Between 536 and 551 AD tree ring growth was very low throughout Europe and many other parts of the world, including North America, New Zealand and China. Contemporary writers in southern Europe described what modern climate scientists call a ‘dust veil event’ which sharply reduced solar radiation reaching the earth’s surface. This depressed temperatures, disrupted weather patterns, reduced biological productivity, including food crops, and resulted in famine and social disruption during the 6th century. The consequences were experienced worldwide. In Britain, the period 535—555 experienced the worst weather of the 6th century. In Mesopotamia there were heavy falls of snow and in Arabia there was flooding follow by famine. In China, in 536, there was drought and famine and yellow dust rained down like snow. In Korea, AD 535 and 536 were the worst years of that century in climatic terms with massive storms and flooding, followed by drought. It has also been suggested that the occurrence of the Justinian Plague, a pandemic which affected the Byzantine Empire, including its capital Constantinople, in the years 541–42 AD is linked to the climatic events five years earlier.
What caused it?
Although historians have sought to explain the ‘dust veil’ in terms of a comet hitting the earth, only recently, with the help of earth scientists, is it becoming clear that we are dealing here with a volcanic event. There was a series of severe volcanic eruptions in central and South America that put so much dust into the atmsophre that it depressed the temperature of the earth for years.1
This catastrophic event can be regarded as the trigger that ended the classical world and the beginning of the Middle Ages. It blotted the sun out and resulted directly and indirectly, in climate chaos, famine, migration, war and massive political change on all continents.
Note: Climatic and environmental disasters are "funnels", not direct causes for historical events. They reinforce already existing historical patterns such as migration or political instability, over exploitation etc.
800: coronation Charlemagne. At the beginning of the 9th century, when Charlemagne is ruling most of Europe, the winter weather turns cold again. This did not prevent Charlemagne from becoming emperor. This is a period of cultural and economic growth and flourishing. The colder conditions did not affect this in a negative way because of political stability and the fact that society was resilient enough to cope with this climatic fluctuation.
During the High Middle Ages in Europe experienced a climate slightly warmer than in the period preceding and the period following it. The summer temperatures were between 1 and 1.4 degrees higher than the average temperature of the 20th century. The winters were even warmer with an average temperature in England of 6 degrees, which is slightly warmer than for most of the 20th century. The warmer conditions were caused by the fact that the air circulation above the Atlantic changed position, as did the warm sea currents, transporting warmer water to the arctic.
In Europe the warm conditions had positive effects. Summer after summer the harvests were good and the population increased rapidly. As a result thousands of hectares were cleared of woodland and farmers expanded their fields high into the hills and on mountain slopes. It was even possible to grow successfully grapes as far north as Yorkshire.
Under these conditions, art, literature and even science were developing apace and we see the height of medieval civilisation. The most visible achievements of this period are undoubtedly the construction of the many cathedrals all over Europe. The good harvests had made Europe rich and the good weather freed people from the burden of the struggle against the elements. It created the wealth and labour force to build cathedrals. It was a golden period for European Architecture and art.
9th & 10th centuries: Vikings reach Island and Greenland during the milder condition that prevailed during Medieval Warm Period.
Norse settlers arrived in Iceland in the 9th and Greenland in the 10th century with an agricultural practice based on milk, meat and fibre from cattle, sheep, and goats. The settlers were attracted by green fields and a relatively good climate and driven there by population pressures in Scandinavia.
They were able to sail to Iceland and Greenland as well as Labrador because of a decrease in sea ice in the north Atlantic.
Environmental upheavals linked to sever climate variability characterised the period from 1300 to 1400.
All tree ring series in northern Europe show a decline in growth rates, indicating an adverse climatic change. This marked the transition from a “Medieval Warm Period” to the “Little Ice Age” when temperatures were on average 1.5 degrees Celsius lower than before and with greater seasonal variation. The cooling trend associated with the Little Ice Age progressively moved from north-west to south-east across Europe, with the Vikings in the far North experiencing the clooing first, British Isles experiencing the effects from the 1290s and the Mediterranean after 1320.
Written records from the 14th century provide accounts of severe weather in the period from 1314 to 1317, which led in turn to crop failure and famine. This episode of failed harvests and its consequences is known as “The Great Famine”. Notwithstanding these ecological calamities, the population of northern Europe was at an all time high by the second quarter of the 14th century. However, the arrival of the Black Death, in Europe in 1347 pushed the European population into a century-long demographic decline and caused long term changes in economy and society.
Germs and microbes are part of our environment. In fact, these creatures can be regarded as the most successful living things on the planet. Our invisible environment of microbes has also shaped events in world history in many ways. Nowhere was this more evident and visible ultimately, in the Black Death that affected, and infected, Eurasia during the 14th century. The Black Death spread from central Asia along trade routes and reached southern Europe in 1347. It swept quickly through the continent and reached northern Scandinavia and Iceland in 1350. Few areas escaped and by late 1350 between 30 and 40% of the European population had perished.
But what catapulted the Black Death on the world stage? Recently it has been suggested that a climatic event similar to the 536 dust veil event is responsible. Based on comparing the chronologies of prices, wages, grain harvests and the corresponding chronologies of growing conditions and climactic variations, taking into consideration dendrochronology, the Greenland ice cores it has emerged that the episodes of the Black Death coincide with depressed temperatures. Find out more in this video lecture by Professor Bruce Campbell of Queens University Belfast.
The dramatic decline of the European population caused by the Black Death coincided with a decline in global temperature. Coincidence? The climate was already getting colder because the northern hemisphere was heading for the Little Ice Age. At the same time agricultural land was taken out of production in Europe because of the 25-40% decline of the European population (depending on region). This means ploughing of less ground, which releases greenhouse gasses (Methane and carbonates) and forest clearance was reversed. More trees and scrubs mean that more carbon (CO2) was taken out of the atmosphere and stored in biomass. The abandoned farmland acted as a significant carbon sink because trees store carbon taken from the CO2 in the air.
Graph showing inervals of low CO2 concentrations in Antarctic ice cores correlating with major epidemics that decimated populations.
After: Ruddiman, William F., Plows, Plagues and Petroleum: How Humans took Control of Climate, p. 133.
From about 1350 CO2 levels in the atmosphere appear to fall following the Black Death. However, a long term declining trend may have already started before the Black Death. We know that the first two decades of the 14th century were wetter, windier and climatically more unstable than before. The declining trend also continued after the recovery of agriculture after 1440. The reforestation that followed the Black Death and the resulting decrease of CO2 in the atmosphere pronounced a natural cooling trend that was already underway. This was the beginning of the LIA. This means the LIA was not triggered by the Black Death but possibly contributed to it, although temporarily.
1. L. B. Larsen et al., ‘New ice core evidence for a volcanic cause of the A.D. 536 dust veil’, Geophysical Research Letters, Vol. 35 (, 2008): L04708. http://www.agu.org/journals/gl/gl0804/2007GL032450/, accessed: 25 November 2008
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