AGS-PRF: Indo-Pacific Hydrology in a Warming World: Modeled and Observed Responses to Climate Forcings from the Little Ice Age to Present

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The future of global rainfall patterns under 21st century climate change scenarios is highly uncertain, due in part to major uncertainties in how tropical Indo-Pacific climate modes (e.g., the El Niño-Southern Oscillation) respond to greenhouse gas (GHG) forcing. Climate models project significant changes in the global hydrological cycle in response to GHG forcing, yet the short instrumental record of precipitation precludes a robust assessment of potential anthropogenic trends. Paleoclimate proxy data and model simulations can be useful in this endeavor by helping to illuminate the Indo-Pacific response to GHGs and other climate forcings in the recent geologic past. During the past 500 years, a combination of changes in solar irradiance, volcanism, and atmospheric GHGs drove global climate out of the "Little Ice Age" (LIA; 1450-1750 C.E.) and into the modern era of warming. Hydroclimate proxy records, many based on oxygen and hydrogen isotopes in precipitation, surface waters, and seawater, document enormous Indo-Pacific hydrological changes from the LIA to present. While the causes of these anomalies are poorly understood, new developments in both "isotope-equipped" climate modeling and paleoclimate data synthesis provide new, promising tools for understanding these changes by directly comparing paleoclimate data with model output.In this project, the postdoctoral research fellow will investigate the response of the Indo-Pacific hydrological cycle to climate forcings during the past 500 years using an integrated paleoclimate modeling and data synthesis framework. Existing "single-forcing" simulations of Last Millennium (850-2000 C.E.) climate with the fully-coupled Community Earth System Model will be used to force new simulations with an isotope-equipped atmospheric model, enabling a characterization of volcanic, solar, and GHG-induced changes in the Indo-Pacific hydrological cycle and associated water isotopic signatures since 1500 C.E. Simultaneously, a synthesis of hydrologic and water isotopic proxy data from the past 500 years will be performed to isolate robust hydrologic and isotopic patterns in the Indo-Pacific since the LIA. Emerging "best-practice" techniques for paleoclimate data synthesis and model comparison will be used to characterize the response of the Indo-Pacific hydrological cycle to individual and combined climate forcings. Results will advance our understanding of how natural and anthropogenic climate change impact the tropical hydrological cycle -- a key source of uncertainty in future projections