Quaternary paleoclimate reconstructions in tropical-subtropical southern Africa (taken here as approximately south of latitude 17oS) require both knowledge of the key relevant elements of the atmospheric and climate systems over the subcontinent and a realistic assessment of the possibilities and limitations of the proxy data sources in the region. Direct insolation forcing and southern hemisphere ocean temperature changes are widely considered as key drivers of temporal and spatial changes in the relative influence of different components of the circulation system (tropical Indian ocean monsoon, tropical Atlantic moisture, and temperate westerlies) that in turn drive precipitation distributions, amounts, and seasonality. Major debates in recent decades have focused on the timing and extent of aridity/humidity shifts, and the relative contribution of temperate and tropical sources of precipitation during the last ca. 100 ka, notably at the Last Glacial Maximum (LGM) and during the Holocene climate optimum. Many of the debates and uncertainties that have emerged are also a function of proxy data sources: where they are located, how they are interpreted, and their resolution. Extrapolation of data from marine core and high-resolution terrestrial records to subregions where proxies are sparse, low resolution, or difficult to transform from environmental to climatic signals, might oversimply representation of the spatial variability of past climates in a region where variability is a norm today. For example, difficulties can occur in the southern African interior, where reliable climate proxies have been limited and where available proxies provide reconstructions of physical changes in landscape systems that can prove difficult to translate to high precision hydrological and rainfall records. Elsewhere, where new proxies have been emerging, such as data from hyrax middens and developments in interpreting palynological and isotope records, notable advances have been occurring, leading to the reanalysis of hydrological fluxes in the last 50 ka, including the development of records with high temporal resolution. In this article some of the key issues surrounding the Quaternary climates of southern Africa are considered, focusing on debates regarding the principal drivers of climate changes, the utility of different proxy data sources, and the temporal and spatial extent of past climate changes.
David S. G. Thomas
Ricardo García-Herrera and David Barriopedro
The Mediterranean is a semi-enclosed sea surrounded by Europe to the north, Asia to the east, and Africa to the south. It covers an area of approximately 2.5 million km2, between 30–46 °N latitude and 6 °W and 36 °E longitude. The term Mediterranean climate is applied beyond the Mediterranean region itself and has been used since the early 20th century to classify other regions of the world, such as California or South Africa, usually located in the 30º–40º latitudinal band. The Mediterranean climate can be broadly characterized by warm to hot dry summers and mild wet winters. However, this broad picture hides important variations, which can be explained through the existence of two geographical gradients: North/South, with a warmer and drier south, and West/East, more influenced by Atlantic/Asian circulation. The region is located at a crossroad between the mid-latitudes and the subtropical regimes. Thus, small changes in the Atlantic storm track may lead to dramatic changes in the precipitation of the northwestern area of the basin. The variability of the descending northern branch of the Hadley cell influences the climate of the southern margin, while the eastern border climate is conditioned by the Siberian High in winter and the Indian Summer Monsoon during summer. All these large-scale factors are modulated by the complex orography of the region, the contrasting albedo, and the moisture and heat supplied by the Mediterranean Sea. The interactions occurring among all these factors lead to a complex picture with some relevant phenomena characteristic of the Mediterranean region, such as heatwaves and droughts, Saharan dust intrusions, or specific types of cyclogenesis. Climate model projections generally agree in characterizing the region as a climate change hotspot, considering that it is one of the areas of the globe likely to suffer pronounced climate changes. Anthropogenic influences are not new, since the region is densely populated and is the home of some the oldest civilizations on Earth. This has produced multiple and continuous modifications in the land cover, with measurable impacts on climate that can be traced from the rich available documentary evidence and high-resolution natural proxies.