to understand where they are hot and why. Athens, Barcelona, and Paris have not only mapped their heat, but also where they have vulnerable populations, working to ensure their citizens have ready access to cool places on hot days. Tokyo has laid down miles and miles of solar-reflective cool pavement and piloted “smog-eating” cool coatings that stay cleaner longer and improve air quality. Washington, D.C. has built cool roofs into their procurement policy for municipal buildings and will save millions of dollars as a result.
Adapting to extreme heat has the great advantage of tangibly improving the quality of life of countless urban citizens. The measures that are being implemented by these cities will not only help them in reducing urban heat but will also bring significant health benefits by improving air quality. Members of the Cool Cities Network are committed to moving towards a climate resilient – and cooler – future.