The Gulf of Alaska (GOA) is highly sensitive to shifts in North Pacific climate variability. Here we present an extended tree-ring record of January-September GOA coastal surface air temperatures ...using tree-ring width data from coniferous trees growing in the mountain ranges along the GOA. The reconstruction (1514-1999), based on living trees, explains 44% of the temperature variance, although, as the number of chronologies decreases back in time, this value decreases to, and remains around ~30% before 1840. Verification of the calibrated models is, however, robust. Utilizing sub-fossil wood, we extend the GOA reconstruction back to the early eighth century. The GOA reconstruction correlates significantly (95% CL) with both the Pacific Decadal Oscillation Index (0.53) and North Pacific Index (-0.42) and therefore likely yields important information on past climate variability in the North Pacific region. Intervention analysis on the GOA reconstruction identifies the known twentieth century climate shifts around the 1940s and 1970s, although the mid-1920s shift is only weakly expressed. In the context of the full 1,300 years record, the well studied 1976 shift is not unique. Multi-taper method spectral analysis shows that the spectral properties of the living and sub-fossil data are similar, with both records showing significant (95% CL) spectral peaks at ~9-11, 13-14 and 18-19 years. Singular spectrum analysis identifies (in order of importance) significant oscillatory modes at 18.7, 50.4, 38.0, 91.8, 24.4, 15.3 and 14.1 years. The amplitude of these modes varies through time. It has been suggested (Minobe in Geophys Res Lett 26:855-858, 1999) that the regime shifts during the twentieth century can be explained by the interaction between pentadecadal (50.4 years) and bidecadal (18.7 years) oscillatory modes. Removal of these two modes of variance from our GOA time series does indeed remove the twentieth century shifts, but many are still identified prior to the twentieth century. Our analysis suggests that climate variability of the GOA is very complex, and that much more work is required to understand the underlying oscillatory behavior that is observed in instrumental and proxy records from the North Pacific region.
ABSTRACT
While paleoclimatic studies have extended our understanding of North Pacific climate variability, these have been almost exclusively based on proxies from western North America. We present a ...tree‐ring reconstruction of June to September coastal air temperatures for Nemuro, northeastern Japan for the past four centuries. It explains 36% of the variance in instrumental temperatures and correlates significantly with indices of the atmosphere–ocean circulation. Spectral analyses reveal robust bidecadal peaks that appear associated with regional modes of western North Pacific variability. At decadal time scales, Nemuro temperatures appear to be influenced by the confluence of the Kuroshio and Oyashio currents, a primary centre of action driving Pacific Decadal Variability. Regime shifts (e.g. 1976) are weakly expressed relative to western North America. These aspects of western North Pacific climate are regionally distinct relative to those elsewhere in the basin, with greater complexity than can be attributed to the Pacific Decadal Oscillation (PDO) alone.
Large-scale millennial length Northern Hemisphere (NH) temperature reconstructions have been progressively improved over the last 20 years as new datasets have been developed. This paper, and its ...companion (Part II, Anchukaitis et al. in prep), details the latest tree-ring (TR) based NH land air temperature reconstruction from a temporal and spatial perspective. This work is the first product of a consortium called N-TREND (Northern Hemisphere Tree-Ring Network Development) which brings together dendroclimatologists to identify a collective strategy for improving large-scale summer temperature reconstructions. The new reconstruction, N-TREND2015, utilises 54 records, a significant expansion compared with previous TR studies, and yields an improved reconstruction with stronger statistical calibration metrics. N-TREND2015 is relatively insensitive to the compositing method and spatial weighting used and validation metrics indicate that the new record portrays reasonable coherence with large scale summer temperatures and is robust at all time-scales from 918 to 2004 where at least 3 TR records exist from each major continental mass. N-TREND2015 indicates a longer and warmer medieval period (∼900–1170) than portrayed by previous TR NH reconstructions and by the CMIP5 model ensemble, but with better overall agreement between records for the last 600 years. Future dendroclimatic projects should focus on developing new long records from data-sparse regions such as North America and eastern Eurasia as well as ensuring the measurement of parameters related to latewood density to complement ring-width records which can improve local based calibration substantially.
•A new northern hemisphere (NH) tree-ring (TR) summer temperature reconstruction.•The most replicated (54 data-sets) TR NH millennial reconstruction to date.•A product of the Northern Hemisphere Tree-Ring Network Development (N-TREND) consortium.•The N-TREND2015 reconstruction is robust at all time-scales from 918 to 2004.•Medieval temperature estimates are warmer than expressed by CMIP5 models.
Climate field reconstructions from networks of tree-ring proxy data can be used to characterize regional-scale climate changes, reveal spatial anomaly patterns associated with atmospheric circulation ...changes, radiative forcing, and large-scale modes of ocean-atmosphere variability, and provide spatiotemporal targets for climate model comparison and evaluation. Here we use a multiproxy network of tree-ring chronologies to reconstruct spatially resolved warm season (May–August) mean temperatures across the extratropical Northern Hemisphere (40-90°N) using Point-by-Point Regression (PPR). The resulting annual maps of temperature anomalies (750–1988 CE) reveal a consistent imprint of volcanism, with 96% of reconstructed grid points experiencing colder conditions following eruptions. Solar influences are detected at the bicentennial (de Vries) frequency, although at other time scales the influence of insolation variability is weak. Approximately 90% of reconstructed grid points show warmer temperatures during the Medieval Climate Anomaly when compared to the Little Ice Age, although the magnitude varies spatially across the hemisphere. Estimates of field reconstruction skill through time and over space can guide future temporal extension and spatial expansion of the proxy network.
•The Northern Hemisphere temperature field is reconstructed using tree-ring proxies.•Point-by-Point Regression is used at the hemisphere-scale for the first time.•Widespread warmth is detected during the Medieval Epoch.•Coherent large-scale cooling follows large volcanic eruptions.•Spatial analysis can guide future collection, updating, and network expansion.
Though tree-ring chronologies are annually resolved, their dating has never been independently validated at the global scale. Moreover, it is unknown if atmospheric radiocarbon enrichment events of ...cosmogenic origin leave spatiotemporally consistent fingerprints. Here we measure the
C content in 484 individual tree rings formed in the periods 770-780 and 990-1000 CE. Distinct
C excursions starting in the boreal summer of 774 and the boreal spring of 993 ensure the precise dating of 44 tree-ring records from five continents. We also identify a meridional decline of 11-year mean atmospheric radiocarbon concentrations across both hemispheres. Corroborated by historical eye-witness accounts of red auroras, our results suggest a global exposure to strong solar proton radiation. To improve understanding of the return frequency and intensity of past cosmic events, which is particularly important for assessing the potential threat of space weather on our society, further annually resolved
C measurements are needed.
A top priority in climate research is obtaining broad-extent and long-term data to support analyses of historical patterns and trends, and for model development and evaluation. Along with directly ...measured climate data from the present and recent past, it is important to obtain estimates of long past climate variations spanning multiple centuries and millennia. Dendroclimatic Studies at the North American Tree Line presents an overview of the current state of dendroclimatology, its contributions over the past few decades, and its future potential. The material included is not useful not only to those who generate tree-ring records of past climate- dendroclimatologists, but also to users of their results-climatologists, hydrologists, ecologists and archeologists. In summary, this book: * Sheds light on recent and future climate trends by assessing long term past climatic variations from tree rings * Is a timely coverage of a crucial topic in climate science portraying recent warming trends which are of serious concern today * Features well-reputed scientists highlighting new advanced methodologies to reconstruct past climate change * Models the tree growth environmental response
Ring-width (RW) records from the Gulf of Alaska (GOA) have yielded a valuable long-term perspective for North Pacific changes on decadal to longer timescales in prior studies but contain a broad ...winter to late summer seasonal climate response. Similar to the highly climate-sensitive maximum latewood density (MXD) proxy, the blue intensity (BI) parameter has recently been shown to correlate well with year-to-year warm-season temperatures for a number of sites at northern latitudes. Since BI records are much less labour intensive and expensive to generate than MXD, such data hold great potential value for future tree-ring studies in the GOA and other regions in mid- to high latitudes. Here we explore the potential for improving tree-ring-based reconstructions using combinations of RW- and BI-related parameters (latewood BI and delta BI) from an experimental subset of samples at eight mountain hemlock (Tsuga mertensiana) sites along the GOA. This is the first study for the hemlock genus using BI data. We find that using either inverted latewood BI (LWBinv) or delta BI (DB) can improve the amount of explained temperature variance by > 10 % compared to RW alone, although the optimal target season shrinks to June–September, which may have implications for studying ocean–atmosphere variability in the region. One challenge in building these BI records is that resin extraction did not remove colour differences between the heartwood and sapwood; thus, long term trend biases, expressed as relatively warm temperatures in the 18th century, were noted when using the LWBinv data. Using DB appeared to overcome these trend biases, resulting in a reconstruction expressing 18th–19th century temperatures ca. 0.5 °C cooler than the 20th–21st centuries. This cool period agrees well with previous dendroclimatic studies and the glacial advance record in the region. Continuing BI measurement in the GOA region must focus on sampling and measuring more trees per site (> 20) and compiling more sites to overcome site-specific factors affecting climate response and using subfossil material to extend the record. Although LWBinv captures the inter-annual climate signal more strongly than DB, DB appears to better capture long-term secular trends that agree with other proxy archives in the region. Great care is needed, however, when implementing different detrending options and more experimentation is necessary to assess the utility of DB for different conifer species around the Northern Hemisphere.
(a) Ensemble of 15 slightly different Northern Hemisphere summer temperature reconstructions from 0 to 2016 CE, together with their mean and median (orange and red), and a closer look into ...temperature changes at the onset of the Late Antique Little Ice Age (LALIA) between 530 and 550 CE. (b) Location of 23 sampling sites of 20 different species from ten genera in both hemispheres (see Table 1 for details), separated into 12 high-latitude sites <580 m asl and 11 high-elevation sites between 1900 and 3800 m asl (triangles and circles), with individual symbol sizes referring to 1–16 core or disc samples per site. (c) The three main wood anatomical responses to abrupt summer cooling: a Blue Ring (lack of cell wall lignification), Frost Ring (cell deformation) and Light Ring (reduced cell formation), formed in 536 CE by larch (Larix sibirica), pine (Pinus balfouriana) and larch (Larix sibirica) trees in the Altai, Arizona, and Yamal, respectively. (d) Temporal distribution of Blue Rings (BRs), Frost Rings (FRs) and Light Rings (LRs) between 530 and 550 CE.
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Linked to major volcanic eruptions around 536 and 540 CE, the onset of the Late Antique Little Ice Age has been described as the coldest period of the past two millennia. The exact timing and spatial extent of this exceptional cold phase are, however, still under debate because of the limited resolution and geographical distribution of the available proxy archives. Here, we use 106 wood anatomical thin sections from 23 forest sites and 20 tree species in both hemispheres to search for cell-level fingerprints of ephemeral summer cooling between 530 and 550 CE. After cross-dating and double-staining, we identified 89 Blue Rings (lack of cell wall lignification), nine Frost Rings (cell deformation and collapse), and 93 Light Rings (reduced cell wall thickening) in the Northern Hemisphere. Our network reveals evidence for the strongest temperature depression between mid-July and early-August 536 CE across North America and Eurasia, whereas more localised cold spells occurred in the summers of 532, 540–43, and 548 CE. The lack of anatomical signatures in the austral trees suggests limited incursion of stratospheric volcanic aerosol into the Southern Hemisphere extra-tropics, that any forcing was mitigated by atmosphere-ocean dynamical responses and/or concentrated outside the growing season, or a combination of factors. Our findings demonstrate the advantage of wood anatomical investigations over traditional dendrochronological measurements, provide a benchmark for Earth system models, support cross-disciplinary studies into the entanglements of climate and history, and question the relevance of global climate averages.
The original version of this Article contained an error in the Data Availability section, which incorrectly read 'All data will be freely available via https://www.ams.ethz.ch/research.html .' The ...correct version states ' http://www.ams.ethz.ch/research/published-data.html ' in place of ' https://www.ams.ethz.ch/research.html '. This has been corrected in both the PDF and HTML versions of the Article.
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