Collaborative Research: Reconstructing Holocene glacier lengths through time to address climate model-data disagreements

The ongoing retreat of glaciers worldwide provides a striking visual consequence of modern climate change. How glaciers responded to past climate changes forms the conceptual basis for evaluating their future behavior, which in turn provides critical information for people who depend on the water supply from glaciers for irrigation, consumption, and energy usage. This research is generating new geologic data that document glacier and climate changes in the past ~12,000 across North and South America. The project is evaluating the new geologic data using novel statistical, glaciological, and climatological models to determine why glaciers in the study region may have responded differently to past climate shifts. Outcomes of this work provide valuable information for understanding past glacier changes which will lead to a better ability to assess future changes of those same glaciers. This project provides scientific training and mentoring for multiple undergraduate and graduate students. International collaborations are also being strengthened through university partnerships. Public outreach occurring as part of this project includes curriculum building with K-12 partners, participation in statewide science festivals, and undergraduate mentoring that is engaging with underrepresented students recruited through college level programs. Global mean temperatures from the early to late Holocene have warmed by ~0.5°C based on a recent model-data assimilation. Glaciers are sensitive recorders of such climate change; however, glaciers across North America and at several locations in the Tropics expanded from the early to late Holocene, at odds with this latest climate reconstruction. This research is examining Holocene alpine glacier conditions at six locations extending from Alaska to southern Patagonia to address this apparent discrepancy. Through a combination of bedrock exposure dating and statistical/glaciological modeling, the project is relating the chronology of glacier length changes to past climate conditions to address unresolved questions regarding global, hemispheric, and regional climate changes. The objectives of this research are threefold: 1) constraining glacier length changes with paired 14C/10Be exposure ages at six locations that span a large latitudinal range from North to South America; 2) determining glacier length through time at these six locations by applying a Monte Carlo forward model guided by Bayesian inferences from these newly collected data; and 3) using a glaciological model forced by existing climate simulations and paleo-proxy climate reconstructions to determine plausible climate scenarios that explain the glacier length histories from the data and forward model output. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.