Medieval Warm Period (MWP) 1

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The Medieval Warm Period (MWP) also known as the Medieval Climate Optimum, or Medieval Climatic Anomaly was a time of warm climate in the North Atlantic region that may have been related to other warming events in other regions during that time, including China and other areas, lasting from c. 950 to c. 1250. Other regions were colder, such as the tropical Pacific. Averaged global mean temperatures have been calculated to be similar to early-mid 20th century warming. Possible causes of the Medieval Warm Period include increased solar activity, decreased volcanic activity, and changes to ocean circulation.


It is thought that between c. 950 and c. 1100 was the Northern Hemisphere’s warmest period since the Roman Warm Period. It was only in the 20th and 21st centuries that the Northern Hemisphere experienced warmer temperatures. Climate proxy records show peak warmth occurred at different times for different regions, indicating that the Medieval Warm Period was not a globally uniform event.

Initial research

The Medieval Warm Period (MWP) is generally thought to have occurred from c. 950–c. 1250, during the European Middle Ages.  In 1965 Hubert Lamb, one of the first paleoclimatologists, published research based on data from botany, historical document research and meteorology, combined with records indicating prevailing temperature and rainfall in England around c. 1200 and around c. 1600. He proposed, “Evidence has been accumulating in many fields of investigation pointing to a notably warm climate in many parts of the world, that lasted a few centuries around c. 1000–c. 1200 AD, and was followed by a decline of temperature levels till between c. 1500 and c. 1700 the coldest phase since the last ice age occurred.”

The warm period became known as the Medieval Warm Period, and the cold period was called the Little Ice Age (LIA). However, that view was questioned by other researchers; the IPCC First Assessment Report of 1990 discussed the “Medieval Warm Period around 1000 AD (which may not have been global) and the Little Ice Age which ended only in the middle to late nineteenth century.” The IPCC Third Assessment Report from 2001 then summarized research: “evidence does not support globally synchronous periods of anomalous cold or warmth over this time frame, and the conventional terms of ‘Little Ice Age’ and ‘Medieval Warm Period’ appear to have limited utility in describing trends in hemispheric or global mean temperature changes in past centuries.” Global temperature records taken from ice cores, tree rings, and lake deposits, have shown that the Earth may have been slightly cooler globally (by 0.03 °C) than in the early and mid-20th century.

Palaeoclimatologists developing region-specific climate reconstructions of past centuries conventionally label their coldest interval as “LIA” and their warmest interval as the “MWP.

Others follow the convention, and when a significant climate event is found in the “LIA” or “MWP” time frames, they associate their events to the period. Some “MWP” events are thus wet events or cold events rather than strictly warm events, particularly in central Antarctica, where climate patterns opposite to the North Atlantic area have been noticed.

Evidence exists across the world, often very sparsely, for changes in climatic conditions over time. Some of the “warm period” events documented below are actually “dry periods” or “wet periods.



Further analysis of the bulk compilation of all paleoclimatology studies that were done in various areas around the globe appear to indicate a global trend of warming, particularly in the northern and southern peaks but less towards the equator. More recently, a study by the Pages-2k consortium suggests the warming was not globally synchronous: “Our regional temperature reconstructions also show little evidence for globally synchronized multi-decadal shifts that would mark well-defined worldwide MWP and LIA intervals. Instead, the specific timing of peak warm and cold intervals varies regionally, with multi-decadal variability resulting in regionally specific temperature departures from an underlying global cooling trend.”

North Atlantic

Central Greenland reconstructed temperature.




By retrieval and isotope analysis of marine cores and from an examination of mollusk growth patterns from Iceland, Patterson et al was able to reconstruct a mollusk growth record at a decadal resolution from the Roman Warm Period to the Medieval Warm Period and the Little Ice Age.

North America



Norse colonization of the Americas has been associated with warmer periods. The common theory is that Norsemen took advantage of ice-free seas to colonize areas in Greenland and other outlying lands of the far north. However a study from Columbia University suggests that Greenland was not colonized in warmer weather, but in fact the warming effect was very short term. c. 1000AD, the climate was sufficiently warm for the Vikings to journey to Newfoundland and establish a short-lived outpost there.

From around 985, Vikings founded the Eastern Settlement and Western Settlement, both near the southern tip of Greenland. In the colony’s early stages, they kept cattle, sheep, and goats, with around a quarter of their diet from seafood. After the climate became colder and stormier around 1250, their diet steadily shifted towards ocean sources; by around 1300, sealhunting provided over three-quarters of their food.


L’Anse aux Meadows, Newfoundland, today, with a reconstruction of a Viking settlement.


Prolonged droughts affected many parts of the western United States and especially eastern California and the west of the Great Basin. Alaska experienced three-time intervals of comparable warmth: 1–300, 850–1200, and post-1800. Knowledge of the North American Medieval Warm Period has been useful in dating occupancy periods of certain Native American habitation sites, especially in arid parts of the western United States. Review of more recent archaeological research shows that as the search for signs of unusual cultural changes has broadened, some of the early patterns (for example, violence and health problems) having been found to be more complicated and regionally varied than it had been previously thought. Others, like settlement disruption, deterioration of long-distance trade, and population movements, have been further corroborated.




A sediment core from the eastern Bransfield Basin, Antarctic Peninsula, preserves climatic events from the Little Ice Age and the Medieval Warm Period. The authors noted, “The late Holocene records clearly identify Neoglacial events of the Little Ice Age (LIA) and Medieval Warm Period (MWP).”

Pacific Ocean


South America

The Medieval Warm Period has been noted in Chile in a 1500-year lake bed sediment core as well as in the Eastern Cordillera of Ecuador.



Adhikari and Kumon (2001), investigating sediments in Lake Nakatsuna in central Japan, found a warm period from 900 to 1200 that corresponded to the Medieval Warm Period and three cool phases, two of which could be related to the Little Ice Age. Another research in northeastern Japan shows that there is one warm and humid interval, from 750 to 1200, and two cold and dry intervals, from 1 to 750 and from 1200 to now.  Ge et al. studied temperatures in China during the past 2000 years and found high uncertainty prior to the 16th century but good consistency over the last 500 years highlighted by the two cold periods, the 1620s–1710s and 1800s–1860s, and the warming during the 20th century. They also found that the warming during the 10–14th centuries in some regions might be comparable in magnitude to the warming of the last few decades of the 20th century, which was unprecedented within the past 500 years.



A 1979 study from the University of Waikato found,”Temperatures derived from an 18O/16O profile through a stalagmite found in a New Zealand cave (40.67°S, 172.43°E) suggested the Medieval Warm Period to have occurred between AD c. 1050 and c. 1400 and to have been 0.75 °C warmer than the Current Warm Period.” More evidence in New Zealand is from an 1100-year tree-ring record.