Modeling the effects of vegetation on Mediterranean climate during the Roman Classical Period: Part I: Climate history and model sensitivity

This is the first of a two-part study to construct a vegetation map around the Mediterranean Sea that is an accurate representation of conditions two millennia ago, and to use this data in general circulation model experiments to better understand historical climate and climate change. Particularly, we want to evaluate the sensitivity of the atmospheric circulation around the Mediterranean Sea to changed land surface conditions. The idea that 2000 years BP, during the Roman Classical Period (RCP), northern Africa and the Mediterranean countries were moister than today is widely acknowledged but has not been discussed within a scientific framework until a few decades ago. Archeological and historical documents provide some qualitative agreement that moister conditions prevailed during Roman times, and interdisciplinary scientific research provides some confidence through proxies that the Mediterranean has been experiencing a trend towards drier conditions. The first step of this work is the multidisciplinary task of organizing all the available information coming from historical and archeological sources, together with what is known from scientific methods, into a coherent history of climate and vegetation. The second step is to run a 25-year general circulation model (GCM) experiment, with a forcing that represents an idealized RCP vegetation distribution. The forcing produces a noticeable effect on the climate, namely a northward shift of the intertropical convergence zone during summer over the African continent