User:JC1/twenty-sixth
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The 100,000-year problem ("100 ky problem", "100 ka problem") of the Milankovitch theory of orbital forcing(英语:orbital forcing) refers to a discrepancy between the reconstructed geologic temperature record(英语:geologic temperature record) and the reconstructed amount of incoming solar radiation, or insolation(英语:insolation) over the past 800,000 years.[1] Due to variations in the Earth's orbit, the amount of insolation varies with periods of around 21,000, 40,000, 100,000, and 400,000 years. Variations in the amount of incident solar energy drive changes in the 氣候 of the Earth, and are recognised as a key factor in the timing of initiation and termination of 冰期s.
![Thumb image](http://upload.wikimedia.org/wikipedia/commons/thumb/f/f0/Delta-O-18_in_deep_sea_sediment-svg.svg/640px-Delta-O-18_in_deep_sea_sediment-svg.svg.png)
While there is a Milankovitch cycle in the range of 100,000 years, related to Earth's 軌道離心率, its contribution to variation in insolation is much smaller than those of 進動 and 轉軸傾角. The 100,000-year-problem refers to the lack of an obvious explanation for the periodicity of 大冰期s at roughly 100,000 years for the past million years, but not before, when the dominant periodicity corresponded to 41,000 years. The unexplained transition between the two periodicity regimes is known as the Mid-Pleistocene Transition(英语:Mid-Pleistocene Transition), dated to some 800,000 years ago.
The related "400,000-year-problem" refers to the absence of a 400,000-year periodicity due to 軌道離心率 in the geological temperature record over the past 1.2 million years.[2]
The transition in periodicity from 41,000 years to 100,000 years can now be reproduced in numerical simulations that include a decreasing trend in 二氧化碳 and glacially induced removal of 表岩屑, as explained in more detail in the article Mid-Pleistocene Transition(英语:Mid-Pleistocene Transition).[3]