June 9, 2021
Today, ecology and the solution of the environmental problems have become one of the officially recognized priorities for the development of the majority of the world countries. A problem of global climate change occupies a highly important place in the list of the environmental problems. To date, there is no single opinion on the causes of this phenomenon among the world experts and scientists. There are two opinions regarding the causes of the climate change. The first group of scientists believes that natural cyclical temperature fluctuations serve as the major reason of the current climate change and a cold snap will follow global warming. The second opinion associates global warming with devastating human activities. The change in the mean values of the temperatures and change in the animal habitats are possible consequences of the climate change connected to this factor. Despite opposite opinion, anthropogenic factors have been more important than natural fluctuations in temperature in the last fifty years.
The Paleocene-Eocene Thermal Maximum
The ongoing Cenozoic era started about 66 million years ago. Together with it, the Paleocene came and after it, the Eocene came about 56 million years ago. The latter was remembered by three warming that resembled the largely modern global warming. The first one happened on the border of two epochs. It is called the Paleocene-Eocene thermal maximum that continued more than 180,000 thousand years. It was followed by the increase in temperature by about 8 degrees (Bowen et al, 2015). In the course of time, the temperature became normal. Nevertheless, two million years later warming came again (McGuire and Maslin, 2012). This time, it was not so strong and the temperature increased by approximately three degrees. The last remarkable warming of the Eocene began in 100 000 years and it was considered the weakest among all three warming the temperature changed by not more than two degrees (McGuire and Maslin, 2012).
The temperature maximum in the Paleocene-Eocene thermal maximum lasted for 200 thousand years and this phenomenon was global. According to the scientists, warming started because of the raise of the level of carbon dioxide in the air (Bowen, et al, 2015). It can be connected with the volcanic activity. At some time, increased underwater volcanism and tectonic activity transformed the channels of the underwater currents of the oceans that moved in non-standard directions in the next 40 thousand years (McGuire and Maslin, 2012). This fact led to the heating of the seabed in the places unusual for these temperatures. Consequently, there was the release of huge amounts of ocean bottom methane into the atmosphere that millions of years accumulated there because of the decomposition of the anaerobic bacteria by great amounts of organic sedimentary rocks. Despite the fact that the majority of the scientists adhere to the version with crystalline hydrates, there is still an opinion that only the fall of a large asteroid or comet on the planet could cause such sharp warming on the planet.
Rising through the water column to the surface, the crystalline hydrates disintegrated keeping methane in it and releasing carbon dioxide. It made the seawater extremely saturated with carbon dioxide. The sedimentary record was rather high during this period that contributed to the acceleration of the processes. This fact resulted in the extinction of about 50% of all foraminifera and the mammalian flowering (McGuire and Maslin, 2012). Moreover, the oxidized water dissolved plenty of bottom carbonates from among the bottom sedimentary rocks. It did not promote to the flourish of life in the worlds oceans as well. Carbon dioxide that escaped from the depths of the sea produced a greenhouse effect leading to sharp and powerful warming of the Eocene climate. It reached the point that the water temperature in the Arctic Ocean was an average of 22 C (McGuire and Maslin, 2012). Thus, the tropical forms that previously preferred to inhabit only equatorial regions of the World Ocean spread in the Arctic Ocean.
Fossils of the Paleocene-Eocene Thermal Maximum period show considerable changes in the life of mammals, as well as the unexpected emergence of several modern species. This period is also characterized by the decrease in the size of existing animals. This fact can be seen from the teeth of adult specimens. For instance, the representatives of the genus Sifrhippus that are similar to the ancient horse decreased in size by more than 30% (McGuire and Maslin, 2012). The Paleocene-Eocene thermal maximum became not only a cause of the extinction of the existing species but also served as a great push for the development of new species of birds and mammals throughout the Earth. Over the next 200 thousand years, new species of animals formed actively and many mammals returned to the aquatic environment.
The Evidence for Glaciations during the Pliocene
The Pliocene epoch is the second epoch of the Neogene following the Miocene and preceding the Pleistocene. According to the abstract calculations, this epoch began nine million years and ended two million years ago. Thus, its duration is approximately seven million years (De Schepper, Gibbard, Salzmann, and Ehlers, 2014). In the Northern Hemisphere, the gradual change in the climate continued. Gradually, the climate became colder and drier. At the end of the Pliocene epoch, the Greenland ice sheet emerged and glaciations began on the continents of the North Hemisphere (De Schepper et al., 2014). Besides, glaciations of the South Hemisphere expanded. Great changes in semi-enclosed basins that started in the Miocene epoch continued. Due to the gradual cooling, vegetation became more cold resistant and the area of steppe associations increased. Until the end of the Pliocene epoch, Hipparions still existed. Nevertheless, a new species adapted to the changed conditions gradually replaced them. New species included elephants, horses, bulls, rams, and elasmotherium. Therefore, the Pliocene epoch is characterized by the decrease in temperatures and the appearance of new species.
Marine isotope stages represent successive cold and warm periods in the history of the planets climate allocated based on the analysis of oxygen isotopes in marine sediments. These stages are numbered in reverse order from the current stage that is denoted by MIS-1. Odd stages with a low level correspond to warm interglacial intervals while even stages with a high level of 18O are cold glacial periods. With the help of marine isotope stages, it is possible to trace glaciations on the planet.
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Today, scientists conduct a great number of research projects dedicated to the study of the Arctic ice cover. It is connected to the fact that over the past several decades, under the conditions of the global warming, the Arctic ice cover is rapidly declining. Scientists made four wells from the bottom of the Arctic Ocean (Stein, Fahl, Gierz, Niessen & Lohmann, 2017). According to the results of the measurements of the contents of biomarkers in sedimentary rocks of four wells, digital models for the spread of the ice cover in the Arctic basin were constructed during the last interglacial period (Stein et al., 2017). As a result of modeling on the maps of the ice situation, it is seen that even in the warm climate of the last interglacial period, which is stage MIS-5e, the ice cover existed in the central part of the Arctic basin throughout the summer. On the contrary, the Barents Sea was ice-free not only in the interglacial stage of MIS-5e but also during the previous glacial stage of MIS-6 (Stein et al., 2017). It was associated with the inflow of warm water from the Atlantic. Another interesting result consists in the fact that for the period of the glacial stage of MIS-6, single detectors of the open water situation were found. Scientists explain this by the fact that in the summer months, polynyas could be formed along the southern shores of the Arctic seas (Stein et al., 2017). They are similar to those formed today off the coast of Greenland and Antarctica. The mechanism of the formation of such areas of open water is well known. It is associated with the fact that during the penultimate glaciers and when the ice sheet covered the coastal surface of the land, the whole coast of North America and Eurasia was covered with an ice sheet of more than one kilometer thick (Stein et al., 2017). Over the surface, there was the formation of cold air flowing towards the side of the ocean according to the slope of the glacier resulting in katabatic winds. They increased approaching the ocean continuously blowing in one direction and repelling the fragments of ice from the shore. Free water was formed in the coastal zone (Stein et al., 2017). In such a way, with the help of marine isotope stages, it was possible to detect the ice cover in the Arctic basin and various processes occurring on different isotope stages.
The Impact of Continued Warming of the Earth
Global warming will have a devastating impact on the planet. In the future, the raise in temperature will cause great transformation of the continental natural zones. Scientists predict that if the situation does not change for the better, the tundra can almost completely disappear (Summerhayes, 2013). The taiga zone will decrease by almost a third while the area of deciduous forests will increase. This will result in the transformation of the habitat of animals. Moreover, the change in the habitats of living organisms is observed in many parts of the globe. For example, the white-headed thrush has already begun to nest in Greenland (Summerhayes, 2013). A white heron has appeared in Britain and there are swallows and starlings in the subarctic Iceland (Summerhayes, 2013). However, the changes will be even greater. Climate changes will reduce the viability and strength of the populations of species limited to small isolated habitats. As ice melts, the narwhal and the bowhead whale will lose the necessary protective coating (Summerhayes, 2013). At the same time, other species will face the threat of further reproduction. Fish and whales are also endangered by the reduction of zooplankton they eat. Therefore, further climate changes will affect all living organisms.
In such a way, habitat disturbance is considered the most important effect of the global warming on wildlife. As a result, ecosystems, which have formed for millions of years, transform rapidly in response to the climate changes reducing the ability to meet the needs of the species (Summerhayes, 2013). The habitat disturbances frequently happen because of extremely low or high temperatures along with the absence or the presence of water. Therefore, the conditions for growth change affect the plant communities. In addition, global warming leads to the shift in the time of different natural cyclic events in the life of animals. A large number of birds changed the terms of reproduction and migration to synchronize with climate changes (Summerhayes, 2013). Several wintering animals end their hibernation earlier because of warmer spring temperatures.
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Climate changes represent fluctuations in the climate of the whole planet or its separate regions expressed in statistically deviations of the weather parameters from long-term values over a period from decades to millions of years. These days, there is considerable climate change on the Earth. It is associated with the anthropogenic factor and the natural fluctuations of temperatures. In the past, the planet experienced both increase and decrease in temperatures connected mainly with natural factors. However, anthropogenic factors are currently more important. If there are no positive changes and the effect of anthropogenic factors continues, the planet will expect transformations associated with the changes in the species composition of animals and plants.