100,000-year issue
Of all the orbital cycles, Milankovitch believed that obliquity had the greatest effect on climate, and that it did so by varying the summer insolation in northern high latitudes. Therefore, he deduced a 41,000-year period for ice ages.[19][20] However, subsequent research[17][21][22] has shown that ice age cycles of the Quaternary glaciation over the last million years have been at a period of 100,000 years, which matches the eccentricity cycle. Various explanations for this discrepancy have been proposed, including frequency modulation[23] or various feedbacks (from carbon dioxide, or ice sheet dynamics). Some models can reproduce the 100,000-year cycles as a result of non-linear interactions between small changes in the Earth's orbit and internal oscillations of the climate system.[24][25] In particular, the mechanism of the stochastic resonance was originally proposed in order to describe this interaction.[26][27]
Jung-Eun Lee of Brown University proposes that precession changes the amount of energy that Earth absorbs, because the southern hemisphere's greater ability to grow sea ice reflects more energy away from Earth. Moreover, Lee says, "Precession only matters when eccentricity is large. That's why we see a stronger 100,000-year pace than a 21,000-year pace."[28][29] Some others have argued that the length of the climate record is insufficient to establish a statistically significant relationship between climate and eccentricity variations.[30]
https://en.wikipedia.org/wiki/Milankovitch_cycles
No comments:
Post a Comment