WTF Fun Fact 12978 – How Does Temperature Affect the Color of Leaves?

Have you noticed that autumn looks a bit different every year? Sometimes the leaves fall early. Other times they’re on the trees much longer to give a full display of color. A lot of this has to do with the temperature outside. But how does temperature affect the color of leaves?

The temperature of fall and its effect on leaves

As the nights get cooler in the northern hemisphere in September and October, we begin to see the trees change. If you’re lucky enough to live around a mixture of trees, you’ll begin to see bright red, orange, and yellow leaves appear.

Without as much daily sunlight, trees don’t go through as much photosynthesis. This is aprocess that produces sugars, which trees use as energy to grow and flower.

A reduction in photosynthesis leads to a reduction in chlorophyll as well, which is the pigment that makes leaves green. As they lose chlorophyll, they lose their green color and prepare to shed for the winter so trees can conserve their energy inside the branches and bark.

How does temperature affect the color of leaves?

But that still doesn’t explain the role of temperature.

The weather leading up to shorter days is actually quite important when it comes to determining how fall plays out for leaves .

We know that a reduction in chlorophyll leads to leaves being less green, but what makes some seasons produce more vibrant red leaves than others? Why does a tree turn bright orange one year and only a dull copper the next year?

Well, it turns out that the pigments that begin to show up once chlorophyll is reduced are dependent on both temperature and moisture conditions right before days start getting shorter. For example, some weather conditions make a leaf turn red early. It also helps it stay on the tree longer, so it goes through its full range of colors before falling off.

The role of weather in fall leaf displays

According to scientists at Michigan State (cited below), lots of warm days and cool nights narrow the veins in leaves. This helps trap the sugars made during photosynthesis in those leaves. When this happens, the sugars produce more vivid pigments.

“The most brilliant leaf displays follow a period of warm days filled with sunshine and cool nights. During this weather cycle, leaves produce an abundance of sugars during the sunny days. The cooler nights and gradual narrowing of leaf veins in the fall, means that a majority of the sugars produced are trapped in the leaf. An abundance of sugar and light in the leaf lead to the production of vivid anthocyanin pigments, which produce red, purple and crimson colors. Yellow and gold leaf colors are produced by carotenoid pigments, which are ever-present in the leaves and are therefore less dependent on the aforementioned conditions.”

Other factors in fall leaves

“Soil moisture also plays a role in the timing and brilliance of leaf color. The best displays are produced when the soil has been adequately moist throughout the year coupled with the aforementioned late summer weather. A late spring, or severe summer drought can delay the onset of color. A warm period during the fall can also decrease the intensity of fall colors by triggering early leaf drop before the colors have had a chance to develop.”

Finally, MSU explains that other factors can play a role in individual trees:

“Trees on the edge of low-lying areas, where cooler air collects at night, often display colors sooner than trees in an upland forested setting. Trees that are diseased or in decline may also display fall colors earlier than their healthy neighbors.

And that’s why no two autumns will ever look the same.  WTF fun facts

Source: “How weather affects fall colors” — Michigan State University Extension


WTF Fun Fact 12771 – The Saraha Desert Forest Mystery

Ok, trigger warning: There’s a high chance of getting Toto’s “Africa” stuck in your head by reading this post. But, the truth is, there used to be plenty of rains down in Africa. Enough to have made the Saraha Desert a rainforest.

It’s not a huge shock, since we know the Earth has gone through different climatic periods, but this was one far more recent and accounts for a more radical change than scientists ever could have imagined. In other words, it really takes a lot to turn a vibrant forest into a bone-dry desert, and this happened a mere 6000ish years ago! It’s pretty interesting.

How did the Sahara go from forest to desert?

So, what’s the deal here? Well, since we don’t have a time machine, we can’t know for certain. It could have to do with the tilt of the Earth’s orbital axis changing, it could also be part of a longer, larger pattern of transition.

African Humid Periods in the distant past meant….you guessed it…more rains down in Africa. In particular, northern Africa (which is where the Sahara is, in case you don’t have a map handy). But at some point, those rains went away.

As Smithsonian Magazine (cited below) explains:

“With more rain, the region gets more greenery and rivers and lakes. All this has been known for decades. But between 8,000 and 4,500 years ago, something strange happened: The transition from humid to dry happened far more rapidly in some areas than could be explained by the orbital precession alone, resulting in the Sahara Desert as we know it today.”

Cool use of archaeological data

We can see from archaeological data (which is not perfect, but is overwhelmingly in favor of showing past water and trees in certain areas) that the area was once forest, and even rainforest. But what’s also interesting – and seals the deal for most people – is that in this period there is also evidence of pastoralists. That means people were raising and herding animals. And you definitely can’t do that in a desert.

Are humans to blame?

If it wasn’t solely an axial issue (regarding the Earth’s tilt), some scientists believe that humans could have played a big role in changing the climate due to overgrazing.

There have been suggestions that the end of the humid period in northern Africa could have been brought about by humans letting domesticated animals eat up all the moisture-loving plants. They would have probably had to use fire as a land management tool as well. And that may have been enough to trigger the big change that turned the forest into a desert.

It’s not that easy, of course, but that’s the general idea. There are also hypotheses that humans had nothing at all to do with it. And neither one of those would be related to whether or not humans are affecting the climate currently, so it’s not a political discussion (thankfully).  WTF fun facts

Source: “What Really Turned the Sahara Desert From a Green Oasis Into a Wasteland?” — Smithsonian Magazine


WTF Fun Facts 12719 – When Weather Kills

Heat waves (typically regarded as 3 or more days in a row with a temperature above 90 degrees) are a time to take special care and to check in on the elderly and those with young children who may need help. While the heat makes many of us miserable, it’s also a killer. And because it gets misdiagnosed and is considered a fact of life in the summer by many, we easily forget what a calamity it can be for some (even for those with A/C who experience increasingly frequent power outages!).

Technically, all heat-related deaths are preventable. That’s why it’s so sad that around 658 Americans are killed by extreme heat each year. And the numbers are likely much higher since heat-related deaths aren’t mandatory to report to public health agencies.

Heat deaths as well as deaths in which heat was a contributing factor are easy to misdiagnose or mislabel. Looking back at deadly heat waves in Chicago and Paris, for example, show that far more deaths were related to heat than were recorded at the time.

Here are some sobering facts from the Environmental Protection Agency:

  • Between 1979 and 2018, the death rate as a direct result of exposure to heat (the underlying cause of death) generally hovered between 0.5 and 2 deaths per million people…
  • A total of more than 11,000 Americans have died from heat-related causes since 1979, according to death certificates.
  • In some years, recording has included heat as a contributing factor, and in other years it has not – but in the years where only direct heat deaths “counted,” the estimates may be twice as high as the records show.
  • There was a peak in heat-related deaths in 2006, one of the hottest years on record in the contiguous 48 states.

And while many kids do get special attention during traumatic weather events, it’s the elderly who are often forgotten. However:

  • Since 1999, people aged 65+ have been several times more likely to die from heat-related cardiovascular disease than the general population, while non-Hispanic Blacks generally have had higher-than-average rates.
  • The interaction of heat and cardiovascular disease caused about one-fourth of the heat-related deaths recorded since 1999.

According to the CDC, those most likely to suffer from heat-related illness and death include:

  • infants and children up to 4 years old
  • People 65 years of age and older
  • People who are overweight
  • People who have existing medical conditions, such as diabetes or heart disease
  • People who are socially isolated
  • Those who take medications that impair the body’s ability to regulate its temperature or that inhibit perspiration
  • People who are poor

Behaviors that put people are at risk for serious illness or death during heat waves include:

  • Those who engage in strenuous exercise during high heat
  • People who drink alcoholic beverages during high heat

Heat is also worse in urban areas where buildings, parking lots, sidewalks, and roads absorb heat and create even hotter “heat islands” that aren’t recorded in the local weather estimates.

From 1999 to 2010, 8,081 heat-related deaths were reported in the United States. In 72% of these cases, excessive heat was actually the underlying cause of death (often in those who already had a cardiovascular condition). Only in 28% of cases was it a contributing factor.

So, what can you do to make sure everyone handles the heat?

  • Check on people at risk, such as the elderly, disabled, or homebound.
  • Never leave any living creature locked in a car. (Sometimes we don’t even know how bad the heat is getting to us until it’s too late.)
  • Limit sun exposure during midday hours, even at places like beaches.
  • Avoid sunburn and treat it right away if it happens by applying aloe vera and hot compresses – never pop blisters.
  • Drink plenty of nonalcoholic fluids (and avoid caffeine).
  • Replace the body’s salts and minerals by eating fruits and vegetables (NOT salty snacks – because while your body needs salt, they have too much for your kidneys to handle).
  • Dress in cool, loose clothing (this also helps avoid heat rash).
  • Shade your (and especially children’s) heads and faces from the sun – use an umbrella if that’s all you have.
  • Provide plenty of fresh water for pets and put it in the shade.
  • Create circulation with fans if you don’t have a/c – and make there’s a fan pointing outward to push hot air out of the room.
  • Put a bowl of cold water (with ice, if possible) in front of a fan for an extra cooling effect.
  • Try closing all doors, windows, and curtains right before the sun comes up to keep cooler evening air inside longer.
  • Cover your feet and shoulders with wet towels and washcloths.
  • Create a space in the basement, if you have one, since it’s often cooler down there.
  • Turn off electronics that give off heat when plugged in (such as computers and lamps with incandescent light bulbs).
  • Try not to use the stove or oven.
  • If there’s no relief in your home, visit public buildings (such as shopping malls or libraries) with air conditioning.
  • Avoid large, protein-rich meals to keep the body from creating its own metabolic heat.
  • Lay down in a shaded area and sip water if you get clammy, pale, lightheaded, nauseous, or develop a headache – this can turn into an emergency quickly, so don’t hide away in a hot room.
  • Keep some Gatorade or Pedialyte (or any oral hydration with essential minerals and potassium) to stave off dehydration.
  • Call 911 if you experience: cramps, swelling, fainting, a temperature over 100 degrees and rising, confusion, a rapid pulse, severe nausea, a severe headache, and skin that’s warm and dry – it could be heat stroke, which can lead to coma and death.

 WTF fun facts

Sources: “Heat-Related Illness” — CDC
“Climate Change indicators” — EPA
“11 Facts About Heat Waves” —


WTF Fun Fact 12622 – Air Conditioning Trees

There’s no arguing with the fact that trees keep the planet alive. And we all know they help keep the Earth cool, though we may not know the exact mechanism by which they do it.

But the amount of influence trees can have over the climates in their immediate areas is still pretty stunning.

Even when trees grow in cities (relatively far apart and under conditions that are probably less ideal than, say, a forest), they can have a large cooling impact.

According to the EPA, cities sometimes create “heat islands”:

“An urban heat island (UHI) is an urban area or metropolitan area that is significantly warmer than its surrounding rural areas due to human activities. The temperature difference is usually larger at night than during the day, and is most apparent when winds are weak.”

Tl; dr – Cities are hotter because of all the stuff we do there.

But what’s cool about trees (see what we did there?) is that they can lower both surface and air temperatures. We all know it’s cooler in the shade (sometimes by as much as 20-45 degrees F!), so that’s part of it. But there’s also something called evapotranspiration that plays a role. That’s the method by which water moves from the earth’s surface (the soil) up into the atmosphere. So, later, when we get precipitation, it can cool off our buildings and sidewalks.

Evapotranspiration (along with shading, in most cases) can reduce peak temperatures on a summer day by 2-9 degrees F.

And chances are that if you have a thoughtful city planning department, the trees planted around your nearest city are planted in very strategic locations to take advantage of this process. (For example, you may find more trees planted to the west of buildings to take advantage of maximum shade.)

There’s a very long list of the benefits of trees, but we’ll add a few that are less obvious about city trees:

  • They reduce energy usage by lowering the demand for air conditioning
  • They help with stormwater management after big storms by absorbing and filtering rainwater
  • They can reduce the need for constant pavement maintenance by keeping sidewalks, roads, and parking lots cool
  • They improve our quality of life, in part, by reducing noise pollution in cities.

Sometimes trees get in the way, but it’s critical to have them around (or replant them when we need to remove them). – WTF fun facts

Source: “Using Trees and Vegetation to Reduce Heat Islands” — US EPA