Attention body clock: it’s time to lose an hour for one day and gain evenings that are lighter, warmer and more inviting throughout summer.

At 2am on Sunday the clocks jump forward an hour for most Australian states. The time stays this way until April.

Changes like this happen in more than 70 countries across the globe – but daylight saving has always been a bit controversial, with debates simmering from time to time in parts of the world. In Australia, a recent survey shows that 80 per cent of our population supports daylight saving time. This includes more than 60 per cent of both Queenslanders and Western Australians – where clocks do not jump forward.

So, how does daylight saving work? How does it impact people and animals? And does it really work?

What is daylight saving and where did it come from?

It might sound like a silly question, but it’s a notoriously confusing one. Daylight saving – there’s no “s” on the end – is the moving of a society’s clocks forwards to make better use of changes of sunlight hours over the course of the year.

The general idea is this: instead of being up and about when the sun rises very early in the morning (for example, 4.45am, as occurs in Queensland in December), it might be better to have extra periods of daylight in the evening, when more people are awake. So pushing the clocks forward an hour (daylight saving) means adjusting the earliest sunrise to 5.45am – and a 6pm sunset becomes a 7pm one.

In the scheme of all time, it’s a relatively new concept: it was first proposed by New Zealand insect expert George Vernon Hudson in 1895, when he suggested a two-hour move forward in October and a two-hour shift back in March. While his idea garnered some interest, it didn’t catch on.

The first place to go-ahead with daylight saving was the former Canadian city of Port Arthur, on July 1 in 1908, after a local businessman urged the council to move the clocks forward in summer so children could enjoy an extra hour of sun. More towns followed. Then Germany and Austria pushed the clocks forward in 1916 to reduce the use of artificial lighting to save fuel for the war effort.

Britain, France, the United States and Australia quickly followed until the end of World War I and reintroduced it during World War II, again to save scarce resources, before it faded away.

Tasmania became the first state to (re)introduce daylight saving in 1967 during a drought, so people would turn on the lights later and not use as much hydroelectric water storage.

Most other states introduced the system in 1971 but Western Australia (which tried it for three years from 2006) and the Northern Territory both rejected the idea and, after trying it, Queensland ditched it the following year (the state tried it again between 1989 and 1992, before voting no – more on that below).

Queensland’s on-again, off-again relationship with the practice comes down to disagreements across the state about whether an extra hour of sunlight is a good thing. South-east Queenslanders have mostly been in favour of daylight saving, but their northern counterparts say it would mean an extra hour of heat during the scorching summer months.

North Queensland MP Robbie Katter (son of MP Bob Katter) has said “don’t poke the bear”. In October 2019, he said residents in the state’s north would “do nothing but suffer under daylight savings” and that it would place “an enormous burden on the liveability and practicality” of working in the region, effectively creating an extra hour of “stifling heat above 40 degrees”.

Queenslanders voted against permanently having daylight saving in a referendum in 1992 – 54.5 per cent said no. But more recently there have been calls for daylight saving to be implemented year-long.

Where does daylight saving happen?

In the Australian states that have it, daylight saving always begins at 2am on the first Sunday in October and ends at 2am (which is 3am daylight saving time) on the first Sunday in April. That is, clocks jump from 1.59am to 3am.

The easy way to remember it, to borrow from our American friends, is that we “spring forward” an hour during spring, and “fall back” an hour during fall (autumn).

Governments can vary this for special occasions: the Olympics in September 2000 prompted early daylight saving in some states, and all states delayed the end of daylight saving for the Commonwealth Games in 2006.

People in Queensland, the Northern Territory, Western Australia, Christmas Island and the Cocos (Keeling) Islands don’t wind their clocks backwards and forwards. And there are other exceptions, too: Broken Hill, on the border of NSW and South Australia, follows SA’s daylight saving time; and Lord Howe Island, off the coast of NSW, has its own time zone 30 minutes ahead of NSW.

The US, Canada, Mexico, New Zealand and even Antarctica all follow daylight saving – more than a billion people across the world are affected by the changes in time.

In effect, Australia’s main three standard time zones (eastern, central and western) become five during daylight saving. If you’re in Sydney and you phone a friend in Perth, for instance, don’t do it first thing in the morning – they’ll now be three hours behind. And there’s an hour’s difference between Queensland and the states directly south.

The US, Canada, Mexico, New Zealand and even Antarctica all follow daylight saving – more than a billion people across the world are affected by the changes in time.

Despite their huge land masses, China and India each have just one time zone.

Most countries near the equator don’t fall back or jump ahead because there is little difference in the length of daylight between winter and summer. Despite their huge land masses, China and India each have just one time zone (Beijing time, since the Communist Revolution in 1949; and India Standard Time, since India became an independent nation in 1947), and neither uses daylight saving.

In 2019, the European Parliament approved a measure to abolish the time changes. But the implementation was stalled by the pandemic, and another key question that stumped regulators: even if a consistent time zone is preferred for the whole year, what time do you pick? Daylight saving or non-daylight saving hours? “We have a real problem,” one French member of the European Parliament admitted.

In 1991, farmer Basil Johnson attempted to sue the Queensland government for damages in lost income when he was injured as he herded his cows into his dairy in the dark while the state was trialling daylight saving. “Whenever man makes laws which are against the laws of nature then he is utterly wrong as far as I am concerned,” he said at the time. “Not even the cows think it’s natural to do anything before sunrise. They don’t like falling all over the place and flipping about in the mud in the dark.”

Cows can get “a little mixed up” by the changes, according to dairy farmer Adrian Parkinson, who looks after his cows in Kirkstall, south-west Victoria. “It’s fair to say you might get a little bit less milk that morning,” he says. “But you make up for it at the afternoon milking because they produce their milk over a 24-hour period.” But after the first day, “there [are] no issues with them or their milk”.

Can daylight saving affect your sleep?

It’s worse when daylight saving starts than when it ends. “We find it harder to spring forward than back,” says Australian Sleep Health Foundation spokeswoman Dr Amy Reynolds. “Our short-term functioning could be a bit impaired the next day and at night it can be harder to fall asleep if it is still light.”

One study in the United States found there were more car crashes in the days immediately following daylight saving. Reynolds says there is a link to traffic accidents if you are tired “but that is common at any time you are not getting enough sleep”. “The main take-home message is if you are doing things that mean you are losing sleep, be mindful of the impact that can have when you are out on the road,” she says. A recent Australian study also found no direct link between daylight saving and poorer daytime functioning or reduced sleep health.

There are three types of clocks that regulate patterns of health, explains Dr Jacob Crouse, from the University of Sydney’s Brain and Mind Centre: the body clock, which is the “master timekeeper” in our brain; the sun clock, “the most predictable time cue in the environment” that our body clock follows; and the social clock, which society agrees to use to function cohesively.

‘We are, essentially, asking people to fight against their genes.’

Daylight saving – a change in our social clock – can “put our body clock out of whack,” Crouse says. “It doesn’t seem like a big change, it’s just one hour of lost sleep, but it takes a little while for our body clock to catch up, and that lag between our body clock and the social clock can cause problems.”

Teenagers and evening types (or night owls) are among those who appear to be particularly affected. That’s because they’re biologically programmed to prefer a “delayed sleep-wake” schedule: they like going to bed late and waking up later (even if they’re supposed to be up early for school). “When we turn the clock back, we are asking these people to fight even harder against their biology,” Crouse says. He points to a study that shows people who find it easy to wake in the morning can adjust to daylight saving within a few days, but those who prefer the evening can take more than a week to adjust. “We are, essentially, asking people to fight against their genes,” he says.

The effects are related to the changing of time, not the new daylight hours themselves – which Crouse believes, from a health perspective, is good enough evidence for a year-long consistent clock.

Dr Sveta Postnova, a senior lecturer in neurophysics and brain dynamics at the University of Sydney, says most people adjust relatively easily to the time changes, but people can lose sleep for “at least a week” after the clocks are moved forward one hour. The autumn transition, on the other hand, is popularised as adding one hour to sleep time, she says, but data shows no evidence of extra sleep on that night.

This explainer was first published in 2019 and has since been updated.

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