Heat waves are days to week-long events with extremely high temperatures. These events are becoming more common with a changing climate and are forecasted to become frequent in many parts of the world in the future. Heatwaves are often part of extended droughts and associated with wildfires. They are major public health risks, especially for very young and older populations as well as the poor who do not have access to air conditioning or basic hydration. In the developing world, heat waves can be very deadly, in India in 2015 more than 2200 people died due to excessive heat.
Some of the most drastic heatwaves occur in Australia, a continent which is also characterized by devastating drought and perilous wildfires. The last few years have seen major heatwaves across the continent shattering local and continental temperature records. In 2013 Australia got so hot that they had to add new colors to the temperature map. There were days that year when the center of the continent topped 125 degrees F (52 degrees C).
In 2019 Australia broke records again in a summer of wildfires, drought, and heat. On December 19, the average high for the whole continent was 107.4 degrees F (41.9 degrees C) shattering the record set the day before by over a degree C.
In the US, heatwaves in the desert southwest including Phoenix and Las Vegas are part of a normal summer. Phoenix regularly reaches 112 degrees F (44.4 degrees C) and it has been known to exceed 120 degrees F (48.9 degrees C). These are shade temperatures, corresponding temperatures can reach 168 degrees F (76 degrees C) in the sun right above the ground level. Because concrete traps heat, cities like Phoenix get particularly hot and are prone to heatwaves.
June 2021 was a sign of things to come in the northwest US and western Canada with temperatures topping out at 116 degrees C in Portland and 108 degrees C in Seattle. Lytton in British Columbia reached 121 degrees C, the hottest temperature ever recorded in Canada. These temperatures smashed records for these cities that are normally cool in the early summer.
Predicted high temperatures for western Washington on June 28, 2021 https://en.wikipedia.org/wiki/2021_Western_North_America_heat_wave
The heat caused a minimum of 500 fatalities in the US and Canada among vulnerable populations including the elderly. These cities are not adapted to extreme heat with a low percentage (about 40%) of homes having air conditioning. The heat was so extreme that up to a billion of clams and other shellfish were cooked inside their shells in an ecologic catastrophe. The heat caused major wildfires to rage throughout the area including the town on Lytton which was virtually destroyed. Several weeks later and further south, temperatures reached 130 deg G in Death Valley, matching the world record hottest temperature ever recorded.
Heatwaves will become more common and more extreme in most places in the future as the planet warms. Australia is going to experience more and more of them, as are places in the Middle East and India. In fact, there may be places in the Middle East and Northern India where it humans cannot live in the future because it is impossible for the human body to stay cool in the searing heat.