Detection and societal impact of global hydroclimate extremes in the late Holocene

Abstract:

Understanding the frequency, causes, and societal impacts of extreme climate events is vital for navigating the contemporary challenge of global climate change. We report on multiple extreme climate events which occurred in the 1^st millennium BC. We identify 2 events occurring at ~2700 and 2400 BP (~750 and 450 BC) which were the most significant global climate anomalies of the 1^st millennium BC based on z-score analysis of over 120 speleothem δ¹⁸O records. Using the NOAA paleoclimate database and the SISAL database, we detected these events across 6 continents in multiple archives, including speleothems, tree rings, and lake and bog sediments. Among the 120 speleothems which have 1^st millennium BC δ¹⁸O records, we found the events 24 times at levels exceeding 2 standard deviations, and 80 times at levels exceeding 1 standard deviation. We discuss the events’ extremity, geospatial distribution, and possible cause(s), such as solar forcing. We further investigate the response of ancient civilizations to these extreme climate events, including the 2650 BP migration of Frisian farming societies in the modern-day Netherlands and the 2400 BP collapse of the Neo-Assyrian Empire in the modern-day Middle East.