Why Do We Change the Clocks Twice a Year?

Source: Photo by Pixabay

I will admit that ever since I was a teenager, I had always been favourably disposed to the idea of putting the clocks back in the autumn. I found the idea of an extra hour in bed when the clock ticked back from 01:59 to 01:00 quite appealing. This feeling lasted until I had kids. What happens then, I discovered, is that your kids wake you up at the same time as they would have done had the clocks not changed, only now that time is called 5 o’clock and not 6 o’clock, which, if anything, feels much worse—seemingly faced with a whole extra hour of the day to get through.

What I have always liked less about the switch away from Daylight Saving Time (DST) is the idea that we lose an hour of daylight in the evening. That first Sunday afternoon when twilight arrives before 5 p.m. is always a shock to the system. I can’t help but feel cheated. I know we get that hour of daylight back in the mornings—that we are not really saving or losing any hours of daylight—but somehow, that morning hour doesn’t feel like adequate compensation.

For me, losing the evening light marks the end of evening runs in the fields away from the glare of the streetlights and the noise of traffic and the end of the kids playing out on the street after tea. In some sense, it feels like the start of a less sociable winter “hibernation” period. Mirroring this melancholic sentiment, the abrupt onset of early darkness has been linked to seasonal depression.

The argument for our autumnal reversion to Standard Time (ST) seems to be largely for the sake of the mornings. It ensures that many people who work a 9-to-5 will always arrive at work in the daylight.

What Does the Science Say?

Opponents of our bi-annual time tug-of-war point out that it is, at best, confusing and, at worst bad for our health. Several studies have shown that the first weekdays after the clocks go forward in spring are associated with an increase in heart attacks of between 10% and 24%. It should be noted, however, that the weekdays following the return to GMT see a roughly commensurate fall in the number of heart attacks and that overall, the number of heart attacks remains unchanged by daylight saving transitions.

Source: Photo by Pixabay / pexels

The transitions between GMT and BST (and vice versa) have been shown to disrupt sleep and circadian rhythms in some people for weeks after. The impact of the changing of the clocks has even been linked to increases in fatal traffic accidents.

So, it seems that this annual switching may be a suboptimal strategy. But if we are to stick with one-time system all year round, which should it be, the lighter mornings of ST or the lighter evenings of DST?

In Favour of Standard Time

In favour of year-round ST is the fact that morning light is thought to help wake us up and improve alertness. The American Medical Association has also argued that ST, for which noon occurs close to solar noon – the point when the sun is highest in the sky – aligns best with human circadian biology. Exposure to light later in the day, as experienced during DST, is believed to delay the body’s release of melatonin – a hormone which, amongst other functions, helps us to feel drowsy. The consequence is that on days with lighter evenings we tend to sleep less overall. It’s well established that too little sleep has all sorts of detrimental health effects, from decreasing our learning capacity to elevating the activity of genes associated with inflammation, stress, heart disease, and diabetes.

To back this up, research suggests that those people living on the western edge of a time zone (and who consequently enjoy light later in the day than their more easterly counterparts) suffer significantly less sleep and experience higher rates of obesity, diabetes, and heart disease.

In Favour of Daylight Saving Time

On the other side of the coin can be found the arguments behind the original introduction of DST. During World War I, first the German Empire and then the Allies introduced DST as a way of saving energy, reasoning that increased light in the evening would reduce the consumption of energy.

More recent studies have, however, suggested that our modern power consumption habits mean that savings in the reduction of energy used for evening lighting are now often offset by increased energy consumption, for example, by air conditioning or travelling to leisure activities in the warmer, lighter evenings.

Not all leisure activities require automotive transport, though, and there is evidence to suggest that when it’s light after school or work people spend more time outside taking exercise or doing other recreational activities and less time inside on the sofa engaged in sedentary activities like watching TV. An early proponent of British Summer Time (the UK equivalent of DST), Sir Winston Churchill, opined that it enlarges “the opportunities for the pursuit of health and happiness among the millions of people who live in this country”.

There’s also a strong argument that the lighter evenings afforded by DST makes our lives safer. One study in the U.S. suggested that year-round daylight saving could reduce pedestrian fatalities by 13% and motor vehicle fatalities by 3%. Other studies have shown that longer daylight hours lead to a reduction in crime.

There have been many attempts in both the UK and the U.S. to block the changing of the clocks and to stick with either permanent DST or Permanent ST. In 2019 the European Parliament even voted to scrap the mandate on daylight saving although rumours that member states have not been able to agree which countries should use which times have meant that four years on, the change has still not been implemented. For many of us across the globe, it looks like our biannual clock-switching routine is here to stay, so enjoy your extra hour in bed this weekend, if you can.