How does rising atmospheric CO2 affect marine organisms?

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Southern Swedish Scandes
Kullman, L. 1998. Tree-limits and montane forests in the Swedish Scandes: Sensitive biomonitors of climate change and variability. Ambio 27: 312-321.

Kullman, L. and Oberg, L. 2009. Post-Little Ice Age tree line rise and climate warming in the Swedish Scandes: a landscape ecological perspective. Journal of Ecology 97: 415-429.

Kullman and Oberg (2009) assessed tree line elevations at over a hundred different sites spread across an 8000 km2 area in the southern Scandes of Sweden (6105'N to 6325'N, 1203'E to 1311E) based on data obtained in 1915, 1975 and 2007, comparing the results with maximum elevations achieved by trees during the Medieval Warm Period. The increases they observed over this period represent, in their words, "a full positional recovery from Little Ice Age tree line regression," which implies a return to equivalent Medieval Warm Period elevations. However, they also state that "to the best of our present-day knowledge, the maximum upshifts of the tree lines seem to have reached slightly above the positions held during the Medieval Warm Period (AD 900-1300)." Yet again, in an earlier study that included the same region but extended a bit further (61-66N, 12-15E), Kullman (1998) said that "tree-limits and high-elevation forests were far from restored to their medieval levels," which by AD 900-1100 "were situated 80-100 meters higher" than they were about a century ago, i.e., ~1900. And he further added that "during the past few decades," i.e., during the latter part of the 20th century, there was widespread "rapid cold-induced dieback." Consequently, it is difficult to reconcile the different conclusions of the two papers; and we thus conclude that the peak temperatures of the two periods for the smaller area of the current study were probably essentially equivalent.