Tree rings and past climate in the Arctic

May 7, 2012, 6:01 pm

This is Section 14.6 of the Arctic Climate Impact Assessment.

Lead Author: Glenn P. Juday; Contributing Authors: Valerie Barber, Paul Duffy, Hans Linderholm, Scott Rupp, Steve Sparrow, Eugene Vaganov, John Yarie; Consulting Authors: Edward Berg, Rosanne D’Arrigo, Olafur Eggertsson,V.V. Furyaev, Edward H. Hogg, Satu Huttunen, Gordon Jacoby, V.Ya. Kaplunov, Seppo Kellomaki, A.V. Kirdyanov, Carol E. Lewis, Sune Linder, M.M. Naurzbaev, F.I. Pleshikov, Ulf T. Runesson,Yu.V. Savva, O.V. Sidorova,V.D. Stakanov, N.M.Tchebakova, E.N.Valendik, E.F.Vedrova, Martin Wilmking.

 

The most recent historical period of Northern Hemisphere warming of similar magnitude (but possibly different in its cause) to that of recent decades is the Medieval Warm Period (MWP) from about AD 900 to 1300 (see also section 2.7.5). However, interpretations of the climate during the MWP do not always agree. Some evidence suggests that the MWP was not general across the planet and did not exceed the current warming in its fluctuations[7]. Other evidence suggests temperatures 1 to 1.5°C higher than at present across the Northern Hemisphere during the MWP[8]. The main tool to compare recent warming with temperature levels during the MWP and earlier periods in most terrestrial regions of the far north is long-term climate reconstructions based on tree-ring data, because few or no other historical records exist and marine proxies and ice cores cannot provide the required geographic coverage or detail.

Tree-ring chronologies serve as a useful basis for reconstructing natural temperature fluctuations in the high latitudes over millennial intervals, although the degree of reliability needs to be assessed carefully in each application. An important potential limitation is that the relationship between tree rings and climate may vary with time. However, compared to other indirect sources of climatic information, tree-ring chronologies have certain important advantages. First, tree rings record a complete annual sequence of climatic information. Second, in northern Eurasia, where trees reach a maximum age of 1,100 years, there is a dense dendroclimatic network allowing spatially detailed quantitative temperature reconstruction for the last 500 to 600 years, and in some regions for more than two millennia[9].

The rate and magnitude of recent Northern Hemisphere temperature increases are unique within the last several centuries[10]. Some climate models that include anthropogenic effects calculate that the greatest temperature increase, in the range of 3 to 4°C, should have occurred over the last several centuries in the high latitudes of the Northern Hemisphere[11]. However, temperature reconstructions (generally of the warm season or even a specific portion of the warm season) based on tree-ring chronologies from subarctic Eurasia, a region that makes up a large part of the projected zone of maximum warming, do not show temperature increases of the projected magnitude[12]. This may be partly due to the disproportionate influence of warm-season temperatures on tree growth, genuine local spatial climate variability, issues in calibrating the tree rings to estimate temperature with uniform reliability throughout the whole period of analysis, or errors or missing factors in climate model scenarios.

Past climate change in central Eurasia (14.6.1)

This section examines several aspects of high-resolution proxy records based on tree-ring chronologies. Subarctic temperature reconstructions for Asia are compared with the main climatic forcing mechanisms during the last several centuries; reconstructed temperature fluctuations during the MWP are compared with recent temperature changes in the high latitudes of Eurasia using the millennial tree-ring chronologies; and recent temperature fluctuations are compared to temperature fluctuations during most of the Holocene in order to reveal warmest and coolest periods as well as rapid temperature changes in the central Asian sector of the subarctic.

caption Fig. 14.11. Sites in the dendroclimatic network of the Asian subarctic (circles) and locations of millenial-length chronologies (stars) [1].

The three main sources of information used for this analysis include local chronologies from the central Asian subarctic dendroclimatic network (Fig. 14.11) based on the analysis of living old trees[13]; super-long (at least two millennia) tree-ring chronologies constructed from cross-dating the abundant dead wood material of northern Siberia; and subfossil wood material excavated from alluvial deposits in terraces of small rivers in the Taymir and Lower Indigirka regions and even from sites north of the modern tree limit.

The radiocarbon dates of subfossil wood were used to define preliminary calendar time intervals and then the cross-dating method was used to identify absolute dates of tree-ring formation. Unfortunately, not enough material was available to build an absolute chronology for the entire Holocene in Taymir, so the "floating" chronologies (chronologies that cannot be tied with certainty to absolute calendar dates) with numerous radiocarbon dates were also used to analyze past temperature deviations[14].

A climatic signal was derived from raw tree-ring measurements using the regional (age) curve standardization (RCS) approach[15]. This approach is applied to remove the age-dependent variations from single tree-ring series and to retain low-frequency climatic deviations (positive or negative trends) as well as high-frequency variations (year-toyear change) when averaging tree-ring index series. More details about this method of standardization can be found in Briffa et al.[16], Esper et al.[17], and Naurzbaev and Vaganov[18]. To verify results, treering chronologies were compared to the instrumental climatic data averaged over a large sector of the subarctic. Finally, the longer-term tree-ring temperature reconstructions were compared to other proxy data including long-term variations in solar radiation[19], long-term variations in volcanic activity derived from ice-core measurements[20], and variations in CO2 concentrations in air trapped in the GISP2 ice core (central Greenland)[21].

Climate change in the central Asian subarctic during the last 400 years (14.6.1.1)

Local tree-ring width series for each of 11 sites were obtained by averaging standardized series of individual trees. Between 60 and 70% of the variation in tree-ring width indices in the Eurasian subarctic is caused by changes in summer temperature[22]. A high correlation of local chronologies with temperature (r=0.69 to 0.84) allows the use of simple regression equations for reconstructing temperature based on tree rings. In effect, tree-ring width is used as a simple predictor of summer temperature. In order to avoid an additional procedure of statistical transformation of local tree-ring index series into normalized values of summer temperature variation, each of the local chronologies was normalized to the mean-square deviation in the generalized curve for the Asian subarctic region[23]. To highlight trends and reduce short-term variability, the transformed local series was smoothed with a five-year running mean. Long-term temperature changes dominate the variability of the resulting generalized series. The generalized curve was compared with other temperature reconstructions for the circumpolar Northern Hemisphere[24] as well as with the main climatic forcing mechanisms.

caption Fig. 14.12. Temperature variations from proxy records for the circumpolar Northern Hemisphere[2] and the Asian subarctic (see Fig. 14.11 for locations of sites).

Temperature variations in the Asian subarctic over the past 400 years correspond well to those observed across the circumpolar north (Fig. 14.12). Both curves clearly illustrate the temperature rise from the beginning of the 19th century to the middle of the 20th century. The main discrepancies between the two curves occur in the second decade of the 19th century and after the 1950s. The correlation of the two reconstructed temperature curves with each other for the preindustrial period is significant, but low (r=0.38, p<0.05), and markedly increases (r=0.65, p<0.001) for the industrial period (1800–1990) due to a distinct temperature increase that is shown in both curves.

More interesting is the correlation analysis of both curves (Fig. 14.12) with the main climatic forcing factors. The Asian subarctic generalized curve shows a significant correlation with all main climatic forcing factors: with solar radiation (r=0.32 for the entire period and 0.68 for the industrial period from 1800 to 1990); with volcanic activity (r=-0.41 for the entire period and -0.59 for the industrial period); and with atmospheric CO2 concentration (r=0.65 for the period since 1850). The circumpolar reconstructed temperature curve (Fig. 14.12) is weakly correlated with solar radiation and atmospheric CO2 concentration, and is not significantly correlated with volcanic activity. This is because more homogenous proxy data (only the tree-ring chronologies) were used for the Asian subarctic reconstruction, while different sources of proxy records (i.e. tree rings, lake sediments, isotopes in ice cores) were used in the circumpolar curve. The correlations with climatic forcing factors further indicate that natural factors (solar irradiance and volcanic activity) explain more of temperature variability that is common to the Asian subarctic and the circumpolar north than does the CO2 concentration. Spatio-temporal analysis of reconstructed summer temperature variations in the Asian subarctic revealed that recent warming is characterized by an increased frequency of years with anomalously warm summers over the entire Siberian subarctic (the latitudinal dendroclimatic network seen in Fig. 14.11 that is replicated across a distance of 5,000 kilometers (km) from east to west)[25].

Medieval and current warming in northeastern Eurasia (14.6.1.2)

Millennium length tree-ring chronologies were constructed from samples at two sites close to the northern treeline: east Taymir (71° 00’ N, 102° 00’ E) and northeast Yakutia (69° 24’ N, 148° 25’ E). These stands are made up of Gmelin larch (Larix gmelinii) and Cajander larch (L. cajanderi) in which the oldest living trees are up to 1,100 years old[26]. Well-preserved dead tree trunks allowed extension of the record farther back than the maximum age of the living samples, allowing the construction of absolutely dated tree-ring chronologies for the periods from 431 BC to AD 1999 (Taymir) and from 359 BC to AD 1998 (Yakutia). The RCS approach was applied to distinguish variation caused by climatic change. These representative tree samples were highly responsive to recorded temperature, allowing the reconstruction of temperatures over the last two millennia with annual resolution. With this long-term record, the instrumental record of 20th-century temperatures can be compared with temperatures during the MWP. Earlier results[27] showed that tree-ring chronologies were highly correlated across distances up to 200 km (up to 500 km in northern regions), so these millennial chronologies represent temperature variations over a large sector of the Siberian subarctic.

caption Fig. 14.13. Long-term changes in tree-ring growth in the circumpolar north[3] and northern Eurasia (combined chronology for east Taymir and northeast Yakutia).

The combined chronology for east Taymir and northeast Yakutia was compared with a generalized tree-ring chronology developed for the circumpolar region by Esper et al.[28] (Fig. 14.13). The two chronologies are significantly correlated during last 1,200 years (r=0.47, p<0.001), suggesting that they represent long-term temperature trends in the entire Northern Hemisphere subarctic. Both curves show the warming characteristic of the MWP (10th to 13th centuries), decreasing temperature during the Little Ice Age (LIA, 14th to 19th centuries), and a 20th-century temperature increase.

The Siberian summer temperature reconstruction indicates that the warmest centuries were AD 1000 to 1200, with anomalies (from the mean over the last millennium) of 0.70°C and 0.57°C for those centuries, and the coolest centuries in were in the LIA period (AD 1600 to 1900), with anomalies for those centuries of -0.42°C, -0.39°C and -0.56°C. The analysis of long-term trends of summer temperature leads to several conclusions. Present-day warming is estimated to represent an increase in summer temperature of approximately 0.6°C above the coolest period of the LIA. The reconstruction clearly reveals the timing of the MWP, which occurs in the 10th to 13th centuries. The reconstructed data indicate a greater warming (by about 1.3°C) above the long-term mean during the MWP compared to the amount of cooling below the mean during the LIA. The results agree well with previous assessments of medieval warming in the Northern Hemisphere[29] but show less warming than that projected by climate models or historical analogues that use natural forcing factors such as solar variability and volcanic activity[30].

Climate change in the eastern Taymir Peninsula over the past 6000 years (14.6.1.3)

The dendrochronological material discussed in this section was gathered from the Kheta-Khatanga plain region and the Moyero-Kotui plateau in the eastern Taymir Peninsula, near the northernmost present-day limit of tree growth in the world. The wood samples were collected from three areas: the modern treeline in the north forest of Ari-Mas; the modern altitudinal treeline (200–300 m above sea level) in the Kotui River valley; and alluvial deposits in terraces of large tributaries of the Khatanga River (one sample location is 170–180 km north of the modern treeline). The total number of wood samples exceeds 400. The RCS approach was used to standardize individual series[31]. Approximate absolute dating (in contrast to the relative dating developed from the ring series) was established from radiocarbon dates of 45 samples of subfossil wood collected throughout the soil organic layer.

The result of this cross-dating is an absolute tree-ring chronology (see Climate change in the central Asian subarctic during the last 400 years above) as well as a series of "floating" chronologies up to 1,500 years in length, evenly spaced within the 6,000-year interval of the mid- to late Holocene. The relative dating of the "floating" chronologies is based on the calibrated radiocarbon age of the samples[32].

The resulting curve of the tree-ring index (relative growth) extends over 6,000 years, and indicates favorable climatic conditions at about 6,000 years BP. This period of warmth represents the latter stages of the postglacial thermal maximum[33] (section 2.7.4.2). The growth of larch trees at that time surpassed the average radial growth of trees during the last two millennia by 1.5 to 1.6 times. Tree growth (and temperature, accordingly) has generally decreased from the end of the postglacial thermal maximum through the end of the 20th century. Several samples of subfossil wood collected in the flood plain of the Balakhnya River were accurately dated in accordance with the "floating" chronology to the period from 4140 to 2700 BC. Due to the geography of the watershed, these samples could not have originated from the more southern regions, which means that during the postglacial thermal maximum the northern treeline was situated at least 150 km further north than at present. The postglacial thermal maximum can also be clearly identified by the relative levels of the stable isotope carbon-13 (13C) in the annual tree rings[34]. Increased 13C concentration in annual layers of wood of this species (Cajander larch) is highly correlated with warm summer temperatures. High 13C content is found in wood dated to the period that ring-width techniques reconstruct as warm, confirming high temperatures during this period.

Quantitative evaluation of mean deviations of average summer and annual temperatures demonstrates higher temperature variability during the postglacial thermal maximum compared to the 3.5°C variability typical of the 20th-century instrumental temperature record. This corresponds well to the earlier published data[35] and to findings of subfossil wood in alluvial deposits of the Balakhnya River 150 km north of the present-day treeline. Reliable dates for the postglacial thermal maximum, in agreement with the "floating" chronologies, indicate that during this period sparse larch forest extended at least 1 to 1.5 degrees of latitude further north than the northernmost present-day forest limits in the Ari-Mas massif.

A comparison of the long-term temperature reconstruction for the Taymir Peninsula with other indicators of long-term temperature change in the high latitudes of the Northern Hemisphere during the Holocene (including summer melting on the Agassiz Ice Cap, northern Ellesmere Island, Canada; summer temperature anomalies estimated from the elevation of carbon-14 dated subfossil pine wood samples in the Scandes mountains, central Sweden; and temperature reconstruction from oxygen isotopes in calcite sampled along the growth axis of a stalagmite from a cave at Mo i Rana, northern Norway[36]) reveals several noteworthy features. During much of the Holocene, and especially starting between 9,000 and 8,000 years BP, the overall high-latitude Northern Hemisphere temperature steadily decreased, although there were shorter fluctuations with significant amplitude. This distinct trend of general temperature decrease agrees with the Taymir chronology. The concurrence of characteristic temperature fluctuations can be seen, for example, in significant decreases at about 6,000 years BP and 4,000 years BP, and increases at about 3,000 years BP and 1,000 years BP (the MWP). This coincidence suggests that some regions of the Arctic experienced long-term temperature changes in common with the high-latitude mean, which has been reconstructed using various proxy data. These interpretations of the data are supported, for instance, by the results of radiocarbon and dendrochronological dating of wood remains from the MWP collected north of the modern treeline in the Polar Urals[37] (section 14.11.1.3). However, some aspects of a reconstruction that infers higher summer temperatures during the postglacial thermal maximum than have been recorded in the late 20th century remain uncertain and subject to confirmation from additional research. The range in estimates obtained from different sources of the degree to which reconstructed temperature at its postglacial maximum exceeded the maximum warmth of the 20th or early 21st centuries is significant: from 0.6°C (glacier and stalagmite layers and bottom deposits) to 3 to 3.5°C (indicated by Taymir tree-ring chronology and the greatest extension of forest in the Scandinavian mountains[38]). These deviations in reconstructed temperature may have been influenced by local conditions, different sensitivities of proxy sources to temperature change, or inadequate calibration models. Unfortunately, at present it is impossible to determine the cause of these deviations.

To detect the anthropogenic component of climate variations at high latitudes it is important to know whether temperature is already affected by increasing greenhouse gas (GHG) concentrations and whether the rate of temperature increase is unprecedented in the period of instrument-based temperature records. A series of synthesizing studies, as well as simulations with GCMs, have established that anthropogenic emissions have had a significant influence on the rate of temperature rise in the Northern Hemisphere[39]. However, in contrast to global trends, in the long-term northern Siberia tree-ring chronologies the present high-latitude summer temperature increase is less than that experienced during the postglacial thermal maximum. In this region, natural climatic forcing factors appear to have been more significant than the combination of human and natural factors producing the current summer warming thus far. In the Siberian study area, the amplitude of the current summer warming is not thus far greater than the warming during the MWP. This may be partly explained by the difference between regional and global trends, and partly by the difference between the trends in summer and annual temperature.

To determine with confidence whether the rate of temperature increase is unprecedented, it is necessary to obtain good quantitative data with high temporal resolution for the Holocene that will help to identify periods of drastic natural temperature increases in the past, and then to examine the amplitude of such drastic increases to see if there are natural limits during such periods of change. Therefore, one of the urgent tasks at present is the construction and analysis of super-long-term tree-ring chronologies for Eurasia with an adequate amount of subfossil wood. Such studies are being intensively conducted in Europe[40] and in north Asia[41]. They should soon provide high-resolution treering chronologies for Eurasia that can be used for quantitative reconstruction of temperature and for calibration of data obtained from other indirect sources of climatic information with lower temporal resolution.

Past climate change in Alaska and Canada (14.6.2)

One of the first large-scale climate reconstructions based on boreal tree-ring data was a study of treeline white spruce across northern North America (primarily Canada) covering about 90 degrees of longitude or about one-third of the circumpolar northern treeline extent[42]. This chronology was based on the positive response of tree growth at treeline to temperature, and allows the reconstruction of mean annual temperature anomalies back to AD 1700 (Fig. 14.14). Key features of the reconstruction are intermediate temperatures during most of the 18th century, sharp cooling during the first half of the 19th century, gradual warming from the mid-19th century to a mid-20th century peak, and a slight cooling from about 1950 to the 1970s. If recent proxy data or climate records are available in a given locality to compare to the overall long-term record, unusual warming during the last decades of the 20th century is often noted[43]. Some of the recent increase in annual temperatures in this reconstruction can be attributed to recovery from the last stages of the LIA.

caption Fig. 14.14. Annual temperature anomaly (from 1671–1973 average) reconstructed from white spruce at the North American treeline (see D’Arrigo et al.[4] and Jacoby and D’Arrigo[5] for details of the reconstruction technique).

Since the studies of the late 1980s, other analyses have added more spatial representation and longer temporal coverage[44] leading to an essentially complete coverage of the 20th century[45]. The most recent reconstructed annual temperature curves confirm the major anomalies in annual temperature of the North American treeline curve of Jacoby and D’Arrigo[46] (see Fig. 14.14) that has served as the basis for standard Arctic temperature reconstructions[47].

The need to splice tree-ring records from overlapping generations of trees introduces some questions about whether the successively earlier generations of tree-ring records have been calibrated correctly and adequately preserve low-frequency variations (longer-term trends) in temperature. Methods of processing tree-ring data to preserve the low-frequency variations correctly have improved, allowing such trends and their possible causes to be identified[48]. The Esper et al.[49] reconstruction shows more prominent low-frequency trends, including the MWP and the LIA, than previous reconstructions or global or Northern Hemisphere-wide averages.

New technology, such as x-ray density[50] and stable isotope techniques, allow measurements of tree-ring properties in addition to ring width. Maximum latewood density of northern conifers increases when mid- to late growing season moisture stress is great[51]. Maximum latewood density of boreal conifers also may represent an index of canopy growth where productivity is temperature-related, as indicated by satellite-sensed normalized difference of vegetation index (NDVI; representing "greenness" of the land surface) values[52]. Carbon-13 isotope content is generally measured as "discrimination", which represents the difference in the amount of the isotope in sampled plant tissue compared to a reference standard. Less 13C discrimination (greater 13C content in sample) indicates production of the sampled plant tissue under a condition of restricted stomatal exchange, generally as a result of moisture stress[53].

Maximum latewood density, 13C isotope discrimination, and ring width of upland white spruce stands in central Alaska are well correlated with each other[54]. Latewood density and 13C isotope discrimination contain information specific to the climatic conditions of the year of ring formation, in contrast to ring width (which is influenced by two or more years of temperature), making them ideal for reconstructing past climates[55]. No continuous instrument-based temperature records exist for the western North American boreal region until the early years of the 20th century, and few records exist until the mid-20th century.

caption Fig. 14.15. Warm-season (Apr–Aug) temperature regimes and regime shifts in central Alaska from 1800 to 1996 from observations and reconstructed from tree-ring density and 13C isotope discrimination[6].

A 200-year reconstruction of warm-season (April to August) temperature at Fairbanks, Alaska, based on tree-ring density and 13C isotope discrimination has been constructed[56] (Fig. 14.15). The warm-season temperature reconstruction for Interior Alaska has been divided into multi-decade segments or warm-season temperature regimes. Regimes represent multi-decadal periods of characteristic temperatures that persist between periods of rapid climate change (Fig. 14.15). Note that the first half of the 20th century experienced extended periods of cool summers, which relieved moisture stress of low-elevation white spruce. The reconstruction of warm temperatures in the mid-19th century is out of phase with overall Northern Hemisphere means, but is strongly established by the proxies (13C isotope discrimination and maximum latewood density) used in the reconstruction. A reconstruction of the annual Pacific Decadal Oscillation (section 2.2.2.2) index using western North American tree-ring records, accounting for up to 53% of the variance in instrumental records and extending back to 1700, also indicates that decadal-scale climatic shifts occurred in the northeast Pacific region prior to the period of instrumental record[57]. These results suggest that rapid temperature shifts followed by semi-stable periods are a fundamental feature of climate change in that region.

From the perspective of two centuries, the recent very high rate of temperature increase in the second half of the 20th century in Interior Alaska is partially explained by a change from some of the lowest warm-season temperatures to some of the highest in the entire period (Fig. 14.15). Unlike the annual temperature reconstruction based on North America-wide treeline white spruce (Fig. 14.14), the Interior Alaska reconstruction (Fig. 14.15) indicates that the mid-19th century (Regimes 19.2A and 19.2C) was one of the warmest periods and the mid-20th century was a period of unusually cool summers. Because many of the climate records available in this part of the world begin only in the late 1940s or early 1950s (during the one of the coldest periods of the 20th century) and continue to the present (the warmest period of the last millennium), the instrument-based record indicates a higher rate of temperature increase than the longer-term reconstructions that incorporate several cycles of temperature increases and decreases. This suggests that the strong late 20th-century warming (during the warm season) in western North America may have a considerable component of natural climate variability in the signal.

There are still regions of the north that are not represented in large-scale temperature reconstructions, especially on the timescale of the past millennium. Recorded data and climate models strongly indicate that there are very likely to be important regional differences in temperature trends across the high-latitude north. In fact, a comparison of the large-scale reconstruction of northern North American annual temperature anomalies with the Interior Alaska reconstruction shows opposite trends (Fig. 14.2) that appear to be a consistent part of the climate system.

Across the Northern Hemisphere and beginning in different regions at different times, northern treeline trees display a reduced sensitivity to growing-season warmth[58]. The reduction in the positive response of some trees to warm-season temperature seems to have occurred around 1970, when warming resumed after a cool interval in the mid-20th century. When late 20th-century warming resumed, some trees continued to increase in radial growth in response to the warmer conditions. However the growth increase per unit of temperature increase was not nearly as great as previously, and in some trees temperature no longer had a reliable predictive relationship to tree growth at all[59]. In Alaska, much of the change can be attributed to greater moisture deficits associated with higher warm-season temperatures[60]. In northern Siberia, the effect is attributed to shorter periods of thawed soil because of increased depth of snow cover, an indirect effect of warmer winters[61]. For other areas, there are hypotheses about air pollution, [[solar radiation|UV radiation[[ damage, and other factors[62].

Past climate change in northwestern Europe (14.6.3)

In the past few decades, Scandinavian tree-ring data have provided an increasing amount of information about past climate variability. Natural reserves preserve a number of old and mature forests virtually untouched by humans, especially in central and northern Scandinavia. Scots pine growing close to altitudinal or latitudinal distribution limits in the Scandinavian Mountains or in northernmost Sweden mainly respond to summer temperatures (with increased growth) and data from such sites have been used to interpret past climate variability[63]. Furthermore, due to the proximity to the Norwegian Sea, and hence the influence of maritime air masses brought in with westerly and south-westerly winds, precipitation may be a growth-limiting factor in moist areas, such as the western slopes of the Scandinavian Mountains or in peatlands[64]. High-frequency North Atlantic Oscillation signals (section 2.2.2.1) have been found in tree-ring data from east-central Scandinavia[65].

The relationship of climate to tree-ring variability in Scots pine in Scandinavia has been studied in a wide range of growth environments. A comprehensive study was made of pine growing on peatlands along a north–south profile through Sweden to see if the trees contained high-resolution climate information[66]. Peatland pines were also compared to pines growing on dry sites. Pines growing on peatlands are dependent on growing-season temperature and precipitation, as well as on local water-table variations, which are influenced by longer-term trends in both temperature and precipitation. There is a lag of up to several decades in the response of the pines to water levels, such that trees are integrating the immediate effects of growing-season climate as well as a delayed effect from the water table, making them unsuitable for high-frequency climate reconstruction. The sensitivity of pines growing on peatland also changes depending on climate. When the growing season is wet and cold, temperature is more important and trees respond positively to temperature, in particular to July temperature. Precipitation response increases to the south but is never as important as for pines growing on dry soils. Precipitation is important mainly in controlling water-table levels[67].

A 1091-year record of tree growth from AD 909 to 1998, developed from living and subfossil Scots pine in the central Scandinavian Mountains, provides evidence of low-frequency climate variation[68]. July temperatures had the largest effect on the growth of these trees, but growth was also positively and significantly correlated with October to December temperatures in the previous year. The response to precipitation during the vegetative period was negative although not significantly. The authors inferred that the chronology represents summer temperatures for the central Scandinavian Mountains, although it is suggested that care should be taken when interpreting the record. The chronology indicates prolonged excursions below the mean (cool conditions unfavorable for tree growth) in the mid-12th and the 13th centuries, and in the mid-16th and late 17th centuries (corresponding to the early and late LIA, respectively). Below-mean conditions in the late 18th century correlate with a "recent cold period"[69]. The chronology also provides evidence for the MWP in the 10th and early part of the 11th centuries as well as warmer periods during the mid-14th, mid-17th, and 20th centuries[70].

 

Chapter 14: Forests, Land Management, and Agriculture
14.1. Introduction
14.2. The boreal forest: importance and relationship to climate
14.3. Land tenure and management in the boreal region
14.4. Use and evaluation of the ACIA scenarios
14.5. Agriculture
14.6. Tree rings and past climate
14.7. Direct climate effects on tree growth
14.8. Climate change and insects as a forest disturbance
14.9. Climate change and fire
14.10. Climate change in relation to carbon uptake and carbon storage
14.11. Climate change and forest distribution
14.12. Effects of ultraviolet-B on forest vegetation
14.13. Critical research needs

References

  1. ^ Vaganov, E. A., S.G. Shiyatov and V.S. Mazepa, 1996. Dendroclimatic Studies in Ural-Siberian Subarctic. Nauka, Novosibirsk, 246p. (In Russian)
  2. ^ Overpeck, J., K. Hughen, D. Hardy, R. Bradley, R. Case, M. Douglas, B. Finney, K. Gajewski, G. Jacoby, A. Jennings, S. Lamoureux, A. Lasca, G. MacDonald, J. Moore, M. Retelle, S. Smith, A. Wolfe and G. Zielinski, 1997. Arctic environmental change of the last four centuries. Science, 278:1251–1256.
  3. ^ Esper, J., E.R. Cook and F.H. Schweingruber, 2002. Low-frequency signals in long tree-ring chronologies for reconstructing past temperature variability. Science, 295:2250–2253.
  4. ^ D’Arrigo, R.D., E.R. Cook and G.C. Jacoby, 1996. Annual to decadalscale variations in northwest Atlantic sector temperatures inferred from Labrador tree rings. Canadian Journal of Forest Research, 26:143–148.
    –D’Arrigo, R.D., R.Villalba and G. Wiles, 2001. Tree-ring estimates of Pacific decadal climate variability. Climate Dynamics, 18:219–224.
  5. ^ Jacoby, G.C. and R.D. D’Arrigo, 1989. Reconstructed Northern Hemisphere annual temperature since 1671 based on high latitude tree-ring data from North America. Climatic Change, 14:39–59.
  6. ^ Barber, V., G. Juday and B. Finney, 2000. Reduced growth of Alaska white spruce in the twentieth century from temperature-induced drought stress. Nature, 405:668–672.
    –Juday, G.P.,V. Barber, S. Rupp, J. Zasada and M. W. Wilmking, 2003. A 200-year perspective of climate variability and the response of white spruce in Interior Alaska. In: D. Greenland, D. Goodin and R. Smith (eds.). Climate Variability and Ecosystem Response at Long-Term Ecological Research (LTER) Sites, pp. 226–250. Oxford University Press.
  7. ^ Hughes, M.K. and H.F. Diaz, 1994. Was there a ‘Medieval Warm Period’ and if so, where and when? Climatic Change, 26:109–142.
    –Mann, M.E., R.S. Bradley and M.K. Hughes, 1998. Global scale temperature patterns and climate forcing over the six centuries. Nature, 392:779–782.
  8. ^ Dahl-Jensen, D., K. Mosegaard, N. Gundestrup, G.D. Clow, S.J. Johnsen, A. W. Hansen and N. Balling, 1998. Past temperatures directly from the Greenland ice sheet. Science, 282:268–271.
    –Esper, J., E.R. Cook and F.H. Schweingruber, 2002. Low-frequency signals in long tree-ring chronologies for reconstructing past temperature variability. Science, 295:2250–2253.
    –Naurzbaev, M.M. and E. A. Vaganov, 2000.Variation of summer and annual temperature in the east Taymir and Putoran (Siberia) over the last two millennia inferred from tree-rings. Journal of Geophysical Research, 105(D6):7317–7327.
  9. ^ Briffa, K.R., T.J. Osborn, F.H. Schweingruber, I.C. Harris, P.D. Jones, S.G. Shiyatov and E. A.Vaganov, 2001. Low-frequency temperature variations from a northern tree ring density network. Journal of Geophysical Research, 106(D3):2929–2941.
    –Hughes, M.K., E. A.Vaganov, S.G. Shiyatov, R. Touchan and G. Funkhouser, 1999. Twentieth-century summer warmth in northern Yakutia in a 600-year context. The Holocene, 9(5):603–608.
    –Vaganov, E. A., S.G. Shiyatov and V.S. Mazepa, 1996. Dendroclimatic Studies in Ural-Siberian Subarctic. Nauka, Novosibirsk, 246p. (In Russian)
    –Vaganov E. A., K.R. Briffa, M.M. Naurzbaev, F.H. Schweingruber, S.G. Shiyatov and V.V. Shishov, 2000. Long-term climatic changes in the Arctic region of the Northern Hemisphere. Doklady Earth Sciences, 375(8):1314–1317.
  10. ^ Briffa, K.R., P.D. Jones, F.H. Schweingruber,W. Karlen and S.G. Shiyatov, 1996. Tree-ring variables as proxy-climate indicators: problems with low-frequency signals. In: P.D. Jones, R.S. Bradley and J. Jouzel (eds.). Climate Change and Forcing Mechanisms of the Last 2000 Years. NATOASI Series I, Global Environmental Change, 41:9–41.
    –Briffa, K.R.,T.J. Osborn, F.H. Schweingruber, I.C. Harris, P.D. Jones, S.G. Shiyatov and E. A.Vaganov, 2001. Low-frequency temperature variations from a northern tree ring density network. Journal of Geophysical Research, 106(D3):2929–2941.
    –Mann, M.E., R.S. Bradley and M.K. Hughes, 1998. Global scale temperature patterns and climate forcing over the six centuries. Nature, 392:779–782.
  11. ^ Budyko, M.I. and Yu. A. Izrael (eds.), 1987. Anthropogenic Forcing of Climate. Gidrometeoizdat, Leningrad, 476p. (In Russian)
    –Kondrat’ev, K. Ya., 2002. Global climate change: reality, assumptions and fantasies. Earth Research From Space, 1:3–23. (In Russian)
  12. ^ Briffa, K.R., F.H. Schweingruber, P.D. Jones, T.J. Osborn, S.G. Shiyatov and E. A.Vaganov, 1998. Reduced sensitivity of recent tree-growth to temperature at high northern latitudes. Nature, 391:678–682.
    –Naurzbaev, M.M. and E. A.Vaganov, 2000.Variation of summer and annual temperature in the east Taymir and Putoran (Siberia) over the last two millennia inferred from tree-rings. Journal of Geophysical Research, 105(D6):7317–7327.
  13. ^ Briffa, K.R., F.H. Schweingruber, P.D. Jones, T.J. Osborn, S.G. Shiyatov and E. A.Vaganov, 1998. Reduced sensitivity of recent tree-growth to temperature at high northern latitudes. Nature, 391:678–682.
    –Vaganov, E. A., S.G. Shiyatov and V.S. Mazepa, 1996. Dendroclimatic Studies in Ural-Siberian Subarctic. Nauka, Novosibirsk, 246p. (In Russian)
  14. ^ Naurzbaev, M.M., O.V. Sidorova and E. A.Vaganov, 2001. History of the late Holocene climate on the eastern Taymir according to long-term tree-ring chronology. Archaeology, Ethnology and Anthropology of Eurasia, 3(7):17–25.
  15. ^ Briffa, K.R., P.D. Jones, F.H. Schweingruber,W. Karlen and S.G. Shiyatov, 1996. Tree-ring variables as proxy-climate indicators: problems with low-frequency signals. In: P.D. Jones, R.S. Bradley and J. Jouzel (eds.). Climate Change and Forcing Mechanisms of the Last 2000 Years. NATOASI Series I, Global Environmental Change, 41:9–41.
    –Esper, J., E.R. Cook and F.H. Schweingruber, 2002. Low-frequency signals in long tree-ring chronologies for reconstructing past temperature variability. Science, 295:2250–2253.
  16. ^ Briffa, K.R.,T.J. Osborn, F.H. Schweingruber, I.C. Harris, P.D. Jones, S.G. Shiyatov and E. A.Vaganov, 2001. Low-frequency temperature variations from a northern tree ring density network. Journal of Geophysical Research, 106(D3):2929–2941.
  17. ^ Esper, J., E.R. Cook and F.H. Schweingruber, 2002. Low-frequency signals in long tree-ring chronologies for reconstructing past temperature variability. Science, 295:2250–2253.
  18. ^ Naurzbaev, M.M. and E. A.Vaganov, 2000. Variation of summer and annual temperature in the east Taymir and Putoran (Siberia) over the last two millennia inferred from tree-rings. Journal of Geophysical Research, 105(D6):7317–7327.
  19. ^ Overpeck, J., K. Hughen, D. Hardy, R. Bradley, R. Case, M. Douglas, B. Finney, K. Gajewski, G. Jacoby, A. Jennings, S. Lamoureux, A. Lasca, G. MacDonald, J. Moore, M. Retelle, S. Smith, A. Wolfe and G. Zielinski, 1997. Arctic environmental change of the last four centuries. Science, 278:1251–1256.
  20. ^ Zielinski, G. A., P. A. Mayewski, L.D. Meeker, S. Whitlow, M.S. Twickler, M. Morrison, D. A. Meese, A.G. Gow and R.B. Alley, 1994. Record of volcanism since 7000 BC from the GISP2 Greenland ice core and implications for the volcano-climate system. Science, 264:948–951.
  21. ^ Wahlen, M., D. Allen, B. Deck and A. Herchenroder, 1991. Initial measurements of CO2 concentrations (1530–1940 AD) in air occluded in the GISP2 ice core from central Greenland. Geophysical Research Letters, 18:1457–1460.
  22. ^ Briffa, K.R., F.H. Schweingruber, P.D. Jones, T.J. Osborn, S.G. Shiyatov and E. A.Vaganov, 1998. Reduced sensitivity of recent tree-growth to temperature at high northern latitudes. Nature, 391:678–682.
    –Vaganov, E. A., S.G. Shiyatov and V.S. Mazepa, 1996. Dendroclimatic Studies in Ural-Siberian Subarctic. Nauka, Novosibirsk, 246p. (In Russian)
    –Vaganov, E. A., S.G. Shiyatov, R.M. Hantemirov and M.M. Naurzbaev, 1998. Summer temperature variations in high latitudes of the Northern Hemisphere during last 1.5 millennium: comparative analysis tree-ring and ice core data. Doklady Akademii Nauk, 338(5):681–684.
  23. ^ Vaganov, E. A., S.G. Shiyatov and V.S. Mazepa, 1996. Dendroclimatic Studies in Ural-Siberian Subarctic. Nauka, Novosibirsk, 246p. (In Russian)
  24. ^ Overpeck, J., K. Hughen, D. Hardy, R. Bradley, R. Case, M. Douglas, B. Finney, K. Gajewski, G. Jacoby, A. Jennings, S. Lamoureux, A. Lasca, G. MacDonald, J. Moore, M. Retelle, S. Smith, A. Wolfe and G. Zielinski, 1997. Arctic environmental change of the last four centuries. Science, 278:1251–1256.
  25. ^ Vaganov, E. A., S.G. Shiyatov and V.S. Mazepa, 1996. Dendroclimatic Studies in Ural-Siberian Subarctic. Nauka, Novosibirsk, 246p. (In Russian)
  26. ^ Vaganov E. A., K.R. Briffa, M.M. Naurzbaev, F.H. Schweingruber, S.G. Shiyatov and V.V. Shishov, 2000. Long-term climatic changes in the Arctic region of the Northern Hemisphere. Doklady Earth Sciences, 375(8):1314–1317.
  27. ^ Hughes, M.K., E. A. Vaganov, S.G. Shiyatov, R. Touchan and G. Funkhouser, 1999. Twentieth-century summer warmth in northern Yakutia in a 600-year context. The Holocene, 9(5):603–608.
    –Vaganov, E. A., S.G. Shiyatov and V.S. Mazepa, 1996. Dendroclimatic Studies in Ural-Siberian Subarctic. Nauka, Novosibirsk, 246p. (In Russian)
  28. ^ Esper, J., E.R. Cook and F.H. Schweingruber, 2002. Low-frequency signals in long tree-ring chronologies for reconstructing past temperature variability. Science, 295:2250–2253.
  29. ^ Esper, J., E.R. Cook and F.H. Schweingruber, 2002. Low-frequency signals in long tree-ring chronologies for reconstructing past temperature variability. Science, 295:2250–2253.
  30. ^ Budyko, M.I. and Yu. A. Izrael (eds.), 1987. Anthropogenic Forcing of Climate. Gidrometeoizdat, Leningrad, 476p. (In Russian)
  31. ^ Naurzbaev, M.M. and E. A. Vaganov, 2000. Variation of summer and annual temperature in the east Taymir and Putoran (Siberia) over the last two millennia inferred from tree-rings. Journal of Geophysical Research, 105(D6):7317–7327.
  32. ^ Stuiver, M. and P.J. Reimer, 1993. Extended 14C data base and revised CALIB 3.0 14C age calibration program. Radiocarbon, 35:215–230.
  33. ^ Lamb, H.H., 1977a. Climate: Present, Past and Future. Methuen, 835p.
  34. ^ Naurzbaev, M.M., O.V. Sidorova and E. A.Vaganov, 2001. History of the late Holocene climate on the eastern Taymir according to long-term tree-ring chronology. Archaeology, Ethnology and Anthropology of Eurasia, 3(7):17–25.
  35. ^ Naurzbaev, M.M. and E. A. Vaganov, 2000. Variation of summer and annual temperature in the east Taymir and Putoran (Siberia) over the last two millennia inferred from tree-rings. Journal of Geophysical Research, 105(D6):7317–7327.
  36. ^ Bradley, R.S., 2000. Past global changes and their significance for the future. Quaternary Science Reviews, 19:391–402.
  37. ^Shiyatov, S.G., 1993. The upper timberline dynamics during the last 1100 years in the Polar Ural Mountains. In: B. Frenzel (ed.). Oscillations of the Alpine and Polar Tree Limit in the Holocene, Palaeoclimate Research, 9:195–203.
  38. ^ Kullman, L. and L. Kjällgren, 2000. A coherent postglacial tree-limit chronology (Pinus sylvestris L.) for the Swedish Scandes: aspect of paleoclimate and ‘recent warming’, based on megafossil evidence. Arctic, Antarctic, and Alpine Research, 32(4):419–428.
  39. ^ Mann, M.E., R.S. Bradley and M.K. Hughes, 1998. Global scale temperature patterns and climate forcing over the six centuries. Nature, 392:779–782.
  40. ^ Baillie, M.G.L., 2000. A Slice Through Time: Dendrochronology and Precision Dating. Routledge. London, 286p.
    –Leuschner, H.H. and A. Delorme, 1988. Tree ring work in Goettingen absolute oak chronologies back to 6255 BC. In: T. Hackens, A.V. Munaut and Claudine Till (eds.). Wood and Archaeology. PACT, 22, II.5: 123–131.
    –Leuschner, H.H., M. Spurk, M. Baillie and E. Jansma, 2000. Stand dynamics of prehistoric oak forests derived from dendrochronologically dated subfossil trunks from bogs and riverine sediments in Europe. Geolines, 11:118–121.
  41. ^Hantemirov, R.M., 1999. Tree-ring reconstruction of summer temperatures on a north of Western Siberia for the last 3248 years. Siberian Ecological Journal, 6(2):185–191.
    –Shiyatov, S.G., 1986. Dendrochronology of Upper Timberline in Polar Ural Mountains. Nauka, Moscow, 186p. (In Russian)
    –Vaganov, E. A., S.G. Shiyatov, R.M. Hantemirov and M.M. Naurzbaev, 1998. Summer temperature variations in high latitudes of the Northern Hemisphere during last 1.5 millennium: comparative analysis tree-ring and ice core data. Doklady Akademii Nauk, 338(5):681–684.
  42. ^ Jacoby, G.C. and R.D. D’Arrigo, 1989. Reconstructed Northern Hemisphere annual temperature since 1671 based on high latitude tree-ring data from North America. Climatic Change, 14:39–59.
  43. ^ Jacoby, G.C. and R.D. D’Arrigo, 1989. Reconstructed Northern Hemisphere annual temperature since 1671 based on high latitude tree-ring data from North America. Climatic Change, 14:39–59.
    –Jacoby, G.C., I.S. Ivanciu and L.D. Ulan, 1988. A 263-year record of summer temperature for northern Quebec reconstructed from tree-ring data and evidence of a major climatic shift in the early 1800s. Palaeogeography, Palaeoclimatology, Palaecology, 64:69–78.
  44. ^ Mann, D.H. and L.J. Plug, 1999.Vegetation and soil development at an upland taiga site, Alaska. Ecoscience, 6(2):272–285.
  45. ^ Esper, J., E.R. Cook and F.H. Schweingruber, 2002. Low-frequency signals in long tree-ring chronologies for reconstructing past temperature variability. Science, 295:2250–2253.
  46. ^ Jacoby, G.C. and R.D. D’Arrigo, 1989. Reconstructed Northern Hemisphere annual temperature since 1671 based on high latitude tree-ring data from North America. Climatic Change, 14:39–59.
  47. ^ Overpeck, J., K. Hughen, D. Hardy, R. Bradley, R. Case, M. Douglas, B. Finney, K. Gajewski, G. Jacoby, A. Jennings, S. Lamoureux, A. Lasca, G. MacDonald, J. Moore, M. Retelle, S. Smith, A. Wolfe and G. Zielinski, 1997. Arctic environmental change of the last four centuries. Science, 278:1251–1256.
  48. ^ Esper, J., E.R. Cook and F.H. Schweingruber, 2002. Low-frequency signals in long tree-ring chronologies for reconstructing past temperature variability. Science, 295:2250–2253.
  49. ^ Esper, J., E.R. Cook and F.H. Schweingruber, 2002. Low-frequency signals in long tree-ring chronologies for reconstructing past temperature variability. Science, 295:2250–2253.
  50. ^ Jacoby, G.C., I.S. Ivanciu and L.D. Ulan, 1988. A 263-year record of summer temperature for northern Quebec reconstructed from tree-ring data and evidence of a major climatic shift in the early 1800s. Palaeogeography, Palaeoclimatology, Palaecology, 64:69–78.
  51. ^ D’Arrigo, R.D., G.C. Jacoby and R.M. Free, 1992. Tree-ring width and maximum latewood density at the North American tree line: parameters of climate change. Canadian Journal of Forest Research, 22:1290–1296.
  52. ^ D’Arrigo, R.D., C.M. Malmstrom, G.C. Jacoby, S. Los and D.E. Bunker, 2000. Tree-ring indices of interannual biospheric variability: testing satellite-based model estimates of vegetation activity. International Journal of Remote Sensing, 21:2329–2336.
  53. ^ Livingston, N.J. and D.L. Spittlehouse, 1996. Carbon isotope fractionation in tree ring early and late wood in relation to intra-growing season water balance. Plant, Cell and Environment, 19:768–774.
  54. ^ Barber, V., G. Juday and B. Finney, 2000. Reduced growth of Alaska white spruce in the twentieth century from temperature-induced drought stress. Nature, 405:668–672.
  55. ^ Barber, V., G. Juday and B. Finney, 2000. Reduced growth of Alaska white spruce in the twentieth century from temperature-induced drought stress. Nature, 405:668–672.
  56. ^ Barber, V. A., G.P. Juday, B.P. Finney and M. Wilmking, 2004. Reconstruction of summer temperatures in interior Alaska from tree-ring proxies: evidence for changing synoptic climate regimes. Climatic Change, 63:91–120.
    –Juday, G.P., V. Barber, S. Rupp, J. Zasada and M. W. Wilmking, 2003. A 200-year perspective of climate variability and the response of white spruce in Interior Alaska. In: D. Greenland, D. Goodin and R. Smith (eds.). Climate Variability and Ecosystem Response at Long-Term Ecological Research (LTER) Sites, pp. 226–250. Oxford University Press.
  57. ^ D’Arrigo, R.D., R.Villalba and G. Wiles, 2001. Tree-ring estimates of Pacific decadal climate variability. Climate Dynamics, 18:219–224.
  58. ^ Briffa, K.R., F.H. Schweingruber, P.D. Jones, T.J. Osborn, S.G. Shiyatov and E. A.Vaganov, 1998. Reduced sensitivity of recent tree-growth to temperature at high northern latitudes. Nature, 391:678–682.
    –Jacoby, G.C. and R.D. D’Arrigo, 1995. Tree ring width and density evidence of climatic and potential forest change in Alaska. Global Biogeochemical Cycles, 9:227–234.
    –Vaganov, E. A., M.K. Hughes, A.V. Kirdyanov, F.H. Schweingruber and P.P. Silkin, 1999. Influence of snowfall and melt timing on tree growth in subarctic Eurasia. Nature, 400:149–151.
  59. ^ Briffa, K.R., F.H. Schweingruber, P.D. Jones, T.J. Osborn, S.G. Shiyatov and E. A.Vaganov, 1998. Reduced sensitivity of recent tree-growth to temperature at high northern latitudes. Nature, 391:678–682.
  60. ^ Jacoby, G.C. and R.D. D’Arrigo, 1995. Tree ring width and density evidence of climatic and potential forest change in Alaska. Global Biogeochemical Cycles, 9:227–234.
  61. ^ Vaganov, E. A., M.K. Hughes, A.V. Kirdyanov, F.H. Schweingruber and P.P. Silkin, 1999. Influence of snowfall and melt timing on tree growth in subarctic Eurasia. Nature, 400:149–151.
  62. ^ Briffa, K.R., F.H. Schweingruber, P.D. Jones, T.J. Osborn, S.G. Shiyatov and E. A.Vaganov, 1998. Reduced sensitivity of recent tree-growth to temperature at high northern latitudes. Nature, 391:678–682.
  63. ^ Briffa, K.R., T.S. Bartholin, D. Eckstein, P.D. Jones,W. Karlén, F.H. Schweingruber and P. Zetterberg, 1990. A 1,400-year tree-ring record of summer temperatures in Fennoscandia. Nature, 346:434–439.
    –Grudd, H., K.R. Briffa,W. Karlén,T.S. Bartholin, P.D. Jones and B. Kromer, 2002. A 7400-year tree-ring chronology in northern Swedish Lapland: natural climatic variability expressed on annual to millennial timescales. The Holocene, 12:657–666.
    –Gunnarson, B. and H. W. Linderholm, 2002. Low frequency climate variation in Scandinavia since the 10th century inferred from tree rings. The Holocene, 12:667–671.
    –Linderholm, H. W., 2002. 20th century Scots pine growth variations in the central Scandinavian Mountains related to climate change. Arctic, Antarctic, and Alpine Research, 34:440–449.
  64. ^ Linderholm, H. W., A. Moberg and H. Grudd, 2002. Peatland pines as climate indicators? A regional comparison of the climatic influence on Scots pine growth in Sweden. Canadian Journal of Forest Research, 32:1400–1410.
    –Linderholm, H. W., B.Ø. Solberg and M. Lindholm, 2003. Tree-ring records from central Fennoscandia: the relationship between tree growth and climate along a west-east transect. The Holocene, 13:887–895.
    –Solberg, B.Ø., A. Hofgaard and H. Hytteborn, 2002. Shifts in radial growth responses of coastal Picea abies induced by climatic change during the 20th century, central Norway. Ecoscience, 9:79–88.
  65. ^ Lindholm, M., O. Eggertson, N. Lovelius, O. Raspopov, O. Shumilov and A. Laanelaid, 2001. Growth indices of North European Scots pine record the seasonal North Atlantic Oscillation. Boreal Environment Research, 6:275–284.
  66. ^ Linderholm, H. W., A. Moberg and H. Grudd, 2002. Peatland pines as climate indicators? A regional comparison of the climatic influence on Scots pine growth in Sweden. Canadian Journal of Forest Research, 32:1400–1410.
  67. ^ Linderholm, H. W., A. Moberg and H. Grudd, 2002. Peatland pines as climate indicators? A regional comparison of the climatic influence on Scots pine growth in Sweden. Canadian Journal of Forest Research, 32:1400–1410.
  68. ^ Gunnarson, B. and H. W. Linderholm, 2002. Low frequency climate variation in Scandinavia since the 10th century inferred from tree rings. The Holocene, 12:667–671.
  69. ^ Fisher, H., M. Werner, D. Wagenbach, M. Schwager,T. Thorsteinnson, F. Wilhelms, J. Kipfstuhl and S. Sommer, 1998. Little Ice Age clearly recorded in northern Greenland ice cores. Geophysical Research Letters, 25:1749–1752.
    –Grove, J.M., 1988. The Little Ice Age. Methuen and Co., 498p.
    –Jones, P.D. and R.S Bradley, 1992. Climate variations over the last 500 years. In: R.S. Bradley and P.D. Jones (eds.). Climate Since A.D. 1500, pp. 649–665. Routledge Press.
    –Lamb, H.H., 1977b. Climate: Present, Past and Future.Vol.2. Climatic History and the Future. Methuen, 603p.
  70. ^ Gunnarson, B. and H. W. Linderholm, 2002. Low frequency climate variation in Scandinavia since the 10th century inferred from tree rings. The Holocene, 12:667–671.

 

 

 

 

 

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Committee, I. (2012). Tree rings and past climate in the Arctic. Retrieved from http://www.eoearth.org/view/article/156694

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