Parts of the US and Canada, beginning in the Pacific Northwest region and moving east to other areas of the northern United States, recently got over a record-breaking heat wave. Unsurprisingly, climate change has been on many people’s minds of late.

Responding to these concerns, climate expert Matthew Lewis recently took to his Twitter account to explain the recent so-called “wet bulb” temperatures and how dangerous they are.

The Dangers of “Wet Bulb” Temperatures

Lewis’ series of posts was prompted by posts from Rob Carlmark, a meteorologist for California’s ABC 10 news station. Carlmark’s post marveled at the extraordinary heat wave, which caused temperatures to hit 116 in British Columbia and about 110 in cities like Seattle and Portland.

As he explained, wet bulb temperature is the temperature at which water stops evaporating off of a wet thermometer bulb. If the air is sufficiently saturated with water — that is, if its sufficiently humid outside — further evaporation of water will not cool the thermometer bulb but will only make things hotter.

This which the combination of heat and humidity often feels significantly more oppressive than mere dry heat.

As a point of comparison, in dry heat, there is usually no risk of people dying from heat stroke until temperatures hit about 120 degrees Fahrenheit, but in wet-bulb conditions, people have been known to die of heat exposure in temperatures as low as 80 degrees.

This is because in wet-bulb conditions, sweat ceases to evaporate off our bodies, and our bodies can’t use their natural process to cool down.

Finally, Lewis points out that in the last 40 years, high wet-bulb temperatures were extremely rare on earth. Recently, however, that trend has been coming to an end. He goes on to explain that this will have enormous implications for human habitability, and that people may find themselves moving to different parts of the earth just to have hospitable places to live.

Needless to say, this information has opened a great many eyes to the imminent threat of climate change.