Heatwaves are currently affecting large portions of the country and around the world. Understanding what they are and what causes them is important as knowing what you can to do to keep yourself as comfortably protected as possible. Definitions vary by region, but a heatwave is a period of unusually hot weather compared to the historical record. In the Northeast, for example, three consecutive days of temperatures 90° F or higher would be designated as a heatwave. According to the Environmental Protection Agency (EPA), heatwaves have increased in frequency, duration, intensity and the overall length of the season every decade since the 1960’s. More specifically, major cities in the U.S. were averaging about two heatwaves per year in the 60’s. Since that time, the number has grown to six. The duration of an average heatwave has also increased over the preceding decades from about three days to four. Compounding the problem, the length of the average heatwave season has increased by 47 days, occurring earlier in the springtime and later into the fall. The intensity of heatwaves is accelerating as well, rising from 2.0°F above the local 85th percentile threshold to 2.5°F.
Heatwaves occur when pressure in the upper atmosphere builds and then lingers over a region for days or weeks on end. Warmer air is pushed downward and trapped, creating the circumstances we experience during a heatwave. This condition is referred to as a heat dome, as it is works similarly to how a lid on a pot maintains and accelerates heating. According to the National Oceanic and Atmospheric Administration (NOAA), heat domes form when a marked change, also referred to as a gradient, in ocean temperatures occurs from west to east in the tropical Pacific Ocean during the preceding winter. Temperatures are higher in the western Pacific than in the eastern Pacific in wintertime, creating the kind of gradient that causes warm air, heated by the ocean’s surface, to rise upward. This is a process known as convection. Prevailing winds move the hot air eastward until high pressure air pushes it downwards over land where it is trapped. Exacerbating the situation, weather patterns move more slowly in the upper atmosphere, and in the summertime, which is how a hot day can turn into a multi-day heatwave.
As the conditions of heatwaves continue to worsen, the danger to human life increases. Currently, it is estimated that more than 1,300 people in the United States die each year due to extreme heat conditions. During the month of June alone, monthly and all time temperature records have been broken in at least a half dozen countries, while Japan is currently experiencing its worst heatwave since records began to be kept in 1875. In addition to the risk to human life and the immense stain on our power grids, wildlife will suffer too. Earlier this month, a heatwave in Kansas killed over 2,000 cattle in less than two days. AJ Tarpoff, associate professor and beef extension veterinarian at Kansas State University was quoted by ABC news, saying, “The temperature spiked, the humidity spiked, but the wind speed dropped. This is quite rare for this region of western Kansas, and it lasted for over one day.” He also noted that the nighttime temperatures were unusually high, giving the cattle no chance to cool off before the sun rose again.
Ultimately, slowing the effects of climate change may be the only way to stop the severity of the heatwave season from continuing to accelerate. In the short-term, understanding how serious of an issue this is from a personal safety standpoint is something everyone can do as individuals.