Little Ice Age Climate near Beijing, China, Inferred from Historical and Stalagmite Records

Transcription

1 Quaternary Research 57, (2002) doi: /qres , available online at on Little Ice Age Climate near Beijing, China, Inferred from Historical and Stalagmite Records Weihong Qian and Yafen Zhu Department of Atmospheric Sciences, Peking University, Beijing , China Received October 18, 2000 Four data sets yield information about Holocene climatic change in China at different scales of space and time: (a) 120-yr ground temperature and precipitation measurements covering eastern China; (b) two NOAA 10-yr 850 hpa wind records that highlight features of data set a; (c) an 1100-year record of annual calcite accumulation on a stalagmite near Beijing, and (d) Lamb-type average wetness and temperature data from Chinese historical records back to A.D and 1450, respectively. Dry wet fluctuations and cold warm oscillations are inferred using the long-term stalagmite thickness series. Quasi-70, 140, 450, and 750-yr oscillations have been detected using a wavelet transform technique. A phase relationship between temperature and precipitation oscillations has been identified based on modern observations and historical records. In northern China, relatively lower temperatures correlate with periods when precipitation shifted from above to below normal. Three colder periods during the Little Ice Age (LIA) in China are inferred, centered in the late 14th century (750-yr oscillation), the early 17th century (450-yr), and the 19th century (140-yr). The latest cool period (1950s 1970s) is found at the 70-yr oscillation. Interdecadal drought flood and cold warm differences are explained using modern circulation patterns. LIA climate in China was likely controlled by East Asian monsoon circulation anomalies that were affected by variations in continent ocean thermal contrast. C 2002 University of Washington. Key Words: China; Little Ice Age climate; stalagmite thickness; historical record. INTRODUCTION It is well known that the global climate during the past 1000 years has displayed some remarkable variations. Two episodes, the so-called Medieval Warm Epoch (MWE) and the Little Ice Age (LIA), are often mentioned in the literature (Wigley et al., 1981; Lamb, 1984; Bradley and Jones, 1992; Wang, 1992). Usually, the MWE is placed from the late 10th to the 13th or 14th century while the LIA extended in many parts of the world from the 15th to 19th century. Of the two, the LIA was the more widespread and included the more severe cool period of the late Holocene. Study of the LIA has become an important scientific problem because modern warming followed it, and there remains the question of whether warming similar to the recent occurred before the LIA. There appear to be considerable differences in the LIA timing. For example, Porter (1986) indicated that it began near the end of the Middle Ages at about A.D and continued until about 1920, whereas Lamb (1977) restricted the LIA to A.D , with a main phase between A.D and Clearly, if the concept is to be useful, it should be better defined in time. This is of great importance in determining what caused the LIA. Continuous quantitative climate series for the past millennium are crucial to both the investigation of the paleoclimate and the assessment of global warming in the past 100 years. In this paper, instrumental meteorological observations, historical documents, and stalagmite records are used to examine the dry wet fluctuations and infer the cold-warm oscillations in China. The wavelet transform technique and rotated empirical orthogonal function are used to reveal temporal spatial variations of those series. It will be emphasized that dry wet and cold warm climate variations should be compared at the same or very similar time scales. DATA SOURCES Briefly, four data sets are used in this paper. The first comprises the 120-yr ground temperature and precipitation measurements for eastern China. The second are the two NOAA 10-yr 850 hpa wind records. The third is an 1100-yr record of annual stalagmite lamina thickness from a cave near Beijing. The fourth is a Lambtype average wetness and temperature compilation from Chinese historical records back to A.D and 1450, respectively. All data sets extend to 1998 or 1999 except the stalagmite thickness series, which ends in Annual Laminae Thickness in a Stalagmite in Beijing Where stalagmites display annual or other periodic laminae, the thickness of the individual layers is controlled by drip rate and supersaturation (Dreybrodt, 1996). Beijing (39.9 N, E) is located in the North China climatic zone, with a relatively dry winter (East Asian continental) climate. However, the moist summer monsoon may reach the area and cause /02 $35.00 Copyright C 2002 by the University of Washington. All rights of reproduction in any form reserved.

2 110 QIAN AND ZHU annual precipitation variability. Annual rainfall days and rainfall strength depend largely on the summer monsoon circulation. More rainy days will increase groundwater recharge and maintain chemical saturation for longer periods. This effect should increase the lamina thickness, although individual heavy rains of several hours may not be detectable. The Beijing stalagmite thickness series thus has possibly recorded the regional climate and environmental conditions of the past. An 1131-yr sequence of stalagmite laminae extending from A.D. 850 to 1980 (Qin et al., 1999) was sampled from Shihua Cave, Beijing, China, and will be used here. This series is valuable for revealing the climate variation in the East Asian monsoon region. Modern Observations In mainland China, annual droughts or floods are largely determined by summer precipitation, whereas annual warm and cold variations are determined by conditions during the winter spring period. The annual surface air temperature anomalies (SATA) for the 10 distinct thermal regions and the annual precipitation for all China, from 1880 to 1998, have been published by Wang et al. (1998) and Ye et al. (1998), respectively. Only the seven regions of eastern mainland China are considered in this paper; Taiwan Island, the Tibetan Plateau, and northwestern China are excluded. The 10 annual temperature regions and 33 annual precipitation stations are plotted in Figure 1. The stations are divided into seven regions: (1) South China, (2) upper Yangtze River, (3) middle Yangtze, (4) lower Yangtze, (5) upper Yellow River, (6) lower Yellow River, and (7) Northeast China. We focus on the climate series for three river valleys from south to north, taking the Xijiang River valley from region (1); the Yangtze valley including regions (2), (3), and (4); and the Yellow River valley in regions (5) and (6). Modern Reanalysis Winds For the period over , the NCEP/NCAR monthly 850 hpa reanalysis winds with a spatial resolution of degrees (Kalnay et al., 1996) are used to examine the decadal circulation changes during winter and summer months over China. Historical Records Since the 1970s, Chinese climatologists have cooperated to extract climatic information from more than 2000 kinds of historical documents for 500 years beginning in 1470 A.D. A fivegrade scale is used to estimate dryness wetness (DW) and rainfall in the main rainy season at 120 sites covering the entire country. As a result of this project, yearly charts of dryness/ wetness in China for the last 500-yr period have been compiled (Central Meteorological Bureau, 1982). Zhang (1988) discussed the methods for constructing these time series in detail. Many of the 120 sites are located in the Yellow and Yangtze River basins. In this paper, DW series from 100 sites (Fig. 1) are used. The DW series of each site, which represents a small region, are expressed by five grades: extremely wet, wet, normal, dry, and extremely dry. These grades are denoted by index values of 1, 2, 3, 4, and 5, respectively. For the period , the grade is mainly based on actual rainfall data; Song (2000) described the method for assigning these data to the five grades. ANALYTICAL METHODS To deal the temporal spatial structures of climate change, two methods are applied here, wavelet transform and the rotated empirical orthogonal function. FIG. 1. Map of China showing locations of 100 dry wet grade (filled circle, ) and 35 precipitation stations (square, including two on Taiwan). Seven regions are marked: (1) in South China; (2), (3), and (4) along the Yangtze River; (5) and (6) covering the Yellow River, and (7) in Northeast China. and denote the locations of Beijing and other five precipitation stations. Wavelet Transform The wavelet transform technique was introduced by Morlet et al. (1982). It is applied widely in signal and image processing using various basic wavelet functions. Gao and Li (1993) applied the Mexican hat, a commonly used wavelet function, to turbulence data. Many have commented on the advantages of this technique when compared with the Fourier transform: Wavelet analysis displays structures on different time scales at different locations in time. The traditional Fourier transform provides information only on the frequency, without its variation in time (or position) on a single frequency in the signal series analyzed. The wavelet transform provides localized time and frequency information without requiring the time series to be stationary. It transforms a one-dimensional function of time into a twodimensional function of time and frequency or, equivalently, scale (Jiang et al., 1997). In this study, we adopt the Mexican hat wavelet to analyze each time series. The continuous wavelet transform coefficients W (a, b) of a real square integrable signal f (x) with respect to

3 LITTLE ICE AGE CLIMATE, BEIJING, CHINA 111 a real integrable analyzing wavelet g(x) are defined as in Gao and Li (1993): W (a, b) = (C g a) 1/2 f (t)g[(t b)/a] dt, where W (a, b) represents the wavelet transform function, or the so-called wavelet coefficients, of the raw data function f (t), and a(a > 0) is the scale parameter. A large a value corresponds to a longer time scale or a lower fluctuation frequency, C g a is an energy normalization term, and b is the location parameter. According to the definition of the wavelet function, the timescale parameter a represents the scale of the fluctuation. The location parameter b corresponds to points in time in a year-toyear sequence. The wavelet transform method has been applied in paleoclimate studies (e.g., Jiang et al, 1997) and can extract major information from the original series such as stalagmite laminae thickness series or precipitation series. The wavelet coefficients W (a, b) with positive and negative anomalies may represent transitions between dry and wet on various time scales (a) and at different points in time (b: yr). W (a, b) > 0 indicates a dry climate and W (a, b) < 0 a wet one for the wetness series, while the reversed situation applies to the stalagmite series. Maximum positive values of W (a, b) indicate severe dryness, whereas the negative minimum denotes severe wetness. A closely placed pair of minimum and maximum centers of W (a, b), with a large gradient between them, suggests an abrupt change from one persistent spell of anomalous conditions to another of opposite sign. The interaction of different time scales may be observed from distribution coefficients of W (a, b). ( ) in China. Those modes explain about 12, 11, 11, 10, 10, and 10%, respectively, of the total variance of the DW series. The modal centers are located at the middle reaches of the Yellow and the Yangtze Rivers, the lower Yellow River, the lower Yangtze River, South China, northern North China, and the central south of the Yangtze River, respectively. Figure 2 shows the third and fifth modes with positive centers in the lower Yangtze and northern North China. The floods in the lower Yangtze region are rather sensitive to the variability of the East Asian monsoon. Figure 3 gives the wavelet coefficients of REOF3 time series in the lower Yangtze River and northern North China for A.D with time scales ranging from 2 to 295 years. From the third mode in the lower Yangtze River, a major dry wet oscillation is observed, with a time span of about 90 Rotated Empirical Orthogonal Function The empirical orthogonal function (EOF) was introduced into atmospheric sciences by pioneers such as Lorenz (1956). EOF analysis is a convenient method for studying spatial temporal variability. Because it splits the spatial temporal field into a set of orthogonal ordered modes, it is a powerful approach for analysis of the characteristics of the spatial patterns and their temporal variations existing in the original field. In the past two decades, EOF analysis, a popular and powerful diagnostic tool, has been widely used in meteorology, climatology, geology, and oceanography. To simplify the physical mechanisms underlying the characteristic patterns, or to seek physical modes that have some useful properties such as simple structure or real physical background, the rotated EOF (REOF) approach was introduced by Richman (1986). REOF supplies a new set of modes by rotating the vector space of the initial EOFs and improves the physical interpretation of the original field. INTERDECADAL VARIABILITY The first six principal components or modes of the REOF have been derived from the 100-site DW series for 530 years FIG. 2. Rotated empirical orthogonal function modes of 100-site dry wet grade with (a) the third mode in the lower Yangtze River and (b) the fifth mode in northern North China. The interval is 0.1.

4 112 QIAN AND ZHU FIG. 3. The wavelet coefficient distributions for (a) the third mode and (b) the fifth mode from A.D to 1999 with a time-scale ranging from 2 to 295 years. Dashed lines denote the major oscillations. years over the period A.D and a time span of 70 years since the 1750s. At the 70-yr time scale, two wet periods (dashed area) have occurred within the last century, in the 1920s 1940s and since the mid-1980s. An oscillation of about 120 years has become dominant since the 1790s with a wet period in the 1910s 1950s, and a dry period since the 1970s. The signals in the 20- and 35-yr time scales are also strong, but there were several intermissions. From the fifth mode in northern North China (Fig. 3b), long-term oscillations are found at time scales of and yr. In the last century, a phase difference of dry wet oscillations at the 70-yr time scale can be noted if the phases in northern North China and the lower Yangtze River are compared. An unknown forcing may be causing the climate system to form a relatively regular oscillation at a predetermined time scale. Performing wavelet transform on the seven regional temperature and precipitation series for the period , two prominent signals (regular variation and large amplitude) at

5 LITTLE ICE AGE CLIMATE, BEIJING, CHINA 113 FIG. 4. Wavelet coefficients of (a) precipitation and (b) temperature in all seven regions at 70-yr time scale for A.D Regions 1 to 7 cross the four valleys, mostly from south to north, in China. The heavy dashed line indicates the negative maximum of wavelet coefficient of precipitation. 20- and 70-yr time scales have been obtained (Qian and Zhu, 2001). Figure 4 shows the wavelet coefficients W (a: 70 yr,b: yr) of precipitation and temperature series for the seven regions at the 70-yr time scale. The 70-year oscillation exists in both the observed precipitation and in the long-term wetness series (Fig. 3a). Positive negative wavelet coefficients indicate the secular oscillation of annual precipitation for all the seven regions in China (Fig. 4a). A phase difference of positive and negative distributions of precipitation anomalies is obvious in the southern zone (regions 1, 2, 3, and 4) and northern China (5, 6, and 7). Before the 1900s, a positive precipitation anomaly appeared in northern China, while it was negative in the Yangtze River and South China. Over the 1910s 1920s, less precipitation occurred in northern China, while there was more rainfall in the upper Yangtze. Between the 1940s and 1950s the situation was reversed. Since the late 1980s, there has been above-normal rainfall along the Yangtze River, while the dry conditions persist in northern China. Although there is difference in phases for these coefficients, the quasi-70-yr oscillation does exist in all these time series. It is worth noting from the dashed line in the figure that the less (or more) precipitation maximum is migrating from north (region 7) to south (the region 1). This migration takes about 70 years to cross China. The reason for this migration with time will be discussed below. At the 70-yr time scale, cold warm oscillations shown in Figure 4b indicate that the positive or negative departures of temperature can influence the whole of China but that the largest departures are found in the north. The current warm spell in northeastern China began in the late 1970s, with the largest departure falling in the late 1990s. Considering this time scale, a warming spell has just started in China. From Figure 4b, the 70-yr oscillation of temperature variability is also dominant in China, with a recent cold spell from 1950s to 1970s in northern China. The phase relation of the secular oscillation between precipitation and temperature at the 70-yr time scale can be identified

6 114 QIAN AND ZHU in different regions. In northern China, maximum precipitation appears at the moment when temperature changes from a positive departure to a negative one, while minimum precipitation occurs at the shift from a negative temperature anomaly to a positive one. In southern China, positive and negative precipitation anomalies are consistent mostly with those positive and negative temperature departures in phase. According to the phase relationship, the climate in northern China may be divided into four categories: wet cold ( s and 1950s 1960s), dry warm ( s and s), wet warm (1940s), and dry cold (1900s, 1970s) periods. Examining the atmospheric circulation during the last wet cold and dry warm periods in northern China, Figures 5 and 6 show the horizontal wind vectors of the 850 hpa surface averaged for the summer and winter periods of and Significant differences in flow patterns appear in these two periods. During the summers of 1960s, the strong southerly flow could reach northern North China, and the edge of an anticyclonic circulation influenced Southeast China. It is easy to understand that there should be more precipitation in northern China and a relatively dry climate in the southeast. During the summers of , the southwesterly winds only reached the lower Yangtze River. This pattern implies that subtropical frontal precipitation will usually appear in southern China while there is drought in the north. Thus, the precipitation changes shown in Figure 4 can be explained by these two circulation patterns. FIG hpa summer (JJA) winds (ms 1 ) averaged for (a) and (b)

7 LITTLE ICE AGE CLIMATE, BEIJING, CHINA 115 FIG hpa winter (DJF) winds (ms 1 ) averaged for (a) and (b) Winter circulation anomalies can be noted in Figure 6. The northerly wind flows in eastern China were stronger in the winters of the 1960s than in , indicating that there would be cold winters in eastern China during the 1960s and warmer conditions after These patterns imply that the interdecadal changes in circulation may be indicators of the evolution of the East Asian monsoon. CENTENNIAL VARIABILITY Long-term series with annual resolution may reflect interdecadal climate variability. Figure 7 shows a stalagmite thickness series from A.D. 850 to 1980 from Shihua Cave, Beijing, (Qin et al., 1999). No doubt some dating error exists in the series, but we are concerned only with certain low-frequency variations. If a thickness of a low-frequency variation is directly proportional to annual precipitation, there should have been more rainfall during the periods A.D and A.D , while there was long-term lesser rainfall between A.D and These secular variations have not been detected in the documented historical series. Due to the chaotic behavior of the atmosphere in motion, the rainfall at an individual station is stochastic. Therefore, five stations located in northcentral China have been selected to represent a large area surrounding Beijing (Fig. 1). From Figure 5a, these five stations fall within the strong southwesterly flows. Figure 8 shows the annual series of the stalagmite thickness and the annual average of five-station precipitation for

8 116 QIAN AND ZHU FIG. 7. The thickness sequence of laminae (pixel number) in the Beijing stalagmite from Shihua Cave for A.D (after Qin et al., 1999). Five variations exist in both five-station average precipitation and the stalagmite thickness series. The correlation coefficient between the two series is 0.34 at a t test confidence level of 0.01, and a consistent relationship in phase can be noted since We believe that the stalagmite thickness series in Beijing are recording the interdecadal dry wet variability over a relatively large area subject to southwesterly monsoon flows. To reveal the linkage between the stalagmite thickness series and the historical documentary evidence, Figure 9 shows the wavelet coefficients of stalagmite thickness from A.D to At the quasi-70-yr time scale, the dry wet oscillations have been rather remarkable since the 1660s. Positive centers appeared around the 1880s and 1940s and negative centers during the 1910s and 1970s, which is basically consistent with the precipitation oscillations for recent decades shown in Figure 4a. For the decadal to centennial time scales the consistent dry wet transitions in the last 200 years can be compared: at the 80-to 100-yr scale, the wet centers indicated by a dashed area in Figure 3b and by a solid area in Figure 9 both appeared in the 1940s in northern China. From such comparisons of Figures 3b, 4a, 8, and 9, we infer that the stalagmite thickness series represents precipitation or dry wet variations quite well, particularly for secular oscillations longer than a few decades. In China, especially the north and east, historical documents for the last years are much more abundant than those for earlier centuries. This is not only due to the great number of government archives, but also because the compilation of local chronicles had become a common practice for every province and district since the Ming Dynasty. In these local chronicles, FIG. 8. Annual layers (pixel number, dashed line) of Beijing stalagmite and the five-station regional mean annual precipitation (solid line, mm) for A.D The five stations are Shenyang (123.5 E, 41.8 N), Jinan (117.0 E, 36.7 E), Zhengzhou (113.6 E, 34.8 N), Yichang (111.3 E, 30.4 N), and Jiujiang (116.0E, 29.7N).

9 LITTLE ICE AGE CLIMATE, BEIJING, CHINA 117 FIG. 9. Wavelet expansion coefficients of the stalagmite thickness sequence for A.D with the time scales from 2 to 295 years. Dashed lines denote the major oscillations. CP = cold period. significant events of climate, economy, and calamity were more or less systematically compiled, with an indication of the locality and date. In previous research, Wang (1992) used some documentary evidence to reconstruct decadal mean temperature anomalies in North China and East China. Notable cold events such as an early first frost, later last frost, heavy snowfall, and freezing of lakes and rivers were classified into three groups according to the severity of the phenomena and denoted as 0.5, 1.0, and 2.0 on a severity index. In a few extremely warm seasons, the severity index was reported as The sum of the severity indices for each of the decades was transformed into a decadal mean temperature anomaly by comparison with severe events and temperature records in the last century. Temperature series for A.D to 1990 were then worked out for North China and East China, respectively. To compare the consequent evidence of cold conditions with the stalagmite thickness series, Figure 10 shows the decadal mean temperature anomalies in North China. Two major cold periods during the 1520s 1740s and 1800s 1890s are identified by shaded areas. The greatest decadal mean temperature anomaly in the cold phase was about 1.0 C or slightly higher. The temperature anomalies averaged for the two cold periods (CP) were 0.5 C and 0.4 C, respectively. We first direct attention to the second cold period, A.D This period is consistent with the phase transition from a positive center in the 1800s to a negative one in the 1890s, marked CP in Figure 9. The last cold period, within an oscillation of about 140 years, and the phase transition of the stalagmite thickness may indicate a cold warm periodicity not only for the quasi-70-yr time scale but also for a longer one. FIG. 10. Decadal mean temperature anomalies ( C) in North China for the A.D. 1370s 1980s (after Wang, 1992).

10 118 QIAN AND ZHU FIG. 11. Wavelet expansion coefficients of the stalagmite thickness sequence for the A.D , with time scales from 2 to 900 years. CP1 through CP5 indicate the five cold periods at different time scales. THE LITTLE ICE AGE IN CHINA For the secular climate variations, the Beijing stalagmite series can be used to represent the dry wet transition in northern China or to reflect the strength of the East Asian monsoon. Figure 11 shows the wavelet coefficients of the stalagmite thickness record from A.D. 850 to 1980 over the range of time scales from 2 to 900 years. Three oscillations with regular variations and large amplitudes at the time scales of about 140, 450, and 750 years can be seen. These regular oscillations may be driven by regular forcing of the monsoon circulation through controls such as solar activity or the variations in the orbital parameters of the Earth, while some extreme small-scale events may be attributed to consecutive volcanic eruptions. The oscillation with the quasi-140-yr time scale is noted in Figure 9. The 450-yr cycle should have yielded more precipitation or a stronger monsoon during the periods A.D , , and after The strong monsoon or more precipitation of the 750-yr oscillation should have dominated during the 1030s 1390s with a peak near the 1200s A.D. The 1780s were the last period when the monsoon commenced a long-term positive departure. In the past 1000 yr, the weakest monsoon occurred around the 1580s. The strength of the East Asian monsoon affects not only the magnitude and location of precipitation but also temperature variations. The LIA, followed by the last century of warming in most areas of the world, was a climatic event that concerns many climatologists. Lamb (1977) and others placed it between the 1550s and 1850s A.D, but Porter (1986) suggested that it began as early as the1250s. At the 70-yr time scale, from the phase relationship between precipitation and temperature in northern China (Fig. 4), the lower temperatures from the 1950s to 1970s can be correlated with strong northerly flows in eastern China (Figs. 6a and 11). This cold spell is denoted by CP5. Using the above relation at the 140-yr time scale, the last cold period in the 19th century is indicated by CP4, and three cold periods have been inferred in Figure 11. At the 750-yr time scale, there is a cold period between A.D and 1590 (CP2). At this scale, the LIA could have started soon after the 1220s, in broad agreement with Porter (1986). The 450-yr oscillation yields cold periods between the 1070s 1280s and the 1520s 1740s, (CP1 and CP3). The beginning of the latter is in good agreement with Lamb s view (1977). Within these cold periods, CP3 and CP4 agree well with the results of documentary analysis in North China (Fig. 10). As indicated in Figure 11, CP1, CP2, CP3, and CP4 were four major cold periods in China. The overlaps are the reflections of the climate anomalies of differing time scale interacting under different forcings. DISCUSSION AND CONCLUSIONS A Beijing stalagmite record spanning more than 1000 years and reflecting natural phenomena sensitive to climate changes has been used to investigate climate variability. Some regular oscillations of the climate anomalies and various time-scale interactions are identified, although some forcings are still unknown. Several features have been clearly identified. Arguments about the beginning and ending of the LIA should be carefully related to time scale. Identifying and comparing climate anomalies such as the Medieval Warm Epoch and Little Ice Age should rest on a single agreed time scale. A 70-yr oscillation in the dry wet transitions in different regions of China has been detected, and the dry or wet migration

11 LITTLE ICE AGE CLIMATE, BEIJING, CHINA 119 from North China to South China has been revealed using modern meteorological observations for the last 100 years. This oscillation is also found in the record of the Beijing stalagmite for the last several hundred years. The 70-yr climate anomaly has also been found widely in some historical documentary series (e.g., Koichiro, 1987). China is strongly influenced by the East Asian monsoon. Droughts and floods and warm and cold intervals are direct reflections of its strength. In the past 50 years, relatively strong monsoon conditions occurred in the 1960s and a weaker monsoon is evident since the 1980s. In the period of strong monsoon, there was more precipitation in northern China, associated with a relatively dry climate in southern China. Based on the analysis of instrumental observations and historical natural records, we infer that quasi-70, 140, 450, and 750-yr oscillations of climate exist in the East Asian monsoon system. It may also be inferred that the LIA in China persisted from the 1300s to the late 1900s. Three pronounced cold periods in the LIA were centered in the late 14th century (750-yr time scale), in the early 17th century (450-yr time scale), and in the 19th century (140-yr time scale). As indicated by Bradley and Jones (1992), evidence provided by continuous records are the most useful to understand the nature of the LIA and its causes. Usually, such records include historical, dendroclimatic, and ice-core data from wide areas. In this paper another source of data, an annual stalagmite thickness series, has been examined using the wavelet transform method and compared with other climatic proxy data spanning the same time interval. The MWE and, particularly, the LIA can be identified from the stalagmite thickness series. From the analysis of the quasi-70-yr climatic oscillation, the strong monsoon in East Asia caused the cold period in North China in the 1960s 1970s, while a warm climate was associated with the weak monsoon during the 1980s 1990s. The strength of the East Asian monsoon depends largely on the continent ocean thermal contrast. Since the mid-1970s, tropical sea-surface temperature has increased relative to that of the previous two decades (Wang 1995; Qian et al., 1999). Linked with the monsoon variation, it may be inferred that the LIA, and three cold periods within it, were related to cold tropical ocean conditions in those periods. ACKNOWLEDGMENTS We wish to thank Professor Derek Ford for improving the revised text. We also thank anonymous reviewers and the editor whose comments and suggestions have helped to improve this paper. This research was supported by the National Key Program for Developing Basic Sciences in China (Grant G ) and the NNFC (Grant ). REFERENCES Bradley, R. S., and Jones, P. D. (1992). When was the Little Ice Age? In Proceedings of the International Symposium on the Little Ice Age climate (T. Mikami, Ed.), pp Department of Geography, Tokyo Metropolitan University. Central Meteorological Bureau. (1982). Atlas of Flood and Drought in China in the Last 500 years. Map Press, Beijing, China. [in Chinese] Dreybrodt, W. (1996). Chemical kinetics, speleothem growth and climate. In Proceeding of the Conference Climate Change: The Karst Record, pp Bergen, August. Gao, W., and Li, B. L. (1993). Wavelet analysis of coherent structure at the atmosphere-forest interface. Journal of Applied Meteorology 32, Jiang, J., Zhang, D., and Fraedrich, K. (1997). Historical climate variability of wetness in East China ( ): A wavelet analysis. International Journal of Climatology 17, Kalnay, E., et al., (1996). The NCEP/NCAR 40-year reanalysis project. Bulletin of the American Meteorological Society 77, Koichiro, T. (1987). An analysis of long-term variation of storm damage in Japan. In The Climate of China and Global climate (D. Ye, C. Fu, et al., Eds.), pp China Ocean Press and Springer-Verlag, Beijing. Lamb, H. H. (1977). Climate, Present, Past and Future. Methuen, London. Lamb, H. H. (1984). Some studies of the Little Ice Age of recent centuries. In Climatic Changes on a Yearly to Millennial Basis (N. A. Morner and W. Karlén, Eds.), pp Reidel, Dordrecht. Lorenz, E. N. (1956). Empirical orthogonal functions and statistical weather prediction. MIT, Dept. of Meteorology, Science Report 1. Morlet, G. A., Fourgeau, I., and Giard, D. (1982). Wave propagation and sampling theory. Geophysics 47, Porter, S. C. (1986). Pattern and forcing of Northern Hemisphere glacier variations during the last millennium. Quaternary Research 26, Qian, W. H., Zhu, Y. F., and Ye, Q. (1999). Interannual and interdecadal variabilities in SST anomaly over the eastern equatorial Pacific. Chinese Science Bulletin 44, Qian, W. H., and Zhu, Y. F. (2001). Climate change in China from 1880 to 1998 and its impact on the environmental condition. Climatic Change 50, Qin, X., Tan, M., Liu, T., Wang, X., Li, T., and Lu, J. (1999). Spectral analysis of a 1000-year stalagmite lamina-thickness record from Shihua Cavern, Beijing, China, and its climatic significance. The Holocene 9, Richman, M. B. (1986). Review article: Rotation of principal components. Journal of Climatology 6, Song, J. (2000). Changes in dryness/wetness in China during the last 529 years. International Journal of Climatology 20, Wang, B. (1995). Interdecadal changes in El Niño onset in the last four decades. Journal of Climate 8, Wang, S. W. (1992). Climate of the Little Ice Age in China. In Proceedings of the International Symposium on the Little Ice Age Climate (T. Mikami, Ed.), pp Department of Geography, Tokyo Metropolitan University. Wang, S. W., Ye, J., Gong, D., and Zhu, J. (1998). Construction of mean annual temperature series for the last one hundred years in China. Quarterly Journal of Applied Meteorology 9, [In Chinese with English abstract] Wigley, T. M. L., Ingram, M. J., and Farmer, G. (1981). Climate and history. Studies in past climates and their impact on man. Cambridge Univ. Press, Cambridge. Ye, J. L., Chen, Z. H., Gong, D. Y., and Wang, S.-W. (1998). Characteristics of seasonal precipitation anomalies in China for Quarterly Journal of Applied Meteorology 9, [in Chinese with English abstract] Zhang, D. (1988). The method for reconstruction of the dryness/wetness series in China for the last 500 years and its reliability. In The Reconstruction of climate in China for historical times (J. Zhang, Ed.), pp Science Press, Beijing.