Collaborative Research: Constraining African Climate Since the Last Glacial Maximum via Integrated Climate and Proxy System Modeling

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Earth surface temperatures in the tropics are an important factor in the global climate system because they directly influence atmospheric water vapor content and heat transport towards the poles. Widely accepted global climate models predict that tropical Africa will warm by 5 degrees Celsius (9 degrees Fahrenheit) in the coming century and these changes are expected to have both regional and global consequences. This research project will provide an important perspective on these predictions from past regional climate histories by evaluating the performance of model simulations of past temperatures based on lake sediment proxy records. The researchers will develop a new proxy system model for use by the scientific community and host webinars to educate and train users on the model. The project will support research opportunities that will reach historically underrepresented groups through programs such as the Girl Scouts of America, Research Experiences for Undergraduates at Rice University and Significant Opportunities in Atmospheric Research and Science at University Corporation for Atmospheric Research, as well as an undergraduate research opportunity at Brown University.Current understanding of past temperature history in the tropics has improved in recent decades with advances in proxies for lake temperature from geochemical records preserved in lake sediment cores. However, these lake sediment proxies fundamentally record lake temperature, while climate models primarily simulate air temperature and other Earth surface variables. This collaborative project will help bridge the gap between the lake proxy records of past climates and global climate models to bolster understanding of the controls on Earth surface temperature. The researchers will create new geochemical proxies from existing lake sediment cores, synthesize regional proxy records from tropical Africa and develop a proxy system model to translate between climate model outputs and recorded lake temperature proxies. This proxy-model comparison will be used to evaluate the patterns, rates, sensitivity and mechanisms of temperature changes in tropical Africa since the Last Glacial Maximum approximately 21,000 years ago. Specifically, the researchers will 1) analyze records of tropical African temperature to determine regional patterns, rates, and amplitudes of past temperature variability; 2) Use a new proxy system model (PSM) for lake archives to quantify the impacts of proxy-system processes on the reconstructions; 3) Use output from paleoclimate model simulations to simulate lake temperatures and proxy uncertainties with the PSM; 4) Compare African lake and air temperatures predicted by the PSM and the Paleoclimate Modelling Intercomparison Project (PMIP 3 & 4) simulations of the LGM, the mid-Holocene (6 kyr BP), and the pre-industrial, and in transient climate simulations of the past 21 kyr to the reconstructions; 5) Test the sensitivity of African temperature changes to orbital, greenhouse gas, and ice-sheet forcing in single-forcing transient simulations, and investigate mechanisms for these changes.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.