Human History Influenced by the Universe, Earth, and Climate: "A 100,000-Year History of Humanity and Climate" (March Anything Goes Shinsho Challenge 9)
Today, I am discussing "A 100,000-Year History of Humanity and Climate".
I can never deeply understand the content of science books, but this is a genre where even knowing superficial information gives me a sense of connection to various things. After biology and medicine, today it is ancient climate and the geology used to understand it.
There are many stories about Earth's past, such as "there were several ice ages in the past" or "dinosaurs went extinct due to rapid cooling." My knowledge was basically not updated from the "Secret Series" books by Gakken that I read as a child.
However, it is now possible to understand past climates through geology, and based on that, we can think about how the Earth's climate will change in the future. It is said that the theory of Serbian geophysicist Milutin Milankovitch, which suggests a link between Earth's orbital path and climate, is being proven one after another.
Of the positional relationships between the Earth and the Sun, it is not only the shape of the orbital path that changes over time. The orientation of the Earth's axis and the magnitude of its tilt also fluctuate regularly according to their own cycles. Today, it is understood that these factors, known as orbital elements, all have a significant impact on climate. Furthermore, the theory that links orbital elements to climate is called the "Milankovitch theory."
Even as a layperson, I understand that the Earth orbits the Sun like a tilted spinning top. But it seems that not only that, but the orientation of the top's axis itself also moves in a constant cycle. This is called precession, and it takes 23,000 years for the axis to complete one rotation.
What shows us that it really moved are the layers deposited on the lake bottom called "varves," and it is said that one of the world's rare sedimentary layers is located at Lake Suigetsu, a scenic spot in the southern part of Fukui Prefecture. It is surprising. It seems that 70,000 years' worth of layers have accumulated there. The author is a specialist in geochronology and paleoclimatology. They carefully extracted and investigated the mud deposited on the lake bottom.
According to the Milankovitch theory, both methane and carbon dioxide should have been decreasing over the last 10,000 years, but in reality, both are increasing. There is a hypothesis that this is due to human activity—specifically, the increase in greenhouse gases caused by Asian rice paddies and European deforestation—and if that is the case, the current debate regarding global warming would not hold up in the first place.
Has humanity actually been warming a planet that should have been cooling? This is a very interesting perspective.
If we are avoiding an ice age that "should have already arrived" through the emission of greenhouse gases, the debate over the morality of global warming is shaken to its core. Do we want to live on an Earth in a naturally occurring ice age, or do we want to live in a climate that is artificially kept warm? This is no longer a question of science, but a question of philosophy.
From astronomy to climate and geology, does it even extend to philosophy?
I thought it was the same eternal theme as what we learn from science, how people receive and think about it, and what I personally take away from reading.
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