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

当今社会面临的最重要挑战之一是如何最好地适应气候变化的问题。这种适应通常在地方、区域或国家一级进行，对区域气候变化的可靠预测显然是制定强有力的适应战略的先决条件。地中海地区可能比其他任何地方都更迫切需要这种信息，因为地中海地区预计将成为气候变化的热点地区，气候变化的综合压力加上人口的快速增长预计将在下个世纪造成更多的干旱、作物歉收和环境迫使的人类迁徙。显然，“大地中海”地区(从欧洲延伸到北非，从北大西洋东部延伸到中东)适应气候变化的成功(或失败)将在全球和区域范围内产生深远的社会影响。为了产生可靠的气候变化预测，仅仅运行气候模型是不够的，即使是最先进的模型也是如此。虽然气专委最近的第四次评估报告(所罗门等人，2007年)使用的90%以上的气候模式显示，地中海大部分地区冬季降水量大幅减少(平均减少约20%)，但详细的模式将取决于风暴路径的反应，该路径描述了横跨北大西洋和地中海盆地的气旋天气系统向东移动的过程。因此，很难调和关于21世纪地中海降水变化的模式间协议和关于北大西洋和地中海风暴路径未来的模式间分歧。关于这些风暴路径的行为，仍有太多悬而未决的问题，这引发了一个重要的问题：如果在气候时间尺度上控制地中海风暴路径的基本过程没有得到很好的理解，我们应该对地中海气候变化的预测有多大信心？这个问题既适用于21世纪的气候，也适用于使用气候模型进行季节性预测或重建过去的气候。目前，人们对地中海风暴路径如何被当地过程(例如山脉、陆地-海洋对比度、湿度可用性)和大尺度大气流动(例如北大西洋地区的环流)的相互作用“控制”的了解很少。案例研究、概念模型和理论提供了一些见解，但至关重要的是，这些知识能够更普遍地应用于地中海出现的复杂大气流动模式。因此，迫切需要能够弥合理论概念或案例研究与观测或最先进的气候模型预测中所见的复杂情况之间的差距。这项建议旨在解决我们对地中海风暴路径理解方面的这一重要差距。特别是，它提出了使用先进的气候模型对基本过程进行系统研究，但简化了表面属性，捕捉到了真实系统的本质，同时减少了不必要的空间复杂性。以这种方式形成的物理理解将被用来更好地检查现有的21世纪最先进的气候预测、当今的可变性以及过去12,000年来看到的变化。所获得的理解将具有广泛的实际用途(见影响摘要和计划)。已经计划并开始建立广泛的联系，包括与气候科学家以及跨学科的联系，以便有效地交流研究成果。

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.