ARTICLES The Causal Source for the Climatic Changes at 2300 BC by Moe Mandelkehr Moe Mandelkehr was born and grew up in Kansas City, and currently lives in New Jersey, USA. He has a BSc and an MSc in Electrical Engineering and an MSc in Systems Engineering and Operations Research. He is a retired Systems Engineering Manager, spending 36 years at RCA, generally in concept development engineering on advanced major military systems, mainly radar, ballistic missile defense, command/control, navigation and undersea warfare. He has written two unpublished books: the first on cultural and geophysical events occurring at 2300 BC (excerpts of this book have been published by the SIS) and the second book dedicated to the thesis that all the early mythology developed from an encounter of the Earth with a massive meteoroid stream in 2300BC. Introduction A number of years ago, I wrote three articles on cultural discontinuities, climatic changes and geological transients - all occurring at about 2300BC [1]. These were published with considerable time separation, with only a limited effort to show the relationship between the phenomena, so their impact in introducing a unified model was correspondingly limited. I now hope to rectify this situation. My premise is outlined below. The primary causal factor for the overall event was the widespread and dramatic climatic changes arising from an abrupt cooling of the Earth. This caused a significant synchronous glacial buildup in both Polar and sub-Polar regions. The increased loading on the land areas and decreased loading in ocean areas (due to water taken by the glaciers) resulted in global crustal stress, leading to earthquakes and crustal deformation. Cultures in all geographical regions were affected by these climatic and geological disturbances. In the areas of the most advanced cultures, climate deterioration brought about survival hardships. The disastrous earthquakes brought about by crustal stress caused large-scale site abandonments but the climatic effects were the dominant influence on people. This paper covers the climatic changes, the global cooling causing the climatic changes and the proposed causal source for the global cooling. A Temperature Drop at 2300BC The last major northern glaciation peaked about 18,000 years ago. Following this, the Earth went through a slow warming phase until about 6,000 years ago. This was followed by a gradual cooling trend, accompanied by a trend toward dryness, particularly in the tropical and sub-tropical zones. At 2300BC, there was an abrupt drop of 2-3-deg C in global temperature, with essentially no recovery to the present. The temperature decrease was formally reported by the Panel on Climatic Variations of the US Committee of the Global Atmospheric Research Program (GARP) (NAS, 1975), which generated information on Earth's temperature in the past. This indicated a general gradual temperature decrease before about 2000BC, a sizeable drop at the time period of interest and then continuing lower temperatures. The temperature shift is recognised in the report as the 'remarkable decrease in temperature about 4000 years ago from the warm period known as the Altithermal' [2]. In 1988, the Intergovernmental Panel on Climate Change (IPCC) (jointly established by the World Meteorological Organization (WMO) and the United Nations Environment Programme) was charged with assessing scientific information relating to climate change and formulating response strategies. The report of Working Group I in 1990 also concluded that there was an approximate 2-deg C global temperature decrease at about 4000BP [3]. Other sources also identify a 2-3-deg C temperature decrease at that time [4]. Karlstrom states, 'The new paleoclimatic data provide striking confirmation of Matthis' early conclusion (1939) that 'we are living in an epoch of renewed but moderate glaciation -- a 'little ice age' that already has lasted about 4,000 years' [5]. According to Crowley and North [6], 'the widespread 'Neoglacial' cooling between 3500 and 4500BP signals the return to the generally cooler conditions of the late Holocene'. PA and HR Delcourt [7], leading investigators of long-term forest dynamics reflecting changing climatic conditions, state that, 'On both continents (North America and Europe), temperate and boreal taxa [8] achieved their maximum interglacial limits in northern distribution, typically between 6000 yr BP and 4000 yr BP. The northern range limits of many arboreal taxa have retracted southward during the last 4000 years in response to late Holocene [9] global climatic cooling'. This temperature drop is shown clearly in temperature profiles obtained from the Greenland Ice Core Project (GRIP) borehole, at the summit of the Greenland Ice Sheet (Figure 1). The horizontal line at about -31.8-deg C is present temperature. The first figure shows the low temperatures during the glacial period, with rising temperatures starting at about 20000BP. The second figure clearly shows a 2.5-deg C temperature drop at about 4000BP to current temperature. The third figure shows fairly constant temperature following that time to the present [10]. [*!* Figure 1: Temperature History Obtained from Greenland Ice Core Project (GRIP) borehole, showing a 2.5-deg C drop at about 4000BP (after Dahl-Jensen, Mosegaard, Gundestrup, Clow, Johnsen, Hansen, Balling [10])] Three features of the temperature change at 2300BC are strikingly unusual: i. it occurred globally, rather than in limited geographical regions. ii. it was abrupt, rather than gradual and iii. the cooling was long-lasting, essentially continuing to the present. According to Overpeck (Paleoclimatology Program, US National Oceanic and Atmospheric Administration, National Geophysical Data Center), 'Over the last decade, paleoclimatic data from ice cores and sediments have shown that the climate system is capable of switching between significantly different modes ... Changes of several degrees in glacial surface air and sea temperatures over large expanses of the high northern latitudes apparently occurred multiple times within years to decades ... Most attention in the growing area of abrupt climatic change research continues to be focused on the large changes observed during glacial periods ... In contrast, the current warm interglacial climate is often characterized as relatively stable ... The weight of the paleoclimatic evidence not being collected, however, suggests that these conclusions of benign warm climate variability may to incorrect ... It is now clear that climate variability in many regions of the world, including Greenland, was significantly greater during the last 10,000 years than during the last 150 years' [11]. The Climatic Changes At 2300BC Just prior to 2300BC, the Earth was considerably different from today: the average surface temperature was several degrees higher and, consequently, a stronger Westerlies pattern existed in the northern hemisphere [12]. This shielded the northern temperate regions of North America, Europe and Asia from Polar air, so these regions were warmer than today. The climate in Europe and Asia was favourable for human habitation, benefiting the active cultural groups distributed throughout them. On the other hand, North America was warm and dry, providing a somewhat limited environment for vegetation and wild animals on which humans depend for survival; settlement was mostly in the coastal regions. The Mexican region had a moister climate, encouraging many settlements. Sub-tropical regions (20-30 deg N latitude) from north Africa through the Mediterranean to northern India and central Asia were heavily populated, enjoying high precipitation, principally from monsoons at specific times of the year. The Sahara had enough rainfall to maintain a river system with lakes. Societies had large herds of cattle and the savannah grasslands provided a home for a wide variety of wild animals. Southern Africa, on the other hand, had a dry climate that inhibited human settlement. The Middle East at about the same latitude had sufficient rainfall for extensive agricultural activity, sustaining a growing population and advanced civilisations. Even the Negev desert in southern Palestine supported sizeable settlements. Northern India and central Asia, also in the monsoon region, had favourable climates encouraging numerous human settlements and also supporting wild animals such as elephant, water-buffalo and rhinoceros. At 2300BC, the climate went through a radical transformation, following the expected theoretical changes from a general cooling. Radical climatic shifts occurred in the continental northern hemisphere reflecting major weakening of the northern Westerlies flow from the colder environment. A weaker Westerlies flow has much greater north-south flow, so colder air was brought from northern to southern regions. A second major effect was the southwards shift of the intertropical discontinuity (ITD). (A major atmospheric flow pattern consists of air at higher altitudes flowing away from the Equator towards the Polar regions and then flowing back along the surface towards the Equatorial region. The ITD is the line near the Equator where the northern and southern surface flows (trade winds) meet.) (Figure 2) [*!* Figure 2: Typical ITD and surface wind patterns (after Bryson, Murray [13])] The movements of air masses from north and the south along the Earth's surface towards the ITD mean that the air at the ITD can escape only by rising. The rising air takes the form of numerous isolated columns or towers, each marked by extensive cloud systems, showers and thunderstorms. Consequently, the ITD is a belt of frequent rainfall, cloudiness and storms, normally referred to as the monsoon region. Because of the Earth's obliquity [14], the latitude of the ITD migrates north in the summer and south in the winter. The time when heavy rainfall occurs in a region is referred to as the 'monsoon season' [15]. An important aspect of a weakened Westerlies pattern is that the average Westerlies flow shifts further south. This creates a pressure condition that in turn shifts the ITD south. As a result, the monsoon rains do not travel as far north as before and lands which depended on the rains become arid. Naturally, southern land regions which did not previously receive monsoon precipitation can benefit from this ITD shift. Subtropical regions which had previously received heavy monsoon precipitation - north Africa, the Middle East and India - became arid, reflecting the southward shift of the ITD. The Sahara became a desert: the river system disappeared, lakes dried up and savannah areas ceased to exist. As a result the people either migrated or remained as nomads. Most of the movement was southwards, as the southern portion of Africa became wetter, allowing human settlements in many localities. Climatic conditions deteriorated in the same manner in the Middle East, probably contributing to settlement abandonment and severe depopulation. In particular, agricultural settlements in the Negev desert were largely abandoned. Similar conditions in northern India created deserts in some areas, replacing vegetation that had supported a wide variety of animal life. Oceanic flow patterns changed globally, causing climatic variations in the continental southern hemisphere - South America, southern Africa and Australia - reflecting mutual influence of the atmospheric and oceanic flows. Interestingly, a possible southward shift of the southern Westerlies starting at 2200BC has been suggested. Although no specific cause was proposed, this indicates a major change in atmospheric flow at that time [16]. The Arctic region became abruptly colder, much colder than the general 2-3-deg temperature drop. Ice shelves grew out from land areas, ice sheets formed over water and there were glacial advances in most localities. The colder temperatures influenced migrations, both into and out of the region. In North America, the modified Westerlies pattern brought cold, moist air from the Polar regions, changing the environment from warm, dry conditions to cooler, moister conditions. The improved environment for vegetation contributed to the proliferation of peoples throughout the continent. The dry air formerly in the northern part of the continent was pushed south. Mexico became largely arid, leading to sharp cultural decline. Significant shifts to both arid and moist conditions occurred in Central and South America along latitude belts. A shift in current flow off the coast of Peru markedly improved climatic conditions, resulting in flourishing cultural activity, both along the coast and in the mountains. In Europe and Asia, cold air from the Polar regions produced a general cooling, with either dryer or moister environments occurring in different regions. The increased dryness in southern Europe was ruinous to its inhabitants. The cultural disappearances and replacements and large migrations were probably influenced by this. Most of Australia became noticeably dryer. At least one culture disappeared in the central region. There is evidence of flow changes in all major oceans - Atlantic, Pacific, Indian, Arctic and Antarctic - as a reaction to the shifts in atmospheric flow and these were probably responsible for climatic variations in the southern hemisphere and to some extent the northern. An analysis by Street-Perrott and Perrott concluded that abrupt climatic fluctuations in the tropics can be influenced by changes in Atlantic Ocean circulation. They correlated onsets of droughts in sub-Saharan Africa and tropical Mexico with such changes [17]. There is evidence that the el Nino disruptions, associated with Pacific flow from the Peruvian coast, started at this time. Phase boundaries are the transition from one climatic environment to another. The global climatic discontinuities were sufficiently great to establish a number of phase boundaries in major geographical regions (Table 1). These boundaries, which agree closely in time, were established essentially independently of each other by regional investigators. All the climatic phases in Table 1 extended both before and after these transition boundaries for hundreds or, in some cases, thousands of years. Table 1 Climatic transitions at about 2300BC Region Time Period Transition Boundary Climate Change Ref. Arctic 2500-2000BC Climatic Optimum - Neoglacial Colder [18] Europe 2500-2000BC Early Sub-Boreal - Late Sub-Boreal Colder (2-3-deg C temp. drop) [19] The Americas 2340BC Altithermal - Medithermal Colder, wetter [20] Africa 2400/2200BC Neolithic Wet Phase - Neolithic Dry Phase Dryer [21] Middle East 2300BC Post-Pluvial II - Post Pluvial III Dryer [22] Japan 2400BC R II Period - R III Period Colder [23] The Effect of Climatic Change on Human Activities Climate is the most important influence on human activities. Invasions seldom drive people out of a region - at worst, they may become vassals and, over time, become assimilated. Natural catastrophes such as volcano eruptions, floods and earthquakes can cause intense suffering but people will doggedly rebuild in the same area. Climate, however, directly controls survival. When conditions are good, only a portion of the society is needed to obtain food and others can engage in constructing buildings, inventing writing, making artefacts and conducting trade - the features of civilisation. When climate worsens, people must leave the region, reorganise at a more basic level, or simply struggle along in a marginal existence. The Cause of the Earth's Cooling The general cooling at 2300BC seems to be responsible for the various climatic changes - but what initiated it? There is an excellent, though not well-known, candidate: the triggering of the Arctic region from an open-water condition to an ice-covered condition. The Arctic region contains the Arctic Ocean, surrounded by Alaska, the Canadian Arctic archipelago, Greenland, the Scandinavian countries and Siberia. The Arctic Ocean comprises the North Polar Sea (north of approximately 80-deg N latitude) and associated waters such as the Greenland, Norwegian, Barents, Kara and Laptev Seas, Baffin Bay and the waters of the Canadian Arctic archipelago. There are three types of ice configuration in the Arctic: glaciers and ice sheets covering land areas; sea ice covering water areas; and ice shelves extending out to sea from land areas. Glaciers and land ice sheets are considered stable, as they do not react to small perturbations, generally extending and receding over long periods of time. Sea ice is considered to be unstable because, under some circumstances, small perturbations can change it from one stable state to another in a short time. Ice shelves are considered to be metastable, being stable for small perturbations and unstable for large ones. Currently, the Arctic Ocean is in an ice-covered configuration, with the extent of the ice varying as a function of climatic environment. Even under stable conditions, the coverage of Arctic sea ice varies considerably. The North Polar Sea is currently covered with permanent sea ice or pack ice, so fluctuations in coverage occur at lower latitudes. At these latitudes, sea ice is no more than 3-4 metres thick, so quick variations in coverage are possible, with correspondingly rapid changes in climatic feedback effects [24]. In February, the entire Arctic Ocean is essentially covered with ice; the coverage decreases to about half in August. As the sea ice consists of many individual ice fields, it is constantly moving under the action of atmospheric and oceanic flows, causing continuous fluctuation of its boundaries. In addition to the seasonal fluctuation, its extent often varies considerably from one year to another [25]. The key to the climatic changes at 2300BC appears to be the fact that the Arctic region can exist in two stable configurations. In one, it may be essentially ice-free, with a resultant low albedo (reflectance) causing high solar energy absorption and surface temperature, maintaining ice-free conditions. In the other configuration, the region may be largely ice-covered, causing high energy reflection and a low surface temperature, maintaining ice-covered conditions. This does not mean there are only two configurations - or that triggering an ice-covered configuration automatically infers full conversion to an Ice Age. The Earth apparently can be triggered into an intermediate condition governed by existing environmental factors. Triggering into an intermediate colder configuration appears to have happened at 2300BC. Three positive feedback mechanisms tend to accelerate the configuration shift once it starts and then stabilise the new configuration once it is established: i. albedo, ii. atmospheric flow and iii. surface water flow. The albedo for an ice-free Polar Sea is 0.10, compared with 0.61 for ice-covered, so significantly more solar energy is absorbed. Another albedo factor is the 'greenhouse' effect provided by the moisture and clouds in the atmosphere overlying an ice-free sea. After being warmed by absorption of direct short-wave Solar energy, the surface reradiates infrared or long-wave radiation. Atmospheric water vapour and clouds return a large amount of this to the surface, further increasing energy absorption. When ice forms over the sea, solar short-wave energy is reflected and the disappearance of cloud cover allows more long-wave energy to escape [26]. The colder surface environment then extends the ice coverage. Increased sea ice coverage may promote greater meridional (north-south) atmospheric flow, bringing colder air south from the polar regions, further expanding the ice cover. The third mechanism is the reduction in the flow of warm surface water to the Polar region. The only source of warm surface water is the North Atlantic Ocean, since there is essentially no corridor from the Pacific. Therefore a cold North Atlantic is a necessary prerequisite for the Polar region to freeze over. This is unlikely as long as the warm water of the Gulf Stream or North Atlantic Current can circulate unhindered in the open Arctic basin [27]. Two factors can move warmer North Atlantic surface water to the Polar region: low altitude atmospheric flow and the oceanic current flow which replaces the colder, more saline water that cools and sinks to the bottom near the ice sheet periphery [28]. As the ice sheet expands, the following new conditions inhibit the northward flow of warm surface water. 1. Colder temperatures cause more meridional atmospheric flow. Cold air from the high-latitude continents (Antarctica, Siberia, Greenland, Canada) flowing over the sea takes up large amounts of heat [29]. Increased ice coverage then produces atmospheric flow that cools North Atlantic surface water. 2. Colder surface conditions move the average low pressure system southwards, reducing the wind in that region which drives warm currents north towards the ice pack. Specifically, the shift in atmospheric flow diverts the warmer, more saline Gulf Stream away from the Polar region [30]. The residual less saline water freezes at a higher temperature, enhancing ice formation. 3. As the ice sheet extends south, its perimeter shortens and the bottom settling water around the periphery is reduced, reducing the replacement surface current flow to the north [31]. The situation is summed up by Vowinckle and Orvig [32]: 'It is apparent that the polar ocean is presently in a delicate radiational balance, and relatively minor variations in any term can result in a process leading to complete freeze-over or to complete melting.' The Rapidity of Arctic Triggering The Arctic region can be quickly triggered from an ice-free to an ice-covered configuration: because of the above positive feedbacks, the shift can take place in as little as tens of years. There is extensive evidence that such shifts have taken place in surprisingly short times in the past. One of the best documented cases is the sudden recurrence of a near-glacial climate in Europe at the beginning of the Younger Dryas epoch, in the transition between Late Glacial and Holocene, about 10,800 years ago. Determinations of summer temperature changes of 10-12-deg C in less than 100 years seem to be reliable [33]. Several hundred years later, at the end of the Younger Dryas and the beginning of the Pre-Boreal epoch, the transition was just as sudden. Detailed heavy-isotope and dust-concentration profiles in two Greenland ice cores suggest that, in less than 20 years, the climate in the North Atlantic region became milder and less stormy, as a consequence of a rapid retreat of the sea ice cover. South Greenland warmed by 7-deg C in about 50 years [34]. Other events at 70,000BP and 55,000BP have been identified where coolings of about 5-deg C/century occurred [35]. The most dramatic short-lived cooling event, the 'Greenland Blitz', was observed in the Greenland ice about 89,000 years ago, when the climate changed within 100 years from warmer than today to full glacial severity. The records indicate that it took 1000 years to recover from this [36]. For the last glaciation, 40-30,000 years ago, several investigators have demonstrated that a group of abrupt temperature changes which occurred over a period of 1-3,000 years each took about 100 years. The temperature level was essentially steady between these [37]. According to the climatologist Budyko [38], 'Systematic calculations show that small positive air temperature anomalies in summer would cause the Arctic pack ice to disappear in a few years, after which the Arctic Ocean would remain ice-free, resulting in important changes in climatic conditions for the Northern Hemisphere. In turn, an ice cover could be re-established on an ice-free Arctic Ocean by anomalies of air temperature arising from various causes. Thus the present Arctic ice cover is in rather delicate balance with the prevailing climate-forming factors, and could possibly be destroyed by artificial means.' Flohn states [39] 'From the viewpoint of a climatologist, the most important result of these investigations is the fact, that within the 'human' time scale of about 100yr or less, our climate is (or can be in some periods) much more variable than hitherto assumed. Especially important, and indeed disquieting, is the evidence of abrupt coolings within warm (interglacial) periods, apparently as rare events with a recurrence time on the order of 10,000 years. Apparently, their intensity can surpass (with up to 5-deg C per 50 years) all climatic changes during the Holocene.' Based on the results of the joint European Greenland Ice-core Project (GRIP), Dansgaard, Clausen and Hammer say [40] 'Recent results from two ice cores drilled in central Greenland have revealed large, abrupt climate changes of at least regional extent during the late stages of the last glaciation, suggesting that climate in the North Atlantic region is able to reorganize itself rapidly, perhaps even within a few decades....We find that climate instability was not confined to the last glaciation, but appears also to have been marked during the last interglacial'. Even though the shifts from one sea ice configuration to another have been described as abrupt, the transition time still appears to be tens of years or longer. I feel that this is compatible with the reported climatic changes at 2300BC. Furthermore, the full transition may not have been completed before its effects were felt in other areas. Arctic Triggering and Global Climate The cooling of the Arctic had a major effect on the Earth's climate. Recent theoretical studies have shown that the effects of anomalous conditions in one region may be propagated to distant regions by atmospheric dynamics, referred to as teleconnections. It has already been demonstrated that the El Nino events, brought about by Pacific oceanic flow changes, are not limited to the Pacific area but may trigger serious climatic anomalies in many areas of the globe almost simultaneously. The same applies to Polar climatic events. A graphic example is a recent snow and ice coverage increase in the Northern Hemisphere. This is reported to have increased by about 12% since 1971. The Bulletin of the World Meteorological Organization lists scores of record-breaking weather extremes observed during 1972 in both hemispheres, linked to the change in snow and ice coverage [41]: 'The general circulation of the atmosphere in 1972, over both the northern and southern hemisphere, differed considerably from the fairly consistent pattern that had prevailed each year from 1968-1971....The general circulation pattern caused the mean temperature distribution, particularly during the winter, to be considerably below normal all over the North American continent and large parts of the mid-Atlantic, as well as over the Mediterranean. Over the Baffin Island area the annual mean temperature was 4-deg C below normal. On the other hand, a large area of annual mean temperatures above normal...was found over the European part of the Arctic Ocean, over most of eastern and northern Europe and over western and central Asia. Large parts of these areas were also characterized by long periods of below normal precipitation or droughts having detrimental effects on agricultural production. Dry weather also persisted for most of the year in western and central Europe. Above normal amounts of precipitation were, however, found in East Asia and along the Pacific coast of North America. The Mediterranean countries and the Near East also received precipitation amounts much above normal. In the southern hemisphere, Australia in particular experienced serious rainfall deficiencies for the year.' Another recent report describes a 25-year study of sea ice observations using satellite imagery, correlated with weather maps, with the objective of determining interrelations between the Arctic sea ice and the general circulation of the atmosphere. Variations in sea ice coverage definitely change the circulation, including meridional flow. There is general agreement that changing the Arctic sea ice would change climatic conditions far from the Arctic region [42]. Specific Conditions at 2300BC Favouring Sea Ice Triggering The next step is to review conditions and mechanisms that could have abruptly shifted the Arctic region to a colder regime specifically at about 2300BC: 1. 1. lower Solar energy level at the time due to the Milankovitch effect would make the region vulnerable to triggering and 2. 2. a trigger comprising dust and/or aerosols over the Arctic region The Milankovitch effect is regarded by most scientists as the overall guiding influence on long term climatic variations. It deals with varying Solar radiation influx on the northern and southern hemispheres due to small cyclical Earth orbital changes: eccentricity, precession and obliquity. The amplitude and time variation of each of these is shown in Figure 3 [43]. [*!* Figure 3: Earth Orbital Variations Applying to the Milankovitch Model] With zero eccentricity, the Earth's orbit is circular and Solar heating is essentially constant throughout the year. With an eccentricity of 0-0.06, the orbit is slightly elliptical and the Earth is closer to the sun at some times of the year than others. Because of the Earth's tilt relative to the ecliptic, this parameter variation increases the seasonal contrast of the northern and southern hemispheres. For example, the Earth may be at perihelion (closest to the sun) at the summer solstice for the southern hemisphere, producing a relatively hot summer. Six months later, it may be at aphelion (furthest from the sun) at the summer solstice for the northern hemisphere, resulting in a cooler summer. Precession is a 'wobble' of the Earth about its rotational axis. This shifts the seasonal equinox and solstice points relative to the previously discussed ellipse, with a period of about 25,800 years. The effect of this parameter variation is to establish which hemisphere, northern or southern, experiences more or less seasonal intensity at various periods of the year at times of orbital eccentricity. The Earth's obliquity is its tilt relative to the ecliptic (plane of orbit), which varies between 22.1-deg -24.5-deg with a 41,000 year average period. Increased tilt results in increased seasonal contrasts in both the northern and southern hemispheres. These three parameters cumulatively determine surface temperatures for both winter and summer in the northern and southern hemispheres at any given time. Theoretically, an unfavourable orbital configuration can produce a solar energy level that will increase ice and snow coverage sufficiently to precipitate an Ice Age. Although some controversy exists, many investigators have produced evidence that times of past maximum ice and snow buildup predicted by the Milankovitch model correlate closely with times of major glaciation and ice ages. Simulation programs appear to substantiate the model. The Milankovitch effect primarily operates through the melting and refreezing ice cover of the Arctic Ocean [44]. Rather than a gradual change with varying solar energy, the Arctic region is triggered in and out of ice and snow coverage configurations abruptly, as described earlier. Furthermore, when Solar energy level conditions are intermediate between extremes, small changes in the climatic or oceanic environment might still trigger intermediate configuration shifts. In the preceding section, a group of abrupt temperature changes during the last glaciation was described. The sudden global climatic changes at about 2300BC could have been the result of the same type of Arctic configuration shift. The next step is to show that environmental conditions and solar energy levels based on the Milankovitch model were conducive to an abrupt change to a colder regime at about 2300BC. The previous Ice Age culminated about 15-19,000 years ago at a time of very unfavourable solar energy conditions [45]. The Arctic was largely ice-covered. The climatic warming starting about 14,000 years ago pushed back the margins of the Arctic ice sheet. This eliminated the ice shelves, leading to collapse of marine ice sheets. The stable terrestrial ice sheets retreated. The Laurentide ice sheet disappeared by 6500BP, leaving separate residual terrestrial ice sheets. During this period, sea ice in the Canadian Arctic archipelago disappeared, including the northern coast of Greenland and Ellesmere Island, with similar action in the European and Siberian Arctic. The Arctic ice sheet was largely removed, with terrestrial fringes left to shrink by melting. By 6,000 years ago, only an ice cap remained over Baffin Island [46]. This period is referred as the Climatic Optimum, until about 4,000 years ago, when the mean temperature of the Arctic was many degrees higher than now [47]. However near the end of the Climatic Optimum two conditions existed that provided an environment conducive to triggering an Arctic sea ice configuration. Firstly, a number of factors had inhibited warmer water from moving into the region, making the Arctic Ocean cooler and more liable to freeze. There is evidence that the ocean was actually 1.5-2-deg C colder than now [48]. Secondly, summers in the northern hemisphere had become much cooler. The Milankovitch model is complex, involving many climatological factors. However, the principal factor is cooler summers in the northern hemisphere which reduce the melting of snow and ice and allow build up. Warmer winters assist this, by allowing more precipitation and resultant snow and ice. There are other factors allowing snow and ice buildup in the Antarctic region but cooler northern summers appear to be the most important [49]. Dust and/or aerosols over the Arctic region The influence of volcanic aerosols and dust particles on solar radiation shielding and consequent climatic change has been intensively studied. The conclusion is that they can produce a temporary cooling effect but not a long-lived global effect. There is, however, a possibility that an intensified occlusion effect in the Polar Arctic region might contribute to the triggering of sea ice coverage. There are two factors unique to the Arctic region. Firstly, solar radiation passes through more of the atmosphere, making aerosols and dust particles in the atmosphere more effective in reducing solar radiation. This increases the temperature drop after a volcanic eruption [50]. Secondly, the residence time of dust particles and aerosols in the stratosphere depends on latitude. Jet stream processes appear to be the principal mechanism for removing particles from the stratosphere and these are rare and inefficient north of about 75-deg N. Impressed by repeated visual observations of a strong dust layer well above the tropopause in the interior Arctic (notably after eruptions of the Agung and Fuego volcanoes), Flohn has proposed a longer residence time in the polar stratosphere (perhaps by a factor of 3) compared to the global average. He states [51]: 'A near coincidence of major eruptions....can thus produce a prolonged and intensified stratospheric dust layer above the polar cap, with significant consequences for thickness and extension of the Arctic ice and for a cooling of the polar vortex during summer.' Budyko states that a 'comparatively short negative anomaly of air temperature' - as low as a few degrees, operating over as short a period as a year - can precipitate the change to the ice-covered configuration [52]. There is a supportive example from the Pleistocene period. An instantaneous glaciation model for the formation of the large Pleistocene ice sheets has been proposed by Bray [53], based on the sudden buildup of permanent snow cover over sub-Arctic upland plateaus including Baffin Island, Ungava, Labrador and Keewatin, Melville Peninsula and the Finnmark Plateau and upland Sweden. The crucial event in this is the survival of snow over a large area for a single summer, which results in a series of feedback reactions leading to the establishment of permanent snowfields and, subsequently, icefields. Bray suggests this could arise from one or several closely-spaced massive volcanic eruptions. An important factor is increased precipitation (many of the coldest and wettest summers in Europe, North America and Japan have followed volcanic eruptions), resulting from increased stratospheric dust of micron and sub-micron size which could descend into the troposphere and serve as freezing nuclei. Thus short-term shielding of the Arctic region by dust particles and aerosols might have encouraged sea ice triggering in the Arctic region. The Producer of the Dust/Aerosols So what started the chain - the triggering of the Arctic into an ice-covered configuration, the resultant worldwide climatic changes, the synchronous glacial buildups, the initiation of global crustal stress, the resultant crustal movements and devastating site destructions from earthquakes and dramatic cultural movements and discontinuities? There are two sources of dust - a meteoroid fall and a volcanic eruption. There is various evidence of eruptions around 2500-2000BC. However, there is the question of whether an eruption was the cause of the Arctic triggering, or if the eruption or eruptions were caused by crustal stress arising from the glacial buildup following the Arctic triggering by something else. A recent paper by Baillie and Munro [54] appears to support a possible major event about 2340BC, based on dendrochronological (tree-ring) measurements. They attempted to obtain a precise dating of volcanic events by their effect on climate, which affects tree growth (i.e. narrowness of tree rings). They found that a number of major volcanic events coincided with established dates from other sources. An intriguing by-product of their investigations was the identification of a 'consistent index peak' at 2345BC, indicating a possible volcanic event. This could also indicate a meteoroid event. I strongly favour a meteoroid event as the cause of the triggering of the Arctic. I support the work of Clube and Napier on the appearance of a giant comet in the Solar System tens of thousands of years ago, with Comet Encke and the Taurid meteoroid stream being its progeny. Voluminous evidence exists on the appearance of religions, mythologies and specific deities at 2300BC graphically associated with an encounter of the Earth with a densely packed meteoroid stream. Commemorations of the event almost always include the appearance of the Taurid stream from the direction of the Pleiades constellation and the association of the event with death [55]. A strong argument could be made for a meteoroid stream encounter. Notes and References 1. Moe Mandelkehr, 'An Integrated Model for an Earthwide Event at 2300BC - Part I, The Archaeological Evidence', SISR V:3 (1980/81), pp. 77-95; 'Part II, Climatology', C&CR Vol. IX (1987), pp. 34-44; 'Part III, the Geological Evidence', C&CR Vol. X (1988), pp. 11-22. 2. WW Kellogg, 'Global Influences of Mankind on the Climate', in J. Gribbin (ed), Climatic Change, Cambridge Univ. Press, 1978, pp. 207,208. 3. CK Folland, TR Karl, K Ya Vinnikov, 'Observed Climate Variations and Change', in JT Houghton, GJ Jenkins, JJ Ephraums (eds), Climate Change. The IPCC Assessment, Cambridge Univ. Press, 1990, p. 202. 4. HH Lamb, RPW Lewis, A Woodroffe, 'Atmospheric Circulation and the Main Climatic Variables Between 8000 and 0 BC: Meteorological Evidence', in JS Sawyer (ed), Royal Meteorological Society: World Climate from 8000 to 0 BC, Proceedings of the International Symposium held at Imperial College, London, 18 and 19 April, 1966, p. 203; see also HH Lamb, 'Climate, Vegetation and Forest Limits in Early Civilized Times', Philosophical Transactions of the Royal Society of London, Vol. 276A (1974), p. 218; HH Lamb, Climate, History and the Modern World, Methuen, 1982, pp. 121, 131; FA Street, AT Grove, 'Global Maps of Lake-Level Fluctuations Since 30,000 Yr BP', Quaternary Research Vol. 12 (1979), p. 103; and RW Fairbridge, The Encyclopedia of Geomorphology, Reinhold, 1968, p. 533. 5. TNV Karlstrom, 'Quaternary Glacial Record of the North Pacific Region and World-Wide Climatic Changes', in DI Blumenstock (ed), Pleistocene and Post-Pleistocene Climatic Variations in the Pacific Area, Tenth Pacific Science Congress, Honolulu, Hawaii, 1961, Bishop Museum Press, p. 166. 6. TJ Crowley, GR North, Paleoclimatology, Oxford Univ. Press, 1991, p. 92. 7. PA Delcourt, HR Delcourt, Long-Term Forest Dynamics of the Temperate Zone, Springer-Verlag, 1987, p. 398. 8. 'Taxa' refers to the particular types of vegetation studied. 9. The Holocene Period covers the last 10,000 years. 10. D Dahl-Jensen, K Mosegaard, N Gundestrup, GD Clow, SJ Johnsen, AW Hansen, N Balling, 'Past Temperatures Directly from the Greenland Ice Sheet', Science, Vol. 282 (1998), p. 270. 11. JT Overpeck, 'Warm Climate Surprises', Science Vol. 271 (1996), p. 1820. 12. A strong Westerlies pattern is a west-to-east atmospheric flow with relatively little north-south (meridional) flow. 13. RA Bryson, TJ Murray, Climates of Hunger, Univ. Wisconsin Press, 1977, p. 102 14. The Earth's obliquity is the angle between the Equator and the ecliptic plane (the plane in which the Earth moves around the Sun) - approx. 23.5 degrees at present. 15. The principal significance of the monsoon is its periodicity. It comes from an Arabic word meaning 'season'. Regions near the equator, such as India, Brazil, Mexico and southeast Asia, currently receive heavy seasonal rainfall (due to the ITD movement), referred to as monsoons. 16. H Veit, 'Southern Westerlies During the Holocene Deduced from Geomorphological and Pedological Studies in the Norte Chico, Northern Chile (27-33-deg S)', Palaeogeology, Palaeoclimatology, Palaeoecology, Vol. 123 (1996), p. 117. 17. FA Street-Perrott, RA Perrott, 'Abrupt Climate Fluctuations in the Tropics: The Influence of Atlantic Ocean Circulation', Nature, Vol 343 (1990), pp. 607-612. 18. W Dansgaard, SJ Johnsen, J Moller, 'One Thousand Centuries of Climatic Record from Camp Century on the Greenland Ice Sheet', Science Vol. 166 (1969), pp. 377-379; see also TG Stewart, J England, 'Holocene Sea-Ice Variations and Paleoenvironmental Change, Northernmost Ellesmere island, N.W.T. Canada', Arctic and Alpine Research Vol. 15 (1983), pp. 2, 12, 13; JT Andrews, 'The Wisconsin Laurentide Ice Sheet: Dispersal Centers, Problems of Rates of Retreat, and Climatic Implications', Arctic and Alpine Research Vol. 5 (1973), p. 187; DA Meese, AJ Gow, P Grootes, PA Mayewski, M Ram, M Stuiver, KC Taylor, ED Waddington, G A. Zielinski, 'The Accumulation Record from the GISP2 Core as an Indicator of Climate Change Throughout the Holocene', Science Vol. 266 (1994), pp. 1680-1682; D Dahl-Jensen, SJ Johnsen, 'Palaeotemperatures Still Exist in the Greenland Ice Sheet', Nature, Vol. 320 (1986), p. 252. 19. E Bonatti, 'North Mediterranean Climate During the Last Wurm Glaciation', Nature, Vol. 209 (1966), p. 985; see also CEP Brooks, 'Geological and Historical Aspects of Climatic Change', in TF Malone (ed), Compendium of Meteorology, American Meteorological Society, 1951, p. 1007. 20. PA Delcourt, HR Delcourt, Long-Term Forest Dynamics of the Temperate Zone, Springer-Verlag, 1987, pp. 264, 281; see also E. Antevs, 'The Great Basin, with Emphasis on Glacial and Post Glacial Times, III. Climatic Change and Pre-White Man', University of Utah Bulletin Vol. 38, No. 20 (1948), pp. 7-9. 21. B Bell, 'The Dark Ages in Ancient History, 1. The First Dark Age in Egypt', American Journal of Archaeology, Vol. 75 (1981), p. 5. 22. KW Butzer, 'Late Glacial and Postglacial Climatic Variation in the Near East', Erdkunde Vol. 11 (1957), p. 29. 23. R Pearson, 'Paleoenvironment and Human Settlement in Japan and Korea', Science, Vol. 197 (1977), pp. 1239, 1240, 1245; N Fuji, 'Climatic Changes of Postglacial Age in Japan', Quaternary Research (Tokyo) Vol. 5 (1966), p. 149; M Miyoshi, N Yano, 'Late Pleistocene and Holocene Vegetational History of the Ohnuma Moor in the Chugoku Mountains, Western Japan', Review of Palaeobotany and Palynology, Vol. 46 (1986), p. 374. 24. RG Johnson, BT McClure, 'A Model for Northern Hemisphere Continental Ice Sheet Variation', Quaternary Research, Vol. 6 (1976), p. 333; WF Ruddiman, A McIntyre, V Niebler-Hunt, JT Durazzi, 'Oceanic Evidence for the Mechanism of Rapid Northern Hemisphere Glaciation', Quaternary Research, Vol. 13 (1980), p. 33; WL Donn, DM Shaw, 'The Maintenance of an Ice-Free Arctic Ocean', Progress in Oceanography, Vol. 4 (1967), p. 105. 25. G Wendler, Y Nagashima, 'Inter-relations Between the Arctic Sea Ice and the General Circulation of the Atmosphere', Journal of Glaciology, Vol. 33 (1987), p. 173. 26. Donn, Shaw, op cit [24], p. 107. 27. RH Fillon, DF Williams, 'Glacial Evolution of the Plio-Pleistocene: Role of Continental and Arctic Ocean Ice Sheets', Palaegeography, Palaeoclimatology, Palaeoecology, Vol. 42 (1983), pp. 18,29; PA Mandich, 'Comment on Some Ice Age Theories', Qartar, Vol. 20 (1969), p. 335. 28. Johnson, McClure, op cit [24], p. 335. 29. J Oerlemans, CJ Van dier Veen, Ice Sheets and Climate, Reidel, 1984, p. 33. 30. Johnson, McClure, op cit [24], p. 335. 31. Ibid, p. 335. 32. E Vowinckle, S Orvig, 'Possible Changes in the Radiation Budget over the Polar Ocean', in JO Fletcher (ed), Proceedings of the Symposium on the Arctic Heat Budget and Atmospheric Circulation, Rand Memorandum MR-5233-NSF, 1966, p. 300. 33. 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Newell, RE, 'Changes in the Poleward Energy Flux by the Atmosphere and Ocean as a Possible Cause for Ice Ages', Quaternary Research, Vol. 4 (1974), p. 123; Brooks, op cit [47], pp. 370,371. 49. Kukla, op cit [38], p. 602; RG Johnson, BT McClure, 'A Model for Northern Hemisphere Continental Ice Sheet Variation', Quaternary Research, Vol. 6 (1976), pp. 333, 334. 50. MI Budyko, 'Climatic Change', Soviet Geography, Vol. 10 (1969), p. 437. 51. Flohn, op cit [39], pp. 141, 142. 52. Budyko, op cit [38], pp. 18, 19. 53. JR Bray, 'Volcanic Triggering of Glaciation', Nature, Vol. 260 (1976), pp. 414, 415. 54. MGL Baillie, MAR Munro, 'Irish Tree Rings, Santorini and Volcanic Dust Veils', Nature, Vol. 332 (1988), pp. 344-346 55. I have written a book on global mythologies and commemorations arising from an encounter of the Earth with the Taurid meteoroid stream (looking for a publisher).