Tree-Ring-Reconstructed Summer Temperatures from Northwestern North America during the Last Nine Centuries*

Abstract

Northwestern North America has one of the highest rates of recent temperature increase in the world, but the putative ''divergence problem'' in dendroclimatology potentially limits the ability of tree-ring proxy data at high latitudes to provide long-term context for current anthropogenic change. Here, summer temperatures are reconstructed from a Picea glauca maximum latewood density (MXD) chronology that shows a stable relationship to regional temperatures and spans most of the last millennium at the Firth River in northeastern Alaska. The warmest epoch in the last nine centuries is estimated to have occurred during the late twentieth century, with average temperatures over the last 30 yr of the reconstruction developed for this study in the Common Era (CE)] approximately 1.38 6 0.48C warmer than the long-term preindustrial mean (1100-1850 CE), a change associated with rapid increases in greenhouse gases. Prior to the late twentieth century, multidecadal temperature fluctuations covary broadly with changes in natural radiative forcing. The findings presented here emphasize that tree-ring proxies can provide reliable indicators of temperature variability even in a rapidly warming climate.

Experiments based on blue intensity for reconstructing North Pacific temperatures along the Gulf of Alaska

“…2), this would result in markedly warm temperature estimates during the Little Ice Age (LIA) compared to the 20th century, which is at odds with previous GOA dendroclimatic analyses (Wiles et al, 2014) and the geomorphological record, which indicate substantial cool conditions and glacial advance from the 17th to 19th centuries (Wiles et al, 2004;Solomina et al, 2016). RCS can impart significant low-frequency bias when the assumptions and requirements of the method are not met (Melvin and Briffa, 2014;Anchukaitis et al, 2013). Furthermore, as the GOA composite utilizes only living trees, this is a far from optimal sample design for this detrending (Table 3).…”

“…Schweingruber, 1988;Briffa et al, 2002;Anchukaitis et al, 2013;Schneider et al, 2015), but such records do not yet exist for the GOA. MXD series are particularly desirable as such records often have stronger correlations with temperatures than RW and result in climate reconstructions with better skill and spectral fidelity (Anchukaitis et al, 2013;Esper et al, 2015;Wilson et al, 2016;Anchukaitis et al, 2017). This is partly because RW chronologies typically exhibit higher autocorrelation and lagged memory effects than MXD (Briffa et al, 2002;Anchukaitis et al, 2012), but also because RW may potentially integrate other ecological signals (e.g.…”

“…disturbance and stand dynamics), which can obscure the climate signal (Rydval et al, 2015). However, only two millennial-length MXD records are currently published for all of north-western North America (Columbia Icefield, Canada, Luckman and Wilson 2005;Firth River, Alaska, Andreu-Hayles et al, 2011;Anchukaitis et al, 2013) and no MXD data have been generated to date for the entire GOA. This situation partly relates to the expensive and labourintensive nature of MXD measurement, but also because the wood of mountain hemlock (Tsuga mertensiana), a dominant conifer species in the GOA, is rather brittle and does not lend itself well to standard sample preparation for MXD measurement.…”

Autumn–winter minimum temperature changes in the southern Sikhote-Alin mountain range of northeastern Asia since 1529 AD

“…Then, the COFECHA program was used to check the accuracy of the cross-dated measurements (Holmes, 1983). To mitigate the potential trend distortion problem in traditionally detrended chronology (Melvin and Briffa, 2008;Anchukaitis et al, 2013), we used a signal-free method (Melvin and Briffa, 2008) to detrend the tree ring series using the RCSigFree program (http://www.ldeo.columbia.edu/ tree-ring-laboratory/resources/software).…”

“…4). It is widely known that tree ring growth in cold and wet ecotopes, situated on sufficiently high elevation in the Northern Hemisphere, strongly correlate with temperature variability in large areas of Asia, Eurasia, and North America (Zhu et al, 2009;Anchukaitis et al, 2013;Thapa et al, 2015;Wiles et al, 2014). The limiting influence of temperature on P. koraiensis growth has been mentioned in many studies Yin et al, 2009;Zhu et al, 2009).…”