Abstract

The reconstruction of the North Atlantic Jet Stream (NAJ) presents a critical paleoclimatic target, albeit largely unconstrained. Models suggest northward migration and variation in the variance of the NAJ in 21st century warming scenarios, but assessment of the significance of such projections is hampered by a lack of long-term observations. Here, we integrate information from a set of climate model simulations using water isotopes from the last millennium and a wide range of mean annual water isotopes (

O) and the snowfall records accumulated each year from Greenland ice cores to reconstruct the mean zonal winds of the North Atlantic up to the 8th century CE. Using this reconstruction, we provide pre-observational constraints on both the annual average position and intensity of the NAJ to show that the variations in the NAJ at the end of the 20th and the beginning of the 21st century were probably not not unique compared to natural variability. On the contrary, information from our 1,250-year reconstruction highlights the preponderant role of natural variability in masking so far the response of mid-latitude atmospheric dynamics to anthropogenic forcing, consistent with recent transient modeling experiments. to large group. However, this masking is not expected to persist in high greenhouse gas emissions scenarios, with the projected annual average position of the NAJ model emerging as distinct from the natural variability range reconstructed as early as 2060 CE.