Holocene climate variations and timber line fluctuations of in the Alps:
After the last glacial maximum (LGM) in N-America and N-Europe, the large ice shields started to melt. After the last smaller glacier advances reforestation started at about 13,000 BP in the Alps, and the full glacial period ended at 10,000 BP. At the onset of the Holocene, climate warming started quickly and the forests reached ca. 2,100 m a.s.l. This warmth period, caused by the perihelion of earth during the boreal summer, lead to higher solar radiation by about 7%. from ca. 9,000-5,000 BP warmring the Earth’s surface by up to 2 K. This Mid-Holocene climate optimum (hypsithermal interval) lasted 4,000 years with annual average temperatures 1-2 K higher, but it was interrupted by five cooler periods with a lowering of timber line by up to 100 m and glacier advances. During the climate optimum (Atlantic) from 8,000- 5,500 BP the forests reached their highest levels with 2,300-2,400 m a.s.l., i.e. 80-100 m higher than their actual position. After the last high forest positions during the Mid-Subboreal at ca. 4,000-3,700 BP followed a lowering by 40-100 m in the Eastern and Central Alps and glacier extensions due to cooler conditions from 3,500-3,100 and 2,830-2,270 BP. Between the warm periods of Roman Times and Early Middle Ages, a cooler period led to glacier advances and a lower timber line, overlapping with an increasing human impact. During the Little Ice Age (ca. 1,320-1,850 AD) marked glacier advances and extreme weather affected social, economic and cultural life.