Scientists of Rutgers University in the US found that recent warming has no parallel at least over the last 66 million years, since all the other major climatic changes occurred mainly due to changes in Earth’s orbit, not greenhouse gases. Modern melting of glaciers, leading to catastrophic flooding due to human activities, and not with the astronomical cycles. Article researchers, revealing the true cause of sea level fluctuations, published in Science Advances.
To trace the history of sea level and ice sheets of the Earth in the Cenozoic era (started 66 million years ago and is still ongoing), experts analyzed the chemical composition of the samples of deep-sea sedimentary rocks in the Pacific ocean. The content of isotopes of oxygen-18 in the remains of the shells of foraminifera it is possible to know the temperature of the sea water and its oxygen saturation in the past, and the ratio of magnesium and calcium (Mg/Ca) serves as an independent indicator of temperature in the deep layers.
The content of isotopes of oxygen-18 in seawater depends on ice cover on the continents and sea level. While previous studies have shown that the Milankovitch cycles — changes in the amount of light reaching the Earth’s surface, due to fluctuations in the orbit and axis of the planet also affect the level of isotopes in the bottom sediments.
It turned out that from 56 to 48 million years ago in Earth’s history came the warm period, characterized by a high content of carbon dioxide in the atmosphere, higher sea levels and no ice cover. Then began the growth of glaciers 34 million years ago the first ice sheets 12.8 million years ago the ice cap covered East Antarctica, and 2.5 million years ago ice covered the southern and the North pole. This drop in sea level to 35 meters 27-20 happened thousands of years ago, then began a period increase with a rate of 40 millimetres per year (19-10 thousand years ago), and before 1900, the sea level remained unchanged. In the XX century it started to increase again accelerated.
These fluctuations except for the modern warming coincide with the chronology of the cycles of Milankovitch. Although the content of carbon dioxide had an impact on the greenhouse effect, melting ice and rise in sea level, in the past the dominant factor in climate change was precisely the small changes in Earth’s orbit.
