Medieval Warm Period

Medieval Warm Period

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The Medieval Warm Period (MWP), Medieval Climate Optimum, or Medieval Climatic Anomaly was a time of warm
Warm
Warm or WARM can refer to:* A somewhat high temperature.* WARM , a radio station licensed to Scranton, Pennsylvania, United States* WARM-FM, a radio station licensed to York, Pennsylvania, United States...

 climate
Climate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...

  in the North Atlantic
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

 region, that may also have been related to other climate
Climate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...

 events around the world during that time, including in China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

, New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...

, and other countries lasting from about AD 950 to 1250. It was followed by a cooler period in the North Atlantic
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

 termed the Little Ice Age
Little Ice Age
The Little Ice Age was a period of cooling that occurred after the Medieval Warm Period . While not a true ice age, the term was introduced into the scientific literature by François E. Matthes in 1939...

. Some refer to the event as the Medieval Climatic Anomaly as this term emphasizes that effects other than temperature were important.

Despite substantial uncertainties, especially for the period prior to 1600 when data are scarce, the warmest period of the last 2,000 years prior to the 20th century very likely occurred between 950 and 1100, but temperatures were probably between 0.1°C and 0.2°C below the 1961 to 1990 mean and significantly below the level shown by instrumental data after 1980. The heterogeneous nature of climate during the Medieval Warm Period is illustrated by the wide spread of values exhibited by the individual records.

Initial research


The Medieval Warm Period (MWP) is generally thought to have occurred from about AD 950–1250, during the Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

an Middle Ages
Middle Ages
The Middle Ages is a periodization of European history from the 5th century to the 15th century. The Middle Ages follows the fall of the Western Roman Empire in 476 and precedes the Early Modern Era. It is the middle period of a three-period division of Western history: Classic, Medieval and Modern...

. In 1965 Hubert Lamb
Hubert Lamb
Hubert Horace Lamb was an English climatologist who founded the Climatic Research Unit in 1972 in the School of Environmental Sciences at the University of East Anglia.-Career:...

, one of the first paleoclimatologists, published research based on data from botany
Botany
Botany, plant science, or plant biology is a branch of biology that involves the scientific study of plant life. Traditionally, botany also included the study of fungi, algae and viruses...

, historical document research and meteorology combined with records indicating prevailing temperature and rainfall in England around 1200 and around 1600. He proposed that "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 A.D. 1000–1200, and was followed by a decline of temperature levels till between 1500 and 1700 the coldest phase since the last ice age occurred."

The warm period became known as the MWP, and the cold period was called the Little Ice Age
Little Ice Age
The Little Ice Age was a period of cooling that occurred after the Medieval Warm Period . While not a true ice age, the term was introduced into the scientific literature by François E. Matthes in 1939...

 (LIA). However, this view was questioned by other researchers; the IPCC First Assessment Report
IPCC First Assessment Report
The Intergovernmental Panel on Climate Change first assessment report was completed in 1990, and served as the basis of the United Nations Framework Convention on Climate Change ....

 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
IPCC Third Assessment Report
The IPCC Third Assessment Report, Climate Change 2001, is an assessment of available scientific and socio-economic information on climate change by the IPCC. The IPCC was established in 1988 by the United Nations Environment Programme and the UN's World Meteorological Organization ".....

 from 2001 summarised research at that time, saying "... current 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, taken globally, the Earth may have been slightly cooler (by 0.03 degrees Celsius) during the 'Medieval Warm Period' than in the early and mid-20th century. Crowley and Lowery (2000) note that "there is insufficient documentation as to its existence in the Southern hemisphere."

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, 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.

By world region


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".

Globally


A 2009 study by Michael Mann et al. finds that the MWP shows "warmth that matches or exceeds that of the past decade in some regions, but which falls well below recent levels globally". Their reconstruction of MWP pattern is characterised by warmth over large part of North Atlantic, Southern Greenland, the Eurasian Arctic, and parts of North America which appears to substantially exceed that of the late 20th century (1961–1990) baseline and is comparable or exceeds that of the past one-to-two decades in some regions. Certain regions such as central Eurasia, northwestern North America, and (with less confidence) parts of South Atlantic, exhibit anomalous coolness.

North Atlantic




A radiocarbon-dated box core
Box corer
The Box corer is a marine geological sampling tool for soft sediments in lakes or oceans. It is deployed from a research vessel with a deep sea wire and suitable for any water depth...

 in the Sargasso Sea
Sargasso Sea
The Sargasso Sea is a region in the middle of the North Atlantic Ocean, surrounded by ocean currents. It is bounded on the west by the Gulf Stream; on the north, by the North Atlantic Current; on the east, by the Canary Current; and on the south, by the North Atlantic Equatorial Current. This...

 shows that the sea surface temperature was approximately 1 C-change cooler than today approximately 400 years ago (the Little Ice Age) and 1700 years ago, and approximately 1 °C warmer than today 1000 years ago (the Medieval Warm Period).

Using sediment samples from Puerto Rico
Puerto Rico
Puerto Rico , officially the Commonwealth of Puerto Rico , is an unincorporated territory of the United States, located in the northeastern Caribbean, east of the Dominican Republic and west of both the United States Virgin Islands and the British Virgin Islands.Puerto Rico comprises an...

, the Gulf Coast
Gulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...

 and the Atlantic Coast from Florida
Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...

 to New England
New England
New England is a region in the northeastern corner of the United States consisting of the six states of Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, and Connecticut...

, Mann et al. (2009) found consistent evidence of a peak in North Atlantic tropical cyclone activity during the Medieval Warm Period followed by a subsequent lull in activity.

Through Retrieval and Isotope analysis of Marine Cores and examination of Mollusc Growth patterns from Iceland
Iceland
Iceland , described as the Republic of Iceland, is a Nordic and European island country in the North Atlantic Ocean, on the Mid-Atlantic Ridge. Iceland also refers to the main island of the country, which contains almost all the population and almost all the land area. The country has a population...

 Patterson et al were able to reconstruct a mollusc growth record at a decadal resolution from the Roman Warm Period
Roman Warm Period
The Roman Warm Period has been proposed as a period of unusually warm weather in Europe and the North Atlantic that ran from approximately 250 BC to 400 AD....

 through the Medieval Warm Period and into the Little Ice Age

North America



The Viking
Viking
The term Viking is customarily used to refer to the Norse explorers, warriors, merchants, and pirates who raided, traded, explored and settled in wide areas of Europe, Asia and the North Atlantic islands from the late 8th to the mid-11th century.These Norsemen used their famed longships to...

s took advantage of ice-free seas to colonize Greenland
Greenland
Greenland is an autonomous country within the Kingdom of Denmark, located between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for...

 and other outlying lands of the far north. Around 1000AD the climate was sufficiently warm for the north of Newfoundland to support a Viking colony and led to the descriptor "Vinland
Vinland
Vinland was the name given to an area of North America by the Norsemen, about the year 1000 CE.There is a consensus among scholars that the Vikings reached North America approximately five centuries prior to the voyages of Christopher Columbus...

". The MWP was followed by the Little Ice Age, a period of cooling that lasted until the 19th century, and the Viking settlements eventually died out. In the Chesapeake Bay
Chesapeake Bay
The Chesapeake Bay is the largest estuary in the United States. It lies off the Atlantic Ocean, surrounded by Maryland and Virginia. The Chesapeake Bay's drainage basin covers in the District of Columbia and parts of six states: New York, Pennsylvania, Delaware, Maryland, Virginia, and West...

, researchers found large temperature excursions (changes from the mean temperature of that time) during the Medieval Warm Period (about 950–1250) and the Little Ice Age
Little Ice Age
The Little Ice Age was a period of cooling that occurred after the Medieval Warm Period . While not a true ice age, the term was introduced into the scientific literature by François E. Matthes in 1939...

 (about 1400–1700, with cold periods persisting into the early 20th century), possibly related to changes in the strength of North Atlantic thermohaline circulation
Thermohaline circulation
The term thermohaline circulation refers to a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes....

. Sediments in Piermont Marsh of the lower Hudson Valley
Hudson Valley
The Hudson Valley comprises the valley of the Hudson River and its adjacent communities in New York State, United States, from northern Westchester County northward to the cities of Albany and Troy.-History:...

 show a dry Medieval Warm period from AD 800–1300.

Prolonged droughts affected many parts of the western United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 and especially eastern California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

 and the western Great Basin
Great Basin
The Great Basin is the largest area of contiguous endorheic watersheds in North America and is noted for its arid conditions and Basin and Range topography that varies from the North American low point at Badwater Basin to the highest point of the contiguous United States, less than away at the...

. Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...

 experienced three time intervals of comparable warmth: AD
Anno Domini
and Before Christ are designations used to label or number years used with the Julian and Gregorian calendars....

 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 U.S. Review of more recent archaeological research shows that as the search for signs of unusual cultural changes during the MWP has broadened, some of these early patterns (e.g. violence and health problems) have been found to be more complicated and regionally varied than previously thought while others (e.g., settlement disruption, deterioration of long distance trade, and population movements) have been further corroborated.

Other regions


The climate in equatorial east Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...

 has alternated between drier than today, and relatively wet. The drier climate took place during the Medieval Warm Period (~AD 1000–1270).

A sediment core
Core sample
A core sample is a cylindrical section of a naturally occurring substance. Most core samples are obtained by drilling with special drills into the substance, for example sediment or rock, with a hollow steel tube called a core drill. The hole made for the core sample is called the "core hole". A...

 from the eastern Bransfield Basin, Antarctic
Antarctic
The Antarctic is the region around the Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica and the ice shelves, waters and island territories in the Southern Ocean situated south of the Antarctic Convergence...

 Peninsula, identifies events of the Little Ice Age
Little Ice Age
The Little Ice Age was a period of cooling that occurred after the Medieval Warm Period . While not a true ice age, the term was introduced into the scientific literature by François E. Matthes in 1939...

 and Medieval Warm Period. The core shows a distinctly cold period about AD 1000–1100, illustrating that during the "warm" period there were, regionally, periods of both warmth and cold.

Corals in the tropical Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

 suggest that relatively cool, dry conditions may have persisted early in the millennium, consistent with a La Niña
La Niña
La Niña is a coupled ocean-atmosphere phenomenon that is the counterpart of El Niño as part of the broader El Niño-Southern Oscillation climate pattern. During a period of La Niña, the sea surface temperature across the equatorial Eastern Central Pacific Ocean will be lower than normal by 3–5 °C...

-like configuration of the El Niño-Southern Oscillation
El Niño-Southern Oscillation
El Niño/La Niña-Southern Oscillation, or ENSO, is a quasiperiodic climate pattern that occurs across the tropical Pacific Ocean roughly every five years...

 patterns. Although there is an extreme scarcity of data from Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

 (for both the Medieval Warm Period and Little Ice Age
Little Ice Age
The Little Ice Age was a period of cooling that occurred after the Medieval Warm Period . While not a true ice age, the term was introduced into the scientific literature by François E. Matthes in 1939...

) evidence from wave-built shingle terraces for a permanently full Lake Eyre
Lake Eyre
Lake Eyre is the lowest point in Australia, at approximately below sea level, and, on the rare occasions that it fills, it is the largest lake in Australia and 18th largest in the world...

 during the 9th and 10th centuries is consistent with this La Niña-like configuration, though of itself inadequate to show how lake levels varied from year to year or what climatic conditions elsewhere in Australia were like.

Adhikari and Kumon (2001), whilst investigating sediments in Lake Nakatsuna
Lake Nakatsuna
is a lake in Nagano Prefecture, Japan. It is one of the "Nishina Three Lakes" . Its sediments have been studied in an effort to better understand climate change in Japan, finding evidence of the Medieval Warm Period and Little Ice Age....

 in central Japan, finding a warm period from AD 900 to 1200 that corresponded to the Medieval Warm Period and three cool phases, of which two could be related to the Little Ice Age. Another research in northeastern Japan shows that there is one warm/humid interval from AD 750 to 1200, and two cold/dry intervals from AD 1 to 750 and 1200 to present. Ge et al. studied temperatures in China during the past 2000 years; they 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 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.

"Temperatures derived from an 18O/16O profile through a stalagmite found in a New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...

 cave (40.67°S, 172.43°E) suggested the Medieval Warm Period to have occurred between AD 1050 and 1400 and to have been 0.75°C warmer than the Current Warm Period." The MWP has also been evidenced in New Zealand by an 1100-year tree-ring record.

See also

  • Description of the Medieval Warm Period and Little Ice Age in IPCC reports
  • Historical climatology
    Historical climatology
    Historical climatology is the study of historical changes in climate and their effect on human history and development. This differs from paleoclimatology which encompasses climate change over the entire history of the earth. The study seeks to define periods in human history where temperature or...

  • Holocene climatic optimum
    Holocene climatic optimum
    The Holocene Climate Optimum was a warm period during roughly the interval 9,000 to 5,000 years B.P.. This event has also been known by many other names, including: Hypsithermal, Altithermal, Climatic Optimum, Holocene Optimum, Holocene Thermal Maximum, and Holocene Megathermal.This warm period...

  • Hockey stick controversy
    Hockey stick controversy
    The hockey stick controversy refers to debates over the technical correctness and implications for global warming of graphs showing reconstructed estimates of the temperature record of the past 1000 years...

  • Little Ice Age
    Little Ice Age
    The Little Ice Age was a period of cooling that occurred after the Medieval Warm Period . While not a true ice age, the term was introduced into the scientific literature by François E. Matthes in 1939...

  • Paleoclimatology
    Paleoclimatology
    Paleoclimatology is the study of changes in climate taken on the scale of the entire history of Earth. It uses a variety of proxy methods from the Earth and life sciences to obtain data previously preserved within rocks, sediments, ice sheets, tree rings, corals, shells and microfossils; it then...

  • Temperature record
    Temperature record
    The temperature record shows the fluctuations of the temperature of the atmosphere and the oceans through various spans of time. The most detailed information exists since 1850, when methodical thermometer-based records began. There are numerous estimates of temperatures since the end of the...


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