How does rising atmospheric CO2 affect marine organisms?

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Polar Ural Mountains, Russia
Mazepa, V.S. 2005. Stand density in the last millennium at the upper tree-line ecotone in the Polar Ural Mountains. Canadian Journal of Forest Research 35: 2082-2091.

Over the period 1999-2001, the author examined evidence related to historical tree growth dynamics along a continuous altitudinal transect 860 meters long and 40-80 meters wide on the eastern slope of the Polar Ural Mountains (6648'57"N, 6534'09"E). This work revealed that "a large number of well-preserved tree remains can be found up to 60-80 meters above the current tree line, some dating to as early as a maximum of 1300 years ago," and that "the earliest distinct maximum in stand density occurred in the 11th to 13th centuries, coincident with Medieval climatic warming." Since Marzepa cites many studies that conclude that "increases in tree-line elevation, and associated increases in tree abundance within the transient tree-line ecotone, are associated with extended warm periods," and that "the vertical gradient of summer air temperature in the Polar Urals is 0.7C/100 m," we conclude that the Medieval Warm Period lasted from approximately AD 700 to 1300 and that significant portions of it were as much as 0.56C warmer than the Current Warm Period.