Daylight Saving Time (DST) begins at 2am on the first Sunday in October, when clocks are put forward one hour. It ends at 2am (which is 3am Daylight Saving Time) on the first Sunday in April, when clocks are put back one hour. This semiannual ritual shifts our rhythms and temporarily makes us groggy at times when we normally feel alert. Moreover, many are confused about why we do it all. (Spoiler: It has nothing to do with farming.)
The practice of resetting clocks is not designed for farmers, whose plows follow the sun regardless of what time clocks say it is. Yet many people continue to believe that farmers benefit, including lawmakers in the US during recent debates over abandoning California DST laws.
Changing our clocks does not create extra daylight. DST simply shifts when the sun rises and sets relative to our society’s regular schedule and routines. The key question, then, is how people respond to this enforced shift in natural lighting. Most people have to be at work at a certain time – say, 8:30 a.m. – and if that time comes an hour earlier, they simply get up an hour earlier. The effect on society is another question, and there, the research shows DST is more burden than boon.
No energy savings
Benjamin Franklin was one of the first thinkers to endorse the idea of making better use of daylight. Although he lived well before the invention of light bulbs, Franklin observed that people who slept past sunrise wasted more candles later in the evening. He also whimsically suggested the first policy fixes to encourage energy conservation: firing cannons at dawn as public alarm clocks and fining homeowners who put up window shutters.
To this day, DST legislation equate daylight saving with energy conservation. However, recent research suggests that DST actually increases energy use.
In a study I co-authored with Yale economist Matthew Kotchen, we used a policy change in the US state of Indiana to estimate DST effects on electricity consumption. Prior to 2007, most Indiana counties did not observe DST. By comparing households’ electricity demand before and after DST was adopted, month by month, we showed that DST had actually increased residential electricity demand in Indiana by 1 to 4 percent annually.
The largest effects occurred in the summer, when DST aligns our lives with the hottest part of the day, so people tend to use more air conditioning, and late Autumn, when we wake up in the dark and use more heating with no reduction in lighting needs.
Other studies corroborate these findings. Research in Australia and in the United States shows that DST does not decrease total energy use. However, it does smooth out peaks and valleys in energy demand throughout the day, as people at home use more electricity in the morning and less during the afternoon. Though people still use more electricity, shifting the timing reduces the average costs to deliver energy because not everyone demands it during typical peak usage periods.
Other outcomes are mixed
DST proponents also argue that changing times provides more hours for afternoon recreation and reduces crime rates. But time for recreation is a matter of preference. There is better evidence on crime rates: Fewer muggings and sexual assaults occur during DST months because fewer potential victims are out after dark.
So overall, the net benefits from these three durational effects of crime, recreation and energy use – that is, impacts that last for the duration of the time change – are murky.
Other consequences of DST are ephemeral. I think of them as bookend effects, since they occur at the beginning and end of DST.
When we “spring forward” in March we lose an hour, which comes disproportionately from resting hours rather than wakeful time. Therefore, many problems associated with springing forward stem from sleep deprivation. With less rest people make more mistakes, which appear to cause more traffic accidents and workplace injuries, lower workplace productivity due to cyberloafing and poorer stock market trading.
Even when we gain that hour back in Autumn, we must readjust our routines over several days because the sun and our alarm clocks feel out of synchronization. Some impacts are serious: During bookend weeks, children in higher latitudes go to school in the dark, which increases the risk of pedestrian casualties.
Pick your own time zone?
Spurred by many of these arguments, several states in the US are considering unilaterally discontinuing DST. These proposals ignore a fundamental fact: Daylight saving time relies on coordination. If one state changes its clocks a week early, neighboring states will be out of sync. In Australia, this is already the case – Queensland, the Northern Territory and WA do not observe DST.