Fifty-three per cent of paintings contain some meteorological information. Not a lot of people know that, but the statistic is based on an exhaustive survey carried out some years ago by an American professor covering 50 major art galleries in the United States and Europe. He analysed 12,000 paintings in all, ranging in the dates of their execution from 1400 to 1967, and he estimated the cloud amounts and visibilities they showed.
Some of the findings are obvious and meteorologically predictable. Average cloud amount, for example, decreases with the latitude of the scene portrayed: those of northern countries feature cloudy skies, whereas a large proportion of paintings done in Spain or Italy are free of cloud.
Clearly, too, it is the cumulus cloud that appeals most to artists. Its attraction lies not just in the interesting shapes that it assumes, but also in the fact that cumulus clouds occur typically on bright, airy, sunny afternoons, when the colours of the countryside are shown to best advantage.
By contrast, clouds formed at higher altitudes are generally layered, often making the landscape dull and unstimulating from an artist's viewpoint, and presenting in themselves a matt, grey sheet less likely to appeal to landscape painters.
But there have been subtle changes with the centuries, which mirror well-documented changes in the climate of the northern hemisphere. From the 10th century to the end of the 15th, the average temperature over Europe and North America was significantly higher than it is now, and climatic conditions were correspondingly benign.
From around 1500 to 1850, however, there occurred what is called the Little Ice Age: winters were long and severe, and summers, in general, were cool, changeable and wet. These developments, it seems, can be deduced from contemporary paintings.
The average cloudiness in paintings of the 15th century, according to the survey, was about 30 per cent, while painted skies of the 1600s show an average cloud cover of four-fifths. Skies became clearer again in the late 19th and early 20th centuries, with the average cloudiness dropping to 70 per cent.
In this way the world of art can be a fruitful source of information for meteorologists in their constant quest to reconstruct the climate of centuries gone by. After all, artists over the years have chronicled the fauna and flora of their time, the foods, the furniture and implements in daily use, and the sports and games that served as entertainment. And of course, as best they could, the artists also chronicled the weather.