Summer's Dog Days Are Here—And Getting Hotter

James Owen
for National Geographic News

July 16, 2004

The dog days of summer have arrived in the Northern Hemisphere. While
they may make many us feel like we're swaddled in fur, the period is
actually named after Sirius, the Dog Star.

Sirius rises with the sun when summer is at its hottest. The dog days traditionally run from July 3 to August 11.

The ancients believed extra heat generated by Sirius in conjunction with the sun caused this sizzling spell of weather. Sirius is the brightest star at night, after all.

But Sirius, which is found in the Canis Major (big dog) constellation, is some 50 trillion miles (80 trillion kilometers) from Earth—too far away to influence temperatures here.

In Roman times the dog days—or dies caniculares in Latin—were associated with intolerable heat, lethargy, disease, and, appropriately enough, mad dogs.

Pliny (A.D. 23-79), in his Natural History, refers to the increased risk of attack by rabid dogs in July and August. Bizarrely, he recommends feeding the animals large quantities of chicken droppings to prevent them from catching the disease.

In Britain The Husbandman's Practice, published in 1729, also offers survival tips for getting through the dog days. It suggests men should "abstain all this time from woman" and "take heed of feeding violently."

Ominously, the book warns, "The Heat of the Sun is so violent that Men's bodies at Midnight sweat as at Midday: and if they be hurt, they be more sick than at any other time, yea very near Dead."

Yet the ancient Egyptians, who experienced much hotter, drier summers, celebrated the return of the dog days, because they heralded a life-sustaining "miracle."

The start of the Egyptian sacred year was marked by the reappearance of Sirius. Soon afterward, the River Nile would flood, reviving parched farmland—despite a seasonal lack of rain. (The Egyptians weren't aware the water flowed from rain-drenched mountains in Ethiopia, more than a thousand miles [1,600 kilometers] to the south.)

Today Sirius appears several weeks later than in ancient times, because the stars and constellations gradually shift their position in relation to the sun.

Freezers and Fans

In modern times, summer's dog days are more bearable, thanks to freezers, electric fans, air-conditioning, and other conveniences. But many residents of the Northern Hemisphere's lower latitudes still find it hard to insulate themselves against the effects of hot weather in July and August.

U.S. government studies have shown that civil disturbances and incidents of domestic violence and abuse are more likely to occur during heat waves.

This is borne out by the long, hot summer of 1967, when riots ravaged 125 cities across the U.S. In Detroit alone, 43 people died. The previous July, in Chicago, a major riot broke out when police turned off fire hydrants residents used to cool off.

Many urbanites in southern Europe flee their sweltering cities for the mountains or coast in summer. Rome, Italy, for example, becomes a virtual ghost town in August as businesses, cinemas, and nightclubs close down. The annual exodus dates back to at least the first century, when Roman emperors escaped to seaside villas.

The tradition appears set to continue, as evidence suggests the dog days of summer are growing even more oppressive.

Meteorologists say last year was the third warmest worldwide since records began in 1891, with the ten warmest years all occurring since 1990. In central Europe, last summer was the hottest in more than 500 years, according to the Climatic Research Unit at the University of East Anglia in England.

On August 10 last year, Britain recorded its highest ever temperature—101° Fahrenheit (38.5° Celsius)—in Kent, England.

Meanwhile, a heat wave in France claimed the lives of an estimated 15,000 people last summer. Temporary mortuaries were set up in Paris as temperatures soared to more than 104° Fahrenheit (40° Celsius).

In the U.S., particularly in southern, southwestern, and western states, temperatures regularly hit such heights during the peak of summer.

California's Death Valley remains one of the hottest places on Earth. In July 1913 temperatures rose to an infernal 134° Fahrenheit (57° Celsius)—the hottest temperature ever recorded in the U.S.

Forty of the fifty U.S. states have recorded their highest temperature during the traditional dog-day period of July 3 to August 11. They include Idaho (118° Fahrenheit/48° Celsius), New York (108° Fahrenheit/42° Celsius), Ohio (113° Fahrenheit/45° Celsius), Utah (117° Fahrenheit/47° Celsius), and Virginia (110° Fahrenheit/43° Celsius).

Hawaii and Alaska share the lowest all-time high temperature recorded in a U.S. state: 100° Fahrenheit (38° Celsius).

California Wildfires

Wildfires in southern California last year burned 743,000 acres (301,000 hectares) of brush and timber, destroyed 3,700 homes, caused 22 deaths, and cost at least 2.5 billion dollars (U.S.). Scientists predict that such wildfires and droughts will become more widespread due to climate change, particularly in western states.

A recent study by the Lawrence Berkeley National Laboratory, in Berkeley, California, and the U.S. National Forest Service indicates that hotter, windier weather in California means that the number of out-of-control fires is set to double at the very least.

And a secret Pentagon report into possible climate change impacts, which became public earlier this year, suggests the U.S. and Europe could soon experience 33 percent more days when temperatures exceed 90° Fahrenheit (32° Celsius).

The Pentagon report also warns of possible megadroughts, famine, and social unrest across the globe, echoing scenarios depicted in over-the-top Hollywood fashion in this year's eco-doom movie, The Day After Tomorrow.

Pessimists might argue that in the future we may all need to find more ways to chill out, before the dog days of summer drive us all barking mad.

For more climate news, scroll down.