Warmer sea surface temperatures are largely caused by global warming, which is primarily caused by the burning of fossil fuels.
Every few years, a naturally occurring weather phenomenon, El Niño, warms the ocean surface in the southern Pacific, causing hot weather globally. The current El Nino is expected to peak in 2024.
In contrast, a mirror phenomenon called La Niña helps cool the ocean surface from time to time.
Rising water temperatures and ocean salinity – also at all-time highs – directly contribute to the process of “stratification”, where water separates into layers that no longer mix.