Medieval Warm Period
He proposed,[9] 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 1000–1200 CE, and was followed by a decline of temperature levels till between around 1500–1700 CE the coldest phase since the last ice age occurred.The era of warmer temperatures became known as the Medieval Warm Period and the subsequent cold period the Little Ice Age (LIA).
The IPCC First Assessment Report of 1990 discussed the:[10] Medieval Warm Period around 1000 CE (which may not have been global) and the Little Ice Age which ended only in the middle to late nineteenth century.It stated that temperatures in the:[10] late tenth to early thirteenth centuries (about 950–1250 CE) appear to have been exceptionally warm in western Europe, Iceland and Greenland.The IPCC Third Assessment Report from 2001 summarized newer research:[11] 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' are chiefly documented in describing northern hemisphere 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 or 0.1 °F) than in the early and the mid-20th century.
Using methods of historical climatology, Christian Pfister and Heinz Wanner reconstructed the seasonal temperature conditions for Western and Central Europe in 2021 on the basis of indices from CE 1000 to 1999 (the autumns only from 1500 onwards).
[22] Much of the Northern Hemisphere showed a significant cooling during the LIA, which the study defines as from 1400 to 1700, but Labrador and isolated parts of the United States appeared to be approximately as warm as during the 1961–1990 period.
[2] Greenlandic winter oxygen isotope data from the MWP display a strong correlation with the North Atlantic Oscillation (NAO).
[28] However, a study from Columbia University suggests that Greenland was not colonized in warmer weather, but the warming effect in fact lasted for only very briefly.
The last document from the settlements dates from 1412, and over the following decades, the remaining Europeans left in what seems to have been a gradual withdrawal, which was caused mainly by economic factors such as increased availability of farms in Scandinavian countries.
[32] In addition to warming induced glacial melt, sedimentary records reveal a period of increased flooding, coinciding with the MWP, in eastern Europe that is attributed to enhanced precipitation from a positive phase NAO.
[35] In Chesapeake Bay (now in Maryland and Virginia, United States), researchers found large temperature excursions (changes from the mean temperature of that time) during the MWP (about 950–1250) and the Little Ice Age (about 1400–1700, with cold periods persisting into the early 20th century), which are possibly related to changes in the strength of North Atlantic thermohaline circulation.
[40] Knowledge of the MWP in North America has been useful in dating occupancy periods of certain Native American habitation sites, especially in arid parts of the Western United States.
[44][45] Review of more recent archaeological research shows that as the search for signs of unusual cultural changes has broadened, some of the early patterns (such as violence and health problems) have been found to be more complicated and regionally varied than had been previously thought.
[47] Off the coast of Africa, Isotopic analysis of bones from the Canary Islands' inhabitants during the MWP to LIA transition reveal the region experienced a 5 °C (9.0 °F) decrease in air temperature.
The authors noted, "The late Holocene records clearly identify Neoglacial events of the LIA and Medieval Warm Period (MWP).
[51] Corals in the tropical Pacific Ocean suggest that relatively cool and dry conditions may have persisted early in the millennium, which is consistent with a La Niña-like configuration of the El Niño-Southern Oscillation patterns.
[55] A reconstruction, based on ice cores, found that the MWP could be distinguished in tropical South America from about 1050 to 1300 and was followed in the 15th century by the LIA.
[58] During the MWP, the East Asian Summer Monsoon (EASM) was the strongest it has been in the past millennium[59] and was highly sensitive to the El Niño Southern Oscillation (ENSO).
[61] Peat cores from peatland in southeast China suggest changes in the EASM and ENSO are responsible for increased precipitation in the region during the MWP.
[65] Adhikari and Kumon (2001), investigating sediments in Lake Nakatsuna, in central Japan, found a warm period from 900 to 1200 that corresponded to the MWP and three cool phases, two of which could be related to the LIA.
[67] The Indian Summer Monsoon (ISM) was also enhanced during the MWP with a temperature driven change to the Atlantic Multi-decadal Oscillation (AMO),[68] bringing more precipitation to India.
