Glacial climate is marked by abrupt, millennial-scale climate changes known as Dansgaard-Oeschger (DO) cycles that have been linked to changes in the mode of Atlantic meridional overturning circulation (AMOC). Here with aid of a fully coupled atmosphere-ocean general circulation model, I show that gradual changes in Northern hemisphere ice sheets, atmosphere CO2 and Earth’s orbit can give rise to tipping feature of glacial AMOC, providing a novel framework to understanding changes in millennial-scale climate activity across time. These results stress on that the existence of AMOC tipping point is a function of changes in climate background, which however are not well considered in our future projections by current climate models. This might lead to an underestimation of potential climate crisis we might encounter in our future and hence suggestions are provided to improve reliability of modeled future scenarios.