Readers: This is the first installment of a two-part report on Urban Heat Islands. Part one focuses on the problem of overheated cities. Part two looks at people and projects that are creating solutions without waiting for government policies.
When I was growing up in Manhattan, I remember blistering summers when simply walking down the block made me feel like Lawrence of Arabia crossing the Nefud Desert. Roads shimmered with heat and were usually swathed in steam from vents that I imagined came from Hades itself. Listen to a local weather report anywhere in North America today, and it’s always warmer in big urban centers than their rural outskirts, even in the dead of winter. But are cities really that much hotter than the country? Recent scientific findings say they are — and they could get much worse in years to come unless we take action.
On a sunny summer afternoon, urban air can be (1-3 degrees C (2-5 degrees F) warmer than nearby rural air. Credit: Lawrence Berkeley National Laboratory’s Heat Island Group
For some two decades climate scientists have been using orbiting satellites to measure land temperatures worldwide. Their data shows that large cities, where buildings far outnumber trees, can be as much as 10 degrees Fahrenheit warmer than the surrounding, more bucolic landscape.1 In summer, city buildings, streets and rooftops can reach 160 degrees F, staying hot long after the sun has set. In fact, during summer months most urban landscapes can be hotter at night than they are during the day!2
When we think of heat most of us don’t think of “pollution”. But too much of anything can be deadly, and the accumulated heat from millions of city cars, air conditioner vents and industrial smokestacks can be as much a form of pollution as sewer sludge. This heat pollution, combined with already hot buildings and streets, creates vast bubbles of sultry air that hover over every major city on Earth like enormous cloches. First identified over London in 1818, scientists now call this weather phenomenon “Urban Heat Islands”(UHIs).3
A key factor to hot cities is lack of vegetation. Plants not only provide the oxygen we breathe and absorb greenhouse gases like C02, they also keep things cool and moist through evapotranspiration: basically sweating out the rainwater they absorb from the soil, which then lowers the ambient temperature through evaporation.4 It’s the same principle that makes the air feel cooler after a thunderstorm. Without porous soil and a clear majority of plant-life, the urban landscape becomes the thermal equivalent of a desert canyon.5
The image on the left shows temperature, ranging from blue (warm) to yellow (hot). The image on the right shows vegetation from beige (sparse) to deep green (dense). A comparison of the images shows that where vegetation is dense, temperatures are cooler. Urban heat islands are worst where there is little or no vegetation. Credit: NASA
When people clear land and construct cities, it probably never occurs to them that they are also creating a desert or a heat island. A hundred years ago, city planners thought constructing buildings and streets out of waterproof, stony material would make life better: no more mud and mold. Indeed it did, but this paving process also turned the city into a giant radiant-heat oven. That’s because concrete can absorb and hold 2000 times more heat than the same volume of air.6 The black tar and asphalt we cover streets and rooftops with is especially good at sucking up heat, as anyone who ever walked barefoot on a “tar beach” rooftop in summer can attest.
“If you think about the city logically, its just a place where you pump huge amounts of energy, and all that energy dissipates into heat.” Says Jerry Yudelson, an expert on sustainable buildings and cities. “So if the environment is hotter, you are trying to (pump) heat into an already hot environment.”7
Urban Heat Islands not only make it uncomfortable to live in a city — they can make it deadly. Scientists at Lawrence Berkeley National Laboratory’s Heat Island Group say that UHIs’ intense heat have been linked directly to cases of heat stroke and even heart attacks. Cities’ lack of fresh breezes also helps intensify pollutants in the air like low-level ozone, exacerbating cases of asthma, bronchitis and other respiratory illnesses, especially in children and the elderly.8 In fact, researchers discovered that as UHI’s magnify the intensity of summer heat waves, human death rates rise exponentially, especially at night when the heat becomes worse.9 On average, about one thousand people die from hot weather annually in the U.S. making heat one of the most deadly kinds of weather conditions on Earth.10
Summer heat waves can be dangerous enough on their own: In 2003, excessive heat killed more than 45,000 people across Europe in two weeks. A 1995 heat wave in the American Midwest also killed thousands, 80 percent of them in big cities like Chicago, St. Louis and Milwaukee.11 Climatologists now know that while UHIs may not cause heat waves, they intensify those that appear, making their resulting illness, deaths, drought and fires much worse than they ordinarily would have been.12 The summer heat wave that struck North America in 2006 lingered for a week and caused power blackouts throughout the U.S. and Canada, killing some 220 people and affecting more than 600,000. Part of this damage came from powerful “inland hurricanes”, called decheros, which downed power lines with winds exceeding 100 mph.13
While UHIs might not seem like culprits in this disaster, scientists now have evidence that they actually help create thunderstorms and possibly tornadoes, by focusing hot, unstable air into phalanxes of roiling thunderstorms.14 According to a 2004 study by the National Center for Atmospheric Research in Colorado, heat waves will become more frequent, last longer and be hotter this century than at any other recorded time, producing “notable impacts on human mortality, regional economies and ecosystems.”15
Keeping cool during weeks of intense heat is not only a stress on human health, but also on electrical grids, which have been working close to their limit just offsetting UHIs. “Ever since air conditioning came into use, its made people less aware of Urban Heat Islands.” Says Stuart Gaffin, a climatologist studying UHIs at Columbia University’s Center for Climate Systems Research. “But now we are using so much air conditioning in summers we barely avoid busting the grid.”16
According to the Environmental Protection Agency, for every degree of heat rise over 77 degrees F, electricity demand rises by two percent, resulting in a permanent 10 percent power increase under most city Heat Islands worldwide.17 Heat-related costs can add up quickly. For example, Los Angeles uses some 1.5 gigawatts of power to offset its heat island yearly. That translates to $100,000 per hour, or $100 million per year — without a heat wave.18 So its no surprise that as a result of the two dozen major heat waves that have occurred worldwide during the last 11 years, more than half resulted in power blackouts, either from higher energy demand or as a result of violent storms intensified by the heat. Researchers now say that as climate change warms our planet over the next century, scorching heat waves like those of 2006 will become more frequent, longer lasting and more intense.
Most of our electrical energy comes from turbines that run on fossil fuels like oil, coal or natural gas — the prime movers of climate change. Scientists report that big cities belch out 80 percent of Earth’s annual greenhouse gases, including emissions from energy use and food production. In a hundred years, cities worldwide have mushroomed 10 times larger than they were in 1900, their populations growing from 250 million to 2.8 billion today. If current trends continue, its estimated that by 2050 some 6 billion people, 75 percent of the future global human population, will live in cities like Tokyo, New York and Sao Paolo.19 To keep all those people healthy and comfortable, cities will need enormous amounts of energy, which will result in equally vast quantities of released heat, and ever larger UHIs.
To date governments have been slow to address climate change or urban heat islands. The Kyoto protocol for reducing greenhouse gases still hasn’t been endorsed by many developed nations, most notably the U.S. As UHIs and their related dangers continue to grow, more and more scientists and ordinary people are deciding not to wait on politicians to come up with solutions to these problems. In the next installment of this report, we will meet groups and individuals who are taking the initiative to develop practical, feasible and economical methods to get rid of Urban Heat Islands today, and create a cooler, more sustainable tomorrow.
Footnotes:
1. NASA: Ecosystem, Vegetation Affect Intensity of Urban Heat Island Affect
2. Ibid.
3. Urban and Rural Temperature Trends in Proximity to Large U.S. Cities: 1957-2006. Presentation to the 2nd International Conference on Countermeasures to Urban Heat Islands, Brian Stone, Ph.D. Associate Professor City and Regional Planning Program Georgia Institute of Technology September 21, 2009.
4. U.S. Geological Survey: Evapotranspiration and Droughts.
5. T. R. Oke The energetic basis of the urban heat island. Article first published online: 15 DEC 2006, DOI: 10.1002/qj.49710845502 Copyright © 1982 Royal Meteorological Society. Quarterly Journal of the Royal Meteorological Society Volume 108, Issue 455, pages 1–24, January 1982.
6. H.-Y. Lee (1993). “An application of NOAA AVHRR thermal data to the study or urban heat islands”Atmospheric Environment 27B: 1–13.
7. Interview with Jerry Yudelson by AICC’s John Tidwell. 2011.
8. S. A. Changnon, Jr., K. E. Kunkel, and B. C. Reinke (1996). “Impacts and responses to the 1995 heat wave: A call to action“. Bulletin of the American Meteorological Society 77: 1497– 1506.
9. R. W. Buechley, J. Van Bruggen, and L. E. Trippi (1972). “Heat island = death island?”. Environmental Research 5 (1): 85-92.
10. Rosenzweig, Cynthia, “All Climate Is Local”. Scientific American September, 2011.
11. Hindwi Publishing Corporation, Advances in Meteorology, The Impact of the Urban Heat Island during an Intense Heat Wave in Oklahoma City.
12. Email correspondance with Stuart R. Gaffin by AICC’s John Tidwell.
13. Hindwi Publishing Corporation, Advances in Meteorology, The Impact of the Urban Heat Island during an Intense Heat Wave in Oklahoma City
14. American Meteorological Society, Dry and Moist Convection Forced by Urban Heat Island, Jong-Jin Baik, Yeon-Hee Kim and Hye-Yeong Chun.
15. American Association for the Advancement of Science, Science Magazine, More Intense, More Frequent, and Longer Lasting Heat Waves in the 21st Century.
16. Interview with Stuart R. Gaffin by AICC’s John Tidwell. 2011.
17. Google Docs, Reducing Urban Heat Islands: Compendium of Strategies.
18. Environmental Energy Technologies Division
19. Scientific America. Street-Savvy: Meeting the biggest challenges starts with the city, Aug. 16, 2011.
Critically important article and research. Should be widely disseminated, especially to politicians. Solutions are important. Thanks for making this available.
My thoughts exactly; I found myself immediately forwarding this to my city’s sustainability director.
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[...] This is the second installment of a two-part report on Urban Heat Islands. Part one focused on the problem of overheated cities. Part two now looks at the people and projects that are creating viable solutions to these growing [...]