Heat waves can occur in almost any country around the world, including the United States, Denmark, Russia, Australia and England. A heat wave is defined as a period of above-average high temperatures, sometimes accompanied by high humidity. While the United States routinely has heat waves during the summer, they are less common in Russia and Denmark.
Heat waves have occurred with increasing frequency across the world since the mid-20th century and are expected to continue to increase in the future. Scientists believe this is the result of global warming caused by increased emissions of greenhouse gases, particularly carbon dioxide and methane. The Heat Index, also known as the apparent temperature or real-feel temperature, is a value based on temperature and humidity that scientists use to measure of the severity of a heat wave.
Heat waves cause thousands of deaths annually, more than any other natural disaster, including tornadoes, hurricanes and extreme cold. Children, the elderly, and those with medical conditions such as heart disease and kidney disease are most at risk of heat-related complications, such as dehydration, hyperthermia and heat stroke. The symptoms of excess heat exposure include fatigue, nausea, rapid heart rate and an elevated temperature, which can rise as high as104 degrees Fahrenheit.