A Tale of 2 Opposing Ocean Warming Narratives! – Watts Up With That?

by Jim Steele

There are 2 narratives claiming to explain most of the observed ocean warming. One suggests recent ocean warming has been totally driven by human emissions that amplified the greenhouse effect. That narrative is supported the correlation with rising CO2 that blankets the globe. The second suggests the El Niño-Southern Oscillation (ENSO) and solar heating have conspired to warm the oceans. This 2nd narrative is supported by data illustrated in NOAA’s graphic (A) of ocean heat flux, with more heat entering into the eastern tropical Pacific and Atlantic (yellow) than is released. That high heat flux region is moderated by ENSO and Pacific Decadal Oscillation (Graphic E). The white regions show no net heat flux into a quarter of the ocean surfaces. Such observations do not support the first narrative of homogeneous warming from a thickening CO2 blanket.

Wherever there is a greater flux of heat into the ocean than ventilates out, the oceans will warm. All scientists agree that any absorbed heat can only be ventilated away through the ocean’s cool skin surface which is just 2-10 microns thick.

Coincidentally, greenhouse infrared heat only penetrates a few microns into that skin surface. Thus, any infrared warming of the skin surface can be quickly radiated back to space. Any warming of the skin surface also increases evaporation which further cools the ocean. Finally, 99% of the time the skin surface is warmer than the layer of air immediately above and so warms the air. Those 3 dynamics make ocean warming by greenhouse gases relatively insignificant. In contrast, because solar heat penetrates the subsurface where it cannot radiate away, solar heating is more capable of heating the ocean.

Oceans can store heat for longer periods of time wherever saltier water is overlaid by fresh water. That condition creates what is known as a subsurface barrier layer that inhibits normal upwards convection of heated water to the skin layer for ventilation. Because a salty barrier layer is more dense it doesn’t rise with limited subsurface heating.

The natural Hadley circulation causes rising moist air around the equator and sinking dry air in latitudes north and south of the equator. That causes high rates of evaporation but reduced precipitation in those latitudes (yellow regions in graphic B) which causes relatively saltier ocean water. As the Trade Winds are pulled towards the equator, they also curl westward driving the saltier ocean water and atmospheric water vapor towards the equator and westward. Where the northern and southern trade winds converge, the Intertropical Convergence Zone forms (blue equatorial region) creating a zone of concentrated water vapor and the greatest rainfall. The freshwater rainfall caps the saltier subsurface water resulting in tropical barrier layers that trap heat which then is redistributed around the globe (graphic C).

The tropics register cooler temperatures than solar heating predicts, while temperatures outside the tropics are warmer than predicted (Graphic D) Although the tropics receive the greatest amount of solar heating, they gain a “surplus” of heat that does not increase air temperatures while stored in the subsurface layers. Ocean currents carry that surplus heat pole-wards into cooler waters. There, it’s easier for heated subsurface waters to rise to the skin surface and ventilate any stored heat (blue regions in graphic A). That ventilation allows air temperatures outside the tropics to be warmer than predicted.

Still, for narrative 2 to best explain the observed ocean warming trend, there must be an increase in absorbed solar heat in the eastern Pacific and eastern Atlantic. Believers in the CO2 narrative dismiss such increased solar heating by simply pointing to the sun’s decreasing solar irradiance. However, observed decreases in cloud cover increase solar heating. A La Nina event and the 20 to 30-years of a La Nina-like (negative) Pacific Decadal Oscillation (Graphic E) create a cooler eastern Pacific that reduces cloud cover and increases solar flux into the ocean.

Furthermore, the increased east-west temperature difference during La Nina-like conditions amplifies the Trade Winds’ intensity. The stronger winds increase the transport of warm surface and subsurface water into the western Pacific where it can be stored down to 200-meter-depths (Graphic F) until ventilated by an El Nino event, as well as supplying heat to the Indian Ocean (Sprintall 2014) or into poleward currents. More warm water transport raises global temperatures. This is why Jones (2022) refers to these dynamics as the Pacific Ocean Heat Engine.

During El Nino events and a positive Decadal Oscillation, a cloudier eastern Pacific and weaker Trade Winds results in ocean cooling. El Nino-like conditions dominated during the Little Ice Age. The switch to more La Nina-like conditions since 1850 increased heat flux and heat redistribution that has contributed to modern warming. La Nina-like redistribution of heat also explains why NOAA doesn’t observe an increase in heat content in the eastern Pacific (gray regions Graphic G) but observes increased heat content in the western Pacific.

Finally, scientists integrating heat and salt transport from all ocean currents construct an Ocean Conveyor Belt that carries warm water from the Pacific, through the Indonesian Island passages into the Indian Ocean, around southern Africa into the Atlantic and northward into the Arctic (Graphic H). The Ocean Conveyor Belt explains why the Atlantic is warmer and saltier. The Conveyor Belt also explains reduced Arctic sea-ice. Where warm Atlantic water first enters the Arctic accounts for most of the observed lost sea ice inside the Arctic Circle. A thick layer of warm Atlantic water exists 100 to 900-meter depths (Graphic I). It slowly ventilates its heat through the insulating sea ice, but open water ventilates 35 times more heat than greenhouse warming, causing the Arctic temperature to be 3 times warmer than the global average.