Environment, ecology, landscape and subsistence 2. Mid-Holocene environMental and cliMatic cHange in iran Mathew Jones, Morteza Djamali, Lora Stevens, Vanessa Heyvaert, Hajar Askari, Dariush Noorollahi and Lloyd Weeks Introduction Past climate and environmental change is of long- standing and fundamental interest to archaeologists. a number of recent syntheses have examined the role of climate change and environmental modiication in understanding the rise, spread, and in some instances collapse of early complex societies across south- west asia (e.g. Staubwasser and Weiss 2006). in an iranian context, various scholars have highlighted the role of human-environment interactions in the expansion of neolithic communities, in the growth and decline of chalcolithic pastoral societies, and for the development of the first urban societies (e.g. Hole 1994, 1998; Henricksen 1985; Miller and Kimiae 2006). Here we review proxy evidence of climatic and environmental conditions to provide an independent background to societal development in iran during the fourth millennium Bc. to put the fourth millennium Bc (i.e. 5000 to 6000 years BP) into a long-term context, we look at the evidence for climate and environmental change from the early to mid-Holocene (c. 10000 to 2000 years BP). antecedent conditions are particularly useful in framing the magnitude and rapidity of climatic changes. as continuous records of change are relatively scarce from iran itself and those that are available have limited spatial extent, we also draw on records from wider south-west asia. the fourth millennium Bc sits at a key transition in global climate from an early Holocene “optimum”, when northern hemisphere temperatures and indian ocean monsoon (ioM) rainfall were highest c. 8 kyr BP (e.g. chen et al. 2008), to a late Holocene climate state (Fig. 2.1). this transition saw a southward shift in the mean position of the inter-tropical convergence Zone (itcZ) during boreal summer and a weakening of the indian monsoon, among other changes worldwide (Wanner et al. 2008). globally, the nature of this transition appears to have varied between proxy record location, with some recording a gradual change in climate that follows the trend of waning summer insolation forcing (Fig. 2.1), e.g. the precipitation record of southern oman speleothems (Fleitmann et al. 2003). other sites experienced an apparently sudden and dramatic shift in conditions, e.g. the Saharan dust record marking the end of the african Humid Period at 5500 yr BP (deMenocal et al. 2000). the type of transition (gradual or abrupt) is intrinsically linked to the characteristics of the archive, the climate proxy, and its location, as well as the nature of the climate change itself. For example, the later, more abrupt change in Saharan dust may relect the sensitivity of the speciic core location to a gradually southward-moving climate front, rather than a sudden change for an entire region, a hypothesis supported by the south- and eastward migration of people out of sub-tropical africa at this time (Kuper and Kröpelin 2006). the timing of abrupt mid-Holocene shifts also varies spatially. Whereas the increase in Saharan dust occurred at around 5.5 kyr BP, the major decrease in ioM rainfall recorded in the northern oman speleothem records occurred at around 6.3 kyr BP (Fleitmann et al. 2007). in addition to longer millennial-scale shifts, there are a number of short-term climatic events, which may have had an impact across diferent parts of the region. during the fourth millennium Bc, a pronounced event at 5.2 kyr BP, clearly evident in the Soreq speleothem record (Bar Mathews et al. 1997), has been potentially linked to drought in other regional records, including those from iran (Staubwasser and Weiss 2006). the timing and nature of these climate shifts have potentially important implications for societies both