Understanding past, present and future climate change in the 'Greater Mediterranean' area: Building confidence in uncertain climate projections

One of the most important challenges facing society today is the question of how best to adapt to climate change. This adaption usually takes place locally, on a regional or national level, and reliable projections of regional climate change are clearly a prerequisite for developing a robust adaption strategy. The need for this information is perhaps nowhere more pressing than in the Mediterranean, which is an area anticipated to be a hotspot of climate change, and where the combined pressure of a changing climate coupled to a rapidly increasing population is expected to cause increased drought, crop failure and environmentally-forced human migration in the coming century. Clearly the success (or otherwise) of climate change adaption in the 'Greater Mediterranean' region (stretching from Europe to North Africa and from the eastern North Atlantic to the Middle East) will have profound social impacts on both global and regional scales. In order to produce reliable projections of climate change, it is not sufficient just to run climate models, even state-of-the-art ones. While over 90% of the climate models used in the recent IPCC fourth assessment report (Solomon et al, 2007) show a strong reduction in winter precipitation over much of the Mediterranean (mean reduction ~20%), the detailed patterns will depend on the response of the storm tracks which describe the eastward passage of cyclonic weather systems across the North Atlantic and the Mediterranean basins. As such, it is difficult to reconcile the inter-model agreement on 21st century precipitation change over the Mediterranean with the inter-model disagreement on the future of the North Atlantic and Mediterranean storm tracks. There remain too many unanswered questions regarding the behaviour of these storm tracks, raising the important question: How much confidence should we have in projections of Mediterranean climate change if the fundamental processes controlling the Mediterranean storm track on climate timescales are poorly understood? This question applies as much to the use of climate models for seasonal forecasting or for the reconstruction past climates as it does to 21st century climates. At present there is a poor understanding of how the Mediterranean storm track is 'controlled' by the interaction of local processes (e.g., mountains, land-sea contrast, moisture availability) and the large-scale atmospheric flow (e.g., the circulation over the North Atlantic area). Case studies, conceptual models and theory provide some insight, but it is essential that this knowledge can be applied more generally to the complex atmospheric flow patterns seen in the Mediterranean. There is therefore a pressing need to be able to bridge the gap between theoretical concepts or case-studies and the complex situations seen in observations or state-of-the-art climate model projections. This proposal sets out to address this important gap in our understanding of the Mediterranean storm track. In particular, it proposes a systematic investigation of the fundamental processes using advanced climate models but with simplified surface properties that capture the essence of the real system while reducing unnecessary spatial complexity. The physical understanding developed in this manner will then be used to better examine existing state-of-the-art climate projections for the 21st century, present day variability, and the changes seen over the last 12,000 years. The understanding gained will be of wide practical use (see the Impacts summary and plan). Extensive links, both with climate scientists and also across disciplines, are planned and have already begun to be established in order to communicate the research effectively.