Climate Variability over the Last Millennium: Making Models and Proxy Data Work Together



02/16/2016 - 3:30pm


Climate variability on interannual to multidecadal timescales is strongly influenced by the tropical 


Pacific, particularly the El Nino/Southern Oscillation (ENSO). But the degree to which climate variability has been influenced by external forcing over the past millennium is still unclear: climate models disagree on the ENSO sensitivity to climate change, and the mechanisms for these differences are still not well determined. Here I will present a set of results from paleoclimate reconstructions, the NCAR Community Earth System Model Last Millennium Ensemble (CESM LME), and the isotope-enabled Regional Ocean Modeling System (isoROMS), demonstrating the utility of synthesizing model results with paleoclimate information to understand the dynamical mechanisms for climate variability. In the case of volcanic eruptions, the CESM shows a robust increase in El Nino likelihood following large events; but care must be taken when comparing with hydroclimate-based proxy reconstructions, as these may appear ‘El Nino-like’ even in the absence of El Nino occurrence. Better reconstructions of ocean conditions can help solve this problem, and I will use isoROMS to illustrate the need for understanding the dynamics of circulation near coral reefs used for paleoclimate reconstruction. I will discuss the implications of these results for understanding multidecadal to centennial modulation of climate, in both paleoclimate and 21st century contexts.