خلاصة:
During the third millennium BC, while most parts of Iran were in cultural decline, the civilizations of the southeast were experiencing a period of prosperity. It was only at the end of this millennium that the stress of the 4.2 ka BP dry event (2200-1900 BCE) was able to lead to the collapse of the Bronze Age civilizations. The Akkadian dynasty, the old Egyptian kingdom, and the Indus Valley civilization were also affected by this great drought. The climatic event was probably due to a decrease in solar energy and, as a result, the cooling of the North Atlantic waters and a drop of westerlies and monsoons related rainfalls. The climate of southeast Iran, which is mainly dominated by monsoons, had been absorbing relatively good humidity for most of the third millennium BCE, but with the occurrence of the 4.2 ka BP event, witnessed a significant drop in rainfall, which led to the gradual decline of civilization in this region. Furthermore, the beginning of the cultural decline of this region from around 2200 BCE could be due to the severe economic recession and the instability of the political system of Mesopotamia due to the pressures of drought, famine, migration, and war that affected the economic system throughout the region. Since then, luxury goods consumers have likely lost their purchasing power due to economic weakness. Besides, the occurrence of severe droughts at the peak of the Mesopotamian population growth no longer allowed the country to export grain. Therefore, the regular customers of Kerman region products decreased sharply, and as a result, these workshops went bankrupt. This article, while reconstructing the climate of southeast Iran in the third millennium BCE based on paleoclimate research of Iran and neighboring regions, tries to explain the direct and indirect effects of climate on the cultural evolution of human societies and the history of ancient civilizations of the Middle East. It seems that unbalanced population growth and socio-economic complexity of societies have been the main reasons for the inability of civilizations of the third millennium BCE to adapt to climate change.