The Holocene Climate Optimum (HCO) was a warm period during roughly the interval 9,000 to 5,000 years BP, 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.
This warm period was followed by a gradual decline until about two millennia ago.
- 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).
- 1 Global effects
- 2 Comparison of ice cores
- 3 Milankovitch cycles
- 4 Other changes
- 5 See also
- 6 References
Global effectsTemperature variations during the Holocene from a collection of different reconstructions and their average. The most recent period is on the right, but the recent warming is only seen in the inset.
The Holocene Climate Optimum warm event consisted of increases of up to 4:°C near the North Pole (in one study, winter warming of 3 to 9:°C and summer of 2 to 6:°C in northern central Siberia). Northwestern Europe experienced warming, but there was cooling in Southern Europe. The average temperature change appears to have declined rapidly with latitude and so essentially no change in mean temperature is reported at low and middle latitudes. Tropical reefs tend to show temperature increases of less than 1:°C; the tropical ocean surface at the Great Barrier Reef about 5350 years ago was 1:°C warmer and enriched in 18O by 0.5 per mil relative to modern seawater. In terms of the global average, temperatures were probably warmer than now (depending on estimates of latitude dependence and seasonality in response patterns). While temperatures in the Northern Hemisphere were warmer than average during the summers, the Tropics and parts of the Southern Hemisphere were colder than average.
Out of 140 sites across the western Arctic, there is clear evidence for conditions warmer than now at 120 sites. At 16 sites, where quantitative estimates have been obtained, local HTM temperatures were on average 1.6±0.8:°C higher than now. Northwestern North America had peak warmth first, from 11,000 to 9,000 years ago, while the Laurentide Ice Sheet still chilled eastern Canada. Northeastern North America experienced peak warming 4,000 years later. Along the ...read more