واکنش‌های فرهنگی جوامع پیش از تاریخ شمال ایران مرکزی به تغییرات اقلیمی هولوسن

در عصر هولوسن، با وجود افزایش پایداری اقلیمی نسبت به عصر آخرین یخبندان، اما تغییرات اقلیمی ناگهانی و شدیدی، به‌طور مکرّر و دوره‌ای، در مقیاس‌های جهانی و منطقه‌ای رخ داده‌اند؛ به‌طوری‌که بر فرهنگ و شیوه‌ی زندگی جوامع انسانی تاثیر گذاشته است. واکنش‌های انسانی موثر به این رویدادهای اقلیمی، همیشه از طریق سازگاری و یا مهاجرت ممکن بوده است. دوره‌های سرمایش و گرمایش که با پیامدهای طبیعی همچون: خشک‌سالی‌های شدید، توفان‌های گرد و غبار، امواج گرما و سرما، بارش‌های حدّی و وقوع سیل‌های سهمگین همراه بوده‌اند، به دلیل تخریب و کاهش محصولات کشاورزی، بروز قحطی، درگیری‌های اجتماعی، مهاجرت‌های گسترده، آوارگی، شیوع امراض کشنده و افزایش مرگ‌ومیر، بر روی سلامتی جسم و روان انسان‌ها نیز تاثیرات قابل‌ملاحظه‌ای داشته‌اند. این پژوهش در پی پاسخ‌گویی به این پرسش اصلی است که تغییرات اقلیمی ناگهانی و شدید هولوسن چگونه باعث تضعیف و اضمحلال فرهنگ‌های پیش‌از‌تاریخی منطقه‌ی فرهنگی شمال ایرانِ مرکزی شده‌اند؟ با توجه به این‌که مجموعه‌ی پیامدهای مذکور در جریان تغییر اقلیمی کنونی جهان (گرمایش زمین) در حال وقوع هستند و همچنین، از دوران تاریخی شواهد و مستنداتی در این‌خصوص، موجود است؛ این احتمال وجود دارد که فرهنگ‌های پیش‌از‌تاریخی نیز طی دوره‌های تغییر اقلیم به علل ذکر شده، دچار افول و فروپاشی شده‌ باشند. بنابراین، این پژوهش به ارتباط احتمالی فرهنگاقلیم در منطقه‌ی فرهنگی شمال ایرانِ مرکزی طی هزاره‌های هفتم تا پنجم قبل‌ازمیلاد می‌پردازد. بر طبق مطالعات دیرین‌اقلیم‌شناختی و اطلاعات باستان‌شناختی، در این مدت، وقوع دست‌کم چهار تغییر اقلیمی موثر محتمل است که می‌توانستند معیشت ساکنان این منطقه را دچار چالش و اختلال کنند. احتمالاً در بخش اعظمی از دوره‌ی فرهنگی سیلک i شرایط اقلیمی خشکی حاکم بوده است، ولی در اواخر این دوره و همچنین، مرحله‌ی چشمه‌علی قدیم، اقلیم نسبتاً معتدل و مرطوبی حاکم شده است. به‌نظر می‌رسد، بین حدود 5300-5000 ق.م.، اولین دوره‌ی شکوفایی فرهنگی در شمال ایرانِ مرکزی رخ داده باشد، و دومین دوره‌ی پیشرفت، مربوط به مرحله‌ی چشمه‌علی جدید، بین حدود 4700-4400 ق.م. بوده است. در اواخر هزاره‌ی پنجم قبل‌ازمیلاد یک افول فرهنگی و کاهش تعداد استقرارها در بیشتر نواحی این منطقه دیده می‌شود که احتمالاً در ارتباط با وقوع یک دوره‌ی خشک اقلیمی بوده است.

Cultural Responses of Prehistoric Societies in North Central Iran to Holocene Climate Change

In the Holocene, despite the increase in climate sustainability compared to the last glacial, Abrupt Climate Change (ACC) has occurred repeatedly and periodically on global and regional scales, which have affected the culture and lifestyle of human societies. Effective human responses to these climatic events have always been possible through adaptation or migration. The cooling/warming climatic periods that have come with natural consequences such as extreme weather events (severe droughts, dust storms, heat waves, cold spells, torrential rainfalls and floods), due to the destruction and reduction of crop production, famine, social conflicts, widespread migration, displacement, disease outbreaks and rising mortality rates have also had significant effects on the physical and mental health of humans. This research seeks to answer the main question of how Holocene Abrupt climate changes have led to the decline and collapse of prehistoric cultures in the cultural region of North Central Iran (NCI). Given that the set of consequences during the current global climate change (global warming) are taking place, and there is also evidence from a historical period in this regard, it is likely that prehistoric cultures, during climate change periods, have fallen for reasons mentioned. This research deals with the possible cultureclimate association in NCI during the 7th to 5th millennia B.C.s. According to the paleoclimate research and the archaeological information, at least 4 effective climate change (Cooling/Warming Drought) events are likely to be a challenge and disruption to the inhabitants of this region. Likely, most of the Sialk I period have been spent in a relatively unfavorable climate, but there was a mild and wet climate in the late period, as well as the early Cheshmeh Ali phase. It seems that the first cultural flourishing period in NCI has occurred between about 53005000 B.C., and the second progress period, related to the late Cheshmeh Ali period, between about 47004400 B.C.. By the late 5th millennium B.C., there has been a cultural decline and a decrease in the number of settlements in most areas of the region.Keywords: North Central Iran (NCI), Holocene, Abrupt Climate Change (ACC), Cultural Response, Sialk, Cheshmeh Ali. Introduction & MethodPaleoclimate studies have shown that climate change has occurred repeatedly in the past and will happen in the future. ACCs occur naturally; however, human intervention in the climate system can also increase in possibility of the events (Alley, 2003). The Holocene epoch began at about 9700 B.C., at the end of the 2.5 millionyearold Pleistocene Age. Although Holocene does not have extreme climatic anomalies similar to the last glacial, it has undergone ACCs that have affected human cultures. The prehistoric societies of Iran, especially NCI, have been affected by climate change and fluctuations since the beginning of the Holocene (Simultaneously with the advent of the Neolithic Age), and their lives have undergone natural disasters. The set of archaeological information and paleoclimate research (with highresolution) clearly show the link between Human Climate, but the reasons for the decline and collapse of ancient cultures and civilizations in Iran have not been studied so far. The main question of this research is about this issue. Given the consequences of the current climate change (global warming), which by creating extreme weather events (such as droughts, floods, heatwaves, cold spells, etc.), greatly affect the environmental conditions of the earth , and threaten the health of human, it is assumed that Probably, Holocene ACCs, with such events and effects, have disturbed the subsistence system of prehistoric societies. This research is based on two main aspects: First, the results of Paleoclimate studies of Holocene in Iran and neighboring regions, as well as Greenland Ice Sheet Project (GISP2) and North Atlantic; secondly, the findings of field surveys and archaeological excavations in NCI is related to the settlements belonging to the 7th to 5th millennium B.C. (Sialk I, Cheshmeh Ali and Sialk III13).  Paleoclimate ResearchAccording to recent studies in Iran (Neor Lake, Hamoun Lake and Jazmourian Playa), the 6200 B.C. cooling event has been associated with air dryness and increased wind and dust activity. Then, another period of drought was caused by an increase in temperature, with the highresolution diagram of Neor Lake showing a significant increase in dry conditions between 56005500 B.C.. Jazmourian Playa diagram also determines a dry period with a peak of 5500 B.C.. Given the low accuracy of Hamoun Lake diagram (with 2 radiocarbon samples), it is likely that the 5300 B.C. drought (with a 200year error) is actually related to the same time. The reason why Zeribar Lake research does not show the 6200 B.C. event is likely to be related to their low resolution. These studies are not capable of showing the climate change of 200300 years. Summarizing the paleoclimate studies carried out elsewhere in the world, it can be concluded with a relatively high confidence that there were periods of dryness from ca. 6500 to 5500 B.C. and from ca. 4400 to 4000, during which, there was a relatively shortlived fluctuation of humid. Probably drought fluctuations occurred during the favorable period of 54004400 B.C.. The onset of a long period of heat and a rise in humidity from the early 6th millennium B.C., which was observed in European and Canadian studies, and the occurrence of successive droughts in the millennium according to Arabia and Jordan studies, shows that probably warm periods in Europe have been accompanied by droughts in the region. Therefore, the occurrence of a dry period in the extreme warming event of Greenland is also possible in 49005000 B.C.. Archaeological EvidenceThe earliest evidence of the Neolithic settlements in NCI belongs to the Shahrud area. Therefore, it seems that the eastern part of NCI (western part of the central desert basin) is probably settled earlier than the western part (Salt Lake basin). The number of settlements across NCI in the first half of the 6th millennium B.C. is limited to 6 tepes. Apart from Eastern Tepe of Sange Chaxmaq (in Shahroud area), the architectural evidence related to the period, which indicates the sedentary, has not yet been obtained from the settlements of the Salt Lake basin. Since about 5400 B.C., due to climatic stability, an increase in humidity and annual rainfall, was provided agricultural conditions and permanent settlement in this region. Since then, the number of settlements has increased considerably. In most settlements of this phase, it was found the evidence of architectural and agricultural activities. The second phase of the flourishing of the Cheshmeh Ali period can be attributed to about 47004400 B.C. During this time, many villages in the region were built up and there was a significant increase in population. Paleoclimate studies indicate a relatively favorable climate for this period. However, another climatic change, which started from about 4400 B.C. and gradually increased, seems to have made life difficult for the people of the region, so that from about 4300 to 4000 B.C., we see a significant decline in the number of settlements. ConclusionThe cultural evolution of human societies in NCI during the 7th to 5th millennium B.C. has been significantly related to the climatic condition, and the occurrence of climate change has challenged the cultures due to the impact on human health and subsistence system.