The concentration of carbon dioxide in the atmosphere reached 412 ppm and was a record high for the past 23 million years. Moreover, almost all of the time, the content of CO2 in the atmosphere is linearly decreased at a speed of five ppm in a million years, but two centuries ago, already beginning to grow at five ppm per decade. To such conclusions scientists have come, having analysed the content of 13C in fossil sediments, vascular plants, capable of C3-photosynthesis. The results of a study published in the journal Geology.
The most important observation is that climatologists are trying to convey to the public — is the current increase of CO2 in the atmosphere to a level higher than trends in the long geological past. Now the concentration of this gas is 412 ppm (parts per million), and earlier researchers have found that this is a record for a period of not less than 800 thousand years: for this period, the science has data of direct measurements of the amount of carbon dioxide in the air bubbles enclosed in ancient ice sheets of Antarctica.
With more ancient epochs, the situation is more complicated: there are data obtained when working with fossil sea by foraminifera, teeth of hoofed animals, deposits of Loess plateau in China, soil carbonates, which accurately describe the situation in some periods — that is, are discrete. The results of these studies, however, is not always convincing to the public: they are heterogeneous, hardly add up to the overall picture and cannot lead to a definite conclusion about the danger of modern trends and the anthropogenic contribution to global warming through greenhouse gas emissions.
Scientists led by Ying Cui (Cui Ying) from the State University Montclair investigated the dynamics of the concentration of carbon dioxide in the atmosphere in the Miocene, Pliocene and Pleistocene, covering the last 23 million years of earth history. For this they used the published data of almost 700 measurements of the radioactive isotope 13C: 441 measurement belonged to the ancient organic matter of the soil, and 259 — for lipids fossils of vascular plants carrying out C3 photosynthesis. This approach made it possible to construct a continuous median curves for 13C and CO2 over such a long period of Earth’s history.