This paper presents updated tree-ring width (TRW) and maximum density (MXD) from Torneträsk in northern Sweden, now covering the period AD . By including data from relatively young trees for the most recent period, a previously noted decline in recent MXD is eliminated. Non-climatological growth trends in the data are removed using Regional Curve Standardization (RCS), thus producing TRW and MXD chronologies with preserved lowfrequency variability. The chronologies are calibrated using local and regional instrumental climate records. A bootstrapped response function analysis using regional climate data shows that tree growth is forced by April-August temperatures and that the regression weights for MXD are much stronger than for TRW. The robustness of the reconstruction equation is verified by independent temperature data and shows that 63-64% of the instrumental inter-annual variation is captured by the tree-ring data. This is a significant improvement compared to previously published reconstructions based on tree-ring data from Torneträsk. A divergence phenomenon around AD 1800, expressed as an increase in TRW that is not paralleled by temperature and MXD, is most likely an effect of major changes in the density of the pine population at this northern tree-line site. The bias introduced by this TRW phenomenon is assessed by producing a summer temperature reconstruction based on MXD exclusively. The new data show generally higher temperature estimates than previous reconstructions based on Torneträsk tree-ring data. The late-twentieth century, however, is not exceptionally warm in the new record: On decadal-to-centennial timescales, periods around AD 750, 1000, 1400, and 1750 were equally warm, or warmer. The 200-year long warm period centered on AD 1000 was significantly warmer than the late-twentieth century (p \ 0.05) and is supported by other local and regional paleoclimate data. The new tree-ring evidence from Torneträsk suggests that this ''Medieval Warm Period'' in northern Fennoscandia was much warmer than previously recognized.

Tree-ring widths from 880 living, dry dead, and subfossil northern Swedish pines (Pinus syl vestris L.) have been assembled into a continuous and precisely dated chronology (the Torneträsk chronology) covering the period 5407 BC to ad 1997. Biological trends in the data were removed with autoregressive standardization (ARS) to emphasize year-to-year variability, and with regional curve stan dardization (RCS) to emphasize variability on timescales from decades to centuries. The strong association with summer mean temperature (June–August) has enabled the production of a temperature reconstruction for the last 7400 years, providing information on natural summer-temperature variability on timescales from years to centuries. Numerous cold episodes, comparable in severity and duration to the severe summers of the seventeenth century, are shown throughout the last seven millennia. Particularly severe conditions suggested between 600 and 1 BC correspond to a known period of glacier expansion. The relatively warm conditions of the late twentieth century do not exceed those reconstructed for several earlier time intervals, although replication is relatively poor and confidence in the reconstructions is correspondingly reduced in the pre-Christian period, particularly around 3000, 1600 and 330 bc. Despite the use of the RCS approach in chronology construction, the 7400-year chronology does not express the full range of millennial-timescale temperature change in northern Sweden.

The increasing carbon dioxide (CO 2 ) concentration in the atmosphere in combination with climatic changes throughout the last century are likely to have had a profound effect on the physiology of trees: altering the carbon and water fluxes passing through the stomatal pores.However, the magnitude and spatial patterns of such changes in natural forests remain highly uncertain. Here, stable carbon isotope ratios from a network of 35 tree-ring sites located Central Europe, a region where summer soil-water availability decreased over the last century.We were able to demonstrate that the combined effects of increasing CO 2 and climate change leading to soil drying have resulted in an accelerated increase of iWUE. These findings will help to reduce uncertainties in the land surface schemes of global climate models, where vegetation-climate feedbacks are currently still poorly constrained by observational data. 4