PALEOSTRAT: PALEOmodelization from a STRATospheric perspective

Abstract

Last Millennium (LM) simulations are crucial to asses the relative roles of internal versus forced variability, the responses to natural and anthropogenic forcings, and the climate sensitivity of the Earth system. However, many open questions still remain regarding the ability of these models to reproduce the LM, since reconstructions suggest more complex patterns than those obtained from LM simulations. Among other factors, these discrepancies could be due to uncertainties in the forcings and/or in model physics. In particular, recent studies have demonstrated the influence of the stratosphere on the surface with important implications in future climate projections. However, most models employed in PMIP3 did not have a well-resolved stratosphere, thus neglecting its potential contribution to explain anomalous periods before the industrial era. PALEOSTRAT is a project funded by the Spanish government which investigates the impact of the stratosphere on the climate of the LM (850-1850 CE). This is addressed by means of a suite of LM simulations with the CESM model which only differ in the representation of the stratosphere, so that their comparisons will provide insights into the impact of the middle-atmosphere on the surface climate. Uncertainties related to external forcings will also be assessed by comparing business-as-usual LM model simulations with LM runs forced with novel external forcing histories and model implementations. This talk will summarize the influence of the stratosphere on the surface climate, its potential role in explaining past changes, the main objectives of PALEOSTRAT and its experimental design.