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Glacier growth was caused by orbital-driven insolation changes.
Although variability in local conditions caused the Neoglacial to start at different times in different glaciological areas, it is generally agreed that it started between 6000-5000 years BP in both hemispheres.
It has become a lot more difficult to identify these changes because their signal is much lower and more difficult to separate from the noise of small high frequency climatic variability.
This has created much confusion about the nature and causes of Holocene abrupt climatic changes and has given many the false impression that the Holocene is characterized by long periods of climate stability. The Holocene is a period of almost constant climate change with climatic stability being the exception. Nature of climatic oscillations during the Ice Age.
Roger Bray identified cooling episodes at 0.3, 2.8, 5.5, 8.2 and 10.2 kyr BP over 45 years ago (figure 46). The Bray cycle delimits five periods that roughly correspond to the Blytt-Sernander sequence.
These episodes give us an average spacing of ~ 2400 years and, at the same time, they define the major climatic states of the Holocene. Northern Hemisphere paleoclimate records showing main Holocene abrupt climate change events. (B) Western Mediterranean (Iberian Margin) core MD95-2043, sea surface temperature (SST) C37 alkenones. (D) North Atlantic Bond series of drift-ice stacked petrologic tracers. Vegetation changes suggest that they constitute distinctive climatic states established by insolation conditions from the obliquity and precession cycles (figure 47).
Glaciers fluctuated with major glacier advances followed by shorter glacier retreats, culminating in the Little Ice Age when globally glaciers reached their maximum Holocene extent (figure 43). Number of areas that display glacier advances for every century during the Holocene.
For a geographical representation of the glaciers included in each area see Solomina et al., 2015, figure 1.
(E) Romania (Steregoiu), mean annual temperature of the coldest month. Every abrupt cooling from the Bray cycle would constitute a tipping point in the gradual insolation changes and the world would settle to a different climatic state after recovering.