With the rise in temperatures, the summer season is now dreaded by part of the population. After the heat waves that hit France in July 2022, other records are being broken this summer. When the thermometer flies away, our body is put to the test. Among the most listed difficulties: lack of sleep, fatigue or dehydration.
Regarding the short-term effects, the heart is not spared. It must pump harder and faster to redistribute and increase blood flow to the skin to cool the body. “The vessels dilate, we have hypotension, and to fight there is an important sweating system which starts to regulate the body’s temperature”, indicated to L’Express Evelyne Chartier, general practitioner.
So many symptoms with which we will have to learn to live, because climate change does not seem ready to subside. Over the period 2013-2022, the warming caused by humanity has increased to an unprecedented level of more than 0.2°C per decade”, write about fifty renowned researchers in the magazine Earth System Science Data, based on the methods of the IPCC, the climate experts mandated by the UN. For his part, the human being needs to maintain his body at a constant temperature, between 36 and 38°C. During hot weather, it must regulate itself and expend energy. “We can endure a while, but after a while the body is exhausted, underlined to L’Express Jacques Battistoni, general practitioner and president of the MG France union. Sweating only lasts a while, we don’t can’t sweat forever”.
Longer bodies?
But could our body better adapt to high heat? While human beings have survived thanks to their ability to evolve over millennia, our morphology is not left out. “In this evolution, there are two components: a component of reversible physiological adaptation and genetic evolution which takes place more slowly”, exhibits at L’Express, Alain Froment, anthropologist and biologist at the National Museum of Natural History (MNHN). The scientist recalls that for 200 years, the height of human beings has increased, which is linked to a “diet richer in carbohydrates”. These evolutions are secular, that is to say on the scale of the century.
To better acclimatize to the heat, the size of the human being might be subject to change. Over the past million years, their average size has changed significantly and according to a study, this is an effect of climate change, reported in July 2021, the American media CNN. To arrive at such conclusions, a team of researchers led by the University of Cambridge in the United Kingdom and the University of Tübingen in Germany collected measurements of brain and body size for more than 300 fossils of the genus or of the Homo family, to which modern humans belong – Homo sapiens. Therefore, larger and smaller bodies would be less suitable for very hot climates.
The change in temperature could therefore lead to a change in corpulence. “It’s the fat that will prevent us from being comfortable when it’s hot. The fat we have under the skin is an insulator,” says Alain Froment. In short: the larger the size and the smaller the volume, the more efficient the refrigeration. If the change were to be prolonged, the human body could become leaner and thinner. Being large allows the surface of the skin to be extended and the exchange surface to be increased, which will eliminate heat more easily […] You just have to see how the physiological adaptation happened in the Sahel countries”, he adds. If the size seems to be able to evolve, the question is also how long it will take.
Air conditioning, clothing, hats… Adaptation innovations are numerous, making the pressure of selection much less strong for human beings than it was before. “We have so many cultural buffers to alleviate this heat stress that biological evolution is not determining, especially since it will take time, on a millennium scale. I don’t really believe in a radical body evolution”, says Alain Forment. In other words, we will have to rely more on our intelligence and our ability to act than on the evolution of our morphology if we want to adapt to the heat.
And what about the rest? Will our brain size also grow due to rising temperatures? This last possibility is less obvious according to the scientists who have studied the subject. Of course, the climate can play a role in this evolution, but it would not be the only factor. In other words, the body and the brain can therefore evolve under different constraints. Another question: our skin color. Could it get darker? No, the increase in temperatures is not linked to an increase in sunshine and therefore UV, but to the greenhouse effect. But the dark color protects against UV: if there is no more, no need to protect yourself.
animals adapt
And what about animals? For some, the impact of climate change has already been seen. According to an Australian study published in the journal Trends in Ecology & Evolution in September 2021, coverage in the scientific media Futura, climate change – in particular the rise in temperatures – increases the size of certain appendages in animals (tail, ears, beak, etc.). For example, animal species that live in hot climates have larger appendages than others that are close to them but live in colder areas. We can think of the fennec with its big ears which lives in the Sahara desert and the Sinai peninsula.
In birds, the beak acts as a regulator of their body temperature. “Thanks to a bibliographic synthesis, the authors show that Australian parrots have seen the surface area of their beaks increase by 4 to 10% since 1871 and that this increase in size is positively correlated with temperature during the summer preceding the sampling of specimens”, resumes Futura. In 2019, a study showed that migratory birds from North America have seen their size decrease over the past four decades due to warming temperatures. However, if species have the ability to adapt, this does not mean that they are perfectly acclimatized to these new conditions. Thus, some could disappear due to climate change.