4.2 kiloyear event
The 4.2 kiloyear BP aridification event was one of the most severe climatic events of the Holocene period in terms of impact on cultural upheaval. Starting in ≈2200 BC, it probably lasted the entire 22nd century BC. It is very likely to have caused the collapse of the Old Kingdom in Egypt as well as the Akkadian Empire in Mesopotamia. The drought may have also initiated southeastward habitat tracking within the Indus Valley Civilization.
A phase of intense aridity in ≈4.2 ka BP is well recorded across North Africa, the Middle East, the Red Sea, the Arabian peninsula, the Indian subcontinent, and midcontinental North America. Glaciers throughout the mountain ranges of western Canada advanced at about this time. Evidence has also been found in an Italian cave flowstone, the Kilimanjaro Ice sheet, and in Andean glacier ice. The onset of the aridification in Mesopotamia near 4100 B.P also coincided with a cooling event in the North Atlantic, known as Bond event 3. Despite this, evidence for the 4.2 kyr event in northern Europe is ambiguous, suggesting the origin and impact of this event is spatially complex. 
In ca. 2150 BC the Old Kingdom was hit by a series of exceptionally low Nile floods, which was instrumental in the sudden collapse of centralized government in ancient Egypt. Famines, social disorder, and fragmentation during a period of approximately 40 years were followed by a phase of rehabilitation and restoration of order in various provinces. Egypt was eventually reunified within a new paradigm of kingship. The process of recovery depended on capable provincial administrators, the deployment of the idea of justice, irrigation projects, and an administrative reform.
The aridification of Mesopotamia may have been related to the onset of cooler sea surface temperatures in the North Atlantic (Bond event 3), as analysis of the modern instrumental record shows that large (50%) interannual reductions in Mesopotamian water supply result when subpolar northwest Atlantic sea surface temperatures are anomalously cool. The headwaters of the Tigris and Euphrates Rivers are fed by elevation-induced capture of winter Mediterranean rainfall.
The Akkadian Empire—which in 2300 B.C. was the second civilization to subsume independent societies into a single state (the first being ancient Egypt at around 3100 BC) —was brought low by a wide-ranging, centuries-long drought. Archaeological evidence documents widespread abandonment of the agricultural plains of northern Mesopotamia and dramatic influxes of refugees into southern Mesopotamia around 2170 BC. A 180-km-long wall, the "Repeller of the Amorites," was built across central Mesopotamia to stem nomadic incursions to the south. Around 2150 BC, the Gutian people, who originally inhabited the Zagros Mountains, defeated the demoralized Akkadian army, took Akkad, and destroyed it around 2115 BC. Widespread agricultural change in the Near East is visible at the end of the third millennium BC.
Resettlement of the northern plains by smaller sedentary populations occurred near 1900 BC, three centuries after the collapse.
In the Persian Gulf region, there is a sudden change in settlement pattern, style of pottery and tombs at this time. The 22nd century BC drought marks the end of the Umm an-Nar Culture and the change to the Wadi Suq period.
The drought may have caused the collapse of Neolithic Cultures around Central China during the late third millennium BC. At the same time, the middle reaches of the Yellow River saw a series of extraordinary floods. In the Yishu River Basin, the flourishing Longshan culture was hit by a cooling that made the paddies shortfall in output or even no seeds were gathered. The scarcity in natural resource led to substantial decrease in population and subsequent drop in archaeological sites. About 4000 cal. yr BP the Longshan culture was displaced by the Yueshi culture which was relatively underdeveloped, simple, and unsophisticated.
- Climate change
- Timeline of environmental history
- Bond event
- 5.9 kiloyear event
- 8.2 kiloyear event
- Kaali crater
- deMenocal, Peter B. (2001). "Cultural Responses to Climate Change During the Late Holocene". Science 292 (5517): 667–673. Bibcode:2001Sci...292..667D. doi:10.1126/science.1059827. PMID 11303088.
- Gibbons, Ann (1993). "How the Akkadian Empire Was Hung Out to Dry". Science 261 (5124): 985. Bibcode:1993Sci...261..985G. doi:10.1126/science.261.5124.985. PMID 17739611.
- Staubwasser, M.; et al. (2003). "Climate change at the 4.2 ka BP termination of the Indus valley civilization and Holocene south Asian monsoon variability". Geophysical Research Letters 30 (8): 1425. Bibcode:2003GeoRL..30h...7S. doi:10.1029/2002GL016822.
- Gasse, Françoise; Van Campo, Elise (1994). "Abrupt post-glacial climate events in West Asia and North Africa monsoon domains". Earth and Planetary Science Letters 126 (4): 435–456. Bibcode:1994E&PSL.126..435G. doi:10.1016/0012-821X(94)90123-6.
- Bar-Matthews, Miryam; Ayalon, Avner; Kaufman, Aaron (1997). "Late Quaternary Paleoclimate in the Eastern Mediterranean Region from Stable Isotope Analysis of Speleothems at Soreq Cave, Israel". Quaternary Research 47 (2): 155–168. Bibcode:1997QuRes..47..155B. doi:10.1006/qres.1997.1883.
- Arz, Helge W.; et al. (2006). "A pronounced dry event recorded around 4.2 ka in brine sediments from the northern Red Sea". Quaternary Research 66 (3): 432–441. Bibcode:2006QuRes..66..432A. doi:10.1016/j.yqres.2006.05.006.
- Parker, Adrian G.; et al. (2006). "A record of Holocene climate change from lake geochemical analyses in southeastern Arabia". Quaternary Research 66 (3): 465–476. Bibcode:2006QuRes..66..465P. doi:10.1016/j.yqres.2006.07.001. Archived from the original on October 29, 2008.
- Booth, Robert K.; et al. (2005). "A severe centennial-scale drought in midcontinental North America 4200 years ago and apparent global linkages". The Holocene 15 (3): 321–328. doi:10.1191/0959683605hl825ft.
- Menounos, B.; et al. (2008). "Western Canadian glaciers advance in concert with climate change circa 4.2 ka". Geophysical Research Letters 35 (7): L07501. Bibcode:2008GeoRL..3507501M. doi:10.1029/2008GL033172.
- Drysdale, Russell; et al. (2005). "Late Holocene drought responsible for the collapse of Old World civilizations is recorded in an Italian cave flowstone". Geology 34 (2): 101–104. Bibcode:2006Geo....34..101D. doi:10.1130/G22103.1.
- Thompson,L.G; et al. (2002). "Kilimanjaro Ice Core Records Evidence of Holocene Climate Change in Tropical Africa". Science 298: 589.
- Davis, Mary E.; Thompson, Lonnie G. (2006). "An Andean ice-core record of a Middle Holocene mega-drought in North Africa and Asia". Annals of Glaciology 43: 34–41. Bibcode:2006AnGla..43...34D. doi:10.3189/172756406781812456. Archived from the original on July 20, 2011.
- Bond, G.; et al. (1997). "A Pervasive Millennial-Scale Cycle in North Atlantic Holocene and Glacial Climates". Science 278 (5341): 1257–1266. Bibcode:1997Sci...278.1257B. doi:10.1126/science.278.5341.1257.
- "Two examples of abrupt climate change". Lamont-Doherty Earth Observatory. Archived from the original on 2007-08-23.
- Roland, Thomas P; et al. (2014). Quaternary Science Reviews 83: 11-27. doi:10.1016/j.quascirev.2013.10.024 http://www.sciencedirect.com/science/article/pii/S0277379113004186
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- Stanley, Jean-Daniel; et al. (2003). "Nile flow failure at the end of the Old Kingdom, Egypt: Strontium isotopic and petrologic evidence". Geoarchaeology 18 (3): 395–402. doi:10.1002/gea.10065.
- Cullen, Heidi M.; deMenocal, Peter B. (2000). "North Atlantic influence on Tigris-Euphrates streamflow". International Journal of Climatology 20 (8): 853–863. Bibcode:2000IJCli..20..853C. doi:10.1002/1097-0088(20000630)20:8<853::AID-JOC497>3.0.CO;2-M.
- Kerr, Richard A. (1998). "Sea-Floor Dust Shows Drought Felled Akkadian Empire". Science 279 (5349): 325–326. Bibcode:1998Sci...279..325K. doi:10.1126/science.279.5349.325.
- Weiss, H; et al. (1993). "The Genesis and Collapse of Third Millennium North Mesopotamian Civilization". Science 261 (5124): 995–1004. Bibcode:1993Sci...261..995W. doi:10.1126/science.261.5124.995. PMID 17739617.
- Riehl, S. (2008). "Climate and agriculture in the ancient Near East: a synthesis of the archaeobotanical and stable carbon isotope evidence". Vegetation History and Archaeobotany 17 (1): 43–51. doi:10.1007/s00334-008-0156-8.
- Wu, Wenxiang; Liu, Tungsheng (2004). "Possible role of the "Holocene Event 3" on the collapse of Neolithic Cultures around the Central Plain of China". Quaternary International 117 (1): 153–166. Bibcode:2004QuInt.117..153W. doi:10.1016/S1040-6182(03)00125-3.
- Chun Chang Huang; et al. (2011). "Extraordinary floods related to the climatic event at 4200 a BP on the Qishuihe River, middle reaches of the Yellow River, China". Quaternary Science Reviews 30 (3–4): 460–468. Bibcode:2011QSRv...30..460H. doi:10.1016/j.quascirev.2010.12.007.
- Gao, Huazhong; Zhu, Cheng; Xu, Weifeng (2007). "Environmental change and cultural response around 4200 cal. yr BP in the Yishu River Basin, Shandong". Journal of Geographical Sciences 17 (3): 285–292. doi:10.1007/s11442-007-0285-5.
- Weiss, H., ed. (2012). Seven Generations Since the Fall of Akkad. Wiesbaden: Harrassowitz. ISBN 9783447068239.