As the eastward-bound thermal dome continues to wrap around western Canada, unleashing a pressure cooker for a heatwave that has produced the highest temperatures ever recorded in the country, some Canadians may be thinking about what summer could look like in the future.
But in the wake of this dangerous weather event, climate experts are pointing to another concept we might need to worry about: wet-bulb temperatures.
Rachel White, an atmospheric scientist in the University of British Columbia’s Department of Earth, Oceanic and Atmospheric Sciences, explains that wet bulb temperatures are theoretical measurements that combine temperature and humidity into a single value.
Basically, it is the temperature at which water stops evaporating from a wet thermometer bulb, which means it is no longer cooling.
“With wet bulb temperatures, you can increase them in one of two ways,” White explains. “You can either increase the temperature or increase the humidity. Obviously it would be worse if you did both.”
What does this have to do with human survival? The wet bulb temperature is basically a metaphor for human sweat. Sweat is the body’s cooling mechanism, which gives a person comfort when the body warms up.
But in order for sweat to cool a person’s skin, it relies on the process of evaporation to keep heat away from the body.
At theoretical temperatures of wet bulbs, evaporation and cooling can no longer occur because the atmosphere is completely saturated with water. And when the temperature of a wet bulb reaches 35 degrees Celsius, it crosses a threshold at which humans are unable to lose internal body heat and cool themselves off.
“In general, the atmosphere rarely has 100 percent relative humidity,” White said.
But research shows that even wet bulb temperatures of less than 35°C can be fatal. This was the case in 2010When Russia was hit by a deadly heat wave, wet-bulb temperatures did not exceed 28 degrees Celsius.
“That’s why people kind of talk about [wet bulbs]Because a very humid heat wave is much more dangerous than a very dry heat wave.”
Under the unprecedented heat wave this week, cities like Vancouver were experiencing high humidity.
“It’s the very humid heat waves that will raise the temperature of the damp bulb,” White said.
In western Canada, wet bulb temperatures are generally not a big problem. Wet temperatures are more likely to occur in areas where large bodies of water tend to warm, White said, such as the Great Lakes.
But while climate change is driving up global temperatures, climate experts are using models to identify future hotspots for wet bulb temperatures.
Modeling suggests that if society does not make a collective effort to reduce greenhouse gas emissions, wet-bulb temperatures could regularly exceed 35 °C in parts of South Asia and the Middle East this century.
“Climate scientists have predicted for decades that as business as usual continues, the frequency and intensity of heat waves will increase globally,” said Hind Al-Abadla, who studies atmospheric chemistry and climate change at Wilfrid Laurier University in Waterloo, Ontario.
Wet bulb temperatures are described as being similar to the temperature forecasters use to describe how hot people feel on a humid day. In extremely humid parts of the world, particularly in coastal areas near warm bodies of water, scientists are already seeing evidence of conditions reaching the limits of human tolerance.
a Study 2020 in Science Advances It looked at global temperature data from weather stations over the past 41 years and found that the intensity and frequency of extreme moist heat are increasing — and this, the authors say, will present a “major social challenge” in the coming decades.
Experts say reducing greenhouse gas emissions is one way to reduce the potential for these dangerous temperatures. But another way is to make sure there is adequate infrastructure to accommodate people who can’t afford cooling.
“Confronting the rising temperatures in the humid bulbs means that governments need to issue warnings for people to stay indoors in climate-controlled places,” Al-Abadla said.
But she noted that running such places requires energy intensive.
“So moving to clean, renewable energy sources and phasing out fossil fuels will not only reduce carbon emissions, but also help people survive heat waves when they occur.”
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