A Powerful Windstorm Changed the Boiling Point of Water in the UK

A windstorm that blew through England last year was so powerful it actually managed to lower the boiling point of water.

Storm Ciaran hit the United Kingdom in early November and, along with winds that gusted up to 70 mph, it brought heavy rainfall, resulting in severe flooding in parts of southern England. But there was a secondary, more subtle effect. Ciaran’s passage through the country resulted in a record low pressure, according to a new study published in the journal Royal Meteorological Society.

Air pressure can have a significant impact on the boiling point of liquids. A liquid’s boiling point is calculated as the point at which its vapor pressure—which increases as the liquid is heated—matches the pressure of the gas above it. So if air pressure drops, so does the temperature needed to get a liquid to a roiling boil. 

Anticipating this effect, researchers at the University of Reading turned to a sensitive barometer at the university’s atmospheric observatory and collected data from other local meteorological measurement sites. This gave them accurate data of Ciaran’s effects as the storm passed. But they also used some far more low-tech gear to see how Ciaran affected the boiling point of water: a kettle and thermometer. As the storm’s peak raged, the scientists boiled some water and found that Ciaran’s effect on air pressure was so significant that it was bubbling up at 98 degrees Celsius, a full two degrees lower than normal. 

While this likely didn’t help residents in the storm’s path save much power in their efforts to get some boiling water (the change in power would be “a needle in a haystack,” the researchers wrote), the team quickly realized that this would have a significant impact on a big chunk of the British population. Namely, that it would make cups of tea taste measurably worse until air pressure returned to normal. The study authors note that optimal temperature for extracting the tannins of black tea, the chemicals that lend the drink its signature taste, is 100 degrees Celsius. 

“During the passage of Ciarán, water’s boiling point at some sites in the southeast would have been less than this,” they wrote. “It therefore seems likely that some tea at breakfast time on 2 November 2023, in London and the southeast (affecting perhaps 20 million people), would have been made with water temperatures beyond the recommended range.”

“Like many Britons, I need my morning cup of tea,” said study co-author Giles Harrison in a press release. “Although I know that the boiling point of water varies with atmospheric pressure, I wasn’t expecting a storm to take the boiling water temperature outside the recommended range for brewing decent tea. Weather can have subtle effects.”