Back in the mid-2000s, I was part of a team of scientists led by Adrian Parker at Oxford Brookes University, who were looking at past
climatic changes in the Arabian Peninsula. Adrian would go off to the United Arab Emirates and come back with a whole lot of samples which we then spent months analysing. The samples came from successive layers of materials that had been laid down in dried up lake beds. Basically the deeper the sample the older it was. I specialised in the plant microfossils known as phytoliths but helped out in some other aspects as well. The fact that there are dried up lake beds there to analyse immediately says something- in the past there were lakes in what is now a very arid land!
When all the geochemical analyses were done we gathered the data and wrote up the paper for the journal, Quaternary Research, in 2006. I won’t go into all of the details here, but what we found was evidence that there were precipitation minima 8200, 5000 and 4200 years ago, dry periods which could happen very abruptly. Strangely, or so it might seem, all three of these minima corresponded with climatic changes known as Bond events in the North Atlantic. These appear to be related to periodic events where large numbers of icebergs moving into the
Atlantic had effects on the Gulf Stream as they melted. They are still not well understood. You might ask how events in the North Atlantic can influence the climate in Arabia? It seems this happens through what are known as teleconnective effects where basically the climate in one region affects that in the neighbouring region, which affects the next region and so on. We noted that the very abrupt, intense dry period around 4200 years ago had been seen before across the Middle East and North Africa, even being detected as far as Pakistan. It was thought to have caused the collapse of the Akkadian Empire, and the end of the urban Harrapan civilization in Pakistan.
Our paper was generally well-received and formed part of a growing body of data on past climate change in Arabia. I moved on to other topics and the strange event that happened 4200 years ago and apparently wiped out previous civilizations receded into my memory until last month. I still keep an eye on this literature, and I spotted a very interesting paper by Carolin et al in PNAS. Their work was on stalagmites in Iran, and they were able to create a very high-resolution record and to detect increased dust influx from Mesopotamia from 4260 years ago. They knew about our previous work and cited
it as background to their paper. Just at the moment the idea of a civilisation collapsing due to climate change seems newsworthy, and the Carolin et al paper was picked up by Newsweek who ran a big article on it. That is well worth reading.
So we had a very rapid climate change event which apparently at least partly caused the collapse of the Akkadian Empire some 4200 years ago. We do not know for sure what caused the sudden drought, but it appears to be connected to changes in circulation in the Atlantic Ocean. Whatever, the cause looks to be “natural”, and nothing to do with human activity. At the time the total world population of humans has been estimated at 28 million. I have two conclusions:
Firstly, with a world population of approaching 7.7 billion in 2019 a very abrupt climate change event could be far more disastrous than what happened to the Akkadian Empire. We look to be in the middle of such an event, already over 1°C above the pre-industrial temperature. And this event is human-induced, mainly due to our burning of fossil fuels.
Secondly, the next time a sceptical friend says, “the climate has always changed”, you can reply, “yes, and look what happened to the Akkadian Empire.”
Dr Martin J. Hodson (JRI Operations Director)
Map of the Akkadian Empire
Jolle at Catalan Wikipedia [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons
Akkadian Cylinder Seal with King or God and Vanquished Lion
Walters Art Museum [Public domain, CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)]