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.(Related: "Extended Daylight Saving Time Not an Energy Saver?")
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."
(See in-depth energy coverage from National Geographic News.)
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.
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