North America 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. Sediments in
Piermont Marsh of the lower
Hudson Valley show a dry MWP from 800 to 1300. In the Hammock River marsh in
Connecticut, salt marshes extended farther westward than they do in the present due to higher sea levels. Prolonged droughts affected many parts of what is now the
Western United States, especially eastern
California and the west of
Great Basin. 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. Aridity was more prevalent in the southeastern United States during the MWP than the following LIA, but only slightly; this difference may be statistically insignificant. Droughts in the MWP may have impacted Native American settlements also in the
Eastern United States, such as at
Cahokia. 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. Other patterns, such as settlement disruption, deterioration of long-distance trade, and population movements, have been further corroborated.
Africa The climate in equatorial eastern
Africa has alternated between being drier than today and relatively wet. The climate was drier during the MWP (1000–1270). 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 decrease in air temperature. Over this period, the diet of inhabitants did not appreciably change, which suggests they were remarkably resilient to
climate change.
Antarctica The onset of the MWP in the
Southern Ocean lagged the MWP's onset in the North Atlantic by approximately 150 years. A
sediment core from the eastern Bransfield Basin, in the
Antarctic Peninsula, preserves climatic events from both the
LIA and the MWP. The authors noted, "The late Holocene records clearly identify Neoglacial events of the
LIA and Medieval Warm Period (MWP)." Some Antarctic regions were atypically cold, but others were atypically warm between 1000 and 1200.
Pacific Ocean 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. In 2013, a study from three US universities was published in
Science magazine and showed that the water temperature in the Pacific Ocean was warmer during the MWP than during the
LIA and warmer than the decades before the study. In the northeastern Pacific, however,
sea surface temperatures (SSTs) were actually cooler during the MWP than the LIA.
South America The MWP has been noted in
Chile in a 1500-year lake bed sediment core, as well as in the
Eastern Cordillera of
Ecuador. 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. Peak temperatures did not rise as to the level of the late 20th century, which were unprecedented in the area during the study period of 1600 years.
East Asia Ge
et al. studied temperatures in
China for 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, 1620s–1710s and 1800s–1860s, and the 20th-century warming. They also found that the warming from the 10th to the 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. Generally, a warming period was identified in China, coinciding with the MWP, using multi-proxy data for temperature. However, the warming was inconsistent across China. Significant temperature change, from the MWP to
LIA, was found for northeast and central-east China but not for northwest China and the
Tibetan Plateau. During the MWP, the
East Asian Summer Monsoon (EASM) was the strongest it has been in the past millennium and was highly sensitive to the
El Niño Southern Oscillation (ENSO). The
Mu Us Desert witness increased moisture in the MWP.
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. However, other sites in southern China show aridification and not humidification during the MWP, showing that the MWP's influence was highly spatially heterogeneous. Modelling evidence suggests that EASM strength during the MWP was low in early summer but very high during late summer. In far eastern
Russia, continental regions experienced severe floods during the MWP while nearby islands experienced less precipitation leading to a decrease in peatland. Pollen data from this region indicates an expansion of warm climate vegetation with an increasing number of
broadleaf and decreasing number of
coniferous forests. 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. Other research in northeastern Japan showed that there was one warm and humid interval, from 750 to 1200, and two cold and dry intervals, from 1 to 750 and from 1200 to now.
South Asia The
Indian Summer Monsoon (ISM) was also enhanced during the MWP with a temperature driven change to the
Atlantic Multi-decadal Oscillation (AMO), bringing more precipitation to
India. Vegetation records in
Lahaul in
Himachal Pradesh confirm a warm and humid MWP from 1,158 to 647 BP. Pollen from
Madhya Pradesh dated to the MWP provides further direct evidence for increased monsoonal precipitation. Multi-proxy records from
Pookode Lake in
Kerala also reflect the warmth of the MWP.
Middle East Sea surface temperatures in the Arabian Sea increased during the MWP, owing to a strong monsoon. During the MWP, the
Arabian Sea exhibited heightened biological productivity. The
Arabian Peninsula, already extremely arid in the present day, was even drier during the MWP. Prolonged drought was a mainstay of the Arabian climate until around 660 BP, when this hyperarid interval was terminated.
Oceania There is an extreme scarcity of data from
Australia for both the MWP and the
LIA. However, evidence from wave-built shingle terraces for a permanently-full
Lake Eyre during the 9th and the 10th centuries is consistent with a
La Niña-like configuration, but the data are insufficient to show how lake levels varied from year to year or what climatic conditions elsewhere in Australia were like. A 1979 study from the
University of Waikato found, More evidence in
New Zealand is from an 1100-year tree-ring record. ==See also==