Penn State NASA




Heat waves are days to week-long events with extremely high temperatures. These events are becoming more common with a changing climate, are forecasted to become frequent in many parts of the world in the future and occur earlier in the year (June 2022 has been a dress rehearsal for that!). 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).

Map of Australia shows maximum temperatures in Dec 2018- Jan 2019. "Cooler" near coast. More ~45C, inland sections 50*C+
This map of Australia shows maximum temperatures in December 2018 and January 2019.

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. In fact, this “heat island” effect makes cities as much as 7 degrees F warmer during the day. Nighttime often does not provide much relief, with temperatures above 80 deg F for many nights in a row.

June 2021 was a sign of things to come in the northwest US and western Canada, with temperatures topping out at 116 degrees F in Portland and 108 degrees F in Seattle. Lytton in British Columbia reached 121 degrees F, the hottest temperature ever recorded in Canada. These temperatures smashed records for these cities that are normally cool in the early summer.

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Predicted high temperatures for western Washington on June 28, 2021 
United States National Weather Service, Public domain, via Wikimedia Commons

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 of Lytton which was virtually destroyed. Several weeks later and further south, temperatures reached 130 deg G in Death Valley, matching the world record the hottest temperature ever recorded.

July 2022 saw record breaking temperatures in Europe and notably in London where it reached 40.2 deg C or 104.4 deg F, an all-time record. That city is not adapted to temperatures that high and will have to invest significantly in areas like air-conditioning public transportation in the future.

Heatwaves will become more common and more extreme in most places in the future as the planet warms. Europe and Australia are going to experience more and more of them, as are places in India. The southern US will seem more like the Middle East in the future, with cities like Austin and El Paso becoming as hot as Dubai is today and Phoenix approaching Baghdad, Iraq temperatures. Washington DC is going to seem more like Austin in the summer, Boston will seem more like Philly and Billings, Montana more like El Paso.

More dramatically, there may be places in the Middle East and Northern India where humans may not be able to live in the future because it is impossible for the human body to cope with the searing heat.  To be more precise, a wet bulb temperature that factors heat and humidity of 95 degrees F or 35 degrees C is where it is thought that a combination of kidney, heart, or even brain failure may commence, especially for vulnerable populations.

Temp in India in June 2019. Northern half of india over 45C getting more hot (~50C) moving north west. South western india around 38C
Temperatures in India in June 2019 (in degrees C).
Credit: NASA Earth Observatory image by Joshua Stevens (using GEOS-5 data from the Global Modeling and Assimilation Office at NASA GSFC) (Public Domain)

Like drought and fire, the 2022 IPCC report stresses the need for adaptation to heat.  This is already taking place in the developed world where cities are reducing the heat island effect by, for example, planting more trees, making roofs green by covering with plants, and using materials for pavement that reflects heat as opposed to absorbing it.  Unfortunately, these strategies are more difficult to apply in developing nations where necessities like air conditioning are also less available.  Thus, it is likely that heatwaves will become increasingly deadly in coming decades.

Aerial view of the green roof of Chicago City Hall
Green roof of Chicago City Hall
Credit: Chicago City Hall Green Roof by TonyTheTiger from Wikipedia is licensed under CC BY-SA 3.0