Holocene climate variability and change; a data-based review

The Holocene Thermal Maximum with peak temperatures prior to 7 ka BP is mostly accentuated in the Northern Hemisphere, still visible in the Southern Hemisphere and possibly did not exist in the tropics. Between this period and the modern warming a remarkable negative temperature trend occurred in the Northern Hemisphere, which was probably the effect of a decreasing orbital-induced insolation during the boreal summer. On average the Northern Hemisphere humidity-precipitation records do not show any significant trend. A mechanistic explanation for the multi-decadal- to century-scale Holocene cold relapses, which mainly occurred in the Atlantic-European regions, exists for only the early Holocene cooling events, which are probably the result of a collapse of the meridional overturning circulation owing to freshwater outbursts from the Laurentide ice sheet. Possibly, the late Holocene cold events after c. 4 ka BP are influenced by the covarying influence of major tropical volcanic eruptions and Grand Solar Minima.