Why the Sun, Not CO2, Heats the Oceans Revisiting the Debate: Does Greenhouse Back-radiation Warm the Oceans?

By Jim Steele – August 1, 2022

Because infrared heat waves penetrates less than a millimeter into the ocean’s surface, many skeptics argued it is impossible to blame rising CO2 for ocean warming. However, several prominent skeptic scientists, people who I have great respect for, also weighed in arguing it was silly and useless to argue infrared heat can’t warm the ocean.

Welcome everyone.

About a decade ago there was a heated and unresolved debate on whether infrared back radiation from greenhouse gases is heating the oceans. Because infrared penetrates less than a millimeter into the ocean’s surface, many skeptics argued it is impossible to blame rising CO2 for ocean warming. However, several prominent skeptic scientists, people who I have great respect for, also weighed in arguing it was silly and useless to argue infrared heat can’t warm the ocean.

After analyzing the physics detailed in this video, I’m convinced it is solar energy that drives the observed ocean heating, and any infrared ocean heating is insignificant at best. If this analysis holds, it is another significant strike against the prevailing CO2 driven global warming theory

To ensure lay people are brought up to speed, here’s a quick summary of where consensus climate science stands today.

Climate scientists construct models of the earth’s energy budget. The amount of energy absorbed by the earth or emitted back to space each second, is measured in Watts and is standardized for an area measuring one square meter. For those unfamiliar with that measurement, simply understand that more Watts signify more energy.

The energy budget illustrated here was published by Stephens 2012. Others have slightly different numbers, but this illustration is one of the best because it is one of the few that lists the range of uncertainties in their measurements.

Because the sun’s surface is so hot it emits high energy shortwave radiation. On average the earth warms as short waves add 75 Watts to the atmospheric water vapor while the earth’s surfaces absorb about 160 Watts, totaling 240 Watts that are heating the earth’s daytime climate.

According to the Stefan-Boltzman law, and remember scientific laws are undisputed, when a surface is heated it causes that surface to respond immediately by releasing an equal amount of energy from that surface.

To maintain the earth’s temperature balance, the 240 Watts of energy from the sun should cause the earth to emit 240 Watts back to space or transfer some of that energy from the surface into the oceans or soils. However, because the earth is so much cooler than the sun, it only emits that energy as longwave infrared waves, which interact very differently with the earth than the sun’s shortwaves.

While some longwaves can escape back to space unimpeded and at the speed of light, other longwaves can be absorbed by greenhouse gases like carbon dioxide and water vapor. Greenhouse gases then re-emit that absorbed energy, and redirect half back towards the earth’s surface. On average the earth’s surface also absorbs an estimated 345 Watts of re-cycled longwave energy which counteracts the rate of cooling and prevents the earth’s nighttime cooling from dropping to the point of global freezing.

However, that longwave energy is not trapped, as many media headlines suggest. Eventually nearly all the energy from the sun escapes back to space. However, the best modeled energy budgets suggest that a slightly less amount of energy radiates back to space relative to what had originally entered from the sun.

Putting aside some large uncertainties, there appears to be a radiative imbalance of 0.6 Watts less energy leaving the earth than is added by the sun. Some researchers estimate that imbalance may be as high as one Watt.

That imbalance does not violate the Stefan-Boltzmann law because that missing heat gets stored below the land surface or below the ocean surface, where the heat cannot radiate back to space in a timely manner.

There is no scientific disagreement that our oceans have been warming since the Little Ice Age ended around 1850 AD. What remains to be debated is, to what degree are oceans naturally warming due to storage of more shortwave energy from the sun, or due to storage of increased downward longwave energy emitted by rising carbon dioxide concentrations.

Some have argued, incorrectly, that the earth’s land surface heats and cools the same as the oceans.

However, in contrast to the ocean, the suns’ shortwave energy doesn’t penetrate soils much deeper than an inch. The combined heating from shortwave & longwave energy plus sensible heat transfer from warm air, increasingly heats soils at the surface reaching summertime highs. Then, primarily via conduction, surface heat slowly passes down the temperature gradient from the warm surface to cooler depths in accord with the second law of thermodynamics. Heat transfer via conduction is slow, so temperatures can remain 8ºC (15 º F) cooler just 10 inches (25 centimeters) below the surface.

During the winter, the colder surface reverses that temperature gradient, so that stored summer heat travels via conduction back to the surface. Again, because surface cooling happens quickly and conduction happens slowly, the deeper soil remains warmer than the surface soil.

Greenhouse longwave energy penetrates only a few microns into the ocean surface and even less into most soils, but the sun’s shortwave energy passes much more deeply into the ocean.

More energetic shortwaves like blue light can penetrate over 100 meters (that’s about 4000 inches) into clear ocean water, with only half its energy absorbed within the first 20 meters. In contrast 50% of less energetic red light is absorbed in just the first few meters. That’s why seaweeds in the deeper ocean cannot use red light to photosynthesize like land plants do.

Although both the heating of the land and ocean depends on surface heating, radiative and convective heating are much more important for heating the ocean. This causes important differences in the way our oceans heat and cool, thus analogies to land surface heating are misleading.

This standard, albeit overly simplistic ocean temperature profile, shows the upper layer of the ocean, often referred to as the epipelagic layer or sunlight layer, extends from the surface to 200 meters depth. Turbulence due to winds and currents mixes and homogenizes the temperature as illustrated here and globally averages 13°C or (55 °F).

Below that mixed surface layer is the thermocline layer, defined as a region of rapidly cooling temperatures, because mixing of warm surface heat into the layers below rapidly declines with depth.

At a depth of about 1000 meters and below there is a more homogeneous temperature of just 4°C or 39°F However, the illustrated homogeneous upper sunlight layer obscures the most important dynamics of the oceans’ surface skin layer that are key to controlling ocean heating and cooling.

A 2018 paper by Wong & Minett analyzed ocean temperatures from data collected during 2 ocean cruises in warm tropical and subtropical waters of the north Atlantic. They reported important differences in heating and cooling patterns in the microns-thick surface skin layer and millimeter thick subsurface layers.

For perspective, the sharpened point of a pencil is about one millimeter wide. It takes one thousand microns to equal just one millimeter. The ocean’s surface gatekeeper is only a couple of microns thick.

Only 4.9 Watts per meter squared of solar energy was absorbed in the first 10 microns. .

In contrast, the subsurface was increasingly heated, so by 10 millimeters deep, 261 Watts of solar energy were absorbed.

Only at the surface can any ocean heat be released back to the atmosphere or space. So, this differential solar heating creates the required temperature gradient that allows the solar heated subsurface water to constantly move up towards the cooler surface.

Heating by longwave energy adds another complication that must be considered. Longwave energy only penetrates the first few microns of the skin layer. And that fact prompts some skeptics to argue CO2 back radiation cannot heat the ocean.

But on the other side of the debate, it is argued that because longwave heating can add 100 times more energy into the skin layer than solar heating, longwave heating can alter and even reverse the temperature gradient required for ocean cooling.

But if true, then how does the ocean ever lose heat.

Nonetheless, the alarmist narrative becomes that added infrared energy must alter the temperature gradient to some degree. Therefore, as more greenhouse gases add more longwave energy to the surface skin layer, it increasingly disrupts the temperature gradient enough to reduce the rate of subsurface cooling. So, rising CO2 is indirectly warming the ocean.

But measurements do not support such narratives.

Satellite measurements determined the oceans’ surface temperature by measuring the longwave radiation emitted from the skin layer. The sub-skin layer below was also measured but via emitted microwaves.

The results show the ocean’s skin layer is always cooler than subsurface layers below, despite the combined surface warming by shortwave and longwave heating plus rising heat from solar heated waters below

In the daytime, there is a deeper solar heated diurnal warm layer. At night, without solar heating, subsurface waters eventually cool and mix with the water below creating a more homogeneous upper layer temperature everywhere except in the cooler skin surface.

No matter the season, or time of day the skin layer is always cooler than the waters immediately below.

Although not intuitive, the constant cool skin surface phenomenon can be explained by the Stefan-Boltzman law. According to that law, when the skin surface layer is heated, by longwave or shortwave energy, the surface skin layer radiates an equal amount of energy back to the atmosphere immediately. Any longwave heating of the skin surface layer is so transitory there is no observable effect on the temperature gradient that’s required to cool the ocean’s solar heated sub-surface layers.

As Wong & Minett’s results illustrated, the micron thick skin layer absorbed 410 Watts of longwave and a negligible amount of shortwave, but simultaneously emitted 470 Watts out of the ocean, maintaining the observed cooler skin layer.

The 470 Watts of longwave-out vs 410 Watts of longwave-in does not violate the Stefan-Boltzman law because the skin surface heating is the combined result of warming from 67 Watts of solar heated water rising from below and the downward longwave radiation from above.

That combined heating also caused the skin surface to lose a total of 7 Watts more from sensible heat loss to the cooler air above via conduction, and more latent heat due to evaporation from the skin surface. Thus, on average the skin surface cooling balances skin surface heating, but the skin surface remains slightly cooler because it radiates heat away faster than subsurface heat can rise from below.

Still their data raises one concern. It is very unusual that their estimated heat loss via sensible and latent heat was a mere 7 Watts of cooling. That is 15 times less than globally averaged ocean cooling rates.

It is well established, that the energy needed to evaporate enough water that’s observed in the earth’s water cycle, oceans must experience over 80 Watts per meter squared of evaporative cooling.

Acknowledging the conundrum that those longwave energies do not penetrate deeper than a few microns and thus cannot warm the oceans directly, the stated intent of Wong & Minett’s analysis was to advance their hypothesis that more co2 longwave energy can still warm the ocean indirectly by reducing the temperature gradient and thus, reduce the rate of cooling of the ocean’s diurnal warm layer.

To support their claim, they argued the absorption of more longwave into the skin layer, did not result in the required increased surface temperature that would immediately increase emissions and balance the longwave energy surface budget.

To that end, they examined the increased longwave heating produced on cloudy days as an analog for the effects of increased longwave heating from rising carbon dioxide.

Their highlighted results illustrated here, show that despite an increase of 40 Watts of longwave heating from cloudy skies, there was no increased cooling via emitted longwave-out and no increased loss of sensible and latent heat so the cooling temperature gradient must have been disrupted. But that would violate the Stefan-Boltzman law, their narrative requires magical thinking.

In reality the Stefan-Boltzman law was never violated. It was simply a bad narrative. Although increased cloud cover did increase longwave heating, cloud cover simultaneously reduced the shortwave solar heating of the layers below the skin surface.

The reason 40 increased Watts of incoming longwave did not also increase outgoing longwave is due to the fact that clouds equally reduced the solar heating of subsurface waters. When long wave and shortwave heating are both considered, the balance between incoming and outgoing heat at the skin surface was maintained as predicted by the Stefan-Boltzman law.

Others have argued that warmth generated by longwave heating of the skin surface would be transported quickly downward by mixing with layers below.

However, downward mixing of the observed cooler skin layer would only cool the warmer subsurface layers. While any mixing that brings warmer subsurface water up to the surface, only enhances its cooling.

Only the mixing of deeper solar- heated subsurface waters with the cooler waters below, carries heat deeper into the ocean. The mixing of solar heated water into deeper layers, then makes solar heat less likely to resurface and cool.

Thus, it is the downward mixing of solar heated waters, not the transitory longwave heating of the skin surface layer that stores energy in the ocean and creates the estimated energy imbalance.

Taking a broader global view, analyses of heat flux into and out of the world’s oceans illustrates where the oceans are warming. Huang’s (2015) illustration of ocean heat flux contradicts claims that a thickening global blanket of CO2 is heating the world’s oceans.

Nearly half of the ocean surfaces, regions colored green, show no net heat flux into or out from the ocean.

The regions of greatest heat flux into the ocean are colored red.

There, the intense tropical heating is further amplified by the reduced cloudiness observed in the tropics, as published in Fasullo and Trenberth’s 2008 study.

Furthermore, the tropical trade winds cause greater upwelling of cold deep water in the eastern Atlantic and eastern Pacific.

Colder waters on the surface can reverse the typical heat flux so that heat flows from the warmer air above into those colder upwelled waters.

The obvious clue to the primary driver of ocean warming is that the regions of greatest solar flux into the ocean are the same regions created by pacific and Atlantic La Ninas. That solar heated water is transported westward and then poleward along ocean currents where the greatest amount heat is vented, (colored dark blue. The Holocene optimum, with temperatures warmer than today happened during perpetual La Nina conditions.

For details on how a solar heated ocean causes our current warming trend, please watch my earlier video: Global warming driven by pacific warm pool, La Nina & ITCZ: an alternative climate change theory or read its transcript.

To date there has been no provable mechanism illustrating how heating from CO2 can heat anything more than the ocean’s skin surface. In contrast the combined climate effects of solar heating, the ITCZ migrations and La Ninas are strongly supported in the peer-reviewed scientific literature.

So, I will ignore the click bait news media’s fear mongering that our oceans are “on the boil” due to rising CO2. There is simply no scientific proof to support such dishonest narratives.

And I will sleep well. There is no climate crisis.

Our democracy depends on a diverse array of good critical thinkers. So, please shun mindless group think.

Instead embrace renowned scientist, Thomas Huxley’s advice Skepticism is the highest of duties and blind faith the one unpardonable sin.

Originally published here at WUWT on 1 August 2022.

Jim Steele is a Member of the CO2 Coalition who was the Director of SFSU’s Sierra Nevada Field Campus from 1984 to 2010 and taught university level classes in ornithology and botany, as well as serving as the Principal Investigator for the Neotropical Migratory Bird Monitoring of Riparian Habitats on the Tahoe National Forest project sponsored by the US Forest Service from 1991 to 2007.

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