Climate Cycles in the Carolingian Era

Cycles in the climate have been found by historians, which have impacted the evolution of civilizations worldwide

click to a diagram of the weather large-scale fluctuations since the beginning of the Christian Era

In the West, periods of cold and warmth alternated since the Little Ice Age. Since the Christian Era, the two first centuries A.D. were cold (or warm, according to some); the period between 200 and 600 was warm as the 600-800 era was cold. More accurately, a period 536-660 A.D., or the 'Late Antique Little Ice Age,' in the northern hemisphere had specially the 6th century A.D. seeing rising and falling civilizations, pandemics, human migrations or political turmoil. Plague in the Byzantine empire and by the Sassanids by about 541-42, people movements in Central Asia, the Arabian Peninsula or of the Slavs, along with political upheaval in China might have resulted. Such a cooler period likely was due for a cluster of large volcanic eruptions (536, 540, 547) sustained further by ocean and sea-ice feedback. A warmer Middle-Ages followed since 850, until 1150. Precisely, the reign of Charlemagne occurred during a period of a very relative climate warming coming along with a same relative drought. Always, drought also occurred by the shores of the Mediterranean Sea. Any drought anywhere in the Mediterranean basin was also endured elsewhere in the basin, yielding a potential for large-scale disruption of food systems. Northern part of the Mediterranean -Greece, Italy, and the coasts of France and Spain- further tended to be dry when eastern North Africa was wet, and vice versa. Two major circulation patterns influence when droughts occur in the Mediterranean are the North Atlantic Oscillation and the East Atlantic Pattern, which determine how winds and weather behave depending on ocean conditions. They have periodic phases that tend to steer rainstorms away from the Mediterranean and bring in dryer, warmer air. Beginning about 1200 and lasting until the 18th century, a 'Little Ice Age' occurred, bringing colder temperatures and lesser crops. The cooling of the climate during the early Middle Ages likely brought a adversarial view of Nature as the following warming, to a collaborative, more optimistic one which likely lasted until the 14th century Black Death with a re-evaluation again then, considering man able to affect the environment. Studies of ice-cores in 2014 have shown that the 13th century was marked by numerous tropical volcanoe eruptions and that these eruptions triggered the start of the Little Ice Age

Enhanced periods of storminess leading to coastal flooding during the last 4500 years in the Central Mediterranean Sea, display long-term correlations with solar activity. Such a enhancement has been recorded during six intervals at 4250-3750, 3400-2550, 2000-1800, 1650-1450, 1300-900 and 400-100 years ago, with peaks and intermediate periods of low activity. The amplitude of the storm phases, generally, appears to be on the decrease since 3000 year ago, due maybe to changes in rivers' deltas configuration. Shipwreck data from the Adriatic and wider Mediterranean region present significant peaks around 2000-1800, 1650-1450 and 1300-900 years ago, correlated with heightened periods of storminess. Main periodicities of the storm signal are centered on 450, 740, and about 2200 years. Storminess cycles also impacted agro-pastoralism with intrusion of saline water into groundwater tables and plains. Alps ice is showing to peaks of lead which were due to Rome's mining industry, at 350-100 B.C. and 0-200 A.D. The natural proportion in metals was multiplied by a factor 10

In eastern Asia, Neolithic populations changed landsape in such a deep manner that monsoons ceased to reach deep into continents. A monsoon cycles in the East have been found too, with those fluctuations lasted from one to several centuries as decade-only-long periods did occur too (with might be the case too for the cycle in the West, as far as the transition periods are concerned). The main cycles spotted there were the following. Swift oscillations occurred between 190 and 530 A.D. The monsoon then was weak, leading to a dry period, from 530 to 850 and kept so after that, with a sharp drop between 910 and 930. The climate became humid again and lasted so until 1020, then about 1340 -with some variations. Back to dryness since that date -with strong fluctuations however- and a final rainy period since 1850. With the monsoon providing rains for crops feeding the inhabitants, its fluctuations had importance in the history of China, for example, with the fate of such or such dynasty. A dryer climate was bringing less crops, famines and decline. Strong monsoons favoured the Song and the weak ones accelerated the demise of the Tang (907 A.D.), the Yuan (1368), and the Ming (1644). The strength of the monsoon, generally, is function of the difference of temperatures between the continental mass of lands, and the Pacific and Indian oceans!

Other cycles likely existed elsewhere in the world, with the Mayas, in the Americas, for example, which might have been hit too by a 9th-century dry period. Earlier in time, about 2,000 B.C., a weakening of the Indian monsoon looks like it was also linked to a larger climate crisis, which had repercussions upon the Ancient Empire in Egypt, the early Bronze Age civilizations of Greece and Crete and the Akkadian Empire