Abrupt weakening of the summer monsoon in northwest India ~4100 yr ago

Yama Dixit et al., Godwin Laboratory for Palaeoclimate Research, Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, UK. First published online on 24 Feb. 2014; http://dx.doi.org/10.1130/G35236.1. OPEN ACCESS

In light of contemporary concerns for the future impact of climate change on humankind, the role of climate change in the collapse of ancient civilizations has become a topic of popular interest. One such time of widespread cultural transformation occurred about 4,000 years ago (4 ka), which marked the end of several early Bronze Age civilizations (Old Kingdom in Egypt, Akkadian Empire in Mesoptamia, Indus Civilization of India). One hypothesis to explain these cultural discontinuities is a "4.2 k.y. BP aridification event" [k.y. = thousand years; BP = before present]. Although a link between climate and the decline of Indus urbanism has been suggested by some and refuted by others, the issue remains unresolved mainly because of a lack of paleoclimate data from the actual region occupied by the Indus Civilization. We report a paleoclimatic record from Haryana, India, for an abrupt climate change at ~4.1 k.y. B.P. These data provide the first paleoclimate evidence for a weakening of the monsoon and shift toward drier climate on the plains of northwest India, supporting a possible role of climate in the transformation of the Indus civilization from an urbanized to village-based rural society.