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Abstract Warming in Central Asia has been accelerating over the past three decades and is expected to intensify through the end of this century. Here, we develop a summer temperature reconstruction for western Mongolia spanning eight centuries (1269–2004 C.E.) using delta blue intensity measurements from annual rings of Siberian larch. A significant cooling response is observed in the year following major volcanic events and up to five years post‐eruption. Observed summer temperatures since the 1990s are the warmest over the past eight centuries, an observation that is also well captured in Coupled Model Intercomparison Project (CMIP5) climate model simulations. Projections for summer temperature relative to observations suggest further warming of between ∼3°C and 6°C by the end of the century (2075–2099 cf. 1950–2004) under the representative concentration pathways 4.5 and 8.5 (RCP4.5 and RCP8.5) emission scenarios. We conclude that projected future warming lies beyond the range of natural climate variability for the past millennium as estimated by our reconstruction. 

A Cedrela odorata tree ring width chronology spanning from 1786 to 2016 was developed in the quasi-equatorial eastern Amazon Basin. Annual calendar dates were assigned using dendrochronological techniques at the Federal University of Lavras, Brazil. Due to its strategic location at the edge of the Equator (approximately 0°57′S), an independent confirmation of the annual periodicity of this century-long chronology would be of great value, allowing its future use for climate reconstruction and for filling gaps in upcoming atmospheric radiocarbon (14C) compilations. For reconstruction of atmospheric 14C, high reliability of the dendrochronological calendar dates is a requirement. Here, we used high-precision 14C bomb pulse dating (BPD) of selected C. odorata tree rings as a robust independent method to validate the dendrochronological dates. Eight calendar years from across the pre-to post-bomb period were tested through 14C analysis of α-cellulose extracts (19 targets in total were produced from those 8 calendar years). All dendrochronologically dated tree rings measured produced 14C values in perfect alignment with the Southern Hemisphere 14C bomb curve, further confirming the annual growth of this important record. Extraction of α-cellulose was attained by a recently implemented procedure at the Lamont-Doherty Earth Observatory (LDEO). The method was 14C assessed by high-precision measurements at the Keck Carbon Cycle Accelerator Mass Spectrometer (KCCAMS) at the University of California, Irvine (UCI) by measuring reference materials and unknown samples. High reproducibility of reference materials (within uncertainties) showed that the novel 150-funnel system and protocol developed at LDEO is reliable and can potentially expedite cellulose extractions for 14C analysis. 

In north-western North America, the so-called divergence problem (DP) is expressed in tree ring width (RW) as an unstable temperature signal in recent decades. Maximum latewood density (MXD), from the same region, shows minimal evidence of DP. While MXD is a superior proxy for summer temperatures, there are very few long MXD records from North America. Latewood blue intensity (LWB) measures similar wood properties as MXD, expresses a similar climate response, is much cheaper to generate and thereby could provide the means to profoundly expand the extant network of temperature sensitive tree-ring (TR) chronologies in North America. In this study, LWB is measured from 17 white spruce sites ( Picea glauca) in south-western Yukon to test whether LWB is immune to the temporal calibration instabilities observed in RW. A number of detrending methodologies are examined. The strongest calibration results for both RW and LWB are consistently returned using age-dependent spline (ADS) detrending within the signal-free (SF) framework. RW data calibrate best with June–July maximum temperatures (Tmax), explaining up to 28% variance, but all models fail validation and residual analysis. In comparison, LWB calibrates strongly (explaining 43–51% of May–August Tmax) and validates well. The reconstruction extends to 1337 CE, but uncertainties increase substantially before the early 17th century because of low replication. RW-, MXD- and LWB-based summer temperature reconstructions from the Gulf of Alaska, the Wrangell Mountains and Northern Alaska display good agreement at multi-decadal and higher frequencies, but the Yukon LWB reconstruction appears potentially limited in its expression of centennial-scale variation. While LWB improves dendroclimatic calibration, future work must focus on suitably preserved sub-fossil material to increase replication prior to 1650 CE.