Although the end of an interglacial period is a slow process requiring the sequential reversal of these conditions, the onset of an interglacial period can be relatively fast. (eos.org)
However, there is plenty of geologic evidence to suggest that our climate is currently nearly as warm as it can get being at or near the end of an interglacial period and that the climate can naturally get warmer than it currently is without harming any ecosystems. (delingpoleworld.com)
(We are at the end of an interglacial period the planet has cooled roughly 2C from the warmest period during this interglacial period. (wattsupwiththat.com)