Why is “10 degrees in autumn” colder than “10 degrees in spring”?

I wonder if you have had a similar experience: the temperature is the same, but the feeling is very different in spring and autumn.

In spring, when the temperature is 10 degrees when we go out in the morning, we walk in the sun wearing only a single layer of clothes, and soon beads of sweat appear on our foreheads; but in autumn, when the temperature is also 10 degrees in the morning, we put on coats and start shivering as soon as the wind blows.

Some netizens analyzed that this is because the autumn is preceded by summer, and people are used to the heat, so 10 degrees is a low temperature compared to the extreme heat; on the contrary, in spring, the body is already used to the cold, so 10 degrees is a high temperature compared to the extreme cold. Although this statement is a bit "emotional", the scientific community has shown some recognition: yes, the body does have such an adaptation process to the temperature.

Before we delve into the topic of “different sensations at the same temperature,” it’s helpful to first understand the process by which the human body responds to cold.

When the temperature drops, the thermoreceptors on our skin are the first to detect the change and transmit the signal to the hypothalamus . The hypothalamus is located on the ventral surface of the brain, below the thalamus. Although it weighs only 4 grams and accounts for 0.3% of the total brain volume, it has a strong ability to regulate body temperature, food intake, reproduction and endocrine activities.

The red part is the hypothalamus

When receiving the cold signal, the hypothalamus generally instructs the body to take two countermeasures: first, vasoconstriction, especially the contraction of peripheral blood vessels such as the skin. Vasoconstriction can reduce the heat exchange between the skin and the external environment, thereby helping the body reduce heat loss; secondly, we also increase heat energy by shivering muscles, which is why people can't help "shivering" in winter.

Knowing the two common reactions of the human body to cold, we can observe whether the human body becomes more cold-resistant due to long-term exposure to cold by monitoring the degree of vasoconstriction and shivering .

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Fortunately, the scientific community has already conducted a large number of experiments that have given a positive answer.

The researchers found that native Arctic peoples experience less vasoconstriction and shivering when exposed to cold than people living in tropical areas because they are accustomed to cold temperatures.

Some fishermen who need to put their hands in cold water frequently have also become "immune" to the cold. An experiment found that when fishermen and ordinary people put their hands in ice water of the same temperature, the temperature of the fishermen's hands will be slightly higher, which is also the body's response to adapt to the cold.

In the spring, we have experienced a long winter and become more tolerant to cold like the people of the Arctic, so when the temperature rises slightly, we immediately feel hot. In the fall, we have just experienced a long summer and are not "immune" to cold like the people of the tropics, so we are frozen when the temperature drops.

This type of adaptation to cold is generally achieved through the regulation of the nervous system. However, if you are exposed to cold enough, the human body will even undergo physiological changes related to "brown fat" and become more cold-resistant.

According to color, the fat in the human body can be roughly divided into two types: white fat and brown fat.

The orange oval is a lipid droplet, the pink oval is a mitochondria, and the blue oval is a cell nucleus. Source: Everyday Health

White fat is roughly equivalent to the so-called "fat meat". As the biology textbook in middle school says, its main function is to store energy. Only when other "energy substances" are exhausted will the body use white fat cells. This is why it is so difficult to lose weight and requires a lot of aerobic exercise to be effective.

Brown fat cells are smaller than white fat cells, and they contain many "energy-generating machines" called mitochondria. Therefore, when we feel cold, brown fat can quickly release heat and is a much more efficient "good fuel" than white fat. This means that the more brown fat a person has in his body, the better he can adapt to the cold and quickly reach a higher body temperature in severe cold.

Scientists have found that when the human body is in a low temperature environment for a long time, it is easier to produce brown fat in the body; when the human body is exposed to a hot environment for a long time, it is less likely to produce brown fat. So compared with autumn, our bodies have more brown fat in spring, which means more " good fuel ". This can also explain why we feel warmer in spring when the temperature is 10 degrees.

The researchers asked the men to sleep in different temperatures every night, A 24 degrees in the first month, B 19 degrees in the second month, C 24 degrees in the third month, D 27 degrees in the fourth month, and found that the amount of brown fat (red shadow) changed. Source: Reference 4

Of course, there are many factors that affect physical sensations: geographers believe that the sun's direct point is closer to the northern hemisphere in spring, and the solar radiation is strong, so it feels warmer; psychologists point out that people's different feelings about the same temperature in spring and autumn may also be affected by "psychological suggestion."

However, we can still overcome the discomfort of changing seasons through some methods, such as exercise. When the temperature changes from hot to cold in autumn, exercise can promote the conversion of white fat into brown fat. When the temperature changes from cold to hot in spring, exercise can make our sweat glands more sensitive and release excess heat in time.

So exercise is always right. Why not go out and move your legs to let the 10 degrees in spring get infinitely close to the 10 degrees in autumn?

References

[1]Why kids don't get as cold as adults do? https://www.youtube.com/watch?v=zpcI_g_zrpk

[2]Why a 65-Degree Day Feels Cold in Fall but Warm in Spring?

https://www.michiganmedicine.org/health-lab/why-65-degree-day-feels-cold-fall-warm-spring

[3]Here's Why a 50-Degree Day Feels Colder in Fall Than in Spring

https://www.nytimes.com/2018/10/24/science/human-bodies-cold-weather-adjustment.html

[4]Lee P, Smith S, Linderman J, Courville AB, Brychta RJ, Dieckmann W, Werner CD, Chen KY, Celi FS. Temperature-acclimated brown adipose tissue modulates insulin sensitivity in humans. Diabetes. 2014 Nov;63(11):3686-98. doi: 10.2337/db14-0513. Epub 2014 Jun 22. PMID: 24954193; PMCID: PMC4207391.

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Source: Bring Science Home (ID: steamforkids)

Author: Liu Liuqi

Editor: He Tong

Proofread by Xu Lailinlin

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