There are 6 theories surrounding the transitions between glacial and interglacial periods. None have unanimous support and the likely cause is a combination of these factors.
Continents are moved to cooler latitudes be convection currents
Compressional plate margins cause land to rise to higher altitudes.
Both factors cause CLIMATIC COOLING
Changes in ocean current circulation change the path of warm air currents
EG. The gulf stream plays a key role in warming the UK.
Movement of warm waters away from shores will reduce temperatures