Conceptually, this is just about that warming a body of water from above tends to result in a thin layer of warm water sitting atop the larger colder body. Any

Conceptually, this is just about that warming a body of water from above tends to result in a thin layer of warm water sitting atop the larger colder body. Anyone who has gone swimming in a temperate lake in summer will experience this; there's a thin warm layer on top. This greatly reduces mixing with the lower body. In winter, such lakes typically 'overturn', i.e. the temperature gradient disappears and the surface water mixes freely with the deep water. A feature of a shallower warm layer with less deep mixing in the ocean is that it's going to be more susceptible to atmospheric forcing (clouds blocking sunlight, or winds driving surface currents, or a warm wet air mass driving heating). This paper presents modeling runs in support of that hypothesis. Since long-term (months) climate forecasts (El Nino estimates etc) rely heavily on sea surface temperature forecasts (SSTs being fixed data fed into short-term forecasts), this will reduce the accuracy of the long-term forecasts (but not of the short-term forecasts, which are based in part on real-time satellite measurements of SSTs). One of the more likely long-term effects of this shallower, warmer mixed layer is a reduction in deep-ocean mixing rates, and what that means is less oxygen gets delivered to the deep ocean, so oceanic anoxia and hypoxia events are more likely to become widespread over time. This is a complex situation, however, as nutrient inputs (i.e. fertilizer runoff from intensive agriculture) can cause a massive drawdown of oxygen in the deeper ocean, due to amplification of local biological breakdown of biomass. https://oceanservice.noaa.gov/podcast/feb18/nop13-hypoxia.html https://oceanservice.noaa.gov/podcast/feb18/nop13-hypoxia.ht... Global oceanic anoxia events have happened in the past, but would really require hundreds-to-thousands of years to develop; what we see now are more regional events linked to the dieoff of large numbers of bottom-dwelling animals. We are definitely headed in that direction under current practices, however: https://en.wikipedia.org/wiki/Ocean_deoxygenation https://en.wikipedia.org/wiki/Ocean_deoxygenation