Chapter 1 - The impact of the Quaternary ice ages on the landscape

Abstract

The existence of ice ages has been extensively studied over the last two centuries focusing on the chronology and spatial extent of glaciers extending across northern Europe and the highest ranges, including the Iberian mountains. The alternation of long glacial cycles (i.e., glaciations) and short interglacial periods, together with the existence of human beings, characterizes the Quaternary (the last 2.6ka). Glacial cycles and interglacials, with average duration of 100 and 10–15ka, respectively, have alternated during the last 700ka. The origin of these glacial cycles was directly related to the cyclical changes of seasonal and latitudinal insolation derived from Earth's orbital changes. The Last Glacial Cycle (115–11.7ka) was a period of large temperature variability, with shifts (8–12°C) that allowed glaciers to reach their maximum extent during or slightly prior to the Last Glacial Maximum (26–19.5ka). From 19ka, glaciers retreated dramatically until the beginning of the last interglacial (the Holocene; since 11.7ka). During the deglaciation, the warm periods (Bølling–Allerød interstadial; 14.6–12.9ka) were interrupted by cold stages, when glaciers either readvanced or stopped retreating, i.e., the Oldest Dryas (17.5–14.6ka) and the Younger Dryas (12.9–11.7ka) in the Northern Hemisphere. Conversely, temperatures were higher again during the Holocene, and especially during the Holocene Thermal Maximum (c. 9–5ka), when they were higher than the present-day average. After that, the climate cooled again during the last millennia until the Little Ice Age (1300–1850 AD), the coldest period during the Late Holocene, just before the last temperature rise of the 20th century.