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The rise and fall of ancient societies have been attributed to rapid climate change events. One of the most discussed of these is the 4.2kya event, a period of increased aridity and cooling posited as the cause of societal changes across the globe, including the collapse of the Akkadian Empire in Mesopotamia. Studies seeking to correlate social and climatic changes around the 4.2kya event have tended to focus either on highly localized analyses of specific sites or surveys or more synthetic overviews at pan-continental scales, and temporally on the event and its aftermath. Here we take an empirical approach at a large spatial scale to investigate trends in population and settlement organization across the entirety of Northern Fertile Crescent (Northern Mesopotamia and the Northern Levant) from 6,000 to 3,000 cal BP. We use Summed Probability Distributions of radiocarbon dates and data from eighteen archaeological surveys as proxies for population, and a dataset of all settlements over ten hectares in size as a proxy for the degree of urbanization. The goal is to examine the spatial and temporal impact of the 4.2kya event and to contextualize it within longer term patterns of settlement. We find that negative trends are visible during the event horizon in all three proxies. However, these occur against a long-term trend of increased population and urbanization supported through unsustainable overshoot and the exploitation of a drier zone with increased risk of crop failure. We argue that the 4.2kya event occurred during a period of unprecedented urban and rural growth which may have been unsustainable even without an exogenous climate forcing.

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During the Late Chalcolithic and Early Bronze Age (c. 6500-4000 BP), the Fertile Crescent in Southwest Asia saw the earliest development of cities anywhere in the world. Climate and environmental factors are generally considered to be significant in these changes because in pre-industrial societies they directly relate to food production and security. The emergence of cities also coincides with a decoupling of settlement and climate trends, suggesting urbanism may have enhanced the adaptive capacity of societies to withstand changing climatic conditions. Urban forms followed a variety of different trajectories, with a much more sporadic and episodic history in the dry farming plains of the North and West of the study region compared to the stable build-up in the irrigated South. Although models dealing with urban growth have emphasized the differential access to agrarian resources as a key driver in promoting hierarchical social systems, climate has rarely been explicitly discussed. In contrast, so-called "collapse" events brought about by extreme, but short-lived, climate changes such as droughts have been blamed for declines in urban and rural populations, social complexity, political systems, and entire empires. However, the extent to which these "collapses" are visible in the archeological record, let alone how far they can be attributed to climate changes, is a matter of intense debate. The archeological and historical record, the variegated environmental conditions, and the deep time perspective on complexity available, make the Fertile Crescent an ideal laboratory for assessing causal links between urban formations and climate fluctuations.

This study presents the results of the first remote sensing survey of hollow ways in Southern Mesopotamia between Baghdad and the Persian Gulf, primarily using the imagery in Google Earth. For archaeologists, hollow ways are important trace fossils of past human movement that inform about how people travelled in the past and what considerations were important to them as they moved through the landscape. In this study, remotely sensed hollow ways were ground-truthed and dated by association with both palaeochannels and known archaeological sites. Contextual and morphological evidence of the hollow ways indicate that they are likely the archaeological manifestation of ethnographically attested "water channels" formed through the dense reeds of marshlands in southern Iraq, not formed by traction overland like other known hollow ways. The map itself documents the first known hollow ways preserved underwater and one of the best-preserved landscapes of past human movement in the Near East.