Natural variability masks climate change sea surface temperature signals: a comparison between the Baltic Sea, North Sea and North Atlantic Ocean

Abstract Climate variability in marine environments, particularly sea surface temperature (SST), is influenced by natural fluctuations occurring at various temporal and spatial scales. Distinguishing between anthropogenic climate change trends and natural variability is crucial for understanding the complex dynamics of ocean temperatures. This study applies the concept of Time of Emergence (ToE) to estimate when the signal of long-term climate change becomes distinguishable from natural variability in SST for different seasons. The study focuses on the North Sea, Baltic Sea, and North Atlantic Ocean, utilizing 30 ensemble members of simulation from a regional climate model system, MPIOM-REMO, with slightly different initial conditions. The results reveal that winter ToEs emerge earlier than summer ToEs in all study areas, mainly driven by larger winter SST changes and show that shallow coastal seas like the North and Baltic Seas experience earlier ToEs than the deep central North Atlantic. These findings emphasize the influence of regional processes, such as sea ice dynamics and changes in stratification, on the spatial and temporal variability of ToE patterns.