Documentary Evidence

Abstract

This section begins with a review of the current state of knowledge concerning the variability of climate in Poland in historical times. A summary and review of different kinds of documentary evidence (e.g. annals, chronicles, diaries, private correspondence, records of public administration, early newspapers) which were used for Poland’s climate reconstructions, are given. Finally, the main findings are summarized in brief.

The existing, incomplete and somewhat unreliable reconstructions of the Polish climate in the last millennium indicate that the first 500 years (and particularly the first 300 years) were warmer than the latter 500 years. It was mainly winters which were warmer, whereas summers could be even cooler. Thus it can be regarded as a period during which a high degree of oceanism influenced the Polish climate. In Polish climatic history we can therefore distinguish a so-called Medieval Warm Period, which most probably lasted until the fourteenth–fifteenth centuries. Air temperature was then most probably higher on average by about 0.5°C–1.0°C.

Thermal conditions in winter throughout the entire period from 1501 to 1840 were colder than the air temperature of the twentieth century. The coldest decades (with anomalies lower than or near 3°C in relation to the 1901–1960 mean) were as follows: 1741–1750, 1541–1550, 1571–1580, 1591–1600, 1641–1650, and 1771–1780. On the other hand, “historical” summers were mainly warmer than those occurring in the twentieth century. Such situations dominated in the sixteenth and seventeenth centuries, as well as at the turn of the eighteenth and nineteenth centuries. Throughout almost the entire period from 1501 to 1840, the thermal continentality of the climate in Poland was greater than in the twentieth century.

Significantly less historical information describing precipitation conditions in Poland has been collected in comparison with that describing air temperature. In the period from 1501 to 1840, wet winters dominated mainly in the periods 1501–1550 and 1701–1750. Very little information exists for dry winters. Their frequency of occurrence was probably greatest in the sixteenth century. Markedly more weather notes concerning precipitation conditions have been found for the summers than for the winters. Wet summers occurred mainly in the sixteenth century, in the period from 1730 to 1750, and at the beginning of the nineteenth century. Dry summers were most often observed in the sixteenth century.