Hypsithermal

The Hypsithermal followed the cool climate of earliest Holocene time (pollen zone IV=Preboreal) and preceded an interval of cool late Holocene climate (pollen zone IX=Subatlantic).

From: 

Encyclopedia of Quaternary Science, 2007

https://www.sciencedirect.com/topics/earth-and-planetary-sciences/hypsithermal