The mid-Holocene climatic transition in the Mediterranean: Causes and consequences

In the Mediterranean there is often no clear time gap separating an early-Holocene period of nature-dominated environmental change from a human-dominated late-Holocene one. This mid-Holocene 'melange' has been the subject of debates that have often been polarised between support for climatic causation and those favouring anthropogenic explanations for changes in vegetation, river flooding, wildfire regimes, etc. One way to shed light on the causes of mid-Holocene landscape changes is to focus on natural archives, such as lake and cave isotopes, the records of which can be unambiguously attributed to climatic forcing. These primary climate proxies can then be compared and contrasted with secondary or response variables, such as pollen and microcharcoal data, which can be the product of either climate changes or human activity or both, ideally using a multiproxy approach. In addition, synthesised primary palaeoclimate data can be compared with regional-scale climate modelling simulations. Both model output and proxy data suggest an east-west division in Mediterranean climate history. They indicate that the eastern Mediterranean experienced an increase in winter-season precipitation during the early Holocene, followed by an oscillatory decline after similar to 6 ka BP. In western parts of the Mediterranean, early-Holocene changes in precipitation were smaller in magnitude and less coherent spatially, and maximum increases occurred during the mid Holocene, around 6-3 ka BP, before declining to present-day values. Coincident with and partly stimulated by these climatic changes, complex societies developed across the Mediterranean, particularly in eastern parts of the basin during the Bronze Age. In consequence, by the mid-first millennium BC, human-induced land cover conversion, a drier and more variable climate, and changed fire regimes combined to establish typical sclerophyllous vegetation and landscapes in the circum-Mediterranean region.