The alignments remain accurate to this day,k there is no need for assumptions.
We know they were built with the purpose of putting various constellations in view through small apertures at certain times of the year and the same with the solstices. We also know that after many millennia they continue to appear at the same locations today.’
Accurate thermometers have only existed for just around 300 years and have only been in wide distribution for less than a century.
Every thing prior to that is based on assumptions and “estimates” that cannot be verified.