Thursday, September 27, 2012

Climate Drives History: A Big Picture Recap

The chart above shows the climate history of the world in a nutshell for the last 10,500 years with a chronology from Greenland that matches a larger global climate history. It is a comprehensive big picture summary of climate history for the entire Holocene era.

History, Prehistory and Climate

There have been eleven distinct global climate events (many of which are Bond events; a more comprehensive list is available here), staring with the Younger Dryas event, when there was a substantial and rapid drop in global temperatures in the amount indicated during the era when modern humans ceased to be exclusively hunters and gatherers. There was also at least one major volcanic erruption not clearly associated with a global climate event in the same era, that is discussed below. These twelve events were historical turning points that can be associated with the rise and fall of historic civilizations and empires, and with mass migrations.

Some of the notable historical events associated with each of these events, predominantly in West Eurasia where I know the history and prehistory best, are set forth below.

1. The chart begins on the right with the end of the warming global temperatures after the Younger Dryas cold spell (5 degrees C to 15 degrees C) that produced the coldest in absolute terms since the Last Glacial Maximum (ca 18000 BCE), brought about the steepest drop in global temperatures in the period discussed by this post. This caused by an impact from outer space in North America and produced a cool period that lasted from roughly 10,800 BCE to 9,500 BCE.

The Younger Dryas brought about the end of the Clovis culture in North America and may have contributed to the megafauna extinction in the Americas.

It coincided with the Neolithic revolution in the Fertile Crescent (first appearing in the Levant and Southeastern Turkey). It was followed by an arid period in North Africa that produced a dry Sahara and concentrated the people who have lived in a wet Sahara around water, particularly, the Nile basin.

2. The 8.2 kiloyear event begins around 6200 BCE (3 degrees C). This is the deepest cooling event from the Younger Dryas through the present, and it led to the coldest temperatures in absolute terms since the Younger Dryas.

According to Wikipedia during the 9.2 kiloyear event: "Drier conditions were notable in North Africa, while East Africa suffered five centuries of general drought. In West Asia and especially Mesopotamia, the 8.2ky event was a three-hundred year aridification and cooling episode, which provided the natural force for Mesopotamian irrigation agriculture and surplus production that were essential for the earliest class-formation and urban life."

This coincides with the divide between the Pre-Pottery Neolithic and the Pottery Neolithic in the Fertile Crescent. The prepottery Neolithic in the Indus River Valley was already in place at this point, as was the early Neolithic civilization in Egypt (domesticated cattle were present no later than about 7000 BCE).

It is around the time that the Neolithic practices of herding and farming starts to spread to Europe from West Asia and the Levant. Farming, herding and pottery arrive simultaneously to Europe. In Southeastern Europe this is when the First Temperate Neolithic archaeological horizon emerges including the Starčevo–Kőrös–Criş culture the included the Balkans and most of Greece (or its immediate Neolithic predecesors depending on the classification system used).

The Neolithic arrives in coastal Southern Europe starting around this point via the Cardium Pottery culture (aka Impressed Ware) starting near the Northern border of modern Greece and then from their up the Adriatic coast and into Southern Italy from a source in the vicinity of Syria and neighboring Southern Turkey; the Cardium Pottery expansion leap frogged over existing Neolithic cultures in Crete and Eastern Greece.

3. A cooling period from about 5500 BCE to 5100 BCE (2.5 degrees C).

The first wave Neolithic Cardium Pottery culture expands from Southern Italy to Northern Italy, Sardinia, Corsica, Southern France and eastern Spain at around this point in time over a 100-200 year period. The oldest known Atlantic megalithic structures appear in Portugal around 5000 BCE, just after this cooling period ends and several centuries after Cardium Pottery arrives there. (There are much older Mealithic structures in the North Levant and Southern Turkey where the Cardium Pottery culture has its origins, but there do not appear to be meaglithic structures in the Balkan, Southern Italian and Western Greek areas that were an intermediate stage of the arrival of Cardium Pottery in Iberia that are old enough to date to predate the arrival of the Cardium Pottery culture in Iberia. Megalithic structure in Southern Italy, Malta and elsewhere appear to have been built long after the earliest megalithic structures of Portugal.)

The Turdaș-Vinča culture of the Balkans (in which the oldest copper metallurgy is attested and an undeciphered symbol system comes into use, although not strictly part of the "Copper Age") starts to emerge in this time period and further North the Danubian Linear Pottery (LBK) culture begins to expand in this time period.

In the Indus River Valley, the cermaic Neolthic era begins at this point in time from the pre-existing Neolithic Indus River Valley civilization.

4. A cooling period starting around 4700 BCE (2.2 degrees C).

This takes place in the prehistoric early Neolithic era. This coincides with the divide between the early and late period of the Vinča archaeological culture in the Balkans, and with the emergence of the Cucuteni-Trypillian culture in Romania, Moldova and the Ukraine. Pre-literate Sumerian civilization starts to emerge after this cooling period ends.   The Chalcolithic era (aka Eneolithic era aka Copper Age) commences at this point.

Atlantic megalithic civilization structures start to appear around the time of this event, although a number of megalithic structures in Portugal appear to be several centuries older. This is also when farming and herding (i.e. the Neolithic revolution) arrived in prehistoric Britain, quite possibly as part of the Atlantic megalithic civilization from the start.

The "formative phase" of the Harappan civilization commences at around this point in time.

5. A cooling period starting around 3600 BCE (1.5 degrees C) (aka the 5.9 kiloyear event).

This is roughly the time that the Kurgan hypothesis of Indo-European origins views the Yamna culture (aka Pit Grave culture) of the Pontic steppe as the proto-Indo-Europeans whose language was ancestral to all of the modern Indo-European language families.

Minoan prepalatial civilization begins to emerge around this time in Crete. This is approximately when the Aegean Bronze Age begins. The first of the Megalithic temples of Malta were built at this time.

6. A cooling period starting around 2900 BCE (2 degrees C). This gave rise to temperatures almost as cold in absolute terms as those at the 8.2 kiloyear event.

Sumerian historical records start at around this point in time as its city-state civilization matures. The original city of Troy is founded at around this time. The Harappan phase of the Indus River Valley civilization and Harappan written symbols begin to emerge around this point in time.

The Bell Beaker culture appears in Portugal at around this time.

7. A cooling period starting around 2100 BCE (1.1 degrees C). (The >4.2 kiloyear event (I eyeballed my dates from the chart).

This coincides with the historically documented drought that caused the collapse of the Akkadian Empire (followed by a brief Sumerian renaissance that soon collapses itself) and also with the historically documented First Intermediate period in ancient Egypt.  This drought is probably when the Semitic taboo against eating pork arose.

The Indo-European Hittite culture begins to expand in Anatolia conquering the non-Indo-European Hattic empire The earliest archaeological evidence of the Indo-Aryan entry into South Asia is found at this point. Tocharian Indo-Europeans establish an easternmost outpost in the Tarim Basin at this point. The Saravesti River that had been at the core of Harappan/pre-Vedic South Asian society dries up in South Asia around that time that this cooling period ends. 

This is approximately when the El Argar civilization of Southeastern Spain is founds its first city at La Bastida, which was the largest city in Bronze Age Europe. Architecture at the city of Las Bastida has precedents "in the second city of Troy (Turkey) and in the urban world of the Middle East (Palestine, Israel and Jordan), influenced by the civilisations of Mesopotamia and Egypt" indicating that this civilization had some cultural ties to an Anatolia and/or the Levant. The Bell Beaker culture appears in Britain at this time.

8. While the global climate impact of the major eruption of the Thera volcano (in modern Santorini, Greece) in the Eastern Mediterranean sometime between 1627 BCE and 1600 BCE was modest in global climate impact compared to the climate events discussed in this post, it is a natural event that may have had important historical consequences.

It had a pivotal impact the Minoan civilization which included the city that was destroyed (excavation of the ash covered Minoan city there has revealed that it was evacuated before the erruption, apparently sparing the lives of everyone there); Mycenean conquest of most of the Minoan civilization followed soon after this event.

The Thera erruption coincides in time with the fall of the Xia dynasty in China which describes events consistent with the atmospheric impacts of a major volcanic erruption historically, and with the Second Intermediate period in Egypt during which a Semitic Hyskos elite from the Levant conquered Egypt.

Some researchers hypothesize that this erruption may have been the historical root of the story of the demise of the lost city of Atlantis described by Plato (another theory proposes the ancient Iberian city of Tartessos as an Atlantis candidate). 

9. A cooling period starting around 1200 BCE (2 degrees C), something that may be associated with the aftermath of the Hekla 3 erruption in Iceland (1159 BCE).

This coincides with Bronze Age collapse noted for the demise of the Bell Beaker culture, major disruptions of cultural patterns in Britain and other parts of the Atlantic Megalithic cultural region, Homer's Trojan War, the fall of the last Minoan palace at Knossos, the Hittite empire's collapse, invasions of "Sea people" including the ethnically Mycenean Philistines who invade Egypt (the Philistines ultimately migrate to the Levant) and the beginning a period during which the Egyptian empire declines and experiences famine.

Bronze Age collapse is followed by the "Iron Age" and coincides with the arrival of Celtic civilization in Western Europe and Italic language speakers in Italy. This is also the approximate dividing line between the early and late periods of the Nordic Bronze Age (a divide that may mark the arrival or emergence of the Indo-European Germanic languages in that region). Thus, the Indo-European languages were probably spoken in Western Europe only after the Bronze Age collapse.

10. A cooling period starting around 100 BCE (1.5 degrees C).

The two century old ethnically Greek-Macedonian Seleuicid Empire created by Alexander the Great that at its greatest extent had included included central Anatolia, the Levant, Mesopotamia, Persia, today's Turkmenistan, Pamir and parts of Pakistan collapses. The Jewish Maccabees in what is now mostly Israel revolt and declare independence from their Seleucid King only to see their new kingdom fall into civil war over succession issues, and solicit a Roman conquest of their kingdom to end this war without enduring rule by the priests. In Egypt, the Hellanistic Ptolemaic Kingdom, a successor kingdom to the one created by Alexander the Great, fell to the Romans during the reign of Cleopatra VII, in this time period.

Germanic tribes (the Cimbri and Teutones) cross the river Rhone and migrate to Roman era Italy engaging Roman soldiers there who prevent them from taking Italy.  The Roman Republic and the other formerly allied city-states of Italy fight a nine year conflict called the Social War and there are three successive serious slave uprisings (the Servile Wars). The Etruscan civilization and language which arrived in Tuscan Italy sometime after 800 BCE (which called themselves the Rasna) finally went extinct in this time period. The last era of the city of Troy ends in this time period and it is no longer inhabited and is not rediscovered for another two millenia.

11. A cooling period starting around 500 CE (1.7 degrees C).  The bottom of this decline was the coldest moment of time in absolute terms, other than the 8.2 kiloyear event, since the Younger Dryas.

This coincides with the fall of the Western Roman Empire (476 CE) and the beginning of the Middle Ages. The Islamic empire's expansion then fills the vacuum created by the fall of the Roman empire in North Africa and Spain. 

12. A cooling period starting around 1100 CE (1.5 degrees C). This cooling period was followed by the Little Ice Age a sustained cooler period, conventionally dated from 1350 CE to 1850 CE, which in turn was followed by a warming period which is probably due to human contributions to climate change associated mostly with the use of fossil fuels like coal and oil, and with deforestation.

The English kings fall to Norman Conquest (1066 CE), and Scandinavian kings also conquer kingdoms in Northern France and Kiev Russia. A North American Viking colony fails soon after it is founded. The Crusades begin.

Colonial era New England was significantly colder as a consequence of the Little Ice Age than it is now.


Maju said...

I haven't read it in full yet (very long) but I'm having problems understanding how cold spells could have favored demic or cultural expansions northwards (to Europe for instance).

Actually we do know that, at a finer-grained resolution, well-studied Neolithic expansions happen in periods of relative warmth and they suffer in the subsequent cooling phases. See here, scroll down for what I think is a better temperature graph including not one but several measures and their average.

Also your graph is impossible to see: you uploaded it with such a tiny size that it's almost useless.

I can only agree with Clovis and the meteorite but that's not too much.

andrew said...

Rapid cooling is usually accompanied by drought, extended winters or other factors that make crops fail.

The dynamic is basically one of causing an old civilization or empire to collapse and leaving an authority vacuum, while encouraging others whose territory has similarly been degraded to migrate into new territory. This is combined with the creation of necessity that encourages innovation, and then expansion of the civilization that emerged in the vacuum in the recovery period.

This post doesn't prove either causation or mechanism, however, even though it suggests this as a plausible hypothesis. Instead, it illustrates that the archaeological and historical cultures we know coincide with climate events to within the margins of error with which we know each of them. This post simply identifies coincidences of archaeological cultures and civilization shifts to gather up evidence for more throough analysis.

While correlation doesn't imply causation, correlation does imply that there is some cause, particularly when it is a strong correlation.

As to the size of the upload, I have it as big as I could get it and was as much looking for eye candy as something you could seriously examine.

The other point of the post, of course, is simply to have a decently well annotated big picture history within a natural framework. For me, getting a bit clearer on the sequence of events in the early Neolithic and Copper Age, getting a more precise grasp of the timing of the Harappan/Indo-Aryan/Saravasti events sequence in South Asia and of Bell Beaker, and recalling the events around 100 CE had value of their own.

Maju said...

I only get a 250px sized graph, impossible to read even the numbers.

Anyhow, as for the rest, I can agree that cooling (and drying) periods are generally bad for any sort of societies but, precisely, that's why you should not expect the Neolithic to spread into Central Europe in that period (#2), which in fact did not: Neolithic spread into Central Europe mostly in the subsequent period of warming after 8000 years ago, which was (apparently) the warmest ever before the ongoing global warming.

It seems that Neolithic of Central Europe shows contraction when colder conditions came (not as intense as those of the "8.2 Ky event" but relatively cool anyhow) and then expansion into Northern Europe (different cultures in some cases) when a third warm spell (the second one was not that influential, it seems) arrived after 6 Ka ago.

For European climate, in cold spells you'd expect, N>S migrations (if anything) and the collapse of Northernmost cultures before those of the South. In warm spells you'd expect instead S>N migrations and the expansion of everything but more markedly in the North. The North is just more extreme, so it's much more a puppet of climatology. The South, excepting maybe some arid corners, is not immune but much more stable because it will support large populations in all cases.

Possibly it's very different in West Asia, never mind North Africa, but in Europe it should work that way and is exactly the kind of pattern we see with Neanderthals in the Ice Age: southern populations persist, northern ones are intermittent.

Then again Greenland is just one possible reference, you should take it with a pinch of salt.

I cannot concur that climate alone drives history, although it is surely an important factor. But what I am in clear disagreement is with suggesting that S>N migrations were caused by cooling: that makes no sense whatsoever.

"the archaeological and historical cultures we know coincide with climate events"...

Let's explore the second spell: you claim it was between 5.5 and 5.1 BCE (7.5-7.1 BP). Well, that's a cold spell according to the Greenland data but not according to the reconstructed North Atlantic temperatures of Lea 2003 ("lime" color in the graph I mentioned), nor in the Eastern Tropical Atlantic of the same authors ("dark blue"). Atlantic temperature is more clearly correlated with European climate than Greenlander glaciars, which may be dislocated from the main trend and actually do look like marking excessive swings of temperature not registered in other references.

So it's very likely that Cardium Pottery arrived to Iberia in a mild or even quite warm period.

In fact if we follow the palinological curve, once the data catches up with other references c. 6.5 Ka BP, there is only one obvious cold spell until present and that one is c. 3.8 Ka ago. Other measures suggest differently but one would think that plants resisted, meaning that the changes in climate were not so radical as we may perceive them.

Whatever the case, it's a too complex matter to make generalizations unless they are very careful.

Andrew Oh-Willeke said...

From the historical reecord, my guess is that temperature is only an indirect indicator of what really matters as a mechanism which is aridity. Drought and rainfall levels seem to be what is most important is actually driving big picture historical events (e.g. at 500 CE, 1200 BCE and 2100 BCE and Younger Dryas where we have historical or good archaeological data), and global temperature changes is probably just serving as a proxy for and driver of that. Droughts turn out to turn out to be highly corollated with each other over scales subcontinent sized and even larger, however, rather than being localized, outside some quirky interiors of mountain ranges (there are more statistically independent drought regions in the Rocky Mountains than in the rest of North America put together) and a few spots where unusual persistent ocean currents break up the general patterns (e.g. in parts of Berginia and a few places along the Baltic Sea/English Channel).

Along the same lines, I recently read, but haven't blogged, a paper that concluded that during the last ice age, the Great Basin in North America (e.g. Nevada and Utah) had prevailing winds from Southern California instead of Canada or over the Casade Mountain range as it does today, making the area full of lakes instead of a desert. The retreat of glaciers after the LGM opened up Canada to being repopulated by fauna but desertifaction in the Great Basin was almost as bad as a glacier in making the Great Basin uninhabitable. Temperature shifted, but it was the not simple shift in moisture levels that resulted that what really mattered.

I don't have direct data on that, but major historic periods of aridity in the Near East, South Asia and Europe seem to coincide reasonably well with periods when temperature rapidly gets cooler.

Maju said...

I don't think it's just a matter of aridity because in Europe there are almost no arid zones, even today. Instead cold and excess humidity may harm or limit the growth of many crops, most of which were adopted in semiarid and rather warm zones (Fertile Crescent).

Your comparisons with North America seem a bit off because most Europe is more like Virginia or New England than like Arizona or Colorado. Even the Mediterranean areas are more like the fertile areas of Central California. There's nothing like Arizona over here, unless you go to Africa... while the central prairies are more like Russia, right?

Certainly conditions in the Ice Age were quite different in Europe as well but we are not discussing the Ice Age, are we?