Composite monthly mean temperature time series for Iceland reaching back to the late 18th century.

Composite record of monthly mean temperatures is presented for Iceland. It is based on over ten series of temperature observations, covering a time interval from 1779 to present. It represents the major temperature variations in Iceland during the last centuries. The longest continuous temperature record in Iceland comes from Stykkishólmur. The observations started in November 1845, by Árni Thorlacius, a merchant in the village of Stykkishólmur. It marks a watershed in the history of meteorological observations in Iceland, with observations at the site continuing to the present. The composite Icelandic time series prior to 1845 is reconstructed using observations from several other locations in the country. Observations of relatively good quality exist from Reykjavík, from 1820 to 1854, made by Jón Thorsteinsson in cooperation with the Danish Scientific Society. There is a strong relationship between the temperature observations at Stykkishólmur and Reykjavík during the overlapping period. Before that time comes the least reliable part of the series. Several short discontinuous series of measurements exist from the late eighteenth century to early nineteenth century from various locations in the country. The observations were in the hands of enthusiastic individuals during this time and the quality of them is very variable. Although the confidence in the reconstruction in the oldest part of the series is low, it gives valuable estimate of the yearly and seasonal temperature variations during this time. Overall, the data show a warming trend, but with significant multi-decadal variability. The temperatures in the 19^th century are lower and the variations are much greater than in the 20^th century. It corresponds to years when sea ice was observed at the coast and the temperature variations are larger when there a is more irregular sea-ice influence.