Baltic Earth Working Group on Climate variability and teleconnections

• How does large-scale climate variability, particularly from the North Atlantic, influence the climate of the
  Baltic Sea region across synoptic to multidecadal timescales?
• How will ongoing global warming modify key teleconnection patterns and their impacts on the Baltic
  Sea region?
• How can improved understanding of teleconnections enhance predictability of extreme events and
  regional climate projections?

Climate change manifests differently across regions, with some experiencing faster warming, altered precipitation regimes, or more frequent extreme events. Understanding regional impacts, and how these evolve under different socio-economic pathways, is therefore increasingly important. While large global model ensembles perform well for global-scale metrics, they often show substantial divergence at regional scales, even producing opposite signs of change for variables such as precipitation. This highlights the need for a focused assessment of regional climate variability and its drivers. Previous BALTEX and Baltic Earth efforts have produced downscaled regional simulations for the Baltic Sea region, but a dedicated focus on how global climate variability connects to North European climate across different timescales has been lacking. Meanwhile, the number and quality of global and regional atmospheric reanalysis products have increased significantly, some extending back more than a century, enabling the study of low-frequency variability that was previously inaccessible. Teleconnections from the North Atlantic strongly shape the climate of the Baltic Sea region. The North Atlantic Oscillation (NAO) influences winter temperatures, storm tracks, and precipitation patterns, while the Atlantic Meridional Overturning Circulation (AMOC) affects heat and salinity distributions. On shorter timescales, synoptic and intraseasonal variability driven by pressure systems and wind patterns produces pronounced seasonal and interannual variability. Understanding how these large-scale modes interact with regional atmospheric dynamics is essential for assessing climate variability and predicting extreme weather events. Several important knowledge gaps remain. The detailed mechanisms linking North Atlantic variability to the Baltic Sea region, particularly on decadal and multidecadal timescales, are not fully understood; for example, the specific pathways through which changes in AMOC influence regional climate patterns remain unclear. The effects of climate change on established teleconnections are also uncertain, including how the frequency and intensity of modes such as the NAO and changes in jet-stream behaviour will evolve under future scenarios. In addition, the interactions between large-scale teleconnections and local climatic and oceanographic factors – such as land–sea contrasts, topography, and regional circulation – are not well documented. The role of teleconnections in modulating extreme events and compound events, where multiple factors combine to produce severe outcomes, is another area requiring deeper investigation. Furthermore, the influence of teleconnection-driven physical variability, particularly regarding salinity, temperature, and nutrient cycles, on biogeochemical processes and marine ecosystems in the Baltic Sea is poorly understood. Finally, current climate models have limitations in simulating teleconnections and their regional impacts, underscoring the need for improved resolution and more advanced modelling strategies. The overarching objectives of RT1 are to deepen understanding of the mechanisms linking global and North Atlantic climate variability to the Baltic Sea region; to determine how ongoing global warming is likely to alter these teleconnections across different timescales; and to enhance the capacity of regional climate models to simulate these interactions and their impacts. A further objective is to integrate physical, biogeochemical, and ecosystem perspectives in order to develop a more comprehensive basis for predicting climate variability, extreme events, and long-term changes affecting the Baltic Sea region.

Potential activities include assessing the quality of global simulations used for dynamic downscaling in the Baltic Sea region, and investigating global datasets such as ERA-20C or ERSST to identify energy and mass transports into the Baltic Sea catchment. Work will also focus on improving climate predictability and forecasts for Northern
Europe by developing regional criteria linked to large-scale climate processes, including storm tracks, blocking events, and ocean–satmosphere interactions in the North Atlantic. Another important activity is examining how dynamically driven climate variability, such as jet-stream fluctuations originating far outside the region, propagates toward the Baltic Sea. Further efforts include identifying teleconnections between the North Atlantic and other critical remote regions and the Baltic Sea region across timescales from synoptic to decadal or centennial, and analysing how changes in atmospheric mass and energy flow over Europe under future climate conditions may affect the Baltic Sea and its catchment.