According to scientists, agricultural activity has led to an increase in the amount of carbon dioxide in the atmosphere.
Climatologists in the United States conducted a comparative analysis of the modern climatic era and a similar period of the previous one. They found a significant difference in the development of climatic conditions and associated it with the activities of ancient farmers. The work was published in Scientific Reports.
Fifteen years ago, one of the study's authors, William Ruddiman of the University of Virginia, studied the traces of methane and carbon dioxide remaining in Antarctic ice. He told how it all began:
“I noticed that the concentration of methane began to decline about ten thousand years ago, but then five thousand years ago, the trend was reversed. A similar situation turned out to be with carbon dioxide: its concentration also decreased ten thousand years ago, but went uphill seven thousand years ago. This struck me as strange, and the only explanation that came to mind was early agriculture."
Scientists have built a climate change model based on data obtained from ice deposits. In this model, they compared our own climatic era - the Holocene - with the one that was 770 thousand years ago. The researchers named it The Marine Isotope Stage 19c (MIS19c).
Changes in surface temperature in Kelvin from MIS19c to 1850.
The analysis showed that both epochs began with the same levels of carbon dioxide and methane. While the amount of gas was decreasing in MIS19c, in the Holocene its concentration began to increase approximately five thousand years ago and peaked by 1850. Experts deliberately limited the model to the 19th century, before the industrial revolution, so as not to account for the sharp jump in greenhouse gases after it.
In their model, the researchers also took into account the largest phenomenon of natural climate formation - the Milankovitch cycles. They determine climatic fluctuations based on changes in the eccentricity of the Earth's orbit. Whether the orbit is circular or ellipsoidal, the amount of sunlight reaching the Earth depends on. Both epochs - MIS19c and Holocene - were in the same phase of Milankovitch cycles. All these facts have further convinced scientists that agriculture is the cause of climate change. In their work, they refer to studies that confirm the massive felling of trees in Europe six thousand years ago and the widespread occurrence of rice fields (a source of methane) in northeast Asia five thousand years ago.
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According to the authors of the study, human activities over the past two thousand years have changed the usual course of climate development and prevented a new ice age, and that is why it is difficult to predict what will happen next.
Alexey Evglevsky
