Migration Period Pessimum

The Migration Period Pessimum (also referred to as Dark Ages Cold Period) was a period of unusually cold climate in the North Atlantic region, lasting from about 450 to about 900 AD. [cite journal |last=Desprat |first=Stéphanie |authorlink= |coauthors=Sánchez Goñia, María Fernanda; Loutre, Marie-France |year=2003 |month= |title=Revealing climatic variability of the last three millennia in northwestern Iberia using pollen influx data |journal=Earth and Planetary Science Letters |volume=213 |issue=1-2 |pages=63-78 |doi=10.1016/S0012-821X(03)00292-9 |url= |accessdate= |quote= ] It succeeded the Roman Age Optimum and was followed by the Medieval Warm Period.

This Migration Period Pessimum saw the retreat of agriculture, including pasturing as well as cultivation of crops, leading to reforestation in large areas of central Europe and Scandinavia. [cite journal |last=Andersen |first=S. T. |authorlink= |coauthors=Berglund, B. E. |year=1994 |month= |title=Maps for terrestrial non-tree pollen (NAP) percentages in north and central Europe 1800 and 1450 yr BP |journal=Paläoklimaforschung |volume=12 |issue= |pages=119–134 |id= |url= |accessdate= |quote= ] This period corresponds to the time following the Decline of the Roman Empire around 480 and the Plague of Justinian (541-542). [Ambrosiani, B. (1984). "Settlement expansion—settlement contraction: a question of war, plague or climate?" In: Morner, N.-A.; Karlén, W. (Eds.), "Climatic Changes on a Yearly to Millennial Basis". Dordrecht:Reidel Publishing Company, pp. 241–247.] Climatically this period was one of rapid cooling indicated from tree-ring data [cite journal |last=Eronen |first=M. |authorlink= |coauthors=Hyvärinen, H.; Zetterberg, P. |year=1999 |month= |title=Holocene humidity changes in northern Finnish Lapland inferred from lake sediments and submerged Scots pines dated by tree-rings |journal=The Holocene |volume=9 |issue= |pages=569–580 |id= |url= |accessdate= |quote= ] as well as sea surface temperatures based on diatom stratigraphy in Norwegian Sea [cite journal |last=Jansen |first=E. |authorlink= |coauthors=Koc, N. |year=2000 |month= |title=Century to decadal scale records of Norwegian sea surface temperature variations of the past 2 millenia |journal=PAGES Newsletter |volume=8 |issue=1 |pages=13–14 |id= |url= |accessdate= |quote= ] , which can be correlated with Bond event 1 in the North Atlantic sediments.cite journal| author = Bond, G. | coauthors = "et al." | url=http://rivernet.ncsu.edu/courselocker/PaleoClimate/Bond%20et%20al.,%201997%20Millenial%20Scale%20Holocene%20Change.pdf | year = 1997 | title = A Pervasive Millennial-Scale Cycle in North Atlantic Holocene and Glacial Climates | journal = Science | volume = 278 | issue = 5341 | pages = 1257-1266 | doi = 10.1126/science.278.5341.1257 ] It was also a period of rising lake levels, increased bog growth and a peak in lake catchment erosion.

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