Quantitative summer-temperature reconstructions for the last 2000 years based on pollen-stratigraphical data from northern Fennoscandia
Quantitative reconstructions of mean July temperatures (Tjul) based on new and previously published pollen-stratigraphical data covering the last 2000 years from 11 lakes in northern Fennoscandia and the Kola Peninsula are presented. Tjul values are based on a previously published pollen-climate transfer function for the region with a root-mean-square error of prediction (RMSEP) of 0.99°C. The most obvious trend in the inferred temperatures from all sites is the general decrease in Tjul during the last 2000 years. Pollen-inferred Tjul values on average 0.18 ± 0.56°C (n = 91) higher than present (where “present” refers to the last 3 decades based on comparison pollen-inferred Tjul in core-top samples) are inferred between 0 and 1100 AD (2000-850 cal yr BP), and temperatures -0.2 ± 0.47°C (n = 78) below present are inferred between 1100 and 1900 AD (850-50 cal yr BP). No consistent temperature peak is observed during the ‘Medieval Warm Period’, ca. 900-1200 AD (1100–750 cal yr BP), but the cooler period between 1100 and 1900 AD (850-50 cal yr BP) corresponds in general with the ‘Little Ice Age’ (LIA). Consistently with independent stable isotopic data, the composite pollen-based record suggests that the coldest periods of the LIA date to 1500 – 1600 AD (450-350 cal yr BP) and 1800 – 1850 AD (150–100 cal yr BP). An abrupt warming occurred at about 1900 AD and the 20th century is the warmest century since about 1000 AD (950 cal yr BP).