In making plans for a trip to Ireland this spring, I checked into weather conditions there to know what kind of clothes to pack. Imagine my surprise to find that summer starts there on May 1! How is this possible? I always thought the seasons were regulated by when the sun crosses the equator and the longest and shortest days of the year. Is this just an American interpretation? What about other European countries, especially Great Britain? I am enclosing a copy of the page from the tourist information booklet provided by the Irish Tourist Board, just so you won't think I'm making this up in my overly optimistic hopes for a sunny vacation.
Mary Z., Oak Park, Illinois
There is a widespread misconception in this country — which extends, I might note, to the makers of most calendars, dictionaries, and encyclopedias — that summer “officially” starts on the day of the summer solstice, June 21 or 22, which is the longest day of the year. Americans also believe (1) that there is some valid scientific reason for doing it that way, and (2) that everybody in the Northern Hemisphere does it that way, and always has.
None of these things is true. So far as I have been able to discover, no scientific or governmental body has ever formally declared that summer starts on the solstice.
Certainly there is no good scientific reason for doing so. In the Northern Hemisphere the period of maximum daylight falls roughly between May 7 and August 7 — in other words, the six weeks before and after the solstice. The period of maximum temperature, on the other hand, is June 4 through September 3. (The period of max temperature in the mid-latitudes always lags about 25 to 30 days behind the period of max daylight, due to the fact that the earth heats up and cools off relatively slowly.)
“It isn’t really clear how the astronomical definition [i.e., summer starts on the solstice] got started,” says Kevin Trenberth, a climate researcher at the University of Illinois in Urbana. “Although the sun-earth geometry is clearly the origin of the seasons on earth, it has nothing directly to do with temperature or weather.”
He notes that meteorologists define summer simply as June, July, and August. “For practical purposes, the meteorological definition is the best one, being very closely to the [weather] statistics,” he says.
In fact, it appears that June 1 was accepted as the beginning of summer in the United States until relatively recently. According to many older reference books, ranging from The American Cyclopedia (1883) to Webster’s Third New International Dictionary (1966), summer in the U.S. comprises the months of June, July, and August. Seasons in Britain, for no particularly good reason, start a month earlier.
The Oxford English Dictionary, somewhat confusingly, says that spring in Britain (and evidently in Ireland) runs from February 1 through April 30, but that summer runs from mid-May to mid-August. This leaves the first two weeks in May mysteriously unaccounted for, by my reckoning, but that is England for you.
The Irish appear to have opted for May 1 as the starting date of their summer, but it was not always thus. I have here an old Irish guidebook (1938) that says summer begins the day after the third Saturday in April (Sunday, presumably) and ends the day after the first Saturday in October. The May 1 starting date may strike Americans as odd, but it sure beats what they were using in 1938.
I should emphasize that just because our Irish friends start their summer earlier does not mean Ireland gets warmer earlier. The cruel truth is that it never gets warm in Ireland, which has one of the most dismal climates on earth.
A July day in which the temperature reaches 72 is considered a scorcher. For the most part, the weather is damp and cloudy (although May and June are fairly sunny), with frequent rain–an average of 180 days a year in the southeast, and over 250 days a year in the west. The humidity averages around 85 percent and seldom drops below 75 percent.
On the plus side, it never gets that cold — the annual mean temperature variation in Dublin is only 18 degrees Fahrenheit. And the weather is extremely variable, which means the sun breaks out pretty frequently. Usually, however, the only effect of this is to convince you that better days are coming, which, for the most part, they ain’t. Enjoy your trip.
Send questions to Cecil via email@example.com.