In Defense of Daylight Saving Time
This weekend, two things will happen. First, we’ll set our clocks forward one hour as we head into eight months of Daylight Saving Time (DST). Second, your social media news feed will fill up once again with lamentations about the switchover. There will be articles and essays denouncing DST as antiquated and unnecessary, and perhaps even harmful. What I find awkward about these rants is that, well-intentioned as they may be, they often fail to say what they’re arguing for.
WHY DO WE USE DAYLIGHT SAVING TIME IN THE FIRST PLACE?
Though Benjamin Franklin is often credited with the idea, the push for DST actually dates back only to the 1890s and first became law in Germany in 1916, in an effort to conserve coal during the First World War. In North America, DST was only widely adopted in the 1970s in response to the so-called energy crisis. Why the link to energy consumption? The theory is that people don’t switch on their lights until sunset, so if sunset can be pushed back, so to speak, we’ll use less energy. Another argument is that retailers benefit from pushing the clock back; people are more likely to go shopping when it’s light out. The extra summer sunlight also means more daylight hours for recreation, from golf to little league baseball to simply taking a stroll.
But not so fast: The energy argument has always rested on inconclusive (and often contradictory) data, and anyway, energy-use patterns have changed over time. As the Washington Post recently noted: “More productive daylight hours might be meant to get you off the couch and recreating outside, but they’re just as likely to lead to increased air-conditioner use if you stay home and gas guzzling if you don’t.” (Indeed, a 2008 study suggested that energy use actually goes up slightly when DST is adopted.)
And then there’s DST’s alleged impact on human health: A 2011 University of Alabama study found that the switch to DST causes a 10 percent increase in the risk of heart attack. A 2007 German study found that the switch causes sleep disruption that the body never truly adjusts to, possibly increasing the susceptibility to illness. Last month, a study of nearly 15,000 people hospitalized in Finland found a small, temporary bump (8 percent) in the rate of stroke among those hospitalized in the first two days after a daylight saving time transition. There was no difference after two days.
The cumulative case against DST was enough to get comedian John Oliver all worked up: In a 2015 viral video from Last Week Tonight, Oliver asked why DST is “still a thing.” (“What you lose in sleep, you gain in mortal danger,” the report noted dryly, referring to the purported health risks.)
What I find most striking about the opposition to DST is that it’s usually framed not as a preference for Standard Time, but as wanting to do away with the twice-a-year switch. (There’s a certain logic there, as the purported negative health effects are due to the switch, not to the actual time shown on our clocks.) That’s certainly the theme of the Oliver video, which makes no claim about wanting to keep Standard Time, or any other system, year-round.
But without DST, there really are only two options: Stay on Standard Time all year, or keep Daylight Time all year.
YEAR-ROUND STANDARD TIME VS. YEAR-ROUND DAYLIGHT SAVING TIME
But here’s the thing: If we stay on Standard Time year round, much of that extra summer daylight, divided equally between morning and evening, goes to waste. Do we really need four and a half hours of daylight before most of us start the work day, in June? Surely that light is more valuable to us in the evenings, when we’re finished work or school and (in theory, at least) can do as we please.
And so we’re tempted by the alternative argument: OK, Daylight Saving Time is good, but I hate the switch; let’s just stay on DST all year. But that, alas, leaves us with a lack of sunlight on winter mornings. We’d be driving to work in the dark, and our kids would be going to school in the dark. In the current system, sunrise in New York occurs at around 7:20 a.m. in late December (it’s about the same in San Francisco and Chicago; it’s 7:42 in Atlanta, which is further west within its time zone). Now imagine adding an hour to those times. Do we really want parts of the country to remain in darkness ’til 8:45 a.m. in mid-winter?
The diagram below sums up the problem: If you plot the amount of daylight that those of us living in mid-northern latitudes receive as a function of the time of the year, you get a big fat yellow bulge in the summer months, and a much thinner band of yellow for fall and winter.
As the diagram shows, DST has the effect of pushing the thickest part of that bulge downward, so that we have nice, late summer sunsets, while keeping the time of sunrise relatively constant throughout the year (yes, the time of sunrise still varies—but not by as much as it would if we stuck with Standard Time year-round).
Let’s face it: We can do what we like with our clocks; it doesn’t affect the amount of daylight that reaches us each day. The only question is when we’d like that daylight to happen. For those who rant against DST—and I’m sure we haven’t seen the last of them—all I ask is this: It’s not enough to say that you hate making the switch. You have to say what system you actually want.