Eight Hundred Years of North Atlantic Jet Stream Variability and its Influence on European Climate Extremes

A recent increase in mid-latitude extreme weather events has been linked to anomalies in the position, strength, and waviness of the Northern Hemisphere polar jet stream. The latitudinal position of the North Atlantic Jet (NAJ) in particular drives climatic extremes over Europe, by controlling the location of the Atlantic storm track and by influencing the occurrence and duration of atmospheric blocking. To put recent NAJ trends in a historical perspective and to investigate non-linear relationships between jet stream position, mid-latitude extreme weather events, and anthropogenic climate change, long-term records of NAJ variability are needed. Here, we combine two tree-ring based summer temperature reconstructions from Scotland and from the Balkan Peninsula to reconstruct inter-annual variability in the latitudinal position of the summer NAJ back to 1200 CE. We find that over the past centuries, a northward summer NAJ position has resulted in heatwaves in northwestern Europe, whereas a southward position has promoted wildfires in southeastern Europe and floods in northwestern Europe. The great famine of 1315-1317 in northwestern Europe, for instance, was associated with prolonged flooding and cold summers that resulted in failed grain harvest and were related to a southern NAJ position. We further find an unprecedented increase in NAJ anomalies since the 1960s, which supports more sinuous jet stream patterns and quasi-resonant amplification as potential dynamic pathways for Arctic warming to influence midlatitude weather.