By Andy May
This is an updated timeline of climatic events and human history for the last 18,000 years. The original timeline was posted in 2013. The updated full size (Ansi E size or 34×44 inches) Adobe Reader version 8 PDF can be downloaded here or by clicking on Figure 1. It prints pretty well on 11×17 inch paper and very well on 17×22 inch paper or larger. To see the timeline in full resolution or to print it, you must download it. It is not copyrighted, but please acknowledge the author if you use it.
References to the images and data are given in this essay as hyperlinks. I’ve done my best to verify the accuracy of the content by checking multiple sources. When references had different dates for the same event, I chose the most commonly cited date or the most prestigious source. All dates (except some in the modern era) are given as “BP” or before the year 2000 for simplicity, using 1950 (the radiocarbon zero) was too cumbersome.
The heart of the poster is the timeline of historical and climatic events. The Last Glacial Maximum (LGM) ended around 19,000 BP, the illustrations on the lower left of the poster illustrate what the world was like then. Much of the land area of the world was under ice or desert at the time and the exposed land had less precipitation than we do today. The history of civilization shows that cooler periods have less precipitation than warmer times. It seems counter-intuitive, but warm air has a higher water carrying capacity and this leads to more rain. For example, the Sahara is now becoming greener as Carbon Dioxide and air temperature go up. If there were any organized human civilizations during the last glacial period we have not found any evidence of it, other than some pottery in China, dated to 20,000 BP. At this time people lived in small communities of a few families and hunted for animals and edible natural vegetation. Domesticated animals (with the exception of dogs) and sedentary agriculture would not appear for another 6,000 to 7,000 years, around 13,000 BP.
Dogs were probably domesticated by man by 14,000 BP and perhaps more than 30,000 BP. The Natufians collected wild grains, fruits and vegetables and probably cultivated small gardens as early as 14,000 BP. But, this early, large scale organized farming was unlikely.
The central part of the poster shows two ice core records. The top chart is the most recent portion of the Vostok Antarctic ice core record. The entire Vostok 400,000 year record is shown in the upper left of the poster with the time scale reversed, this chart also includes the Carbon Dioxide concentration (in green) and the dust concentration (in red). The roughly 100,000 year Milankovitch cycles are very apparent in the Vostok record. These cycles are composed of a dominant period of 413,000 years and lesser periods that fall between 95,000 years and 136,000 years. The tilt of the Earth’s axis is what produces our seasons and it varies about 3° on a 41,000 year cycle. Finally, the Earth’s axis wobbles (the precession cycle) on a cycle that should be 25,772 years. Due to modifications in the precession cycle predominantly by the Moon, Jupiter and Saturn, the dominant precession period is roughly 19,000 years with a secondary peak periodicity of around 23,000 years. The 25,772 year cycle is in theory only.
The precession cycle determines when orbital perihelion occurs, or the time of year when the Earth is closest to the Sun (see Figure 2). Currently, perihelion occurs in January. This means that in the Northern Hemisphere we currently receive 6.5% more solar radiation (88 Watts/m2) in the middle of winter than we do in the summer. This makes the seasonal variation in air temperature less than normal which reduces extreme weather. It is the opposite in the Southern Hemisphere. Thus, now their winters are colder than normal and the summers hotter, increasing their weather extremes. When this flips, as it will approximately 10,000 years from now, the North will have extreme summers and extreme winters and the Southern Hemisphere will be quieter. The last Northern Hemisphere maximum effect was between 12,000 BP and 10,000 BP around the end of the Younger Dryas cold period. The Holocene Thermal Optimum (roughly 9,500 BP to 5,000 BP) occurred as the Earth moved from the lower position in Figure 2 to the left position. The long cooling period from then to the present day occurred as the Earth moved from the left position to its present position with perihelion in January. The dates in the figure are approximate.
Figure 2 (click to see at source)
It is interesting that Tarling, 2010, concludes that
“Solar radiation is thus the driving force for terrestrial climatic change during the last 1-2 Myr, as suggested by Milankovitch (1941) and supported by Hays et al. (1976) but it is the planetary gravitational influences on the Sun itself that causes the dominant 100 Kyr periodicity in the Earth’s climate during the last 1-2 Myr. “
Changing the ellipticity of the Earth’s orbit changes the minimum and maximum amounts of solar radiation reaching the Earth. Changing the time of year that perihelion occurs through the precession cycle doesn’t change TSI (total solar irradiance) but it does change the extremes of summer and winter. This so-called “latitudinal change” in insolation can have a huge effect on hemispherical climate, some believe that the total radiation reaching the Earth at 65°N latitude is critical to the growth and decay of glacial ice sheets.
In the plot of the full Vostok ice core record in the upper left, you might just be able to see that the middle graph (Carbon Dioxide concentration, green line) slightly lags the temperature by about 800 years on average. This suggests that the changes in temperature might cause the Carbon Dioxide changes rather than the other way around. The airborne dust concentration (red line) increases when the world is cooler because in the cool periods it is also dryer. One of the primary reasons colder periods are a problem is that they are accompanied by drought.
Next to the complete Vostok record is a reconstruction of the temperature record for the last 600 million years. Temperatures, today, are lower than they have been for over 250,000,000 years according to this data. The bottom large chart is the actual central Greenland temperature, calculated by the Greenland Ice Sheet Project.
More recently, both the Vostok record and the Central Greenland record by Alley, et al, show a decreasing temperature trend since the Minoan Warm Period about 3400 BP. The trend is more subtle in the Antarctic record than in the Greenland record. Shorter term changes in the temperature records do not correlate well. But, warming from the Younger Dryas, a long flat warm period until about 3400 BP (Holocene Thermal Optimum) and then cooling to the present day is clear in both records. The start and end dates for the Holocene Thermal Optimum marked on the timeline are my best guess. There are no agreed dates. Many start and end dates are seen in the literature, for example here, here, here, here, and here. Long term trends that correlate between the Arctic and Antarctic are likely due to external events, such as changes in total solar irradiance (TSI) or certain orbital changes.
Just below the Central Greenland ice core record some of the “Bond” cooling events are noted. The Bond cooling events average 1,470 years +-500 years apart and some are more dramatic than others. The 8.2, 5.9, 4.2 and 2.8 Kiloyear events were major events, with dramatic cooling and they disrupted civilization around the world. Some major climate events, such as the 3177 BP climatic event that ended the Bronze Age in the Mediterranean, are slightly off of the Bond Event, but appear related. Timing of climate changes is fuzzy. Some researchers believe that the Little Ice Age was a Bond event.
During the last glaciation, the Greenland ice core record shows climatic change events called Dansgaard-Oeschger events or “D-O events.” These are very rapid warming events, followed by slower cooling, that occur in a cycle of roughly 1,470 years +- 12%. These events are probably the glacial period equivalent of the Bond events. They have a similar timing but the climate effect is different or, maybe, the events are the same but the record shows warming easier during a glaciation. Because the timing of these events stays about the same during glaciations and interglacials, solar variability is the probable cause. Internal oscillations due to ocean circulation patterns, etc. are unlikely to stay stable in their period as the Earth goes from the glacial state to the interglacial state.
In modern times, cooling is more noticeable than warming. Cooling and droughts are simply more disruptive than warming. This is particularly true in the Sahara. About 10,000 years ago the perihelion (Earth closest to the Sun) occurred in the Northern Hemisphere summer and the summers were warmer and more humid than we see today. This was the beginning of the aforementioned Holocene Thermal Optimum. During this period the Sahara became a savannah. This is called the African Humid Period (AHP). The AHP ended between 5900 to 4000 BP when the Sahara turned back into a desert as the climate began to cool. Towards the end of the period the progressive desiccation of the region led to widespread migrations and the abandonment of many North African villages. This exodus was coincident with the rise of sedentary life and the pharaonic culture along the Nile River.
Moving just to the right of the Last Glacial Maximum map on the lower left of the poster, you can see an artist’s (Robert Rohde) rendition of the rise in global eustatic sea level after the glaciers started melting. The data used to make the graph is from numerous sources listed in this web site. The earliest well documented evidence of human civilization dates to the middle of the most rapid rise in sea level in this period, roughly 12,000 BP at Gobekli Tepe. From 11,500 BP to 11,000 BP sea level rose an astonishing 28 meters (Meltwater Pulse 1B) or 6 cm/year on average. This is over 18 feet per 100 years! According to the University Of Colorado Sea Level Research Group, the current rate of sea level rise is about 13 inches per 100 years or 3.3 mm per year, much less dramatic.
Earliest evidence of civilization
Gobekli Tepe is near Urfa in southern Turkey. This site is roughly 300 meters by 300 meters and contains intricately carved stones. It predates Stonehenge and the earliest Egyptian pyramids by 7,400 years. Construction at Gobekli Tepe began during the Younger Dryas “Big Freeze.” The Younger Dryas was a sudden and short lived (geologically speaking, it lasted over 1,000 years) return of very cold and dry weather, similar to the cold that existed in the Last Glacial Maximum. The Gobekli Tepe site is composed of multiple circular stone monuments. The tallest pillars in these monuments are 16 feet high and weigh over seven tons. The rings are 65 feet across and probably have religious significance. Construction of the site appears to have occurred during a hiatus in the sea level rise between 11,000 and 12,000 BP. Then the site was mysteriously and deliberately buried around 10,000 BP, during a period of rapid sea level rise. The reasons for its construction and later burial are not known. But, one can probably safely speculate that it was buried to protect and preserve it. This task was accomplished, it is remarkably well preserved.
It is interesting that the wild wheat that grows in the area around Gobekli Tepe is a close relative, genetically, to modern domestic wheat. One can speculate that the early religious fervor that caused Gobekli Tepe to be built, may have inspired farming. After all, the construction of the religious monument would have required a number of people to live in one spot for a long time and they could not migrate in search of food.
The earliest evidence of large scale organized agriculture is seen in the Levant region of the Middle East in present day Syria and Israel. This occurred about 13,000 BP. There are some preserved pottery fragments from 13,000 BP in Japan and perhaps even older. Others have reported that pottery existed in China 20,000 BP. However, there is no evidence that the Japanese or Chinese pottery came from sedentary farmers. It is possible that rice was farmed to some extent in China 13,900 BP. It disappears from the record during the Younger Dryas cold period and reappears after 10,000 BP. The type of rice we eat today was originally farmed in China’s Yangtze Valley around 8,200 BP.
Between 13,000 and 14,000 BP a lot seemed to happen at various archaeological sites in the Middle East. Buildings improved, villages got larger and were more advanced. But, they were mostly abandoned as temperatures cooled during the Younger Dryas. This cool period was very dry. According to Steven Mithen few advances in human civilization happened in the period, people were just trying to survive. This is evident as the late Natufians, who lived during the Younger Dryas period, were in much poorer health (fewer teeth, often with caries) and smaller than the earlier Natufians from the Late Glacial Interstadial period. Further, the animal bones in their garbage dumps held bones of smaller animals than the earlier period.
When the Natufians began to build small villages the climate in the Levant was ideal, with abundant precipitation and lots of wild grain to harvest. The Younger Dryas cold and dry weather caused some of the Natufians to give up village life. Others began to cultivate the grain more intensely by watering it, saving the best seed for the next crop and so on. They also invented better farming tools and silos for grain storage. We know this from archaeological digs in the area around Jericho, Israel.
The Middle Eastern Pre-Pottery Neolithic B (PPNB) culture began around 9,500 BP. It is a significant period in the history of human civilization because at this time man became more dependent upon domesticated animals and organized large scale (beyond single family) farming. It has also been found that the earliest Indian agriculture appears to have started in the Indus valley and in Pakistan around 10,000 BP. As noted by Anil Gupta, climate influenced the onset of man’s agricultural revolution.
As large scale agriculture took hold and the climate improved, man began building larger settlements in the Levant. Rectangular buildings appeared and larger more organized communities. Plaster and pottery are first seen in Middle East at this time, although they had existed for many thousands of years in China and Japan. It has been suggested by Ryan and Pittman that many people from many cultures gathered around the modern day Black Sea (which was a fresh water lake at the time) during the Younger Dryas since it was a reliable source of water. They exchanged technology and when the climate warmed and precipitation increased they returned to their historic homes bringing what they had learned with them. Thus, the new PPNB technology may have begun as people migrated back to the Levant from the Black Sea area. Other researchers believe that pottery, new domesticated crops and animal technology spread to the Levant from modern day Iran. Either way it seems likely that the new technology typical of the PPNB came from the East.
The PPNB ended with the 8,200 year BP event or Bond event 5, this was another sudden cold period that affected civilization and caused massive migrations of people in search of food and water. This period was undoubtedly another period of technology exchange between cultures. Over a period of 20 years, temperatures cooled roughly 3.3°C in Greenland. It was not as severe as the Younger Dryas, but still significant. It lasted 200 to 400 years. The fact that the Black Sea became connected to the Mediterranean at about this time is not in dispute. But exactly when (8400 BP or 7600 BP or in several episodes between these dates) is a subject of debate. If the Black Sea was filled catastrophically, as described by Ryan and Pitman; it may have created the Great Flood legend. For example, Noah’s Flood or the older Gilgamesh story.
During the PPNB period evidence of relatively large settlements is found. Catalhoyuk, a city of 8,000, existed near present day Cumra in Konya Province, Turkey. This is a large, relatively modern “city” that existed 9,400 BP.
Jericho, in the biblical kingdom of Judea, is often considered the world’s oldest continually occupied city, but Aleppo and Damascus, Syria may be older. Remains of early settlements, villages of 500 people or so, in Jericho have been dated to 11,600 BP. The first woven cloth known was found in Nahal Hemar cave in Israel. It is around 10,000 years old, it was found with bone shuttles that were used to weave the cloth. The cloth was a type of linen and not cotton, cotton was developed later in India.
Simple writing appears in Jiahu, China around 9,200 years ago and in Tartaria, Romania before 7400 years ago. Whether either is true writing or not is a subject of debate, the symbols on the Tartaria tablets have not been translated and may be a “picture” story. The Chinese writing has some symbols that are similar to modern Chinese writing. Because Chinese writing is not phonetic, it is hard to tell where “picture writing” stops and true modern writing begins.
True writing has been discovered from 5,500 BP in Syria in the Uruk period. By this time very large cities existed and the city of Uruk had over 50,000 people in it. The Uruk period was characterized by large scale urbanization, irrigation, roads and canals. It may have begun as early as 6,200 BP. The end of the Sumer Uruk period and the sacking of Uruk by Sargon of Akkad formed the Akkadian Empire, which may have been the world’s first multinational empire. The end of the Akkadian empire 100 to 200 years later, coincides with the third Bond event roughly 4,174 BP. Some researchers believe that climate change, cooler temperatures and more arid conditions, played a role in the collapse of the Akkadian empire. The 4.2 Kiloyear Bond event is highlighted in yellow on the timeline.
5.9 Kiloyear Bond Event
About 5,900 BP the Sahara became a desert. This is the 5.9 Kiloyear event or Bond event 4. This cooling event ended the Ubaid Empire and caused a huge migration of people from the Sahara region in search of food and water. Many migrated to the Nile Valley in Egypt, in order to be close to a reliable water supply. Claussen, et al., 1999 has suggested that this drought was caused by a severe cooling event that occurred at the same time. He concludes that warmer temperatures cause more evaporation and more precipitation. The Sahara never recovers from this event. But, since the drought forces people into river valleys, larger cities are built and societies become more complex.
Following the end of the 5.9 Kiloyear event and the end of the Holocene Thermal Optimum the earliest Egyptian pyramids are built, Stonehenge is constructed in present day England and the first large cities appear in India. The earliest Mayan cities appear around 3,900 BP. Recently, some evidence has been uncovered that India may have had a large city as long ago as 9,500 BP. If this is true it would rival Catalhoyuk in age.
4.2 Kiloyear Bond Event
The 4.2 Kiloyear event was a very cool period in the Arctic (Bond Event 3) and it caused a severe drought in the Middle East. This probably caused the sudden collapse of the Egyptian Old Kingdom, famines and social disorder. Similar disruptions occurred in the Akkadian Empire as noted above, the Indus Valley and in China. It is interesting that the Monsoons in India, which are critical to farming in the Indus Valley, stopped between 4,200 BP and 4,000 BP.
Around 3,200 BP, the great Bronze Age civilizations in the Middle East collapsed or were disrupted. These included the Minoan, Mycenaean, Hittite and the Egyptian New Kingdom. This sudden collapse was probably caused by “climatological cataclysms that affected the entire eastern Mediterranean” in the words of Itamar Singer, as described by Eric Cline in “1177 B.C.” One could say this drought and famine was of Biblical proportions as the Exodus of Hebrews and the 10 famous plagues of Egypt took place at this time. As Cline notes in the afterword of “1177 B.C.” there was a century [actually 100 to 400 years] long drought at this time and it caused famine, upheaval, rebellion and war. The onset of this drought coincides with a sudden and extended cooling period in the Central Greenland ice core data. In general, most large scale droughts in the last 18,000 years appear to be associated with cooling in the Arctic. This drought and cold period marks the end of the Minoan Warm Period.
Greek Dark Age
After the collapse of the Bronze Age cultures the Mediterranean entered into a period called the Greek Dark Ages. This is a hiatus in the development of Middle Eastern civilization and not much happens until after 2,800 BP. The first phonetic alphabet was probably created just before this period by the Phoenicians. Little is seen of writing or the alphabet during the Dark Age, but it flowers in several forms as the Roman Warm Period unfolds. This alphabet was used, with alterations, by the Greeks and the Romans. It was the beginning of modern writing in the West.
Brandon Drake (2012) describes this period well:
“A sharp increase in Northern Hemisphere temperatures preceded the collapse of [the Minoan] Palatial centers, a sharp decrease occurred during their abandonment. Mediterranean Sea surface temperatures cooled rapidly during the Late Bronze Age, limiting freshwater flux into the atmosphere and thus reducing precipitation over land. These climatic changes could have affected Palatial centers that were dependent upon high levels of agricultural productivity. Declines in agricultural production would have made higher-density populations in Palatial centers unsustainable. The ‘Greek Dark Ages’ that followed occurred during prolonged arid conditions that lasted until the Roman Warm Period.”
This is the time of the Xia Dynasty in China, 4,070 to 3,600 BP. This part of Chinese history is poorly documented, but canals and crop irrigation existed at the time. It is followed by the Shang Dynasty which existed from 3,600 to about 3,050 BP. True Chinese writing began during the Shang Dynasty. It is the first dynasty with a written record. They also had an accurate calendar. The Shang Dynasty utilized bronze extensively. There is some speculation that both volcanism and climate change hurried the end of the Shang Dynasty, but no firm evidence has been found to support this. More likely the final Shang King, who was quite corrupt and very unpopular, was overthrown with the help of the Zhou provincial army.
More seems to have happened on the Indian subcontinent during this period. Little is known about the Indus Valley kingdoms and city-states prior to 3,200 BP. But after this, much happened during the rise of the Kuru Kingdom (3,200 to 2,850 BP), which marked the beginning of the Iron Age in India. Iron artifacts and furnaces in India have been dated to between 3,800 and 3,000 BP. The earliest iron artifacts in the Middle East are some Egyptian iron beads that have been dated to 5,200 BP, but these appear to have been made from an iron meteorite. Actual iron smelting in the Middle East probably did not begin until 4,000 BP, so it probably began there at roughly the same time as in India.
Mayan settlements begin to appear about 4,700 BP in Belize. The first well established Mayan cities (or large settlements) are dated to 3,800 BP in Soconusco, Mexico. This is near the beginning of the cold period in the Iron Age. However, evidence of a true Mayan civilization does not appear until 2,900 BP. The first written Maya history dates to 2,350 BP. This is also the time of the first large scale cities and significant intellectual and artistic development. The rise of the Mayan civilization is roughly the same time as the rise of Rome in the Mediterranean. The Mayan Golden Age was from 1700 BP to 1200 BP. Mayan civilization suddenly collapsed around 1100 BP during a cold and very dry period in Central America. DeMenocal provides evidence of a 200 year long severe drought between 800 AD and 1000 AD in the Mexican Yucatan Peninsula. The Mayan collapses are a few hundred years out of sync with those in the Mediterranean, suggesting that big climatic changes did not happen at the same time in North America as in the Middle East.
Roman Warm Period
Once we enter the Roman Warm Period, roughly 2,400 BP, robust civilizations have developed in the Americas, around the Mediterranean, China and India. By the time Alexander invaded India (2,326 BP) they had a very advanced civilization. Major cities existed in India before 4,100 BP, but history is not well established until around 2,400 BP. This warm period truly marks the beginning of modern civilization, written records document all major events over most of the world since this time. Writings at this time suggest that temperatures during the Roman Warm Period were comparable to temperatures today.
European Dark Age
Normally the end of the Roman Warm Period is given as around 450 AD (1,550 BP) and the Central Greenland temperature cooled by almost 2°C from 1,500 BP to 1,200 BP, the height of the Dark Ages in Europe. It is interesting that the worst megadrought in the California and Nevada area lasted from 832 AD to 1074 AD, right at the end of the Dark Ages according to a recent study. Desprat, et al, 2003, identifies a very cold period from 450-950 AD.
Medieval Warm Period
The Medieval Warm Period is normally given as 950 AD to 1250 AD or 1050 to 750 BP. In the beginning of this period, temperatures in Central Greenland rose by almost 2°C in a little over 200 years. This has been fairly well documented as a worldwide event. It is uncertain what the global average temperature was during the period and whether the world as a whole was warmer than now. But, certainly in areas where we have records, such as Greenland, the UK, and in China, temperatures were comparable to today and in some cases warmer.
Little Ice Age
The Little Ice Age was not a true ice age, but the cooler period after the end of the Medieval Warm Period. It is generally considered to have started by 1350 AD and it ended by 1850 AD. In Central Greenland, temperatures drop about 1.5°C from 964 BP to 597 BP (1036-1403 AD). It was not cold over the entire period, but the Little Ice Age saw many periods that were very cold, from the famous year without a summer (1816) to the great famine of 1315, New York Harbor completely froze over in 1780, the Norse colonies in Greenland starved and were abandoned in the 1300’s. A recent study notes several droughts in Europe during the Little Ice Age. These occurred in AD 1540, 1590, 1626 and 1719, plus an especially intense drought from 1437-1473 AD. Colder times are the worst times.
Modern Warm Period
The Modern Warm Period starts around 1850 AD, which is also the time when people began systematically recording and collecting surface air temperature data from around the world. These temperatures were spotty in the beginning, but by the middle of the 20th Century a fairly good worldwide temperature database was developing. Finally, in 1979, satellites were launched that could give us a reasonably accurate and complete lower Troposphere temperature record over nearly the entire globe. A discussion of the accuracy of the satellite temperature measurements can be found here. In the poster, on the lower right, both datasets are shown. The satellite dataset is from UAH MSU and the surface temperature data shown is from the HADCrut dataset. The satellite temperatures show warming of 0.35°C from 1979 to the present. This is not particularly significant by historical standards.
The period from 1850 to 1979 is not well documented globally and the records used to construct the global surface temperature average have been significantly edited, thus raising doubts about their accuracy. They show a warming of just under 1°C in a period of 165 years. This is not unusual by historical standards. Over this length of time warming of over 13°C was seen at the end of the Younger Dryas in the Central Greenland ice core. In the same core, the beginning of the Holocene Thermal Optimum saw a warming of 5°C in less than 800 years.
Correlation is not causation, but many, if not all, of man’s worst times since the last glacial maximum occur during colder and dryer periods. Often these times were made worse by warfare as in the Greek Dark Ages, the sacking of Rome, the collapse of the Akkadian Empire, etc. The colder and more arid climate could have been part of the cause of the wars. We go to war when we are starving and thirsty. More importantly, I was unable to find evidence of a crisis that was due to warming.
Given that man-made Carbon Dioxide is a very recent phenomenon, the radical climatic changes before 200 years ago cannot be attributed to man’s influence. They must be natural. The recent warming of 0.85°C from 1880 to 2012 is pretty small compared to other temperature changes in the Holocene. It is clear from history that natural forces can cause significant climate changes. It is also clear that droughts are usually associated with colder periods, not warmer periods. Some climate changes are probably due to variations in the Earth’s orbit, but some might be due to variations in TSI (total solar irradiance) or other solar influences. How much is due to nature and how much is due to man is unknown.
Much of the last 18,000 years is characterized by more rapid sea-level rise than we see today. The current rise of sea level is very slow relative to the past and we are arguably more adaptable due to modern technology.
In the words of Professor Steven Mithen (page 507)
“The next century of human-made global warming is predicted to be far less extreme than that which occurred at 9600 BC [11,600 BP]. At the end of the Younger Dryas, mean global temperature had risen by 7°C in fifty years, whereas the predicted rise for the next hundred years is less than 3°C. The end of the last ice age led to a 120 meter increase in sea level, whereas that predicted for the next fifty years is a paltry 32 centimeters at most,…”