Two SST products gave positive summer-minus-winter trend estimates south of Greenland in 1950-2024

We tested summer and winter sea surface temperature (SST) trends at 50-60 N, 50-20 W in two monthly data products. In 1950-2024, the June-August minus December-February trend was 0.0588 C per decade in ERSSTv5 and 0.0650 C per decade in HadISST1. The 95% five-year block intervals were -0.0007 to 0.1185 and 0.0097 to 0.1198 C per decade. Thus the estimates agreed in sign, but the primary intervals did not both exclude zero. All planned checks gave positive point estimates. Some intervals included zero, and the product with an interval above zero changed in the 1982-2024 check. Annual mean trend intervals included zero in both products. The result supports a test of seasonal change where annual means have weak trends. It does not prove a change in ocean circulation or establish a cause. The products share observations. Time range, native grid support, reconstruction error and the block model limit inference. The package gives monthly means, annual values, code, source hashes, all uncertainty draws, a figure and numerical checks.

sea surface temperature · seasonal contrast · North Atlantic · south Greenland · ERSSTv5 · HadISST1 · block bootstrap