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The Medieval Warm Period (also known as the Medieval Climate Anomaly) was a period of relatively warm and stable climate that lasted from approximately 950 to 1250 CE, with significant regional variations. The warming was not uniform across the globe, but in much of Europe it produced milder winters, longer growing seasons, and more reliable harvests than the centuries before or after. The Medieval Warm Period had a profound impact on European agriculture, settlement, and economy, and it is now recognized as one of the major factors in the demographic and economic expansion of the High Middle Ages.
The climatic optimum of c. 950–1250 is now well-attested in ice-core and tree-ring data, and the medieval Norse settlement of Greenland and the medieval English vineyards are its visible markers. The debate is over how much of the period’s economic and demographic growth to attribute to the warmth.
Evidence for the Medieval Warm Period
The evidence for the Medieval Warm Period comes from a variety of scientific and historical sources. Tree rings from old timber show periods of rapid growth that correspond to the warm period, with the most rapid growth occurring in the eleventh and twelfth centuries. Ice cores from glaciers in the Alps, the Andes, and the Himalayas show layers of reduced dust and increased chemical activity that correspond to the warm period. Pollen records from lake sediments show the expansion of certain plant species — especially the vineyard and the olive — into regions where they could not have been cultivated in colder periods. Historical documents — chronicles, manorial records, monastic chronicles — describe a series of mild winters, long growing seasons, and abundant harvests that are consistent with a warm climate.
The most striking evidence for the Medieval Warm Period comes from the North Atlantic. The Viking settlements in Iceland (begun in the late ninth century) and Greenland (begun in the late tenth century) were made possible by the relatively ice-free seas and the milder climate. The Norse voyages to North America (L’Anse aux Meadows and other sites) were also made possible by the favorable climate. The vineyard was cultivated as far north as England and Poland, regions where it could not have been cultivated in the colder periods before or after. The grain harvest in many parts of Europe was generally abundant, and the famine that had characterized the early Middle Ages was largely absent.
Causes of the Medieval Warm Period
The causes of the Medieval Warm Period are still debated by climate scientists, but the major factors are now becoming clearer. The most important factor was the reduced volcanic activity of the period, which allowed more solar radiation to reach the Earth’s surface. The major volcanic eruptions of the early medieval period (the 536 event, the 535–550 series, the 1108 eruption of Mount Asama, the 1171 eruption of Mount Hekla) were followed by cooler periods, while the relatively quiet period of the eleventh and twelfth centuries was followed by a warmer period.
Other factors that contributed to the Medieval Warm Period include the increased solar activity of the period (the so-called Medieval Maximum of solar activity, c. 950–1250), the changes in ocean circulation (the Atlantic Multidecadal Oscillation and the North Atlantic Oscillation), and the changes in land use (the deforestation of the early medieval period followed by the reforestation of the High Middle Ages, which may have affected the regional climate). The causes of the Medieval Warm Period are complex and interrelated, and they are still the subject of active research.
Effects of the Medieval Warm Period
The effects of the Medieval Warm Period on European agriculture were profound. The longer growing season allowed for the cultivation of crops that had previously been marginal, especially in northern Europe. The milder winters reduced the loss of livestock and made it possible to keep animals alive through the winter that would otherwise have been slaughtered. The more reliable harvests reduced the frequency and severity of famine, and the expansion of cultivation into new lands was made possible by the favorable climate.
The Medieval Warm Period also had a major impact on settlement patterns. The expansion of settlement into previously marginal lands — the uplands of Scotland and Scandinavia, the forests of Germany and Poland, the marshes of the Low Countries and the English Fenlands — was made possible by the favorable climate. The Viking expansion across the North Atlantic was a direct consequence of the milder climate, and the Norse settlements in Iceland, Greenland, and North America were made possible by the relatively ice-free seas and the longer growing seasons.
The Medieval Warm Period also had a major impact on the economy of medieval Europe. The abundant harvests supported a growing population, and the growing population stimulated the demand for manufactured goods, the growth of towns, and the expansion of trade. The commercial revolution of the eleventh and twelfth centuries was, in part, a consequence of the favorable climate, and the demographic expansion of the period was, in part, a consequence of the abundant harvests and the reduced mortality.
The End of the Medieval Warm Period
The end of the Medieval Warm Period came in the late thirteenth and early fourteenth centuries, with a return to a cooler and more variable climate. The cooler climate was associated with a series of crop failures, livestock deaths, and famines that culminated in the Great Famine of 1315–1317. The cooler climate also degraded the soil, reduced the yields of the grain crops, and made cultivation in the northern and upland regions more difficult.
The end of the Medieval Warm Period is thought to have been caused by a combination of factors, including the increased volcanic activity of the late thirteenth and early fourteenth centuries, the decreased solar activity of the period (the Wolf Minimum of solar activity, c. 1280–1350), and the changes in ocean circulation that accompanied the cooling. The end of the Medieval Warm Period was a major factor in the demographic and economic crisis of the Late Middle Ages, and it prepared the way for the catastrophic events of the fourteenth century — the Great Famine, the Black Death, and the Hundred Years’ War — that would mark the end of the medieval world.
Sources
Principal sources used in this article:
- William Chester Jordan, The Great Famine (Princeton, 1996).
- B. M. S. Campbell (ed.), Before the Black Death: Studies in the “Crisis” of the Early Fourteenth Century (Manchester, 1991).
Further reading:
- R. I. Moore, The First European Revolution (2000), ch. 1.
For a recent single-volume synthesis with full scholarly apparatus, see the relevant chapter of Barbara H. Rosenwein, A Short History of the Middle Ages (University of Toronto Press, 2014).