INTERNATIONAL JOURNAL OF CLIMATOLOGY Int. J. Climatol. 21: 285–298 (2001) DOI: 10.1002/joc.611 INSTRUMENTAL PRESSURE OBSERVATIONS AND ATMOSPHERIC CIRCULATION FROM THE 17TH AND 18TH CENTURIES: LONDON AND PARIS V.C. SLONOSKY b,c, *, P.D. JONES a and T.D. DAVIES a a Climatic Research Unit, Uniersity of East Anglia, Norwich, NR47TJ, UK b Laboratoire des Sciences du Climat et de l’Enironnement, LSCE-Orme, Orme -des -Merisiers, 91191 Gif -sur -Yette, Cedex France c Climate Research Branch, Meteorological Serice of Canada, 4905 Dufferin Street, Downsiew, Ontario, Canada M3H 5T3 Receied 18 December 1999 Reised 25 August 2000 Accepted 31 August 2000 Published online 22 February 2001 ABSTRACT Daily pressure observations recorded by William Derham (1657 – 1735) at Upminster, Essex (near London), from 1697 to 1706 and 1708 have been corrected, converted to modern units and the Gregorian calendar, and adjusted for homogeneity. These pressure readings have been compared with previously published contemporary observations from Paris, and the two sets of early instrumental data used to calculate a daily series of the pressure difference between Paris and London. Frequency analysis of the daily series reveals that reversals of the south – north pressure gradient and easterly winds were more common from 1697 to 1708 than during the 1990s. Monthly mean values of Paris – London pressure differences have been compared with previously published monthly mean reconstructed surface pressure maps and to a reconstructed North Atlantic Oscillation (NAO) index. There is a good agreement between the strength and direction of monthly mean flow between London and Paris estimated from the circulation maps and the sign and magnitude of the Paris–London westerly flow index, but the correlation between the Paris – London index, known to be a good proxy for European zonal circulation, and the reconstructed NAO index, is low (0.2). Correlations between the monthly mean Paris – London zonal circulation index and central England temperatures suggest a strong relationship during winter and late summer from 1697 to 1708. The meticulous daily instrumental observations and the monthly and seasonal climate descriptions of Derham, his collection of instrumental observations and climatic descriptions from contemporary observers throughout Europe, and his early theories on the causes of climate change make his publications a valuable source of information for studies on climate during the early instrumental period. It is hoped that more of Derham’s papers related to weather and climate may eventually come to light. Copyright © 2001 Royal Meteorological Society. KEY WORDS: atmospheric circulation; climate variability; early instrumental data; Europe; historical climatology; Late Maunder Minimum; Little Ice Age; sea-level pressure; William Derham 1. INTRODUCTION The study of climate change has become more popular in recent times as a result of increasing concern regarding the effect of human activity on the climate system. Increasing amounts of carbon dioxide and other greenhouse gases emitted into the atmosphere as a result of human economic activity, as well as changes to the Earth’s land surface, such as deforestation or desertification, have prompted the concern that global temperatures are rising owing to anthropogenically-induced climate change. Climate, however, displays a large amount of natural variability, ranging from astronomically-induced Ice Ages on the millennial time scale to interannual variability generated through atmosphere – ocean interactions, such as the El Nin˜ o – Southern Oscillation, so that an unambiguous signal of anthropogenic climate change is difficult to detect. Moreover, the natural variability of climate may add to or detract * Correspondence to: Climate Research Branch, Meteorological Service of Canada, 4905 Dufferin Street, Downsview, Ontario, Canada M3H 5T3; e-mail: Vicky.Slonosky@ec.gc.ca Copyright © 2001 Royal Meteorological Society