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Unusual twentieth-century summer warmth in a 1,000-year temperature record from Siberia
Abstract
IN the current debate on the magnitude of modern-day climate change,
there is a growing appreciation of the importance of long, high-resolution proxies
of past climate13. Such records provide an indication of natural
(pre-anthropogenic) climate variability, either singly at specific geographical
locations or in combination on continental and perhaps even hemispheric
scales4. There are, however, relatively few records that are well
dated, of high resolution and of verifiable fidelity in terms of climate response,
and conspicuously few that extend over a thousand years or more5.
Here we report a tree-ring-based reconstruction of mean summer temperatures over the
northern Urals since AD 914. This record shows that the mean temperature of the
twentieth century (190190) is higher than during any similar period since AD
914.
... To investigate the relationship between tree radial-growth rate and temperature prior to the availability of climatic data from weather stations in 1966, we compared our results with reconstructed temperatures from the surrounding region ( Figure 7). Specifically, we compared the regional %GC with the temperature reconstructed by the ring-width chronology of the Siberian larch (Larix sibirica) in the Northern Urals [41] and the temperature reconstructed by the cell dimension chronology of the larch (Larix cajanderi Mayr.) in Siberia [42]. The periods of positive and negative growth rate anomalies mostly match the relatively warm and cool periods or the processes of warming and cooling of those reconstructed temperatures in this study area, respectively. ...
... results with reconstructed temperatures from the surrounding region (Figure 7). Specifically, we compared the regional %GC with the temperature reconstructed by the ringwidth chronology of the Siberian larch (Larix sibirica) in the Northern Urals [41] and the temperature reconstructed by the cell dimension chronology of the larch (Larix cajanderi Mayr.) in Siberia [42]. The periods of positive and negative growth rate anomalies mostly match the relatively warm and cool periods or the processes of warming and cooling of those reconstructed temperatures in this study area, respectively. ...
... Figure 7. Comparison of (a) the regional %GC, (b) 10-year moving-average reconstructed summer temperature in the Northern Urals [41], and (c) 10-year moving-average reconstructed summer temperature in Siberia [42]. Light-grey and dark-grey shaded areas highlight the periods of positive and negative growth rate anomalies in this study matching the relatively warm and cool periods of those reconstructed temperatures. ...
Climate warming and subsequent drought are predicted to alter local forest production and carbon budgets, the sensitivity of which may be site- and species-specific. Although a warmer and drier climate often constrains tree growth, whether trees grown in cool, wet regions across the Siberian forest can in turn be promoted remains unknown. Here, we aimed to investigate the historical growth tendency of Siberian forests in the Sayan Mountain areas and to explore how climate interacts to regulate their growth. We used ring-width data from Siberian pine (Pinus sibirica Du Tour) sampled from three sites in this area to establish a regional chronology and calculate percentage growth change (%GC) over the past 250 years. Bootstrapped correlation analysis between the regional ring-width chronology and climatic factors indicates the mean air temperature, though not precipitation, is more often positively linked to the radial growth of Siberian pines. The %GC series shows that, from 1966 to 2006, the rising temperatures in May resulted in a significant increase in the radial-growth rate of Siberian pines (r = 0.47, p < 0.05). Our study suggests that the positive growth rate anomaly is more likely to occur as temperatures rise in Southern Siberia.
... The interpretation of these results should be treated with caution for two reasons. Firstly, multi-proxy climate reconstructions have failed to find convincing evidence for the existence of a multi-century Mediaeval Warm Period across Europe (Hughes and Diaz, 1994;Briffa et al., 1995). Secondly, the documentary evidence cited by Lamb (1995) suggests an increase in summer temperatures during the Mediaeval period. ...
... It should be noted that is unlikely to respond solely to climate, but also to such factors as atmospheric CO2 content and local growing conditions (see Chapter 4). A 1000 cal yr temperature reconstruction based on ring widths shows that the eleventh and twelfth centuries in the northern Urals were characterised by cool conditions at the supposed height of the Mediaeval Warm Period (Briffa et aL, 1995). Likewise, the period associated with the Little Ice Age (c. ...
... The main features are 1) temperatures 1°C warmer than the modem mean during the Roman period from 0-400 AD, 2) the 'Dark Age (Mediaeval) Cold Epoch' from 500-1000 AD, 3) the 'Mediaeval Optimum' from 1100-1300 AD with temperatures 1°C above present, 4) Little Ice Age deterioration from 1450 AD with cold periods during the seventeenth and nineteenth centuries. However, given that the nature of both the Mediaeval Warm Period and the Little Ice Age are currently under debate (Briffa et aL, 1990(Briffa et aL, , 1995Bradley and Jones, 1993;Hughes and Diaz, 1994) it is possible that the interpretation of the speleothem data may need revision. ...
Recent research has shown that many mountain lakes are particularly sensitive to environmental change, including climate change. Lochan Uaine, at an elevation of 910 m in the Cairngorms of Scotland, is thought to be one such lake. Previous high resolution analyses undertaken at the lake reveal quasi-cyclic variations in the loss-on- ignition profiles of two cores. It is hypothesised that these cycles are driven by fluctuations in lake primary productivity. In turn, this productivity is thought to be driven by climatic variability, possibly through the influence of winter ice cover duration on growing season. Fluctuations in LOI comparable to those seen previously are evident in a more recent core from Lochan Uaine (core UACT6) representing the last c. 2000 yr of sediment accumulation. This core is dated by correlation of the LOI profile with that of a radiometrically-dated core, although attempts to validate the chronology by identifying microtephra layers were unsuccessful. Analysis of the sediment organic fraction reveals concurrent fluctuations in total organic carbon content, chlorin content, and bulk organic δ13C with LOI. Although few studies have been undertaken in lake sediments, the chlorin profile is thought to represent variations in lake primary productivity. Similarly, bulk organic δ13C may reflect variations in the relative inputs of autochthonous and allochthonous material to the sediment. To further investigate these hypotheses, organic geochemical analysis of the unbound lipid fraction is described. Certain lipids identified in the sediment record are assigned to particular organic sources through comparison with published data, analysis of vegetation collected from the lake catchment, and compound-specific δ13C analysis. Lipid biomarkers attributed to higher plant sources show little downcore variation in concentration, whereas those attributed to algal and bacterial sources show variations similar to the LOI profile. These results support the hypothesis that LOI fluctuations are driven by changes in lake productivity. The productivity changes are discussed in relation to late Holocene climate variability, although an unambiguous correlation between productivity and climate is prevented by the uncertain chronology of UACT6, and our current inadequate understanding of Holocene climate variability in temperate latitudes.
... Additionally, the Expressed Population Signal (EPS) statistic is used to evaluate the degree of error that a ring-width chronology can have as a function of the number of series and its variance over time. The threshold of 0.85 is used to evaluate if a chronology is reliable over time (Wigley et al., 1984;Briffa et al., 1995). The chronology of C. macrocarpa exceeded this threshold throughout its entire length, beginning in 1929 (Table 1). ...
... The two main trend changes (N50,000 tons·year −1 or more) in copper production occurred in 1977 and 1995. Hence, three periods were selected: 1960-1975(period I), 1976-1995(period II), and 1996. These same periods were used to compare patterns between the VIA and the INE control site. ...
... This was the case for Zn, Cr, Fe, V, and Al. For the case of Zn, this was true for all periods studied (Fig. 4), whereas for Cr only for the last two evaluated periods (1976( -1995 . 4). ...
... Additionally, the Expressed Population Signal (EPS) statistic is used to evaluate the degree of error that a ring-width chronology can have as a function of the number of series and its variance over time. The threshold of 0.85 is used to evaluate if a chronology is reliable over time (Wigley et al., 1984;Briffa et al., 1995). The chronology of C. macrocarpa exceeded this threshold throughout its entire length, beginning in 1929 (Table 1). ...
... The two main trend changes (N50,000 tons·year −1 or more) in copper production occurred in 1977 and 1995. Hence, three periods were selected: 1960-1975(period I), 1976-1995(period II), and 1996. These same periods were used to compare patterns between the VIA and the INE control site. ...
... This was the case for Zn, Cr, Fe, V, and Al. For the case of Zn, this was true for all periods studied (Fig. 4), whereas for Cr only for the last two evaluated periods (1976( -1995 . 4). ...
... During winter, glacier melt and output of sediment with meltwater is minimal. Climate change primarily affects the length of the summer (melt) season, which for Russkaya Gavan', at sea level, has been less than two months (July and August) during the exceptionally warm 20th century (> 1 °C anomaly; Briffa et al. 1995). The net annual mass balance may be determined during these summer months by a few melt days, and thus by cloudiness and sea ice, which limits heat transport to the region. ...
... However, prolonged warming and summer temperature anomalies > 0.5 °C result in a declining Shokal'ski Glacier mass balance (Chizov et al. 1968; Mikhalov & Chizov 1970 ). Summer temperature anomalies are well documented by tree-ring derived temperature time series for northern Russia (Briffa et al. 1995) and temperature composites (including ice cores) for the Northern Hemisphere (Mann et al. 1999). Strongly negative summer temperature anomalies may herald the advance of glaciers on Novaya Zemlya in the early 14th century (and also in the 19th century). ...
... AD 1650 the NAO remains comparatively weak until the 20th century. Strong negative summer temperature anomalies (Briffa et al. 1995; Mann et al. 1999 ) in combination with increased precipitation , as suggested by strengthening of the Icelandic Low (Meeker & Mayewski 2002 ), probably caused signifi cant glacier advance on Novaya Zemlya in the 19th century. We suggest that the second glacier cycle inferred from the glaciomarine sequence from Russkaya Gavan' corresponds to the 19th century glacier maximum and subsequent decay. ...
Climate variability in the Eurasian Arctic is signifi cantly modulated by North Atlantic oceanic heat fl ux. Weather stations on Novaya Zemlya since 1961 document summer temperatures 0.3 - 0.5 °C and winter temperatures 2.3 - 2.8 °C lower than in the fi rst half of the 20th century (Zeeberg & Forman 2001). This temperature decrease is associated with a prolonged negative phase of the North Atlantic Oscillation (NAO), decreased advection of North Atlantic Water, and below-average southern Barents Sea
... A warm phase at the same time (~600-700 cal. yr BP) has also been detected in a 1000-year-long tree-ring-based reconstruction from the eastern side of northern Urals (Briffa, 2000;Briffa et al., 1995). However, we found no clear evidence of the presence of the Medieval Climate Anomaly (MCA), a warm climate episode around 1200-800 cal. ...
... Similar to our findings, also the tree ring-based evidence from the eastern side of the northern Urals indicated a progressive climate warming from ~350 cal. yr BP (Briffa et al., 1995). Again in common with our results, Briffa et al. (1995) showed that the recent warmth was unusual, with the summer temperatures of the 20th century warmer than during any similar period over the last millennium. ...
... yr BP (Briffa et al., 1995). Again in common with our results, Briffa et al. (1995) showed that the recent warmth was unusual, with the summer temperatures of the 20th century warmer than during any similar period over the last millennium. Therefore, it appears that the general trends in summer air temperatures were similar during the examined time period on opposite sides of the Ural Mountains. ...
A lake sediment record from the north-eastern European Russian Arctic was examined using palaeolimnological methods, including subfossil chironomid and diatom analysis. The objective of this study is to disentangle environmental history of the lake and climate variability during the past 2000 years. The sediment profile was divided into two main sections following changes in the lithology, separating the limno-telmatic phase between ~2000 and 1200 cal. yr BP and the lacustrine phase between ~1200 cal. yr BP and the present. Owing to the large proportion of semi-terrestrial chironomids and poor modern analogues, a reliable chironomid-based temperature reconstruction for the limno-telmatic phase was not possible. However, the lacustrine phase showed gradually cooling climate conditions from ~1200 cal. yr BP until ~700 cal. yr BP. The increase in stream chironomids within this sediment section indicates that this period may also have had increased precipitation that caused the adjacent river to overflow, subsequently transporting chironomids to the lacustrine basin. After a short-lived warm phase at ~700 cal. yr BP, the climate again cooled, and a progressive climate warming trend was evident from the most recent sediment samples, where the biological assemblages seem to have experienced an eutrophication-like response to climate warming. The temperature reconstruction showed more similarities with the climate development in the Siberian side of the Urals than with northern Europe. This study provides a characteristic archive of arctic lake ontogeny and a valuable temperature record from a remote climate-sensitive area of northern Russia.
... Tree-ring width series from the northern Urals (Graybill and Shiyatov, 1992) indicate that in this area 20th century summers have been somewhat warmer than average. A recent analysis, using tree-ring density data, has attempted to reproduce more of the century time-scale temperature variability in this region (Briffa et al, 1995). This shows that the 20th century was clearly the warmest in the last 1000 years in this region, though shorter warmer periods occurred, for example, in the 13th and 14th centuries. ...
... Overall, however, it appears that the 2,0th century has been at least as warm as any century since at least 1400 AD. In at least some areas, the recent period appears to be warmer than has been the case for a thousand or more years (e.g.. Briffa et al., 1995;Thompson etal., 1995). Alpine glacier advance and retreat chronologies (Wigley and Kelly, 1990) suggest that in at least alpine areas, global 20th century temperatures may be warmer than any century since 1000 AD, and perhaps as warm as during any extended period (of several centuries) in the past 10,000 years. ...
... The climatic conditions in the Polar Urals contributed to the preservation of fragments of trunks and tree roots that grew in the study area and died during medieval cooling (Shiyatov 2003;Mazepa 2005;Hagedorn et al 2014;Shiyatov and Mazepa 2015). The duration of this cooling period, also known as the Little Ice Age, was from the late 13th to the late 19th centuries (Briffa et al 1995;Shiyatov 2003;Oosthoek 2018). The remnants of large trees that died during this period can be seen in some of the landscape photographs ( Figure 2). ...
... A comparative analysis of the number of trees in the early 1960s and in 2015 suggests that regional climate warming, which is observed in the Polar Urals (Briffa et al 1995;Shalaumova et al 2010;Hagedorn et al 2014;Shiyatov and Mazepa 2015), was accompanied by significant changes in the ecotone of the upper boundary of woody vegetation. ...
Woody vegetation at the upper limit of its growth is a sensitive indicator of climate change. The aim of this study is to provide an analysis of the centuries-old spatiotemporal dynamics of larch trees at the upper limit of their growth (mountain massif Rai-Iz, Polar Urals, Russia). We used a ground-based method of mapping the remnants of trees that grew in the study area and died during the Little Ice Age. Aerial photographs from the 1960s and high-spatial-resolution satellite images from 2015 were used as data sources to define the locations of trees. Maps of the forest–tundra phytocoenochoras (areas of the terrain that are relatively homogeneous for one or more components of vegetation and/or other indicators) were created using a modified method of boundary detection between forest parcels with different stand densities. The proposed method of boundary detection between the main types of phytocoenochoras allowed us to identify a 15% total increase in areas of closed and open forest and areas with sparse tree growth, as well as a decrease in areas of tundra with single trees over these last decades. Using our spatiotemporal analysis of forest– tundra demographics over the last 50 years, we found that the number of trees in the ecotone had doubled. However, modern trees have not yet reached the areas occupied by trees in the past.
... The mountains and plateaus in many parts of inner and northern Asia is covered by coniferous forests which play an important role in the earth's climate and ecosystems (Suzuki et al. 2003;Knorre et al. 2006). Inner and northern Asia is also one of the most sensitive areas to climate change in Asia, and many treering-based climate reconstructions have been conducted in this area (Briffa et al. 1995;Esper et al. 2001Esper et al. , 2010Pederson et al. 2001;Solomina et al. 2007;Agafonov and Kukarskikh 2008;Magda et al. 2011;Chen et al. 2013Chen et al. , 2015Liu et al. 2013;Gou et al. 2014;Bao et al. 2015). Dendroclimatological studies at the high-latitude sites of northern Asia have been focused on temperature reconstruction and provided the information about the summer temperature variations and recent global warming (Briffa et al. 1995(Briffa et al. , 2013Naurzbaev et al. 2002;Esper et al. 2010). ...
... Inner and northern Asia is also one of the most sensitive areas to climate change in Asia, and many treering-based climate reconstructions have been conducted in this area (Briffa et al. 1995;Esper et al. 2001Esper et al. , 2010Pederson et al. 2001;Solomina et al. 2007;Agafonov and Kukarskikh 2008;Magda et al. 2011;Chen et al. 2013Chen et al. , 2015Liu et al. 2013;Gou et al. 2014;Bao et al. 2015). Dendroclimatological studies at the high-latitude sites of northern Asia have been focused on temperature reconstruction and provided the information about the summer temperature variations and recent global warming (Briffa et al. 1995(Briffa et al. , 2013Naurzbaev et al. 2002;Esper et al. 2010). Some studies revealed that the role of temperature as a limit factor of tree growth was shown to decrease from high latitude to low latitude (Fritts 1976;Hantemirov et al. 2000;Agafonov and Kukarskikh 2008;Kucherov 2010;Briffa et al. 2013). ...
Based on the significant positive correlations between the regional tree-ring width chronology and local climate data, the total precipitation of the previous July to the current June was reconstructed since AD 1760 for the northwestern Chinese Altay. The reconstruction model accounts for 40.7 % of the actual precipitation variance during the calibration period from 1959 to 2013. Wet conditions prevailed during the periods 1764–1777, 1784–1791, 1795–1805, 1829–1835, 1838–1846, 1850–1862, 1867–1872, 1907–1916, 1926–1931, 1935–1943, 1956–1961, 1968–1973, 1984–1997, and 2002–2006. Dry episodes occurred during 1760–1763, 1778–1783, 1792–1794, 1806–1828, 1836–1837, 1847–1849, 1863–1866, 1873–1906, 1917–1925, 1932–1934, 1944–1955, 1962–1967, 1974–1983, 1998–2001, and 2007–2012. The spectral analysis of the precipitation reconstruction shows the existence of some cycles (15.3, 4.5, 3.1, 2.7, and 2.1 years). The significant correlations with the gridded precipitation dataset revealed that the precipitation reconstruction represents the precipitation variation for a large area of the northern part of inner Asia. A comparison with the precipitation reconstruction from the southern Chinese Altay shows the high level of confidence for the precipitation reconstruction for the northwestern Chinese Altay. Precipitation variation of the northwestern Chinese Altay is positively correlated with sea surface temperatures in tropical oceans, suggesting a possible linkage of the precipitation variation of the northwestern Chinese Altay to the El Niño-Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO). The synoptic climatology analysis reveals that there is the relationship between anomalous atmospheric circulation and extreme climate events in the northwestern Chinese Altay.
... Tree rings are one of the most useful tools for paleoclimate reconstructions (Briffa et al., 1992;Esper et al., 2002;Helama et al., 2017). In particular, tree-ring datasets from mid to high latitudes (Briffa et al., 1990(Briffa et al., , 1995D'Arrigo et al., 2001;Gennaretti et al., 2014), high elevations (Liu et al., 2009;Yang et al., 2014;Shi et al., 2017) and arid regions (Couralet et al., 2005;Shao et al., 2005Shao et al., , 2010 contribute greatly to the global network of tree-ring based climate reconstructions. These regions are typically covered with old forests which have not been strongly disturbed by human. ...
... TRW of P. taiwanensis is controlled by temperature in two different seasons, previous spring to summer and previous winter to current spring, a result in line with previous studies (Zheng et al., 2012;Shi et al., 2013;Cai and Liu, 2017;Cai et al., 2018). Such growth-climate relationships imply more complex seasonal physiological processes compared to northern conifers, whose TRW growth tends to be strongly controlled by current summer temperatures (Briffa et al., 1990(Briffa et al., , 1995D'Arrigo et al., 2001;Gennaretti et al., 2014). ...
... These rose to levels considerably above average for the period roughly from A.D. 1920 to 1970. The prolonged middle-l900s warming was reported from a number of sites across Fennoscandia (Kullman, 1985(Kullman, , 1987bBriffa et al., 1990Vorren et al., 1993;Zenerberg et al., 1996;Eronen and Zetterberg, 1996;Kullman and Engelmark, 1997), Siberia (Briffa et al., 1995;Mac-Donald et al., 1998a) and much of northern Eurasia (Briffa et a. Vaganov et aI., 1996). ...
... 40 yr) to have occurred in the last 400 yr. Similar 20th-century warming has been reported from the Polar Urals (Graybill and Shiyatov, 1993;Briffa et al., 1995) and Siberia (Shiyatov et aI., 1996a(Shiyatov et aI., , 1996bMacDonald et aI., 1998a), the Taimir (Vaganov et aI., 1996) and across much of northern Eurasia (Briffa et aI., 1996). Temperature reconstructions from northern Fennoscandia provide some evidence of mid-20th century warming, but do not indicate that it is exceptional relative to warming episodes of the past several centuries (Briffa et aI., 1990;. ...
A 403-yr tree-ring chronology (A.D. 1595–1997) was developed from living and dead Pinus sylvestris L. (Scots pine) from near treeline on the Kola Peninsula in northwestern Russia. Ring-width is significantly correlated with mean July temperatures. A reconstruction of mean July temperatures generally parallels similar dendroclimatic reconstructions from northern Fennoscandia. The Kola reconstruction indicates that the early- to mid-20th century experienced an exceptional period of warm summer temperatures. Dendrochronological techniques were used to estimate the timing of establishment and mortality of Pinus sylvestris at the site. Tree recruitment and mortality appear inversely related and episodic, with pulses of recruitment occurring during the late-17th, 18th, and mid- to late-20th centuries. The mid-20th century pine recruitment episode lags several decades behind the initiation of 20th-century summer warming. Analysis of instrumental climate records and pine recruitment suggests a link between warm fall and early spring conditions in the mid-20th century and increased pine regeneration. The results of this study are similar to findings from northern Fennoscandia and extend this pattern of recent climatic variation and associated treeline response eastward into the Kola Peninsula.
... Although the MWP phase is found in many of the proxy records, it may not have been a globally synchronous event. As dendrochronology is able to date proxy records to an annual, and seasonal, resolution, further work has been able to show that over the Urals in Siberia summers were cool in the 11th and 12th centuries (Briffa et al., 1995), times which have been shown to be warm in Fennoscandia. Regional disparities also occur over Britain; ...
p>Changes in Holocene palaeoclimates in Scotland have been reconstructed from seven sites: six ombrotrophic raised mires (Longbridge Moss, Langlands Moss, Temple Hill Moss, Shirgarton Moss, Mallachie Moss, and Craigmaud Moss) and one ombrotrophic blanket mire (Ben Gorm Moss) located across geographical and climatological gradients in Scotland.
Detrended correspondence analysis (DCA) has been used to reconstruct a climatic proxy record from plant microfossil data. The testate amoebae data were subjected to a transfer function which produces quantitative reconstructed mire water table values using a calibration program (WACALIB). The results show coherent wet and dry phases over the last ca. 5000 years ( ca. 7500 years at Temple Hill Moss), with the three proxy reconstructions supporting each other extremely well. Significant wet phases were identified at ca. cal. AD 1350-1550, AD 870-1150, AD 500-600, 750-940 BC, 1240-1390 BC, 1450-1630 BC, 1700-1900 BC, and ca . cal. 2200-2300 BC. Additional wet phases were recognised at Temple Hill Moss at ca. cal. 3350 BC, 3900 BC, and ca. cal. 4700 BC. Significant dry phases were documented at ca. cal. AD 920-1340, AD 350-520, and ca. cal. 540-390 BC. Correlations at the time of the Glen Garry and Hekla-4 isochrones revealed a significant difference between climatic phases in the north and south of Scotland, highlighting the possibility of asynchronous changes between northern Scotland and the rest of Britain.
The local extinctions of Sphagnum imbricatum in the four sites where it previously grew occurred at different dates, but were all associated with a wet phase.
Spectral analyses of the DCA and humification data revealed identical significant periodicities in both sets of data from four sites, either between 520-580 years or around 280 years.</p
... Alternatively, only ring width is insufficient for evaluating the relationship between radial growth and carbon sequestration, and the density of wood is an important parameter to determine carbon sequestration in the stem (Fujiwara 2007). Annual ring density can be measured using soft X-ray densitometry (Polge 1970;Parker 1970), which has been used as indicators of the climate reconstruction in dendrochronological studies (Schweingruber et al. 1993;Briffa et al. 1995;Briffa et al. 2013). The ring weight can be calculated using ring width and density , which can also be used as the fundamental indicator of carbon sequestration in the stem. ...
Key Message
The tree ring weight of Betula ermanii was primarily controlled by the ring width, but not by its ring density. The climate responses of them were clarified by dendrochronological analysis.
Abstract
Global warming scenarios have made the understanding of carbon sequestration changes in the stems of forest trees important. However, there is a lack of understanding about climate change’s effects on the wood density of hardwood, which is a crucial indicator of wood biomass. Therefore, we investigated the effects of climatic factors on the ring density and ring weight of B. ermanii, a dominant tree species in cool temperate regions and subalpine regions of Japan. We calculated the annual ring weight growth by multiplying the ring width and density. We developed the residual chronologies of the ring density and weight and performed a correlation analysis between the chronologies and the climate data. We deduced that the ring density was independent of the ring width for individual cores. The ring weight chronology showed a positive correlation with the ring width but not with ring density. The ring density decreased due to higher temperature, long sunshine duration, and less precipitation from mid-July to early October in the previous year. Conversely, those from mid-June to mid-August increased the ring density in the current year. The previous year’s high nighttime temperature in autumn and dry conditions during the current year’s summer decreased the ring weight, similar to the climate responses of ring width. Therefore, we concluded that ring weight was not controlled by ring density, but majorly regulated by ring width. Conclusively, this study’s results can evaluate the impact of climate change on the carbon sequestration potential of the stem of B. ermanii.
... The distribution of the Pinus sibirica extends to East Kazakhstan, Siberia (Russia) and Mongolia. Several tree-ring chronologies and proxy records have been developed in recent years (Briffa et al., 1995;Chen et al., 2012a;Dulamsuren et al., 2010;Frank et al., 2007;Loader et al., 2010;Myglan et al., 2008;Ovchinnikov et al., 2000;Sidorova et al., 2012). In the light of these studies, several climate-growth relationships in different regions and across environmental gradients were evaluated ( Dulamsuren et al., 2010;Frank et al., 2007). ...
Climatic factors play an essential role in the growth of tree ring width. In this study, we aimed to evaluate the
correlation between climatic variables and tree-ring growth characteristics of Pinus sibirica in Altai mountains,
northwestern China. This study being is first of its kind on climate growth analysis of Pinus sibirica in northwestern
China. The study showed great potential to understand the species growing under the specific climatic conditions.
Total of 70 tree cores collected from three sites in the sampling area, out of which 63 tree cores considered for
this study. The effect of climatic variables which was studied include precipitation, temperature and PDSI. Our
results showed that Tree Ring Width chronology has a significantly positive correlation with the late winter
(March) temperature and significant negative correlation with the July temperatures. A significant correlation
was observed with the late summer precipitation whereas no significant relation found with the Palmer Drought
Severity Index. These significant correlations with temperature and precipitation suggested that this tree species
had the potential for the reconstruction of the past climate in the area.
... They typically extend from the present to several centuries or more into the past, and so are useful for documenting climate change in terrestrial regions of the globe. Many recent studies have sought to reconstruct warm-season and annual temperatures several centuries or more ago from either the width or the density of annual growth rings (Briffa et al., 1995;D'Arrigo et al., 1996;Jacoby et al., 1996;D'Arrigo et al., 1998;Wiles et al., 1998;Cook et al., 2000). Recently, there has been a concerted effort to develop spatial reconstructions of past temperature variations (e.g., Briffa et al., 1996) and estimates of hemispheric and global temperature change (e.g., Briffa et al., 1998b;Briffa, 2000). ...
... They typically extend from the present to several centuries or more into the past, and so are useful for documenting climate change in terrestrial regions of the globe. Many recent studies have sought to reconstruct warm-season and annual temperatures several centuries or more ago from either the width or the density of annual growth rings (Briffa et al., 1995;D'Arrigo et al., 1996;Jacoby et al., 1996;D'Arrigo et al., 1998;Wiles et al., 1998;Cook et al., 2000). Recently, there has been a concerted effort to develop spatial reconstructions of past temperature variations (e.g., Briffa et al., 1996) and estimates of hemispheric and global temperature change (e.g., Briffa et al., 1998b;Briffa, 2000). ...
... The distribution of the Pinus sibirica extends to East Kazakhstan, Siberia (Russia) and Mongolia. Several tree-ring chronologies and proxy records have been developed in recent years (Briffa et al., 1995;Chen et al., 2012a;Dulamsuren et al., 2010;Frank et al., 2007;Loader et al., 2010;Myglan et al., 2008;Ovchinnikov et al., 2000;Sidorova et al., 2012). In the light of these studies, several climate-growth relationships in different regions and across environmental gradients were evaluated ( Dulamsuren et al., 2010;Frank et al., 2007). ...
Climatic factors play an essential role in the growth of tree ring width. In this study, we aimed to evaluate the
correlation between climatic variables and tree-ring growth characteristics of Pinus sibirica in Altai mountains,
northwestern China. This study being is first of its kind on climate growth analysis of Pinus sibirica in northwestern
China. The study showed great potential to understand the species growing under the specific climatic conditions.
Total of 70 tree cores collected from three sites in the sampling area, out of which 63 tree cores considered for
this study. The effect of climatic variables which was studied include precipitation, temperature and PDSI. Our
results showed that Tree Ring Width chronology has a significantly positive correlation with the late winter
(March) temperature and significant negative correlation with the July temperatures. A significant correlation
was observed with the late summer precipitation whereas no significant relationship found with the Palmer Drought
Severity Index. These significant correlations with temperature and precipitation suggested that this tree species had the potential for the reconstruction of the past climate in the area.
... The distribution of the Pinus sibirica extends to East Kazakhstan, Siberia (Russia) and Mongolia. Several tree-ring chronologies and proxy records have been developed in recent years (Briffa et al., 1995;Chen et al., 2012a;Dulamsuren et al., 2010;Frank et al., 2007;Loader et al., 2010;Myglan et al., 2008;Ovchinnikov et al., 2000;Sidorova et al., 2012). In the light of these studies, several climate-growth relationships in different regions and across environmental gradients were evaluated ( Dulamsuren et al., 2010;Frank et al., 2007). ...
Climatic factors play an essential role in the growth of tree ring width. In this study, we aimed to evaluate the correlation between climatic variables and tree-ring growth characteristics of Pinus sibirica in Altai mountains, northwestern China. This study being is first of its kind on climate growth analysis of Pinus sibirica in northwestern China. The study showed great potential to understand the species growing under the specific climatic conditions. Total of 70 tree cores collected from three sites in the sampling area, out of which 63 tree cores considered for this study. The effect of climatic variables which was studied include precipitation, temperature and PDSI. Our results showed that Tree Ring Width chronology has a significantly positive correlation with the late winter
(March) temperature and significant negative correlation with the July temperatures. A significant correlation was observed with the late summer precipitation whereas no significant relation found with the Palmer Drought Severity Index. These significant correlations with temperature and precipitation suggested that this tree species
had the potential for the reconstruction of the past climate in the area.
... Еще большую изменчивость (2-3 недели) в сроках начала роста побегов в разные годы наблюдал Н. В. Шкутко (1991 Усова (1972), А. С. Лантратова (1973) и С. А. Потапова (1985). Целый ряд исследователей установили зависимость интенсивности роста также и древесины ствола от температурного режима воздуха (Елагин, 1962;Briffa et al., 1995;Graybill, Shiyatov, 1997;Bengtsson et al., 2004;Esper et al., 2010;Nikolaev et al., 2011b;Babushkina, Belokopytova, 2014;Belokopytova et al., 2018). (Worrall, 1973), Д. А. Грейбилом и С. Г. Шиятовым (Graybill, Shiyatov, 1997) и Дж. ...
The study reports results of research carried out from April to October during 1988–2016 at the Botanical Garden of Petrozavodsk State University (South Karelia, middle taiga subzones). Three introduced species of the genus Larix (Larix sibirica Ledeb., L. leptolepis (Sieb. et Zucc.) Gord, and L. dahurica Turcz. ex Trautv.) were studied. The growth of shoots and needles in different species begins, reaches its culmination, and ends almost simultaneously, differing by no more than one week across the species. L. sibirica shows the highest growth rate. The timing of growth, culmination, and the dynamics of growth of shoots and needles are largely determined by variations in precipitation, temperature, and humidity. The direction and strength of such an effect may vary from year to year. The dates of phenological phases of the Larix species studied here are chiefly determined by the air temperature in the current growing season and the dates of formation of wintering buds in the previous growing season. Bud swelling and opening begins almost simultaneously in the studied species. Most of the other phenological phases begin and end earliest in L. sibirica and latest in L. leptolepis. All the studied species, primarily L. sibirica, are promising for residential landscaping and creation of artificial plant communities in Karelia
... We used a 20-year cubic smoothing spline curve to remove non-climatic signals, such as the age-and size-related trends, while retaining the high-frequency variability (Cook, 1987). We also calculated the rbar to quantify the common-growth signal, which is the mean correlation coefficient of all pairwise combinations of all trees in the dataset (Briffa et al., 1995), and the EPS (Expressed Population Signal) that shows how well the samples represent an infinitely replicated chronology (Briffa and Jones, 1990). For this study, we used both the standard tree-ring chronology, to represent the population growth signal, and the detrended individual mean series to evaluate growth signals at the individual level. ...
Forests worldwide are facing increasingly frequent climate extremes due to global warming. The negative effects of climate change on tropical forests have been extensively reported by both permanent plots and tree-ring studies that targeted forest's responses to climate. While they focus mostly on community and population levels, the effects of landscape heterogeneity on trees’ sensitivity to climate is often not accounted for, overlooking the diverse responses of individual trees to climate variation. We tested the hypotheses that trees may differ in sensitivity to climate and that some microenvironmental conditions may exert the role of climate-change refugia. We built the first tree-ring chronology of Amburana cearensis trees sampled across a Seasonally Dry Tropical Forest (SDTF) in Brazil. We ensure a robust tree-ring dating using dendrochronological methods and ¹⁴C dating of trees inhabiting various conditions characterized here through the seasonality of the local Normalized Difference Vegetation Index. At the population level, the standard tree-ring chronology suggests that tree growth depends on rainfall and temperature, leading to a common conclusion that drier and warmer conditions would impact interannual tree growth in the tropics. However, the cluster analyses revealed groups of individual trees with distinct growth sensitivities to climate. The most sensitive trees were the individuals located in the highly seasonal vegetation of the epikarst, in contrast to the complacent trees (non-sensitive to regular interannual climate variability) inhabiting the less-seasonal vegetation in the deep soil epikarst and valley. Based on these groups of trees, we built two mean chronologies and assessed their climate-growth relationships. In accordance with the individual analysis, the tree-ring chronology of complacent trees showed no association with wet season precipitation and only moderate association with temperature. The areas supporting these complacent trees of A. cearensis in the less seasonal vegetation correspond to a quarter of the entire sampling site. The climate buffering capacity of these refugia may only be compromised in years of climate extremes when all sampled trees share low growth rates during years with anomalous low rainfall and high temperature. Assessing individual’s climate sensitivity is therefore paramount for a comprehensive understanding of the heterogeneous responses of tropical forests to climate change. The hidden individual tree responses in the population can help identify priority areas of management in a rapidly changing environment.
... The volcanic aerosols emitted into the atmosphere during large eruptions decrease temperatures on hemispheric and global scales for several years following the eruption (Self et al. 1981;Robock 2000;Adams et al. 2003;Ning et al. 2017;Briffa et al. 1992Briffa et al. , 1995Briffa et al. , 1998Yamaguchi et al. 1993;Jones et al. 1995;Hantemirov et al. 2004). The volcanic eruptions can also be recorded in tree rings by changing the climate (Salzer and Hughes 2007;Liang et al. 2019). ...
Although global warming is an indisputable fact, there is still uncertainty about how climate change will occur at regional levels. Kazakhstan is the largest landlocked country in the world. To best manage this country’s limited water resources, socio-economic development and environmental protection, a solid understanding of regional climate change impacts is needed. In this study, tree-ring width and δ13C chronologies were established based on 99 tree-ring samples of Schrenk spruce (Picea schrenkiana Fisch. et Mey.) collected in Almaty, Kazakhstan. Climate response analysis between the tree-ring chronologies and climate data indicates that summer mean temperature is the strongest climate signal recorded by tree-ring δ13C. We reconstructed temperature change in southern Kazakhstan since 1850 C.E. using the tree-ring δ13Ccorr chronology. The results show that the temperatures in southern Kazakhstan have risen at a rate of about 0.27 °C per decade over the past 166 years. However, the rate has increased by as much as 0.44 °C per decade over the past 30 years. Analyses of temperature and precipitation data show that the climate has alternated between warm-dry and cold-humid periods over the past 166 years. The extreme droughts of 1879, 1917 and 1945 were caused by the combination of continuously high temperatures and reduced precipitation.
... Consistent with the observed response of intra-annual P to environmental variables, AP was thus best explained by the interaction of both T and w effects (Fig. 6b). Regardless of site elevation, the effect of T alone was a surprisingly poor predictor of annual growth, given the well-known effect of T on tree growth in cold environments (Briffa et al., 1995;Luckman et al., 1997;D'Arrigo et al., 2001;Vaganov et al., 2006b). The control of T on tree growth commonly switches from positive to negative from cold toward hotter environments, as a consequence of the effect of increasing T on drought stress (Mart ınez-Vilalta et al., 2008;King et al., 2013b;Peters et al., 2017;Klesse et al., 2018). ...
Efforts to develop mechanistic tree growth models are hindered by the uncertainty of whether and when tree growth responses to environmental factors are driven by carbon assimilation or by biophysical limitations of wood formation.
In this study, we used multiannual weekly wood‐formation monitoring of two conifer species (Larix decidua and Picea abies) along a 900 m elevational gradient in the Swiss Alps to assess the biophysical effect of temperature and water potential on wood formation. To this end, we developed a model that simulates the effect of water potential on turgor‐driven cambial division, modulated by the effect of temperature on enzymatic activity.
The model reproduced the observed phenology of tracheid production, as well as intra‐ and interannual tracheid production dynamics of both species along the elevational gradient, although interannual model performance was lower. We found that temperature alone explains the onset of tracheid production, yet water potential appears necessary to predict the ending and the total amount of tracheids produced annually.
We conclude that intra‐annual cambial activity is strongly constrained by both temperature and water potential at all elevations, independently of carbon assimilation. At the interannual scale, biophysical constraints likely interact with other factors.
... Le bois enregistre au cours du temps la réponse de l'arbre aux variations climatiques dans la structure des cernes. Beaucoup d'études de dendrochronologie se sont servies de cette particularité pour effectuer des analyses rétrospectives de reconstruction des climats passés (Briffa et al. 1995;Esper et al. 2002;González-Elizondo et al. 2005). ...
Plusieurs dépérissements du début du XXe siècle ont montré que le Douglas français était vulnérable à la sécheresse. La question de savoir si les forêts de Douglas peuvent s'adapter au nouveau climat plus chaud et plus sec est une préoccupation majeure en France. Nous avons estimé la variation de la résistance à la cavitation d'un ensemble de provenances de Washington, de l'Oregon et de Californie dans deux expériences de jardins communs situées dans le sud de la France. Nous avons étudié les relations entre la résistance à la cavitation, la microdensité du xylème et l'anatomie du tronc et des branches. Nous avons constaté que la pression de sélection climatique dans la zone naturelle a façonné l'adaptation locale pour la résistance à la cavitation, la microdensité et l'anatomie des ponctuations du xylème. Les provenances de Californie intérieure tendent à être plus résistantes à la cavitation, avec une plus grande densité de bois d'été et des ponctuation plus sûres que les provenances de Californie côtière, puis de Washington et d'Oregon. Cependant, nous avons également constaté des variations importantes à l'intérieur d'une même région qui ne pouvaient pas être expliquées par les données climatiques disponibles. Nous avons trouvé différentes relations structure-fonctions, selon le niveau d'observation (arbre ou provenance) et la partie de l'arbre (tronc ou branche). Par exemple, au niveau individuel, les arbres les plus résistants à la cavitation ont des branches plus denses avec une ouverture de ponctuation plus petite, tandis qu'au niveau de la provenance, les arbres les plus résistants à la cavitation ont du bois moins dense dans le tronc et les branches, et des ponctuations plus sûrs. Dans l'ensemble, nous concluons qu'il existe un potentiel d'adaptation évolutive pour la résistance à la sécheresse du Douglas, disponible à différents niveaux, individuel et de provenance. Cependant, dans un contexte d'amélioration des arbres, le réseau complexe de relations entre la résistance à la cavitation, la microdensité et les traits anatomiques doit être soigneusement examiné afin d'éviter une éventuelle réponse corrélative défavorable à la sélection.
... We therefore accept that using temperature-sensitive tree-ring series for drought reconstruction may be problematic if used in isolation, e.g. only from the Polar Urals ( Briffa et al. 1995). However, the inverse relationship driven by evapotranspiration demand is not universal even in the high northern latitudes because temperature sensitivity there varies considerably in strength due to varying site locations and conditions (St George and Ault 2014;Hellmann et al. 2016). ...
We present the European Russia Drought Atlas (ERDA) that covers the East European Plain to the Ural Mountains from 1400–2016 CE. Like the Old World Drought Atlas (OWDA) for the Euro-Mediterranean region, the ERDA is a one-half degree gridded reconstruction of summer Palmer Drought Severity Indices estimated from a network of annual tree-ring chronologies. Ensemble point-by-point regression is used to generate the ERDA with the identical protocols used for developing the OWDA. Split calibration/validation tests of the ERDA indicate that it has significant skill over most of its domain and is much more skillful than the OWDA where they overlap in the western part of ERDA domain. Comparisons to historical droughts over European Russia additionally support the ERDA’s overall validity. The ERDA has been spatially smoothed and infilled using a local regression method to yield a spatially complete drought atlas back to 1400 CE. EOF analysis indicates that there are three principal modes of hydroclimatic variability in the ERDA. After Varimax rotation, these modes correlate significantly with independent climate data sets extending back to the late nineteenth century in a physically interpretable way and relate to atmospheric circulation dynamics of droughts and heatwaves over European Russia based on more recent instrumental data.
... On the other hand, the definition of the onset of the CWP varies by author. Some of them consider it to be since 1850 CE (Deng et al., 2017) or the entire 20th century (Briffa et al., 1995;Briffa, 2000;Jones et al., 1998), while other authors refer to the "mid-20th century" (e.g., Crowley and Lowery, 2000;Levitus et al., 2000) or the "late 20th century" (e.g., Mann et al., 2003;Jones and Mann, 2004;Osborn and Briffa, 2006). Recently, Díaz and Vera (2018) considered the CWP in South America to be the period between 1951 and 2000 CE, also taking into account the negative rainfall trend observed in the southern Andes. ...
The South Pacific Subtropical High (SPSH) is a predominant feature of the South American climate. The variability of this high-pressure center induces changes in the intensity of coastal alongshore winds and precipitation, among others, over southwestern South America. In recent decades, strengthening and expansion of the SPSH have been observed and attributed to the current global warming. These changes have led to an intensification of the southerly winds along the coast of northern to central Chile and a decrease in precipitation from central to southern Chile. Motivated by improving our understanding about the regional impacts of climate change in this part of the Southern Hemisphere, we analyzed SPSH changes during the two most extreme climate events of the last millennium, the Little Ice Age (LIA) and the Current Warm Period (CWP: 1970–2000), based on paleoclimate records and CMIP5/PMIP3 model simulations. In order to assess the level of agreement of general circulation models, we also compare them with ERA-Interim reanalysis data for the 1979–2009 period as a complementary analysis. Finally, with the aim of evaluating future SPSH behavior, we include 21st century projections under a Representative Concentration Pathway (RCP8.5) scenario in our analyses. Our results indicate that during the relative warm (cold) period, the SPSH expands (contracts). Together with this change, alongshore winds intensify (weaken) south (north) of ∼35∘ S; also, southern westerly winds become stronger (weaker) and shift southward (northward). Model results generally underestimate reanalysis data. These changes are in good agreement with paleoclimate records, which suggest that these variations could be related to tropical climate dynamics but also to extratropical phenomena. However, although models adequately represent most of the South American climate changes, they fail to represent the Intertropical Convergence Zone–Hadley cell system dynamics, emphasizing the importance of improving tropical system dynamics in simulations for a better understanding of its effects on South America. Climate model projections indicate that changes recently observed will continue during the next decades, highlighting the need to establish effective mitigation and adaptation strategies against their environmental and socioeconomic impacts.
... Higher temperatures might advance the beginning of the growing season, and then increase the duration of the growth period. Although most dendrochronological studies have not examined the effects of the insolation duration on tree-ring width, many researchers reported that tree growth is promoted by high summer temperatures at high altitudes and high latitudes (Gervais & MacDonald 2000;Briffa et al. 2002;Kirdyanov et al. 2003;Grudd et al. 2008). Therefore, the negative effects of shorter insolation and low temperatures on the growth of Siberian larch are believed to be more significant near the timberline, while lower precipitation with high temperatures in the same month reduces the growth of Siberian larch in the drought-stressed forest at the low elevation area of the Altay Mountains. ...
Siberian larch (Larix sibirica) trees were studied in a drought-stressed, low-elevation Taiga forest in the Altay Mountains for their potential to be used for reconstructing precipitation. A climate/growth analysis provided evidence that the tree-ring widths were strongly determined by the climatic conditions from May to July, positively by precipitation and negatively by temperature. Nevertheless , the resulting regional tree-ring chronology of Siberian larch offers only a limited possibility to perform reliable reconstructions of precipitation as only 30.8% of the total variation of the actual April-July precipitation was explain-able. Drought events reflected by the chronology were compared with historical records and other tree-ring derived climate reconstructions, showing some common events of climate extremes over much of Central Asia. This new Siberian larch chronology and an earlier maximum latewood density (MXD) chronology from the neighboring region reveal that the local climate is mainly characterized by cold/wet and warm/dry situations over the past 251 years. This study demonstrates that the use of both tree-ring width and MXD data may increase information of past climate variability in the Altay mountain region.
... On the other hand, the definition of the onset of the CWP varies regarding the author. Some of them consider it since 1850 CE (Deng et al., 2017) or the entire 20 th century (Briffa et al., 1995;Briffa, 2000;Jones et al., 1998), while 10 other authors refer to 'mid-20 th century' (e.g., Crowley and Lowery, 2000;Levitus et al., 2000) or 'late-20 th century' (e.g., Mann et al., 2003;Jones and Mann, 2004;Osborn and Briffa, 2006). Recently, Díaz and Vera (2018) considered the CWP in South America as the period between 1951 and 2000 CE, taking into account also the negative rainfall trend observed in the southern Andes. ...
The South Pacific Subtropical High (SPSH) is a predominant feature of South American climate. The variability of this high-pressure center induces changes in the intensity of coastal alongshore winds and precipitation, among others, over southwestern South America. In recent decades, a strengthening and expansion of the SPSH have been observed and attributed to the current global warming. These changes have led an intensification of the southerly winds along the coast of northern to central Chile, and a decrease in precipitation from central to southern Chile. Motivated by improving our understanding about the regional impacts of climate change in this part of the Southern Hemisphere, we analyze SPSH changes during the two most extreme climate events of the last millennium: the Little Ice Age (LIA) and the Current Warm Period (CWP: 1970–2000), based on paleoclimate records and CMIP5/PMIP3 model simulations. In order to assess the level of agreement of general circulation models, we also compare them with ERA-Interim reanalysis data for the 1979–2009 period as a complementary analysis. Finally, with the aim of evaluating future SPSH behaviour, we include 21th century projections under a RCP8.5 scenario in our analyses. Our results indicate that during the relative warm (cold) period, the SPSH expands (contracts). Together with this change, alongshore winds intensify (weaken) south (north) of ~ 35º S; also, Southern Westerly Winds become stronger (weaker) and shift southward (northward). Model results generally underestimate reanalysis data. These changes are in good agreement with paleoclimate records, which suggest that these variations could be related to tropical climate dynamics but also to extratropical phenomena. However, although models adequately represent most of the South American climate changes, they fail in representing the Intertropical Convergence Zone - Hadley Cell system dynamics. Climate model projections indicate that changes recently observed will continue during next decades, highlighting the need to establish effective mitigation and adaptation strategies against their environmental and socio-economic impacts.
... Linear regression (correlation analysis, multiple regression, principal component regression, etc.) is commonly used to analyze the statistical relationship between the TRW (as a proxy) and climate data [21,87]. Pearson's product-moment correlation has become a workhorse for analyzing complex dendroclimatic relationships. ...
Dendroclimatology and dendroecology have entered mainstream dendrochronology research in subtropical and tropical areas. Our study focused on the use of the chronology series of Masson pine (Pinus massoniana Lamb.), the most widely distributed tree species in the subtropical wet monsoon climate regions in China, to understand the tree growth response to ecological and hydroclimatic variability. The boosted regression trees (BRT) model, a nonlinear machine learning method, was used to explore the complex relationship between tree-ring growth and climate factors on a larger spatial scale. The common pattern of an asymptotic growth response to the climate indicated that the climate-growth relationship may be linear until a certain threshold. Once beyond this threshold, tree growth will be insensitive to some climate factors, after which a nonlinear relationship may occur. Spring and autumn climate factors are important controls of tree growth in most study areas. General circulation model (GCM) projections of future climates suggest that warming climates, especially temperatures in excess of those of the optimum growth threshold (as estimated by BRT), will be particularly threatening to the adaptation of Masson pine.
... There are evidences of advancement of natural tree line at some places in the Himalayan region (Dube et al. 2003;Gaire et al. 2014;Shrestha et al. 2014;Tiwari et al. 2017;Yadava et al. 2017) and other parts of globe (Gehrig-Fasel et al. 2007;Kullman & Oberg 2009;Lloyd et al. 2003;Moen et al. 2004;Moiseev & Shiyatov 2003). The warming trend that followed the little ice age event witnessed unprecedented 20th century warming (Briffa et al. 1995;IPCC 2013;Jones & Moberg 2003;Mann et al. 1999;Pant & Rupakumar 1997) that might have played important role in the tree line shifts. Local site factors, such as physiography, species richness and interactions, herbivory, historical disturbances (natural or anthropogenic) or other biotic factors may also modulate or override the impact of climate on tree line position and responsiveness (Cairns et al. 2007;Holtmeier & Broll 2005, 2007Odland 2015;Payette 2007). ...
The impact of climate change on trees is conspicuous in the form of tree line
response at the higher mountain region. Based on tree ring data, we investigated the age stand structure and tree line dynamics of the Himalayan fir (Abies spectabilis) at Tungnath, Uttarakhand, western Himalaya. This species forms the upper ecotone limit at ~3335 m asl in association with Rhododendron campanulatum, the latter extending further and forming the krummholz ecotone limit. The stand structure and age distribution of fir reveals the presence of high girth class trees at lower altitudes with the oldest tree of ~379 years age at ~3000 m asl. A good number of trees older in age than the age of uppermost tree (~109 years) at ~3353 m asl show the recruitment of fir at the ecotone limit by the early 20th century AD with the shift rate of ~13 m per decade. The highest advancement rate of ~39 m per decade is found during 18th Century AD. Over 300 years old ring width chronology of silver fir indicates that the temperature of winter months, especially February, have positive influence on the tree growth. The presence of trees younger than 100 years within the forest stand near ecotone limit indicates subsequent
infilling of forest and also explains the growth behavior of fir trees in relation to increasing
temperature of winter months during the last century. Evidences of no regeneration above the present fir limit and the presence of few seedlings within the upper ecotone limit could be related to mixed response to climate and other local factors at this site. In spite of rapid warming silver fir tree line in Tungnath area has not shown upslope advance. It seems that the positive effect of warming in tree growth is nullified by water stress resulting from increased evapotranspiration.
... There are evidences of advancement of natural tree line at some places in the Himalayan region (Dube et al. 2003;Gaire et al. 2014;Shrestha et al. 2014;Tiwari et al. 2017;Yadava et al. 2017) and other parts of globe (Gehrig-Fasel et al. 2007;Kullman & Oberg 2009;Lloyd et al. 2003;Moen et al. 2004;Moiseev & Shiyatov 2003). The warming trend that followed the little ice age event witnessed unprecedented 20th century warming (Briffa et al. 1995;IPCC 2013;Jones & Moberg 2003;Mann et al. 1999;Pant & Rupakumar 1997) that might have played important role in the tree line shifts. Local site factors, such as physiography, species richness and interactions, herbivory, historical disturbances (natural or anthropogenic) or other biotic factors may also modulate or override the impact of climate on tree line position and responsiveness (Cairns et al. 2007;Holtmeier & Broll 2005, 2007Odland 2015;Payette 2007). ...
The impact of climate change on trees is conspicuous in the form of tree line response at the higher mountain region. Based on tree ring data, we investigated the age stand structure and tree line dynamics of the Himalayan fir (Abies spectabilis) at Tungnath, Uttarakhand, western Himalaya. This species forms the upper ecotone limit at ~3335 m asl in association with Rhododendron campanulatum, the latter extending further and forming the krummholz ecotone limit. The stand structure and age distribution of fir reveals the presence of high girth class trees at lower altitudes with the oldest tree of ~379 years age at ~3000 m asl. A good number of trees older in age than the age of uppermost tree (~109 years) at ~3353 m asl show the recruitment of fir at the ecotone limit by the early 20th century AD with the shift rate of ~13 m per decade. The highest advancement rate of ~39 m per decade is found during 18th Century AD. Over 300 years old ring width chronology of silver fir indicates that the temperature of winter months, especially February, have positive influence on the tree growth. The presence of trees younger than 100 years within the forest stand near ecotone limit indicates subsequent infilling of forest and also explains the growth behavior of fir trees in relation to increasing temperature of winter months during the last century. Evidences of no regeneration above the present fir limit and the presence of few seedlings within the upper ecotone limit could be related to mixed response to climate and other local factors at this site. In spite of rapid warming silver fir tree line in Tungnath area has not shown upslope advance. It seems that the positive effect of warming in tree growth is nullified by water stress resulting from increased evapotranspiration.
... noting samples that contained reaction wood. In studies of tree ring-width variability associated with climate change (e.g., Briffa et al., 1990Briffa et al., , 1995, it is common to estimate the systematic changes in ring-width associated with age and remove them from the measurement. This correction of ring-width for the changing age and geometry of the tree is known as standardization, and the transformed values are called ring-width indices (Fritts, 1976). ...
Not only do high-latitude tree-ring data reveal minor and major Holocene climatic variation, but the distribution in time of subfossil trees provides information about former tree-line fluctuation. Over 152 samples of Scots pine (Pinus sylvestris) were collected and measured from lake Lilla Rörtjärnen, situated close to the present treeline. Five floating chronologies were built spanning 498 B.C.–A.D. 19, A.D. 50–390, A.D. 431–884, A.D. 946–1256, and A.D. 1337–1865. The floating chronologies were crossdated with a dendrochronology from Torneträsk. No trees were dated from 20–49 A.D., 391–430 A.D., 885–945 A.D., and 1257–1336, A.D. The temporal distribution of pines in the lake suggests periods of intensive germination, with each phase occurring within 80 to 100 yr from the beginning of each floating chronology. At the end of each phase higher lake levels drowned trees close to the shore. Both the existence and the preservation of the dead pines is likely to have been controlled by changes in lake level.
... Multicentury-long proxy records of climate provide baseline information to assess the full range of natural variability (National Research Council, 1995). Tree-ring chronologies have proved particularly useful to reconstruct monthly, seasonal, and annual climate variables (Stahle et al., 1988;Briffa et al., 1995;Jacoby et al., 1996;Mann et al., 1998). On a global scale, relatively few such records are long enough to cover most of the last millennium, and even fewer are capable of effectively resolving multidecadal variability because of the "segment length curse" . ...
An 861-yr Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) tree-ring chronology has been recently developed for the Salmon River Valley, Challis National Forest, Idaho. Its potential for climatic reconstruction is investigated using monthly instrumental records of precipitation, temperature, and Palmer Drought Severity Index from 1895 to 1995. The temporal stability of climate-tree growth relationships is analyzed by means of evolutionary (backward and forward) and moving response functions. When precipitation and temperature are used as predictors, the strongest (and temporally stable) signal is a negative response to July temperature. Another relevant signal, albeit less temporally consistent, is a positive response to May precipitation. When the Palmer Drought Severity Index is used as an integrated predictor to highlight response to summer moisture stress, the strength of the association with tree growth increases in recent decades. This information can be used to maximize the reliability of dendroclimatic reconstructions, and has important implications for expanding the range of recent studies on altered climate-tree growth relationships during the 20th century.
... Various chronology statistics like mean sensitivity, standard deviation, autocorrelation, within tree correlation, between tree correlation, mean series correlation, signal-to-noise ratio (SNR), expressed population signal (EPS) and variance explained were calculated to assess the quality of the site chronologies. Chronology quality was estimated using rbar [25] and expressed population signal statistics [26]. Field observation and tree ring data show that radial growth of Larix in current study sites ceases in September-October. ...
... High-resolution, paleo-records of climate and environmental processes are increasingly important to put modern processes in perspective (Swetnam and Lynch 1993;Mann et al. 1998;Briffa et al. 2002;IPCC 2014;Black et al. 2016). Framing the isolated and interacting role of drought and disturbance such as episodic insect outbreaks and fire has become an increasingly important research topic (Swetnam et al. 1995;Kulakowski et al. 2003). ...
We reconstruct pandora moth (Coloradia pandora Blake) outbreaks and climate from a 1572-year (435-2006 CE) ponderosa pine (Pinus ponderosa Dougl. ex Laws.) chronology from a lava flow in central Oregon. We took samples from 128 living trees and remnant logs and crossdated the samples using skeleton plots and COFECHA for quality control. After cutting out and removing those time periods from the chronology during which insects become the main limiting factor to growth, we examine the response of tree rings to climate. Evidence of species longevity (up to 877 years), presence of periodic pandora moth defoliations (13 total), and a significant relationship with the Palmer Drought Severity Index were observed (R² = 0.34, p < 0.001). Suppressions related to pandora moth outbreaks were recorded back to 618 CE, with a mean return interval of 104 years. Previous-fall to current-spring PDSI was reconstructed over 1376 years (630-2006 CE), where the most prolonged drought periods were 1136-1166 CE and the Dust Bowl 1924-1941. Our research documents longevity of ponderosa pine, resilience in the presence of multiple disturbances, and demonstrates a technique to separate insect outbreak signals from climate reconstructions in long chronologies while embracing the entire signal available in tree rings.
... For dendroclimatologists, the acceptable EPS was set to ≥0.85 by Wigley et al. [1984]. The closer the EPS value is to one, the stronger the signal is [Wigley et al., 1984;Briffa et al., 1995]. Using this metric, a coral core composite can be considered statistically significant when its EPS value is ≥0.85. ...
The limited availability of oceanographic data in the tropical Pacific Ocean prior to the satellite era makes coral-based climate reconstructions a key tool for extending the instrumental record back in time, thereby providing a much-needed test for climate models and projections. We have generated a unique regional network consisting of five Porites coral δ18O time-series from different locations in the Fijian archipelago. Our results indicate that using a minimum of three Porites coral δ18O records from Fiji is statistically sufficient to obtain a reliable signal for climate reconstruction, and that application of an approach used in tree ring studies is a suitable tool to determine this number. The coral δ18O composite indicates that while sea surface temperature (SST) variability is the primary driver of seasonal δ18O variability in these Fiji corals, annual average coral δ18O is more closely correlated to sea surface salinity (SSS) as previously reported. Our results highlight the importance of water mass advection in controlling Fiji coral δ18O and salinity variability at interannual and decadal time scales despite being located in the heavy rainfall region of the South Pacific Convergence Zone (SPCZ). The Fiji δ18O composite presents a secular freshening and warming trend since the 1850s coupled with changes in both interannual (IA) and decadal/interdecadal (D/I) variance. The changes in IA and D/I variance suggest a re-organization of climatic variability in the SPCZ region beginning in the late 1800s to a more dominant interannual variability, which could correspond to a southeast expansion of the SPCZ.
... They typically extend from the present to several centuries or more into the past, and so are useful for documenting climate change in terrestrial regions of the globe. Many recent studies have sought to reconstruct warm-season and annual temperatures several centuries or more ago from either the width or the density of annual growth rings (Briffa et al., 1995;D'Arrigo et al., 1996;Jacoby et al., 1996;D'Arrigo et al., 1998;Wiles et al., 1998;Cook et al., 2000). Recently, there has been a concerted effort to develop spatial reconstructions of past temperature variations (e.g., Briffa et al., 1996) and estimates of hemispheric and global temperature change (e.g., Briffa et al., 1998b;Briffa, 2000). ...
... It is related to tree growth through relationships with tree physiology and ecology (Hacke et al., 2001;Chave et al., 2009), and with climate (Franceschini et al., 2013). Due to this relationship with climate, wood density is used in dendrochronology and dendroclimatology studies to determine past climate from trees (Schweingruber et al., 1978;Briffa et al., 1995). ...
... The positive correlation has been also found between J. semiglobosa ring width and June temperature, highest with the minimum temperature ( Figs. 9 and 10). The positive influence of summer temperature on trees growing in the vicinity of upper timberline was described for many mountain ranges, also in Central Asia, for example trees from the southern part of the Tibetan Plateau (Cook et al., 2003;Liang et al., 2009;Yang et al., 2009Yang et al., , 2010Yadav et al., 2011;Lv et al., 2012), Northern Urals (Briffa et al., 1995) and Tien Shan Solomina et al., 2006Solomina et al., , 2014. The results of the above research also indicated that tree growth is significantly correlated with summer seasons, but slightly stronger and longer for the maximum latewood density data (MXD) than tree-ring width (TRW) data. ...
Millennial long tree-ring records are crucial for better understanding temperature and hydroclimatic variability over the globe. Juniper is one of particularly long-lived species, which can provide more than a thousand-year record, especially in Central Asia. However, there is a lack of dendrochronological series from the Pamir Mountains. Here we report the first 1010-year (AD 1005–2014) juniper tree-ring chronology from the mountain ranges of north-western Tajikistan, the western Pamir-Alay. We present the potential of Juniperus semiglobosa and Juniperus seravshanica in developing millennia-long records. We sampled three study sites at the elevations from 2200 to 3500 m. In general, the climate-growth analyses show that radial growth of the Himalayan pencil juniper is positively correlated with the winter precipitation and spring temperature. At some sites tree rings were also positively correlated with summer temperature. Our findings demonstrate the importance of developing the tree-ring data network for the Pamir-Alay and its potential for reconstruction of hydroclimatic variability over the last thousand years in this region.
... Temperature limited forest growth generally enables sensitive TRW chronologies to be developed (i.e. time-series with a high degree of inter-annual variation ), which have frequently been utilized for reconstructing summer temperatures at regional (Briffa et al 1995, Luckman et al 1997, Naurzbaev and Vaganov 2000, Kirchhefer 2001, Briffa et al 2008, Esper et al 2012) and larger scales (D'Arrigo et al 2006, Mann et al 2009, Christiansen and Ljungqvist 2012, PAGES2k Consortium 2013 Wilson et al 2016). Composite TRW chronologies of living and relict material from Fennoscandia (Linderholm et al 2010), the Polar Urals (Shiyatov 1995, Briffa et al 2013), eastern Taimyr (Naurzbaev et al 2002), the Yamal Peninsula ( Shiyatov 2002, Briffa et al 2013), and northeastern Yakutia (Hughes et al 1999 , Sidorova and Naurzbaev 2002), so far represent an important backbone for high-resolution paleoclimatology in Eurasia and during the common era (Briffa et al 2013, PAGES2k Consortium 2013). ...
The area covered by boreal forests accounts for ∼16% of the global and 22% of the Northern Hemisphere landmass. Changes in the productivity and functioning of this circumpolar biome not only have strong effects on species composition and diversity at regional to larger scales, but also on the Earth’s carbon cycle. Although temporal inconsistency in the response of tree growth to temperature has been reported from some locations at the higher northern latitudes, a systematic dendroecological network assessment is still missing for most of the boreal zone. Here, we analyze the geographical patterns of changes in summer temperature and precipitation across northern Eurasia >60 °N since 1951 AD, as well as the growth trends and climate responses of 445 Pinus, Larix and Picea ring width chronologies in the same area and period. In contrast to widespread summer warming, fluctuations in precipitation and tree growth are spatially more diverse and overall less distinct. Although the influence of summer temperature on ring formation is increasing with latitude and distinct moisture effects are restricted to a few southern locations, growth sensitivity to June–July temperature variability is only significant at 16.6% of all sites (p0.01). By revealing complex climate constraints on the productivity of Eurasia’s northern forests, our
results question the a priori suitability of boreal tree-ring width chronologies for reconstructing summer temperatures. This study further emphasizes regional climate differences and their role on the dynamics of boreal ecosystems, and also underlines the importance of free data access to facilitate the compilation and evaluation of massively replicated and updated dendroecological networks.
p>The aim of this thesis is to test the sensitivity of the palaeoclimatic proxy-record from the peat stratigraphy of six paired ombrotrophic raised mires (Bolton Fell Moss and Walton Moss, Raeburn Flow and Bell's Flow; and Coom Rigg Moss and Felecia Moss), and one ombrotrophic blanket mire (Shaft Hall, Moor House), located along a rainfall gradient in Northern England and the Scottish Borders.
Three techniques to reconstruct proxy-climate via mire surface wetness have been used - colorimetric humification, quantitative plant macrofossil, and testate amoebae analyses. Weighted averages ordination (Dupont index) and Detrended Correspondence Analysis (DCA), were used to transform the raw floral and faunal data into indices of mire surface wetness. The chronology of each peat profile was determined by radiocarbon assay, supported by spheroidal carbonaceous particle (SCP) analyses and pollen / landuse correlations. Palaeoclimatic reconstructions have been made by linking known documentary / historical changes in climate, and other proxy-climate records, to those inferred from the sites investigated in the study region.
The adoption of multiple proxies to reconstruct mire surface wetness has led to improved palaeoclimate reconstructions, whilst the pollen and SCP chronologies have served to highlight deficiencies in the radiocarbon chronology and the existence of a possible hiatus in the stratigraphy of the blanket mire investigated.
The latter stage of the Little Age (LIA), is the only climatic deterioration registered in all of the study sites. The largest inferred changes in mire surface wetness in Bell's Flow and Coom Rigg Moss occur coevally with the LIA, and suggest it was a severe climatic departure. Conflicting dates between the pollen and calibrated radiocarbon chronology for these two sites suggest the LIA may have occurred between 1420-1800 AD.</p
The Ural Mountain Range spans from the arctic tundra in the north to temperate forest and steppes in the south. Between these two biomes lie vast acreages of taiga (boreal forest) at varied elevations within the mountains and across the adjacent foothills and plains. This includes large intact forest landscapes and Europe's largest remaining primeval forest—the Virgin Komi Forest—as well as second growth forests and severely degraded areas impacted by modern commercial activities such as mining and conversion to agricultural and other land uses. Mining, fossil fuel extraction and climate change are the main threats, while logging is a relatively modest threat to the remaining intact forest landscapes. Although impacts from indigenous peoples have occurred for thousands of years, these impacts were well integrated with the natural dynamics, including the disturbance dynamics of fire and wind, the relationships of forest types to landscape physiography, natural ecotones between tundra, taiga, temperate forest and steppes, and intact predator-prey systems with large predators and other top-level carnivores still present. Conservation strategies should prevent mining and logging from extending into extant primary forests, and use restoration and close-to-nature forestry in second growth forests so that they provide a buffer zone from more intense human activities. Taiga in the Ural Mountains is very sensitive to climate change because of climate-dependent boundaries with nearby tundra, temperate broadleaf forest, and grassland biomes. A warming climate could lead to replacement of large swaths of the existing taiga by temperate forests and grasslands. Mitigation of climate change by reducing global CO2 emissions would make these climate impacts less extreme.
Mountain forests fulfil multiple functions, including the provision of goods as timber, fuelwood, non-wood forest products, and services as regulation of flows, purification of air and water, carbon storage, protection from natural hazards, and provision of cultural services. The role of mountain forest to provide a wide range of ecosystem services is increasingly acknowledged especially in the context of environmental changes in a social aspect. Currently, there is a strong scientific interest to what extent the potential of mountain forests to store carbon could be enhanced under global environmental changes. The aim of this study is to analyse the carbon sequestration of mountain forests from different vegetation zones in Bulgaria under realistic and pessimistic scenarios of climate change using LPJ-GUESS Ecosystem Model and to define tendencies in their vulnerability and adaptive potential. The general trends are presented and vulnerability zones are defined for forest mountainous territories of Bulgaria.
Keith R. Briffa was one of the most influential palaeoclimatologists of the last 30 years. His primary research interests lay in Late-Holocene climate change with a geographical emphasis on northern Eurasia. His greatest impact was in the field of dendroclimatology, a field that he helped to shape. His contributions have been seminal to the development of sound methods for tree-ring analysis and in their proper application to allow the interpretation of climate variability from tree rings. This led to the development of many important records that allow us to understand natural climate variability on timescales from years to millennia and to set recent climatic trends in their historical context.
This article deals with the spatio-statistical analysis of temperature trend using Mann–Kendall trend model (MKTM) and Sen’s slope estimator (SSE) in the eastern Hindu Kush, north Pakistan. The climate change has a strong relationship with the trend in temperature and resultant changes in rainfall pattern and river discharge. In the present study, temperature is selected as a meteorological parameter for trend analysis and slope magnitude. In order to achieve objectives of the study, temperature data was collected from Pakistan Meteorological Department for all the seven meteorological stations that falls in the eastern Hindu Kush region. The temperature data were analysed and simulated using MKTM, whereas for the determination of temperature trend and slope magnitude SSE method have been applied to exhibit the type of fluctuations. The analysis reveals that a positive (increasing) trend in mean maximum temperature has been detected for Chitral, Dir and Saidu Sharif met stations, whereas, negative (decreasing) trend in mean minimum temperature has been recorded for met station Saidu Sharif and Timergara. The analysis further reveals that the concern variation in temperature trend and slope magnitude is attributed to climate change phenomenon in the region.
This book is a continuation of previous review the mathematical methods for nonlinear estimation in dendrochronology, denroсlimatology and dendroecology based on simulation modeling methods, spectrum analysis and nonparametric statistics. As an addition of the theoretical basis the tutorial provides the practical application examples of these methods with an adequate interpretation the results. The proposed methods of detection in different tree growth space-time patterns in high-latitude Eurasia will be an interest to professionals who work with analysis of spatially distributed systems in geography, biology, geophysics, economics and sociology.
The book is intended for specialists, undergraduate and graduate students of
higher educational institutions.
Estimates of mean July-August temperatures for northern Fennoscandinavia are made back to 1700 using ring width and maximum latewood density chronologies of Pinus sylvestris L. (Scots pine) as predictors. Several prediction models are used and the best results are achieved with a simple two-variable model where climate in year t is estimated as a function of tree growth in years t and t + 1 at each site. The best reconstruction equation accounts for 56% of the temperature variance over a 74yr fitting period and 45% of the variance over a 39yr independent verification period. Relatively short-period variability (periods <10yr) is better reproduced in the reconstruction than is that at longer wavelengths. -from Authors
The comparison of means derived from samples of noisy data is a standard pan of climatology. When the data are not serially correlated the appropriate statistical tool for this task is usually the conventional Student's t-test. However, frequently data are serially correlated in climatological applications with the result that the t test in its standard form is not applicable. The usual solution to this problem is to scale the t statistic by a factor that depends upon the equivalent sample size ne.It is shown, by means of simulations, that the revised t tea is often conservative (the actual significance level is smaller than the specified significance level) when the equivalent sample size is known. However, in most practical cases the equivalent sample size is not known. Then the test becomes liberal (the actual significance level is greater than the specified significance level). This systematic error becomes small when the true equivalent sample size is large (greater than approximately 30).The difficulties inherent in difference of means tests when there is serial dependence are reexamined. Guidelines for the application of the `usual' t test are provided and two alternative tests are proposed that substantially improve upon the `usual' t test when samples are small.
A new compilation of monthly mean surface air temperature for the Northern Hemisphere for 1851-1984 is presented based on land-based meteorological station data and fixed-position weather ship data. This compilation has been included, thus improving both spatial and temporal coverage. Second, the station data have been analyzed to assess their homogeneity. Only reliable or corrected station data have been used in calculating are averages. Grid point temperature estimates have been made by interpolating onto a 5° latitude by 10° longitude grid for each month of the 134 years. In the period of best data coverage, 58% of the area of the Northern Hemisphere is covered by the available data network. (The remaining area is mainly ocean too far from land based stations to warrant extrapolation.) The reliability of hemisphere estimates is assessed for earlier periods when coverage is less than this maximum. Year-to-year estimates are considered reliable back to about 1875. Estimates earlier than this are judged sufficiently good to indicate trends back to 1851. This new land-based hemisphere temperature curve is compared with recent estimates of Northern Hemisphere temperatures based on marine data. The two independent estimates agree well on the decadal time scale back to the start of the century, but important discrepancies exist for earlier times.
IN addition to the well-known warming of ~0.5 °C since the middle of the nineteenth century, global-mean surface temperature records1-4display substantial variability on timescales of a century or less. Accurate prediction of future temperature change requires an understanding of the causes of this variability; possibilities include external factors, such as increasing greenhouse-gas concentrations5-7 and anthropogenic sulphate aerosols8-10, and internal factors, both predictable (such as El Niño11) and unpredictable (noise12,13). Here we apply singular spectrum analysis14-20 to four global-mean temperature records1-4, and identify a temperature oscillation with a period of 65-70 years. Singular spectrum analysis of the surface temperature records for 11 geographical regions shows that the 65-70-year oscillation is the statistical result of 50-88-year oscillations for the North Atlantic Ocean and its bounding Northern Hemisphere continents. These oscillations have obscured the greenhouse warming signal in the North Atlantic and North America. Comparison with previous observations and model simulations suggests that the oscillation arises from predictable internal variability of the ocean-atmosphere system.
Climatic changes resulting from greenhouse gases will be superimposed on natural climatic variations. High-resolution proxy records of past climate can be used to extend our perspective on regional and hemispheric changes of climate back in time by several hundred years. Using historical, tree-ring and ice core data, we examine climatic variations during the period commonly called the 'Little Ice Age'. The coldest conditions of the last 560 years were between AD 1570 and 1730, and in the nineteenth century. Unusually warm conditions have prevailed since the 1920s, probably related to a relative absence of major explosive volcanic eruptions and higher levels of greenhouse gases.
A fully coupled ocean-atmosphere model is shown to have irregular oscillations of the thermohaline circulation in the North Atlantic Ocean with a time scale of approximately 50 years. The irregular oscillation appears to be driven by density anomalies in the sinking region of the thermohaline circulation (approximately 52°N to 72°N) combined with much smaller density anomalies of opposite sign in the broad, rising region. The spatial pattern of see surface temperature anomalies associated with this irregular oscillation bears an encouraging resemblance to a pattern of observed interdecadal variability in the North Atlantic. The anomalies of sea surface temperature induce model surface air temperature anomalies over the northern North Atlantic, Arctic, and northwestern Europe.
In a number of areas of applied climatology, time series are either averaged to enhance a common underlying signal or combined to produce area averages. How well, then, does the average of a finite number (N) of time series represent the population average, and how well will a subset of series represent the N-series average. We have answered these questions by deriving formulas for 1) the correlation coefficient between the average of N time series and the average of n such series (where n is an arbitrary subset of N) and 2) the correlation between the N-series average and the population. We refer to these mean correlations as the subsammple signal strength (SSS) and the expressed population signal (EPS). They may be expressed in terms of the mean interseries correlation coefficient r-barm as SSS = (R-bar/sub n/,N)/sup 2/roughly-equaln(1+(N-1)r-bar)/N(1+(n+1)r-bar), EPS = (R-bar/sub N/)/sup 2/roughly-equalNr-bar/1+(N-1)r-bar. Similar formulas are given relating these mean correlations to the fractional common variance which arises as a parameter in analysis of variance. These results are applied to determine the increased uncertainty in a tree-ring chronology which results when the number of cores used to produce the chronology is reduced. Such uncertainty will accrue to any climate reconstruction equation that is calibrated using the most recent part of the chronology. The method presented can be used to define the useful length of tree-ring chronologies for climate reconstruction work.
Climate changes during the next 100 years caused by anthropogenic emissions of greenhouse gases have been simulated for the Intergovernmental Panel on Climate Change Scenarios A (business as usual) and D (accelerated policies) using a coupled ocean-atmosphere general circulation model. In the global average, the near-surface temperature rises by 2.6 K in Scenario A and by 0.6 K in Scenario D. The global patterns of climate change for both IPCC scenarios and for a third step-function 2 x CO2 experiment were found to be very similar. The warming delay over the oceans is larger than found in simulations with atmospheric general circulation models coupled to mixed-layer models, leading to a more pronounced land-sea contrast and a weaker warming (and in some regions even an initial cooling) in the Southern Ocean. During the first forty years, the global warming and sea level rise due to the thermal expansion of the ocean are significantly slower than estimated previously from box-diffusion-upwelling models, but the major part of this delay can be attributed to the previous warming history prior to the start of present coupled ocean-atmosphere model integration (cold start).
It has frequently been suggested that the period encompassing the ninth to the fourteenth centuries A.D. experienced a climate warmer than that prevailing around the turn of the twentieth century. This epoch has become known as the Medieval Warm Period, since it coincides with the Middle Ages in Europe. In this review a number of lines of evidence are considered, (including climate-sensitive tree rings, documentary sources, and montane glaciers) in order to evaluate whether it is reasonable to conclude that climate in medieval times was, indeed, warmer than the climate of more recent times. Our review indicates that for some areas of the globe (for example, Scandinavia, China, the Sierra Nevada in California, the Canadian Rockies and Tasmania), temperatures, particularly in summer, appear to have been higher during some parts of this period than those that were to prevail until the most recent decades of the twentieth century. These warmer regional episodes were not strongly synchronous. Evidence from other regions (for example, the Southeast United States, southern Europe along the Mediterranean, and parts of South America) indicates that the climate during that time was little different to that of later times, or that warming, if it occurred, was recorded at a later time than has been assumed. Taken together, the available evidence does not support a global Medieval Warm Period, although more support for such a phenomenon could be drawn from high-elevation records than from low-elevation records.
The available data exhibit significant decadal to century scale variability throughout the last millennium. A comparison of 30-year averages for various climate indices places recent decades in a longer term perspective.
A time series of ring-width indices from 27 cores of 13 white spruce trees from Yukon Territory shows growth response to summer temperatures and other climatic variables. The correlations with various temperature parameters are high enough that past temperature information can be inferred for the last 400 yr. The highest simple correlation is between tree growth and total degree-days above 10oC for June and July. A substantial moisture stress in the trees towards the end of the growing season is also indicated. The cronology shows effects of the 'Little Ice Age', of the subsequent Northern Hemisphere warming, and of a recent cooling trend. -from Authors
Tree-ring data have been used to reconstruct the mean summer (April-August) temperature of northern Fennoscandia for each year from AD 500 to the present. Summer temperatures have fluctuated markedly on annual, decadal and century timescales. There is little evidence for the existence of a Medieval Warm Epoch, and the Little Ice Age seems to be confined to the relatively short period between 1570 and 1650. This challenges the popular idea that these events were the major climate excursions of the first millennium, occurring synchronously throughout Europe in all seasons. An analysis of past warming trends suggests that any summer warming induced by greenhouse gases may not be detectable in this region until after 2030.
We review and compare two alternative spatial regression methods used in dendroclimatology to reconstruct climate from tree rings. These methods are orthogonal spatial regression (OSR) and canonical regression (CR). Both the OSR and CR methods have a common foundation in least-squares theory and converge to the same solution when all p candidate tree-ring predictors of climate are forced into the model. However, the perfomance of OSR and CR may differ when only subsets p′ < p predictors are used. Theory cannot predict how either method is likely to perform when best-subset selection is applied, especially with regards to reconstruction accuracy. Consequently, empirical comparisons of OSR and CR are made using three tree-ring and climate networks from western Europe and eastern North America that have been used in previous dendroclimatic studies. These comparisons rely on a suite of regression model verification statistics to validate the accuracy of the climatic reconstructions produced by the best-subset models. The results indicate little real difference between OSR and CR, with each performing equally good or bad depending on the amount of recoverable climatic information in the tree rings. Canonical regression may perform slightly better in high signal-to-noise cases; conversely, OSR may perform slightly better when the signal-to-noise ratio is low. None of these apparent differences are large enough to select one method in preference to the other, however, and many more comparisons would be needed to determine if such indications are generally valid.
Quantitative estimates of 1480 years of summer temperatures in northern Fennoscandia have previously been derived from continuous treering records from northern Sweden. Here we show the results of spectral analyses of these data. Only a few peaks in the spectra are consistently significant when the data are analyzed over a number of sub-periods. Relatively timestable peaks are apparent at periods of 2.1, 2.5, 3.1, 3.6, 4.8, 32–33 and for a range between 55–100 years. These results offer no strong evidence for solar-related forcing of summer temperatures in these regions. Our previously published reconstruction was limited in its ability to represent long-timescale temperature change because of the method used to standardize the original tree-ring data. Here we employ an alternative standardization technique which enables us to capture temperature change on longer timescales. Considerable variance is now reconstructed on timescales of several centuries. In comparison with modern normals (1951–70) generally extended periods when cool conditions prevailed, prior to the start of the instrumental record, include 500–700, 790–870, 1110–1150, 1190–1360, 1570–1750 (A.D.) with the most significant cold troughs centred on about 660, 800, 1140, 1580–1620 and 1640. Predominantly warm conditions occurred in 720–790, 870–1110 and 1360–1570 with peaks of warmth around 750, 930, 990, 1060, 1090, 1160, 1410, 1430, 1760 and 1820.
We describe a recently completed network of densitometric tree-ring time series representing various aspects of tree-growth for up to 200 years at 69 sites spread across the northern North American conifer zone from Yukon to Labrador. Duplicate cores, from 12 to 15 trees per site, provide time series for a suite of growth parameters including earlywood (spring), latewood (summer) and total (annual) ring widths and mean earlywood, mean latewood, minimum and maximum ring density. These data form the basis for extensive analyses of intra- and inter-site parameter comparisons and regional climate/tree-growth comparisons. Five large-scale regional chronologies do not suggest that any anomalous growth increases have occurred in recent decades, at least on these regional scales, despite the observed changes in atmospheric composition and climate.
Global Changes of the Past (University Corporation for Atmospheric Res./Office of Interdisciplinary Earth Studies
- R S Bradley
Dendrochronology in the Upper Tree Line in the Urals
- S G Shiyatov
- SG Shiyatov