A decade of cold Eurasian winters reconstructed for the early 19th century

A cold season climate reconstruction for the northern midlatitudes based on freezing and thawing dates of rivers shows a cold spell 1808/9-1815/6 affecting Eurasia. In addition to two volcanic eruptions, increased snow cover played an important role. Annual-to-decadal variability in northern midlatitude temperature is dominated by the cold season. However, climate field reconstructions are often based on tree rings that represent the growing season. Here we present cold-season (October-to-May average) temperature field reconstructions for the northern midlatitudes, 1701-1905, based on extensive phenological data (freezing and thawing dates of rivers, plant observations). Northern midlatitude land temperatures exceeded the variability range of the 18th and 19th centuries by the 1940s, to which recent warming has added another 1.5 degrees C. A sequences of cold winters 1808/9-1815/6 can be explained by two volcanic eruptions and unusual atmospheric flow. Weak southwesterlies over Western Europe in early winter caused low Eurasian temperatures, which persisted into spring even though the flow pattern did not. Twentieth century data and model simulations confirm this persistence and point to increased snow cover as a cause, consistent with sparse information on Eurasian snow in the early 19th century.

Automated summary

A reconstruction of the cold season climate in the northern midlatitudes based on freezing and thawing dates of rivers reveals a cold spell that affected Eurasia from 1808/9 to 1815/6. Alongside two volcanic eruptions, increased snow cover played a significant role in this phenomenon. The study presents temperature field reconstructions for the northern midlatitudes from 1701-1905 using extensive phenological data. The findings show that northern midlatitude land temperatures have exceeded the variability range of the 18th and 19th centuries, with recent warming contributing an additional 1.5 degrees Celsius.