How hot is too hot for humans?Understand the wet bulb temperature


As the eastward heat dome continues to envelope western Canada, causing the pressure cooker to generate the highest temperature heat wave in the country’s history, some Canadians may be thinking about what the summer will look like in the future.

But with This dangerous weather event, Climate experts pointed out another concept we might need to worry about: wet bulb temperature.

Rachel White, an atmospheric scientist in the Department of Earth, Ocean and Atmospheric Sciences at the University of British Columbia, explained that wet bulb temperature is a theoretical measurement that combines temperature and humidity into one value.

Basically, it is the temperature at which the water stops evaporating from the wet thermometer bulb, which means it can no longer be cooled.

“For wet bulb temperatures, you can increase them in one of two ways,” White explained. “You can increase the temperature, you can increase the humidity. Obviously, if you do both, the situation will be worse.”

What does this have to do with human survivability? Wet bulb temperature is essentially a metaphor for human sweat. Sweat is the body’s cooling mechanism. When the body heats up, it can provide relief for humans.

But sweat really cools human skin, it relies on the process of evaporation to take heat away from the body.

At the theoretical wet bulb temperature, evaporation and cooling no longer occur because the atmosphere is completely saturated with water. When the wet bulb temperature reaches 35 degrees Celsius, it will cross a threshold under which humans can no longer lose body heat and allow themselves to cool down.

This week, during the heat wave in Western Canada, the Canadian tire store in Vancouver was short of air conditioners and fans. Climate experts say that an extreme high temperature measurement we need to consider is wet bulb temperature. (Ben Nilms/Canadian Broadcasting Corporation)

“In general, the atmosphere rarely has 100% relative humidity,” White said.

But research shows that even if the wet bulb temperature is lower than 35 degrees Celsius, it can be fatal. This is the case in 2010When Russia experienced a fatal heat wave, the wet bulb temperature did not exceed 28 degrees Celsius.

“That’s why people are talking about [wet bulbs], Because a very humid heat wave is much more dangerous than a very dry heat wave,” White said.

Under the unprecedented heat wave this week, cities such as Vancouver are experiencing high humidity.

“And a very humid heat wave will produce a higher wet bulb temperature,” White said.

In Western Canada, wet bulb temperature is usually not a big issue. White said wet bulb temperatures are more likely to occur in areas where large areas of water tend to warm up, such as the Great Lakes region.

But as climate change pushes up global temperatures, climate experts are using models to determine hot spots for future wet bulb temperatures.

Modeling shows that if society does not work together to reduce greenhouse gas emissions, the wet bulb temperature in parts of South Asia and the Middle East may often exceed the 35 degrees Celsius benchmark this century.

In this 2019 file photo, wet bulb temperature (WBGT) measurements test the conditions of Tokyo Shiokaze Park as part of the effort to relieve heat on the eve of the Olympics. As the earth heats up, this situation may become more common. (Beruz Mehri/AFP)

“Climate scientists have been predicting for decades that under business as usual conditions, the frequency and intensity of heat waves will increase globally,” said Hind Al of Wilfrid Laurier University of Waterloo, Ontario, who studies atmospheric chemistry and climate change. -Abdleh said.

She described the wet bulb temperature as similar to the wet bulb temperature used by weather forecasters to describe how people feel heat in humid weather. In very humid areas of the world, especially coastal areas near warm waters, scientists have seen evidence of conditions reaching the limits of human tolerance.

A kind Science Progress Research in 2020 Looking at the global temperature data of weather stations in the past 41 years, it is found that the severity and frequency of extreme heat and humidity are increasing-the author said, this will represent a “major social challenge” for the next few decades.

Experts say that reducing greenhouse gas emissions is a way to reduce the possibility of these dangerous temperatures. But the other is to ensure that there is proper infrastructure to accommodate people who cannot be cooled.

“Responding to rising wet bulb temperatures means that the government needs to issue recommendations to keep people in climate-controlled rooms,” Al-Abdleh said.

However, she pointed out that operating such a space is energy intensive.

“Therefore, transitioning to clean and renewable energy and phasing out fossil fuels will not only reduce our carbon emissions, it will also help people survive the heat wave.”

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