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Reconstructed proteins from Precambrian organisms have also provided evidence that the ancient world was much warmer than today. [ 12 ] [ 13 ] However, other evidence suggests that the period of 2,000 to 3,000 million years ago was generally colder and more glaciated than the last 500 million years.
Azolla event may have ended a long warm period 5.3–2.6: Pliocene climate became cooler and drier, and seasonal, similar to modern climates. 2.5 to present: Quaternary glaciation, with permanent ice on the polar regions, many named stages in different parts of the world
The Earth's average surface absolute temperature for the 1961–1990 period has been derived by spatial interpolation of average observed near-surface air temperatures from over the land, oceans and sea ice regions, with a best estimate of 14 °C (57.2 °F). [44] The estimate is uncertain, but probably lies within 0.5 °C of the true value. [44]
During the Cretaceous Thermal Maximum (CTM), atmospheric carbon dioxide levels rose to over 1,000 parts per million (ppm) compared to the pre-industrial average of 280 ppm. Rising carbon dioxide resulted in a significant increase in the greenhouse effect , leading to elevated global temperatures. [ 1 ]
During the 1,900 years before the 20th century, it is likely that the next warmest period was from 950 to 1100, with peaks at different times in different regions. This has been called the Medieval Warm Period, and some evidence suggests widespread cooler conditions during a period around the 17th century known as the Little Ice Age.
The warm period was followed by a gradual decline, of about 0.1 to 0.3 °C per millennium, until about two centuries ago. However, on a sub-millennial scale, there were regional warm periods superimposed on this decline. [2] [3] [4] For other temperature fluctuations, see temperature record. For other past climate fluctuation, see paleoclimatology.
In any case, significant terrestrial ice sheets and sea-ice did not exist during the late Paleocene through early Eocene. [13] Earth surface temperatures gradually increased by about 6 °C from the late Paleocene through the early Eocene. [13] Superimposed on this long-term, gradual warming were at least three (and probably more) "hyperthermals".
The second is a shift in the tilt of Earth's axis, or obliquity. The third is the wobbling motion of Earth's axis, or precession. [1] In the Southern Hemisphere, warmer summers occur when the lower-half of Earth is tilted toward the Sun and the planet is nearest the Sun in its elliptical orbit. Cooler summers occur when Earth is farthest from ...