500-year paleoclimate record inferred from Greenland Juniper wood contextualizes current climate warming

Domain: earth_science
Published: 2025-11-26
Editorial outcome: major_revision

Abstract
Contextualising Arctic warming and sea ice loss requires high-resolution climate proxy archives, which are rare across the high northern latitudes. Here, we present annually resolved and absolutely dated tree-ring width measurements of living and dry juniper (Juniperus communis) shrubs, as well as herbarium specimens, all from southern Greenland. We develop a continuous chronology for 1526–2023 CE that correlates at 0.67 with mean June‒August temperatures (p<0.001). We then identify reduced cell wall lignification (i.e., “Blue Rings”) during exceptionally cold summers that often occurred after large volcanic eruptions, with Laki in 1783 and Tambora in 1815 CE causing the strongest responses. Our findings at the interface of dendroclimatology and wood anatomy provide a high-resolution paleoclimate record for southern Greenland that places anthropogenic warming in the context of natural climate variability.

Introduction
The Arctic is warming at approximately 2–4 times the global average1. Known as Arctic Amplification, driven by human-induced greenhouse gas emissions, and manifested in the rapid loss of large ice masses2, this trend is particularly strong during the past decades3. Understanding past temperature changes is essential to provide a baseline for assessing how the Arctic may respond to future warming. High-resolution climate proxy records are, however, sparse across the high northern latitudes4. Greenland, with a large body of rapidly melting ice cap, plays a pivotal role in advancing our understanding of the impact of climate change on the natural environment, not only in the Arctic but also globally5.

Climate reconstruction from Greenland primarily refers to using ice cores extracted from Greenland’s ice sheets to understand past climate conditions6. These ice cores contain trapped air bubbles, isotopes, dust, and other compounds that can reveal information about environmental changes over time. Using ice cores has challenges, such as limited geographical coverage (ice sheet), dating uncertainties, and limited temporal resolution7. It should be, however, emphasised that ice cores provide the most comprehensive record of volcanic eruptions that have contributed to periods of cooling8–10. The results from the sediment cores recovered from Greenlandic lakes provide an invaluable addition to the findings derived from the ice core samples. The continuous archive of past environmental changes based on these proxy data spans the entire Holocene11,12. Nevertheless, a potential limitation of these studies is the possibility of errors in the interpretation of 14C and 210Pb-dated sediment cores, involving e.g. problems of dating calibration and different sedimentation rates and disturbances13,14. Tree rings, one of the most widely used climate proxies, are invaluable and powerful sources of climate information due to their high resolution, accurate year-by-year dating, and the ability to reconstruct decadal to millennial-scale climate conditions15. However, the age of the tundra plants has limited the application of the dendrochronological method in Greenland. Existing shrub records of Alnus viridis, Salix glauca and Juniperus communis from West Greenland16–20, Salix arctica from north-eastern Greenland21 or from the only natural forest with Betula pubescens located in Qinngua Valley, southern Greenland22,23 do not reach the pre-instrumental period. Until now, the existing dendrochronological data for Greenland have been insufficient for reconstructing the climate over the centuries.

Here, we present the combined dendrochronological and wood anatomical assessment of living and dead juniper wood from southern Greenland to reveal annually resolved and absolutely dated insights about natural summer temperature variability back into the Little Ice Age. This reconstruction extends beyond the instrumental period in Greenlandic terrestrial areas outside the ice sheet. Additionally, we aimed to assess the usefulness of the so-called “blue rings” as an indicator of post-volcanic cooling and as a key anatomical feature allowing for the synchronisation of juniper samples. Our study contributes to the understanding of the effects of volcanic eruptions on climate by combining wood anatomical observation with superposed epoch analysis to explore the significance of selected eruptions on growth ring width and blue ring formation. In order to more accurately evaluate the reliability of the reconstruction, we conducted thorough comparisons with other proxy data from southern Greenland and dendroclimatic reconstructions from the Arctic.

Results
Dendrochronological dating and construction of long-term composite juniper chronology
The oldest living shrub contained 367 growth rings, which, combined with historic and dry wood samples accounting for up to 354 years, made it possible to construct a reliable, well-replicated 498-year growth-ring chronology (1526–2023 CE). The mean width of annual growth was 0.400 (±0.227) mm/yr. Owing to the typical features of junipers, such as slow, irregular growth; eccentricity of growth; and high frequency of missing rings, juniper cross-dating was challenging; thus, from a total of 127 samples, only 51 samples were incorporated into the composite chronology (Table 1, Fig. 1). To obtain the best possible climate signal, only the well-correlated samples were selected. Statistical indicators of the quality of chronology, such as the average correlation between series (rbar) and expressed population signal (EPS), are variable over time but remain above the accepted critical thresholds (Fig. 2). Juniper is a very challenging species for dendrochronological investigations. The reliability of our dating is enhanced by implementing the serial sectioning method and several microscopic cross-sections, which significantly improve the legibility of extremely narrow growth, as well as the use of blue rings as time markers (Fig. 3). We detected 8 years with frost and 13 years with blue rings, most of which appeared after significant volcanic eruptions (Fig. 1). This was significantly less than in the few existing works on the occurrence of blue rings worldwide24,25, making them unambiguous biochronological features. Difficulties in dating the juniper samples and the rejection of half the samples were already indicated by Pellizzari et al.26 and Carrer et al.27 for alpine areas. In only a few dendrochronological studies to date, it has been possible to assemble a multi-century chronology of junipers from Arctic sites, of which the longest, based on both living and dry branches, comes from the Kola Peninsula (>500 yrs28), the Polar Urals (>600 yrs29), and northern Iceland (>800 yrs30). Recently, very old specimens of junipers have also been described for sites in northern Fennoscandia (Sør-Varanger, Kevo, Abisko) by Lehejček et al.31 and Carrer et al.32. The assembled juniper chronologies for Greenland mainly concerned the area around Nuuk, where the relation to climate and Greenland Ice Sheet melting was elaborated over the last century18,33. Juniper discs with more than 200-300 rings were collected from southernmost Greenland during the scientific expeditions to Greenland at the end of the 19th century34, and have recently been reconfirmed.

Climate sensitivity
Although the usefulness of Greenland dendrochronological data as a climate proxy has previously been questioned35, in our study, the significant climate sensitivity of juniper ring width was demonstrated (Fig. 4A, B). Unlike in alpine tundra, where juniper growth is mainly controlled by the amount of winter precipitation26,27, the growth of juniper shrubs from the Greenlandic tundra zone is limited by the temperature in the current summer. Similarly, junipers from other circum-Arctic sites are temperature-stressed18,29,30,36; however, the strength of the signal varies depending on inter alia sampling strategy (adequate replication, proximity to the root collar) and site characteristics (homogeneity, geomorphic disturbances). To determine the suitability of juniper rings from southern Greenland as a climate proxy for reconstruction, dendroclimatic tests with several factors were carried out (Fig. 4A, B). The results primarily indicated time-stable, strong positive correlations between the growth ring index and summer air temperature (r = 0.72, AD 1961–2023, p<0.001). The positive correlation between winter-spring minimum temperature and juniper growth (r = 0.38, r = 0.34, 1961-2013, p<0.01) corresponds with the negative correlation with snow cover, indicating that less snow cover and faster snow melt have a positive effect on juniper growth. However, it should be noted, that precipitation was not statistically significant, as plants have access to moisture through both precipitation and high air humidity. So, long-lasting snow cover is unfavourable to juniper growth, thereby significantly shortening the length of the growing period during a short Arctic summer. These results concur with findings from other parts of Greenland where deciduous shrubs exhibit a consistent negative response towards the amount of snow precipitation37,38. A statistically significant dependence of the annual growth of junipers on cloud cover during the winter months was found (r = 0.32, 1961–2013, p<0.05), as the strong radiation of heat from the ground during cloudless periods, especially in winter, led to large temperature decreases. This was also confirmed by the results of the negative effect of low winter temperatures on juniper growth.

Sea ice loss may have a dominant effect on local coastal temperatures but a small contribution to overall warming in Greenland39. Given the lack of complete consensus on the effects of sea ice loss on shrub growth, we investigated the relationships between juniper growth and sea ice extent (Fig. 4C). The results of the present study revealed an increasing trend in juniper growth with decreasing sea ice extent (r = −0.59, 1901–2015, p<0.001), particularly during notable recurrent periods of significant ice cover increases in 1907, 1935–1936, 1983–1984 and 2008, resulting in low growth. However, attempts to reconstruct this element have been unsuccessful and require future study, as sea ice extent does not necessarily have a simple linear relationship with summer temperature.

Five-century-long reconstruction of summer temperatures
A mean summer temperature reconstruction from 1526 to 2023 CE was obtained via the linear regression equation. The coefficient of determination was 0.52, indicating that 52% of the variance was predicted by the model, which passed commonly used calibration and verification statistics (Fig. 4D-F). The reconstructed mean annual temperature during the last 498 years was 9.4°C, similar to that of the reference period of 1961–1990 (9.3°C), but much warmer in the 21st century (10.6°C) (Fig. 5). The long-term trend in the five hundred-year-long June–July–August (JJA) temperature reconstruction was insignificant. However, there has been a warming trend over the last century, especially since the second half of the 20th century and throughout the first decade of 21st century (the mean annual temperature trend +0.15°C decade-1, the JJA trend was 0.25°C decade-1 (p≤0.01) from 1961–2010). The meteorological and tree ring data are consistent and show that the southern part of Greenland experienced decadal periods of both cooling and warming during 1961–2023, with an inflection point around the mid-1990s, and no significant warming after ∼2010 (Fig. 6). The reasons for this variability can be found in the regional influence of the large-scale circulation, represented by the indices for the NAO (North Atlantic Oscillation) and GBI (Greenland blocking index). Zhang et al.40 concluded that, since 2011, there has been a shift towards a more negative phase for GBI and a more positive phase for NAO, but at the same time, these have been highly variable, with more modest values and reduced warming recently.

Similarly, a warming trend was recorded only during the decade of 1650–1660, but the summer temperatures in the 2000s and 2010s were significantly higher than those in previous centuries (anomaly of +1.5°C). These results had significant environmental consequences, as each 1°C increase in summer temperature corresponds to approximately 116 Gt*yr−1 of GrIS (surface) mass loss and a 26 Gt*yr−1 increase in solid ice discharge41. Recently, using ice core-based temperature reconstruction, Hörhold et al.42 reported that the warming in central and northern Greenland in the first decade of the 21st century exceeded the range of preindustrial temperature variability in the past millennium. Even though warming has not progressed at the same rate across the island, on the basis of dendroclimatological reconstruction, it can be concluded that the warming in southern Greenland in the first decades of the 21st century has been unprecedented over the last 500 years. Strong warming in the 20th century, which contrasts sharply with the preceding cooling trend, was documented in the Arctic on the basis of multi-proxy records; however, records from Greenland were mostly from glacier ice43.

It was assumed that the Little Ice Age (LIA) for the Northern Hemisphere occurred over a period of approximately 480 years, spanning AD 1440–1920. The available proxy data suggest that the LIA in Greenland began in approximately 1250 AD, peaked in the 15th century, and ended in the mid-18th to early mid-19th centuries. However, the exact timing of individual fluctuations remains problematic due to poor chronological resolution44 or asynchronous advances of mountain glaciers during the LIA. Interestingly, the glaciological evidence for southernmost Greenland, i.e., the 10Be surface exposure age of the prominent Narsarsuaq moraine, does not confirm that the LIA was the most notable period, thereby dating the maximum extent of the Kiagtût Sermiat glacier to much earlier, i.e., to the late Holocene pre-LIA maximum45.

Owing to juniper growth-ring-based JJA temperature reconstruction, we accurately traced summer temperature fluctuations in the southern fjords of Greenland from the present to the mid-16th century. While we could not pinpoint the start of the LIA, three periods were identified: the first was a long cool period (1570–1650) preceded by brief warming; the second was a period of highly dynamic cool and warm periods (1651–1815); and the third was another long cool period ending the LIA at the beginning of the 20th century (1816–1918), when the long-term trend of rising temperatures began. In light of the dendrochronological data, it should be concluded that the LIA was not a period of uniform cold weather in southern Greenland. We found substantial increases in temperature in approximately 1550–1570, 1650–1670, and 1740–1750, but the warming of the early 20th century did not appear very clearly. Particularly interesting was the reconstruction of the solar activity-related cooling during the Maunder Minimum (MM) period (1637–1717), which was a very dynamic period in southern Greenland. The early MM started as a very cold decade and then was split by the warmest two decades, 1654–1674, and the late MM showed evident strong cooling, culminating in the early 18th century. The following century was a period of climatic fluctuations with distinct cooling after the eruption of Tambora in 1815. Another very cool period was the turn of the 19th and 20th centuries, with the lowest temperatures occurring from 1915 to 1917.

A comparison of the dendroclimatic reconstruction from unglaciated coastal areas of southern Greenland with other climate proxy-based reconstructions (marine sediment core, ice core, and lake sediment) and historical climate data46 revealed similarities in the climate history of the southern coast of Greenland (Fig. 7). In the closest vicinity of the juniper study sites, climate variability was previously inferred from Lake Igaliku sediments47. A comparison of the data obtained from the chironomid assemblages with the juniper-based reconstruction reveals a number of similarities, except for the periods between 1640 and 1790, and between 1920 and 1970. The most consistent signals are the strong modern warming and the relatively warm conditions during the Dalton Minimum and the warming of the early 17th century (Fig. 7E). There was also a remarkable correspondence between the diatom-inferred August sea surface temperature from the marine sediment core48 and the terrestrial record of Juniperus communis growth rings (Fig. 7B). Common cooling occurred at the end of the 16th century, followed by abrupt, significant warming in the mid-17th century, a colder turn in the 17th and 18th centuries, and a relatively warm turn in the 18th and 19th centuries, culminating in marked cooling concentrated in the mid-19th century. Most of these fluctuations, especially the pronounced warming of the mid-17th century, were also exhibited by ice core-based reconstruction49 (Fig. 7D). The least concordant was the compilation of the 59 proxy data for the Arctic50, although the high degree of concordance in the 16th and 17th centuries was noteworthy (Fig. 7G). Interestingly, this strong mid-17th-century warming in all the proxy data from southern Greenland was quite pronounced, and the warming is also known from early instrumental data from England and Western Europe.

Comparisons of the new dendrochronological record from southern Greenland with dendrochronological data from the northern treelines of Eurasia and North America revealed similarities and significant differences in pan-Arctic temperature variability (Fig. 8). The greatest agreement was found in the Northern Quebec temperature reconstruction51, which shows similar fluctuations in both warm (recent warming; turn of the 18th and 19th centuries; first half of the 18th century) and cool (1840s–1950s) periods. By contrast, the common warm periods in Greenland and Alaska52 are the recent warming period, the 18th century, and the mid-16th century. The most notable inconsistency concerns the Maunder Minimum period, which is distinctly cold in many reconstructions, but not clearly marked in Greenland. Similarly, this MM cooling is absent in data from the Russian Arctic29. The reconstruction of temperature variability from the Kola Peninsula53 differs most significantly, with only the warming and subsequent cooling in the 17th century being consistent with that observed in southern Greenland (Fig. 8).

Extreme years
Extreme years are manifested by the occurrence of narrow rings or disrupted cell formation, such as BRs and FRs (Fig. 3). Most of these extreme years, associated with volcanic eruptions, are consistent with studies carried out at the northern tree limit in both Asia and North America, e.g. 1600, 1641, 1783, 1815-1817, 1868, 1884, 1912, 1916-191754–58. Interestingly, the cooling after the Laki and Tambora eruptions was visible in the reconstruction as a pronounced temperature drop 1 year after the eruption, but not the largest occurring at the 500-year scale analysed. Similarly, the Katamai eruption barely registered at all. However, the record of these events in wood anatomy was very clear (FR in 1912; BR in 1783 and 1815). In total, we detected 8 years with FR and 13 years with BR, of which BRs were most common in 1783 (33%) and 1815–16 (24%) (Fig. 5A). The growth-ring width integrates favourable conditions of a longer growing season, whereas BR and FR wood anomalies reflect rapid and short-term temperature drops. For example, the FRs in 1999 and 2007 were associated with daily temperatures below freezing in May. However, determining the meteorological reasons for the formation of blue rings is difficult, as they occur mainly during periods for which no instrumental data are available. Interestingly, BRs were more common in the earlier period (and dry wood samples) than in the modern period, when FR mostly occurred. In general, BRs appear to occur during warm periods, such as the 1720–1820 period and the modern warm period. In contrast, FRs occur more frequently during the cool episodes of the Little Ice Age. These results corroborate the hypothesis that prolonged cooling does not diminish lignification but rather increases the likelihood of frost-related damage. These observations coincide with the results of studies conducted at the upper treeline in the Swiss Alps59.

We evaluated the accuracy of our dendrochronological data by comparison with volcanic signals from the Greenland ice sheet10. Volcanic aerosol peaks contained in the ice core (NEEM-2011-S1) are consistent with dendrochronological signals (narrow rings, BRs, FRs), which are closely related to major volcanic eruptions (Fig. 5A, B). This is particularly pronounced in years of volcanic eruptions: Huaynaputina (1600), Mt. Parker (1641), Hekla (1963), Laki (1783), Tambora (1815), Mt. Katmai (1912). These events were followed by the occurrence of BRs, FRs or strong growth reduction in tree-ring records. Superposed epoch analyses show a clear post-volcanic cooling signal after most major eruptions, or with a response lagged by one year (Fig. 5C). Of particular interest is the response of Greenland’s junipers to the major eruptions of Laki and Tambora, where BRs were recorded in the year of the eruption and narrow growth a year later (Fig. 5Ca).

Imprint of the Laki (1783–1784) eruption on the dendrochronological record from Greenland
The 8-month Laki eruption in southern Iceland, from 8 June 1783 to 7 February 1784, was one of the largest and best-documented eruptions in historic times. It produced the second-largest basaltic lava flow and the second-largest pyroclastic fall deposit from an Icelandic eruption. The Laki eruption had a major impact on Northern Hemisphere temperatures, causing a cooling of 1–2°C below average. The year 1783 was referred to in Europe as ‘Annus Mirabilis’, and there are many historical records (weather logs, diaries, scientific publications and newspaper articles) of the occurrence of phenomena such as widespread sulfuric aerosol clouds, referred to as dry fog and haze in chronicles in Europe at this time60.

The initial appearance of the Laki haze is well documented. The eruption was most intense during the first 1.5 months. Analysis of synoptic weather maps suggests that bulk transport occurred at the level of the polar jet stream, and those that reached Greenland were most likely tropospheric; they were first transported east or northeast by southwesterly winds and then sank and deposited material on the Greenland ice cap after circumnavigating the polar region60. Several observations from Iceland, Greenland and other Nordic countries were recorded at the end of June 1783. Smoky haze was observed around Nuuk (Godthab) in Greenland, where, according to the Ephemerides Societatis Meteorologicae61, “the sky was covered with clouds resembling smoke”. This coincides with the immediate appearance of the Laki signal in the early summer snow of 1783. Highly elevated acidity levels were detected in the Greenlandic ice cores62. Unfortunately, the available meteorological data (SW Greenland series) do not cover 1783 or the first half of 1784. However, the average monthly temperatures for the second halves of 1784 and 1785 were significantly lower than the average for the period of 1900–2020.

A dendrochronological and cellular-scale record from Greenlandic Juniper facilitates the cell-by-cell tracing of this extraordinary Laki event (Fig. 3). The annual growth in 1783 was relatively wide (comprising approximately 10–15 rows of cells), and the growth of shrubs started as it would have in any “normal year”. However, following the eruption of the Laki volcano, the final rows of cells exhibited incomplete lignification of the cell walls, as evidenced by the presence of the blue ring in the dyed wood samples. This phenomenon serves as an exemplary illustration of the efficacy of the BR as a sensitive indicator of a sudden temperature decrease following a major eruption. Intriguingly, the subsequent year of 1784 was characterised by a remarkably narrow ring, which was a consequence of the deterioration of weather conditions that ensued after the eruption. This record stands as the sole explicit dendrochronological documentation of extreme environmental conditions following the Laki eruption, with prior research indicating that ring width values for 1783 are not atypical for treeline sites in Alaska and the Yukon Territory. However, analysis of wood density has attributed the unusually low density and lighter appearance to the cold, volcanic summer of 178363. Newer research, on the basis of anatomical analysis of wood from Alaskan trees, confirmed a very thin cell wall in the ring of 178364. It is hypothesised that the Inuit ‘Time Summer Time Did Not Come’, described in oral history as a disaster caused by extreme cold and an abrupt end of the warm season after June passed, with no warm weather until the next spring, occurred in 1783 because of the eruption of Laki63. According to Jones et al.65, the years 1783 and 1784 are not considered extremely low density for Europe. The limited work on the occurrence of blue rings shows no wood anatomical effects of the Laki eruption in 1783–1784, a small signal following the Tambora eruption in 1815, a clear record of the Samalas eruption, and a highly visible cluster of BRs near 536 CE24,25,66.

In conclusion, the results extend the research potential of dendrochronology beyond the northern treeline into polar tundra areas, which have not been entirely represented in long-term dendroclimatological reconstructions. The developed record is one of the longest growth ring chronologies for Arctic shrubs to date. We reconstructed a half millennium of summer temperatures in southern Greenland using annual ring chronologies and wood anatomical anomalies of living, dry and historical junipers. The unique results obtained through the use of specimens from historical scientific expeditions, currently preserved in herbaria, highlight the importance of reanalysing old botanical collections using modern analytical techniques. Since the area of our research, located within Eriksfjord, was inhabited by the Vikings from 985 CE to the mid-15th century (Eastern Settlement), research into past climate change is becoming increasingly important. Integrating wooden archaeological finds from this area with the established five-century-long juniper growth ring chronology will be the next step in reconstructing past changes in this area over a period of environmental changes at the turn of the 15th and 16th centuries.

We have made the absolute dating of extremely challenging research material more reliable by using not only a classical cross-dating method but also independent chronological markers—blue rings—a thermally induced, disturbed cell wall lignification visible on double-stained thin sections of wood. The analysis of these anatomical changes has allowed for a significant deepening of conclusions. Wood samples from southern Greenland made it possible to study the effect of a large explosive eruption on the anatomical structures of wood. Despite numerous tephra deposits, meteorological data and historical accounts indicating a harsh summer in 1783 and a severe winter 1783/1784, the blue rings are the first biological evidence of climate disturbances associated with the Laki volcano eruption in the Arctic. Detecting these anatomical features will provide a more complete and accurate understanding of the eruption’s dynamics and atmospheric effects, and will help to create a useful model for assessing the impact of past volcanic activity on the Earth’s climate.

This study has important implications for palaeoclimatological research in the Arctic and adjacent regions in the context of ongoing climate change. By providing a 500-year context for long-term climate variability, it has been confirmed that the observed recent warming is unprecedented, even in the southernmost part of Greenland. The remarkable consistency of the magnitude of the mid-17th century warming and the timing of cold and warm subperiods during the LIA was found with other biological proxy-based data from southern Greenland.

Methods
Permits and permissions
The historical juniper specimens originate from the Herbarium at the Natural History Museum, University of Copenhagen, Denmark. Permission to conduct the museum query was granted by Collection Manager Olof Ryding and Collection Assistant Karen Bach in 2021. No destructive sampling was performed. The research used high-resolution photographs of juniper cross-sections collected during historical polar expeditions, which were made available by the collection manager of the Greenland Herbarium at the Natural History Museum of Denmark in Copenhagen. In the field, samples were collected outside protected areas and archaeological sites.

Site description
The sites selected for this study are located within the extensive ice-free land area (c. 60–61°30’ N, 44°30–47° W) near the southernmost part of the Greenland ice cap, rendering it a pivotal location for climate variability research. The ice sheet margin is approximately 100 km inland to the northeast of the Labrador Sea coastline, whereas the ice-free zone extends between 150 and 200 km in width between the southwest and southern lobes of the ice sheet. The area is distinguished by its high landscape diversity. In the eastern and northeastern parts of the area, there are high mountains up to 2000 m above sea level with numerous cirque and valley glaciers. Lowlands are found mainly in valley zones, with the broadest valleys around Narsarsuaq and Igaliku. The varied landscape results in very high spatial variability in climate conditions and vegetation cover. The mean annual air temperature in Narsarsuaq is 1.1°C. The mean summer temperatures markedly differ between the outer coast and inland areas. The interior of southern Greenland has a subarctic, subcontinental climate with the highest temperature of 10.8°C in July (Narsarsuaq) and a yearly precipitation of approximately 600 mm. Strong, desiccating warm and dry Foehn winds from the ice cap are frequent all year round. In winter, this wind causes sudden warming and melting. The temperatures are lower near the coast because of the cold sea. The average July temperature in Qaqortoq is 7.6°C, with a yearly precipitation of 900 mm. Favourable climatic conditions influence the occurrence of rich thickets in the most favoured places, among others, in sheltered parts of the valley near the Narsarsuaq. Dwarf-shrub heath is the most widespread plant community and is dominated by Betula glandulosa, Vaccinium uliginous, Empetrum nigrum and Salix glauca. Juniperus communis can be found both in coastal areas and inland fjords and plateaus. Willows cover relatively large areas in lowlands, especially on slopes with abundant snow cover during the winter. Ground vegetation is commonly dominated by different species of ferns, grasses, or forbs, such as Ranunculus acer and Lathyrus japonicus67. Betula pubescens constitutes open woodlands or tall tundra and subarctic communities.

Wood material
Juniperus communis L. subsp. nana Syme. of the Cupressaceae, the only indigenous conifer in Greenland, occurs sporadically in the SE and SW parts of the island. It has prostrate growth with spreading branches but occurs most frequently as espalier forms, growing preferably over rock surfaces and against upright rocks. This low shrub, which is up to 50 cm tall and has a stem diameter rarely exceeding 10 cm, has a relatively long lifespan. Although early work on juniper from southernmost Greenland indicated its potential longevity, very limited tree-ring research has been undertaken in the study area. C. Lytzen indicated that the oldest juniper samples may be as old as 380 years, and this is the first published scientific information on the age of juniper from Greenland34. J. Lange68 and C. Kruuse69, who worked comprehensively with juniper samples from this area, presented the characteristics of the species, highlighting the varying degrees of eccentricity and the small amount of wood produced each year, but of comparatively old age. Similar observations were subsequently performed on juniper wood collected by Daniels, De Molenaar, and Ferwerda during the Dutch Botanical East Greenland Expedition in 1966. Importantly, the phenomenon of cambium dormancy, cessation of growth in the upper part of the branch, and sometimes partially dying off, was pointed out, while the area deeper under the snow continues to grow. Such interruptions lead to the production of discontinuous growth rings69,70. Additionally, studies by Miller70 demonstrated that the stems of juniper from West Greenland were indicators of its age of at least 200 years, which was also confirmed later by Buras et al.33 and Lehejcek et al.18, who examined the potential of shrub ring width and wood anatomy as proxies for climate and GrIS-melt. Tumajer et al.71 point to the intensification of growth rates during the short growing seasons in the Arctic.

Historical and field dendrochronological data
In August 2021, through the search for and exploration of the resources of the Greenland Herbarium in Copenhagen, housed at the Natural History Museum of Denmark, fifty-six museum artefacts and pieces of juniper wood were found that were collected during past scientific expeditions to Greenland. Most of the historical botanical samples had brief metadata on the collector, date and location of sampling, which is crucial for further dendrochronological analyses72. The samples came from 13 locations, including southern Greenland (Tasermiut, Igaliku, Qaqortoq, Sermilik, Unartoq), and were collected from 1873 to 1902 by C. Kruuse, E. Warming, C. Lytzen, N. Hartz and anonymous collectors (Supplementary Table 1). A detailed report on these research expeditions contains an interesting description of the juniper samples that were collected; this description includes the number of rings and their average width34.

The labels on the herbarium specimens were used to identify the exact locations where they were collected at the turn of the 19th and 20th centuries, so that contemporary samples could be taken from the same area. Living and dry juniper samples were collected in southern Greenland in the upper parts of the Tunulliarfik Fjord (Eriksfjord) during the field research campaign in the summer of 2023. The sampling sites were located at elevations of 180–280 m a.s.l. in two key areas: the northern part of the Akuliaruseq Plateau, northeast of Narsarsuaq, between the Kiattuut and Qooqqup outflow glaciers, and the hilly area of Sammisup Timaa to the north of Qassiarsuk (Supplementary Table 2). In general, sampling was random, taking into account the location of the plant to ensure site homogeneity and to exclude the influence of abiotic factors on growth, such as mass movements. Particularly noteworthy was the discovery of a large amount of dead, dry wood collected for dendrochronological studies. In most cases, these dry samples were found to be attached to the ground with remnants of the root system, indicating that they were discovered in situ. Straight sections of the main prostrate stems were sampled for analysis to exclude the possible presence of reaction wood. Samples were also taken from contemporary growing specimens for calibration with meteorological data. For these specimens, discs with a thickness of 2-3 cm were collected from one of the main stems to avoid destroying the entire plant.

Laboratory analysis and construction of the chronology
Two analytical paths were adopted: one for the historical samples and another for samples collected in the field. A total of 127 samples were analysed, 92 from the field and 35 from the herbarium. Owing to the great value of historical samples, measurements were made on the basis of high-resolution scans. For these samples, it was impossible to carry out invasive examinations, i.e., serial sectioning or microscopic cross-section preparations. The scans were taken from the original sanded surface prepared by the collectors and botanists, who analysed the number of rings on these samples at the turn of the 19th and 20th centuries, and the images were subjected to further analytical processing. This noninvasive approach has limitations; therefore, only 35 usable images were obtained from all 56 historical samples.

A comprehensive anatomical investigation was conducted on both living and dry juniper samples collected in the field. For each type of juniper sample, depending on the length of the shoot collected in the field, 2–3 anatomical thin sections that were 15 μm thick were prepared73 using a rotary microtome (Leica RM2125). At least two repetitions were performed for each cross-section. Anatomical wood features were emphasised using a complex laboratory procedure. In the first step, each sample was bleached with sodium/potassium hypochlorite to decolorize the cell walls and to remove undesired cell contents24. Next, we applied the double-staining procedure to all microsections using Safranin (red) and Astra Blue (blue) dyes to visualise lignified and less lignified cell walls in red and blue, respectively73. The samples were then washed with distilled water, dehydrated with increasing concentrations of ethanol, and permanently fixed via an Euparal mounting medium on single microscope slides. Permanent thin sections were dried for 12–24 h at 60°C. All microslides were photographed using a Leica DFC420C camera connected to a Leica DM4500B microscope. Leica LAS-X was used for image acquisition. Multiple images taken at 10× magnification were subsequently stitched together using PTGui software (http://www.ptgui.com, New House Internet Services B.V., Rotterdam, NL) to create single high-resolution images for each cross-section.

Measurements of the width of annual growth rings were made on the basis of digital images using WinDENDRO software (Regent Instruments Canada Inc.) at 2–3 radii per section, depending on circularity. Cross-dating was accomplished by applying two levels: first, the different radii within each sample were visually compared, an average of these measurements was created (or a distorted course was rejected if needed), and then dating and measurement errors were checked with the standard dendrochronological software COFECHA. Some of the samples used in the dendrochronological analyses were excluded from further analysis due to the presence of anatomical anomalies, such as wounds, large eccentricity, or inconsistency of the measurement sequence with the population mean. The data obtained are characterised by sufficiently high statistics of the constructed chronology (mean r, rbar, eps). To evaluate multiple detrending methods, we calculated a set of common ring width indices for each individual series using the [dplR] R package74. We tested all common detrending and smoothing methods, both data-adaptive and biological approaches, including modified negative exponential curves, generalised negative exponential curves, Hugershoff curves, cubic smoothing spline methods, means, and age-dependent splines. As no or negligible age trends were observed in the juniper ring width series, after different types of standardisation were carried out, the most justifiable was a horizontal straight line and a biological approach using regional curve standardisation (RCS). All the detrended series were averaged using the biweight robust mean to reduce the influence of outliers during the assembly of the standard ring width chronology.

To synchronise the samples, we determined the occurrence of extreme events using anatomical irregularities in growth rings, i.e., blue and frost rings. The so-called ‘frost rings’ are attributed to collapsed and deformed early or late wood cells and rays, illustrated by irregular cellular areas filled with wound parenchyma resulting from frost during the growing season/boreal summer54. Blue rings (BRs) are defined as growth rings with a layer of unlignified axial tracheids visible in blue after the double-staining thin transverse sections of shrubs rings with Safranin and Astra blue dyes. The cell walls, which are richer in lignin, were stained red, and the cell walls, which are richer in cellulose, were stained blue; thus, BRs reflect incomplete lignification, serving as excellent and sensitive proxies for past rapid cooling75. Chronologies of anatomical irregularities were created by assigning these structures to calendar years. In chronologies, all these occurrences were considered yearly, whereas in the text, the position of these structures within the growth ring, size or degree of formation was additionally considered and discussed for selected cases. Superposed epoch analysis (SEA) was used to test the significance of a mean shrub growth response to certain events, such as volcanic eruptions. In this study, intervals of 5 years before and after a volcanic eruption were analysed using SEA computation from the dplR package81,82.

Meteorological and glaciological data
Climate data from the Narsarsuaq station (WMO code 04270, elevation 30 m a.s.l.) for 1961–2023 (63 years) were used to explore the relationships between climate and growth-ring width records. We analysed available parameters, such as the mean, minimum and maximum air temperatures; atmospheric pressure; total precipitation; highest 24-hour precipitation; number of days of snow cover (>50%) (only 1961–1999); and average cloud cover (only 1961–2008). For comparison, we also utilized a longer series of monthly temperatures over the period of 1784–2013 for Qaqortoq (series based on observations from four sites (Ivittuut, Nanortalik, Narsarsuaq and Paamiut) infilled with regressed values, or, in recent times with values from Qaqortoq Heliport if missing data; sites situated along the southern coast of Greenland) and merged SW Greenland series (based on infilled temperature series from Ilulissat, Nuuk and Qaqortoq situated along the southern and western coasts of Greenland) complied by Cappelen & Vinther76. Records from selected stations were among the most comprehensive and reliable available for Greenland77. All the data were obtained from the Danish Meteorological Institute (DMI).

The dendrochronological record was also correlated with different seasonal and annual datasets of sea ice. Satellite-derived Arctic sea ice extent data from 1978–2023 were obtained from the National Snow and Ice Data Centre (NSIDC). The pre satellite data extending back to 1900 were developed by Walsh et al.78, Hadley Centre’s HadISST dataset, adjusted and recalibrated by Connolly et al.79. Notably, there is a long tradition of sea ice observations in our area of interest. The region is characterised by large inherent decadal variability in multi-annual ice cover, and analysis back to the 1950s revealed recurrent periods of up to five years with significantly increased ice cover. Ice Patrol Narsarsuaq was established in 1959 on the basis of the abandoned American military airfield in Narsarsuaq in southern Greenland. Ice reconnaissance has been completed 1–3 times a week, covering inshore waters and fjords along southern Greenland.

Dendroclimatological analysis and climate reconstruction
To establish the relationship between growth and climate, simple Pearson’s correlation and bootstrapped correlation analyses were carried out between the ring width index (RWI) chronology and different climate elements noted at Narsarsuaq meteorological station for the overlapping period (1961–2013) via the treeclim R package80. On the basis of growth‒climate response analysis, the primary growth-limiting climatic factor was identified. An 18-month dendroclimatic window starting from May of the previous year to October of the current year, along with seasonal aggregation of the monthly data, was used to identify growth-limiting climatic factors. The moving correlation between the chronology and climate data was also analysed in the treeclim R package to investigate the temporal stability of the dendroclimatic response and to check for possible divergence in the data. Temperature reconstruction in the summer season (June–August, JJA) is theoretically possible; thus, it was targeted for reconstruction. A model for reconstructing the sea ice extent was also tested, but the validation results were weaker than those of the other model. A split-sample validation (with the calibration performed on the last half and validation on the first half) was conducted to check the stability of the relationships. The full period of 1961–2023 was split into 1961–1992 and 1992–2023 as the calibration and verification periods, respectively. To evaluate the model ability, we used Pearson’s correlation coefficient (r), explained variance (R2), reduction in error (RE), the coefficient of efficiency (CE), and Durbin–Watson (DW) statistics. Once the model was judged to be effective and stable, a transfer function was established to reconstruct past June to August temperatures for the period covered by the regional composite tree-ring width chronology, up to the point at which the expressed population signal value of the chronology became less than the threshold value of 0.80. Superposed epoch analysis (SEA) was used to test the significance of a mean shrub growth response to certain events, such as volcanic eruptions. In this study, intervals of 5 years before and after a volcanic eruption were analysed using SEA computation from the dplR package81,82.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "Dear authors, dear Editor,\nthanks for the opportunity to review the manuscript with highly relevant topic. The manuscript is concise yet comprehensive\nand well written to keep the attention of the reader. Presented results are original and methods used are adequate, although\nnot anyhow innovative. This does not necessarily have be taken as criticism, methods applied serves the purpose very well\nand they have been routinely used by community for long time. Impressive is the broad combination of methods (wood\nanatomy, standard dendroclimatology, inclusion of historical material, etc.) which definitely was very labour demanding.\nRecent literature which dealt with climate sensitivity of junipers or environmental reconstructions using studied specie´s\nannual rings as well as quantitative wood anatomy from the Arctic (including Greenland) is nevertheless almost completely\nabsent. This is very disappointing because a lot has been done on that species in the Arctic and authors should build on that\nknowledge and discuss it. I also have some concerns regarding introductory, discussion and conclusions part which I list\nbellow.\nIntroductory part to me is concise too much. It provides only the link between climate change and ice melt and contextualize\nthe topic based on three (!) citations only. I think the authors should put more effort here to introduce the complete variety of\nstudied issues (e.g. volcanic eruptions, plant growth…) and link them into meaningful block which in the end proves the\nneed for their research and results.\nAnd here is actually another issue I have with intro part (lines 38 – 41). The paragraph with hypothesis reads quite weak,\nbasically: “develop a chronology and reconstruct climate conditions”. If only this is provided in the manuscript (which is not\nthe case!) than it does not merit publication in Nature as it has been done many times before (climate reconstruction) by\nmany other proxy archives. In my opinion, achieved results may offer more with the connection to climate-environmental\ndynamics and this should be incorporated in hypothesis and in the aim of the study.\nResults are well presented but insufficiently discussed. To give the example chapter on extreme years does not include\neven one literature reference although the authors present findings which should be attempted to interpret (“Interestingly,\nBRs were more common in the earlier period…”).\nConclusions. To me Conclusions should provide upscaled yet informative synthesis of findings (not just their summary\nthough!). I would find it beneficial for the reader to rework this section in this respect or just not include it and foster the result\npart with more discussion. Plus the first sentence of the conclusions is not truth or bold/disrespectful to the authors who\npublished already a lot on annual rings from polar tundra areas (including Greenland and including\njuniper shrub). The\nauthors surely provide the longest climate reconstruction based on juniper growth from the Arctic, but similarly or even\nlonger chronologies of juniper were published (with worse Rbar or EPS though) as well as long term dendroenvironmental\nreconstructions have already been presented. I understand the reason for this first sentence but it needs to be more specific\nto be fair.\nOther concrete comments and concerns:\nLine 57-58: I am convinced there are already quite a few juniper studies from the Arctic as well as Greenland in particular\nwhich may lack some of the aspects you cover but are closely related to climate or environmental change or even ice melt\n(GRIS).\nLine 68 – 73: dtto important literature is missing. No objections to discuss the sensitivity of junipers from alpine tundra but\nmany studies have been published on junipers from the Arctic and you do not address those at all in your manuscript as the\nresults are the closest geographicaly and environmentally.\nLine 77: “important ecological significance” – it is vague, please, be concrete.\nLine 89 – 92: illogical wording. Better refer to increasing or decreasing sea ice extent consistently and relate it to growth.\nNow, it swifts in the middle of the sentence.\nLine 244 and hereafter: to my understanding juniper is not dwarf shrub (those are shrubs rather from High Arctic like Salix\npolaris). I think better adjective for tundra juniper is prostrate.\nLine 287 – 302: you mention very limited research of the species but last work you cite is from 1974. Quite a lot has been\npublished on juniper from SE Greenland since that time. (probably not exactly from the spot you did your field work but still\nrelatively nearby).\nLine 322: root collar or the main stems were not sampled from the living individuals, then? Just the branches and than serial\nsectioning? But from your description it seems that fossil individuals were analysed from the main stem (“were found\nattached to the ground with remnants of the root system”). Could you explain if this methodologically different approach\ncould not compromise the results?\nLine 346: was there any minimal angle between analysed radii?\nLine 371: why did you decided to use the meteodata from one station and on the CRU-TS or similar integrated datasets?\nLine 549: almost four centuries preservation time of fossil samples since die off is almost unbelievable considering high\nhumidity of the region (600 mm) and relatively high temperatures plus snow directly affecting and melting at the surface. Are\nyou sure about the cross-dating here or could you provide maybe field picture of those three oldest fossil individuals? I may\nbe of course wrong but in such climatic conditions I can imagine fossil junipers 4 centuries old only maybe bellow some\n“rock roof” at the very steep cliff.\nLine 585: Fig. 4 – in figure caption you mention part E and F but those are not in the picture itself.\nLine 603: Fig. 5 – in Fig. 1 I counted 13 blue rings but here in Fig. 5 I counted 14 blue rings.\nLine 627: sea at Sermilik Fjord is influenced solely by East Greenland Current while your site also by Irminger Current.\nWould it be possible to use reconstruction from geographically and environmentally closer locality?\nLine 631: upper index for 18.", "reviewer_2": "This study presents a high-resolution dendroclimatological reconstruction of summer temperatures in southern Greenland\nusing shrubs, spanning the period 1526–2023 CE. The research provides valuable insights into Arctic climate variability,\nparticularly during the Little Ice Age (LIA), and assesses the impact of volcanic eruptions using wood anatomical features\nsuch as blue rings (BRs) and frost rings (FRs). The findings are significant for understanding recent warming trends in the\ncontext of natural variability. However,there are several aspects which require clarification and further discussion. Major\nrevision is needed before the publication.\nI have several major concerns regarding this study.\n1 stability of the temperature reconstruction. The correlation between temperature and tree-ring width shows significant\ndifferences between 1960-1992 (r=0.34) and 1992-2023 (r=0.7) periods (Figure 4). What causes this instability in the\nrelationship? Supplementary Table 2 also shows that the temperature-width correlation gradually increases with rising\ntemperatures. How might this unstable width-temperature relationship affect the reliability of the 500-year reconstruction?\nand 5). What is the reason for this？While there is evidence of global warming hiatus, what specifically accounts for the\ntemperature decrease in this record? Does this decline appear in observational data? Is there any mismatch between ring\nwidth and observed temperatures?\nthe same period. What explains this discrepancy?\nevents coinciding with volcanic eruptions. How do other Greenland records (e.g., ice cores) with potential dating errors\ncapture these volcanic-induced cold periods? I recommend to add superposed epoch analysis (SEA) of volcanic events.\nComparison with other Greenland temperature reconstructions. This would better demonstrate the reliability of tree-ring\nreconstructions.\n5. Polar region comparisons. The study would benefit from comparing with tree-ring based temperature reconstructions from\nother Arctic regions (e.g., Alaska, Russian Arctic) to examine pan-Arctic temperature variability.\nSpecific comments:\nFigure 4 caption doesn't match the figure - the caption references panels A-F but only A-D are shown.", "reviewer_3": "This is a very interesting study using a fairly groundbreaking set of juniper samples to reconstruct temperature in southern\nGreenland. Adding paleoclimate chronologies such as this in areas that are typically not covered by the usual paleoclimate\nproxies is very important for understanding regional variations in climatic trends. I commend the authors on their collection of\na both living, dead, and historical samples to create an unprecedented juniper chronology. The research is sound and the\nmanuscript is well written.\nOne important revision I would request is to include the climate-growth table that is currently in the supplemental information\nas a figure in the main manuscript. I did not see anywhere else that the list of climatic variables assessed was reported, nor\nany other indication of the strength of these correlations. I believe this revision is absolutely necessary for the manuscript to\nstand on its own.\nThe Laki section seems excessively long. The results are interesting, but could be conveyed much more concisely (probably\none paragraph). If the details of this event are a primary focus of the research, it should be included in the introduction and\nstated as a research goal. Similarly, if assessing the utility of blue rings is a significant goal of the project, then that should be\nclearly stated in the introduction and the idea of blue rings should be introduced there.\nOther more minor revisions I would request:\nPage 2, Line 63: \"relatively less\" than what? Why is this significant?\nPage 3, line 70: here is the perfect place to reference the climate-growth table\nPage 3, line 77: you state that a positive response to high minimum temperatures has \"important ecological significance\" but\ndo not elaborate. What is the important significance here?\nPage 3, line 93: I am skeptical of the feasibility of reconstructing sea ice with this proxy because sea ice extent does not\nnecessarily have a simple linear relationship with summer temperature.\nPage 3, line 99: \"the model revealed a 46% variance\" does not make sense to me. Do you mean the R^2 was .46, indicating\nthe 46% of the variance was predicted by the model?"}, "author_response": "Point-by-point response letter\nDear Editor,\nWe thank the reviewers for their detailed and constructive comments. Their evaluations greatly\ncontributed to the improvement of our manuscript. All reviewers’ comments and suggestions are in\nblack, our responses in blue, and quotations from the revised text in italic.\nOn behalf of all authors\nMagdalena Opała-Owczarek\nREVIEWER COMMENTS and AUTHORS' ANSWERS\nReviewer #1 (Remarks to the Author):\nDear authors, dear Editor,\nthanks for the opportunity to review the manuscript with highly relevant topic. The manuscript is\nconcise yet comprehensive and well written to keep the attention of the reader. Presented results\nare original and methods used are adequate, although not anyhow innovative. This does not\nnecessarily have be taken as criticism, methods applied serves the purpose very well and they have\nbeen routinely used by community for long time. Impressive is the broad combination of methods\n(wood anatomy, standard dendroclimatology, inclusion of historical material, etc.) which definitely\nwas very labour demanding.\nWe sincerely appreciate the encouraging words and positive feedback on our idea and the efforts.\nWe highly appreciate the reviewer’s comments and suggestions for improvements. In the following\nsections of the review, we have answered all the questions and introduced suggested changes.\nRecent literature which dealt with climate sensitivity of junipers or environmental reconstructions\nusing studied specie´s annual rings as well as quantitative wood anatomy from the Arctic (including\nGreenland) is nevertheless almost completely absent. This is very disappointing because a lot has\nbeen done on that species in the Arctic and authors should build on that knowledge and discuss it. I\nalso have some concerns regarding introductory, discussion and conclusions part which I list below.\nWe appreciate the reviewer’s suggestion to strengthen the literature review. We agree with the\nreviewer that this section on ‘state of art’ should be expanded. In the first draft of the manuscript,\nwe included that information, but we have to cut it down for reasons of volume. We thank the\nreviewer for this comment. We are very pleased to have the opportunity to describe the previous\nstudies in more detail now. We have added the appropriate references to all the contributions on\nthis topic (see our detailed answers below).\nIntroductory part to me is concise too much. It provides only the link between climate change and ice\nmelt and contextualize the topic based on three (!) citations only. I think the authors should put more\neffort here to introduce the complete variety of studied issues (e.g. volcanic eruptions, plant\ngrowth…) and link them into meaningful block which in the end proves the need for their research\nand results.\nWe agree with the reviewer. We have expanded the introduction by adding new sections focusing\non other proxies used in paleoclimate research in Greenland: ice cores, lake sediments, and plant\ngrowth. We followed the reviewer's suggestion and updated the \"Introduction\" section with a\nbroader review of prior dendrochronological studies from Greenland, adding key references to\ncontextualise our work within the existing literature. The need for the development of new\ndendrochronological data is illustrated in the context of this background:\n“Climate reconstruction from Greenland primarily refers to using ice cores extracted from\nGreenland's ice sheets to understand past climate conditions (Gkinis et al., 2021). These ice cores\ncontain trapped air bubbles, isotopes, dust, and other compounds that can reveal information about\nenvironmental changes over time. Using ice cores has challenges, such as limited geographical\ncoverage (ice sheet), dating uncertainties, and limited temporal resolution (Masson-Delmotte et al.,\n2006). It should be, however, emphasised that ice cores provide the most comprehensive record of\nvolcanic eruptions that have contributed to periods of cooling (Hammer et al., 1980; Abbott & Davies,\n2012; Sigl et al., 2015). The results from the sediment cores recovered from Greenlandic lakes provide\nan invaluable addition to the findings derived from the ice core samples. The continuous archive of\npast environmental changes based on these proxy data spans the entire Holocene (Axford et al.,\n2013; Lasher et al., 2020). Nevertheless, a potential limitation of these studies is the possibility of\nerrors in the interpretation of 14C and 210Pb-dated sediment cores, involving e.g. problems of dating\ncalibration and different sedimentation rates and disturbances (Lusas et al., 2017; Anderson et al.,\n2019). Tree rings, one of the most widely used climate proxies, are invaluable and powerful sources\nof climate information due to their high resolution, accurate year-by-year dating, and the ability to\nreconstruct decadal to millennial-scale climate conditions (LaMarche, 1978). However, the age of the\ntundra plants has limited the application of the dendrochronological method in Greenland. Existing\nshrub records of Alnus viridis, Salix glauca and Juniperus communis from West Greenland (Jørgensen\net al., 2015; Hollesen et al., 2015; Lehejček et al., 2017; Wilmking et al., 2018; Prendin et al., 2022),\nSalix arctica from north-eastern Greenland (Schmidt et al., 2006) or from the only natural forest with\nBetula pubescens located in Qinngua Valley, southern Greenland (Kuivinen & Lawson, 1982; Xu et\nal., 2021) do not reach the pre-instrumental period. Until now, the existing dendrochronological data\nfor Greenland have been insufficient for reconstructing the climate over the centuries.”\nAnd here is actually another issue I have with intro part (lines 38 – 41). The paragraph with\nhypothesis reads quite weak, basically: “develop a chronology and reconstruct climate conditions”. If\nonly this is provided in the manuscript (which is not the case!) than it does not merit publication in\nNature as it has been done many times before (climate reconstruction) by many other proxy\narchives. In my opinion, achieved results may offer more with the connection to climate-\nenvironmental dynamics and this should be incorporated in hypothesis and in the aim of the study.\nThe reviewer is right that this issue should be addressed more thoroughly. In the revised manuscript,\nwe extended the \"Introduction\" section: “Here, we present the combined dendrochronological and\nwood anatomical assessment of living and relict juniper wood from southern Greenland to reveal\nannually resolved and absolutely dated insights about natural summer temperature variability back\ninto the Little Ice Age. This reconstruction extends beyond the instrumental period in Greenlandic\nterrestrial areas outside the ice sheet. Additionally, we aimed to assess the usefulness of the so-\ncalled “blue rings” as an indicator of post-volcanic cooling and as a key anatomical feature allowing\nfor the synchronisation of juniper samples. Our study contributes to the understanding of the effects\nof volcanic eruptions on climate by combining wood anatomical observation with superposed epoch\nanalysis to explore the significance of selected eruptions on growth ring width and blue ring\nformation. In order to more accurately evaluate the reliability of the reconstruction, we conducted\nthorough comparisons with other proxy data from southern Greenland and dendroclimatic\nreconstructions from the Arctic.”\nResults are well presented but insufficiently discussed. To give the example chapter on extreme years\ndoes not include even one literature reference although the authors present findings which should\nbe attempted to interpret (“Interestingly, BRs were more common in the earlier period…”).\nWe agree with the reviewer. For clarity, we removed the first sentence of this chapter, and instead\nwe added a comparison with literature, as suggested:\n“Extreme years are manifested by the occurrence of narrow rings or disrupted cell formation, such\nas BRs and FRs (Fig. 5). Most of these extreme years, associated with volcanic eruptions, are\nconsistent with studies carried out at the northern tree limit in both Asia and North America, e.g.\n1600, 1641, 1783, 1815-1817, 1868, 1884, 1912, 1916-1917 (LaMarche & Hirschboeck, 1984; Filion et\nal., 1986; Delwaide et al., 1991; Briffa et al., 1998; Hantemirov et al., 2004).”\nAccording to the reviewer's suggestion, we extended the discussion: “In general, BRs appear to occur\nduring warm periods, such as the 1720–1820 period and the modern warm period. In contrast, FRs\noccur more frequently during the cool episodes of the Little Ice Age. These results corroborate the\nhypothesis that prolonged cooling does not diminish lignification, but rather increases the likelihood\nof frost-related damage. These observations coincide with the results of studies conducted at the\nupper tree line in the Swiss Alps (Körner et al., 2023).”\nConclusions. To me Conclusions should provide upscaled yet informative synthesis of findings (not\njust their summary though!). I would find it beneficial for the reader to rework this section in this\nrespect or just not include it and foster the result part with more discussion.\nWe appreciate the reviewer’s suggestion to rework the conclusions. In response, we added new\ninformation that synthesises our findings and provide a broader context for our achievements:\n“…. The unique results obtained through the use of specimens from historical scientific expeditions,\ncurrently preserved in herbaria, highlight the importance of reanalysing old botanical collections\nusing modern analytical techniques. Since the area of our research, located within Eriksfjord, was\ninhabited by the Vikings from 985 CE to the mid-15th century (Eastern Settlement), research into\npast climate change is becoming increasingly important. Integrating wooden archaeological finds\nfrom this area with the established five-century-long juniper growth ring chronology will be the next\nstep in reconstructing past changes in this area over a period of environmental changes at the turn\nof the 15th and 16th centuries.”\n“…The analysis of these anatomical changes has allowed for a significant deepening of conclusions.”\n“Despite numerous tephra deposits, meteorological data and historical accounts indicating a harsh\nsummer in 1783 and a severe winter 1783/1784, the blue rings are the first biological evidence of\nclimate disturbances associated with the Laki volcano eruption in the Arctic. Detecting these\nanatomical features will provide a more complete and accurate understanding of the eruption's\ndynamics and atmospheric effects, and will help to create a useful model for assessing the impact of\npast volcanic activity on the Earth's climate.”\nPlus the first sentence of the conclusions is not truth or bold/disrespectful to the authors who\npublished already a lot on annual rings from polar tundra areas (including Greenland and including\njuniper shrub). The authors surely provide the longest climate reconstruction based on juniper\ngrowth from the Arctic, but similarly or even longer chronologies of juniper were published (with\nworse Rbar or EPS though) as well as long term dendroenvironmental reconstructions have already\nbeen presented. I understand the reason for this first sentence but it needs to be more specific to be\nfair.\nWe agree with the reviewer, we should have been clearer about this in the original manuscript. We\nmodified this sentence by adding “….which have not been entirely represented in long-term\ndendroclimatological reconstructions”, and “The developed record is the one of the longest growth\nring chronologies for Arctic shrubs to date”. We have added information about other works on\njuniper, including works from Greenland, to the body of the article and to the references list.\nOther concrete comments and concerns:\nLine 57-58: I am convinced there are already quite a few juniper studies from the Arctic as well as\nGreenland in particular which may lack some of the aspects you cover but are closely related to\nclimate or environmental change or even ice melt (GRIS).\nWe changed this part according to the reviewer's suggestion and added relevant citations. Some of\nthe most recent work was not known at the time the manuscript was prepared, but we can now add\nit. We agree with the reviewer that this section should be expanded. Thanks to the editor's decision,\nwe can now expand this paragraph accordingly. Now is: “In only a few dendrochronological studies\nto date, it has been possible to assemble a multi-century chronology of junipers from Arctic sites, of\nwhich the longest, based on both living and dry branches, comes from the Kola Peninsula (>500 yrs,\nShumilov et al. 2007), Polar Urals (>600 yrs, Hantemirov et al. 2011), and northern Iceland (>800 yrs,\nOpała-Owczarek et al. 2025). Recently, very old specimens of junipers have also been described for\nsites in northern Fennoscandia (Sør-Varanger, Kevo, Abisko) by Lehejček et al. (2024) and Carrer et\nal. (2025). The assembled juniper chronologies for Greenland mainly concerned the area around\nNuuk, where the relation to climate and Greenland Ice Sheet melting was elaborated over the last\ncentury (Buras et al. 2017 and Lehejček et al. 2017). Juniper discs with more than 200-300 rings were\ncollected from southernmost Greenland during the scientific expeditions to Greenland at the end of\nthe 19th century (Meddelelser om Grønland…, 1888), and have recently been reconfirmed.”\nLine 68 – 73: The important literature is missing. No objections to discuss the sensitivity of junipers\nfrom alpine tundra but many studies have been published on junipers from the Arctic and you do not\naddress those at all in your manuscript as the results are the closest geographicaly and\nenvironmentally.\nWe agree with the reviewer that this section should be expanded. Thanks to the editor's decision\nwe can now expand our text and add this relevant information: „Similarly, junipers from other\ncircum-Arctic sites are temperature-stressed (Hallinger et al., 2010; Hantemirov et al. 2011; Lehejček\net al. 2017; Opała-Owczarek et al. 2025), however, the strength of the signal varies depending on\ninter alia sampling strategy (adequate replication, proximity to the root collar) and site\ncharacteristics (homogeneity, geomorphic disturbances). ”\nLine 244 and hereafter: to my understanding juniper is not dwarf shrub (those are shrubs rather from\nHigh Arctic like Salix polaris). I think better adjective for tundra juniper is prostrate.\nThank you for this comment. We referred to “dwarf juniper”, not „dwarf shrub”, but for clarity we\ndeleted “dwarf”.\nLine 287 – 302: you mention very limited research of the species but last work you cite is from 1974.\nQuite a lot has been published on juniper from SE Greenland since that time. (probably not exactly\nfrom the spot you did your field work but still relatively nearby).\nThank you for this comment. We agree with the reviewer that this section should be expanded.\nThanks to the editor's decision, we can now expand our text and add these relevant citations:\n“….. which was also confirmed later by Buras et al. (2017) and Lehejcek et al. (2017), who examined\nthe potential of shrub ring width and wood anatomy as proxies for climate and GrIS-melt. Tumajer\net al. (2021) point to the intensification of growth rates during the short growing seasons in the\nArctic.”\nLine 322: root collar or the main stems were not sampled from the living individuals, then? Just the\nbranches and than serial sectioning? But from your description it seems that fossil individuals were\nanalysed from the main stem (“were found attached to the ground with remnants of the root system”).\nCould you explain if this methodologically different approach could not compromise the results?\nWe apologise for the unclear description. We did not take samples from the root collars because the\ngrowth disturbances present there may negatively influence the dendroclimatic signal. Our\nexperience suggests that samples from the root collar are important when studying polar willows,\ndwarf birch and other dwarf shrubs. Our aim was not to check the maximum age of the plant, but to\nmake the most accurate synchronisation between samples and a robust climate reconstruction. We\nshould have been clearer about this in the original manuscript. We took samples from the main\nstems. For clarity, we modified this description; now it is: “Straight sections of the main prostrate\nstems were sampled for analysis to exclude the possible presence of reaction wood. Samples were\nalso taken from contemporary growing specimens for calibration with meteorological data. For\nthese specimens, the discs from one of the main stems were collected to avoid destroying the whole\nplant.”\nLine 346: was there any minimal angle between analysed radii?\nNo minimum angle was set, but measurement paths were arbitrarily chosen to best represent the\ngrowth over the entire cross-section. This was dependent on the appearance of each cross-section.\nLine 371: why did you decided to use the meteodata from one station and on the CRU-TS or similar\nintegrated datasets?\nIn the case of Greenland, a single grid can cover very different environments, covering part of the\nice sheet, part of the sea area and part of the land area. Our aim was to reconstruct the climate of\nthe unglaciated land area (based on terrestrial proxy) as the only one of its kind for Greenland. In\nview of this, in order to represent the relationship between shrub ring width and climate conditions\nas accurately as possible, we took into account complete, homogeneous data for different climate\nelements, from the meteorological station Narsarsuaq closest to our sampling sites. We made a\nnumber of comparisons, e.g. between the two official nearest met stations, Narsarsuaq and\nQaqortoq, located within the fjord and near open sea, which shows variation in the distribution of\nmeteorological elements throughout the year. Station data are much more precise, but they could\nrepresent very unique (particular) local conditions. In the future, spatial analyses using\ndendrochronological data from the whole of coastal Greenland should be considered. The\noverarching aim of our work is not spatial analyses, which, due to their volume and multi-faceted\nnature, require a separate article.\nLine 549: almost four centuries preservation time of fossil samples since die off is almost\nunbelievable considering high humidity of the region (600 mm) and relatively high temperatures plus\nsnow directly affecting and melting at the surface. Are you sure about the cross-dating here or could\nyou provide maybe field picture of those three oldest fossil individuals? I may be of course wrong but\nin such climatic conditions I can imagine fossil junipers 4 centuries old only maybe bellow some “rock\nroof” at the very steep cliff.\nWe realise that these results are surprising. However, note that we only included three such old\nsamples in the chronology, as these were characterised by very high statistical metrics (cofecha\noutput “correlation of series by segments” between 1525 – 1649 was: .58, .52, .58, .59 ); thus, we\nare confident of the dating result. We also enclose below the pictures of the oldest sample, another\nexample is visible on figure 1B. It is indeed not known whether all the rings on these samples are\npresent due to their state of preservation, but the preserved ring sequences were long enough to be\ndated.\nThe possibility of finding such old specimens of juniper branches in the field is also confirmed by\nRussian (Hantemirov et al., 2004) and Icelandic (Opała-Owczarek et al., 2025) works. Recently,\nsimilar dating of dead juniper branches was shown by Carrer et al. (2025) for samples from Kevo,\nFinland (last year on sample 1469) and Chernaya, Russia (last year on sample 1438).\nArchaeological finds from Viking-era sites in Greenland, Iceland and the Faroe Islands also contain\njuniper wood. The existence of archaeological objects and samples from juniper wood also proves\nthat it can survive in the field for several hundred years (both in a bad and good state of\npreservation). This is confirmed by our observations of archaeological wood from Greenland\n(unpublished data). For example, counting sticks, part of a decoration, as well as charcoals, were\ndeposited ca. 1000 AD. Other samples preserved in the waterlogged layers were in a much better\nstate of preservation due to the constantly cold, wet and anaerobic conditions (dated AD 770-1015).\nWood of conifers and dwarf shrubs was much better preserved than the wood of larger broad-leaved\ntrees, which was generally more decayed. The juniper wood, used for ropes, bucket loops, and short\npointed sticks, is common on Viking Age sites. Descriptions of such artefacts and their archaeological\ndating have been provided by, among others, Larsen (1991), Malmros (1994), Pinta (2018),\nGuðmundsdottir (2021), and Mooney et al. (2022).\nData from the literature indicate that juniper is a very resistant species, as discussed by Opała-\nOwczarek et al. (2025): In the context of establishing the composite juniper chronology, it is crucial\nto recognise the unique preservation of relict juniper wood in the cold environments. Juniper\ngrowing in such conditions exhibits a notably high natural resistance to decay (Scheffer & Morrell,\n1998; Morrell et al., 1999; Opała-Owczarek et al., 2018). Its wood is characterised by high density\nand durability, which is related to harsh ecological conditions. The juniper wood is also extremely\ndurable in contact with the soil, little shrinks and does not tend to crack. Furthermore, it displays\nexcellent resistance to fungal attack (Xylophagous fungi) (Morrell et al., 1999). Even after contact\nwith water does not decay, and after drying do not reduce their size (Mukhamedshin and Talancev,\n1982). In semi-arid cold ecosystems, the time of wood decay is significantly longer than in wet areas\n(Murphy et al., 1998).\nIn addition to strictly scientific research, practical studies have been carried out on preserving dry\njuniper, which indicates its exceptional resistance to climatic conditions. Experimental pole farm\ntests conducted in the Cascade Mountains in Oregon revealed that juniper exhibits exceptional\nnatural durability (Morrel et al., 1999). It should be noted that the test studies were carried out in\nan area with a mild and humid climate (average annual precipitation 1050 mm), typically\nexperiencing dry summers and rainy winters. This climate favours the growth of wood-destroying\norganisms throughout the year.\nGuðmundsdottir (2021), Wood procurement in Norse Greenland (11th to 15th c. AD), Journal of Archaeological\nScience 134 (2021) 105469\nLarsen (1991), Norsemen’s use of juniper in Viking Age Faroe Islands. Acta Archaeologica, 61, 60-72.\nMalmros, C., 1994. Exploitation of local, drifted and imported wood by the vikings on the Faroe Islands. Bot. J.\nScotl. 46, 552–558.\nMooney et al. (2022), Wood resource exploitation in the Norse North Atlantic: a review of recent research and\nfuture directions, Expanding Horizons UBAS 13.\nMorrell, J.J., Miller, D.J., Schneider, P.F., 1999. Service life of treated and untreated fence posts: 1996 post-\nfarm report. Forest Research Laboratory. Oregon State University. Research Contribution 26. 24 pp.\nPinta (2018), Norse Management of Wooden Resources across the North Atlantic: Highlights from the Norse\nGreenlandic Settlements, Environmental Archaeology, DOI: 10.1080/14614103.2018.1547510\nLine 585: Fig. 4 – in figure caption you mention part E and F but those are not in the picture itself.\nWe apologise for this oversight. Captions A and B referred to the results, which appeared in the\nsupplementary materials (as Table 2). Now it was all properly compiled in Figure 4, with appropriate\ncaptions from A to F.\nLine 603: Fig. 5 – in Fig. 1 I counted 13 blue rings but here in Fig. 5 I counted 14 blue rings.\nThank you for this comment. We apologise for this oversight. It should be 13 BR on both graphs. We\ncorrected the mistake on Fig.5, where in 1816 should be FR, not BR.\nLine 627: sea at Sermilik Fjord is influenced solely by East Greenland Current while your site also by\nIrminger Current. Would it be possible to use reconstruction from geographically and environmentally\ncloser locality?\nWe made comparisons with the existing reconstructions for the Sermilik fjord, as they had a\nrelatively higher resolution and thus could be compared with our dendrochronological\nreconstruction. In the vicinity of our site there are only reconstructions interred from Lake Igaliku\nsediments. In response to this comment, we added chironomid assemblages stratigraphy, as a proxy\nof climate variability, to Fig. 6. We also added sentences to the text: ”In the closest vicinity of the\njuniper study sites, climate variability was previously inferred from Lake Igaliku sediments (Millet et\nal., 2014). A comparison of the data obtained from the chironomid assemblages with the juniper-\nbased reconstruction reveals a number of similarities, except for the periods between 1640 and 1790,\nand between 1920 and 1970. The most consistent signals are the strong modern warming and the\nrelatively warm conditions during the Dalton Minimum and the warming of the early 17th century\n(Fig. 6E).”\nLine 631: upper index for 18.\nThank you. Corrected.\nReviewer #2 (Remarks to the Author):\nThis study presents a high-resolution dendroclimatological reconstruction of summer temperatures\nin southern Greenland using shrubs, spanning the period 1526–2023 CE. The research provides\nvaluable insights into Arctic climate variability, particularly during the Little Ice Age (LIA), and\nassesses the impact of volcanic eruptions using wood anatomical features such as blue rings (BRs)\nand frost rings (FRs). The findings are significant for understanding recent warming trends in the\ncontext of natural variability. However,there are several aspects which require clarification and\nfurther discussion. Major revision is needed before the publication.\nThank you for appreciating our idea and our efforts. We are very grateful for your suggestions for\nadditional analyses, which will certainly enrich this text. In the following sections of the review, we\nhave addressed all the questions and comments, as well as incorporated the suggested additions.\nI have several major concerns regarding this study.\n1 stability of the temperature reconstruction. The correlation between temperature and tree-ring\nwidth shows significant differences between 1960-1992 (r=0.34) and 1992-2023 (r=0.7) periods (Figure\n4). What causes this instability in the relationship? Supplementary Table 2 also shows that the\ntemperature-width correlation gradually increases with rising temperatures. How might this unstable\nwidth-temperature relationship affect the reliability of the 500-year reconstruction?\nWe thank the reviewer for this insightful comment and for paying attention to the stability of the\ntemperature-width correlation. We agree that this issue is particularly important, as reduced\nsensitivity of tree growth to temperature has been evidenced at high northern latitudes and alpine\nlocations. In our research, we do not observe an issue of \"Divergence Problem\". And the designated\ndendroclimatic model indicates a strong temperature signal, especially in recent decades.\nWe performed the JJA temperature reconstruction based on data from the Narsarsuaq station, but\nin developing the reconstruction model, we also tested for data from Qaqortoq. Thank you for\npointing out the inconsistency in the figures. By an editorial mistake, the statistics for the model\n(measures of reconstruction skill: r, RE, CE, and ST) appeared with the data from Qaqortoq. We have\nnow corrected this, and the respective data for Narsarsuaq are presented. For clarity we also added:\n“….noted at Narsarsuaq meteorological station” to the Dendroclimatological analysis and climate\nreconstruction section.\nOnce again, we have re-checked the source data. Indeed, differences between temperature and\ntree-ring width are observed, but this is evident mostly for Qaqortoq station. These lower correlation\nvalues in the earlier period can be observed in Fig. 4B. The Qaqortoq series, as we indicated in the\nMaterial paragraph, is based on observations from four sites (Ivittuut, Nanortalik, Narsarsuaq and\nPaamiut), infilled with regressed values, or, in recent times, with values from Qaqortoq Heliport.\nAdditionally, Qaqortoq station was relocated in September of 2003, and earlier location/relocations\nare not known or certain (Cappelen, 2014; Cappelen and Vinther, 2014). These elements may have\ninfluenced the quality of the data in the earlier period. For Narsarsuaq, these correlations are more\nstable over time, which has to do with the better quality and continuity of instrumental data from\nthe Narsarsuaq airport.\nAlthough the data for Narsarsuaq are homogeneous, slightly lower r value in the earlier period is\napparent. Other researchers have pointed to the possibility of insect gradation affecting the stability\nof the climate signal from south-eastern Greenland (Wilmking et al., 2018), but the juniper species\nthat we studied was not infected. Perhaps another environmental factor contributed to minor\ninaccuracies in the chronology and instrumental data (e.g. 1973–1982), but we are unable to identify\nthem unequivocally. However, this is a short period of time, and in our opinion, this does not\nsignificantly affect the overall reconstruction, and the model is characterised by good measures of\nreconstruction skills. As Capplen (2014) points out, southern Greenland is characterised by a very\nlarge variation in weather conditions, which can affect the stability of the climate signal. This is due\nto the very strong interplay between sea and land areas in close proximity to the ice sheet. The large\ntemperature differences in the area – between the cold sea and the warm inland area in the summer\nand between the warm sea and the cold inland area in the winter – give rise to a local but dominant\nmonsoon system in the fjords. This pattern is often disrupted during periods of unstable weather.\ntrend after 2000 (Figures 2 and 5). What is the reason for this？While there is evidence of global\nwarming hiatus, what specifically accounts for the temperature decrease in this record? Does this\ndecline appear in observational data? Is there any mismatch between ring width and observed\ntemperatures?\nWe appreciate the reviewer’s suggestion to strengthen the discussion on this valid issue, so we\nadded supplementary information to the text: “The meteorological and tree ring data are consistent\nand show that the southern part of Greenland experienced decadal periods of both cooling and\nwarming during 1961–2023, with an inflection point around the mid-1990s, and no significant\nwarming after ∼2010 (Suppl. Fig. 1). The reasons for this variability can be found in the regional\ninfluence of the large-scale circulation, represented by the indices for the NAO (North Atlantic\nOscillation) and GBI (Greenland blocking index). Zhang et al. (2022) concluded that, since 2011, there\nhas been a shift towards a more negative phase for GBI and a more positive phase for NAO, but at\nthe same time, these have been highly variable, with more modest values and reduced warming\nrecently.”\nWe also added new reference:\nZhang, Q., Huai, B. J., Van Den Broeke, M. R., Cappelen, J., Ding, M. H., Wang, Y. T., & Sun, W. J.,\n2022: Temporal and spatial variability in contemporary Greenland warming (1958–2020). Journal\nof Climate, 1(9), 2755–2767. https://doi.org/10.1175/JCLI-D-21-0313.1\ndecreasing width during the same period. What explains this discrepancy?\nThe data series shown in these graphs is the same. The visual impression that the trend is different\nis due to the fact that the data in Fig.2. covers the entire period of the five centuries. While the data\nseries in Fig. 4a covers the last 100 years, and is truncated to 2020 to be consistent with the ice extent\ndata. The last 5 years have been a period of decreasing juniper growth-ring width.\nidentify extreme cold events coinciding with volcanic eruptions. How do other Greenland records (e.g.,\nice cores) with potential dating errors capture these volcanic-induced cold periods? I recommend to\nadd superposed epoch analysis (SEA) of volcanic events. Comparison with other Greenland\ntemperature reconstructions. This would better demonstrate the reliability of tree-ring\nreconstructions.\nThis is an excellent comment, although in the primary version of the text, we did not plan to include\nSEA analysis. We followed the reviewer's suggestion and compared the BR signal in the Greenland\njuniper with the volcanism recorded in the Greenlandic ice cores. We have added to Figure 5 a panel\nshowing the amount of sulphur from NEEM ice core. Taking into account the reviewer's suggestion,\nwe also made an additional comparison between the occurrence of dendrochronological signals of\neruptions (visible as blue rings ‘BR’), with the increased amount of non-sea-salt sulphur records from\nGreenland for the NEEM ice core (after Sigl et al. 2015). According to the suggestion, we also\nperformed superposed epoch analysis (SEA) of volcanic events, which is now presented as lower\npanel in Fig. 5.\nBeyond the new elements added to Figure 5, we added relevant comments in the text: “We\nevaluated the accuracy of our dendrochronological data by comparison with volcanic signals from\nthe Greenland ice sheet (Sigl et al. 2015). Volcanic aerosol peaks contained in the ice core (NEEM-\n2011-S1) are consistent with dendrochronological signals (narrow rings, BRs, FRs), which are closely\nrelated to major volcanic eruptions (Fig.5 A, B). This is particularly pronounced in years of volcanic\neruptions: Huaynaputina (1600), Mt. Parker (1641), Hekla (1963), Laki (1783), Tambora (1815), and\nMt.Katmai (1912). These events were followed by the occurrence of BRs, FRs or strong growth\nreduction in tree-ring records. Superposed epoch analyses show a clear post-volcanic cooling signal\nafter most major eruptions, or a response lagged by one year (Fig. 5C). Of particular interest is the\nresponse of Greenland's junipers to the major eruptions of Laki and Tambora, where BRs were\nrecorded in the year of the eruption and narrow growth a year later (Fig. 5Ca).”\nIn Figure 6, we additionally show a comparison with different temperature reconstructions from\nGreenland. We have also added new sentences to the paragraph with multi-proxy comparison: ”In\nthe closest vicinity of the juniper study sites, climate variability was previously inferred from Lake\nIgaliku sediments (Millet et al. 2014). A comparison of the data obtained from the chironomid\nassemblages with the juniper-based reconstruction reveals a number of similarities, except for the\nperiods between 1640 and 1790, and between 1920 and 1970. The most consistent signals are the\nstrong modern warming and the relatively warm conditions during the Dalton Minimum and the\nwarming of the early 17th century.”\n5. Polar region comparisons. The study would benefit from comparing with tree-ring based\ntemperature reconstructions from other Arctic regions (e.g., Alaska, Russian Arctic) to examine pan-\nArctic temperature variability.\nThank you for these suggestions. According to the reviewer’s advice, we added comparisons with\nthe existing reconstructions from northern Quebec, northern Alaska, the Polar Urals and the Kola\nPeninsula to the newly created Figure 7. We also added a few sentences with discussion:\n“Comparisons of the new dendrochronological record from southern Greenland with\ndendrochronological data from the northern tree lines of Eurasia and North America revealed\nsimilarities and significant differences in pan-Arctic temperature variability (Fig. 7). The greatest\nagreement was found in the Northern Quebec temperature reconstruction (Gennaretti et al., 2017),\nwhich shows similar fluctuations in both warm (recent warming; turn of the 18th and 19th centuries;\nfirst half of the 18th century) and cool (1840s–1950s) periods. By contrast, the common warm periods\nin Greenland and Alaska (Anchukaitis et al., 2013) are the recent warming period, the 18th century,\nand the mid-16th century. The most notable inconsistency concerns the Maunder Minimum period,\nwhich is distinctly cold in many reconstructions, but not clearly marked in Greenland. Similarly, this\nMM cooling is absent in data from the Russian Arctic (Hantemirov et al., 2011). The reconstruction\nof temperature variability from the Kola Peninsula (Kononov et al., 2009) differs most significantly,\nwith only the warming and subsequent cooling in the 17th century being consistent with that\nobserved in southern Greenland (Fig. 7).” We also added relevant citations to the Reference list:\nAnchukaitis, K.J., D’Arrigo, R.D., Andreu-Hayles, L., Frank, D., Verstege, A., Curtis, A., Buckley, B. M.,\nJacoby, G. C., Cook, E. R. (2013). Tree-ring-reconstructed summer temperatures from\nNorthwestern North America during the last nine centuries, J. Clim., 26 (10), 3001–3012.\nGennaretti, F., Huard, D., Naulier, M. et al. (2017). Bayesian multiproxy temperature reconstruction\nwith black spruce ring widths and stable isotopes from the northern Quebec taiga. Clim Dyn 49,\n4107–4119.\nHantemirov R., Shiyatov S., Gorlanova L. (2011). Dendroclimatic study of Siberian juniper,\nDendrochronologia 29, 119–122.\nKononov, Y. M., Friedrich, M., Boettger, T., (2009). Regional Summer Temperature Reconstruction\nin the Khibiny Low Mountains (Kola Peninsula, NW Russia) by Means of Tree-ring Width during\nthe Last Four Centuries, Arctic, Antarctic, and Alpine Research, 41:4, 460-468.\nSpecific comments:\nFigure 4 caption doesn't match the figure - the caption references panels A-F but only A-D are shown.\nThank you for this remark. We apologise for this oversight. Captions A and B referred to the results,\nwhich appeared in the supplementary materials (as Table 2). Now it was all properly compiled in\nFig.4, with appropriate captions from A to F.\nReviewer #3 (Remarks to the Author):\nThis is a very interesting study using a fairly groundbreaking set of juniper samples to reconstruct\ntemperature in southern Greenland. Adding paleoclimate chronologies such as this in areas that are\ntypically not covered by the usual paleoclimate proxies is very important for understanding regional\nvariations in climatic trends. I commend the authors on their collection of a both living, dead, and\nhistorical samples to create an unprecedented juniper chronology. The research is sound and the\nmanuscript is well written.\nWe sincerely thank the reviewer for the positive feedback and encouraging words.\nOne important revision I would request is to include the climate-growth table that is currently in the\nsupplemental information as a figure in the main manuscript. I did not see anywhere else that the list\nof climatic variables assessed was reported, nor any other indication of the strength of these\ncorrelations. I believe this revision is absolutely necessary for the manuscript to stand on its own.\nWe followed the reviewer's suggestion and have added the climate-growth table to our main text,\nas part of Figure 4.\nThe Laki section seems excessively long. The results are interesting, but could be conveyed much\nmore concisely (probably one paragraph). If the details of this event are a primary focus of the\nresearch, it should be included in the introduction and stated as a research goal. Similarly, if\nassessing the utility of blue rings is a significant goal of the project, then that should be clearly stated\nin the introduction and the idea of blue rings should be introduced there.\nThe reviewer is correct that this part can be more concise. We have shortened this paragraph (by\naround 90 words) as suggested. We have also added information about the utility of blue rings,\nand the Laki case study is also added as a significant goal to the introduction: “Additionally, we aimed to\nassess the usefulness of the so-called “blue rings” as an indicator of post-volcanic cooling and as a\nkey anatomical feature allowing for the synchronisation of juniper samples. Our study contributes\nto the understanding of the effects of volcanic eruptions on climate by combining wood anatomical\nobservation with superposed epoch analysis to explore the significance of selected eruptions on\ngrowth ring width and blue ring formation. ”\nOther more minor revisions I would request:\nPage 2, Line 63: \"relatively less\" than what? Why is this significant?\nThe reviewer is correct that this should be clarified. We changed to “significantly less”. The lower\nnumber of blue rings detected in Greenlandic juniper than in other studies is favourable for dating,\nbecause if there are too many, it is difficult to find a common pattern in their occurrence.\nPage 3, line 70: here is the perfect place to reference the climate-growth table\nWe have added the reference to climate-growth results (now incorporated in Figure 4, as A,B\npanels).\nPage 3, line 77: you state that a positive response to high minimum temperatures has \"important\necological significance\" but do not elaborate. What is the important significance here?\nFor clarity, we removed this sentence, and instead we have added a more concise description, and\na reference to earlier work on deciduous shrubs from Greenland, as requested by other reviewer:\n“The positive correlation between winter-spring minimum temperature and juniper growth\ncorresponds with the negative correlation with snow cover, indicating that less snow cover and\nfaster snowmelt have a positive effect on juniper growth. However, it should be noted that\nprecipitation was not statistically significant, as plants have access to moisture through both\nprecipitation and high air humidity. So, long-lasting snow cover is unfavourable to juniper growth,\nthereby significantly shortening the length of the growing period during a short Arctic summer.\nThese results concur with findings from other parts of Greenland where deciduous shrubs exhibit a\nconsistent negative response towards the amount of snow precipitation (Schmidt et al. 2010; Gamm\net al. 2018).”\nPage 3, line 93: I am skeptical of the feasibility of reconstructing sea ice with this proxy because sea\nice extent does not necessarily have a simple linear relationship with summer temperature.\nThank you for this comment. We supplemented the sentence: “However, attempts to reconstruct\nthis element have been unsuccessful and require future study, as sea ice extent does not necessarily\nhave a simple linear relationship with summer temperature.”\nPage 3, line 99: \"the model revealed a 46% variance\" does not make sense to me. Do you mean the\nR^2 was .46, indicating the 46% of the variance was predicted by the model?\nThank you for this comment. For clarity, we modified it in the text: “The coefficient of determination\nwas 0.46, indicating that 46% of the variance was predicted by the model…”"}, {"round": 2, "reviewer_comments": {"reviewer_1": "I would like to thank the authors for the large input they had to invest into the revised manuscript. I can clearly state that the long list of my comments and concerns was entirely addressed. I hereby support the publication of the manuscript and I am honoured that I could read this among the first scientists. Good job! Thank you :)", "reviewer_2": "My main concerns have been addressed.The manuscript is ready for publication. Congratulations.\nI have one specific suggestion. In line 98 and Figure7, Hantemirov et al., 2011 reconstruction was used. In fact, Hantemirov et al., 2022 (Nature Communication,Current Siberian heating is unprecedented\nduring the past seven millennia) reconstruciton is longer than Hantemirov et al., 2011, Hantemirov et al., 2022 should be\ncited and used in Figure 7."}, "author_response": "Point-by-point response letter 2\nDear Editor,\nWe sincerely appreciate recognition of our work. We have implemented a minor suggestion from one\nof the reviewers. We have also responded to all of your technical comments.\nOn behalf of all authors\nMagdalena Opała-Owczarek\nREVIEWERS' COMMENTS and AUTHORS' ANSWERS\nReviewer #1 (Remarks to the Author):\nI would like to thank the authors for the large input they had to invest into the revised manuscript.\nI can clearly state that the long list of my comments and concerns was entirely addressed. I hereby\nsupport the publication of the manuscript and I am honoured that I could read this among the first\nscientists. Good job! Thank you :)\nThank you very much for appreciating our work.\nReviewer #2 (Remarks to the Author):\nMy main concerns have been addressed. The manuscript is ready for publication. Congratulations.\nI have one specific suggestion. In line 98 and Figure7, Hantemirov et al., 2011 reconstruction was\nused. In fact, Hantemirov et al., 2022 (Nature Communication,Current Siberian heating is\nunprecedented during the past seven millennia) reconstruciton is longer than Hantemirov et al.,\n2011, Hantemirov et al., 2022 should be cited and used in Figure 7.\nWe sincerely appreciate your recognition of our work. We have taken into account the proposed\nchange in citation. Thank you."}]

Decision letter