Researchers from Spain have said that they have evidence that the weekends are more rainy in some parts of Europe, a result of air pollution produced by humans.
According to a report in New Scientist, the research establishes the fact that the weather in certain parts of the world, including the US, Japan and China, can be driven by the weekly cycle of human activity.
This is because human activities result in the production of more air pollution during the week and less at the weekend.
Evidence that such an effect occurs in Europe is controversial and has been harder to come by.
Now, Arturo Sanchez-Lorenzo of the University of Barcelona, Spain, and his colleagues examined data gathered between 1961 and 2004 from weather stations across Spain to see whether such a pattern existed.
They claim to have found it in Spain, as well as hints of weekly changes in air circulation more broadly over western Europe.
This weekly pattern changes with the season, however.
In winter, there is a tendency for more rain during the week than on weekends, while in summer the effect is opposite and less pronounced.
The result is puzzling, but it is known that soot and other airborne pollutants produced by human activity can affect the weather in a variety of ways.
For example, particles can be heated by absorbing sunlight, which in turn heats the air and changes air circulation patterns. Pollutant particles can also provide seeds for cloud formation.
Exactly which effect has the greatest influence seems to depend on conditions that vary season by season.
They also found signs that air pressure in western Europe tends to be lower midweek than at the weekend in data from a global database, which suggests that the human influence on weather goes beyond known local effects.