page_title: Medieval Warm Period
section_title: North Atlantic
hierarchical_section_title: Medieval Warm Period / North Atlantic
caption_attribution_description: English: The temperature reconstruction produced using data from all six ice cores is shown by the black line in the attached figure, and spans the period from 9690BC to AD1970. The blue lines represent two focus on the dataset, first on the Late Holocene (or Meghalayan) and then on the last millenium. It has a resolution of around 20 years, meaning that each data point represents the average temperature of the surrounding 20 years. So, the end of the record – 1970 – shows the average temperature between 1960 and 1980. The original data for the creation of these figures have been downloaded from the NOAA website: ftp://ftp.ncdc.noaa.gov/pub/data/paleo/icecore/greenland/vinther2009greenland.txt ORIGINAL REFERENCE: Vinther, B.M., S.L. Buchardt, H.B. Clausen, D. Dahl-Jensen, S.J. Johnsen, D.A. Fisher, R.M. Koerner, D. Raynaud, V. Lipenkov, K.K. Andersen, T. Blunier, S.O. Rasmussen, J.P. Steffensen, and A.M. Svensson. 2009. Holocene thinning of the Greenland ice sheet. Nature, Vol. 461, pp. 385-388, 17 September 2009. doi:10.1038/nature08355 SEE ALSO: Factcheck: What Greenland ice cores say about past and present climate change https://www.carbonbrief.org/factcheck-what-greenland-ice-cores-say-about-past-and-present-climate-change
context_page_description: The Medieval Warm Period also known as the Medieval Climate Optimum, or Medieval Climatic Anomaly was a time of warm climate in the North Atlantic region lasting from c. 950 to c. 1250. It was likely related to warming elsewhere while some other regions were colder, such as the tropical Pacific. Average 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.
  The period was followed by a cooler period in the North Atlantic and elsewhere termed the Little Ice Age. Some refer to the event as the Medieval Climatic Anomaly as this term emphasizes that climatic effects other than temperature were important.
  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 higher 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.
context_section_description: Lloyd D. Keigwin's 1996 study of radiocarbon-dated box core data from marine sediments in the Sargasso Sea found that its sea surface temperature was approximately 1 °C (1.8 °F) cooler approximately 400 years ago (the Little Ice Age) and 1700 years ago and approximately 1 °C warmer 1000 years ago (the Medieval Warm Period).
  Using sediment samples from Puerto Rico, the Gulf Coast, and the Atlantic Coast from Florida to New England, Mann et al. (2009) found consistent evidence of a peak in North Atlantic tropical cyclone activity during the Medieval Warm Period that was followed by a subsequent lull in activity.
  By retrieval and isotope analysis of marine cores and from examination of mollusc growth patterns from Iceland, Patterson et al were able to reconstruct a mollusc growth record at a decadal resolution from the Roman Warm Period to the Medieval Warm Period and the Little Ice Age.
caption: Greenland ice sheet temperatures interpreted with 18O isotope from 6 ice cores (Vinther, B., et al., 2009). The dataset ranges from 9690BC to AD1970 and it has a resolution of around 20 years, meaning that each data point represents the average temperature of the surrounding 20 years.
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