GEOSCIENCES IN MODERN SOCIETY Example – Climate Change and the Egyptian Empire
The introduction of Milankovitch Cycles impacting cyclic migration of the ITCZ and the consequent results of the migra- tion permit the discussion of causes of climate change and the impacts of such migrations on human habitability and empire development in areas outside the regions where glacial condi- tions inhibited development of non-hunter-gatherer human populations.
Figure 3 – Locations of the First Major Empires. Source:
https://sites.google.com/a/
roundrockisd.org/coach-rosse-
world-history/home/unit-1-1/lesson-3-formation-of-government Comments:
The above diagram illustrates a controlling factor in the development of ancient empires, the availability of water from streams that originate in remote areas but that flow through arid or semi-arid climates providing reliable moisture for crops. That location tends to insulate them from major problems with drought and permits continuity of cultural growth.
Divergent
Convergent ITCZ
Figure 5 – Historical migration of the ITCZ over the past 10,000 years and impacts on climatic zones in Africa. (David Wright, 2017)
The above diagram illustrates the migration of the ITCZ over the past 10,000 years and the consequent impacts of that migration on African climate zones. This migration was grad- ual and is cyclic, recurring every 22,000 years with minor fluc- tuations during each cycle due to regional fluctuations caused by oceanic cycles such as (EL Nino Southern Oscillation), Pacific Decadal Oscillation, North Atlantic Oscillation and oth- ers. It also illustrates the variability of rainfall with potential modifications of human habitability for the area we now know as the Sahara Desert.
Divergent
Due to secondary variability in short- term high pressure air masses which can expand or contract the edges of the ITCZ, this example can be repeated for any area within 40 to 45° north or south of the equator modifying rainfall charac- ter and quantity within that migration range on a yearly/decadal cycle as well as a solar-controlled, 22,000-year cyclic basis.
Beginning about 7,500 BP, the ITCZ shifted southward, reducing the fre- quency of monsoonal events and induc- ing eastward migration of the surviving communities toward the only reliable water source, the Nile River, which not impacted by the ITCZ shift since its headwaters were in the mountains south of the developing Egyptian Empire.
Figure 4 – Intertropical Convergence Zone and Climate Control. (Modified from Sonjia Leyva, Copyright (2018)
Comments:
This diagram permits introduction of atmospheric physics into the discussion by illustrating the presence of the ITCZ (Intertropical Convergence Zone) which controls the location of precipitation and climate zones. It also can be used to identify and describe monsoonal climatic regimes and allow discussion of such zones as controls on the viability of human cultural development in the areas impacted by monsoons, (India, Central America, Southeast Asia, Africa, etc.) in both modern and pre-modern cultures.
The presence of a consistent and predictable water supply allowed the re-concentrated population to gradually
evolve from a hunter-gatherer society to a more sophisticated heavily agricultural society. Population expanded and avail- ability of excess labor permitted specialization in areas which were supportive of technical advancement and provided a base for development of the Egyptian Empire. Subsequent periodic fluctuations in the ITCZ in conjunction with competition from adjacent empires resulted in the rise and fall of the various segments of the Egyptian Empire we know today as the Old, Middle and New Empires.
Continued on p.44
www.aipg.org Apr.May.Jun 2021 • TPG 41
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