From the University of Cambridge, it makes you wonder how climate could just go and change abruptly on its own back then, with CO2 levels being in the “safe zone” and all that:
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Decline of Bronze Age ‘megacities’ linked to climate change
Climate change may have contributed to the decline of a city-dwelling civilization in Pakistan and India 4,100 years ago, according to new research
Scientists from the University of Cambridge have demonstrated that an abrupt weakening of the summer monsoon affected northwest India 4,100 years ago. The resulting drought coincided with the beginning of the decline of the metropolis-building Indus Civilisation, which spanned present-day Pakistan and India, suggesting that climate change could be why many of the major cities of the civilisation were abandoned.
The research, reported online on 25 February, 2014, in the journal Geology, involved the collection of snail shells preserved in the sediments of an ancient lake bed. By analysing the oxygen isotopes in the shells, the scientists were able to tell how much rain fell in the lake where the snails lived thousands of years ago.
The results shed light on a mystery surrounding why the major cities of the Indus Civilisation (also known as the Harappan Civilisation, after Harappa, one of the five cities) were abandoned. Climate change had been suggested as a possible reason for this transformation before but, until now, there has been no direct evidence for climate change in the region where Indus settlements were located.
Moreover, the finding now links the decline of the Indus cities to a documented global scale climate event and its impact on the Old Kingdom in Egypt, the Early Bronze Age civilisations of Greece and Crete, and the Akkadian Empire in Mesopotamia, whose decline has previously been linked to abrupt climate change.
“We think that we now have a really strong indication that a major climate event occurred in the area where a large number of Indus settlements were situated,” said Professor David Hodell, from Cambridge’s Department of Earth Sciences. “Taken together with other evidence from Meghalaya in northeast India, Oman and the Arabian Sea, our results provide strong evidence for a widespread weakening of the Indian summer monsoon across large parts of India 4,100 years ago.”
Hodell together with University of Cambridge archaeologist Dr Cameron Petrie and Gates scholar Dr Yama Dixit collected Melanoides tuberculata snail shells from the sediments of the ancient lake Kotla Dahar in Haryana, India. “As today, the major source of water into the lake throughout the Holocene is likely to have been the summer monsoon,” said Dixit. “But we have observed that there was an abrupt change, when the amount of evaporation from the lake exceeded the rainfall – indicative of a drought.”
At this time large parts of modern Pakistan and much of western India was home to South Asia’s great Bronze Age urban society. As Petrie explained: “The major cities of the Indus civilisation flourished in the mid-late 3rd and early 2nd millennium BC. Large proportions of the population lived in villages, but many people also lived in ‘megacities’ that were 80 hectares or more in size – roughly the size of 100 football pitches. They engaged in elaborate crafts, extensive local trade and long-ranging trade with regions as far away as the modern-day Middle East. But, by the mid 2nd millennium BC, all of the great urban centres had dramatically reduced in size or been abandoned.”
Many possible causes have been suggested, including the claim that major glacier-fed rivers changed their course, dramatically affecting the water supply and the reliant agriculture. It has also been suggested that an increasing population level caused problems, there was invasion and conflict, or that climate change caused a drought that large cities could not withstand long-term.
“We know that there was a clear shift away from large populations living in megacities,” said Petrie. “But precisely what happened to the Indus Civilisation has remained a mystery. It is unlikely that there was a single cause, but a climate change event would have induced a whole host of knock-on effects.
“We have lacked well-dated local climate data, as well as dates for when perennial water flowed and stopped in a number of now abandoned river channels, and an understanding of the spatial and temporal relationships between settlements and their environmental contexts. A lot of the archaeological debate has really been well-argued speculation.”
The new data, collected with funding from the Natural Environment Research Council, show a decreased summer monsoon rainfall at the same time that archaeological records and radiocarbon dates suggest the beginning of the Indus de-urbanisation. From 6,500 to 5,800 years ago, a deep fresh-water lake existed at Kotla Dahar. The deep lake transformed to a shallow lake after 5,800 years ago, indicating a weakening of the Indian summer monsoon. But an abrupt monsoon weakening occurred 4,100 years ago for 200 years and the lake became ephemeral after this time.
Until now, the suggestion that climate change might have had an impact on the Indus Civilisation was based on data showing a lessening of the monsoon in Oman and the Arabian Sea, which are both located at a considerable distance from Indus Civilisation settlements and at least partly affected by different weather systems.
Hodell and Dixit used isotope geochemical analysis of shells as a proxy for tracing the climate history of the region. Oxygen exists in two forms – the lighter 16O and a heavier 18O variant. When water evaporates from a closed lake (one that is fed by rainfall and rivers but has no outflow), molecules containing the lighter isotope evaporate at a faster rate than those containing the heavier isotopes; at times of drought, when the evaporation exceeds rainfall, there is a net increase in the ratio of 18O to 16O of the water. Organisms living in the lake record this ratio when they incorporate oxygen into the calcium carbonate (CaCO3) of their shells, and can therefore be used, in conjunction with radiocarbon dating, to reconstruct the climate of the region thousands of years ago.
Speculating on the effect lessening rainfall would have had on the Indus Civilisation, Petrie said: “Archaeological records suggest they were masters of many trades. They used elaborate techniques to produce a range of extremely impressive craft products using materials like steatite, carnelian and gold, and this material was widely distributed within South Asia, but also internationally. Each city had substantial fortification walls, civic amenities, craft workshops and possibly also palaces. Houses were arranged on wide main streets and narrow alleyways, and many had their own wells and drainage systems. Water was clearly an integral part of urban planning, and was also essential for supporting the agricultural base.
At around the time we see the evidence for climatic change, archaeologists have found evidence of previously maintained streets start to fill with rubbish, over time there is a reduced sophistication in the crafts they used, the script that had been used for several centuries disappears and there were changes in the location of settlements, suggesting some degree of demographic shift.”
“We estimate that the climate event lasted about 200 years before recovering to the previous conditions, which we still see today, and we believe that the civilisation somehow had to cope with this prolonged period of drought,” said Hodell.
The new research is part of a wider joint project led by the University of Cambridge and Banaras Hindu University in India, which has been funded by the British Council UK-India Education and Research Initiative to investigate the archaeology, river systems and climate of north-west India using a combination of archaeology and geoscience. The multidisciplinary project hopes to provide new understanding of the relationships between humans and their environment, and also involves researchers at Imperial College London, the University of Oxford, the Indian Institute of Technology Kanpur and the Uttar Pradesh State Archaeology Department.
“It is essential to understand the link between human settlement, water resources and landscape in antiquity, and this research is an important step in that direction,” explained Petrie. “We hope that this will hold lessons for us as we seek to find means of dealing with climate change in our own and future generations.”
Reply to johndo ==> There are many professionals who disagree rather sharply with Jared Diamond’s hypotheses to the point where they put some of his “findings” in parentheses.
Regardless, it doesn’t take a drought of too many years duration to suppress the general well-being of a large urban population….the more recent — pre-Roman times — of Palestine are a good example, in which the population moves more-or-less enmass to areas better watered for periods of years until the drought breaks.
Even if some climate change in the region is identified that correlates with the decline in the civilization, how does that rise to any level of causation? Seems to me there would have to be some other indicator to show that climate was more likely than say, attempting socialized IndusCare, or inflating their currency and going bankrupt, or slashing their defense budget and getting invaded, or over-regulating themselves, or over taxing themselves, or institutionalized corruption and cronyism, etc.
The dating of the destruction or abandonment of these Indian cities coincides with the time when the Hindu calendar changed from 360 days per annum to the present 365.25 days per annum. Whatever the event was which caused this calendar change, it was a global rather than a local event as all the calendars around the world (Mayan, Chinese, Hindu, Greek, Hebrew & Egyptian) all changed from a 360 day year to 365.25.
Civilizations have come and gone.
Sometimes it was disease, sometimes it was a particularly inept ruler, sometimes it was war, sometimes it was loss of agricultural productivity (salinity build-up), sometimes it was climate change, sometimes it was a meandering river changing course, sometimes it was new technology in another region, sometimes it was new trade networks being developed bypassing them, sometimes it was a growth in another near-by region out-competing them for people, sometimes it was just bad luck.
And, as we seen in the last two decades and in the last few days in Ukraine, sometimes the 90% of time effective in replacing a government million man march in the central square fells the central government and nothing replaced it.
Hog trough research. A one-celled animal could reason that climate change would severely affect larger communities and mega cities in the past. Some things are just common sense and we don’t need to spend money researching it. So I call it like I see it. Hog trough research.
Has there been an observed “abrupt weakening of the summer monsoon affected northwest India”? That’s what the second paragraph says.
Egypt in the 3rd millennium BC (4000-5000 years ago) also recorded a warm period, which coincides, at least as to its end, with the collapse of the Indus civiliastion.
The change lingered for 200 years!
An interesting graph. Minimum of about 260 ppm at roughly 6000 to 5500 BC – about the time of the flooding of the Black Sea. Gradual growth to about 273 ppm, when the Egyptian Empire flourished. Continued growth to about 279-280 ppm at about 0 AD. These surely were “pre-industrial” times? If so, where did all the CO2 come from? Growth again to a maximum of about 285 ppm in about AD 800, then a decline to about 278 ppm in about AD 1350 – AD 1400. Where did all that CO2 go?
Did Man really cause the growth of CO2 from 260 ppm to 285 ppm? What are the error bands on this curve – and was the sampling really done at intervals of about 110 years, as counting the changes in slope of the curve would make it appear?
Running those beloved “climate models” back, it should be possible to, using the “known” rate of temperature increase in the last 100 years with the increase of CO2, to retrodict (opposite of predict) the temperatures in those distance periods, and compare with the temperatures as deciphered from Ice cores and other methods.
Oh great, another hockey stick….
All the warmth is from the stupid….it burns….
We all know about Bond Events (~1500 year major shifts in climate) and Dansgaard-Oescher (sp) Events and we all know that climate change usually is one of the major elements in civilizations’ decline/destruction (this idea includes invaders, emigration, and declination due to lack of resources). The climate change usually is rapid and the causes are complex. The one word that is most common is DROUGHT. Lesser causes are earthquakes and volcanoes, or plate tectonics, impact events, or a large population of warriors bent on conquest with their superior weaponry maybe plague, but that seems to an effect rather than a cause.
There is no reason today for drought to be the cause of any decline. Seventy percent of our world, our beloved Earth, is comprised of water on the surface. Technology has brought us relatively inexpensive ways to desalinate; we know how to build efficient pipelines; we know something about the problems of diverting water and the problems of irrigation. (Soon –maybe 300 years into the future — we might need new technology to melt advancing glaciers/ice sheets.) Given this wisdom, hard won through the ages, humans no longer must go silent and passive into that dry night. I wish all societies — the “wacky one” in California first and foremost — would end the focus on CO2 and turn to drought as a problem to be solved. No humans ever should suffer from drought again.
The simultaneous decline of the Han and Roman civilizations, the cyclic pump of the steppes flinging their nomads at the beaurocratic civilizations; the seeming antiphase between the Eurasian dark ages and the Mayan apogee, and Easter Island, Nazca, and Anasazi flowering.
All very interesting, but the only definitive message is that civilizations have repeatedly foundered on climate. All civilizations have their shamans. Many humans and animals have been sacrificed to no avail. Our own shamans have accused a certain trace gas of witchcraft…
I realize we are in a hellfire hurry to revise history to fit the greenhouse gas paradigm, but there still is the strong possibility that this was a period of low solar activity and increased volcanic/meteoric activity, resulting in plummeting temps, and badly interrupted trade which would cause economic devastation. One or two disrupted cities (think Solini and 6 cities of Crete, etc) which are trading hubs would reduce the demand for the wares of an accomplished civilization like the Indus Valley people. If you add to this problems with local agriculture, a prosperous period could come to an abrupt end.
And as is usually the case, ancient cultures without any texts and with undeciphered languages are a favorite target for progressive scientists and clever comparative mythologists; pick up a shell, a shard, and prophesy the past. Just use language that sounds like Sherlock Holmes breaking a case, and confirm the new paradigm. Bada bing, bada boom.
Can I ask these people what sort of Climate Record snail shells at the bottom of the Aral Sea (what’s left of it) are telling them
rgbatduke says:
February 26, 2014 at 2:35 pm
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The sst anomalies have changed considerably from last year in the waters that surround India. Many coastal cities from Abu Dhabi eastward across the Indian Ocean are below average in temps. The waters off of northwestern Africa and up into the north Atlantic have also switched from warm to -1.5C in the course of one year. I have been wondering lately if this might be indicative of an upcoming cooling of the Gulf Stream. Australia is also slowly being surrounded by cool anomalies that started moving in that direction over the last 4 months. Same thing, I wondered if that might lead to a cooling in Australia, and that appears to now be the case. The much talked about hot spot of Melbourne is showing 66F. All last week and the upcoming 5 days are also well below average. The entire northern Indian Ocean and over to southern China has switched to cold anomalies in a complete turn around from last year at this time.
ezra abrams says:
February 26, 2014 at 3:08 pm
I am undecided on climate change, and think this is a silly post
Your logic is, drastic climate change occurs naturally, therefore *adding* manmade change is not worse ???
it is just a basic logic fail: if the system is metastable, or variable, adding energy or heat or whatever is going to increase the variablilty, which by this very post caused really bad things to happen…not sure as skeptics that is the message you want out there, but , hey it is your blog
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Ezra:
1) Do you have a clue as to any climate that man has changed?
2) And whether or not change is bad or good?
3) Is the world’s climate now “optimum” ?
4) Is cooling going to be good or bad?
5) What if it continues to cool…, what then?
Apply some logic when thinking of answers to these questions.
Jimbo says:
February 26, 2014 at 5:57 pm
Has there been an observed “abrupt weakening of the summer monsoon affected northwest India”? That’s what the second paragraph says.
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I thought that the Indian monsoons had been out of phase over the last two years or so. I remember that last year there was concern about the timing of the monsoon.
This has to be a case of connections, that is, not just one thing changed in one place but a whole lot of things had to change. These seasonal changes occur when the jet stream shifts over the Himalayan mountains – to the north thereof or to the south**. If these things changed as described, there would we changes in other places as well.
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** http://www.scientificbangladesh.com/en/news/jet-stream-effect-on-the-climate-of-bangladesh#.Uw7cPuNLWXs
ezra abrams says: adding energy or heat or whatever is going to increase the variablilty
This seems confused. Energy & heat with the word “adding” out front suggest an equivalence and the “whatever” is suggestive of nothing other than confusion.
Next, the general argument is that if the atmosphere and oceans warm there will be a decrease in “variability” insofar as weather/storms result from contrasts between tropical and polar air. The latter is supposed to warm more than the former so the contrast will be less.
Ezra and others of the “undecided” variety are advised to go to Jo Nova’s site and near the top left find a link to The Skeptic’s Handbook. This is some years old now but still is a good place to start.
The reference is about Sahara turning green 12.000 years ago and dried up 3500 years agp.
http://knowledge.allianz.com/environment/climate_change/?621/green-sahara-how-climate-change-transformed-the-desert
“About 12,000 years ago, slight changes in the Earth’s orbit around the sun brought the northern hemisphere into the limelight. Summers became warmer as more solar radiation hit the lands north of the Equator. Solar ‘insolation’ levels were up to 8 percent higher than today.
With insolation driving monsoonal climates like a huge heat engine, rainfall increased. One climate model estimated that the 8 percent increase in radiation in North Africa resulted in a 40 percent increase in precipitation.
Today, the West African monsoon avoids the Sahara, passing further south. But as the Earth’s orbit changed the rains intensified and shifted five degrees north. Slowly, the desert started to bloom. By 10,000 years ago, the Sahara had turned into a savanna-like ecosystem with trees and grass and grazing animals.
It wasn’t just down to the sun. The so-called ‘African Humid Period’ was also reinforced by newly grown vegetation that absorbed the sun’s energy, which strengthened the monsoon system, rather than reflecting the sun’s energy back into space.
Increased surface ocean temperatures of about 0.4 degrees Celsius also supported a stronger monsoon, as well as numerous permanent lakes such as the 330,000 square kilometer Lake MegaChad, four times the size of Lake Superior. Now, Lake Chad is a pitiful shadow of its former glory.”
And:
“Peter deMenocal, an expert at Columbia University’s Lamont-Doherty Earth Observatory, argues that it started and ended very abruptly—within a few decades to centuries—triggered largely by summer insolation crossing the threshold of 470 Watts per meter squared, 4.2 percent higher than today.
He speculates that there could be an insolation tipping point “whereby subtropical African climate flips abruptly between humid and arid”.”
Not sure if anyone has mentioned it, but Indians were Australia’s first boat people.
http://www.abc.net.au/pm/content/2013/s3670159.htm
I also receive the monsoons in my part of the world. Being out of phase and variable once in a while is not uncommon.
Two years is the weather and not the climate. Four years out of phase would not have been sufficient to destroy those civilizations. In fact being out of phase occasionally is ‘normal’.
You maybe referring to Menon et. al.
See the take on from NTZ. Take a look at my comment too.
http://notrickszone.com/2013/06/21/menon-et-al-publish-latest-crystal-ball-forecast-for-indian-monsoons-claiming-it-is-a-robust-indicator/
“Interannual Variations of Indian Summer Monsoon
The All-India area-weighted mean summer monsoon rainfall, based on a homogeneous rainfall data set of 306 raingauges in India, developed by the Indian Institute of Tropical Meteorology”
http://www.tropmet.res.in/~kolli/mol/Monsoon/Historical/air.html