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New research reveals the Arctic Circle cooling over the longterm
Researcher Håkan Grudd used tree proxy data to reconstruct the temperature record of Torneträsk, deep inside the Arctic Circle. Sampling was done on Scots pines, which have grown in the region for millenia, allowing for reconstruction of a continuous record.
Grudd, of Stockholm University's Department of Physical Geography and Quaternary Geology, compared both tree ring width and maximum density, to construct the most accurate data yet seen for the region. He found a sharp warming trend since the year 1900. However, over the entire period, several such warming events were seen with temperatures in at least four periods (AD 750, 1000, 1400, and 1750) all equally warm or warmer than at present.
Most surprising of all, he noted, when taken as a whole temperatures in the Arctic have actually declined 0.3 degrees over the past 1,000 years. As Grudd himself says, temperatures at present are "not especially warm."
The full temperature record also reveals why the last 100 years has appeared unusual -- the year 1900 was actually the coldest of the entire period.
According to Grudd, the Torneträsk data aligns well with ice core isotope records from Greenland, demonstrating these climate changes were widespread throughout the Arctic region.
Grudd's results contradict his earlier reconstructions of Arctic temperatures, which demonstrated significantly cooler temperatures prior to 1900. The difference, he claims, is due to more accurate scanning of samples, along with a better understanding of how tree ring widths and density respond to temperature changes.
Text of the full paper can be found here. The work is forthcoming in the peer-reviewed journal Climate Dynamics.
Researcher Håkan Grudd used tree proxy data to reconstruct the temperature record of Torneträsk, deep inside the Arctic Circle. Sampling was done on Scots pines, which have grown in the region for millenia, allowing for reconstruction of a continuous record.
Grudd, of Stockholm University's Department of Physical Geography and Quaternary Geology, compared both tree ring width and maximum density, to construct the most accurate data yet seen for the region. He found a sharp warming trend since the year 1900. However, over the entire period, several such warming events were seen with temperatures in at least four periods (AD 750, 1000, 1400, and 1750) all equally warm or warmer than at present.
Most surprising of all, he noted, when taken as a whole temperatures in the Arctic have actually declined 0.3 degrees over the past 1,000 years. As Grudd himself says, temperatures at present are "not especially warm."
The full temperature record also reveals why the last 100 years has appeared unusual -- the year 1900 was actually the coldest of the entire period.
According to Grudd, the Torneträsk data aligns well with ice core isotope records from Greenland, demonstrating these climate changes were widespread throughout the Arctic region.
Grudd's results contradict his earlier reconstructions of Arctic temperatures, which demonstrated significantly cooler temperatures prior to 1900. The difference, he claims, is due to more accurate scanning of samples, along with a better understanding of how tree ring widths and density respond to temperature changes.
Text of the full paper can be found here. The work is forthcoming in the peer-reviewed journal Climate Dynamics.
Abstract:
This paper presents updated tree-ring width (TRW) and maximum density (MXD) from Tornetra¨sk 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 producingTRWandMXDchronologies 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 Tornetra¨sk. 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 onMXD exclusively. The new data show generally higher temperature estimates than previous reconstructions based on Tornetra¨sk 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 Tornetra¨sk suggests that this ‘‘Medieval WarmPeriod’’ in northern Fennoscandia was much warmer than previously recognized.
This paper presents updated tree-ring width (TRW) and maximum density (MXD) from Tornetra¨sk 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 producingTRWandMXDchronologies 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 Tornetra¨sk. 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 onMXD exclusively. The new data show generally higher temperature estimates than previous reconstructions based on Tornetra¨sk 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 Tornetra¨sk suggests that this ‘‘Medieval WarmPeriod’’ in northern Fennoscandia was much warmer than previously recognized.
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