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During the Pliocene epoch (5.3 Ma to 2.6 Ma) climate became cooler and drier, and seasonal, similar to modern climates. The global average temperature in the mid-Pliocene (3.3 Ma–3 Ma) was 2–3 °C higher than today,〔 〕 global sea level 25m higher 〔 〕 and the northern hemisphere ice sheet was ephemeral before the onset of extensive glaciation over Greenland that occurred in the late Pliocene around 3 Ma.〔 〕 The formation of an Arctic ice cap is signaled by an abrupt shift in oxygen isotope ratios and ice-rafted cobbles in the North Atlantic and North Pacific ocean beds.〔Van Andel (1994), p. 226.〕 Mid-latitude glaciation was probably underway before the end of the epoch. The global cooling that occurred during the Pliocene may have spurred on the disappearance of forests and the spread of grasslands and savannas.〔 〕 During the Pliocene the earth climate system response shifted from a period of high frequency-low amplitude oscillation dominated by the 41,000 year period of Earth's obliquity to one of low frequency-high amplitude oscillation dominated by the 100,000 year period of the orbital eccentricity characteristic of the Pleistocene glacial-interglacial cycles.〔 〕 The equatorial pacific ocean sea surface temperature gradient was considerably lower than it is today, mean sea surface temperature in the east were substantially warmer than today but similar in the west, this condition has been described as a permanent El Niño state or El Padre〔 〕 ==Setting== During the late Pliocene and early Pleistocene Series of the Cenozoic Era, 3.6 to 2.2 Ma (million years ago), the Arctic was much warmer than it is at the present day (with summer temperatures from 3.6-3.4 Ma some 8 °C warmer than today). That is a key finding of research into a lake-sediment core obtained in Eastern Siberia, which is of exceptional importance because it has provided the longest continuous late Cenozoic land-based sedimentary record thus far. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Pliocene climate」の詳細全文を読む スポンサード リンク
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