An Integrated Model for an Earthwide Event at 2300 BC. Part II: The Climatological Evidence M. M. MANDELKEHR M. M. Mandelkehr holds a B.Sc. and M.Sc. in Electrical Engineering (University of Kansas) and an M.Sc. in Systems Engineering and Operations Research (University of Pennsylvania). Formerly working in advanced radar system design, he has now retired and is writing a book for publication in 1988. This article, and his previous (in SIS Review V:3), represent extended extracts of two chapters in the book. Introduction This article is the second in a series presenting evidence for a possible earthwide event at 2300 BC. The first article covering the archaeological evidence presented strong indications of site destructions widespread around the globe as well as migrations [1]. The climatological evidence in this article shows very distinct climatic changes at that time which could have been a major stimulus for the migrations. Furthermore, the climatic changes were most likely to have been brought about by a global temperature drop which has also been established at about 2300 BC. The somewhat unique nature of this temperature decrease may provide a link to the determination of the overall causal event, to be discussed in a later article. The climatic change which took place around 2300 BC is clearly discernible; it took the form of a global cooling, with substantial trends toward either increased wetness or dryness in all regions of the Earth. The change at this time was sufficiently large so that climatic phase boundaries have been established for various geographical regions, as shown in Table 1. These boundaries have been established essentially independently of each other, and are based on regional studies. Four of the six transitions are dated at, or close to, 2300 BC. In the case of the Atlantic/Sub-Boreal and Altithermal/Medithermal transitions, although the estimated dates from researchers vary from 2500 to 2000 BC, specific European and North American climatic variation dating reports cluster well around the postulated 2300 BC date for the event. In all regions of the Earth, the above climatic phases are described in the literature as extending both previous to and following these transition boundaries for at least hundreds, and in some cases, thousands of years. The designated climatic phase transitions consequently have the same high degree of importance as the cultural discontinuity boundaries discussed in my previous article. In most areas of the Earth, clear correlations have been established between the climatic changes described in this article and the cultural discontinuities in my first article. In areas which suffered climatic deterioration, such as the Middle East, India and Mexico, there were decreases in population as well as cultural regressions. In the Sahara desert and certain areas of Canada, the environment could no longer even sustain people, so that there were migrations out of the areas. On the other hand, in the regions of North America and Peru, there appears to have been cultural expansion in response to a more favourable environment. The primary technique employed for climatological dating is palynology, based on the relative affinity or tolerance of different types of vegetation to cold or heat, wetness or dryness. Although the technique has the advantage of a large sampling count, care must obviously be taken to separate effects of climate and surface/subsurface hydrological effects. Other techniques which are applied on a more limited level are marine organism population behaviour and growth, and animal migrations. Lake and river levels can be a good index of precipitation level as long as hydrological factors are relatively separated. The inaccuracies of these techniques combined with those of radiocarbon measurements would be expected to yield a larger spread in the dating of the evidence: surprisingly, the dates cluster around 2300 BC fairly closely. As a general comment, whenever a date of 2500 or 2000 BC is given by an investigator, it represents a gross estimate rounded off to 500 year increments: this writer indicates those values with a circa to remind the reader of that fact. Table 1: Climatic Transitions Around the 2300 BC Time Period Region Time Period Transition Climatic Change Reference Europe/General 2500-2000 BC Atlantic-Sub-Boreal Colder [2] Europe/General 2200 BC Early Sub-Boreal Colder (2-3°C Late Sub-Boreal temperature drop) [3] Western Hemisphere 2500-2000 BC Altithermal-Medithermal Colder, wetter [4] Africa 2340 BC Neolithic Wet Phase- Neolithic Dry Phase Drier [5] Middle East 2400 BC Post-Pluvial II-Post-Pluvial III Drier [6] Japan 2300 BC R II Period/R IIIa Period Colder [7] [*!* image: Figure: Strong Westerlies Pattern Weak Westerlies Pattern Figure 1: Strong and weak patterns of Northern Westerlies Flow (after R. A. Bryson, T. J. Murray, Climates of Hunger [University of Wisconsin Press 1977], pp.26,27)] Throughout this article there will be chronological charts showing variations in climatic conditions and resultant effects on the environment with time. Most of the charts have been reproduced from the original sources. In some cases, the charts are drawn in calendar years; in others, radiocarbon years. In all cases, I have marked the date of 2300 BC on the charts for clarity of presentation. On those charts showing the dating in radiocarbon years, the 2300 BC marker will be lined up approximately with 1800 BC or 3800 BP on that chart, reflecting the approximate 500 year correction between radiocarbon and calendar years. As in the case of the archaeological evidence presented in my earlier article, all of the radiocarbon data expressed here is given as calendar year dates, either obtained directly from the sources of information, or derived from radiocarbon dates using dendrochronologic conversion tables based on the generally accepted conventions of a 5568 year carbon-14 isotope half-life, and with AD 1950 as the zero time reference [8]. The Climatological Scenario at 2300 BC Based on the palaeoclimatological evidence that is available to us at the present time, a number of investigators have attempted to establish a climatic scenario before and after 2300 BC, describing the environmental sequence of events that may have happened at that time to create the reported set of climatic changes. There appears to be general agreement [9] on the following aspects of the climatic transition occurring around 2300 BC. 1. Although the change was not uniform over the Earth, there was a general global cooling of about 2°C to 3°C. 2. Again, although not uniform, the cumulative global environment was drier after the transition. 3. The cooler temperatures altered the northern Westerlies flow from a strong to a weak pattern with large meridional (north-south) flows, as shown in Figure 1, thereby drastically changing weather conditions over most of the Earth's surface. 4. This global environmental shift apparently was not a short term transient. Although there were significant fluctuations in both temperature and dryness following the transition, the environmental conditions existing immediately after 2300 BC essentially extended to the present time. [*!* image: Figure: Thousands of years BP. Figure 2: Southward Latitudinal Shift of the Highest Barometric Pressure (at Sea Level) in the European Region (J. Abery - after H. H. Lamb [ref.9], p.221)] The North American continent prior to about 2300 BC was in the Altithermal phase, and was relatively warm and dry. An apparent southern excursion of the Westerlies flow at this general longitudinal region brought cold, wet, maritime polar air over the northern portion of the continent, resulting in the shift to the Medithermal phase with generally cooler, moister conditions. The relatively dry air which previously had been prevalent in the north was pushed to the south, causing drier conditions in the southern half of the continent. A similar southern excursion also appears to have occurred in the European area, except in this case, the polar air originated from a land area and was therefore dry. The estimated 15 degree latitude southward shift over Europe at about 2300 BC is shown in Figure 2 [10]. All areas of Europe experienced a temperature drop. The northernmost region of Europe became drier due to the dry polar air; central Europe (with southern Sweden as the northern boundary) became wetter as the moisture carrying air circulation flow was pushed to the south; and southern Europe received the drier air that had previously belonged to central Europe, intensified by the cooler conditions [11]. The most dramatic climatic change was produced by a shift of the northern Westerlies to a more southern latitude because of the developing weak flow pattern. This in turn created a pressure system that shifted the inter-tropical discontinuity to the south, thus depriving areas such as north Africa, the Middle East, India and Arabia of the warm, moist, southern trade winds. These areas immediately became arid [12]. Equatorial regions of South America also became dry at this time, presumably due to the same cause. The shift of the inter-tropical discontinuity to the south may have also shifted the convergence of the two coastal ocean currents along the western South American coast, and consequently may have been responsible for the increased wetness of the climate of Peru, starting at about 2300 BC [13]. The evidence indicates that Australia became drier at this time, whereas southern Africa became moister. It is generally accepted that the changes were likely to have been caused by southern ocean current shifts. I fully expect that the average reader is not impressed by the 2-3°C temperature drop. It is highly important to emphasise that the disruption of the Westerlies flow due to the temperature change is the key to major climatic changes. A further aspect of climatic deterioration is that a lowered global temperature of 2-3°C has been found to reduce the moisture carrying capacity of the atmosphere, and consequently the precipitation, by an amount in the order of 20-30% at all latitudes [14]. This is combined with the reduced ability of thinner vegetation cover (due to poorer climatic conditions) to provide thermal convection to affect moisture-carrying air passing overhead; and the inability of dry hardened soil to retain runoff. The second two factors amplify the effect of the first factor. The effect of the combined drop in temperature and reduction in precipitation is critical to agriculture. The effects of reduced rainfall are easily understood. The effect of a temperature decrease is clearly indicated by the statement that a 0.4°C temperature decrease in Great Britain would reduce the growing season by about 5-10% [15]. Extending the temperature change to the aforementioned 2-3°C level, even without climatic anomalies due to irregular westerlies, the growing season could be reduced below that needed for plant maturation. It should be pointed out that the above values apply to temperature reductions below the current levels, not the levels that initially existed before 2300 BC; however, the point to be made is that there were very likely greatly deteriorating environmental conditions relative to their state before c.2300 BC. Last, but not least, is a self-propagating trend by which a lowered surface temperature results in less vegetation and greater snow and ice cover - which increases the Earth's albedo (or reflectance), thus resulting in lower absorption of solar energy and a further lowering of surface temperature. Several sources state that a temperature drop of only 5°C would be sufficient to start this negative feedback or 'avalanche' effect, to move the Earth into an Ice Age. This last aspect underlines the importance of an apparently trivial temperature drop of several degrees. A survey of the climatological evidence from the end of the 3rd millennium BC now follows. _________________ [*!* image: Figure 3: A Tentative Reconstruction of the Position of the Northern Limit of Continuous Forest Along the 100°W Meridian in Central Canada During the Holocene Showing a Southward Retreat at About 2300 BC (J. Abery - after J. M. Grove [ref.109], p.2)] _________________ Table 2: Evidence for Climatic Change in the Arctic Region Time Period Evidence Climatic Change Reference North-central Canada c.2000 BC Southward tree line movement Colder [16] Eastern Canada 2400 BC Marine fauna Colder [17] Central and southern Finland 2300-2100 BC Spruce increase Colder [18] Siberia 2500-2300 BC Southward tree line movement Colder [19] Labrador and Greenland 2300 BC Colder water marine organisms Colder [20] Ellesmere Island c.2500 BC Oxygen isotope analysis of ice core Colder [21] Table 3: Evidence for Climatic Change in Europe Region Time Period Evidence Climatic Change Reference Sweden 2500-2000 BC Tree line mountain retreat Colder [30] Southern Sweden 2300 BC Bog growth Wetter [31] Belgium 2340 BC Elm decrease Colder [32] Britain 2300 BC Bog growth Wetter [33] Britain 2500-2000 BC Pollen analysis Colder, 2°C temperature drop [34] Britain, Scotland 2200, 2000 BC Forest recession Colder [35] Ireland 2400-2200 BC Pine decline, bog growth Wetter [36] Shetland Islands 2250 BC Vegetation decrease Colder [37] Southeast France 2320 BC Sedimentology Colder, Drier [38] Southwest Germany 2400 BC Vegetation change Drier [39] Switzerland 2200 BC Dwellings on lake bottoms Drier [40] Italy circa 2000 BC Shift from oak to pine Drier [41] Cyprus 2400 BC Vegetation change Drier [42] The Arctic The Arctic area is important in that it represents a relatively marginal environment. Consequently, climatic changes should produce noticeable results - and there definitely is evidence of noticeable results of a climatic change at about 2300 BC, as summarised in Table 2. This table (just as the other tables in the article) contains only representative data belonging to a much larger body of independent reports. The clearest evidence for a climatic change comes from a study of the relative abundance of driftwood at northern locations at various times in the past. A radiocarbon analysis of driftwood at northernmost Ellesmere Island shows the greatest abundance of driftwood from 4000 BC to 2200 BC, with sharply reduced levels after that time. The same reduction in driftwood quantities has been found in other Queen Elizabeth Islands and in the Greenland High Arctic. The dates vary a little from 2100 BC to a rounded off 2500 BC, but the 2300 BC date is well bracketed. The most likely reason for the decline has been determined to be the formation of ice shelves which kept the driftwood from the shore; the ice shelf formation points to a temperature drop at that time [22]. The second category of evidence is peat formation, vegetation change and tree line movements to the south. Again, although a number of the dates are rounded off to 2500 BC or 2000 BC, more precise dating in some cases places the change close to the time period of interest. A graphic presentation of the tree line southward retreat in central Canada just south of the Arctic Circle is shown in Figure 3 [23]. As shown in the insert of the Figure, the tree line movement is thought to reflect a 3°C drop in temperature at about 2300 BC. Similar to the other diagrams in this article, there has been apparently no return to the temperature prior to 2300 BC. The third and fourth categories of evidence come from oxygen isotope analysis of ice cores and from marine fauna analysis in bay waters in the Arctic area. The last category of evidence relates to archaeological correlation and is much more speculative in nature. In my first article, I described the appearance of the palaeo-Eskimo Independence I culture in northeast sub-Arctic Canada at about this time [24]. It has been determined that the emigration to Peary Island occurred only because a climatic change to cold dry conditions made it possible for the muskoxen to multiply in this region [25], which provided subsidence for this culture. As an interesting comparison, another source describes the caribou hunters who occupied the Barren Grounds west of Hudson Bay at least from 5000 BC; they are reported as disappearing from this region at about 2200 BC, presumably because of the onset of cold, wet summers that adversely affected the caribou calving [26]. From data available to them, at least one team of investigators reached the same conclusion as I have. The statement is made: "There can be no question that a sudden climatic deterioration began 4500 to 4100 years ago throughout much of the Arctic." [27] A final comment for the area, which will be repeated for other areas, is, although there were some fluctuations, the altered climatic conditions at about 2300 BC remain more or less unchanged to the present day. This is reported separately for the Canadian Arctic [28] and Siberia [29]. Europe There are numerous statements in the literature concerning the appearance of generally colder conditions in Europe sometime between 2500 and 2000 BC, typified by the entries in Table 3. Because of the descent of the polar front at this time, and the consequent influence of the dry polar air, northern Europe became dry. In Central Europe, on the other hand, precipitation tended to increase due to polar depressions moving further south [11]. Southern Europe became drier at this time. The dates are largely derived from calibrated radiocarbon results, and cluster nicely around the 2300 BC date. An important point is that weather conditions at the present are essentially the same as existed immediately after the change. A representative depiction of this change is the decrease in rainfall in the Crimea shortly after 2300 BC, shown in Figure 4 [43], again with no return to previous conditions before the discontinuity. _________________ [*!* image: Figure 4: Rainfall Variations in the Crimea as Indicated by the Thickness of the Yearly Mud Layers in the Bottom Deposit of Lake Saki Showing a Precipitation Drop Shortly After 2300 BC (J. Abery - after H. H. Lamb [ref.9], p.225)] _________________ Table 4: Evidence for Climatic Change in North America Region Time Period Evidence Climatic Change Reference Southern Alaska 2300 BC Vegetation change 30% precipitation increase, 2°C temperature drop [44] Northwestern US c.2000 BC Shift from pine to spruce, fir Cooler, moister [45] Southeastern Canada, northeastern US c.2000 BC Shift from hemlock to beech Cooler, wetter [46] Central US c.2000 BC Vegetation change Cooler, wetter [47] Western US c.2500-2000 BC Vegetation change Cooler, drier [48] South central US c.2500 BC Appearance of bison Drier [49] North central Mexico c.2000 BC Shift from grassland to desert scrub Drier [50] The Americas The climatic transitions on the North American continent are well attested to by a large number of sources. In about half the cases, the transition is referred to in the more globally recognised terms as the boundary between the Atlantic and Sub-Boreal phases. Other authors use the term which is unique to North America - the boundary between the Altithermal (warm, dry) and the Medithermal (cool, moist) phases. The dating is largely reflected in Table 4, which shows collected evidence for climatic changes in specific regions of North America. Although there are small anomalies, the pattern is for the most part consistent. The meridional flow associated with the weak pattern of the Westerlies at this time apparently brought cold, moist air to Canada, Greenland and at least the northern half of the United States. There appears to be a small region on the northeast Atlantic seaboard of the United States where the climate is reported to have become warmer and drier rather than wetter; this can be rationalised on the basis of possible patterns of atmospheric circulation. It is possible that the dry air that was previously in the north was shifted to the south; the available evidence indicates that the southern half of the United States as well as Mexico became cooler and drier at this time. The drier climate in the southern part of the continent resulted in the spread of grasslands over a wide area, which provided a favourable environment for grazing animals. This is supported by an unusual study involving 160 archaeological and palaeontological sites, in which the conclusion was reached that herds of bison greatly increased around 2500 BC in the southern plains, Texas and Oklahoma [51], presumably due to the availability of the grasslands. To the south, in Guatemala (in Central America), there is evidence that some time before 2000 BC there was a change from a former warm dry climate to a rainy and cooler climate [52]. In Peru, Lanning [53] states that the aridity reached a peak about 2500 BC, with a subsequent improvement allowing the large cultural expansion described in my previous article [54]. In Colombia and Guyana, there is evidence that the open savannah (low semi-arid vegetation) changed to a savannah woodland around 2300 BC, indicating a wetter climate. This date is based on calibrated radiocarbon measurements [55]. Again, the climatic changes were long lasting. North America is considered to be in the Medithermal phase at the present time. The wetter climate starting in Colombia and Guyana is reported to have lasted for 2000 years [56]. Table 5: Evidence for Climatic Change in Africa Region Time Period Evidence Climatic Change Reference Northwest Africa c.2000 BC Lake level decrease Drier [63] West Africa c.2000 BC Dune formation, river degradation Drier [64] East central Africa 2350 BC Vegetation change Drier [65] Central Africa 2300 BC Lake Chad - maximum to low level Drier [66] South central Africa 2500-2000 BC Lake level decrease Drier [67] South Africa 2400 BC Vegetation change Wetter [68] Africa and Egypt The most dramatic climatic change was the severe aridity that commenced about 2300 BC in northern and central Africa as well as Egypt. The discontinuity has been designated as the transition between the Neolithic Wet Phase and the Neolithic Dry Phase. As I discussed earlier, this appears to be due to a southward shift of the inter-tropical discontinuity moving the monsoon precipitation southward out of the region. Surprisingly, the Sahara region prior to 2300 BC supported sufficient vegetation to allow significant human and animal populations. The following is a statement about the climate at that earlier time [57]. The Holocene period mentioned in the quotes refers to the last ten thousand years. "The climate in Egypt and north Africa before about 2300 BC has been described as rainy, or at least variable with more rain than at present, with monsoon rains falling in the central Sahara. Maximum lake development throughout most of north Africa peaked at about 8000 BC to 6000 BC. In subsaharan Africa, lake expansion was particularly spectacular, with Lake Chad expanding in area to a size comparable to the Caspian Sea today. Profound ecological changes accompanied these periods of more effective precipitation, enabling human occupancy and cultural activities to take place in Saharan Africa at a scale which is almost inconceivable today. The high lake phase continued until 4500-4000 BP (2500-2000 BC)." A number of Egyptian 5th Dynasty reliefs show wild animals in the open, on undulating desert sands studded with tree-sized sycamores and acacias as well as desert shrubs [58]. There is some indication of a gradually increasing aridity starting about 3000 BC, but this apparently was not a critical variation, since high African stream activity with correspondingly high Nile floods is described as continuing after this time [59]. After the Egyptian 5th Dynasty, the desert reliefs show a sharply deteriorated picture of existing conditions. All hunting scenes are depicted within artificial enclosures, and vegetation is no longer illustrated [60]. As I stated in my previous article, the most likely date for the end of the 5th Dynasty is 2340 BC [61]. Because of the poorer environment, there appears to have been a general exodus of the Nubian C-people from the Sahara during the 6th Dynasty, whereafter the rock paintings at the abandoned sites ceased. This movement is verified by records during the reign of Pepi II (2280-2190 BC) [62]. There is evidence of widespread aridity throughout north and central Africa at this time, as illustrated by the reports listed in Table 5. In general, in this geographical region there has been limited recovery toward the climatic situation before 2300 BC. This change in conditions could have been a contributor to the reported site abandonments and cultural deterioration throughout the region at about 2300 BC. The climatic change greatly affected Egypt, of course. Evidence indicates that the rain levels corresponding to the Neolithic Wet Phase pretty much declined to their modern low level by the beginning of the 6th Dynasty - as derived from a large body of contemporary texts. The decrease in the mean discharge of the Nile at that time has been estimated to be 29% [69]. Apparently, there was accelerated aeolian activity causing sand dunes to form on the Nile's west bank, starting around 2300 BC [70]; at this date there are good indications that sands blown from the desert covered much of the rich soil [71]. As I commented in my previous article, Egyptian literature and art depict extensive suffering and famine during this time period [72]. One author states that whereas the Nile flooding had previously been taken for granted, the economic life of Egyptian society became heavily dependent on the whims of the Nile, as of this date [73]. A short digression is in order at this point, so as to comment on two Egyptian documents that could describe the situation then. These documents are the 'Admonitions of an Egyptian Sage' and the 'Prophecy of Neferti'. I have already presented substantial evidence in my previous article that most Egyptologists date the 'Admonitions of an Egyptian Sage' (from the Leiden Papyrus) to the First Intermediate Period [74]. The 'Prophecy of Neferti' (from the Papyrus Ermitage) has been convincingly assigned to the reign of Amenemhet I of the 12th Dynasty, circa 2000 BC, but it describes conditions existing at an earlier date - either during the First Intermediate Period or immediately afterward [75]. An interesting comparison can be made between the passages in the two documents, the climatic effects described as occurring around 2300 BC, and weather conditions in Egypt at the present time. Severe dust storms called khamsins are now prevalent in Egypt during late winter and early spring [76]. The present khamsin conditions could be indicative of more severe conditions which may have first appeared during the 6th Dynasty, as the following discussion will point out. Beginning with the 'Prophecy of Neferti', a key passage is "(IV)... the land is entirely lost, without that a remainder exists, without the black of a nail remains from its dunes". I would agree with Wilson [77] in interpreting that the soil was covered by dunes. Another related passage is "(VI) The watercourses of the arable land are empty: One can cross the water on foot,... Its course has become riparian land: The riparian land will silt up the water-place until what is in the water-place will be riparian land". The term 'riparian' refers to the sides or banks of the water courses. This passage seems to refer to the disappearance of water and the silting up of the waterways due to drought, shifting sand and dust storm conditions. This was Goedicke's conclusion [78]. It is also reflected in the 'Admonitions' passage, "(3.1) Indeed, the desert is throughout the land" [79]. Another important, although somewhat controversial, passage in the 'Prophecy of Neferti' is "(VIII)... When this land will be seized and recovered, is another event not known - as what will be hidden" [80]. Although this is normally interpreted in the political sense, I feel that it could refer to the rearrangement of the landscape by Mother Nature. There is evidence of heavy winds, both in the literature and from actual archaeological findings. The inscriptions of Ankhtifi, whose writings have been dated to the beginning of the First Intermediate Period, include the following, "... at a time when the sky was (in) clouds/storm (igp) (was in a tumult?) and the land was in the wind" [81]. A predynastic cemetery was found to be denuded by wind action, which removed up to two metres of fairly resistant silt and exposed the burials, probably some time after the 6th Dynasty [82]. The amount of material that can be carried in dust storms is impressive. For example, reports state that the great dust storm of November 12-13, 1933, in the plains states of the USA deposited 25 tons of dust per square mile in the New England area, more than 2000 kilometres away [83]. One can imagine substantial terrain changes within the smaller area of Egypt. Another interesting 'Neferti' passage is "(XI) Re [the sun god] removed himself from men: He shines and the daytime exists, but one knows not that noon happened, and one is not able to calculate his shadow. The face is not clear when one looks, nor do the eyes fill with water, as he is in the sky like the moon" [84]. This can only be interpreted as a haze condition, where the Sun is sufficiently dim so that it can be looked at directly with the naked eye. This corresponds with the present day widespread dust haze conditions which may occur at any time of the year, and may persist for long time periods. Dust from the frequent squalls in the Sudan is spread by the prevailing easterly winds; so that for much of the year the whole of west and central Africa from 5 to 30 degrees north latitude (which includes Egypt) experiences a persistent dust haze [85] (and which is troublesome to aviation). The last item to be covered is the 'Admonitions' passage: "(2,10) Indeed, the river is blood, yet men drink from it" [86]. A normal aspect of the khamsin, which carries large amounts of fine dust in the air, is reddish and yellowish discolouration of the ground and water areas. (Precipitation has been called "blood rain" [87]). This could be a very natural interpretation of that 'Admonitions' passage. It is important to stress at this point that I have interpreted passages from the two documents as being related to severe environmental conditions rather than anything connected with even more unusual conditions. I don't see any strong justification for the latter association. Extreme climatic conditions causing famine are reported to have existed in Egypt until about 1950 BC [88], and lasted in Africa for a much longer time. This region has never regained the more favourable climatic conditions that existed before 2300 BC. Table 6: Evidence for Climatic Change in the Middle East Region Time Period Evidence Climatic Change Reference Palestine 2300 BC Vegetation change Drier [90] Palestine 2300 BC Deposition of evaporites in Dead Sea Drier [91] Mesopotamia (Iraq) 2500-2400 BC Cessation of flood occurrence Drier [92] Mesopotamia (Iraq) circa 2000 BC Desertification Drier [93] Iran 2500-2400 BC Low lake levels in Zagros Mountains Drier [94] Iran 2200 BC Drought indications Drier [95] Eastern Arabia circa 2500 BC Vegetation change Drier [96] Middle East The drought conditions occurring in Africa apparently extended to this region as well, as indicated by the individual reports in Table 6. The extreme dryness in the Middle East apparently lasted for about 1500 years [89]. As in the case of Africa, this region has not recovered the more favourable pre-2300 BC conditions. Asia, India and the Pacific Documented climatic changes in Asia, India and Australia are consistent with those in the other areas. The most dramatic change occurred in the Rajasthan desert region of India - an area that had previously supported the Indus Valley cultures. The desertification of this area was as significant as that of the Sahara; previous to this time, the area supported human settlements as well as animals such as the elephant, water-buffalo and rhinoceros [97]. An analysis indicates that the development of the Thar desert in this region was directly linked to a 70% drop in the yield of the monsoon rains in the north-western part of the Indian subcontinent; the abrupt drop in precipitation shortly after 2300 BC is shown in Figure 5 [98]. The sudden onset of aridity may have been a factor in the abandonment of pre-Harappan sites throughout the area. Pollen profiles from Liaotung Pantao peninsula in eastern China and from central Formosa indicate a cooler environment starting about 2000 BC [99]. This evidence is substantiated by another source reporting that climatic cooling in Japan is well documented in pollen records at the end of the Middle Jomon phase, dated to about 2300 BC. The climatic transition has been designated as the R II to R IIIa boundary [100]. Middle Jomon settlements in the Honshu mountains were reported to have been deserted at this time, possibly due to the lower temperatures. There are a number of reports indicating increased dryness for Australia and New Zealand, based on increased lake salinity, vegetation and animal changes. All of the reports are dated to the time period of interest, with one specific date centred on 2250 BC [101]. The poorer conditions in Japan have been determined to have lasted for about 2000 years, and similar to the other regions, to have not returned to the pre-2200 BC temperature levels [102]: only limited recovery has occurred in India and Australia up to the present time. [*!* image: Figure 5: Estimated Variations of the Rainfall in Rajasthan, Northwest India Over the Last 10,000 Years, from Lake Levels and Botanical Evidence Showing a Sharp Precipitation Drop Shortly After 2300 BC (J. Abery, after H. H. Lamb, 'Reconstruction of the Course of Postglacial Climate Over the World', in A. Harding {ed.} [ref.11], p.30)] Ocean Temperatures An extremely important element of the climatological evidence is the determination of deep oceanic cooling, since this is a direct indicator of mean global cooling. Measurements have been taken in the Atlantic, Pacific and Antarctic Oceans; although these measurements have not been calibrated in terms of actual degrees of temperature, they represent significant decreases. Two reports of cooling in the south Atlantic Ocean have been issued, dated at 2500 and 2100 BC, based on the relative abundance of Antarctic and sub-Antarctic diatom flora [103]. Diatoms are unicellular animals related to algae: the two types of diatom exist under different temperature conditions. Interestingly, this temperature decrease is supported by other oceanic organism changes. A sharp temperature drop is also indicated at about 2300 BC by a shift from right-handed to left-handed coiling of planktonic marine organisms in the vicinity of the Bahamas, as shown in Figure 6 [104]. Dating of both diatoms and plankton is based on calibrated radiocarbon measurements. The data indicate that the temperature remained at the lower values to the present time. In the Pacific Ocean, major deep oceanic cooling has been determined to have started about 2500 BC, based on radiocarbon measurements of coral reefs in eastern Asia. The coral reef growth at different times is an indicator of water temperature. Similar to the Atlantic measurements, no recovery from the cooling is indicated, except for a short term transient at about 500 BC [105]. [*!* image: Figure 6: Climatic Curve Based on Coiling Direction of Foraminifera, Obtained from Deep-Sea Core Near Bermuda Showing Ocean Temperature Decrease at About 2300 BC (J. Abery, after T. K. Turekian, The Late Cenozoic Ages [Yale University Press 1971], p.207)] The Pattern of the Evidence The preceding sections presented evidence for four important climatological aspects of the 2300 BC event model. 1). There is considerable evidence, particularly from deep oceanic changes in both the Atlantic and the Pacific, of a general global cooling some time around 2300 BC. From a number of palynological reports, it would appear that the decrease was about 2-3°C. Climatological theory as well as historical experience indicates that this magnitude is sufficient to cause considerable climatic changes on the Earth. 2). There is clear evidence that there actually were large climatic changes on the Earth, and that these changes very closely follow the expected changes postulated by the climatic model. It is considered that even with the increased moistness in northern Europe and in a large portion of the western hemisphere, the Earth in general became drier at this time. 3). A large body of evidence shows that the climatic change did not occur as a transient effect lasting only a few years, but continued for hundreds or thousands of years in some areas. An extremely important point is that, in general, Earth's climate has not returned to the conditions that existed before 2300 BC. As a small comment, this long term change is well known to climatologists; what I have endeavoured to do has been to show that it occurred very close to the era of the cultural discontinuities and the site destruction and abandonment. 4). The pattern of climatic changes corresponds very closely with the cultural variations described in the first article. Cultural regression occurred throughout the lower latitude regions of deteriorating climate. On the other hand, the shift from a relatively warm and arid climate to a more cooler and moist one produced a favourable environment in the Americas for cultural expansion. The next aspect that I would like to cover is the part that the climatological material plays in the overall event model - what makes this information important to the model. There are three areas of importance: a). The validity of the event model to a very large extent depends upon the establishment of credible cause-and-effect relationships. The climatic changes go a long way toward explaining the cultural discontinuities and major movements of groups at this time. It is considerably more difficult to establish site destructions or notions such as fear as a motivation for these cultural changes, even if they may have entered the picture to some extent. b). The temperature change at 2300 BC is in itself a link in the overall cause-and-effect structure of the event model. The temperature drop and resultant climatic changes may have strongly influenced cultural changes, but they were not a cause of the site destructions. However, the extended temperature drop did occur, and a change of this magnitude would certainly indicate the existence of some determinable cause. If a cause of the site destruction is postulated, and this cause can be established also as a valid cause of the temperature drop, then the overall event model is strengthened. c). The mythology which appears at 2300 BC, and describes a catastrophic event, clearly indicates climatic changes occurring at the same time. This is jumping ahead a little, and violates my principle of not making statements without supporting evidence; however, there are too many interlocking pieces to this puzzle to allow a simple step by step development of ideas. Potential Causes of Temperature Drop The last order of business is to examine possible causes for the temperature drop, emphasising the long term nature of the change. The first candidate to be considered is variation in the solar radiation level. Although no long term record of solar flux reaching the Earth has been compiled, the measurements that have been taken do not show more than 0.1% change lasting only for a period of less than 30 days; the resultant effect on Earth surface temperature would only be about 0.1-0.2°C, a small fraction of the decrease that appeared to have happened at about 2300 BC. An unusually strong long term negative transient might have accomplished the change, but this is considered to be extremely unlikely [106]. A second potential cause for the temperature change could be volcanic eruptions throwing sulphur-bearing aerosols and fine dust into the atmosphere, which would settle at higher and lower altitudes respectively. The general effect of even the more violent eruptions has been to lower the global temperature by 0.5 to 1.0 degrees Centigrade for a period of 1 to 3 years, and less than 7 years in all cases. Although I have come across some vague speculation that major volcanic activity could sustain a prolonged cooler interval, there are specific arguments against this having occurred in the volcano/glacier causal relationships for the Mesozoic, Tertiary and Pleistocene eras [107]. One author advances an argument that the effects of multiple volcanic eruptions may be self-governing, in that the increase in sulphate aerosol mass density in the atmosphere results in rapid particle growth with faster settling times. Since the dust settles faster than the aerosols, the cumulative effect of multiple volcanic eruptions would be more in terms of intensity than time duration [108]. I should also comment that the geological evidence in my next article includes a possible significant, but only modest, peak in volcano activity [for 2300 BC]; in fact, the nature of the eruption process itself would probably preclude a very large peak of activity. Volcanic eruptions must therefore be tagged as questionable in regard to causing a long term global cooling. Even though volcanic eruptions are unlikely to have caused the long term cooling, a question arises as to the possibility of a short term effect changing the Earth's heat budget, and causing it to stabilise at a level corresponding to a lower surface temperature. It seems to me that this could not be accomplished without a stabilised shift to a higher albedo level. The two main contributors to the Earth's albedo are the planetary surface and the cloud cover. Planetary surface albedo could increase due to glacier expansion and/or vegetation deterioration. Determination of glacier expansion is made very difficult because of sample impurities that result in very large dating errors. However, the one survey paper that I found shows only uncorrelated short term glacier movements, and definitely precludes the occurrence of the general large sustained expansion that would have the necessary effect on the Earth's albedo [109]. Incidentally, the lack of a major glacier change at this time does not negate the evidence for a temperature drop. Firstly, the cyclic nature of the glacier mass build-up, extrusion and retreat process does not lend itself to an instantaneous response. Secondly, the regions of glacial geology were still in a recovery stage from the last glaciation period; the land regions had subsided so that the glacier masses were not sufficiently high to affect the high altitude saturated air and obtain large precipitation for growth [110]. A determination of altered albedo due to cloud cover is even more uncertain. It would seem to me that a decrease in global temperature would reduce the atmospheric moisture-carrying capacity, thereby reducing cloud albedo, and allowing more solar energy to reach the planet surface - this would actually provide negative feedback against the cooling trend. In summary, there is no evidence for albedo variations that would change the Earth's heat balance (and thereby modify surface temperature); in fact, the general evidence would indicate the improbability of this occurring on a significant level. The next causal candidate to consider is the Milankovitch effect, based on time coincidence of individual Earth orbital variations in the order of tens of thousands of years - rotational axis tilt relative to the plane of the ecliptic, eccentricity, and precession. The relevance of the orbital variations to past climatological conditions has been verified by a number of simulation programs [111]. It appears unlikely, however, that this was a causative factor for the 2300 BC temperature cooling: the Milankovitch model applies to much longer duration changes than the 2300 BC transient; it tells nothing of cycles of less than 20,000 years [112]. In summary, there is strong evidence for a sustained global temperature drop, supported by both deep ocean temperature changes and earthwide climatic changes. The important aspect of this sustained temperature change is the absence of a recognised cause. I have not brought up the subject of a small orbital change - this certainly could have produced the long term (or even possibly permanent) climatic change; but the implications of this phenomenon are so great that a very large body of information is necessary to support credibility. I will discuss this subject in a later article. In conclusion: climatic change is a very pervasive element in the event model, which will surface again in each of the following articles in this series. References 1. M. M. Mandelkehr, "An Integrated Model for an Earthwide Event at 2300 BC (Part I: The Archaeological Evidence)", SIS Review V:3 (1983), pp.77-95 2. C. E. P. Brooks, "Geological and Historical Aspects of Climatic Change", in T. F. 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Shackleton, "Variations in the Earth's Orbit: Pacemaker of the Ice Ages", Science 194 (1976), pp.1121-31 112. J. Gribbin, "Astronomical Influence", in Gribbin, op. cit. [55], p.142 Copyright: M. M. Mandelkehr, 1987 _________________________________________________________________ \cdrom\pubs\journals\review\v1987\34model.htm