Caves, Civilization & Climate: The Stories Earth Left Behind by Dr. Annapureddy Phanindra Reddy.

Understanding future hydroclimatic risks requires long-term perspectives on how monsoon systems have varied under different climate states and how societies responded to these changes. This talk presents high-resolution speleothem-based reconstructions of Indian Summer Monsoon variability spanning the last two millennia and the late Holocene, with particular emphasis on extreme wet and dry phases and their forcing mechanisms. Near-annually to multidecadally resolved oxygen isotope records from peninsular India reveal distinct monsoon regimes during the Dark Age Cold Period, Medieval Warm Period, and Little Ice Age, modulated by shifts in the Intertropical Convergence Zone, ENSO variability, volcanic forcing, and North Atlantic influences. Spectral analyses of irregular paleoclimate datasets further highlight coherent monsoon variability across interannual to centennial timescales and demonstrate teleconnections between the Indian monsoon, Pacific, and North Atlantic climate systems. The talk also explores the relationship between hydroclimatic extremes and human societies. Integrated analyses of speleothem records, archaeological settlement patterns, and historical data from South India show how consecutive wet and dry climatic stresses around 2.9-2.8 ka led to settlement abandonment in vulnerable low-lying regions, while simultaneously driving adaptive innovations such as water-harvesting and tank-based irrigation systems in interior regions. These findings underscore how past societies responded to climatic thresholds through migration, technological adaptation, and landscape modification. Finally, ongoing and unpublished work on coastal South India and glacial–interglacial hydroclimate variability will be briefly introduced, highlighting the role of U–Th geochronology and speleothems in bridging paleoclimate science, archaeology, and climate-resilient water management. The talk emphasizes why understanding Earths climatic past is essential for addressing future challenges related to water security and societal sustainability.