There are good reasons we switch clocks twice a year

On Nov. 6, two days after our clocks “fall back” an hour to standard time, Californians will vote on whether to start a process to abandon standard time completely. Advocates of Proposition 7 argue this would reduce energy use and avoid the semiannual clock adjustments that disrupt our sleep and schedules.

These proposals always trigger the retelling of the probably-not-apocryphal story of the gardener who remarked that daylight saving time is wonderful because the extra sunlight makes tomatoes grow faster. Let us now pause to chuckle smugly, because we all know that DST does not change the amount of light any location receives over a 24-hour period.

Some people, however, seem to think that the timing of human behavior is as immutable as the rotation of the earth. Opeds, discussions and even news reports on the subject are filled with assertions that changing how we designate time necessarily gives us more or less opportunity for outdoor leisure. But that’s only true if people would not adapt at all to changes in what is a completely arbitrary numbering system for the hours of the day.

Benjamin Franklin argued that DST would save energy, and many policymakers today make that argument, but numerous careful studies have failed to find evidence of savings. There are many reasons why not, among them that humans can adjust their schedules to a renaming of the hours.

But wait, you say, I can’t simply adjust my schedule because it depends on the schedules of dozens or hundreds of other people — my family, my co-workers, the operator of my neighborhood coffee shop, whoever controls the start time at my kids’ schools — and we would all have to coordinate on the readjustment.

That’s right! The numerical designation of hours is completely arbitrary, but it is still crucial for coordinating activities. That’s why there are real benefits to adjusting those designations as the amount of daylight changes over the seasons.

In December, when we get about 9 ½ hours of daylight in the Bay Area, we need those hours to accomplish everything our busy lives demand, so most of us (reluctantly) start our days before the 7:21 a.m. sunrise. But in June, when we get 14 ½ hours of daylight, maintaining the same clock schedule would mean waking up hours after the 4:47 a.m. sunrise. We’d like to shift our schedule to start the day earlier in the summer, but not if stores are closed, our work hours are unchanged and our toddler’s day care isn’t open yet.

DST coordinates a shift of all activities to start earlier on summer days when there is lots of sunlight, and later on winter days when we’d rather not leave for work — or have children leave for school — in darkness.

DST is certainly not costless. The shifts between DST and standard time are jarring, with research suggesting there may be a rise in heart attacks and auto accidents on the day after we “lose an hour” at the March start of DST.

But sticking to a single time would also have adverse effects. Permanent DST would likely lead to more pedestrian accidents on winter mornings, as more adults and children venture out in darkness, with the sun rising as late as 8:21 a.m. in the Bay Area.

Equally important, there would be open/close time chaos as workplaces, day cares, schools and stores established their own idiosyncratic summer and winter hours in order to adapt to the seasonal changes in daylight. (Many hardware stores and restaurants do this even with the current DST shifts.) Coordination headaches for parents, workers, students and customers would be monumental.

DST’s energy conservation value is likely minuscule, but its coordination value is not. Sticking to DST or standard time year-round would avoid the time-change disruptions, but at the cost of inconveniently timed activities and uncoordinated seasonal schedule changes, reducing the fundamental value of standardized time.

Are the disruptive transitions worth it to maintain better coordination? That’s the core of the debate about daylight saving time.