European winter climate storylines based on changes in the North Atlantic jet stream’s eastward extension

The North Atlantic jet stream is generally projected to shift poleward and extend eastward in winter in response to global warming. However, the spread of climate model projections of the jet stream changes is large, causing substantial uncertainty in projections of future European climate. The uncertainty in changes of surface variables such as precipitation may be better understood by forming storylines of jet stream changes. Storylines are defined here as physically self-consistent unfoldings of future events. They are often formed by regression with possible remote drivers of circulation changes, such as sea surface warming patterns. However, the regression framework leads to a long chain of causality from drivers to effects of circulation changes. Here, we utilize a novel method for forming storylines of European future climate based directly on relevant jet stream changes using k-means clustering. We cluster the 850 hPa zonal wind field changes in 303 simulations from 50 models in the sixth phase of the Coupled Model Intercomparison Project (CMIP6). The aim of this work is to form storylines of different possible types of North Atlantic jet stream changes to understand the spread of European winter climate projections by the end of the century in CMIP6 simulations. We investigate changes in precipitation, surface air temperature, solar radiation, and surface wind speed due to their connections to renewable energy resources.

We find that the most important North Atlantic jet stream changes for European winter climate are related to the eastward extension of the jet over Europe. We form four clustering-based storylines characterized by different levels of intensification and poleward shift of the eastward extension. These storylines capture a major part of the climate projection uncertainty in Europe. The storyline with the strongest extension intensification projects the strongest wettening in northern Europe and strongest surface wind speed increase in western Europe, while the storyline with the strongest poleward shift of the extension projects the weakest wettening and strongest increase in solar radiation in western Europe. Our results highlight the interconnections between future changes in different variables and in different parts of Europe.