Developments in historical climatology

ZESZYTY NAUKOWE MCLXXXVI UNIWERSYTETU PRACE GEOGRAFICZNE - ZESZYT JAGIELLONSKIEGO 102 1996 Jean M. GROVE Girton College Cambridge, GREAT BRITAIN DEVELOPMENTS ABSTRACT: IN HISTORICAL CLIMATOLOGY The recent evolution of historical climatology, involving increased precision, improvements in the methodology of data handling and analysis and widened scope, is characterised by the contributions of Manley, Lamb and Pfister. Future extensions of the field of study could greatly increase understanding of climatic variations and their impact on society. Introduction Anxiety about global warming has increased the perceived need to investigate the characteristics of climate during past warm periods and caused greater interest in the incidence and causes of changes on century and decadal scales, which might increase or miligate the effects of increased greenhouse gases in the atmosphere. In recent decades the methodology of climatic reconstruction has advanced, increasing its accuracy, and its scope widened lo include identification of circulation changes, synoptic patterns and teleconnections. The presentation of climatic descriptions from unspecified and unverified sources has almost ceased, and the need for critical approaches accepted. Handling of written sources has become more sophisticated, and extraction of information more complete, as methods such as content and frequency analysis have been introduced. Many scholars, including Landsberg (e.g. 1980) in America and Flohn (e.g. 1950), in Germany, have played important roles, but the evolution of the subject may be epitomised by the work of thrce pioneers, Gordon Manley, Hubert Lamb and Christian Pfister. 72 73 The contributions of Manley, Lamb and Pfister Gaps in data required for European climate reconstruction Gordon Manley made many contributions to climatology (publishing over 180 papers apart from books) but his (1974) reconstruction of monthly mean temperatures for central England, the fruit of more than thirty years work, without modern computing aids, stands out as a model of meticulous scholarship. He gave full explanations of the ways in which values were derived, and the extent to which estimates should be considered reliable. He carefully published details of his sources and the methods whereby overlapping records from different places were scrutinised and used in the construction of a single serics of monthly values for lowland sites in central England. Long, series are now homogeneous available for many other locations; Jones and Bradley temperature (1992, Table 13.1) list forty nine, of which scventcen are European, but Manley’s reconstruction is still the longest. His indefatigable searches for weather diaries and early meteorological measurements have since been emulated by many others. Kington (1994), working in the Climatic Research Unit set up by Hubert Lamb, was able to specify forty six diaries and weather journals kept in Great Britain alone between 1636 and 1731. Lamb (1977) led the way in attempting to construct indiccs of summer dryness/wetness and winter mildness/severity, constructing diagrams showing decadal excess of wet or dry months in different longitudes of Europe around 50°N, and producing maps show- ing weather reports, wind directions, suggested mean sea-level pressure, and synoptic patterns for specified times. Lamb’s (1972) interest in southwesterly wind {requencies over England between the fourteenth and twentieth centuries typified his concern with changes in circulation over time, a high frequency of southwest surface winds giving an indication of the prevalence of zonal flow, and a low frequency of generally blocked or meridional circulation. Manley and Lamb, who were in close contact, showed the possibility of as- sembling accurate and detailed series of values for particular localities, and the importance of synoptic approachs, recognising regional weather patterns and relationships. Pfister (e.g. 1992, 1994a, b) succeeded in cross-dating documentary proxy data, both physical and phenological, with descriptive evidence, and instrumental values. He used computer listing and analysis, to produce quantitative estimates of temperature and pre- cipitation and carcfully based thermal and wetness indices, Turning his attention to the spatial dimension of climatic change he set up a European-wide data base (the CLIM- HIST project) by persuading other European workers to adopt his methods and cooperate. This makes possible regional synthesis, identification of synoptic patterns and se- quences, and production of maps based on denser evidence than Lamb’s original pioneer sketches. It is appropriate that one of the papers emerging from the CLIMHIST cooper- ation, concerned with European circulation pattcrns, makes use of Manley’s temperature series and has Lamb as well as Pfister among its authors (Wanner e¢ al. in press). This cooperation has already resulted in clearer understanding of the climatic characteristics of the Maunder Minimum period in Europe (Frenzel et al. 1994). But data is still lacking or inadequate for several regions, as well as for the earlier part of the present millennium, Synoptic sequences occurring during the Maunder Minimum could be defined more exactly given better data coverage, especially from the south and east of Europe. Much more data could be retrieved even in western Europe, especially for the medieval period. The value of intensive archival search was demonstrated by the quantity of verifiable data found by Alexandre (1987), which greatly enlarged knowledge of climatic variations between 1000 and 1425 AD. Similar efforts are required in other areas. Little is yet known about the climatic history of several European regions, particularly Iberia and the southeast. Some Spanish studies are appearing (e.g. Martin-Vide, Vallvé 1995) but verification and analysis of the great wealth of material in the Spanish archives has scarcely begun and few of the thousands of documents in the Venetian archives concerning the Eastern Mediterranean have been examined. Only the climate of Crete in the sixteenth and seventeenth centuries has been investigated in detail (Grove, Conterio 1995). Documents from the Turkish archives remain largely unused, but are known to contain relevant data. Possibilities for future The new methods extension of climatic reconstruction of climatic reconstruction could be extended outside Europe. Archival sources are richest and stretch back furthest in Eurasia, because literate so- cietics have been recording climatic events and conditions for longer there than elsewhere. But Arabic documents may well contain information about climate in the Near East and parts of Africa. Detailed exploration of Spanish, Portugese, Dutch and other colonial records could extend knowledge of climatic history, especially in South America, and the Far East. Indian archives contain documents frora Mogul times and earlier, but no attempt whatever has been made to extract climatic data from documents written in any of the Indian languages. Even those in English are practically unexamined. In Japan and China however historical climatology is developing rapidly, and opportunities for Eurasian cooperation are beginning to arise. In the last twenty years interest in climatic reconstruction has surged in J apan (Mika- mi 1992). The Japanese Historical Weather Data Base (Yoshimura, Yoshino 1988) in- cludes such long records as the dates of appearance of cherry blossom, going back as far as the ninth century, the date of cracking of the ice on Lake Suwa, in central Japan, recorded trom 1443 to 1953 (Fukaishi, Tagami 1992), and a wide range of sources con(ain data on the incidence of precipitation (Mikami 1992), Phenological observations, made since 1927, provide a base for interpretation. 75 74 Historical climatology in China was initiated as an academic subject by Chu Coching (or Zhu Kezhen), whose status is comparable with that of Lamb (Yoshino 1990). He was primarily a meteorologist and climatologist, but was much interested in phenology. His paper on temperature variations in China over the last 5,000 years (1973) used records of flowering dates and times of arrival of migrant birds. His efforts led in 1970 to a nationwide effort to extract climatic information from historical sources (Zhang, Crowley 1989), leading to reconstruction of time series of temperature and precipitation, of regional extent of drought and flood, and variations in synoptic patterns including the western Pacific high (e.g. Wang Shao-wu 1991, Wang, Zhang 1992; Huang Jia-You, Wang Shao-wu 1985). Significantly it has already been possible to make a continental scale comparison of climate in Western Europe and China during the Maunder Minimum (Pfister ef al. 1994), Further use of Pfister’s methods should lead to many more such studies, and eventually assist identification of the factors responsible for smaller scale climatic fluc- tuations, and changes in the frequency and severity of anomalies, as well as studies of the impact of climatic fluctuations on society. Pfister C. 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