| Summary: | To set the current 20th century warming in a long-term context, significant efforts have been made to reconstruct hemispheric-to-global temperatures beyond the instrumental period. Tree-rings, which have annual resolution and can be precisely dated, have been widely used to infer past climate variability. In Fennoscandia, tree-ring maximum latewood density (MXD) provides so far the best high-resolution natural archive of summer temperature, and has been used to infer regional temperature variability for the last millennium. However, most of the temperature reconstructions have been based on data from northern Fennoscandia. In central Scandinavia, MXD based temperature reconstructions have not been able to reach the Medieval Climate Anomaly (MCA) when the climate conditions in some regions are analogue to the current warming, but without strong influences from human activities. This is a key period to evaluate if current warming can be reached without anthropogenic influences. To improve our understanding of past summer climate variability in central Scandinavia, in this thesis work, efforts were made to 1) find Scots pine (Pinus sylvestris L.) tree-ring samples from the central Scandinavian Mountains to increase the sample replication before 1750 CE and to extend it over the MCA, 2) examine if tree-ring data can represent annual conditions by comparing annual and summer temperature variability at different timescales in central Scandinavia. The results show that the local tree line in central Scandinavia during the MCA and early Little Ice Age (LIA) was about 140 m higher than at present. The temperature sensitivity of pine growth might be dampened by more humid growth condition. The result implies that temperature reconstructions predominantly based on the tree-ring widths from lake-shores may need to be re-evaluated. Focusing on tree-ring density, it was shown that mean absolute MXD values varied notably with elevation, with higher elevation having lower MXD values due to occurrence of the temperature ...
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