Extreme heat pushes our body beyond its bounds. Under normal conditions, the internal thermostat of our body produces sweat that evaporates to cool the body. In high humidity and extreme heat, however, the evaporation slows down and our body must work doubly hard to maintain our normal body temperature.

Extreme heat can kill. In 2003, Western Europe had one of the hottest summers ever recorded in the continent. From June to August, a heat wave killed around 35,000 people in this part of the world (France accounted for almost half of the death toll), mostly elderly.

What is a heat wave?

A heat wave is an extended period of uncomfortably and abnormally hot and humid weather. In order to be considered a "heat wave," it should last at least a day. However, it usually lasts from a number of days to a number of weeks.

According to the World Meteorological Organization, there's a heat wave when the daily maximum temperature of more than 5 successive days is higher than the average maximum temperature by 9 degrees Fahrenheit (5 degrees Celsius). An extended heat wave is called a heat storm.

How do heat waves occur?

Some regions (Mediterranean-type climates, inland desert, and semi desert climates) are more prone to heat waves than other regions in the globe. One of the causes of heat waves is when winds from dry areas and large desert zones push warm, dry air towards normally cooler areas. This usually happens during the summer months, especially near the solstice, to areas that have no geographic features to cool and mitigate winds that come from the hot deserts.

A heat wave can also originate from air over tropical seas that penetrate into the middle latitudes. It often happens in the southeastern Canada and eastern United States. The heat island effects only worsen the condition in large cities because of the lack of night-time cooling effect. An area could also get abnormally hot and uncomfortably humid even without the transport of warm air from other areas.

What are the effects of heat waves?

The effects of heat waves can be massive. Many people suffer from heat exhaustion and heat stroke. It affects the health of young children, elderly people, ill people, or overweight people the most. Men are also more susceptible to heat illness than women as they perspire more and thus become more quickly dehydrated.

Heat waves often cause wildfires, destroying forests and agricultural lands. It also causes power outages since more people use air conditioning and other air cooling devices. Heat waves in recent times have caused bursting water lines, buckling roads and highways, and detonating power transformers.