No Internal Connections Detected Between Low Frequency Climate Modes in North Atlantic and North Pacific Basins

Previous studies documented possible connections between low frequency climate modes in the Northern Hemisphere ocean basins. We use observed sea surface temperatures and 270 large ensemble climate model simulations, which allows for improved methods of separating external and internal variability, such as removing the ensemble mean from each simulation. Detrending methods for observations have also improved since some of these previous studies were conducted. We also devise a modified statistical test using bootstrapping that is tuned specifically to this analysis. With these tools, we reexamine relationships among these modes. While previous studies have argued for the existence of an inter‐basin link, our results suggest that any internal connections between these modes are indistinguishable from random noise. Further, we show that external forcing affects each region in similar ways. This suggests that anthropogenic warming can cause an indirect link between the two basins, confounding the interpretation of a potential relationship. Plain Language Summary We reexamine possible connections between climate patterns in the North Atlantic and North Pacific oceans. Improved climate model simulations and appropriate statistical methods allow us to build on previous research of these linkages. In contrast to previous studies, no natural connections are detected. However, global warming is shown to affect each region in similar ways, suggesting that climate change could cause an indirect link between the two basins. Key Points A multi model large ensemble archive and modified statistical assumptions provide a framework for studying climatic relationships An analysis of relationships between leading Northern Hemisphere climate modes does not show any internal connections External forcing such as global warming is shown to be a possible confounding factor in climate relationships