One interesting possibility for the sudden increase in witchcraft and witch hunts during the Middle Ages is linked to a global period of colder climate, commonly known as the Little Ice Age, (LIA) which is thought to have begun in the 11th century and lasted up until the 19th century. (These dates are highly contested, some schools believing the Little Ice Age really began in the 15th century and the three hundred years before were just a period of climatic fluctuation and deterioration culminating in the cold period.)
The beginning of the LIA brought about a time of increased precipitation, heavy snowfall and frequent unpredictable and violent stroms, as well as seasonally low temperatures. These climatic trends are particularly noticeable during the 14th, 15th and 16th centuries, beginning to stabilise by the 17th century. The environmental factors, combined with various outbreaks of plague and other epidemics, put many rural areas of Northern Europe into economic and social crisis. Due to the severe weather conditions, which shortened growing seasons, flattened crops and flooded landscapes, food became more and more scarce and rural subsistence farmers struggled to support themselves and their families. This change in weather pattern was particularly bad as it followed a period of warmer climate, in which population density had increased and warmer environment crops had been favoured. These crops were badly hit by the colder conditions and a widespread increase in infant mortality, famine and malnutrition seems to dominate the human landscape of Early Medieval Europe.
But what does this have to do with a rise in witchcraft?
It was not unusual for minority groups to be blamed for freak events that were out of human control. Epidemics were frequently blamed on lepers, and the Black Death was thought to have been related to the Jews. These people were not responsible for the events, but were used as a convenient scape-goat by a populace driven to distraction by hunger, disease and fear. Witches were just the next convenient scape-goat to be named and persecuted. (A similar type of scape-goating can be seen in Britain today in the mutterings of 'Thatcher' every time something goes wrong...)
The first reported witch hunts began during the trials of the Spanish Inquisition in the late 14th Century, when magic and weather control became popular as a sign of heresey (unsurprisingly). The Christian church, however, refused to get involved in this debate maintaining that it was impossible for people to control the weather as this could only be an act of God, or of the Devil. In 1484 Heinrich Kramer, a dominican friar of the Alsation Republic, urged the Pope to persecute witches as the harbingers of crop destruction and for working in league with the devil. Kramer had already tried to incite witchhunts on religious grounds and after his endorsment by the Pope, wrote the Malleus maleficarum, or Witches Hammer - a notorious book detailing why to not believe in and work towards destroying witches was heretical, and how to go about spotting witches. Over the next three decades this book became the accepted truth in the hunting of witches and was used to justify the persecution, torture and murder of many thousands, if not hundreds of thousands, of innocent people.
In the early 16th Century, humanitarians such as Erasmus of Rotterdam and Agrippa von Nettesheim appealed against the witches hammer, and the belief in witches altogether. Their voices, along with the changing ideas brought about by the Reformation brought an end to the use of the malleus maleficarum in Inquisitions and witch hunts. Weather control once again became something thought to be impossible by people and everyone thought that the witch trials were a thing of the past.
The early 16th century had been a period of stability within the LIA, but the effects were not yet over. During the 1560's the weather once again became wetter and colder, with violent and 'unnatural' storms began to occur across Europe once more. This was combined with a period of political instability with many landowners attempting to increase their power. As the suspicion of witchcraft and weather control once again gained credence, many landowners gave in to the wishes of their communities and reinstated the hunting, imprisonment and torture of witches. Large cities did not seem to suffer from the widespread panic that rocked the smaller communities with very little mention of witchcraft occuring in Imperial centres. Peasant communities however, on the verge of perishing in the harsh conditions, demanded retribution.
The late 16th century was to be the peak of the witch hunts, and also the peak of the weather conditions associated with the Little Ice Age. Prolonged winters, wet summers and frequent storms destroyed vineyards and orchards, fields and pastures, instilling a 'Great Fear' in the people dependant on those resources for their livelihood. It is during this time that we see the greatest amount of mob mentality as communities took witch hunting into their own hands and would frequently hunt down suspected witches and obtain confessions from them, (through any means possible) before taking them to the authorities to be formally eradicated. The death toll is unclear but from the numbers cited in the nodes above, it is a very large and distubing number. Especially when many, if not all, of these people were just those on the margins of society who perhaps didn't conform to the social norm of the time, or who disagreed with the Catholic Church.
By the 17th century the effects of the LIA were lessening, and a new era, the Age of Enlightenment swept away many of the old beliefs of the previous centuries. The political situation in Europe also stabilised, small landowners once again being able to take control in their rural communities. In areas where there was still political unrest, witch persecution continued as late as the 18th century but was becoming less and less widespread with every passing decade.
Links between the Little Ice Age and the rise in the European belief in witches is a relatively new theory, but seems to bear up quite well. Periods of intense witch hunting activity can be closely linked to episodes of severe climatic change. There are, of course, other factors at work, such as the political and religious framework of Europe at the time, but it cannot be denied that the deteriorating environmental conditions went some way to increasing the fear and mania within local communities.
Sources:
Wolfgang Behringer's recent report on the links between the LIA and witchcraft formed the basis for this discussion.
http://www.york.ac.uk/depts/hist/staff/wmb1
See also:
http://www.malleusmaleficarum.org/
http://il.essortment.com/witchhuntingg_rckm.htm
For two sites filled with information about the witches hammer and the early 16th century witch hunts.