The climate of our planet under the influence of man began to change 7 thousand years ago. And it saved us from the ice age.
In 2018, the weather once again surprised both Russia and many other countries. Most earthlings have experienced the very same global warming that scientists have been arguing about a lot. In Moscow, the summer, instead of three months, lasted five whole months - from May to almost the end of September. The Baltic Sea was covered with algae from overheating. The beaches on the White Sea competed with the Black Sea, if not in the number of tourists, then in the temperature of the air and water. Throughout Europe, and especially in the north, in Scandinavia, Great Britain, Germany - as well as in the northern regions of Russia - summer 2018 was abnormally hot and sunny.
It is believed that anthropogenic, that is, man-made, global warming began at the end of the 21st century and accelerated towards the end of the 20th. The smoking chimneys of factories and thermal power plants, cars and airplanes are to blame for it.
But American scientists Stephen Vavrus from the Center for Climate Research at the University of Wisconsin and William Raddiman from the University of Virginia assure that everything started much earlier, 5-7 thousand years ago. Ancient farmers began to change the planet's climate - with their own hands, in the literal sense of the word. They cut down forests, plowed fields in their place, developed new territories, brought in cows and other livestock.
There is more carbon dioxide in the atmosphere (since the area of the forests absorbing it has decreased) and methane (one of its main sources, both then and now, is the very cows). Ancient global warming was not as noticeable and rapid as it is now. But the process was started just then.
Methane and carbon dioxide
But. Everything that is done is for the best! If humanity in antiquity had not organized global warming, now it would simply freeze. A new ice age would have fettered the Earth already in the 19th century. And this summer we would not be basking on the beaches, but freezing in fur coats. The first farmers by their interference in the natural course of things slowed down the change of climatic eras.
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How did Vavrus and Raddiman come to such conclusions? Using a computer model and paleoclimatic data, they compared our time, the Holocene (ours - in a broad sense, on the scale of geological eras), that is, the interglacial period, with a similar warm era that was on Earth 800 thousand years ago. When, of course, there was no agriculture or industry at all.
Why was the time chosen for comparison? Then there were similar astronomical conditions, scientists explain. The Earth's orbit periodically changes its shape slightly, which affects the distance of our planet from the Sun. This, in turn, determines the climatic cycles.
So that's it. All other things being equal, 800 thousand years ago it was 1.3 degrees colder than in our era, and even 4-5 degrees in the Arctic. This is the first difference.
The second is the amount of greenhouse gases in the atmosphere. The “basic” period (the one that is 800 thousand years ago) and the Holocene, which began 12 thousand years ago and continues to this day, started from the same level. But if in the first case the amount of carbon dioxide and methane gradually decreased until the next ice age, then in the second the curve also first went down, and then suddenly jumped up again.
What ice remembers
William Ruddiman has been studying ice from Antarctica for many years, which stores information about the Earth's climate for tens of thousands of years. Including - about the concentration of greenhouse gases.
- Their level has been decreasing since the beginning of the Holocene. But 7 thousand years ago, first the carbon dioxide curve went up, and then, 5 thousand years ago, the same thing happened with methane, - the paleoclimatologist shares his discoveries. - Some strange interglacial, I thought. The only logical explanation for the sudden change is the beginning of mass farming.
In Europe, massive deforestation began 6 thousand years ago. In China, 7 thousand years ago, large agricultural communities appeared, flooding fields for the sake of growing rice. Wheat by that time was grown in Egypt and Mesopotamia.
- If not for this turn, now the climate on Earth would be much colder, - says Stephen Vavrus.
Raddiman called his conjecture an "early anthropogenic hypothesis." In contrast to the simply man-made, classical, leading global warming since the beginning of the industrial era.
It will be warmer and warmer all the time
With the help of a computer model, Varvus and Raddiman checked what the climate would be like if mankind had not learned to engage in agriculture. Most likely, the same thing would have happened as after the interglacial 800 thousand years ago: a sharp cooling in the Arctic, giant glaciers and snow all year round over vast territories.
In reality, the opposite is true: in the Arctic, global warming is going many times faster than on the planet as a whole.
- The climate has long gone beyond the natural course of things. And what will happen next, we do not know, - Vavrus admits. - There is an opinion in the scientific community that the climate changes provoked by mankind postponed the onset of the next ice age for a long time. Even if we stop emitting greenhouse gases into the atmosphere at all, the process of warming will not easily end. Perhaps we have stopped the natural cycle altogether, when periods of warming and cooling alternate. And now it will be warmer and warmer all the time.
YULIA SMIRNOVA
