Source
With daylight saving time (also called daylight savings time) happening this weekend, clock confusion is once again ticking away, giving rise to various questions: Why do we spring forward? Does daylight saving time really save energy? Is it bad for your health? Here are answers from experts.
How and When Did Daylight Saving Time Start?
Ben Franklin—of "early to bed and early to rise" fame—as apparently the first person to suggest the concept of daylight savings.
While serving as U.S. ambassador to France in Paris, Franklin wrote of being awakened at 6 a.m. and realizing, to his surprise, that the sun would rise far earlier than he usually did. Imagine the resources that might be saved if he and others rose before noon and burned less midnight oil, Franklin, tongue half in cheek, wrote to a newspaper.
It wasn't until World War I that daylight savings were realized on a grand scale. Germany was the first state to adopt the time changes, to reduce artificial lighting and thereby save coal for the war effort. Friends and foes soon followed suit.
Daylight Saving Time: Energy Saver or Just Time Suck?
In recent years several studies have suggested that daylight saving time doesn't actually save energy—and might even result in a net loss.
Environmental economist Hendrik Wolff, of the University of Washington, co-authored a paper that studied Australian power-use data when parts of the country extended daylight saving time for the 2000 Sydney Olympics and others did not. The researchers found that the practice reduced lighting and electricity consumption in the evening but increased energy use in the now dark mornings-wiping out the evening gains.
Likewise, Matthew Kotchen, an economist at the University of California, saw in Indiana a situation ripe for study.
Prior to 2006 only 15 of the state's 92 counties observed daylight saving time. So when the whole state adopted daylight saving time, it became possible to compare before-and-after energy use. While use of artificial lights dropped, increased air-conditioning use more than offset any energy gains, according to the daylight saving time research Kotchen led for the National Bureau of Economic Research in 2008.
That's because the extra hour that daylight saving time adds in the evening is a hotter hour. "So if people get home an hour earlier in a warmer house, they turn on their air conditioning," the University of Washington's Wolff said.In fact, Hoosier consumers paid more on their electric bills than before they made the annual switch to daylight saving time, the study found.
But other studies do show energy gains.
In an October 2008 daylight saving time report to Congress, mandated by the same 2005 energy act that extended daylight saving time, the U.S. Department of Energy asserted that springing forward does save energy.
Extended daylight saving time saved 1.3 terawatt hours of electricity. That figure suggests that daylight saving time reduces annual U.S. electricity consumption by 0.03 percent and overall energy consumption by 0.02 percent.While those percentages seem small, they could represent significant savings because of the nation's enormous total energy use.
What's more, savings in some regions are apparently greater than in others.
California, for instance, appears to benefit most from daylight saving time—perhaps because its relatively mild weather encourages people to stay outdoors later. The Energy Department report found that daylight saving time resulted in an energy savings of one percent daily in the state.
Daylight Saving Time: Healthy or Harmful?
For decades advocates of daylight savings have argued that, energy savings or no, daylight saving time boosts health by encouraging active lifestyles—a claim Wolff and colleagues are currently putting to the test."In a nationwide American time-use study, we're clearly seeing that, at the time of daylight saving time extension in the spring, television watching is substantially reduced and outdoor behaviors like jogging, walking, or going to the park are substantially increased," Wolff said. "That's remarkable, because of course the total amount of daylight in a given day is the same."
But others warn of ill effects.
Till Roenneberg, a chronobiologist at Ludwig-Maximilians University in Munich, Germany, said his studies show that our circadian body clocks-set by light and darkness-never adjust to gaining an "extra" hour of sunlight to the end of the day during daylight saving time.
"The consequence of that is that the majority of the population has drastically decreased productivity, decreased quality of life, increasing susceptibility to illness, and is just plain tired," Roenneberg said.
One reason so many people in the developed world are chronically overtired, he said, is that they suffer from "social jet lag." In other words, their optimal circadian sleep periods are out of whack with their actual sleep schedules.Shifting daylight from morning to evening only increases this lag, he said.
"Light doesn't do the same things to the body in the morning and the evening. More light in the morning would advance the body clock, and that would be good. But more light in the evening would even further delay the body clock."
Other research hints at even more serious health risks.A 2008 study in the New England Journal of Medicine concluded that, at least in Sweden, heart attack risks go up in the days just after the spring time change. "The most likely explanation to our findings are disturbed sleep and disruption of biological rhythms," lead author Imre Janszky, of the Karolinska Institute's Department of Public Health Sciences in Stockholm, told National Geographic News via email.
Words
concept - понятие
friends and foes - друзья и враги
tongue-in-cheek (intended to be humorous and not meant seriously) - насмешливый
ambassador - посол
follow suit (to do the same thing as someone else) - следовать примеру
annual - годовой
consumption - потребление
circadian - околосуточный
adjust - регулировать
drastically - радикально
susceptibility - восприимчивость
out of whack - не в порядке
disruption - нарушение
assert - утверждать
