In this paper , Jia-Rui Shi and co-authors present scientific evidence indicating that a human-caused signal has already emerged in the seasonal cycle amplitude of Sea Surface Temperature (SST), distinct from the background noise of natural variability. The geographical patterns of the forced SST seasonal cycle change reveal two notable features: an increase in mid-latitudes of the Northern Hemisphere, which is associated with alterations in mixed-layer depth, and a robust dipole pattern in the Southern Hemisphere mid-latitudes, primarily driven by changes in surface winds. These observed changes in the SST seasonal cycle have significant implications for marine ecosystems.