Reading this chart: the cross-ocean temperature gap over time

• At comparable latitudes, Western European cities tend to be substantially warmer than US East Coast cities, a difference largely attributed to heat transported across the Atlantic by the Gulf Stream system. This chart tracks whether that temperature differential is changing over time, which would serve as one observational test of AMOC weakening.
• At ~40°N (orange line, roughly New York / Lisbon latitude), the gap has narrowed by approximately −0.82 °C from the 1966–1990 mean to the 2010–2025 mean. This reduction is consistent with declining Gulf Stream heat delivery, though changes in regional land-use, urban heat, and atmospheric circulation may also contribute.
• The ~45°N band (red, New England / northwest France) shows wider year-to-year swings associated with North Atlantic Oscillation variability, with no sustained narrowing trend apparent, suggesting that any AMOC-related signal may not be spatially uniform across latitudes.
• The shaded blue region marks the post-2006 era identified in recent AMOC research as a period of potentially accelerated weakening. The ~40°N gap shows its most consistent decline within this era.
• Filled shading between each rolling-average line and its dashed 1966–1990 baseline visualizes the accumulated departure: a widening filled area below the baseline indicates the warming anomaly is diminishing relative to the reference period.