Why Did The Laurentide Ice Sheet Melt During The Younger Dryas?

Written by Koen Vogel, Ph.D. on January 5, 2023. Posted in Current News

Alternate models for planetary processes, epilogue

This post is the epilogue of the PSI posts in support of the PROM article “An integrated physical model characterizing planetary magnetism and heat”, which proposes an alternate origin for the geomagnetic field versus the consensus geodynamo theory.

The PROM-related PSI posts dealt with planetary processes, i.e. physical processes that distribute and focus energy on planetary scales. This epilogue post uses the PROM article to explain why the North American (Laurentide) ice sheet melted and retreated during a period at the end of the last ice age – the Younger Dryas – that is commonly believed to have been a brief global return to ice age conditions.

The prevailing theory on the Younger Dryas

The Pleistocene Glaciation started roughly 2.6 million years ago ^[1]. The Earth is currently in an interglacial period that is commonly believed to have started with a brief global return to cool temperate conditions during the Bølling–Allerød (BA; 14,700-12,900 years ago), followed by a brief global return to ice age conditions known as the Younger Dryas (YD; Fig. 1; 12,900 – 11,700 years ago) ^[1]. These beliefs are largely based on paleotemperature data derived from ice (Fig. 1) and sediment (Fig. 3) cores.

In Europe, the YD was accompanied by a distinct vegetation change – warmer climate BA vegetation was replaced by a glacial YD plant assemblage that often contained Dryas octopetala – as well as glacial advances in Scandinavia ^[2].

Yet during the YD the (North American) Laurentide ice sheet was rapidly melting and retreating, significant runoff from melting ice sheets caused a 20 m global sea level rise (Fig. 2), and a 5 °C temperature increase was measured in Antarctic ice cores (Fig. 1, right).

Figure 1: Temperature variations during the late Pleistocene / early Holocene Epochs, determined from ice cores extracted from the central part of the Greenland ice sheet. [left; Source: ^[1]] and from the EPICA Dome C Ice Core in Antarctica [Source: https://en.wikipedia.org/wiki/Younger_Dryas]

The Pieces of the Puzzle

The end of the Pleistocene was accompanied by a sequence of unusual events:

• A 120 m sea-level rise (Fig. 2) that started around 17,000 years ago, that is started roughly the same time the Antarctic paleotemperature data (Fig. 1) start to show significant temperature increases.
• Solar cosmic ray (solar wind) intensity was 50 times higher than present around 16,000 years ago, declining to 15 times higher by 12,000 years ago ^[3]
• The Lake Missoula Floods: over 40 catastrophic floods in the Northwestern USA area that occurred between 15,000-13,000 years ago ^[4] and that indicate large-scale Laurentide ice sheet melting was occurring during this time
• An abrupt rise in atmospheric radiocarbon concentration around 12,840 years ago (Fig. 3), that is around the start of the YD. ^[5]
• An abnormally low geomagnetic field strength around 14,000 and 10,000 years ago ^[6] (Fig. 4), flanked by field recoveries around 12,000 and 8,000 years ago.
• The Quaternary megafaunal Extinction peaked around the start of the YD ^[7].
• Göbekli Tepe, a large, Neolithic city in southwest Asia that was founded around 11,500 years ago, was abandoned and purposely buried roughly 10,000 years ago ^[8].

Figure 2: Sea level change since the Last Glacial Maximum.
[Source, downloaded 27 November 2022]

Figure 3: Radiocarbon abundance excess relative to the trend line value for the Cariaco Basin (Venezuela) sediment core (upper profiles) compared to (lower profiles): (left) the core’s grayscale climate profile whereby higher grayscale values indicate warmer temperatures; (right) Radiocarbon excess relative to the trendline (b) and ¹⁰Beryllium deposition rate (c) [Source: ^[5]]

Figure 4: Snapshots from a model reconstructing the geomagnetic field between 12,000-6,000 BC [Source: ^[6]]

Catastrophism versus Uniformitarianism

Many authors suggest the Pleistocene ice age ended with a catastrophic event. For example, the Ancient Apocalypse series on Netflix suggests a series of meteorite impacts caused its demise. Dr. R. Schoch rejects such a theory in favor of massive solar flares (Source retrieved 27 November 2022), enormous solar plasma emissions that observations suggest occurred around that time. Such theories belong to a geological philosophy known as Catastrophism, whereby geological epochs end with violent, cataclysmic events.

Many early geologists were Catastrophists, who scoured the geologic record for evidence confirming biblical events, such as Noah’s Flood. As more was learned Catastrophism gave way to Uniformitarianism, the philosophy whereby slow processes that can be observed today such as erosion, plate tectonics, 100-year storm events, etc. are interpreted to be responsible for Earth’s geology. Uniformitarianism is generally preferable, as it does not require deus-ex-machina, low-probability events to explain something that can adequately be explained by higher-probability, common events.

Some events however defy uniformitarian explanations, and Catastrophism has made something of a comeback following the general acceptance that the Chicxulub and Popigai meteorites were probably responsible for the Cretaceous–Paleogene and Eocene–Oligocene extinction events resp. A catastrophic end to the YD is favored by many authors: the Pleistocene glaciation terminated abruptly over a short time period (17,000-8,000 years ago) after roughly 2.5 million years of relative stability.

Global temperature variations at the end of the Pleistocene

No uniformitarian mechanisms can be envisioned that cause abrupt 8-12 °C changes in global temperatures (Fig. 1). A large, global temperature drop during the YD – and a global return to ice age conditions – is however sharply contradicted by reconstructions that indicate the Laurentide ice sheet was rapidly shrinking during this time, by the 20 m YD global sea level rise (Fig. 2) that indicates significant runoff from melting ice sheets, and by the 5 °C YD temperature increase that was measured in Antarctic ice cores (Fig. 1, right). Clearly, paleotemperature indicators reflect local, not global conditions, and care needs to be taken when extrapolating any analyses.

The temperature increases measured in glacial cores (Fig. 1) are therefore misleading in that they document local, not global temperature variations. For example, both Central Greenland and the Cariaco Basin (Venezuela) show a rapid increase in temperatures around 14,700 years ago (start BA) that is not observed in the Antarctic data, which shows a fairly gradual increase in paleotemperature between 17,000 – 14,200 years ago.

The observed rapid temperature rise was therefore likely limited to the northern hemisphere, and possibly only occurred locally in the North Atlantic Basin. Near Central Greenland this increase declined gradually between 14,800-12,900 years ago (Fig. 1), whereas the Cariaco Basin (Caribbean) experienced a long period of stable, higher temperatures prior to the YD, followed by a sharp temperature decline that persisted during the YD (Fig. 3).

Figure 5 documents the current 6-8°C Arctic temperature increase measured by the Danish Meteorological Institute. Arctic winter ice that formed between 1995 and 2020 will document this rapid temperature increase, despite the fact that these local Arctic temperature increases have small to no correlation with North American or global temperatures:

• global temperature increases over this period are on the order of 0.5°C
• the Hudson Bay ice cover appears to indicate a return to the colder conditions last seen in 1980

A better proxy for global temperatures is therefore the global sea level rise curve (Fig. 2): the large volumes of water necessary to raise global sea levels by 20 m over the YD can only have come from melting ice sheets during periods when the global average temperature was higher than during the Pleistocene ice age.

Figure 5: Temperature anomalies of the Arctic +80N region: annual mean (black line), summer anomaly (red line; averaged over June, July, August), and winter anomaly (blue line; averaged over December, January, February). The reference climate is ECMWF-ERA40 1958-2002. (Source)

The start of the YD (North Atlantic Basin temperatures drop) is associated with a marked increase in sea level (temperatures over some ice sheets above freezing), which is only possible if:

• local catastrophic events caused ice sheet melting despite catastrophic global cooling.
• rapid Northern Hemisphere ice melting caused a huge cold water influx into the North Atlantic Basin that locally/regionally decreased temperatures.

The second (uniformitarian) option is far more likely: the massive cold water influx from the BA and YD melting glaciers was redistributed by ocean currents ^[8], which in turn caused local temperatures to gradually drop in offshore Central Greenland and precipitously drop in the Cariaco Basin. The YD very likely was not a “brief global return to ice age conditions” but a period of intense melting – though not in Europe – during a period (17,000-8,000) of gradual, global temperature increase.

Energy considerations

Any catastrophic explanation must consider whether its energy budget is physically realistic. A quick back-of-the-envelope calculation provides some insights. Consider the Laurentide ice sheet that covered most of Canada (area: 10⁷ km2) during the Last Glacial Maximum. Its maximum thickness was likely over 3 km, though at its edges its thickness tapered out ^[1].

Assuming an average thickness of 1 km, the total volume of ice contained in the ice sheet was on the order of 10⁷ km3, or 10¹⁶ m3, or an order of magnitude 10¹⁹ kg of ice. Melting a kg of ice requires 80 kcal, so melting the ice sheet requires roughly 10²¹ kcal, or approximately 10²¹ W.h, or 10⁹ TW.h.

A billion TW.h is an astronomical amount of energy that realistically can only be supplied by shortwave solar radiation. For example, the largest recent meteorite impact – the Tunguska event – caused a 12 megaton (14 TW.h) explosion, and the largest US thermonuclear warhead tested at roughly 25 megatons (29 TW.h). To melt just 5% of the Laurentide ice would therefore require either 1.7 million large thermonuclear bombs or over 3.5 million large meteorites.

Another example: the largest recent solar flare was the Carrington event, which caused roughly 6 TW of Joule heating over a roughly 48-hour period (~300 TW.h). Despite being 20 times more energetic than a large meteorite it would still take an enormous amount of extremely large solar flares occurring over a geologically short time interval to melt just 5% of the Laurentide ice sheet.

The bulk of the melting power can therefore have only been supplied by the 170 10³ TW ^[9] Earth-incident shortwave solar radiation. Even if the full radiation power of the sun was fully absorbed by the ice sheet for 12 hours per day, it would still take over a year just to melt the Laurentide ice sheet, without even increasing its meltwater temperature.

Scenarios whereby the Earth’s global temperature increases by 8°C over decadal time periods are therefore entirely unrealistic: the Sun would have to accomplish catastrophic climate change and catastrophic glacial melting at the same time, that is the Sun would have to increase Earth’s temperature by 8°C in addition to melting its ice caps. A more realistic scenario is that global temperatures increased gradually and that the glacial melt was aided by a series of catastrophic events, each of which created a perfect storm of accelerated melting.

At present only about 60% of the solar irradiation power is absorbed by the Earth (Source accessed 27 November 2022), and at the end of the Pleistocene, even less than this would have been absorbed due to the high albedo of the Pleistocene ice sheets. Albedo is defined as the percentage of shortwave solar energy that is reflected by a surface. Fresh snow has a relatively high albedo (~0.8-0.9), indicating snow-covered ice sheets can be very hard to melt directly by shortwave solar energy.

However, old or wet snow has a much lower albedo (~0.4-0.6) indicating that if a catastrophic event were to melt the upper snow layer over a large area, such an event would act as a catalyst in accelerating ice sheet melt by shortwave solar energy. In addition, once the Laurentide ice sheet started melting, its transported sediments (clay, sand, boulders, etc.) would accumulate at its surface, further lowering its albedo. Plus, newly ice-free areas would have significantly lower albedos and could absorb more solar energy, thereby contributing to local warming and accelerated local melting.

Solar radiation energy over the Northern Hemisphere was different during the YD than today. It was very likely at least 3% stronger than at present, as the cyclic precession of the Earth’s axis of rotation follows a ± 26,000 year (Milankovitch) cycle that every 13,000 years causes different hemispheres to be closest to the sun at Earth’s perihelion in January.

This means that at the start of the YD the Northern Hemisphere – during its (December) summer – was around 3% closer to the sun than during its (June) summer today, which would have significantly increased both its summer solar radiation and incident solar wind strength. Also note that Zook et al. ^[8] concluded that solar cosmic ray (solar wind) intensity was 50 times higher than present around 16,000 years ago, declining to 15 times than present by 12,000 years ago, from a study of tracks in lunar micrometeorite craters.

The pre-YD period (17,000-12,840 years ago)

The PROM article details how the geomagnetic field is generated by Solar Wind Induced Currents (SWICs), high-intensity, planet-scale electrical currents that circuit in the outermost shell of the Outer Core. These circuits generate both the geomagnetic field as well as waste heat at the circuit periphery. The circuit peripheries in turn act as high-resistivity barriers to future currents, forming a stable feedback loop that ensures Earth’s heat anomalies, such as the mid-Atlantic ridge, remain stable over millions of years. Fig. 6 presents schematics of the North American SWIC circuit and its associated North American heat anomalies.

The PROM article demonstrates that the strength of a steady-state geomagnetic field increases during periods of lower solar wind activity, e.g., during the Maunder minimum, when a smaller percentage of the solar wind power is stored as core heat, and a larger percentage is stored as geomagnetic energy.

Under the current “normal” solar wind power (~6 TW) the geomagnetic field strength is decreasing and the core is heating up. Zook et al. ^[8] concluded from a study of tracks in lunar micrometeorite craters that the solar cosmic ray (solar wind) intensity was 50 times higher than present around 16,000 years ago, declining to 15 times higher by 12,000 years ago. This higher solar wind power had two effects:

• a severely increasing outer core temperature, resulting in very high geothermal heat flow at the SWIC circuit boundaries
• a severely weakening geomagnetic field strength due to an overheating core.

Evidence for the first is found in the pathway between the eastern and western Laurentide ice sheets (Fig. 6) that was carved by geothermal heat between 16,100- 14,800 years ago, while evidence for the second is found in the dramatically weakened geomagnetic field 14,000 years ago (Fig. 4).

Figure 6: (Left) Schematics of the North American SWIC circuit. Top: on a World Geothermal Potential Map (Map Source); Bottom: on a globe; red circled X indicates circuit center and corresponding geomagnetic non-dipole anomaly. (Right) Reconstructions of Laurentide ice sheet at 16,100 (Top) and 14,800 years ago (Bottom; start Bølling–Allerød); M=location of Missoula, MT (Source), showing developing geothermally carved pathway between the eastern and western Laurentide ice sheets

The sea level change (Fig. 2) of ±25 m between 17,000-14,700 years ago suggests that significant ice sheet melting was already occurring before the start of the Bølling–Allerød (BA). A comparison of the 16,100 and 14,800 maps of the Laurentide ice sheet indicates two main melting areas in North America: 1) offshore Greenland; 2) a curvilinear pathway that was melted through the western part of the ice sheet, and that by 14,800 years ago had divided the ice sheet in two (Fig. 6).

This pathway was likely caused by geothermal heating from below the sheet, as any solar melting would preferentially melt the southern parts of the ice sheet. A geothermal origin is confirmed by Fig. 6: the curvilinear pathway precisely follows the edge of the North American SWIC circuit (Fig. 6) and its associated heating.

From the PROM article: The strength of the geomagnetic field is transient in nature. Intervals of stable geomagnetic field geometries with constant polarity are interrupted by magnetic reversals (rate: 2-3 per Ma) when the geomagnetic poles switch locations, as well as geomagnetic excursions (rate: 1 per 5-10 ka) when the magnetic pole directions significantly shift. A large geomagnetic excursion can progress to a geomagnetic reversal.

Recent data (downloaded 2021 January 11) suggest that the geomagnetic field may currently be roughly halfway through a geomagnetic excursion: between 1900 and 1990 the Earth’s dipole moment reduced from 8.29 to 7.84 10²² Am², and its North Magnetic Pole moved from its North American location in 1900 to its current position near to the geographic north pole. PSI Posts one and two explain that the current geomagnetic excursion has likely caused the current Arctic heat anomaly (Fig. 5).

The Pavón-Carrasco et al. study [4] only covered the 12,000 BC – present time interval, so no paleomagnetic field information is available for the start of Bølling–Allerød (BA) around 14,700 years ago. Still, the almost-absent geomagnetic field over the Americas 14,000 years ago (Fig. 4) suggests the geomagnetic field could only have weakened during the BA.

Both the temperature data (Figs. 1, 5) and a weakening geomagnetic field suggest major geomagnetic realignments, such as geomagnetic excursions, were occurring prior to and during the BA. The similarity in temperature spikes between the start of the BA in Fig. 1 and the Arctic warming in Fig. 5 suggests that a geomagnetic excursion happened at the start of the BA, one that progressed to a (failed) magnetic reversal during the YD (below).

The pre-YD sequence, therefore, was likely:

A dramatic increase in solar wind energy (~300 TW) around 16,000 years ago, led to severe core overheating and extremely hot geothermal anomalies. The energy necessary to melt the corridor – assuming a 50 km wide by 2000 km long by 1 km thick corridor (that is roughly 1% of the total Laurentide ice sheet) – is on the order of 10⁷ TW.h. The time required to melt the corridor – assuming 1% of the total solar wind energy (3 TW) was focused along the corridor – is around 400 years, indicating the scenario is energetically plausible.

Arctic heat anomalies and low-albedo, newly ice-free zones globally caused temperatures to gradually rise between 16,000-14,700 years ago (Fig. 1, 2). In the Northern Atlantic, the Arctic heat anomaly melted the offshore Greenland ice sheet by 14,700 years ago (Fig. 6), causing a local temperature spike at the start of the BA (Fig. 1).

The collapse of the geomagnetic field in the Americas around 12,840 years ago, resulted in a different mode of melting.

Figure 6 also explains the Lake Missoula flooding and why the Laurentide ice sheet split into a western and an eastern sheet: geothermal heating along the periphery of the North American SWIC circuit was melting a path through the ice sheet. Western Laurentide ice dams ponded meltwaters and caused catastrophic flooding when they collapsed.^[4]

Reconstructions suggest the Laurentide ice sheet withdrew quicker along its western edge and had almost completely disappeared in western North America by the end of the YD, at which time the Laurentide ice sheet was completely encircled by the North American SWIC circuit and its heating zone: the remnants remained in the relatively cold, low geothermal heat zone (Fig. 7).

The fact that the Lake Missoula Floods ended around 13,000 years ago ^[2] also indicates that the Laurentide ice sheet withdrew further into Canada after the BA, and never returned to the Lake Missoula area, which is consistent with North American warming, not cooling during the YD.

Figure 7: (Left) Schematic of the North American SWIC circuit on a globe; red circled X indicates circuit center and corresponding geomagnetic non-dipole anomaly. (Right) Reconstruction of the Laurentide ice sheet 11,400 years ago (Source), which is 300 years after the end of the YD.

The Younger Dryas (12,900 – 11,700 years ago)

The most evident catastrophic event occurred at the start of the Younger Dryas:

• Large-scale ice melting, whose runoff caused sea levels to rise (Fig.2), and likely caused temperatures to drop in offshore Greenland and the Cariaco Basin ^[8]
• Intense proton bombardments of the atmosphere and Earth’s surface ^[5], as testified by increased radiocarbon abundance and 10Be in Cariaco Basin sediments and Greenland ice cores (Fig. 3). This intense radiation in turn likely caused the large North American megafaunal extinction that peaked around 12,900 years ago ^[5].

LaViolette ^[5] argues that YD Solar Proton Emissions (SPEs, i.e. solar flares) that were over two orders of magnitude stronger than the (observed) 1956 SPE overpowered the geomagnetic field, and affected the observed increases in radiocarbon and ¹⁰Be abundance. This calculation however relies on a YD geomagnetic field strength over the Americas equal to the current strength, while Fig. 4 suggests that 12,800 years ago it was likely much weaker.

A more uniformitarian explanation is therefore that due to the almost-disappearance of the geomagnetic field over North America around 12,840 years ago, the solar wind plasma (mainly protons, electrons, and alpha particles) was no longer being mostly deflected by Earth’s magnetosphere, but directly striking the North American surface.

This solar wind radiation caused:

• Increased Laurentide ice melting. Unlike shortwave solar radiation (sunlight), which is largely reflected by the high-albedo snow and ice, most of the high velocity (500 m/s) solar wind particles would have impacted and penetrated the upper parts of the ice sheet, thereby imparting their kinetic energy, melting and structurally weakening its upper surface and lowering the Laurentide ice sheet albedo over large areas, even in winter.
• A megafaunal extinction peaked around 12,900 years ago ^[5].

Note that the geomagnetic field was much weaker over North America than over Europe (Fig. 4), so its ice sheet melting and faunal extinctions were significantly more severe.

LaViolette ^[5] recognizes solar cycles (arrows in the upper right graph in Fig. 3) in the 13,000-12,840 intense increase in radiocarbon abundance that is consistent with a quick collapse (over 160 years) of the geomagnetic field strength. At present, the solar wind particles are mostly deflected around the Earth by its magnetosphere ^[11], but during periods of low field strength an increasing number of solar wind particles directly strike the Earth.

Between 13,000-12,840 years ago the solar wind, whose strength follows solar cycles, was able to progressively inflict more radiation damage to Earth’s atmosphere, ice sheets, and fauna and flora due to the geomagnetic field collapse. In addition, the solar wind was likely 15 times stronger than today ^[3] during the YD.

Figs. 3 & 4 suggest the Earth may have undergone a failed geomagnetic reversal around 12,900 years ago: the geomagnetic field weakened severely up until 12,840 years ago, but gradually returned to low strength by 12,000 years ago, at the end of the YD.

A failed magnetic reversal is more consistent with the Fig. 3 data than SPEs: the SPEs would have to have been occurring regularly and gradually increasing in strength at the start of the YD, while gradually decreasing in strength during the YD, which seems unlikely. Note that several magnetic reversals and even a few failed reversals occurred during the Pleistocene, which begs the question of why this failed reversal was more successful in melting the Laurentide ice sheet.

It was likely the following sequence of catastrophic events, a series of perfect storms:

• A catastrophic increase in solar wind strength around 16,000-12,000 years ago, caused a dramatic weakening of the geomagnetic field, major geothermal anomalies in western North America, and Arctic heat anomalies.
• A severely weakened geomagnetic field at the start of the Younger Dryas, whereby a strong Earth-incident solar wind accelerated ice melting.
• A geomagnetic field recovery by the end of the Younger Dryas caused a second Arctic heat anomaly, and additional increased Northern Atlantic and western North America geothermal heating
• A second period of abnormally low geomagnetic field strength around 10,000 years ago (Fig. 4), whereby Earth-incident solar wind particles accelerated ice melting

In essence, the ice age ended due to the changes in Earth’s response to incident solar energy caused by geomagnetic field variations, that are caused by two successive failed geomagnetic reversals, that were caused by catastrophic solar winds between 16,000-12,000 years ago.

At the end of the YD, about half of Canada was ice-free (Fig. 7), which lowered its surface albedo, which in turn contributed to a warming climate feedback loop. The 12°C temperature spike at the end of the YD in Fig. 1 indicates conditions similar to the start of the BA had returned, that is a period whereby geomagnetic instability – the recovering geomagnetic field – caused an Arctic heat anomaly.

The resurgent geomagnetic field around 12,000 years ago resulted in the solar wind particles being – once again – diverted around the Earth, instead of directly impacting it. It was during these relatively benign (in southwestern Asia) times that Göbekli Tepe was founded ^[7].

The Start of the Holocene (11,700 – 10,000 years ago)

Around 10,000 years ago the geomagnetic field dramatically weakened again, leading to solar wind radiation again striking Earth directly, though in contrast to the start of the YD the lower field strength was mainly confined to the equatorial zone (Fig. 4). Around the same time the inhabitants of Göbekli Tepe abandoned their city. Curiously, they buried it entirely, likely meaning to return when whatever calamity was causing them to leave had gone away.

The calamity was likely not a meteorite, as is suggested by the Netflix series Ancient Apocalypse. If a meteor hits a city there’s nothing left to bury, while a near hit would likely be interpreted as a warning from the gods that necessitated appeasement (sacrifices, more rituals, etc.). The calamity may have been solar flares, as has been suggested by Dr. Schoch.

Any solar flares that occurred during times of low geomagnetic field strength would cause significant and dramatic visuals in the sky that might be interpreted by the Göbekli Tepe inhabitants as evidence that the gods were truly angry and wanted them to leave. But once again these solar flares would be incidental, and would more likely result in god appeasement, not city abandonment.

The scenario that makes the most sense is that the city experienced a prolonged calamity, whereby it gradually became uninhabitable: the gods were clearly angry, appeasement wasn’t helping, and the city’s leaders were facing an existential threat that forced them to abandon the city. The inhabitants buried their city, likely because they were hoping to return one day when the calamity had subsided. The fact that they had the time to do this indicates the existential threat was not immediate, but rather long-term. A prolonged and increasing exposure to solar wind radiation explains most of the observations.

Around the time of abandonment, 10,000 years ago, the geomagnetic field was again very weak, likely heading for another (failed) reversal. If the weakening resembled that of the YD (Fig. 3) then over a period of 160 years the solar wind radiation would get progressively worse: the solar wind particles were directly striking the Earth, increasingly causing radiation poisoning of humans, fauna, and flora. These particles would also ionize the atmosphere, leading to more and more violent lightning strikes, aurora borealis at lower latitudes, and intense plasma phenomena in the sky resembling snakes and humanoid deities (humans with bird heads, etc.).

All of these events have been described by Dr. Schoch as likely occurring around this time as part of his solar flare theory. A weakened geomagnetic field allows a more uniformitarian explanation: all of these events can also be caused more and more continually by a strong solar wind under a weakened geomagnetic field.

Prolonged exposure to gradually increasing solar wind radiation would have convinced the Göbekli Tepe inhabitants that staying put was not an option. They would have observed that those staying inside stone dwellings suffered less and would be motivated to move to caves or subterranean cities, such as the underground cities of Cappadocia, to escape the calamity.

[1] Williams, R.S., Jr., and Ferrigno, J.G., eds., 2012, State of the Earth’s cryosphere at the beginning of the 21st century–Glaciers, global snow cover, floating ice, and permafrost and periglacial environments: U.S. Geological Survey Professional Paper 1386–A, 546 p.

[2] Björck, S., 2007, Younger Dryas oscillation, global evidence. In S. A. Elias, (Ed.): Encyclopedia of Quaternary Science, 3, 1987–1994. Elsevier B.V., Oxford.

[3] Zook H.A., Hartung J.B., Storzer D., 1977, Solar flare activity: Evidence for large-scale changes in the past. Icarus, 32,106-126.

[4] Waitt, R.B., Jr, 1984, Periodic jökulhlaups from Pleistocene Glacial Lake Missoula—New evidence from varved sediment in northern Idaho and Washington, Quaternary Research. 22, 46–58. doi:10.1016/0033-5894(84)90005-X

[5] LaViolette, P. A., 2011, Evidence for a solar flare cause of the Pleistocene mass extinction, Radiocarbon 53, p 303-323.

[6] Pavón-Carrasco, F.J., Osete, M.L., Torta, J.M., De Santis, A., 2014, A geomagnetic field model for the Holocene based on archaeomagnetic and lava flow data, Earth and Planetary Science Letters, 388, 98-109, //doi.org/10.1016/j.epsl.2013.11.046.

[7] Clare, L., 2020, Göbekli Tepe, Turkey. A Brief Summary of Research at a New World Heritage Site (2015–2019), e-Forschungsberichte 2, 81–88

[8] Meissner, K.J., 2007, Younger Dryas: A data to model comparison to constrain the strength of the overturning circulation, Geophysical Research Letters, 34, doi:10.1029/2007GL031304.

[9] Chen, C. J., 2011, Physics of solar energy. Wiley, 370 pp. ISBN 978-0-470-64780-6

[10] Bindoff, N.L., Stott, P.A., AchutaRao, K.M. et al., 2013: Detection and Attribution of Climate Change: from Global to Regional. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., et al. (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

[11] Kivelson, M.G., Bagenal, F., 2014, Planetary Magnetospheres In: Encyclopedia of the Solar System (Third Edition), Academic Press; ISBN: 978-0-12-415845-0, p. 137-157

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