Abstract
Recent studies have revealed a reduced sensitivity of tree-growth to temperature at high Northern Hemisphere (NH) latitudes during recent decades. Causes of this reduction are not known, but it seems to be for certain that this reduction has important implications for paleoclimatic reconstructions based on tree-rings because there is a risk that warmer phases of paleoclimates can be essentially underestimated if the problem is not taken into account. We add some more observational evidences of the reduction and argue: it is a signal that temperatures recently have reached above optimum levels for the tree-growth in some areas of NH. If such equally warm, or warmer, phases existed in the past, and if tree-growth responded negatively to temperatures during these phases, it would be necessary to apply separate transfer functions to calibrate tree-ring records in terms of temperature for warmer and colder phases of the past climates.
Highlights
Much focus has been placed on reconstruction of hemispheric mean air temperature variations during the latest millennia.A number of reconstructions were published based on calibrations of various, but mainly high-resolution, climate proxy data series against available instrumental surface air temperature observations in the XIXth and XXth centuries (e.g., Jones et al [1998]; Mann et al [1998, 1999]; Crowley and Lowery [2000]; Moberg et al [2005])
DATA SELECTION AND ANALYSES To begin, we present some additional analyses of correlations between regionally grouped tree-ring width series and the Northern Hemisphere (NH) annual mean near surface air temperatures after 1856, emphasizing a general change in correlation during the last few decades
If the 935 year-point is the first transition year-point the year-points of the Tornetresk tree-ring series before 935 (1000) AD must be calibrated according to the first correlation graph of Fig 3. It means the correlation between the tree-ring indices and the NH annual mean near surface air temperatures must be considered positive for the previous calendar period
Summary
Much focus has been placed on reconstruction of hemispheric mean air temperature variations during the latest millennia.A number of reconstructions were published based on calibrations of various, but mainly high-resolution, climate proxy data series (tree-rings, corals, historic documents, etc.) against available instrumental surface air temperature observations in the XIXth and XXth centuries (e.g., Jones et al [1998]; Mann et al [1998, 1999]; Crowley and Lowery [2000]; Moberg et al [2005]). A number of reconstructions were published based on calibrations of various, but mainly high-resolution, climate proxy data series (tree-rings, corals, historic documents, etc.) against available instrumental surface air temperature observations in the XIXth and XXth centuries (e.g., Jones et al [1998]; Mann et al [1998, 1999]; Crowley and Lowery [2000]; Moberg et al [2005]).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
