WCD-08. Using Bayesian Methods to Detect Abrupt Transitions in Transient Holocene Climate Model Simulations

Abstract
Abrupt climate transitions that operate on the timescales of decades to a century impact both humans and ecosystems. That said, our understanding of abrupt changes during the Holocene is limited. Although some paleoclimate proxy records indicate intervals of abrupt change during the Holocene, the spatial extent and temporal evolution of these changes remain uncertain. Furthermore, model-data discrepancies exist, with many climate models unable to simulate the abrupt transitions observed in proxy records. To reconcile these disagreements and develop a more comprehensive picture of abrupt climate change, here we investigate key factors for simulating abrupt climate change under Holocene background conditions. Given that orbital forcing varies gradually through the Holocene, smaller and higher-frequency external forcings (e.g., solar irradiance changes or volcanic eruptions) or additional feedbacks and processes are likely needed to generate abrupt transitions. To test this hypothesis, we use Bayesian methods to identify abrupt transitions (change points) in transient climate simulations from version 3 of the Community Climate System Model (CCSM3) forced with and without solar and volcanic forcing. The Bayesian methods quantify uncertainties in the timing of abrupt changes, allowing us to identify temporally and regionally coherent responses. We find that a transient Holocene simulation with solar and volcanic forcing has a larger number of abrupt transitions compared to simulations with only orbital and greenhouse gas forcing. These findings suggest a key role for higher-frequency forcings in explaining abrupt climate change. Together, this work sets-up a framework for a model-data comparison with available Holocene temperature and hydroclimate-sensitive paleoclimate records, and will help resolve long-standing model-data disagreements.