Millions of Australians will turn the clocks back an hour next Sunday — but what if they didn't?
It's a scenario which may well come to be in the US, where year-round daylight saving time from 2023 is on the legislative table.
Last week, the US Senate passed the so-called Sunshine Protection Act, which would permanently shift local time across all states to daylight saving time — that is, if it also gets the green light from the House of Representatives and President Joe Biden.
(The exceptions to the Act are Hawaii and some parts of Arizona, which don't do daylight saving time at all.)
The bill's most ardent advocate was Florida senator Marco Rubio, who said doing away with the current practice of changing the clocks twice a year could reduce heart attacks, car accidents, crime, childhood obesity and seasonal depression.
But science paints a much less sunny picture of year-round daylight saving time.
Oliver Rawashdeh from the University of Queensland was "gobsmacked" when he saw the bill had passed the Senate.
"Wherever you look, it's a bad idea," says Dr Rawashdeh, who studies what happens when biological clocks are out of whack.
Another biological clock researcher, Monash University's Sean Cain, was similarly scornful.
The Senate vote, which took place two days after the nation ticked over into daylight saving time for 2022, "is the kind of thing people do when they're sleep deprived and making poor decisions", Dr Cain says.
They're just two of a chorus of scientists around the world who have expressed disbelief and derision for this latest push for perennial daylight saving time.
So why is a permanent shift of just one hour such a shocker of a move?
And surely it's better than switching clocks back and forth each year … right?
We know changing clocks isn't great for us
First up, there's plenty of research on the health effects of daylight saving time.
When it starts, the clocks go forward and you lose an hour of sleep (assuming you need to get up at the same time each day).
This seemingly small temporal hop might mean you're just a bit tired first thing for a couple of weeks, but it has measurable effects when you look at the population as a whole, Dr Cain says.
And it doesn't help that a fair proportion of the population is already sleep deprived too.
A 2017 Sleep Health Foundation report discovered 40 per cent of Australian adults experience some kind of "inadequate sleep".
Multiple recent studies found the pandemic didn't help matters either.
"So if you instantly steal an hour of sleep away from people who are already living with a lot of sleep deprivation, there are short-term negative health impacts, such as more heart attacks and more accidents on a population level," Dr Cain says.
So eliminating clock changes, and simply sticking with daylight saving for the entire year, should be better for us, yeah?
Well … no.
And to discover why that's the case, we need to get a better understanding of the timekeepers inside our body and out.
The 'clocks' that coordinate your body
Your body contains a bunch of "clocks" of sorts, scattered through our organs, which switch genes on and off (and get each organ doing different things) at certain times of the day.
Coordinating most of these organ-based clocks is a bundle of nerve cells, tucked away in your brain, called the suprachiasmatic nucleus.
Dr Rawashdeh likens our body's internal cycles — the circadian rhythm — to an orchestra, with the suprachiasmatic nucleus acting as a conductor, and the organ's clocks as musicians.
The thing is, the whole orchestra must be reset every 24 hours. And that's where daylight comes in.
The conductor in your brain receives direct input from the light-sensing cells in the back of your eyes, and it's this initial light exposure that triggers the start of a new symphony.
In summer, getting up an hour earlier due to daylight saving time isn't so bad, because the Sun comes up earlier too, so the circadian conductor still gets that early dose of light.
But getting up an hour earlier during the shorter days of winter — especially nearer the poles, where seasonal changes in day length are more pronounced — means getting up and heading off to work or school when it's still quite dark.
With even less bright morning light, the conductor loses its rhythm. And instead of a harmonious symphony of your bodily processes, it produces something more like a cacophony.
But, I hear you ask: we can switch on lights at home and in the office or classroom. Surely they're bright enough to reset our circadian conductor?
Not usually, Dr Rawashdeh says.
"You sit inside and you get a couple of thousand lux [a measurement of light intensity] — that's about as much as you can get.
"But go outside, and we're talking tens of thousands of lux."
But it's just an hour. How bad can it be?
To find out why permanent daylight saving time is problematic, we need to compare it to standard time.
"Standard time" is fairly well aligned with the movement of the Sun across the sky. So at 12pm local time, the Sun is at or very close to its highest point in the sky (with a few exceptions — more on that later).
This means standard time best matches your biological clock, Dr Cain says.
But year-round daylight saving time forces your body into a routine that's ever-so-slightly out of sync with the Sun, and you can end up with what boils down to chronic jet lag.
Not only are you waking up in the dark, but your alarm's going off right when your internal clocks are actively trying to keep you in slumber, which happens in the second half of the night.
"So now in the winter time, we're waking up at a time when our bodies are saying 'sleep, sleep sleep,'" Dr Cain says.
This interruption also interferes with processes like your body's routine maintenance.
"For instance, your heart works really hard in the day, but it repairs itself at night.
"You mess up its clocks, then any vulnerabilities you have to disease are more likely to come out."
Once you've dragged yourself out of bed, it's time for breakfast.
But when you start eating in the dark, you're forcing food into a digestive system that's not ready to process it, Dr Cain adds.
"We now know that will impact your glucose metabolism and your insulin levels."
On top of that, eating earlier can also produce duelling circadian conductors.
Light is the main cue your body uses to reset its clocks, but food is another, Dr Rawashdeh says.
When you start eating earlier, it may trigger a second conductor — called the food-entrainable oscillator — to step up to the podium.
"Many of the peripheral clocks in your liver, pancreas and so on, they favour listening to food [and the food-entrainable oscillator] for their time cue.
"So now you have two conductors in the orchestra, and each is telling the body something different.
And you've not even left the house.
This simple act of getting up in the dark can start a feedback spiral that affects your circadian cycles in days to come, Dr Rawashdeh adds.
"When exposure to sunlight in the morning is reduced, our biological clocks will drift later and later, making it harder to wake up."
How do we know all this happens?
These are just a few ways permanent daylight saving time might disturb your body's natural rhythms.
Of course, not everyone is affected the same way. We all have our own natural "chronotype", with some thriving in the early morning and others functioning better later in the day.
Still, researchers have been able to see the effects of something akin to long-term daylight saving time on a population scale, Dr Cain says.
People residing on the western edge of a time zone see the Sun come up later than their eastern counterparts.
"Essentially within the same time zone, you have people [in the west] living out of phase with their body by an hour, and others [in the east] living in phase.
"There's more illness on the western side of time zones, because at a population level, living a little bit out of phase with their body is having these negative effects."
So now what for the US?
Dr Cain is pretty sure the bill won't progress any further, partly because of the recent uproar from the scientific community, but mostly because it's been tried before — and failed.
In the 1970s, the US gave year-long daylight saving a go. The plan was to see how it went for two years, then suss out if it was worth keeping full time.
They pulled the pin well before the trial period was up, because people hated getting up in the dark.
Take the example of Williston, North Dakota, a town less than 100 kilometres from the Canadian border.
It's on the western edge of the North American Central Time Zone. For around seven weeks during winter, the sun rises after 8.30am. With daylight saving time, the sunrise is after 9.30am.
So if the worst-case scenario transpires — and the Sunshine Protection Act is passed and implemented — Dr Cain suspects it will be swiftly changed back following public backlash.
And really, from a public health perspective, Dr Cain and Dr Rawashdeh (and many of their circadian and sleep biology colleagues) say countries should consider making standard time permanent.
Russia did it in 2014 after enduring three full years of daylight saving time.
But that's a harder sell to the voting public.
"One of the problems is daylight saving sounds good, right? Who doesn't want more daylight?" Dr Cain says.
"Standard time is not so sexy."
So next weekend, when most of the Australian population reverts to the not-so-sexy standard time, it might be better for the nation's health and wellbeing as a whole.
