Temperature-based diagnosis of the Gulf Stream path overestimates its northward shift in a warming ocean

Abstract. Temperature-based criteria for diagnosing the location of the Gulf Stream (GS) are widely used and suggest a northward shift of the GS is underway. The apparent northward shift in the GS path has been causally linked to the recent rapid warming in the northwest Atlantic Ocean. This study uses high-resolution climate models to show that temperature-based criteria for diagnosing the GS path overestimate its northward shift in warming scenarios and, for one of the models, indicate a northward shift that does not occur. In contrast, a sea surface height (SSH)-based criterion for diagnosing the GS path remains closely aligned with the true GS core in a warming ocean and thus provides a more reliable estimate of shifts in its path. The temperature-based assessments are biased by the rising background temperature in the ocean, thus creating a misleading indication of a GS migration. These results call into question the notion that warming in the northwest North Atlantic is causally related to a northward migration of the GS and emphasize the need for more robust indicators of its position.