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Scandinavian palynologists established the Blytt-Sernander sequence which divided the Holocene into five periods. An example of the Blytt-Sernander climatic zones established with the traditional pollen indicators, with the distinct elm-fall at the Atlantic/Sub-Boreal transition, and the rise of beech at the Sub-Boreal/Sub-Atlantic transition. Insolation changes due to precession are represented in figure 34 with three month insolation curves for a North and South latitude, relative to present values.They used the terms Boreal for drier, and Atlantic for wetter (figure 33). These changes increase or decrease seasonality or the difference between summer and winter.A comparison between temperatures and obliquity over the past 800,000 years shows that while variable, the thermal inertia of the planet delays the temperature response to obliquity changes by an average of 6,500 years (figure 35). Grey curve changes in obliquity of the planetary axis in degrees. This general pattern of Holocene temperatures was already known by the late 1950’s from a variety of proxy records from different disciplines (Lamb, 1977; figure 36 A). Green curve, simulated global temperatures from an ensemble of three models (CCSM3, FAMOUS, and LOVECLIM) from Liu et al., 2014, show the inability of general climate models to replicate the Holocene general temperature downward trend. The mean temperatures of an ensemble of three models (CCSM3, FAMOUS, and LOVECLIM; Liu et al., 2014; figure 38) show a constant increase in temperatures during the entire Holocene, driven by the increase in GHG.The drop of obliquity always terminates interglacials. Greenland ice cores confirmed this pattern, when corrected for uplift (Vinther et al., 2009), and greatly improved the dating of temperature changes (figure 36 B). This disagreement between models and data-derived reconstructions of Holocene climate has been termed by the authors the Holocene temperature conundrum (Liu et al., 2014).Therefore they are responsible for the African Humid Period, monsoon patterns and the important Mid-Holocene Transition (MHT), that changed the climate mode of the Holocene globally. Insolation changes due to orbital variations of the Earth. But unlike precession changes, obliquity alters the amount of annual insolation at different latitudes in a 41,000 year cycle.The insolation changes for the last 40,000 years are represented. This is represented by the background color of figure 34, that shows how the polar regions received increasing insolation from 30,000 yr BP to 9,500 yr BP. The transition from Sub-Boreal to Sub-Atlantic took place at the end of the Bronze Age.So, Northern Hemisphere seasonality was minimal at the Last Glacial Maximum, and maximal at the start of the Holocene, 10,500 yr BP, and will become minimal again in a thousand years.

These changes are driven by variations in the obliquity of the Earth’s axis. At the time other scientists believed in a more gradual climatic change, but recent studies on the 2.8 kyr abrupt cooling event (Kobashi et al., 2013) agree with Sernander.Changes in seasonality insolation caused by the precession cycle (modified by eccentricity) are asymmetric and less important for the global response, although they cause profound changes in regional climatic differences. In the Holocene, the precession cycle and the obliquity cycle are almost aligned so that maximal obliquity and maximal northern summer insolation are almost coincident at the beginning of the interglacial about 10,000 years ago. Available data indicates that despite significant changes in GHG concentration in the atmosphere during the period of 10,000 to 600 yr BP, their contribution to temperature changes cannot have been important. (2004), CO concentrations measured in Antarctic ice cores decreased from 267 to 258 ppm between 10,000 and 6,800 yr BP, and afterwards increased more or less linearly to 283 ppm by 600 yr BP, just prior to the LIA (figure 38).The Holocene Climatic Optimum corresponds to high insolation surplus in polar latitudes (red area), while Neoglacial conditions represent the first 5,000 years of a 10,000 year drop into a high glacial insolation deficit in polar latitudes (blue area). See in figure 34 how the thick red curve representing northern summer insolation reaches maximal values 10 kyr BP, almost coinciding with the center of the background polar red color, representing highest warming from maximal obliquity about 9.5 kyr BP. 19,000 years ago obliquity was the same as it is now (only increasing), and the precession cycle was at the same position as it is now (same 65 °N summer insolation; figure 34). This increase of 25 ppm represents about 10% of a doubling.Precession changes do not alter the annual amount of insolation at any latitude, since whatever insolation they take from one month at a particular location, they give back in another month within the same year.Precession changes are also asymmetrical, as their effect is opposite in each hemisphere, so the Northern Hemisphere summer (June-August, N-JJA thick red line in figure 34) has become progressively cooler during most of the Holocene, while Southern Hemisphere summer (December-February, S-DJF thick blue line in figure 34) has become progressively warmer during most of the Holocene. Changes due to obliquity have the effect of redistributing insolation between different latitudes following an obliquity cycle of 41,000 years.

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