How does rising atmospheric CO2 affect marine organisms?

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Jämtland, Central Scandinavian Mountains, Sweden
Gunnarson, B.E., Linderholm, H.W. and Moberg, A. 2011. Improving a tree-ring reconstruction from west-central Scandinavia: 900 years of warm-season temperatures. Climate Dynamics 36: 97-108.

Gunnarson et al. note that "dendroclimatological sampling of Scots pine (Pinus sylvestris) trees has been made in the province of Jämtland, in the west-central Scandinavian mountains, since the 1970s," and they say that "a maximum latewood density (MXD) dataset, covering the period AD 1107-1827 (with gap 1292-1315) was presented in the 1980s by Fritz Schweingruber." Working in the same general area, they combined these historical data with "recently collected MXD data covering AD 1292-2006 into a single reconstruction of April-September temperatures for the period AD 1107-2006," using regional curve standardization (RCS), which "provides more low-frequency variability than 'non-RCS' and stronger correlation with local seasonal temperatures." This work revealed "there is a steep increase in inferred temperatures at the beginning of the twelfth century, followed by a century of warm temperatures (ca. 1150-1250)," which falls within the temporal confines of the Medieval Warm Period; and they state that "the record ends with a sharp increase in temperatures from around 1910 to the 1940s, followed by decreasing temperatures for a few decades," after which they indicate that "another sharp increase in April-September temperature commenced in the late 1990s," such that "the two warmest periods are the mid to late twentieth century and the period from AD 1150-1250," and they emphasize that the temperatures of both of these periods have been so similar that "it is not possible to conclude whether the present and relatively recent past are warmer than the 1150-1250 period."