The Science of Sustainability

Saving Daylight and Energy

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In the wee hours of Sunday morning, the little hand on the clock ticked backwards one hour and Daylight Saving Time ended. Now we’re on Standard Time, which will last for about 4 months, until we click forward to Daylight Saving Time again in March. Daylight Saving Time (DST) started in Europe during WWI, to save energy, and has been used consistently in the US since 1966. DST was temporarily extended in 1974 and 1975, to save energy during the Arab Oil Embargo. It was extended in 1986 and again in 2007—DST now begins earlier in the spring and ends later in the fall than ever before.

When we turn the clock forward in the spring, we move an hour of daylight from the morning to the evening. The idea is that we save energy in the evenings, because we don’t need to turn our lights on for an extra hour. A 2008 report to Congress quantified the amount of energy saved after the 3-week extension of DST that began in 2007: 1.3 Tera Watt-hours, a decrease of 0.03% of the country’s annual energy usage. The amount of energy saved depends on where you live. You might actually use MORE energy during DST, if you need to run your heater on a cold, dark morning or if you come home at the end of a workday to a hot, stuffy house and need to run your air conditioner.

And that extra hour of daylight impacts more than just the energy bill, as reviewed in an article in National Geographic Daily News. People tend to be more active outdoors during DST. This is beneficial for tourism. Plus, crime rates drop because crime tends to happen in darkness. There are fewer traffic accidents because people aren’t driving home from work in the dark. And there are effects on human health: there is evidence that springing forward is linked with increased risk of heart attacks.

There are places in the world that don’t observe Daylight Saving Time; their inhabitants don’t have to deal with the bi-annual adjustment of their internal clocks. In areas close to the equator, day length remains relatively consistent throughout the year; there is not much daylight to save. Many tropical lands don’t observe DST, including Hawaii. (Neither do parts of Arizona—don’t ask me why). Russia observes DST year round, and in the summer turns its clock forward an hour anyway—Double DST. In 2001, in the wake of rolling blackouts, California requested to observe Daylight Saving Time year round, and observe double DST during the summer. This report details small but measurable energy savings, but the request was never approved.

Turning clocks back and forth doesn’t make the airlines happy, as they try to schedule international connecting flights that originate in one time zone and end in another, which may or may not be observing DST, depending on the day of the year. The whole idea of a standard time, at least in the US, began with the advent of the railroad. Before that, towns set their own time.

When I was a kid, I went to summer camp in New Brunswick, pretty far north, where summertime sunsets occur around 9:00. We would have “camp time”—we’d turn the clock back, so it would seem to get dark earlier in the evening. We could sing camp songs and cook bannock around a campfire, and still be in our bunks by 10. Time, I guess, is relative.

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Category: Environment

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Jennifer Skene

About the Author ()

Jennifer Skene develops curriculum on climate change and ocean sciences at the Lawrence Hall of Science and teaches biology and science communication at Mills College and the University of California Berkeley. She has a degree in biology from Brown University and a Ph.D. in Integrative Biology from UC Berkeley. She started working with QUEST in 2008 as an intern. She has written for the Berkeley Science Review and the UC Museum of Paleontology’s Understanding Evolution and Understanding Science websites.
  • Scott

    Actually the opposite has been shown to be true… While the benefits of increased daylight mentioned in the article, crime, accidents and so forth are true as study done on Indiana shows that daylight savings time actually causes an increase in energy use. There are numerous references on the web but here is a link to one of them:
    http://www.physorg.com/news187946326.html

    During WWII odds are it did save energy since the largest use of electricity was lighting, now far and away the largest use of electricity in warm climates is air conditioning. With daylight savings time people leave work (generally with 24/7 climate control) during a hotter part of the the day and go home and turn on the air conditioning resulting in an increase in the demand for electricity. It was possible to prove with Indiana which didn't go on DST until the most recent change so it was possible to compare modern year on year data.

  • http://www.jenniferskene.com Jennifer Skene

    Hi Scott,

    Thanks for pointing out the study from Indiana! I'm familiar with it—parts of the state didn't observe Daylight Saving Time until 2006. The researchers compared energy usage in 2006 (when they first started observing DST) to energy usage in prior years—and people used more energy when they observed DST. And you're right, a lot of that energy use came from air conditioning.

    But other studies have seen different results. After the country extended DST in 2007 (moving the start date a few weeks earlier), a study was done to compare energy use in 2006 and 2007. There was a net energy savings—that's the report to Congress that I linked to above. The savings, over the 3 weeks, was 0.02 percent of the country's annual energy use. This seems like a small percentage, but it is actually a whole lot of energy.

    I think these studies were different because they looked at different geographic areas. The use of air conditioning is huge! Parts of the country that don't use AC (the northern part of the country) use less energy when DST is observed. Parts of the country that rely on AC (the south) use more energy. So it really depends on where you live.