How Does the Boiling Temperature of Water Depend On the Weather?

The weather has only a small effect on the boiling temperature of water.

When people go around saying that water boils at 212 degrees Fahrenheit (100 degrees Celsius) at sea level, they’re speaking rather loosely. The standard definition of the boiling temperature of pure water says nothing about sea level.

It is defined in terms of a specific atmospheric pressure 29.92 inches (760 millimeters) of mercury, which is a typical, but hardly guaranteed, value for sea-level locations. Every TV weather fan knows that the air pressure changes as the weather changes, whether you live by the seaside or anywhere else. So the temperature of boiling water will indeed depend on whatever the weather conditions happen to be at the time.

Quite arbitrarily, scientists have chosen exactly 760 millimeters of mercury as the standard pressure they call one atmosphere. (That strange-looking number, 29.92 inches of mercury, is simply a quirk of conversion from millimeters to inches: 25.4 millimeters per inch.) The boiling temperature at that standard pressure is called the normal boiling temperature or the normal boiling point. That’s what 212 degrees Fahrenheit or 100 degrees Celsius really is.

While knowing these facts might impress your friends, the effect of atmospheric pressure on the boiling temperature of water isn’t big enough to worry about.

Even if you were brewing a cup of tea while sitting smack in the eye of a hurricane, where the pressure might drop as low as 28 inches or 710 millimeters of mercury (the world’s record low is 25.9 inches or 658 millimeters), the boiling temperature would only go down to 208 degrees Fahrenheit (98 degrees Celsius).

It’s comforting to know that your tea would still be hot enough.

About Karen Hill

Karen Hill is a freelance writer, editor, and columnist. Born in New York, her work has appeared in the Examiner, Yahoo News, Buzzfeed, among others.

Leave a Comment