There appears to still be active research about mechanisms that explain the historical data but here's a clearly written article [1] discussing a few factors su

There appears to still be active research about mechanisms that explain the historical data but here's a clearly written article [1] discussing a few factors such as: variation in solar radiation due to variation in Earth's orbit, changing ocean currents which may lead to huge upwellings of carbon dioxide from previously sunken dead algae. [1] https://blogs.princeton.edu/research/2013/04/30/how-the-ice-ages-ended/ https://blogs.princeton.edu/research/2013/04/30/how-the-ice-...