Source: The Conversation/Merrill Singer
Last week’s record-setting heat in the Pacific Northwest and current triple-digit temperatures in Arizona are the latest reminders that climate change is heating up the Earth. This trend is a serious threat to cities, which are warming at higher rates than other parts of the planet.
A recent multi-country analysis found that from 1950 through 2015, 27 percent of cities and 65 percent of urban populations experienced greater warming than the planetary average of 1 degree Fahrenheit. About 60 percent of the world’s city dwellers experienced warming twice as great as the rest of the world.
One or two degrees may not seem like much, but for especially vulnerable groups like the elderly, the sick, the poor, pregnant women and infants, it may be enough to tip the scales. In a time of global warming and intensifying summer heat waves, life in cities is becoming more perilous. As I found in a recent study, this is especially true for marginalized groups such as minorities and the poor.
Studies of the urban heat island effect date to the 1830s, when British chemist Luke Howard demonstrated that temperatures in London were consistently warmer than those at sites outside the city. Heat islands develop when a large portion of the natural land cover in an area is replaced by built surfaces like roads and buildings. These structures trap incoming solar radiation during the daylight hours and release it at night.
Cities, in effect, have their own climates. During recent decades, the largest urban heat islands in the U.S. experienced warming at twice the level of the “cooler sea” of smaller urban and nonurban areas. As the human population continues to urbanize and consume more fossil fuel, the health, social and economic impacts of summer urban overheating loom as major threats to the well-being of city dwellers worldwide.
Human bodies are not designed to handle heat above certain levels, especially if there is no cooling respite at night. The human body core, which includes the brain, lungs and other organs, functions only within a narrow temperature range. A core body temperature of 103°F or above can be a sign of heat stroke.
How bad might it get? One recent study estimates that about 30 percent of the world’s population currently is exposed to deadly heat episodes for 20 days or more each year. By 2100, this figure is projected to climb as high as 74 percent unless there are reductions in greenhouse gas emissions. New York City could be subjected to 50 such days per year, while southern cities like Orlando, New Orleans and Houston could see 100 deadly hot days each year. Even with reductions, the study estimates that by the end of the century, half of the people on Earth will likely face at least 20 days each year when extreme heat can kill.