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The hydroclimatic response of the El Niño‐Southern Oscillation (ENSO) to external radiative forcing remains controversial and difficult to project with confidence for the 21st century. Annually resolved paleoclimatic reconstructions spanning the pre‐ and post‐industrial eras from the Indonesian maritime continent may provide hindcasting and diagnostic targets. Here we report δ18O observations from dendrochronologically dated teak (Tectona grandis L. f.) α‐cellulose samples collected at Muna Island, Sulawesi (5.3°S, 123°E, elevation 10 m), for November‐April growing seasons during the period 1969/70–2004/5. Age‐modeled, annually averaged α‐cellulose δ18O anomalies are significantly correlated with simulated α‐cellulose δ18O at the study site. We show that the correlation is largely explained by the amount effect in local and regional precipitation δ18O. Significant correlation with SST anomalies over the study period suggest that replicated multicentury α‐cellulose records from this archive may be interpreted as ENSO indicators. Does El Niño change when the energy balance of the climate is altered? This study sets the stage for addressing this question by developing an indirect record of El Niño from the oxygen isotopic composition of Indonesian trees growing adjacent to the warm equatorial western Pacific Ocean. The data are consistent with modeling of the record as a function of local precipitation amount, and the pattern of ocean surface temperature changes El Niño events produce. Extension of these records hundreds of years into the past should enable us to detect hypothesized changes in El Niño event occurrence over the recent geological past. We developed a modern composite oxygen isotopic record from cross‐dated teak samples from Muna, Sulawesi (5.3°S, 123°E)Observations are consistent with data simulations, and a primary response to rainfall amountSignificantly correlated with ENSO, the data point to future analysis of its forced response and the unforced variation over centuries We developed a modern composite oxygen isotopic record from cross‐dated teak samples from Muna, Sulawesi (5.3°S, 123°E) Observations are consistent with data simulations, and a primary response to rainfall amount Significantly correlated with ENSO, the data point to future analysis of its forced response and the unforced variation over centuries

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 resolution. Here we review the current understanding and merits of wood density for tree‐ring research, associated microdensitometric techniques, and analytical measurement challenges. The review is further complemented with a careful comparison of new measurements derived at 17 laboratories, using several different techniques. The new experiment allowed us to corroborate and refresh “long‐standing wisdom” but also provide new insights. Key outcomes include (i) a demonstration of the need for mass/volume‐based recalibration to accurately estimate average ring density; (ii) a substantiation of systematic differences in MXD measurements that cautions for great care when combining density data sets for climate reconstructions; and (iii) insights into the relevance of analytical measurement resolution in signals derived from tree‐ring density data. Finally, we provide recommendations expected to facilitate futureinter‐comparability and interpretations for global change research. Paleoclimatology, the study of how the climate has changed throughout earth history, is an important component of climate change research. The wood density of tree rings is a widely used parameter to study past temperature changes. Despite wood density being widely used and considered excellent for this type of research, deriving comparable measurements at different laboratories and using a variety of techniques are proving challenging. This review compiles the current understanding and merits of wood density as a proxy in paleoclimate research. We further describe and review prevalent measurement techniques and associated analytical measurement challenges. The review is also complemented with a careful comparison of a set of new measurements derived at 17 laboratories, using several different techniques. We find that there are substantial differences in measurements performed among laboratories. The main challenge is associated with the analytical resolution when measuring small features such as the density of the latewood. We provide recommendations for future work to overcome systematic differences and towards the prospect of combining measurements from different techniques in integrative studies. We review the merits and state of the art of tree‐ring wood microdensitometry and its associated analytical challengesWe show that systematic level offsets in mean wood density from different techniques and laboratories require correctionMeasurement resolution—notoriously difficult to control—is identified as the major challenge for future research applications

Volcanic eruptions have global climate impacts, but their effect on the hydrologic cycle is poorly understood. We use a modified version of superposed epoch analysis, an eruption year list collated from multiple data sets, and seasonal paleoclimate reconstructions (soil moisture, precipitation, geopotential heights, and temperature) to investigate volcanic forcing of spring and summer hydroclimate over Europe and the Mediterranean over the last millennium. In the western Mediterranean, wet conditions occur in the eruption year and the following 3 years. Conversely, northwestern Europe and the British Isles experience dry conditions in response to volcanic eruptions, with the largest moisture deficits in posteruption years 2 and 3. The precipitation response occurs primarily in late spring and early summer (April–July), a pattern that strongly resembles the negative phase of the East Atlantic Pattern. Modulated by this mode of climate variability, eruptions force significant, widespread, and heterogeneous hydroclimate responses across Europe and the Mediterranean. We investigate volcanic forcing of spring‐summer European hydroclimate over the last millennium using three paleoclimatic reconstructionsWe find significant wetting over the western Mediterranean and drying over northwestern Europe up to 3 years posteruptionPost eruption hydroclimate anomalies strongly resemble a negative phase of the East Atlantic Pattern

Two large volcanic eruptions contributed to extreme cold temperatures during the early 1800s, one of the coldest phases of the Little Ice Age. While impacts from the massive 1815 Tambora eruption in Indonesia are relatively well‐documented, much less is known regarding an unidentified volcanic event around 1809. Here, we describe the spatial extent, duration, and magnitude of cold conditions following this eruption in northwestern North America using a high‐resolution network of tree‐ring records that capture past warm‐season temperature variability. Extreme and persistent cold temperatures were centered around the Gulf of Alaska, the adjacent Wrangell‐St Elias Mountains, and the southern Yukon, while cold anomalies diminished with distance from this core region. This distinct spatial pattern of temperature anomalies suggests that a weak Aleutian Low and conditions similar to a negative phase of the Pacific Decadal Oscillation could have contributed to regional cold extremes after the 1809 eruption. Extreme post‐1809 cooling in northwestern North America was centered around the Gulf of Alaska and the southern YukonSpatial temperature patterns in North America post‐1809 are consistent with the influence of North Pacific decadal variability Extreme post‐1809 cooling in northwestern North America was centered around the Gulf of Alaska and the southern Yukon Spatial temperature patterns in North America post‐1809 are consistent with the influence of North Pacific decadal variability

Here, we present a 420‐year‐long winter lake level reconstruction for Lake Erie based primarily on temperature‐sensitive tree‐ring chronologies from Alaska, Oregon, and California. This well‐verified model explains more than 51% of the variance in winter lake levels over a 131‐year calibration period (1860–1990) and shows strong decadal fluctuations related to changes in sea surface temperatures in the North Pacific and the North Atlantic, which alternate in terms of their relative influence. Decadal variability is superimposed on a persistent secular lake level rise that began in the mid‐1900s coinciding with a growing influence of the Atlantic sector. In the context of the last 420 years, the instrumental period experienced extreme lake levels, with the lowest over the entire record during the Dustbowl and the highest in 2020. Fluctuations in Lake Erie water levels are primarily determined by climate, and their variability greatly impacts the region's infrastructure and ecosystems. Tree rings are annually resolved records of past climate. Here, we use 49 tree‐ring records from Western North America to reconstruct Lake Erie winter water levels back to CE 1600. The record shows that the lowest and one of the highest stands of the lake have occurred over the past 100 years with the lows recorded during the American Dustbowl years in the 1930s and the high in 2020. The analyses of this extended record can help to better anticipate future lake level changes in a warmer climate, which greatly affect infrastructure and ecosystems along Erie's shorelines. Western North American tree‐ring records are used to reconstruct changes in Lake Erie winter water levels for the past 420 yearsOne of the highest lake levels in the past 420 years occurred in 2020, which is the highest value in the observational record. The lowest levels occurred during the 1930s Dust BowlCorrelation of lake levels with the Pacific Decadal Oscillation and the Atlantic Multidecadal Oscillation reveal a shift from a strong North Pacific signal to one in the North Atlantic around 1960 Western North American tree‐ring records are used to reconstruct changes in Lake Erie winter water levels for the past 420 years One of the highest lake levels in the past 420 years occurred in 2020, which is the highest value in the observational record. The lowest levels occurred during the 1930s Dust Bowl Correlation of lake levels with the Pacific Decadal Oscillation and the Atlantic Multidecadal Oscillation reveal a shift from a strong North Pacific signal to one in the North Atlantic around 1960

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. We have reconstructed nearly 750 years (1269–2004 C.E.) of summer temperatures in Mongolia based on Siberian Larch tree rings, using a relatively new analysis method called delta blue intensity (DBI). This is a region of the world with relatively few long records of climate, and one that is experiencing unprecedented warming over the last three decades. This warming is projected to intensify and reach levels that go beyond the range of natural climate variability that is estimated by our reconstruction. In our analysis, we capture the warming trends observed in instrumental records as well as extreme‐cold events that coincide with the well‐documented, large‐scale volcanic events of 1459, 1601, 1810–1816, and 1885. Our results add to an increasing number of studies detailing the potential of DBI to improve paleoclimate models as compared to traditional tree‐ring width analysis, especially in Siberian Larch and other species that express a significant heartwood/sapwood color change. Optical blue intensity techniques are used to reevaluate Siberian larch cores, resulting in an eight‐century temperature reconstructionCentral Asia warmed rapidly over the past few decades; future projections exceed both observed and reconstructed temperaturesLarge tropical volcanic eruptions resulted in about a 0.6°C cooling at 1‐year post event with subsequent cooling for up to 5 years Optical blue intensity techniques are used to reevaluate Siberian larch cores, resulting in an eight‐century temperature reconstruction Central Asia warmed rapidly over the past few decades; future projections exceed both observed and reconstructed temperatures Large tropical volcanic eruptions resulted in about a 0.6°C cooling at 1‐year post event with subsequent cooling for up to 5 years

Abstract:  Distinct periods of warmth have been identified in instrumental records for New Zealand and the surrounding southwest Pacific over the past 120 years. Whether this warming is due to natural climate variability or the effects of increasing greenhouse gases is difficult to determine given the limited length of instrumental record. Longer records derived from tree rings can help reduce uncertainties in detection of possible causes of climatic change, although relatively few such records have been developed for the Southern Hemisphere. In this work, we describe five temperature-sensitive tree-ring width chronologies for New Zealand which place the recent warming trend into a long-term (pre-anthropogenic) context. Included are three pink pine (Halocarpus biformis) chronologies, two for Stewart Island and one for the North Island of New Zealand. Two silver pine (Lagarostrobus colensoi) series, one each from the North and South Islands, are updated from previous work. The length of record ranges from AD 1700 for Putara, North Island to AD 1400 for Ahaura, South Island. The pink and silver pine are different species from those used previously to reconstruct temperatures for New Zealand. All five chronologies are positively and significantly correlated with warm-season (November-April) individual station temperature records, a New Zealand-wide surface air temperature index and gridded land/marine temperatures for New Zealand and vicinity. The highest 20 and 40-year growth periods in all five tree-ring series coincide with the New Zealand temperature increase after 1950. An exception is found for the 40-year interval at Ahaura, the least temperature-sensitive of the five sites. A t-test comparison indicates that these recent growth intervals are significantly higher (0.01 to 0.0001 level) than any of those prior to the twentieth century for three of the five sites, dating as far back as AD 1500. The results suggest that the recent warming has been distinctive, although not clearly unprecedented, relative to temperature conditions inferred from tree-ring records of prior centuries.

Tree-ring widths from millennium-old Huon pine (Lagarostrobos franklinii) trees have been used to reconstruct warm season (November-April) temperatures back to AD 900 for Tasmania. The reconstruction indicates that the most recent 100 years of climate have been highly unusual, with the coldest and warmest 25-year periods occurring from 1890 to 1914 and 1965 to 1989, respectively. Although the most recent 25-year period is warmer than any comparable period over the past 1090 years, it is not yet statistically unprecedented. Some evidence for the Medieval Warm Period and the 'Little Ice Age' can be found in the reconstruction, especially during the twelfth and seventeenth centuries respectively. However, the latter is weakly expressed compared to many records from the northern hemisphere, suggesting that the southern oceans may have significantly moderated its effect on Tasmania. Regular oscillations on the order of 30, 56, 80 and 180 years in length have been identified in the reconstruction using spectral analysis. These oscillations cannot be easily linked to climatic forcing functions related to solar or volcanic activity. Thus, they are best regarded as arising from the internal dynamics of the ocean-atmosphere-cryosphere system.

Abstract.:  A tree-ring chronology network recently developed from the subantarctic forests provides an opportunity to study long-term climatic variability at higher latitudes in the Southern Hemisphere. Fifty long (1911–1985), homogeneous records of monthly mean sea-level pressure (MSLP) from the southern latitudes (15–65 °S) were intercorrelated on a seasonal basis to establish the most consistent, long-term Trans-Polar teleconnections during this century. Variations in summer MSLP between the South America-Antarctic Peninsula and the New Zealand sectors of the Southern Ocean are significantly correlated in a negative sense (r=−0.53, P<0.001). Climatically sensitive chronologies from Tierra del Fuego (54–55°) and New Zealand (39–47°) were used to develop verifiable reconstructions of summer (November to February) MSLP for both sectors of the Southern Ocean. These reconstructions, which explain between 37 and 43% of the instrumentally recorded pressure variance, indicate that inverse trends in MSLP from diametrically opposite sides of Antarctica have prevailed during the past two centuries. However, the strength of this relationship varies over time. Differences in normalized MSLP between the New Zealand and the South America-Antarctic Peninsula sectors were used to develop a Summer Trans-Polar Index (STPI), which represents an index of sea-level pressure wavenumber one in the Southern Hemisphere higher latitudes. Tree-ring based reconstructions of STPI show significant differences in large-scale atmospheric circulation between the nineteenth and the twentieth centuries. Predominantly-negative STPI values during the nineteenth century are consistent with more cyclonic activity and lower summer temperatures in the New Zealand sector during the 1800s. In contrast, cyclonic activity appears to have been stronger in the mid-twentieth than previously for the South American sector of the Southern Ocean. Recent variations in MSLP in both regions are seen as part of the long-term dynamics of the atmosphere connecting opposite sides of Antarctica. A detailed analysis of the MSLP and STPI reconstructions in the time and frequency domains indicates that much of the interannual variability is principally confined to frequency bands with a period around 3.3–3.6 y. Cross spectral analysis between the STPI reconstruction and the Southern Oscillation Index suggests that teleconnections between the tropical ocean and extra-tropical MSLP variations may be influencing climate fluctuations at southern latitudes.

A polypropylene-based material has been formulated to be suitable for fused deposition modelling (FDM). In fact, the high volumetric shrinkage and the rheological behaviour are main problems whereby polypropylene (PP) is not commonly used as a 3D printing filament. Experimental results have evidenced how material modifications have a strong impact on rheological behaviour, providing critical features that permit and improve material printability. An optimised 20 wt% talc filled heterophasic PP copolymer has been developed. The peculiar properties of the materials have been assessed by thermal characterisation and rheological analysis. Several process parameters (extrusion temperature, screw speed, cooling conditions) have been evaluated in order to obtain a proper filament. Finally, a model part has been printed using different settings to check printing quality by morphological analysis.

As the Arctic warms, tundra wildfires are expected to become more frequent and severe. Assessing how the most flammable regions of the tundra respond to burning can inform us about how the rest of the Arctic may be affected by climate change. Here we describe ecosystem responses to tundra fires in the Noatak River watershed of northwestern Alaska using shrub dendrochronology, active‐layer depth monitoring, and remotely sensed vegetation productivity. Results show that relatively productive tundra is more likely to experience fires and to burn more severely, suggesting that fuel loads currently limit tundra fire distribution in the Noatak Valley. Within three years of burning, most alder shrubs sampled had either germinated or resprouted, and vegetation productivity inside 60 burn perimeters had recovered to prefire values. Tundra fires resulted in two phases of increased primary productivity as manifested by increased landscape greening. Phase one occurred in most burned areas 3–10 years after fires, and phase two occurred 16–44 years after fire at sites where tundra fires triggered near‐surface permafrost thaw resulting in shrub proliferation. A fire‐shrub‐greening positive feedback is currently operating in the Noatak Valley and this feedback could expand northward as air temperatures, fire frequencies, and permafrost degradation increase. This feedback will not occur at all locations. In the Noatak Valley, the fire‐shrub‐greening process is relatively limited in tussock tundra communities, where low‐severity fires and shallow active layers exclude shrub proliferation. Climate warming and enhanced fire occurrence will likely shift fire‐poor landscapes into either the tussock tundra or erect‐shrub‐tundra ecological attractor states that now dominate the fire‐rich Noatak Valley. Tundra fires occur preferentially in more productive areas, and tundra vegetation is highly resilient to burningPostfire greening occurs in two phases. Phase one occurs in all plant communities immediately after a fire. Phase two occurs where and when postfire shrub expansion is facilitated by permafrost thawThe tussock and shrub fire regimes operating in the Noatak may become ecological attractor states elsewhere as tundra fires expand northward Tundra fires occur preferentially in more productive areas, and tundra vegetation is highly resilient to burning Postfire greening occurs in two phases. Phase one occurs in all plant communities immediately after a fire. Phase two occurs where and when postfire shrub expansion is facilitated by permafrost thaw The tussock and shrub fire regimes operating in the Noatak may become ecological attractor states elsewhere as tundra fires expand northward