This winter is not only very cold but also extremely dry, thanks to a high-pressure system stuck over the UK.

Curiously, this weather system has also turned temperatures upside down. Usually if you walk up a mountain it gets colder, which is why mountaintops are often capped with snow.

In December 1784 the naturalist Gilbert White, in Selborne, Hampshire, recorded temperatures that were vastly out of place. He asked an acquaintance who lived on higher ground at Newton Valence to read his thermometer morning and night. White wrote that he had been “expecting wonderful phenomena, in so elevated a region, at two hundred feet or more above my house”, but he was utterly baffled when it turned out that Newton was up to 18 degrees fahrenheit (10C) warmer than his home down below in Selborne.

At Selborne the temperature difference was plain to see in severe frost damage with leaves on many shrubs and trees scorched by the cold. White also described ice needles floating down from a clear sky, the fur of his cat was electric and two of his workmen suffered frostbite. He was so disturbed by this unexpected turn of results that he had both sets of thermometers sent away for checking, but their readings were correct.

It took another 130 years to get a decent explanation for this topsy-turvy weather. Cold air is dense and on calm, clear nights it flows like water down hillsides and collects in pools in valley bottoms and sheltered low ground. These frost hollows have some of the coldest temperatures.