Every day, we hear the weather presenter explain what to expect from the weather in the next 48 or 72 hours. Meteorological satellites, monitoring stations, and simulations run on the most advanced supercomputers make these forecasts possible. But, how were the first weather forecasts made? A thousand or two thousand years ago, such predictions also existed, and although they were made using leeches, plants, insects, and other natural phenomena, they were often reliable.
Today, science can predict with reasonable accuracy the weather we will have in the coming days. Although some mistakes do occur — especially with "extended forecasts" — those that refer to events more than 72 or 96 hours in the future — these predictions are reliable enough for billions of people to step out each morning knowing what the weather will be like throughout the day, or to plan weekend activities.
To produce weather forecasts, we employ the most advanced technology we have: meteorological satellites orbiting our planet thousands of kilometers above, ground stations that record minute-by-minute parameters such as temperature, atmospheric pressure, and humidity, and supercomputers capable of simulating the state of the weather over the coming hours from all available data. However, weather forecasts have been made for centuries, long before humanity had technology worthy of the name. How did they do it?
Ancient Forecasters
In ancient times, changes in the weather were associated with the movement of the stars. For example, the Egyptians linked the Nile's flood cycles to the movements of the stars — which in turn obeyed the whims of the gods — and the Babylonians made precarious weather predictions based on the appearance and color of the Moon or the sky. One of the first works related to meteorology and carried out with scientific rigor was "Meteorologica", a book written around the 4th century BC by Aristotle that gave rise to the term "meteorology".
In it, Aristotle explained how to make mixed observations and speculated on the origin of atmospheric and celestial phenomena. One of the most used celestial bodies in ancient weather predictions was the Moon. In fact, many of these beliefs — often false — have been immortalized in proverbs and sayings. The phase and position of our natural satellite were associated with rain, wind, or any other atmospheric phenomenon.
Generally, those whose work depended most on weather conditions were the first to take an interest in these matters. Sailors and shepherds were the first "meteorologists". For example, one of the first texts on weather prediction, dating from the 17th century, was published in England under the title "The Shepherd's Legacy." Its pages were full of examples of predictions based on the study of winds, clouds, the Sun, and fog, such as "Red sun, water in the eye." Although many of the suggested methods were erroneous, modern meteorologists assure that some of the mechanisms used correspond to basic principles of current meteorology. In fact, since 1920 it has been known that seven out of ten times, the "red sun" appears before rains.
The behavior of plants and animals was also (and still is) very useful for weather prediction. The scarlet pimpernel, for example, is almost as accurate as a barometer and reacts quickly to atmospheric changes. When these flowers open their petals, we will surely have good weather, because with the approach of rain, the flowers react due to humidity and close their petals to keep pollen dry.
In the early 17th century, the Italian scientist Evangelista Torricelli — intrigued by the curious variations in the level of mercury contained in a glass tube, open at the bottom and placed with the open end over a vessel full of that element — discovered that these changes reflected variations in atmospheric pressure. He officially invented the barometer in the early 17th century. It soon became clear that — although not the only important signal — variations in atmospheric pressure could be used to predict storms, something first done by the German physicist Otto von Guericke later in the 17th century.
In the 18th century, it was discovered that variations in atmospheric pressure were related to wind speed, and in the mid-19th century, the British Meteorological Institute was created, which would be responsible for offering weather forecasts based on barometer readings and other instruments.
However, the existence of reliable instruments did not discourage those who wanted to make predictions based on "sui generis" systems. For example, a certain Dr. Merryweather presented, at the Universal Exposition held at the Crystal Palace in London, a "Storm Indicator." It was an invention based on the fact that "at least one of the twelve leeches placed in glass bottles filled with water would ring a bell when a storm approached." Merryweather claimed that his leeches would rise to the surface of the water as the storm approached, making the bells ring. Confident in the accuracy of his device, he even suggested to the government that they install them along the coast of Great Britain to predict storms. Obviously, the suggestion was dismissed and the invention forgotten.
Are current methods more accurate than Merryweather's leeches? Surely yes. However, the complexity of analyzing the behavior of a sphere 12,800 km in diameter with an irregular surface, rotating at more than 1,600 km/h, wrapped in a layer 40 km thick composed of a mixture of different gases (whose concentrations vary spatially and temporally), and heated by a huge nuclear reactor located 150 million kilometers away is enormous, and it is logical that meteorologists make some errors. Even so, their work is good enough for us to use it daily to plan our day. Isn't that incredible?
