"Milankovitch cycles
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Milankovitch theory describes the collective effects of changes in the Earth's movements upon its climate, named after Serbian geophysicist and astronomer Milutin Milanković, who worked on it during his internment as a First World War POW. Milanković mathematically theorized that variations in eccentricity, axial tilt, and precession of the Earth's orbit determined climatic patterns on Earth through orbital forcing.
The Earth's axis completes one full cycle of precession approximately every 26,000 years. At the same time the elliptical orbit rotates more slowly. The combined effect of the two precessions leads to a 21,000-year period between the astronomical seasons and the orbit. In addition, the angle between Earth's rotational axis and the normal to the plane of its orbit (obliquity) oscillates between 22.1 and 24.5 degrees on a 41,000-year cycle. It is currently 23.44 degrees and decreasing.
Similar astronomical theories had been advanced in the 19th century by Joseph Adhemar, James Croll and others, but verification was difficult due to the absence of reliably dated evidence and doubts as to exactly which periods were important. Not until the advent of deep-ocean cores and a seminal paper by Hays, Imbrie, and Shackleton, 'Variations in the Earth's Orbit: Pacemaker of the Ice Ages', in Science (1976)[1] did the theory attain its present state. (...)"
https://en.wikipedia.org/wiki/Milankovitch_cycles



"Past and future Milankovitch cycles. VSOP allows prediction of past and future orbital parameters with great accuracy.
— ε is obliquity (axial tilt).
— e is eccentricity.
— ϖ is longitude of perihelion.
— e sin(ϖ) is the precession index, which together with obliquity, controls the seasonal cycle of insolation.
— \overline{Q}^{\mathrm{day}} is the calculated daily-averaged insolation at the top of the atmosphere, on the day of the summer solstice at 65 N latitude.
— Benthic forams and — Vostok ice core show two distinct proxies for past global sealevel and temperature, from ocean sediment and Antarctic ice respectively.
The vertical gray line shows current conditions, at 2 ky A.D."
https://en.wikipedia.org/wiki/Milankovitch_cycles