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This is is climatic precession, and it is linked to major shifts in Earth’s climate from glacial to warm interglacial
states. An area of intense study is understanding how this happened to the Eemian period 125,000 years ago,
and how it triggered the most recent deglaciation starting about 21,000 years ago.
And this only scratches a surface of this topic. The forces changing the orbit do vary, and that’s why precession varies from 19-23,000 years. It would take sophisticated calculations beyond my abilities to describe the
exact motions, but it is not difficult to appreciate the effect and understand how the data can be used in published climate science.
Efforts to link orbit and climate have a long history. In the 1840s, Joseph Adhemar proposed that the ice-sheet
in Antarctica could be linked to the southern hemisphere winter occurring at aphelion: a “smaller” sun resulting in less sunlight which could sustain colder temperatures.
In the 1870s, James Croll offered an alternative hypothesis: Because Earth travels more slowly as it approaches
aphelion, the southern winter was longer by 8 days than the northern winter, thus the southern hemisphere
spends more time farther from the sun.
In the 1930s, Milutin Milankovitch turned the idea around by suggesting that orbital parameters creating cool
summers and warm winters at high northern latitudes may explain the rise and fall of ice sheets. This theory is
currently held by climatologists. But the solar energy changes and the timing of these changes is a small part of
the climate picture. These energy changes alone are not enough to explain the shifts in climate over the past
million years. Calculating orbita