Figure 3. Multi-proxy reconstructions of climate change, human diffusion and delta progradation.

The last 3 millennia were characterized by several climatic oscillations, synchronous at northern Hemisphere scale, with two major extremes in the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). The trend of pollen record from the central Alps³⁰ reflects temperature and precipitation changes all over the Europe region⁹ and can be compared with the temperature record derived from Greenland ice core¹⁰. Growth rates of the main four northern Mediterranean and Black Sea river deltas (see Supplementary S1, each step is one order of magnitude) increased during the Roman Empire, and dramatically since the onset of the Little Ice Age (LIA), characterized by closely-spaced intervals of advancing and waning of Alpine Glaciers¹⁹, increased flood frequency²³, high storm activity³¹, but only a slight increase of total precipitation⁹. These natural factors may reflect the occurrence of repeated and closely spaced NAO-index anomalies (11, positive, red, and negative, blue) and several centuries of overall decreasing T¹⁰. While human expanded, in the past, during intervals of milder climate (Roman Empire), this was the first substantially cooler interval severely impacted by humans through, inter alia, forest clearance¹², increasing population¹² and related land consumption. The change in land use is well reflected by increased shrub+herb vs. tree in pollen spectra both in the alpine region and in the Mediterranean, especially in the second half of the LIA.