Abstract/Summary

How can we compare the temperature of one summer’s day to another, and how much can we trust the measurements of record air temperatures such as those of July 2019? The basics of air temperature measurement are simple enough – put a thermometer in the shade and keep air moving past it. However, the flurry around summer temperature records suggests that the details of how to do this aren’t so widely appreciated. For example, how many times have you heard a radio phone-in programme asking listeners for car or garden temperature readings to compare, or a tennis commentator mentioning the temperature on centre court at Wimbledon? For a thermometer anywhere in direct sunlight, sheltered from the wind, its temperature is just that of a hot thing in the Sun. It’s highly unlikely to be a reliable air temperature. Only by using well calibrated sensors with standardised exposures can we expect measured temperatures to be both representative and consistent, spatially and temporally.