Citation: Hu, H.-M.; Michel, V.; Valensi, P.; Mii, H.-S.; Starnini, E.; Zunino, M.; Shen, C.-C. Stalagmite-Inferred Climate in the Western Mediterranean during the Roman Warm Period. Climate 2022, 10, 93. https://doi.org/10.3390/ cli10070093 Academic Editor: Salvatore Magazù Received: 2 June 2022 Accepted: 22 June 2022 Published: 23 June 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). climate Article Stalagmite-Inferred Climate in the Western Mediterranean during the Roman Warm Period Hsun-Ming Hu 1,2 ,Véronique Michel 3,4 , Patricia Valensi 5,6 , Horng-Sheng Mii 7 , Elisabetta Starnini 8,9 , Marta Zunino 10 and Chuan-Chou Shen 1,2, * 1 High-Precision Mass Spectrometry and Environment Change Laboratory (HISPEC), Department of Geosciences, National Taiwan University, Taipei 10617, Taiwan; hsunming.hu@gmail.com 2 Research Center for Future Earth, National Taiwan University, Taipei 10617, Taiwan 3 CEPAM—Cultures et Environnements Préhistoire, Antiquité, Moyen Âge, CNRS, Université Côte d’Azur, 06300 Nice, France; veronique.michel@cepam.cnrs.fr 4 Laboratoire Géoazur, OCA, CNRS, IRD, Université Côte d’Azur, 06560 Valbonne, France 5 HNHP, UMR 7194, MNHN, CNRS, UPMC, UPVD, Sorbonne Universités, 75013 Paris, France; pvalensi06@gmail.com 6 Musée de Préhistoire, 06690 Tourrette-Levens, France 7 Department of Earth Sciences, National Taiwan Normal University, Taipei 11677, Taiwan; t44006@ntnu.edu.tw 8 Department of Civilizations and Forms of Knowledge, University of Pisa, Via dei Mille 19, 56126 Pisa, Italy; elisabetta.starnini@unipi.it 9 Archaeological Superintendency of Liguria, Via Balbi 10, 16126 Genova, Italy 10 Toirano Cave, Piazzale D. Maineri 1, 17055 Toirano, Italy; martazunino@tiscali.it * Correspondence: river@ntu.edu.tw Abstract: The circum-Mediterranean region is the cradle of ancient civilizations that had their roots in the Holocene. Climate change has been considered a key element that contributed to their rise or fall. The Roman Warm Period (RWP), 200 B.C. to 400 A.D., was the warmest period in Europe during the last two thousand years. Hydroclimatic change at the end of the RWP has been suggested as a possible influence on the stability of the Roman political regime and the eventual collapse of the Roman Empire in 476 A.D. A lack of precise proxy records hampers our understanding of hydroclimatic variability over the RWP. Here we present a stalagmite-based climate record from 550 ± 10 B.C. to 950 ± 7 A.D. (2σ) from northern Italy, which reveals a climatic trend of warming and increased humidity throughout the RWP. By comparison with other proxy records in Europe and the circum-Mediterranean region, we argue that the warm, humid climate in southern Europe could be linked to the multi-centennial warming of the Mediterranean Sea. Our record further suggests a century-long rapid drying trend from the early-4th to early-5th century, followed by a 100-year-long drought event, which could have influenced the fall of the Roman Empire. Keywords: Roman warm period; Mediterranean; Roman empire; stalagmite; climate change 1. Introduction Climate change has widely affected society, ecosystems, and agriculture [1]. Today, the circum-Mediterranean region, with over 500 million inhabitants, has been threatened by severe drought and extreme climate, including floods, heat waves, and cold spells [2–4]. Such climate changes have been proposed as significant factors in the stability of ancient civilizations [5–7]. For example, the well-known 4.2-k dry event (4.2 thousand years ago) may have induced the collapse of the Old Kingdom and Akkadian Empire [8,9]. Increasing climate variability at ~0 A.D. has been suggested as a trigger of the Celtic Expansion and Roman Conquest [6]. Human societies have been forced to adapt to severe and unstable hydroclimatic conditions, with consequent climate-driven famine, warfare, diseases and/or political collapse [10]. Complete and detailed paleoclimate records provide a means to investigate human responses to past climate change. Climate 2022, 10, 93. https://doi.org/10.3390/cli10070093 https://www.mdpi.com/journal/climate