On the darkest morning of winter, the sun rises across Colorado — depending on where you are — sometime between about 7:05 a.m. and 7:40 a.m.
Now imagine that your morning routine stays the same, but the sun stays in bed an hour later. You would head off to work in the dark. School for many children would begin in the dark.
This is the situation Colorado would be facing during the darkest days of winter if the nation switched to permanent daylight saving time, and it’s why University of Colorado sleep science professor Kenneth Wright thinks the idea is so horrible.
“Every morning, sunlight helps us to reset ourselves,” said Wright, who teaches integrative physiology and the head of the university’s Sleep and Chronobiology Lab. “And that way we are in sync with the 24-hour light-dark cycle of Earth.”
Standard time — what Wright believes the country should be on full-time — roughly tracks the sun in each time zone, with the sun at its highest point in the sky around noon. Colorado and most other states observe standard time during the winter months. Daylight time, meanwhile, pushes the clock ahead an hour during the spring, summer and fall, meaning people will see later sunsets — something advocates for changing to permanent daylight time tout as a benefit that will allow people to be more active after work or school.
The idea of switching Colorado to permanent daylight saving time is an old one, with efforts in the state legislature stretching back more than a decade. On Monday, a Colorado state House committee gave approval to the latest effort — a bill that would make daylight time permanent in Colorado but only if either the federal government authorizes it or if four other states in the Mountain time zone do the same.
But the idea of going to daylight saving time full-time really gained new momentum earlier this month when the U.S. Senate passed a measure to make daylight saving time permanent across the country.
Wright said there is no debate about the idea among sleep experts globally. At the same time the Senate voted to make daylight saving permanent, Wright was in Rome, attending World Sleep 2022, an annual conference that is so big that the World Sleep Society dubs it a “congress.”
The reaction among attendees at the meeting? It’s a really bad idea.
“There is expert consensus here that, if we have to choose one of these, permanent standard time is the healthier choice,” Wright said.
Ending the spring forward
Wright wants to be clear: He is not in favor of clock-switching, the most loathsome feature of the nation’s annual change from standard time to daylight time and back again.
A robust body of research shows that the annual springing forward, when we shift clocks an hour ahead at the start of daylight saving time, causes a surge in fatal car accidents, heart attacks and strokes.
“No question, we need to stop the change, going back and forth,” Wright said.
Changing to permanent daylight saving time will compound the problems by interrupting our bodies’ natural circadian rhythms, Wright said.
As he explains it, light in the morning is different to our bodies than light at night. The morning light signals to our circadian clocks that it’s time to get moving. The ebbing of evening light tells our clocks it’s time to slow down. So stealing light from the morning to give to the evening, especially in winter, pushes that clock rhythm back.
This would likely lead to later bedtimes in the winter, especially when coupled with the impact of artificial light at night on sleep. (A CU study published earlier this year found that even minor exposure to light in the hour prior to bedtime can disrupt the sleep of preschoolers.)
This might not be such a big deal if our schedules were fungible and we could just plan to wake up later in the morning. But they’re not. School start times are fixed, as are most people’s work start times. Both could be changed, of course, but it would require a big cultural movement to do so.
That means, when alarm clocks start going off during those dark morning hours, our circadian rhythms would likely rather we still be fast asleep. The resulting sleep deprivation could lead to greater risk for a litany of health problems, from weight gain, heart attacks and cancer to poor mental health and substance abuse.
“This change,” Wright said of a move to permanent daylight saving time, “is likely going to make these types of problems worse.”
Be glad we’re not Idaho
Colorado, though, wouldn’t get the worst of it if the nation moved to full-time daylight time. That’s because the state sits on the eastern side of the Mountain time zone.
The latest the sun will rise in Denver this year is 7:32 a.m., which will happen in early November right before the clocks fall back to standard time. Things stay darker a little longer as you go farther west and north. But, even in Grand Junction, the latest the sun will rise this year is 7:45 a.m.
If daylight saving time were made permanent, those latest-sunrise times would change to 8:19 a.m. and 8:31 a.m., respectively, and they would fall right around the first of the year. Wright said switching to daylight time year-round would mean about two months out of the year when the sun wouldn’t rise before 8 a.m. in the state. (It wouldn’t change the latest sunset times because those occur in summer when the state is already on daylight time, but it would push the earliest sunset times back an hour — to about 5:36 p.m. at the earliest in Denver, occurring in early December.)
This year, with both standard and daylight time in place, Denver will see 107 days without a sunrise before 7 a.m. If daylight saving were made permanent, that number would rise to 166 days without a sunrise before 7 a.m.
The number of days with late sunset times in Denver — those after 7 p.m. — would remain virtually unchanged under permanent daylight time, rising to 198 this year instead of the 193 we will see under the status quo. There would be a greater increase in the number of days with sunset times after 6 p.m. — 291 under permanent daylight time, instead of 238 with the status quo.
This is nothing, though, compared to what people in Boise, Idaho, on the western edge of the Mountain time zone, would experience. There, residents would endure roughly two months out of the year without a sunrise before 9 a.m.
But, to Wright, this just underscores the problem with permanent daylight saving time. Some places will see greater impacts than others, but all places will see more darkness on winter mornings.
“It’s not that we won’t be impacted, we certainly will be impacted,” he said. “And others further west they will be impacted more by this. That doesn’t mean that because we’re less impacted is the right thing to do.”
It appears that Congress might be starting to come around to that thinking. At last report, the Sunshine Protection Act — the bill passed in the Senate to make daylight saving permanent — is facing a much, ahem, dimmer outlook in the U.S. House.
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