Over the course of the project we designed and populated a database for the archaeological settlement data, which now contains about 70,000 sites and is being used by scholars around the world. We also produced a second population proxy dataset of over 11,000 radiocarbon dates. Comparing these two datasets means we can get a better grasp of past population fluctuations.
We have examined the collapse of societies due to the Rapid Climate Change phase known as the 4.2kya event. This was a period of drought around 4,200 years ago, which some have argued resulted in the collapse of the Akkadian Empire, as well as urban abandonment and population decline. We used our settlement and radiocarbon dataset to see if this was really the case, and looked at the periods before and afterwards to try to make sense of the ‘collapse’. We showed that the real anomaly was not the collapse, but the period of unprecedented urban growth which preceded these declines. We used our climate simulations to look at the 4.2kya event in more detail (Cookson et al. 2019) and show that the event may not have had as significant an impact as some have claimed. We also produced an open access set of rainfall data for the region across the whole Holocene.
On the long term, we investigated the relationship between climate and population changes across the last 10,000 years. For the first half of the Holocene dryer periods cause population decline. This is what we would expect in a relatively arid environment. However, during the second half of the Holocene this relationship gets much weaker, and population is decoupled from climate fluctuations. This coincides with the emergence of more complex social organisations, including cities, states and empires. More complex societies have a different relationship with climate – they are better able to ride out periods of aridity.
We showed that the decoupling outlined above does not correlate with major changes in the types or proportions of plants and animals that past communities were eating. This suggests the resilience we see in the past was not due to changes in what was being eaten, but rather in how food was produced and distributed. Urban sites were reliant on rural sites for some animal products. It seems that one of the ways in which resilience was achieved was through larger and more integrated organisational systems. Our recent research has also looked at fuel use. During periods of high population and urbanisation we found good evidence for the use of dung as fuel, which may indicate the exhaustion of local wood supplies.
In the last phase of the project we began to tie all of this together to understand how population, subsistence strategies and social organisation affected land use and sustainability. This included publishing the first ever comprehensive land use map for Southwest Asia, and investigating how land use impacts the longevity of urban formations and subsistence practices. We have teamed up with other projects to look at the role of inequality and warfare in relation to climate. These new collaborations demonstrate the legacy of CLaSS - the datasets collected will be of use to both the project team and the wider discipline for decades to come, helping us to answer questions which we may not even have thought of yet!
