The Earth's Apsides & Long Term Climate Change

The proposed calendar change would help fix the dates of the equinoxes and solstices better but the perihelion and aphelion of the Earth's orbit will still move about within the year. The process involved is known as apsidal precession. I've computed the rate of motion of the equinoxes within the Julian calendar and the rate of apsidal precession for the Julian, Gregorian and "Tropical" calendars. The "P"s are the periods or "days per year" and the "n"s are the rates of the mean motions.* One can use the relative difference in rates to find the period of the cycle since dividing by a rate is equivalent to multiplying by the length of its year.

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This prcession will affect the motion of the Sun within the year and consequently the length of the seasons since the Earth moves faster in its orbit near perihelion and slower near aphelion. The lengths of summer and winter are an important factor in long term climate change.

*Edit: The subscript "a" refers to the anomalistic year which is the time between one perihelion and the next. It is slightly different than the time between successive Vernal Equinoxes.

Supplemental: With apsidal precession one could "fix" the date of the Vernal Equinox but the Autumnal Equinox and the solstices would vary slightly relative to it over time due to changes in the length of the seasons. All the dates would still vary over a four year period because of the leap day.