Wet-Bulb Temperature

Very simply, this is a measure of temperature that accounts for humidity.

From an article entitled Why you need to worry about the ‘wet-bulb temperature’:

Wet-bulb temperature (WBT) combines dry air temperature (as you’d see on a thermometer) with humidity – in essence, it is a measure of heat-stress conditions on humans.

It’s named for how it’s measured – a wet cloth is held over the bulb of a thermometer (or something, I wasn’t quite sure).

Wet-bulb temperatures are more extreme that “normal” temperatures. From Wikipedia:

Even heat-adapted people cannot carry out normal outdoor activities past a wet-bulb temperature of 32 °C (90 °F), equivalent to a heat index of 55 °C (131 °F). A reading of 35 °C (95 °F) – equivalent to a heat index of 71 °C (160 °F) – is considered the theoretical human survivability limit for up to six hours of exposure.

Why I Looked It Up

I saw it in a tweet during the recent heat wave in the US. I don’t have the link for the tweet, but (from a screencap) it read:

Yesterday parts of the US south experienced wetbulb temperatures of up to 94F (34.5C). At these temperatures, no amount of shade or hydration will save you. Without AC, you die. And this is just the beginning.

Someone on the /r/conservative subreddit had annotated it with:

Are people really this dumb?

I think this – the tweet and the annotation – were posted as a way of pointing out that the conservative annotator didn’t understand the difference between normal and wet-bulb temperatures.

Postscript

From On the Move:

Very few scientists have looked at what happens when the hot temperatures projected for the United States intersect with rising humidity – an especially miserable combination described as “wet-bulb temperature” (measured by wrapping a water-soaked cloth around the bulb of a thermometer and blowing air over it).