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1.
The Initiation of the "Little Ice Age" in Regions Round the North Atlantic   总被引：3，自引：0，他引：3  
The "Little Ice Age" was the most recent period during which glaciers extended globally, their fronts oscillating about advanced positions. It is frequently taken as having started in the sixteenth or seventeenth century and ending somewhere between 1850 and 1890, but Porter (1981) pointed out that the "Little Ice Age" may 'have begun at least three centuries earlier in the North Atlantic region than is generally inferred'. The glacial fluctuations of the last millennium have been traced in the greatest detail in the Swiss Alps, where the "Little Ice Age" is now seen as starting with advances in the thirteenth century, and reaching an initial culmination in the fourteenth century. In the discussion here, evidence from Canada, Greenland, Iceland, Spitsbergen and Scandinavia is compared with that from Switzerland. Such comparisons have been facilitated by improved methods of calibrating radiocarbon dates to calendar dates and by increasing availability of evidence revealed during the current retreat phase. It is concluded that the "Little Ice Age" was initiated before the early fourteenth century in regions surrounding the North Atlantic.  相似文献   

2.
We reconstructed decadal to centennial variability of maximum sea ice extent in the Western Nordic Seas for A.D. 1200–1997 using a combination of a regional tree-ring chronology from the timberline area in Fennoscandia and δ18O from the Lomonosovfonna ice core in Svalbard. The reconstruction successfully explained 59% of the variance in sea ice extent based on the calibration period 1864–1997. The significance of the reconstruction statistics (reduction of error, coefficient of efficiency) is computed for the first time against a realistic noise background. The twentieth century sustained the lowest sea ice extent values since A.D. 1200: low sea ice extent also occurred before (mid-seventeenth and mid-eighteenth centuries, early fifteenth and late thirteenth centuries), but these periods were in no case as persistent as in the twentieth century. Largest sea ice extent values occurred from the seventeenth to the nineteenth centuries, during the Little Ice Age (LIA), with relatively smaller sea ice-covered area during the sixteenth century. Moderate sea ice extent occurred during thirteenth–fifteenth centuries. Reconstructed sea ice extent variability is dominated by decadal oscillations, frequently associated with decadal components of the North Atlantic Oscillation/Arctic Oscillation (NAO/AO), and multi-decadal lower frequency oscillations operating at ~50–120 year. Sea ice extent and NAO showed a non-stationary relationship during the observational period. The present low sea ice extent is unique over the last 800 years, and results from a decline started in late-nineteenth century after the LIA.  相似文献   

3.
A new reconstruction of the climate and sea-ice record for Iceland from medieval times to A.D. 1780 is presented, based on all available documentary sources. The importance of careful historical analysis to separate reliable from unreliable material is stressed, and these reconstructions are the first to have been produced using only reliable data. The major previous works on the subject (those of Thoroddsen, Koch, and Bergþórsson), which all include unreliable material, are discussed. Prior to A.D. 1600 the data are not considered to be full enough to permit a quantitative interpretation. For the period A.D. 1601 to 1780 decadal temperature and sea-ice indices are given.Although there is very little evidence for the first few centuries of settlement in Iceland (from c. 870 to c. 1170) the data suggest a fairly mild climatic period. Cold periods occurred around 1200, and at the end of the thirteenth century. The fourteenth century was very variable with a cold period in the 1350s to c. 1380. Between 1430 and c. 1560 there are very few contemporary sources and it is difficult to draw any conclusions on the climate during this time. The latter part of the sixteenth century was undoubtedly cold. From 1601 there are sufficient data to permit a decade by decade analysis. This shows a mild period between 1640 and 1670, and severe decades in the 1630s, 1690s, 1740s, and 1750s. Year to year and decade to decade variability is appreciable. The correlation between temperature and sea ice is not perfect but is still quite strong (similar to today). Because data have been gathered from different regions of Iceland it has been possible to demonstrate the spatial variability of Iceland's climate during the period 1601 to 1780. For example, during 1660 to 1700 there was a cooling in the north and west but warming in the south. The 1690s, the coldest decade of the Little Ice Age in Europe, was extremely cold in the west of Iceland, but less severe elsewhere.
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4.
We review here proxy records of temperature and precipitation in China during the Holocene, especially the last two millennia. The quality of proxy data, methodology of reconstruction, and uncertainties in reconstruction were emphasized in comparing different temperature and precipitation reconstruction and clarifying temporal and spatial patterns of temperature and precipitation during the Holocene. The Holocene climate was generally warm and wet. The warmest period occurred in 9.6-6.2 cal ka BP, whereas a period of maximum monsoon precipitation started at about 11.0 cal ka BP and lasted until about 8.0-5.0 cal ka BP. There were a series of millennial-scale cold or dry events superimposed on the general trend of climate changes. During past two millennia, a warming trend in the 20th century was clearly detected, but the warming magnitude was smaller than the maximum level of the Medieval Warm Period and the Middle Holocene. Cold conditions occurred over the whole of China during the Little Ice Age （AD 1400-AD 1900）, but the warming of the Medieval Warm Period （AD 900-AD 1300） was not distinct in China, especially west China. The spatial pattern of precipitation showed significant regional differences in China, especially east China. The modern warm period has lasted 20 years from 1987 to 2006. Bi-decadal oscillation in precipitation variability was apparent over China during the 20th century. Solar activity and volcanic eruptions both were major forcings governing the climate variability during the last millennium.  相似文献   

5.
Annually resolved ice core records from different regions over the Greenland ice sheet (GrIS) are used to investigate the spatial and temporal variability of calcium (Ca2+, mainly from mineral dust) and sodium (Na+, mainly from sea salt) deposition. Cores of high common inter-annual variability are grouped with an EOF analysis, resulting in regionally representative Ca2+ and Na+ records for northeastern and central Greenland. Utilizing a regression and validation method with ERA-40 reanalysis data, these common records are associated with distinct regional atmospheric circulation patterns over the North American Arctic, Greenland, and Central to Northern Europe. These patterns are interpreted in terms of transport and deposition of the impurities. In the northeastern part of the GrIS sea salt records reflect the intrusion of marine air masses from southeasterly flow. A large fraction of the Ca2+ variability in this region is connected to a circulation pattern suggesting transport from the west and dry deposition. This pattern is consistent with the current understanding of a predominantly Asian source of the dust deposited over the GrIS. However, our results also indicate that a significant fraction of the inter-annual dust variability in NE and Central Greenland is determined by the frequency and intensity of wet deposition during the season of high atmospheric dust loading, rather than representing the variability of the Asian dust source and/or long-range transport to Greenland. The variances in the regional proxy records explained by the streamfunction patterns are high enough to permit reconstructions of the corresponding regional deposition regimes and the associated circulation patterns.  相似文献   

6.
"Little Ice Age" Research: A Perspective from Iceland   总被引：5，自引：0，他引：5  
The development during the nineteenth and twentieth centuries of the sciences of meteorology and climatology and their subdisciplines has made possible an ever-increasing understanding of the climate of the past. In particular, the refinement of palaeoclimatic proxy data has meant that the climate of the past thousand years has begun to be extensively studied. In the context of this research, it has often been suggested that a warm epoch occurred in much of northern Europe, the north Atlantic, and other parts of the world, from around the ninth through the fourteenth centuries, and that this was followed by a decline in temperatures culminating in a "Little Ice Age" from about 1550 to 1850 (see e.g. Lamb, 1965, 1977; Flohn, 1978). The appelations "Medieval Warm Period" and "Little Ice Age" have entered the literature and are frequently used without clear definition. More recently, however, these terms have come under closer scrutiny (see, e.g. Ogilvie, 1991, 1992; Bradley and Jones, 1992; Mikami, 1992; Briffa and Jones, 1993; Bradley and Jones, 1993; Hughes and Diaz, 1994; Jones et al., 1998; Mann et al., 1999; Crowley and Lowery, 2000). As research continues into climatic fluctuations over the last 1000 to 2000 years, a pattern is emerging which suggests a far more complex picture than early research into the history of climate suggested. In this paper, the origins of the term "Little Ice Age" are considered. Because of the emphasis on the North Atlantic in this volume, the prime focus is on research that has been undertaken in this region, with a perspective on the historiography of historical climatology in Iceland as well as on the twentieth-century climate of Iceland. The phrase "Little Ice Age" has become part of the scientific and popular thinking on the climate of the past thousand years. However, as knowledge of the climate of the Holocene continues to grow, the term now seems to cloud rather than clarify thinking on the climate of the past thousand years. It is hoped that the discussion here will encourage future researchers to focus their thinking on exactly and precisely what is meant when the term "Little Ice Age" is used.  相似文献   

7.
通过对小冰期研究文献进行综述,并对已发表的小冰期温度和降水数据进行综合对比分析,探讨小冰期时期中国气候特征的区域性.结果表明,小冰期在中国地区不同区域代用指标记录中均存在,但是小冰期的起讫及持续时间具有区域差异性,温湿配置也不尽相同.小冰期的起始时间主要呈现出由西向东推移的趋势,即青藏高原最早,华北地区次之而东部地区最晚.温湿配置的差异主要体现在东部季风区小冰期时期总体上是冷干的气候环境,而西部地区气候变化则呈现冷湿的气候特征.  相似文献   

8.
Comparison of an ice core glaciochemical time-series developed from thePenny Ice Cap (PIC), Baffin Island and monthly sea-ice extent reveals astatisticallysignificant inverse relationship between changes in Baffin Bay spring sea-iceextent andPenny Ice Cap sea-salt concentrations for the period 1901–1990 AD.Empiricalorthogonal function analysis demonstrates the joint behavior between changesin PICsea-salt concentrations, sea-ice extent, and changes in North Atlanticatmosphericcirculation. Our results suggest that sea-salt concentrations in snowpreserved on thePIC reflect local to regional springtime sea-ice coverage. The PIC sea-saltrecord/sea-ice relationship is further supported by decadal and century scalecomparisonwith other paleoclimate records of eastern Arctic climate change over the last700 years. Our sea-salt record suggests that, while the turn of the century wascharacterized bygenerally milder sea-ice conditions in Baffin Bay, the last few decades ofsea-ice extentlie within Little Ice Age variability and correspond to instrumental recordsof lowertemperatures in the Eastern Canadian Arctic over the past three decades.  相似文献   

9.
We review here proxy records of temperatare and precipitation in China during the Holocene,especially the last two millennia.The quality of proxy data,methodology of reconstruction,and uncertainties in reconstruction were emphasized in comparing different temperatare and precipitation reconstruction and clarilying temporal and spatial patterns of temperature and precipitation during the Holocene.The Holocene climate was generally warm and wet.The warmest period occurred in 9.6-6.2 cal ka BP,whereas a period of maximum monsoon precipitation started at about 11.0 cal ka BP and lasted until about 8.O-5.0 cal ka BP.There were a series of millennial-scale cold or dry events superimposed on the general trend of climate changes.During past two millennia,a warming trend in the 20th century was clearly detected,but the warming magnitude was smaller than the maximum level of the Medieval Warm Period and the Middle Holocene.Cold conditions occurred over the whole of China during the Little Ice Age (AD 1400-AD 1900),but the warming of the Medieval Warm Period(AD 900-AD 1300)was not distinct in China,especially west China.The spatial pattern of precipitation showed significant regional differences in China,especially east China.The modern warm period has lasted 20、years from 1987 to 2006.Bi-decadal oscillation in precipitation variability was apparent over China during the 20th century. Solar activity and volcanic eruptions both were major forcings governing the climate variability during the last millennium.  相似文献   

10.
A 2.5 × 2.5° gridded summer (April–September) drought reconstruction over the larger Mediterranean land area (32.5°/47.5°N, 10°W/50°E; 152 grid points) is described, based on a network of 165 tree-ring series. The drought index used is the self-calibrated Palmer Drought Severity Index, and the period considered is 1500–2000. The reconstruction technique combines an analogue technique for the estimation of missing tree-ring data with an artificial neural network for optimal non-linear calibration, including a bootstrap error assessment. Tests were carried out on the various sources of error in the reconstructions. Errors related to the temporal variations of the number of proxies were tested by comparing four reconstructions calibrated with four different sized regressor datasets, representing the decrease in the number of available proxies over time. Errors related to the heterogeneous spatial density of predictors were tested using pseudo-proxies, provided by the global climate model ECHO-G. Finally the errors related to the imperfect climate signal recorded by tree-ring series were tested by adding white noise to the pseudo-proxies. Reconstructions pass standard cross-validation tests. Nevertheless tests using pseudo-proxies show that the reconstructions are less good in areas where proxies are rare, but that the average reconstruction curve is robust. Finally, the noise added to proxies, which is by definition a high frequency component, has a major effect on the low frequency signal, but not on the medium frequencies. The comparison of the low frequency trends of our mean reconstruction and the GCM simulation indicates that the detrending method used is able to preserve the long-term variations of reconstructed PDSI. The results also highlight similar multi-decadal PDSI variations in the central and western parts of the Mediterranean basin and less clear low frequency changes in the east. The sixteenth and the first part of the seventeenth centuries are characterized by marked dry episodes in the west similar to those observed in the end of the twentieth century. In contrast, the eighteenth and nineteenth centuries (Little Ice Age) are characterized by dominant wet periods. In the eastern part of the Mediterranean basin the observed strong drought period of the end of the twentieth century seems to be the strongest of the last 500 years.  相似文献   

11.
This reconstruction of the ice winter severity in the Western Baltic is based for the period 1878-1993 on the accumulated areal ice volume along the German Baltic coast with observations from 13 coastal stations; for the period 1701-1877 it is based on the accumulated areal ice volume divided into 7 classes (ice winter severity types). The various types of data consulted in the latter case provided ice data of good spatial and temporal resolution.Speerschneider's compilation of data relating to ice conditions in Danish Baltic waters was found to be a valuable source of information. Using a classification table for the periods 1907-1943 and 1947-1992, five of the seven ice winter types have been derived with certainty as they are characterized by typical stages of maximum ice cover throughout the Western Baltic.The Gaussian lowpass-filtered time series of the ice winter index numerals with a 20 year cutoff period shows four periods of varying ice winter severity over a secular range: 1701-1720: slightly increased ice winter severity with regard to the mean of the 1701-1993 time series; this period can be assigned to the end of a cooling phase during Little Ice Age which in central Europe peaked in the second half of the 17th c. 1721-1760: ice winter severity is clearly reduced in this period. 1761-1860: ice winter severity is clearly increased (maximum occurs around 1800) towards the end of the Little Ice Age, associated with increased variability of ice production. 1861-1993: the present-day ice winter regime when three short intervals with increased ice winter severity (the 1890s, 1940s and 1980s) and a period of greatly reduced ice winter severity (between 1900 and the mid-1920s) stand out.  相似文献   

12.
Future Greenland temperature evolution will affect melting of the ice sheet and associated global sea-level change. Therefore, understanding Greenland temperature variability and its relation to global trends is critical. Here, we reconstruct the last 1,000 years of central Greenland surface temperature from isotopes of N2 and Ar in air bubbles in an ice core. This technique provides constraints on decadal to centennial temperature fluctuations. We found that northern hemisphere temperature and Greenland temperature changed synchronously at periods of ~20 years and 40–100 years. This quasi-periodic multi-decadal temperature fluctuation persisted throughout the last millennium, and is likely to continue into the future.  相似文献   

13.
A 1053-year reconstruction of spring rainfall (March-June) was developed for the southeastern United States, based on three tree-ring reconstructions of statewide rainfall from North Carolina, South Carolina, and Georgia. This regional reconstruction is highly correlated with the instrumental record of spring rainfall (r = +0.80; 1887–1982), and accurately reproduces the decade-scale departures in spring rainfall amount and variance witnessed over the Southeast during the past century. No large-magnitude centuries-long trends in spring rainfall amounts were reconstructed over the past 1053 years, but large changes in the interannual variability of spring rainfall were reconstructed during portions of the Medieval Warm Period (MWP), Little Ice Age (LIA), and the 20th century. Dry conditions persisted at the end of the 12th century, but appear to have been exceeded by a reconstructed drought in the mid-18th century. High interannual variability, including five extremely wet years were reconstructed for a 20-yr period during the late 16th and early 17th centuries, and may reflect amplified atmospheric circulation over eastern North America during what appears to have been one of the most widespread cold episodes of the Little Ice Age.  相似文献   

14.
Snow accumulation and its moisture origin over Dome Argus, Antarctica   总被引：1，自引：0，他引：1  
The spatial and temporal variability of snow accumulation near Dome Argus, Antarctica, is assessed using new snow pit and stake measurement data together with existing snow pit, ice core and automatic weather station records. Snow accumulation rate shows large inter-annual variations, but stable multi-decadal levels over the last seven centuries. Spatial variations in snow accumulation within the space of 50 km of Dome Argus are relatively small, probably thanks to the smooth topography. A comparison of theses accumulation observations with ECMWF reanalyses (ERA-40 and ERA-Interim) suggests ECMWF reanalysis captures the seasonal variations, but underestimates the overall snow accumulation at Dome Argus by ~50 %. The moisture sources for precipitation over Dome Argus are examined by means of a Lagrangian moisture source diagnostic, based on the tracing of specific humidity changes along air parcel trajectories, for the period 2000–2004 using operational ECMWF analysis data. Dome Argus mainly receives moisture from the mid-latitude (46 ± 4°S) South Indian Ocean, with a seasonal latitudinal shift of about 6°. Compared to other central East Antarctic deep ice core sites such as Dome F, Dome C, Vostok, and EPICA Dronning Maud Land, Dome Argus has a more southerly moisture origin, probably due to topographic influences on the moisture transport paths. These results have important implications for the interpretation of future ice cores at Dome Argus.  相似文献   

15.
A new paleoclimatic reconstruction for western France is obtained from tree-ring cellulose stable isotopes. Living trees from Rennes Forest and beams from two ancient buildings in Rennes city have been combined to cover the past four centuries with a gap from 1730 to 1750. The cellulose 13C reflects the progressive changes in atmospheric CO2 isotopic composition. The combined 13C and 18O measurements are used to propose a reconstruction of interannual fluctuations in local summer temperature and water stress. At the decadal time scale, the reconstructed water stress profile exhibits a significant similarity with the historical wine harvest dates, an indicator of warm and dry growth seasons, as well as with the summer central England and central Alps instrumental temperature records and climate model results. Combined with instrumental precipitation records from Paris, these reconstructions suggest a dramatic and widespread change in the seasonality of the precipitation at the beginning of the nineteenth century, with drier winters and wetter summers, which may have contributed to the Alpine glacier decline at the end of the Little Ice Age. The tree-ring isotope records also show a relationship with large-scale North Atlantic circulation changes and the interannual variability is modified between the nineteenth and twentieth centuries (7–8 year periodicities) and the seventeenth century (11–14 year periodicities). By classifying 20-year-long subsets of the reconstructed climatic parameters, we estimate that a decadal mean summer warming of 0.8±0.1°C induced extreme dry years to be 2.2±0.7 times more frequent.  相似文献   

16.
Summary Climate variability and flood events in the Yangtze Delta, which is a low-lying terrain prone to flood hazards, storm tides and typhoons, are studied in terms of a trend and detrended fluctuation analysis of historical records. The data used in this paper were extracted from historical records such as local annuals and chronologies from 1000–1950 and supplemented by instrumental observations since 1950. The historical data includes frequencies of floods, droughts and maritime events on a decadal basis. Flood magnitudes increase during the transition from the medieval warm interval into the early Little Ice Age. Fluctuating climate changes of the Little Ice Age, which are characterised by arid climate events, are followed by wet and cold climate conditions with frequent flood hazards. For trend analysis, the Mann-Kendall test is applied to determine the changing trends of flood and drought frequency. Flood frequency during 1000–1950 shows a negative trend before 1600 A.D. and a positive trend thereafter; drought frequency increases after 1300. The detrended fluctuation analysis of the flood and drought frequencies reveals power law scaling up to centuries; this is related to long-term memory and is similar to the river Nile floods.  相似文献   

17.
Reconstructing the temporal and spatial climate development on a seasonal basis during the last few centuries, including the ‘Little Ice Age’, may help us better understand modern-day interplay between natural and anthropogenic climate variability. The conventional view of the climate development during the last millennium has been that it followed a sequence of a Medieval Warm Period, a cool ‘Little Ice Age’ and a warming during the later part of the 19th century and in particular during the late 20th/early 21st centuries. However, recent research has challenged this rather simple sequence of climate development. Up to the present, it has been considered most likely that the ‘Little Ice Age’ glacial expansion in western Scandinavia was due to lower summer temperatures. Data presented here, however, indicate that the main cause of the early 18th century glacial advance in western Scandinavia was mild and humid winters associated with increased precipitation and high snowfall on the glaciers.  相似文献   

18.
Cloud cover currently represents the single greatest source of uncertainty in General Circulation Models. Stable carbon isotope ratios (δ13C) from tree-rings, in areas of low moisture stress, are likely to be primarily controlled by photosynthetically active radiation (PAR), and therefore should provide a proxy record for cloud cover or sunshine; indeed this association has previously been demonstrated experimentally for Scots pine in Fennoscandia, with sunlight explaining ca 90% of the variance in photosynthesis and temperature only ca 4%. We present a statistically verifiable 1011-year reconstruction of cloud cover from a well replicated, annually-resolved δ13C record from Forfjord in coastal northwestern Norway. This reconstruction exhibits considerable variability in cloud cover over the past millennium, including extended sunny periods during the cool seventeenth and eighteenth centuries and warm cloudy periods during the eleventh, early fifteenth and twentieth centuries. We find that while a generally positive relationship persists between sunshine and temperature at high-frequency, at lower (multi-decadal) frequencies the relationship is more often a negative one, with cool periods being sunny (most notably the Little Ice Age period from 1600 to 1750 CE) and warm periods more cloudy (e.g. the mediaeval and the twentieth century). We conclude that these long-term changes may be caused by changes in the dominant circulation mode, likely to be associated with the Arctic Oscillation. There is also strong circumstantial evidence that prolonged periods of high summer cloud cover, with low PAR and probably high precipitation, may be in part responsible for major European famines caused by crop failures.  相似文献   

19.
A.T. Grove 《Climatic change》2001,48(1):121-136
Alpine glacier advances in the "Little Ice Age" took place in the decades around 1320, 1600, 1700 and 1810. They were the outcome of snowier winters and cooler summers than those of the twentieth century. Documentary records from Crete in particular, and also from Italy, southern France and southeast Spain point to a greater frequency in Mediterranean Europe's mountainous regions of severe floods, droughts and frosts at times of "Little Ice Age" Alpine glacier advances. Deluges, when more than 200 mm of rain fall within 24 hours, are most frequent on mountainous areas near the coast. An instance is given of the geomorphological consequences of a great deluge which struck the Tech valley in the eastern Pyrenees on 17 October 1940. An increased frequency of deluges, probably at times when Alpine glaciers were advancing in the "Little Ice Age" and earlier in the Holocene, in areas known to be tectonically unstable and underlain by soft sediments, could better explain the occurrence of fluvial terraces in Mediterranean Europe sometimes known as the "younger fill", than soil erosion resulting from deforestation.  相似文献   

20.
Greenland ice cores offer seasonal to annual records of δ18O, a proxy for precipitation-weighted temperature, over the last few centuries to millennia. Here, we investigate the regional footprints of the North Atlantic weather regimes on Greenland isotope and climate variability, using a compilation of 22 different shallow ice-cores and the atmospheric pressure conditions from the twentieth century reanalysis (20CR). As a first step we have verified that the leading modes of winter and annual δ18O are well correlated with oceanic (Atlantic multidecadal oscillation) and atmospheric [North Atlantic oscillation (NAO)] indices respectively, and also marginally with external forcings, thus confirming earlier studies. The link between weather regimes and Greenland precipitation, precipitation-weighted temperature and δ18O is further explored by using an isotope simulation from the LMDZ-iso model, where the 3-dimensional wind fields are nudged to those of 20CR. In winter, the NAO+ and NAO? regimes in LMDZ-iso produce the largest isotopic changes over the entire Greenland region, with maximum anomalies in the South. Likewise, the Scandinavian blocking and the Atlantic ridge also show remarkable imprints on isotopic composition over the region. To assess the robustness and model dependency of our findings, a second isotope simulation from the isotopic model is also explored. The percentage of Greenland δ18O variance explained by the ensemble of weather regimes is increased by a factor near two in both LMDZ-iso and IsoGSM when compared to the contribution of the NAO index only. Similarly, weather regimes provide a net gain in the δ18O variance explained of similar magnitude for the whole set of ice core records. Greenland δ18O also appears to be locally affected by the low-frequency variations in the centres of action of the weather regimes, with clearer imprints in the LMDZ-iso simulation. This study opens the possibility for reconstructing past changes in the frequencies of occurrence of the weather regimes, which would rely on the sensitive regions identified here, and the use of additional proxies over the North Atlantic region.  相似文献   

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