Heat Waves Are Increasing and More Dangerous Than We Realize
The impacts of severe heat are badly underestimated by everyone.
Why?
Probably because a proper lab study using human volunteers to test the impacts of heat on health hadn’t been done until 2022.
That study found that the cardiovascular strain in healthy young adults sitting in a chair began at a wet-bulb temperature of 29.4 degrees C. (This roughly equates to a temperature of 35C (95F) and 65% humidity or 45C with 50% humidity ). Health authorities had long believed that anything below a wet-bulb temperature (WBT) of 32C was safe for most people.
Wet-bulb temperature (WBT) takes temperature, humidity, wind speed, and other variables into account. This is similar to the Heat Index, often shown in weather reports as the “feels like” or “real feel” temperature.
Need-to-Know: The danger zone for heat is lower than you think
During slow walking cardiovascular strain increased at a WBT of 27 C and the body’s core temperature started to heat up at a WBT of 28C.
Remember, these are healthy young adults being tested.
Prolonged exposure to these levels of heat and humidity may become dire for vulnerable populations such as the elderly, and those with heart disease and other chronic conditions, the study concluded.
Experts previously considered a few hours of exposure to a WBT of 35C, even in the shade with a fan, to be deadly for most people. The new study suggests the fatality zone is much lower.
Even in dry and hot environments, there is a limit to how much the body can sweat and stay cool enough. For example, a WBT of 27C (45C with 19% humidity) results in cardiovascular strain for a young person while at rest.
Our bodies sweat to cool off via evaporation. When it’s humid, water evaporates slower, making it harder to cool down. If we can’t cool off, our body’s core temperature rises which causes our hearts to work harder to pump more blood to the skin to help dissipate the heat. Should our core temperature continue to rise, our internal organs can be damaged and death can occur within a few hours.
Need-to-Know: Dangerous levels of heat are no longer rare.
These dangerous levels of extreme heat are happening far more often than is widely recognized. Last summer the city of Phoenix had a record 55 days of temperatures at, or above, 43 degrees C (110F) that resulted in more than 600 heat-related deaths.
It is difficult to know how many people die during a heat wave because a heat-related heart attack looks like any other heart attack. For example, the 2,300 official heat-related deaths in the U.S. last year, more likely to have been more than 11,000, according to a study.
Here’s the US National Weather Service WBT forecast for Thursday June 6. A record-breaking heat wave is affecting over 30 million people. Large parts of Florida, Texas, Arizona and California were in the danger zone.
I couldn’t find an easy-to-decipher WBT scale so here are a few examples:
Temp 30C; humidity 70% = WBT 25.5C
40C /70% = WBT 35C ( 104F/70% = WBT 95F)
40C/35% = WBT 27.3C
50C/35% = WBT 35C
(Here’s an online WBT calculator.)
There been an astounding number of record heat waves worldwide this year. These have lasted longer and have been hotter than in the past. And summer hasn’t even started yet!
More heat records will be broken this summer—and in the years to come if the planet’s temperature continues to rise. So we all need to understand the health risks of severe heat.
Until next time, be safe and stay cool.
Stephen