Nature’s Fall Clocks: Daylight, Circadian and Leaf Color

On November 5, 2023, daylight saving time (DST) will end and standard time will once again reign. While recently there have been many attempts to do away with Americans’ “springing forward” and “falling back” each year, it looks like we’ll be continuing with the practice for some time to come. Often, detractors of DST mention only the extra electricity consumption needed for artificial lighting in the late afternoon or early evening hours when pressing their case. But in a new study, researchers investigated whether DST also has an impact on the cooling and heating energy required for office buildings—and what role climate change might play in that.

Energy needs aside, another aspect of DST is how it affects our circadian rhythms and thus our health. Now, researchers are using mathematical models to determine how altering time causes changes in our biological cycles.

And there’s a third fall clock that a lot of us experience. This one isn’t politically or socially controversial, nor does it have the potential to be physically harmful. It’s pure enjoyment and a nature traveler’s delight. I’m talking about the changing colors of fall leaves.

Daylight saving time results in lower energy consumption

Daylight saving time was first implemented in the United States with the Standard Time Act of 1918, a World War I measure that was intended to add more daylight hours in order to conserve energy resources. Since then, discussions about whether we should eliminate the time change have been frequent and sometimes heated. Opponents argue that the time change impacts our health, for instance, through sleep disturbances. Proponents of daylight saving time, on the other hand, say we’re saving electricity because of the longer days, which means that less artificial light is needed.

To look at not only the impact daylight saving time has on electricity savings in lighting but also on the overall energy consumption of a building, scientists at Switzerland’s Empa Urban Energy Systems Lab recently examined whether and how the time change affects cooling and heating energy costs.

The scientists’ hypothesis was that since employees start their work an hour earlier in summer due to the time change and leave the office earlier in the afternoon—and since most cooling of buildings happens later in the afternoon—DST can save energy. They assumed that in an empty office building, cooling can be reduced or turned off completely. As buildings become more intelligent, this would be easy to accomplish in the future.

To test the hypothesis, the researchers simulated the cooling and heating energy used with and without daylight saving time for different climatic regions based on data from various office buildings in 15 U.S. cities. To include the influence of climate change, they considered not only the current climate, but also future climate scenarios up to the year 2050. This was crucial, as climate change has an enormous impact on a building’s energy consumption.

Their research results should please proponents of daylight saving time: switching to DST can reduce an office building’s cooling energy by up to almost 6%. At the same time, heating demand can increase by up to 4.4% due to the earlier start of work in the morning. However, since much more cooling than heating energy is needed in summer, the time change has a positive overall effect on the energy balance of a building. Across the different climate zones and scenarios, the overall energy savings varied—peaking at around 3%—but they were evident everywhere.

The scientists say this study, published in the journal Environmental Research Letters in January 2023, shows that the time change can contribute to climate protection. In discussions about eliminating daylight saving time, policymakers should, therefore, not only consider the electricity savings in artificial lighting, but also the impact on the energy balance of office buildings as a whole. At the same time, the researchers emphasize that the time change is only one of many ways to influence the energy consumption of a building. Adjustments of our working hours, changes in our behaviors and technical improvements in buildings can also contribute to energy savings and thus CO2 reductions, regardless of whether we change the time every six months or not.

Circadian rhythm disruptions end in “broken” body clocks

Events such as daylight saving time can also affect another type of clock: our internal body clock, or our “circadian rhythm,” the roughly 24-hour cycle that many of our body systems follow, usually alternating between wakefulness and rest. Recently, researchers have started using mathematical models to better understand the effects of disruptions such as daylight saving time, jet lag, working night shifts or even late-night phone scrolling on the body’s circadian rhythm.

Your brain has a master clock that is made of a cluster of neurons—known as the suprachiasmatic nucleus (SCN)—that coordinates your body’s other internal rhythms. Sustained disruptions to circadian rhythm have been linked to diabetes, memory loss and many other disorders.

Now researchers at the University of Waterloo in Ontario, Canada, and the University of Oxford in Oxford, England, have developed a new mathematical model to help scientists better understand the resilience of the brain’s master clock. They patterned the SCN as a macroscopic, or big-picture, system comprised of a seemingly infinite number of neurons. They were especially interested in understanding the system’s couplings: the connections between neurons in the SCN that allow it to achieve a shared rhythm.

Their findings revealed that frequent and sustained disturbances to the body’s circadian rhythm eliminated the shared rhythm, implying a weakening of the signals transmitted between SCN neurons.

In their report, published in the Society for Industrial and Applied Mathematics Journal on Applied Dynamical Systems in 2023, the scientists state that today society is experiencing a rapid increase in demand for work outside of traditional daylight hours. This will greatly disrupt how we are exposed to light, as well as other habits, such as eating and sleeping patterns.

Turning leaves conclude in higher seasonal enjoyment

The natural world around us, too, has a fall clock that is often beautifully apparent. That’s when what we call “fall color” turns us all into “leaf peepers.”

For a tree to make its food, its leaves need carbon dioxide (from the air), sunlight, water and chlorophyll (a green, photosynthetic pigment). Green is the dominant color of a leaf during the spring and summer—hiding all the other colors—as the chlorophyll absorbs as much sunlight as it can. As autumn starts to arrive, the days get shorter, the nights longer and the temperatures cooler. When this happens, trees start to produce less chlorophyll, eventually producing none at all. As the chlorophyll fades, other colors, such as orange, red and yellow—which have been there all along—start to show.

When it comes to fall colors, no two years are the same. That’s because two of the three factors that influence autumn leaf color—leaf pigments and weather (the third is length of night)—can vary widely from year to year. The intensity of the fall color season is influenced by the weather during September and October. A series of fall days filled with bright sunshine and cool but frost-free evenings results in the most brilliant and vibrant fall color displays.

A color palette needs pigments, and there are three types that are involved in autumn color:

• Chlorophyll: Aforementioned, chlorophyll gives leaves a green color. It’s necessary for photosynthesis, the chemical reaction that enables plants to manufacture sugars for food. Trees in the temperate zones store these sugars for the winter dormant period.

• Carotenoids: Carotenoids produce brown, orange and yellow colors in such things as bananas, buttercups, carrots, corn, daffodils and rutabagas.

• Anthocyanins: Anthocyanins gives color to flowers, foods and plants, including blueberries, cherries, Concord grapes, cranberries, plums, red apples and strawberries. They are water soluble and appear in the watery liquid of leaf cells.

Both chlorophyll and carotenoids are present in the chloroplasts of leaf cells throughout the growing season. Most anthocyanins are produced in the autumn, in response to bright light and excess plant sugars within leaf cells.

During the growing season, chlorophyll is continually being produced and broken down; and leaves appear green. As night length increases in the autumn, chlorophyll production slows down and then stops, eventually destroying all the chlorophyll. The carotenoids and anthocyanins that are present in the leaves are then unmasked and show their colors.

While these colors are fairly consistent from year to year, they still can vary in brightness and timing. Yellow and orange hues may be more muted or take longer to show through, for example, if fall temperatures stay warmer for longer. That means more chlorophyll remains in the leaves, keeping them green at the start of fall. Cooler nighttime temperatures tend to amplify the brightness of reds and purples in leaves, while warmer nights will mute this color change.

Rainfall, or lack of it, also affects autumn leaf color. Drought and wet weather can lower color intensity, while drought can affect the timing of fall colors, as well. An early arriving, severe frost will kill the leaves, causing them to turn brown and drop prematurely.

The timing of color changes and the onset of falling leaves is primarily regulated by the calendar as nights become longer. None of the other environmental influences—such as food supply, rainfall and temperature—are as unvarying as the steadily increasing length of night during autumn.

In response to autumn’s shortening days and declining intensity of sunlight, leaves begin the processes leading up to their fall from the trees. The veins that carry fluids into and out of the leaf gradually close off as a layer of cells forms at the base of each leaf. These clogged veins trap sugars in the leaf and promote production of anthocyanins. Once this separation layer is complete and the connecting tissues are sealed off, the leaf is ready to fall.

Unfortunately, autumn color is not very predictable. But it generally starts in late September in New England and moves southward, reaching the Smoky Mountains by early November. It also appears around this time in the high-elevation mountains of the West. And cooler high elevations will color up before the valleys. Fall color predictions by American Forests, the first national nonprofit conservation organization created to protect and restore the country’s forests, are based on mathematical algorithms that factor in day length, health, historical leaf peak, leaf volume, precipitation and temperature.

Autumn finishes in letting go and moving on to new “places”

The clocks of fall can conserve energy, complicate our lives or capture our hearts with stunning beauty. They, like fall itself, can also connote a time of change.

There’s a quote, whose author is unknown, that goes “Autumn shows us how beautiful it is to let things go.” I hope during the remainder of your fall 2023 that you’ll take the time to let go of what you no longer need or want.

Hopefully, that will make some room—and time—in your life for the natural world, in whatever form appeals to you.

Here’s to finding your true places and natural habitats,

Candy