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— CH. 1 · DEFINING THE MEDIEVAL WARM PERIOD —

Medieval Warm Period

~4 min read · Ch. 1 of 6
6 sections

  • The era spanning from 950 CE to 1250 CE marked a distinct period of warmth in the North Atlantic region. Historians and scientists refer to this interval as the Medieval Warm Period, though some prefer the term Medieval Climate Anomaly. This alternative name highlights that climatic effects extended beyond simple temperature changes. Hubert Lamb published foundational research on this topic in 1965 using data from botany and historical documents. He analyzed prevailing temperatures and rainfall patterns in England around specific years within that timeframe. Modern consensus suggests peak warmth occurred at different times for different regions rather than simultaneously worldwide. A study by the Pages-2k consortium confirmed in 2019 that no single warmest 51-year period existed across all areas. This regional framing helps researchers understand preindustrial climate variability without assuming global uniformity.

  • Researchers rely on ice cores, tree rings, and sediment records to reconstruct past temperatures before modern instruments existed. Lloyd D. Keigwin conducted a 1996 study of radiocarbon-dated box core data from marine sediments in the Sargasso Sea. His analysis revealed sea surface temperatures were approximately warmer 1000 years ago compared to later periods. Patterson et al. reconstructed stable oxygen and carbon isotope records from Iceland with decadal resolution spanning from the Roman Warm Period through the Little Ice Age. Christian Pfister and Heinz Wanner used indices from CE 1000 to 1999 to reconstruct seasonal temperature conditions for Western and Central Europe in 2021. These methods allow scientists to see how summer temperatures stayed high while winter temperatures decreased after initial settlement periods. The data set ranges from 950 to 1250 with a resolution of around 20 years per data point. Each point represents the average temperature of the surrounding two decades rather than a specific daily reading.

  • Warmth during this era occurred asynchronously across different continents instead of as a global uniformity. In central Antarctica, climate patterns often oppose those found in the North Atlantic region. Some events labeled within the Medieval Warm Period timeframe are actually wet or cold events rather than strictly warm ones. The onset of warming in the Southern Ocean lagged the North Atlantic onset by approximately 150 years. Corals in the tropical Pacific Ocean suggest relatively cool and dry conditions persisted early in the millennium. Sea surface temperatures in the northeastern Pacific were actually cooler during the Medieval Warm Period compared to the subsequent cooling phase. In eastern Africa, the climate alternated between being drier than today and relatively wet during these centuries. The Arabian Peninsula was even drier during this time despite increased sea surface temperatures in the Arabian Sea due to strong monsoons.

  • Possible drivers for this period include increased solar activity, decreased volcanic activity, and changes in ocean circulation. Modelling evidence indicates natural variability alone is insufficient to explain the Medieval Warm Period without external forcing. Changes in the strength of North Atlantic thermohaline circulation may relate to large temperature excursions found in Chesapeake Bay sediments. A positive phase of the North Atlantic Oscillation contributed to enhanced precipitation and flooding in eastern Europe. The East Asian Summer Monsoon reached its strongest point in the past millennium and remained highly sensitive to El Niño Southern Oscillation patterns. Vegetation records from Lahaul in Himachal Pradesh confirm a warm and humid interval driven by atmospheric shifts. Pollen data from southeast China suggests changes in monsoon strength and ENSO cycles are responsible for increased precipitation in that region.

  • Iceland was first settled between 865 and 930 during a time believed warm enough for sailing and farming. Vikings founded Eastern and Western Settlements near the southern tip of Greenland around 985. In early stages, these communities kept cattle, sheep, and goats with about a quarter of their diet coming from seafood. After climate became colder and stormier around 1250, their food sources shifted steadily toward ocean origins. By 1300, seal hunting provided over three quarters of their total food supply. The last written record from Norse Greenlanders comes from an Icelandic marriage in 1408 recorded later at Hvalsey Church. Reduced demand for exports caused trade with Europe to fall away by 1350. Over following decades remaining Europeans left due mainly to economic factors like increased farm availability in Scandinavian countries. A coastal region in western Sardinia abandoned by Romans expanded into a lagoon without human influence before populations returned to reestablish ports.

  • The Medieval Warm Period ended as a regionally cooler period emerged in the North Atlantic and elsewhere known as the Little Ice Age. Much of the Northern Hemisphere showed significant cooling during this subsequent phase defined from 1400 to 1700. Labrador and isolated parts of the United States appeared approximately as warm as during the 1961, 1990 period despite general trends. Winters in Central Europe remained almost consistently cold between 1000 AD and the late 19th century. Substantial glacial retreat occurred in southern Europe during the earlier warm phase while larger glaciers survived and now provide historical insight. The Gorner glacier advanced during cool and wet summers between 1140 and 1151 culminating in 1168. Prolonged droughts affected many parts of what is now the Western United States especially eastern California and the west of Great Basin. Knowledge of these shifts has been useful in dating occupancy periods of certain Native American habitation sites particularly in arid regions.

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Little Ice Age

Common questions

What years define the Medieval Warm Period in the North Atlantic region?

The era spanning from 950 CE to 1250 CE marked a distinct period of warmth in the North Atlantic region. Historians and scientists refer to this interval as the Medieval Warm Period, though some prefer the term Medieval Climate Anomaly.

Who published foundational research on the Medieval Warm Period in 1965?

Hubert Lamb published foundational research on this topic in 1965 using data from botany and historical documents. He analyzed prevailing temperatures and rainfall patterns in England around specific years within that timeframe.

When did Vikings settle Greenland during the warm phase of the Medieval Warm Period?

Vikings founded Eastern and Western Settlements near the southern tip of Greenland around 985. In early stages, these communities kept cattle, sheep, and goats with about a quarter of their diet coming from seafood.

How do researchers reconstruct past temperatures before modern instruments existed for the Medieval Warm Period?

Researchers rely on ice cores, tree rings, and sediment records to reconstruct past temperatures before modern instruments existed. Lloyd D. Keigwin conducted a 1996 study of radiocarbon-dated box core data from marine sediments in the Sargasso Sea.

What caused the end of the Medieval Warm Period and what followed it?

The Medieval Warm Period ended as a regionally cooler period emerged in the North Atlantic and elsewhere known as the Little Ice Age. Much of the Northern Hemisphere showed significant cooling during this subsequent phase defined from 1400 to 1700.

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All sources

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