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Clintel
Date: 27 April 2026

May’s central argument is that solar radiation and greenhouse gas radiation affect the ocean in fundamentally different ways, and that these differences are often misunderstood or oversimplified in climate discussions.

May begins by challenging the idea that greenhouse gas infrared radiation is as effective—or even more effective—than solar radiation in heating the oceans. He outlines two key physical distinctions. First, solar radiation consists of higher-energy photons than GHG infrared radiation because photon energy increases with frequency. Second, and more importantly, the depth of penetration differs dramatically: solar radiation, particularly in the blue-green spectrum, can penetrate many meters into the ocean (and in very clear water, up to 100 meters), directly heating the bulk water. In contrast, GHG infrared radiation is absorbed almost entirely within the top micrometers to millimeter of the ocean surface.

Heating mechanisms

This leads to a critical distinction in heating mechanisms. Solar radiation directly warms the ocean’s mixed layer by depositing energy at depth. Greenhouse gas IR radiation, however, does not penetrate deeply enough to heat the bulk ocean directly. Instead, it is absorbed in the very thin “thermal skin layer” (TSL) at the surface. Because the atmosphere is generally cooler than the ocean, heat normally flows upward from the ocean to the atmosphere. The absorbed IR energy modifies the temperature gradient in this thin layer, effectively reducing the rate at which heat escapes from the ocean, rather than adding new heat directly to the bulk water.

A substantial portion of the presentation is devoted to explaining the structure of the ocean’s upper layers. The topmost region includes the electromagnetic skin layer, where GHG IR is absorbed, and the broader thermal skin layer, which governs heat exchange between ocean and atmosphere. Below this lies the viscous layer, where turbulence is suppressed. These layers are extremely thin—on the order of fractions of a millimeter to a few millimeters—but play a crucial role in regulating heat flux. The “cool skin effect,” where the very surface is slightly cooler (by about 0.2 to 0.5°C) than the water just below, is especially important because satellite instruments measure this topmost layer rather than the bulk ocean temperature.

May emphasizes that this thin surface layer dynamically adjusts to maintain energy balance. When additional infrared radiation is absorbed, it alters the temperature gradient within the TSL, thereby reducing heat loss from the ocean. However, because the net heat flux is upward and the layer is extremely thin with limited heat capacity, it cannot effectively transport heat downward into the ocean interior.

The discussion then turns to the concept of photon energy and wave-particle duality. While some critics argue that only total energy flux matters (not the energy per photon), May maintains that photon energy is relevant because higher-energy solar photons penetrate deeper into the ocean. He also briefly explains that photons behave as waves during propagation and only exhibit particle-like behavior upon interaction with matter, referencing well-known quantum mechanical principles.

Surface temperature

Another major theme is the ambiguity of “surface temperature.” The term can refer to several different things: the actual air–water interface, the temperature measured by satellites (infrared emission), the temperature slightly below the surface, or the mixed layer temperature. These can differ significantly due to steep temperature gradients near the surface. This ambiguity complicates both measurement and modeling.

May also critiques widely used energy balance diagrams, such as those produced by NASA. These diagrams often show large downward infrared radiation fluxes (e.g., ~340 W/m²), which can give the impression that greenhouse gases are a major direct heat source for the ocean. However, he argues that these are “gross fluxes” in a two-way radiative exchange, not net heat transfer. The key quantity is the net longwave flux, which is upward (approximately 58 W/m²), meaning the ocean is losing heat via radiation overall. By comparison, incoming solar radiation (~163 W/m²) represents a net gain of energy. Thus, he concludes that solar radiation is the primary driver of ocean heating, while GHG IR mainly modulates heat loss.

The presentation highlights uncertainties in measuring Earth’s energy imbalance and ocean heat content. While some estimates suggest a positive EEI consistent with global warming, the magnitude is uncertain due to measurement limitations. Satellite instruments lack the precision to directly measure the small imbalance, so estimates are often inferred from ocean heat content data. However, these data sets are inconsistent, particularly before the widespread deployment of Argo floats around 2005.

May underscores that ocean temperature measurements vary depending on methods (satellites, ships, buoys) and data processing choices (interpolation, corrections, coverage). For example, some datasets fully infill missing regions, while others leave gaps, leading to different global averages and trends. Coverage is especially sparse in regions like the Southern Ocean and at depths below 2000 meters. As a result, estimates of ocean heat content—and by extension EEI—are highly uncertain, especially over short time scales.

Ocean oscillations

He also notes that natural variability, such as ocean oscillations (e.g., ENSO, AMO, PDO), significantly influences surface energy balance and can produce variations comparable to or larger than estimated long-term anthropogenic effects over shorter periods. Additionally, regional differences are substantial, with some areas warming while others cool, further complicating interpretation.

In his concluding remarks, May reiterates that longwave infrared radiation cannot meaningfully heat the deeper ocean because it is confined to the thin surface layer, which is too shallow, too cool, and too dominated by heat loss processes to transfer energy downward. Instead, its role is indirect—reducing the rate at which heat escapes from the ocean. Solar radiation remains the only mechanism that directly increases heat content in the ocean’s mixed layer.

Ultimately, May emphasizes the complexity of the climate system and the limitations of current data and models. He argues that ocean heat content estimates are not precise enough to accurately determine the Earth’s energy imbalance or its trends in recent decades. The relatively short duration of reliable measurements, combined with large natural variability and measurement uncertainties, makes it difficult to confidently attribute observed changes. His “bottom line” is that significant uncertainties remain, and that the relative contributions of solar radiation and greenhouse gases to ocean warming are not as well understood as often portrayed.