Holocene climatic optimum

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The Holocene Climate Optimum (HCO) was a warm period in the first half of the Holocene epoch, that occurred in the interval roughly 9,500 to 5,500 years BP,^[1] with a thermal maximum around 8000 years BP. It has also been known by many other names, such as Altithermal, Climatic Optimum, Holocene Megathermal, Holocene Optimum, Holocene Thermal Maximum, Hypsithermal, and Mid-Holocene Warm Period.

The warm period was followed by a gradual decline, of about 0.1 to 0.3 °C per millennium, until about two centuries ago. However, on a sub-millennial scale, there were regional warm periods superimposed on this decline.^[2][3][4]

• For other temperature fluctuations, see temperature record.
• For other past climate fluctuation, see paleoclimatology.
• For the pollen zone and Blytt–Sernander period, associated with the climate optimum, see Atlantic (period).