Hot facts about urban heat islands

Fall's cool breezes are finally replacing the summer heat and humidity. But while hot summers are familiar to most, less-known is how city heat is boosted by a phenomenon known as the urban heat island effect.

Urban heat islands occur when city temperatures are higher than those of surrounding rural areas due to physical differences in the environment. Asphalt, concrete, and other city surfaces absorb and radiate heat far more intensely than soil does. Furthermore, vegetation such as trees supply shade and cool the surrounding air by releasing water vapor, unlike roads and building surfaces. Most U.S. cities experience the heat island effect, experiencing average temperatures at least a couple degrees above their average environment. For example, Chicago experiences average summer temperatures over 2°F higher than surrounding rural areas, even with the moderating effects of nearby Lake Michigan; its heat island is centered toward the western suburbs. And Las Vegas--despite its environment being mostly desert--suffers average summer temperatures over 7°F higher than its surroundings because it does not cool as quickly as the nearby sands. Both cities also experience more days above 90°F than neighboring rural areas.

Single-digit temperature increases might seem harmless at first. But as global warming trends continue, the heat island effect will push temperatures higher, and with them will rise heat-related risks and cooling costs. Heat exhaustion and heat stroke are well-known hazards of high temperatures, and many diseases spread more easily in warmer weather. Children and the elderly will be most vulnerable, and heat waves have proven fatal for those lacking the resources to cope. Less obviously, high temperatures spark aggression; increased heat is associated with higher rates of violent crime. Furthermore, air conditioning requires electricity-and, consequently, money.

Thankfully, the urban heat island effect can be reduced, especially with help from plants. Trees and other vegetation are excellent moderators of their environment; expanding green spaces and planting more trees decreases ambient temperatures and air conditioning costs. Green roofs take this to the next level by creating green spaces on surfaces that would otherwise absorb heat from sunlight. Additionally, these roofs can provide insulation, helping manage both temperature extremes by moderating indoor temperatures. Other measures to combat the heat island exist, too; solar panels, for example, can shade rooftops while also providing renewable energy. However, government investment will also be vital in assisting with the initial costs; a quick call to a representative can show much-needed support for programs to combat the urban heat island effect.

Heat islands will not only create difficulties themselves but will also aggravate climate troubles ahead. Don't be fooled by some of the cool temperatures we've seen this year-last winter's polar vortex is not at odds with the overall trend of climate change. Variations in weather are short-term while climate patterns are long-term, and the past four years have been the hottest on record. Instead, the polar vortex demonstrates the pattern of increasing frequency and intensity of weather extremes with climate change. Cold snaps and heat waves will continue to worsen, and the urban heat island will only intensify the hazards of future heat waves. Mitigation of heat island effects and climate change is more vital than ever.