INTERNATIONAL JOURNAL OF CLIMATOLOGY Int. J. Climatol. 25: 773–791 (2005) Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/joc.1149 TEMPERATURE CHANGES IN POLAND FROM THE 16TH TO THE 20TH CENTURIES RAJMUND PRZYBYLAK, a, * JACEK MAJOROWICZ, b,c GABRIEL W ´ OJCIK, a ANDRZEJ ZIELSKI, d WALDEMAR CHOR ¸ A ˙ ZYCZEWSKI, e KAZIMIERZ MARCINIAK, a WIESLAW NOWOSAD, e PIOTR OLI ´ NSKI e and KRZYSZTOF SYTA e a Nicolaus Copernicus University, Department of Climatology, Danielewskiego 6, PL 87-100 Toru´ n, Poland b Northern Geothermal Cons. Ltd, 105 Carlson Close, Edmonton, AB T6R 2J8, Canada c Department of Geology and Geological Engineering, University of North Dakota, Northern Plains Climate Research Centre, Grant Forks, ND, USA d Nicolaus Copernicus University, Dendrochronological Laboratory, Gagarina 9, PL 87-100 Toru´ n, Poland e Nicolaus Copernicus University, Institute of History and Archival Sciences, Pl. Teatralny 2a, PL 87-100 Toru´ n, Poland Received 23 July 2004 Revised 12 November 2004 Accepted 12 November 2004 ABSTRACT A standardized tree-ring width chronology of the Scots pine (Pinus sylvestris L.) along with different types of documentary evidence (e.g. annals, chronicles, diaries, private correspondence, records of public administration, early newspapers) have been used to reconstruct air temperature in Poland. The ground surface temperature (GST) history has been reconstructed based on the continuous temperature logs from 13 wells, using a new method developed recently by Harris and Chapman (1998; Journal of Geophysical Research 103: 7371–7383) which is compared with the functional space inversion (FSI) method applied to all available Polish temperature–depth profiles analysed before. Response function calculations conducted for trees growing in Poland (except in mountainous regions) reveal a statistically significant correlation between the annual ring widths of the Scots pine and the monthly mean air temperatures, particularly from February and March, but also from January and April. Therefore, it was only possible to reconstruct the mean January–April air temperature. The following periods featured a warm late winter/early spring: 1530–90, 1656–70 (the warmest period), 1820–50, 1910–40, and after 1985. On the other hand, a cold January–April occurred in the following periods: 1600–50, 1760–75, 1800–15, 1880–1900, and 1950–80. Reconstructions of thermal conditions using documentary evidence were carried out for winter (December–February) and summer (June–August) from 1501 to 1840 and, therefore, their results cannot be directly compared with reconstruc- tions based on tree-ring widths. Winter temperatures in this period were colder than air temperature in the 20th century. On the other hand, ‘historical’ summers were generally warmer than those occurring in the 20th century. Such situations dominated in the 16th and 17th centuries, as well as at the turn of the 18th and 19th centuries. Throughout almost the entire period from 1501 to 1840, the thermal continentality of the climate in Poland was greater than in the 20th century. GST reconstructions show that its average pre-instrumental level (1500–1778) is about 0.9–1.5 ° C lower than the mean air temperature for the period 1951–81. Lower amplitude of GST warming (0.9 ± 0.1 ° C) results from the individual and simultaneous inversions of well temperature data using the FSI method. A very good correspondence of the results has been found between series of annual mean GSTs from the FSI method and mean seasonal air temperatures reconstructed using documentary evidence. Copyright  2005 Royal Meteorological Society. KEY WORDS: Poland; temperature variability; proxy data; temperature reconstructions 1. INTRODUCTION Our present knowledge concerning temperature changes in Poland for the last 500 years is somewhat piecemeal in character. It is obvious that it is best for the instrumental period. In the last decade of the * Correspondence to: Rajmund Przybylak, Department of Climatology, Danielewskiego 6, PL 87-100 Toru´ n, Poland; e-mail: rpll@geo.uni.torun.pl Copyright  2005 Royal Meteorological Society