0000000000185544
AUTHOR
Mauri Timonen
Detection and evaluation of an early divergence problem in northern Fennoscandian tree-ring data
Although not yet fully understood, reduced sensitivity of tree growth to temperature at high northern latitudes during the last ˜ 40 years is often linked to concurrent anthropogenic changes of atmospheric composition and global warming. The idea that a temporal localization of the problem could improve its understanding initiated a search for erratic growth-patterns in earlier periods of high quality dendrochronological archives. An extensive network of maximum latewood density (MXD) measurements from northern Fennoscandia likely represents one of the most reliable regional summer-temperature reconstructions. The strong coherence between proxy and instrumental data is, however, interrupted…
Ranking of tree-ring based temperature reconstructions of the past millennium
German Science Foundation [161/9-1]; National Natural Science Foundation of China [41325008]; [RNF 15-14-30011]
Old World Megadroughts and Pluvials During the Common Era
An atlas of megadroughts in Europe and in the Mediterranean Basin during the Common Era provides insights into climate variability.
Orbital forcing of tree-ring data
Based on an analysis of maximum latewood density data from northern Scandinavia, along with published dendrochronological records, this study finds evidence that previous tree-ring-reliant reconstructions of large-scale near-surface air temperature underestimated long-term pre-industrial warmth during Medieval and Roman times. Solar insolation changes, resulting from long-term oscillations of orbital configurations1, are an important driver of Holocene climate2,3. The forcing is substantial over the past 2,000 years, up to four times as large as the 1.6 W m−2 net anthropogenic forcing since 1750 (ref. 4), but the trend varies considerably over time, space and with season5. Using numerous hi…
Scientific Merits and Analytical Challenges of Tree‐Ring Densitometry
X-ray microdensitometry on annually resolved tree-ring samples has gained an exceptional position in last-millennium paleoclimatology through the maximum latewood density (MXD) parameter, but also increasingly through other density parameters. For 50 years, X-ray based measurement techniques have been the de facto standard. However, studies report offsets in the mean levels for MXD measurements derived from different laboratories, indicating challenges of accuracy and precision. Moreover, reflected visible light-based techniques are becoming increasingly popular, and wood anatomical techniques are emerging as a potentially powerful pathway to extract density information at the highest resol…
On the hidden significance of differing micro-sites on tree-ring based climate reconstructions
Tree-ring chronologies are commonly extended back in time by combining samples from living trees with relict material preserved in man-made structures or natural archives (e.g. lakes). Although spatially close, these natural archives and living-tree-sites often comprise different micro-climates. Inhomogeneous growth conditions among these habitats, which may yield offsets in growth-rates, require caution in data processing. Here we assess species-specific growth dynamics in two micro-habitats and their potential effects on long chronologies by combining tree-ring data from different living-tree-sites with an âartificialâ subfossil dataset. Well replicated (nâ>â80) Norway spruce (…
Causes and consequences of past and projected Scandinavian summer temperatures, 500-2100 AD
Tree rings dominate millennium-long temperature reconstructions and many records originate from Scandinavia, an area for which the relative roles of external forcing and internal variation on climatic changes are, however, not yet fully understood. Here we compile 1,179 series of maximum latewood density measurements from 25 conifer sites in northern Scandinavia, establish a suite of 36 subset chronologies, and analyse their climate signal. A new reconstruction for the 1483–2006 period correlates at 0.80 with June–August temperatures back to 1860. Summer cooling during the early 17th century and peak warming in the 1930s translate into a decadal amplitude of 2.9°C, which agrees with existin…
Micro-site conditions affect Fennoscandian forest growth
Abstract The long tradition of dendroclimatological studies in Fennoscandia is fostered by the exceptional longevity and temperature sensitivity of tree growth, as well as the existence of well-preserved subfossil wood in shallow lakes and extent peat bogs. Although some of the world’s longest ring width and density-based climate reconstructions have been developed in northern Fennoscandia, it is still unclear if differences in micro-site ecology matter, and if so, whether they have been considered sufficiently in previous studies. We developed a Fennoscandia-wide network of 44 Scots pine ring width chronologies from 22 locations between 59°–70 °N and 16°–31 °E, to assess the effects of moi…
Variability and extremes of northern Scandinavian summer temperatures over the past two millennia
article i nfo Palaeoclimatic evidence revealed synchronous temperature variations among Northern Hemisphere regions over the past millennium. The range of these variations (in degrees Celsius) is, however, largely unknown. We here present a 2000-year summer temperature reconstruction from northern Scandinavia and compare this timeseries with existing proxy records to assess the range of reconstructed temperatures at a regional scale. The new reconstruction is based on 578 maximum latewood density profiles from living and sub-fossil Pinus sylvestris samples from northern Sweden and Finland. The record provides evidence for sub- stantial warmth during Roman and Medieval times, larger in exten…
Climate signal age effects in boreal tree-rings: Lessons to be learned for paleoclimatic reconstructions
Abstract Age-related alternation in the sensitivity of tree-ring width (TRW) to climate variability has been reported for different forest species and environments. The resulting growth-climate response patterns are, however, often inconsistent and similar assessments using maximum latewood density (MXD) are still missing. Here, we analyze climate signal age effects (CSAE, age-related changes in the climate sensitivity of tree growth) in a newly aggregated network of 692 Pinus sylvestris L. TRW and MXD series from northern Fennoscandia. Although summer temperature sensitivity of TRW ( r All = 0.48) ranges below that of MXD ( r All = 0.76), it declines for both parameters as cambial age in…