Unusual climate in northwest Europe during the period 1730 to 1745 based on instrumental and documentary data

This study focuses on one of the most interesting times of the early instrumental period in northwest Europe (from 1730–1745) attempting to place the extremely cold year of 1740 and the unusual warmth of the 1730s decade in a longer context. The similarity of the features in the few long (and independent) instrumental records together with extensive documentary evidence clearly indicates that remarkable climatic changes occurred rapidly in this period. We use unpublished subjective circulation charts developed by the late Hubert Lamb, to assist in understanding the course of events, particularly during the extreme year of 1740 and the four subsequent years. We also compare these subjective charts with others recently developed using more objective modern reconstruction techniques. Apart from evidence of a reduction in the number of explosive volcanic eruptions following the 1690s, it is difficult to explain the changes in terms of our knowledge of the possible factors that have influenced this region during the 19th and 20th centuries. The study, therefore, highlights how estimates of natural climatic variability in this region based on more recent data may not fully encompass the possible known range.