You’ve Been Warned
Carbon monoxide and other toxic gasses are among the many occupational dangers to coal miners, and the practice of bringing canaries into coal mines persisted from 1911 to 1986. If the bird suddenly got sick or died, it suggested that a deadly gas was present, and the miners should get out, hence the metaphor “canary in the coal mine” as an early indicator. Animals that serve an environmental warning role to humans are sometimes called “sentinel species.”
The old saying “Red sky at night, sailor’s delight; red sky in the morning, sailor’s warning” has variations in Shakespeare and the Bible. Since this red color is attributable to water vapor or dust splitting sun rays into their color spectrums when they pass sideways through the most atmosphere, color hints at the atmosphere’s contents at these times, which play a big role in weather. However, the saying is most accurate in the middle latitudes when weather systems move from west to east.
Talking about a “shot across the bow” is similar to saying “a warning shot,” or a warning gesture to show that you’re serious, even about using force. In the nautical sense, this means deliberately firing in front of another vessel, sometimes forcing that ship to change course or stop. This gesture has also been used to signal to an unknown ship to fly its flag, but in the modern time these efforts at identification also include attempts at radio contact.
“Beware the Ides of March,” the emperor is famously warned in Shakespeare’s play “Julius Caesar.” In the Roman calendar, the Ides was the 15th of each month, the day in March of 44BC that Ceasar was assasinated.
Not surprisingly, air raid sirens became widely used when air raids themselves started happening. In the early days of aerial attacks during WWI, London was unexpectedly attacked by German zeppelins, and the sirens became a more effective way to warn people than church bells or “take cover” signs displayed in public.
Animals which are especially sensitive to environmental changes often portend natural dangers in advance. Sharks head to deeper waters before a hurricane, birds keep down before a storm, worms flee rising groundwater, and some domestic animals’ behavior has accurately predicted earthquakes, at least when they are housed near one another.
The sinking of the British passenger ship Lusitania in 1915 by a German submarine, killing nearly 1,200 civilians, was a major WWI tragedy, but it shouldn’t have been an utter surprise. The German embassy had run ads in the New York Times and other papers for weeks before the event warning that they would torpedo British-flagged ships.