On this day, he had come to take the first reading from his thermometer, still a new technology at the time. Derham’s was custom-built: a 2-foot shaft of glass with a bulb at the bottom filled with alcohol. The Fahrenheit and Celsius scales weren’t yet invented, so he read the temperature on his instrument using his own system: 1 degree for every tenth of an inch. When Derham read the thermometer that winter morning, it was mild — 11.00 inches of alcohol, or 110 degrees — roughly 48 degrees Fahrenheit. He would continue reading the temperature thrice daily for the next seven years, recording it along with the wind, rain, barometric pressure and clouds.
Derham could not have known, but his hobby would one day mark the beginning of something monumental: the Central England temperature record, the earliest thermometer readings now included in the massive datasets that track global warming. Eventually, scientists would use Derham’s readings — among others — to better understand human-caused climate change.
The vast majority of the world’s temperature readings don’t go back further than the 1900s, when large-scale burning of fossil fuels was already underway, and with it the release of planet-warming greenhouse gases. Such a short record makes it difficult to measure natural variations in climate that existed before humans began warming the world; as a result, it complicates efforts to tease apart how much of the planet’s warming has been caused by humans versus natural factors.
The Central England record covers a longer period than any other thermometer series, reaching from 1699 to the present. It owes its beginnings to Derham and a handful of other clergymen, physicians and philosophers in 18th-century England who happened to be early adopters of the thermometer. Modern researchers have combined the fragmentary, overlapping records they left behind into a series of annual temperatures averaged over the region, which stretches from England’s south coast 175 miles north to Manchester.
Thermometer readings going back to 1880 or so tell scientists Earth has warmed about 1.5 F since then, mostly due to greenhouse gas emissions. But even earlier readings can provide a record of natural climate variation caused by volcanic eruptions or cycles in ocean circulation. This thermometer record is imperfect, but researchers are working on improving it using new mathematical methods and experiments with some of the same centuries-old thermometers. Unfortunately, this historical data is showing scientists that warming might be worse than we thought.
The First Temperatures
The earliest temperature measurements by Derham and others amounted to a sort of religious inquiry: They documented not only the weather, but also the body sizes of gnats and wasps and the dates on which snowdrop flowers bloomed and thrushes began to sing each spring. “Let us examine them with all our Gauges, measure them with our nicest Rules, pry into them with our Microscopes, and most exquisite Instruments,” wrote Derham in his 1713 book, Physico-Theology. Hidden in the minuscule details of nature, he believed, were insights into the Creator.
By the early 1700s, scientists had developed the Fahrenheit and Celsius scales. Mass production of standardized thermometers was underway by the mid-1800s. Meteorology emerged as a formal science in about 1870, as the United States and other countries established national weather services and started keeping records. But it wasn’t until the 1930s that anyone tried to use this information to measure changes in climate.