From Glossary of Meteorology
The period from about 7000 to 500 B.C., proposed by E. S. Deevey and R. F. Flint (1957), during which global climate was thought to be warmer than today.
Spanning the Boreal through SubBoreal periods of the Blytt–Sernander sequence of inferred climates in northern Europe, it includes both wet and dry periods. It is followed by the general expansion of glaciers known as the Neoglacial.
Deevey, E. S., and R. F. Flint 1957. Postglacial hypsithermal interval. Science. 125. 183–184.
Sernander, R. 1908. On the evidence of postglacial changes of climate furnished by the peat-mosses of northern Europe. Geol. Fören. Förh.. 30. 456–478.