A new paper published in Climate Dynamics claims a temperature trend of -0.3°C over the last 1,500 years in an Arctic location. The paper by Håkan Grudd is entitled: ‘Torneträsk tree-ring width and density ad 500–2004: a test of climatic sensitivity and a new 1500-year reconstruction of north Fennoscandian summers’
The Abstract states:
This paper presents updated tree-ring width (TRW) and maximum density (MXD) from Torneträsk in northern Sweden, now covering the period ad 500–2004. 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 low-frequency 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. The paper concludes: The Tornetra¨sk records of MXD and TRW are updated to AD 2004. By including MXD data from relatively young trees in the most recent period, a previously noted apparent loss of sensitivity to temperature is eliminated. These new data enable a much improved reconstruction of summer temperature for the last 1,500 years in northern Fennoscandia. Previous climate reconstructions based on tree-ring data from Tornetra¨sk were biased by a divergence phenomenon in TRW around AD 1800 and therefore show erroneously low temperature estimates in the earlier part of the records. Tornetra¨sk MXD does not show this ‘‘divergence problem’’ and hence produces robust estimates of summer temperature variation on annual to multi-century timescales. The late-twentieth century is not exceptionally warm in the new Tornetra¨sk record: On decadal-to-century timescales, periods around AD 750, 1000, 1400, and 1750 were all equally warm, or warmer. The warmest summers in this new reconstruction occur in a 200-year period centred on AD 1000. A ‘‘Medieval Warm Period’’ is supported by other paleoclimate evidence from northern Fennoscandia, although the new tree-ring evidence from Tornetra¨sk suggests that this period was much warmer than previously recognised. The paper is available under 'Open Access.' See also World Climate Report: ‘1500 Years of Cooling in the Arctic’
Jennifer Marohasy BSc PhD has worked in industry and government. She is currently researching a novel technique for long-range weather forecasting funded by the B. Macfie Family Foundation.
