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During the past 1，000 years, the climates of the British Isles and continental Europe have undergone various episodes of change. It has long been believed that the demographic and economic expansion of Europe between the tenth and thirteenth centuries coincided with, and was perhaps encouraged by, a period of relative warmth, favorable to the expansion of cereal cultivation and the colonization of previously inhospitable environments. This benign phase, although variously dated, was seen to lie between a period of less favorable conditions in the late and post-Roman centuries and the so-called Little lce Age of the early modern period, which was characterized by an overall cooling of the climate and, in particular, by an increased severity of winters. Climatic deterioration was seen to have begun by circa 1300, presaged by an increase in stormy conditions in Europe, and associated with runs of wet and cool summers and the widespread harvest failures and livestock mortality of the years 1315-1322.

The integrity of the so-called medieval warm period, once considered a global phenomenon, has, however, been called into question by recent paleoenvironmental research. The picture that now emerges is of a less coherent and perhaps more geographically restricted phase- variously dated- of relative warmth, when temperatures in northwest Europe and the North Atlantic area were on average higher than in the post-Roman and early modern periods, although probably not warmer than in the late twentieth century.Some types of evidence, including the records of the advance and retreat of Alpine glaciers, suggest that the later fourteenth and early fifteenth centuries may have seen a notable climatic downturn, followed by a temporary amelioration around 1500, before renewed cooling into the L ate Maunder M inimum period of 1675- -1715. The relationship between glacial advance or retreat and temperature is,however, complex. A study of winter severity in central Europe during the fourteenth century found no clear trend, rather the alternation of runs of cold and mild winters, with the most sustained period of severe winters falling in the period 1301- 1328. English documentary sources have been used to suggest a cooling trend from circa 1240- 1340, with a subsequent amelioration followed by renewed cooling from circa 1510. but the sporadic nature of this data series necessitates caution. A long-term cooling trend in the northern hemisphere between the twelfth/thirteenth and the seventeenth centuries does. however. emerge from a plethora of sources. including tree-ring data. the study of lake and ocean sediments. and analysis of Greenland ice cores.

The primary purpose of the passage is to

summarize a scholarly debate about a particular phenomenon discuss a shift in scholarly views of a particular phenomenon note a discrepancy in the data supporting an account of a particular phenomenon present an unexpected finding about the causes of a particular phenomenon dispute the relevance of the evidence on which a long-standing view of a particular phenomenon has been based

正确答案： B 耗时：