for National Geographic News
With daylight saving time (also called daylight
savings) about to begin again, clock confusion is once again ticking
away: When exactly does daylight saving time end? Why do we spring
forward? Does it really save energy? Is it bad for your health? Get
expert answers below.
When Does
Daylight Savings Begin in 2011?
For
most Americans, daylight saving time 2011 starts at 2 a.m. on Sunday,
March 13, when most states spring forward an hour. Time will fall back
to standard time again on Sunday, November 6, 2011, when daylight saving
time ends.
The federal government doesn't
require U.S. states or territories to observe daylight saving time,
which is why residents of Arizona,
Hawaii,
Puerto Rico, the Virgin Islands, American Samoa, Guam, and the Northern
Marianas Islands won't need to change their clocks this weekend.
Where it is observed, daylight savings has been known
to cause some problems.
National surveys by Rasmussen Reports, for
example, show that 83 percent of respondents knew when to move their
clocks ahead in spring 2010. Twenty-seven percent, though, admitted
they'd been an hour early or late at least once in their lives because
they hadn't changed their clocks correctly.
It's
enough to make you wonder—why do we do use daylight saving time in the
first place?
How and When Did Daylight
Saving Time Start?
Ben Franklin—of
"early to bed and early to rise" fame—was apparently the first person to
suggest the concept of daylight savings, according to computer
scientist David
Prerau, author of the book Seize the Daylight:
The Curious and Contentious Story of Daylight Saving Time.
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.
"Franklin seriously realized it would be beneficial
to make better use of daylight but he didn't really know how to
implement it," Prerau said.
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.
In the U.S. a
federal law standardized the yearly start and end of daylight saving
time in 1918—for the states that chose to observe it.
During World War II the U.S. made daylight saving time
mandatory for the whole country, as a way to save wartime resources.
Between February 9, 1942, and September 30, 1945, the government took it
a step further. During this period daylight saving time was observed
year-round, essentially making it the new standard time, if only for a
few years.
Since the end of World War II,
though, daylight saving time has always been optional for U.S. states.
But its beginning and end have shifted—and occasionally disappeared.
During the 1973-74 Arab oil embargo, the U.S. once
again extended daylight saving time through the winter, resulting in a
one percent decrease in the country's electrical load, according to
federal studies cited by Prerau.
Thirty years
later the Energy Policy Act of 2005 was enacted, mandating a
controversial monthlong extension
of daylight saving time, starting in 2007.
But
does daylight saving time really save any energy?
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 [PDF] 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 (PDF), 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—still in practice in 2011—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.
But Wolff, one of
many scholars who contributed to the federal report, suggested that the
numbers were subject to statistical variability and shouldn't be taken
as hard facts.
And daylight savings' energy
gains in the U.S. largely depend on your location in relation to the
Mason-Dixon Line, Wolff said.
"The North might
be a slight winner, because the North doesn't have as much air
conditioning," he said. "But the South is a definite loser in terms of
energy consumption. The South has more energy consumption under daylight
saving."
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.
Daylight Savings Lovers, Haters
With verdicts on the benefits, or costs, of daylight
savings so split, it may be no surprise that the yearly time changes
inspire polarized reactions.
In the U.K., for
instance, the Lighter Later
movement—part of 10:10, a group advocating cutting carbon
emissions—argues for a sort of extreme daylight savings. First, they
say, move standard time forward an hour, then keep observing daylight
saving time as usual—adding two hours of evening daylight to what we
currently consider standard time.
The folks
behind Standardtime.com, on
the other hand, want to abolish daylight saving time altogether. Calling
energy-efficiency claims "unproven," they write: "If we are saving
energy let's go year round with Daylight Saving Time. If we are not
saving energy let's drop Daylight Saving Time!"
But
don't most people enjoy that extra evening sun every summer? Even that
remains in doubt.
National telephone surveys by
Rasmussen Reports from spring 2010 and fall 2009 deliver the same
answer. Most people just "don't think the time change is worth the
hassle." Forty-seven percent agreed with that statement, while only 40
percent disagreed.
But Seize the Daylight
author David Prerau said his research on daylight saving time suggests
most people are fond of it.
"I think the first
day of daylight saving time is really like the first day of spring for a
lot of people," Prerau said. "It's the first time that they have some
time after work to make use of the springtime weather.
"I think if you ask most people if they enjoy having
an extra hour of daylight in the evening eight months a year, the
response would be pretty positive."
Source : National Geographic News
