In examining the Skeptical Science (SkS) blog essay “How Increasing Carbon Dioxide Heats the Ocean“ written by Rob Painting (an “environmentalist, scuba diver, spearfisherman, kayaker and former police officer” who has “researched climate science, in an amateur capacity, for 4 years” according to his website bio), we learn that (A) the Sun heats the surface layers of the ocean; (B) the heat “trapped” by CO2 at the ocean surface cannot penetrate past the ocean’s hair-thin “skin” layer, meaning that this alleged CO2-induced heat doesn’t enter the ocean itself; and (C) we learn that no empirical observation or physical experiment confirms that CO2 heats the ocean waters, so assumptions about CO2 are necessarily derived using proxy experimental evidence (i.e., clouds) instead.
Let’s review each of these directly quoted points individually.
(A) “Sunlight penetrating the surface of the oceans is responsible for warming of the surface layers.”
(B) “Adding further greenhouse gases to the atmosphere warms the ocean cool skin layer, which in turn reduces the amount of heat flowing out of the ocean. … Greenhouse gases, such as carbon dioxide, trap heat in the atmosphere and direct part of this back toward the surface. This heat cannot penetrate into the ocean itself, but it does warm the cool skin layer, and the level of this warming ultimately controls the temperature gradient in the layer. … Despite being only 0.1 to 1 mm thick on average, this skin layer is the major player in the long-term warming of the oceans.”
(C) “Obviously, it’s not possible to manipulate the concentration of CO2 in the air to carry out real world experiments, but natural changes in cloud cover provide an opportunity to test the principle [that CO2 heats water].”
(A) The Sun heats the oceans’ surface layers
As for the first SkS point (A), indeed the Sun heats the oceans’ surface layers. According to NOAA, the surface layer is referred to as the “sunlight zone” and extends to depths of 200 meters. Further, the Sun directly heats the first 20-30 m of the ocean (the “shortwave attenuation depth”), and the Sun’s irradiance can deposit 2.0 K of heat (500 W/m-2) uniformly in the first 2 m of the ocean in a matter of 12 daylight hours.
“This surface layer is also called the sunlight zone and extends from the surface to 660 feet (200 meters). It is in this zone that most of the visible light exists. With the light comes heating from sun. This heating is responsible for wide change in temperature that occurs in this zone, both in the latitude and each season. The sea surface temperatures range from as high as 97°F (36°C) in the Persian Gulf to 28°F (-2°C) near the north pole. The sea surface temperature also ‘follows the sun’.”
“The incoming solar irradiance, which is absorbed by the upper ocean, is the main energy source in the ocean heat budget, and hence strongly impacts the oceanic thermal structure, heat transport and the global circulations. Shortwave radiation is attenuated exponentially with depth. The attenuation depth (e-folding depth) depends on the wavelength and biogenic components of the water. Traditionally, the water types are classified Jerlov I, IA, IB, II and III (Jerlov, 1976). The shortwave attenuation depth (SWAD) in open oceans (almost Jerlov I) is about 20–30 m, and it decreases with increasing water turbidity, particularly in coastal regions.”
“First, the penetration of solar radiation through the [Pacific warm water pool] mixed is large and is an important component of the [Pacific warm water pool] heat budget. The cruise <Tr(z)> observations indicate that 9.8% of the incident solar radiation penetrates to a depth of 30 m“
“On a clear day the Sun deposits an average of about 500 W/m2 of heat into the ocean over the 12 daylight hours. Roughly half of this heat is absorbed in the upper 2 m. In the absence of mixing this is sufficient heat input to warm this 2-m-deep layer uniformly by 2.0 K. … Measurable warming occurs as deep as 20 m and may persist well past sundown.”
Magnitude of CO2 Radiative Forcing Insufficient to Heat the Oceans
It should be noted here that because CO2 concentrations have risen from 280 ppm to 400 ppm since 1750, the IPCC (2013) has assessed that the total amount of radiative forcing attributed to the CO2 change for the last 265 years combined is less than 2 W/m2 (1.8 W/m2). According to Dr. Roy Clark, this 2 W/m2 of total forcing from CO2 since 1750 is clearly not sufficient to heat the ocean to any detectable degree.
It is simply impossible for the observed increase in downward LWIR flux from a 120 ppm increase in atmospheric CO2 concentration to heat the oceans. The increase in flux from CO2 is nominally 2 W.m^-2 or 0.18 MJ.m^-2 per day. The oceans are heated by the sun – up to 25 MJ m^-2 per day for full tropical or summer sun. About half of this solar heat is absorbed in the first 1 m layer of the ocean and 90% is absorbed in the first 10 m layer. The heat is removed by a combination of wind driven evaporation from the surface and LWIR emission from the first 100 micron layer. That’s about the width of a human hair. In round numbers, about 50 W.m^-2 is removed from the ocean surface by the LWIR flux and the balance comes from the wind driven evaporation. The heat capacity of the cooled layer at the surface is quite small – 4.2 kJ.m^-2 for a 1 mm layer. This reacts quite rapidly to any changes in the cooling flux and the heat transfer from the bulk ocean below and the evaporation rate change accordingly. The cooler water produced at the surface then sinks and cools the bulk ocean layer below. This is not just a diffusion process, but convection in which the cooler water sinks and warmer rises in a complex circulating flow pattern (Rayleigh-Benard convection). This couples the surface momentum (wind shear) to lower depths and drives the ocean currents. At higher latitudes the surface area of a sphere decreases and this drives the currents to lower depths.”
“In round numbers, the temperature increase produced by a 2 W.m^-2 increase in LWIR flux from CO2 is overwhelmed by a 50 ± 50 W.m^-2 flux of cold water and a 0 to 1000 W.m^-2 solar heating flux. Over the tropical warm pool the wind driven cooling rate is about 40 W.m^-2.m.s^-1 (40 Watts per square meter for each 1 m/sec change in wind speed). This means that a change in wind speed of 20 cm.s^-1 is equivalent to the global warming heat flux. (20 centimeters per second).”
(B) CO2 heat “cannot penetrate into the ocean itself” — but it controls the heat in the skin layer?
According to the “basic physics” and “settled science” as understood by the dangerous anthropogenic global warming (DAGW) advocates at SkS, the heat trapped at the ocean surface via the “blanketing” greenhouse effect is not capable of actually penetrating into the ocean itself or affecting ocean heat content directly. Nonetheless, it is claimed that CO2 can control how much heat is contained in the skin layer, and the heat energy in the “0.1 to 1 mm thick” skin layer is “the major player” in determining the heat content of the global oceans to depths of thousands of meters.
First of all, it is nonsensical to admit that the Sun predominantly determines the temperature gradient of the first 30 meters of the ocean, but yet is simultaneously incapable of modulating the temperature of the first few tenths of a millimeter of the ocean. Not surprisingly, scientists have found that “solar heating overcomes the net upward longwave energy flux and warms the skin” of a body of water.
“[D]aytime skin effect was strongly influenced by direct solar illumination and typically had a mean of 0.5 K in the morning that decreased to 0.1 K by midday.…. [D]aytime solar heating stratifies the temperature profile of the surface. With this in mind the negative skin effect results from two separate processes: (1) intense daytime solar heating overcomes the net upward longwave energy flux and warms the skin, or (2) the right combination of low wind and solar heating creates a warm layer of water above the floating thermistor.”
Sun Heats Surface Ocean, Surface Ocean Heats Atmosphere
The main reason why the ocean skin is cooler than the waters directly below it is due to vertical heat flux, or evaporative processes. The skin layer’s temperature is largely determined by the natural flux of warmer subsurface waters (heated by the Sun) rising to the surface from below. In this way, atmospheric processes (the CO2 greenhouse effect as envisioned by modelers) do not exert control over internal ocean processes (surface heat flux) more than internal ocean processes exert control over atmospheric processes. The heat flux is “almost always” from ocean to atmosphere, not the other way around .
“Skin SST is typically 0.1 -0.5 K cooler than the immediate sub-surface water, although considerable variation in the skin-bulk difference has been observed (e.g. Donlon et al., 1999). This temperature difference is due to the vertical heat flux through the thermal boundary layer in the top millimeter of the ocean; net surface heat flux is almost always from ocean to atmosphere, resulting in a cool ocean skin.”
“There is a strong diurnal [sunshine] component to the magnitude of these temperature gradients, as well as a dependence on cloudcover, which modulates the insolation, and wind speed, which influences the turbulent mixing. The surface skin layer of the ocean, much less than 1 mm thick, is nearly always cooler than the underlying water because the heat flux is nearly always from the ocean to the atmosphere“
“The current eager acceptance of oceanic thermal lag as the “explanation” as to why CO2 warming remains undetected, reemphasizes that the atmosphere cannot warm until the oceans do.”
CO2 Unmentioned as an Important Heat Flux Variable
It should also be pointed out that the peer-reviewed scientific literature lacks references to CO2 as a “major player” — let alone a player at all — in the determination of surface heat flux, skin temperature gradient, or ocean heating processes altogether. One would think that if CO2 is the primary variable in net ocean heat content changes it would at least be routinely referred to as such in scientific journals. It isn’t. Below are just a few examples of the many instances in which CO2 is not mentioned when discussing the key components involved the ocean surface heat flux processes.
“The heat balance of the global ocean surface layer is calculated using bulk flux formulations. Maps of the long-term monthly and annual means of the net surface energy flux together with the four components of the total flux (latent heat flux, sensible heat flux, incoming radiation, and outgoing radiation) for the global oceans are presented. Incoming solar radiation and latent heat flux are the two dominant components that control net surface energy fluxes. Wind speed, cloud cover, and the gradient of specific humidity are the three most important meteorological parameters in determining surface flux.“
[CO2 is not mentioned as a factor affecting heat energy fluxes, nor anywhere in the paper.]
Observations of the Infrared Radiative Properties of the Ocean …
“[I]t is necessary to understand the physical variables contributing to sea surface emitted and reflected radiation to space. The emissivity of the ocean surface varies with view angle and sea state, the reflection of sky radiation also depends on view angle and sea state, and the absorption of atmospheric constituents such as water vapor, aerosols, and subdivisible clouds affect transmittance.”
[CO2 is not mentioned as an IR variable, nor anywhere in the paper.]
“[I]n-water solar fluxes can vary by 40 W/m-2 within the upper few meters of the ocean (based on a climatological surface irradiance of 200 W/m-2) and that a significant portion of the variation can be explained by upper ocean chlorophyll concentration, solar zenith angle, and cloud amount.”
[CO2 is not mentioned as a factor affecting the heat flux variation, nor anywhere in the paper.]
(C) No observational evidence or “real world” scientific experiment confirms CO2 heats water
Let’s emphasize this last point (C) by citing the exact wording once again:
“Obviously, it’s not possible to manipulate the concentration of CO2 in the air to carry out real world experiments, but natural changes in cloud cover provide an opportunity to test the principle [that CO2 heats water].”
Over at RealClimate (RC), the blog founded by the likes of Michael Mann, Gavin Schmidt, and William Connolley (among others), there is an essay written by Peter Minnett entitled “Why greenhouse gases heat the ocean”. (This was the original blog essay on the topic that Rob Painting appears to have borrowed heavily from in writing for SkS a few years later.) The RC version of the above quote looks like this:
“Clearly it is not possible to alter the concentration of greenhouse gases in a controlled experiment at sea to study the response of the skin-layer. Instead we use the natural variations in clouds to modulate the incident infrared radiation at the sea surface.”
So here we have explicit acknowledgement that the conceptualization of CO2 as a primary determinant of net ocean heat content variations is not rooted in observational evidence and experimental science. It’s a conceptualization that has not been tested or subjected to falsification.
Observational evidence of the alleged physical process that says raising or lowering CO2 heats or cools water bodies is not required, apparently. A controlled scientific experiment to test the presumption that CO2 is “the major player” in determining ocean heat content because it allegedly controls the temperature of the “0.1 to 1 mm thick” skin layer is also not required, apparently. Climate science is apparently not like the other sciences.
Clouds and CO2: Apples to Apples?
SkS and RC claim that, because there aren’t any physical measurements or controlled experiments or empirical observations that can verify the CO2-heats-water assumption found in models, cloud cover changes can suitably be used as a proxy for CO2 changes so as to “test the principle”. But clouds and CO2 do not offer an apples-to-apples comparison in their long-wave or “greenhouse” function, nor in their magnitude of influence on radiation budgets. That’s because clouds are far more powerful agents of radiative change when altered (both in the shortwave and longwave) than CO2 concentrations are.
In their highly-cited paper entitled “Cloud Radiative Forcing,” Ramanathan et al. (1989) conclude:
“The size of the observed net cloud forcing is about four times as large as the expected value of radiative forcing from a doubling of CO2. The shortwave and longwave components of cloud forcing are about ten times as large as those for a CO2 doubling. … The greenhouse effect of clouds may be larger than that resulting from a hundredfold increase in the CO2 concentration of the atmosphere.”
Even RC acknowledges in that variations in cloud have a far more dominant effect on ocean heat changes and radiation budgets than do variations (doubling) of CO2. In the very same RC blog essay about why CO2 is predominantly responsible for heating the oceans, we read this:
“Of course the range of net infrared forcing caused by changing cloud conditions (~100W/m2) is much greater than that caused by increasing levels of greenhouse gases (e.g. doubling pre-industrial CO2 levels will increase the net forcing by ~4W/m2)”
So if changes in cloud are acknowledged to be in excess of an order of magnitude more powerful than CO2 changes in affecting heat energy changes in the oceans, why is it that clouds are assumed to be suitable as a comparison variable when “testing the principle” that CO2 is “the major player” in the determination of net ocean heat changes? Symbolically speaking, why are refrigerators being used as a proxy for apples?
CO2-Heats-Water Assumption: Physical Measurements?
Probably the most critical feature underpinning the authentic physical sciences is the ability to obtain real world measurements. A fundamental question for those who are convinced that CO2 is the primary cause of net ocean heat changes would therefore be this:
If the air’s CO2 concentration was raised or lowered by +/-10 parts per million over a body of water, what heat changes will occur in that body of water at depths of, say, 1 m? What are the observed physical measurements?
Of course, no one has an answer to this question. We don’t have the physical measurements because this CO2-heats-water process has been neither observed nor tested or subjected to falsifiable scientific experiment. The models might calculate a suggested W/m2 radiative forcing value for each CO2 change, but the models are based on assumptions, not real world observation.
And contrary to SkS and RealClimate claims, it would seemingly not be impossible to test the assumption that CO2 heats water bodies, and if so, by how much. A physical experiment could indeed be carried out for purposes of providing at least some enlightenment on these questions with direct, non-proxy observational evidence involving both CO2 and water. For example, consider this proposed physical experiment:
Find or create two empty and identical glass-covered greenhouses (or other transparent buildings) that are located side-by-side, with neither structure affected differently by trees or shade or other outdoor environmental conditions. Inside each building place matching containers (large, preferably) filled with the same amount of water in each. Measure the baseline conditions of water temperature with precise thermometers, and measure the baseline CO2 concentration each building — which will presumably be the same or similar in each. In the first building (control), do not alter the internal natural CO2 concentration, but leave it at baseline (somewhere close to 400 ppm). In the second building, inject incrementally increasing quantities of CO2 (e.g., 500 ppm, 1,000 ppm, 1,500 ppm) with a CO2 generator (which are used in greenhouses to stimulate plant growth). Use a CO2 monitor (also used routinely in greenhouses) to measure and control the amount of CO2 contained in the experimental building. After a specified time lapse, measure the water temperature change, if any, for both the control building and the building with added CO2 from identical depths and locations for each container. Finally, reverse the process and incrementally draw down the CO2 injection in the experimental building while again gauging water temperature changes for each building.
This experiment (or something similar) might provide at least some basic answers to the question of how much, if any, change occurs in a body of water as a consequence of changing the air’s CO2 concentration above it.
Do DAGW advocates even want to subject their assumptions to an achievable controlled physical experiment like this, though? It’s doubtful they do. The results might very well invalidate the CO2-heats-water assumption.