Anthropogenic Ocean Heating?
Part 1: Skeptical Science Offside
By Richard Cumming, March. 2013 (v2)
Introduction
Anthropogenic attribution to sea level rise and ocean heat accumulation relies on there being a verified mechanism or process by which rising anthropogenic greenhouse gas (aGHG) emissions impute heat to the ocean. John Cook’s Skeptical Science has been promoting one such posited mechanism in particular as explaining the accumulation of heat in the ocean over the last 40 years or so, the most prominent example being How Increasing Carbon Dioxide Heats The Ocean posted in 2011 by Rob Painting. That post adapts a 2006 Real Climate article by Professor Peter Minnett, Why greenhouse gases heat the ocean, where an enhanced ocean surface insulation effect was posited.
Subsequent comments as recent as 6 February, 2013 at Skeptical Science (Duelling Scientists in The Oregonian) promote the in-house opinion that an enhanced insulation effect is the “mainstream view.” For example:
Rob Painting — “As for Stefan Rahmstorf, I know for a fact that he ascribes to the mainstream view that greenhouse gases warm the ocean through the reduced thermal gradient in the cool-skin layer. He was involved in a disagreement between myself and other commenters on Real Climate some months back and made his views on this known.
Is it really any surprise that he agrees with the established research?”
Rob’s facts are off the mark. A minor misunderstanding is that he backs up his claim by quoting a copy of a response Rahmstorf made in the 2006 Real Climate Minnett article thread, thinking it was made in 2012 in view of where he got it from but which wasn’t. More to the point, Rahmstorf was describing the cool-skin effect and Peter Minnett’s posited aGHG modification of it (more on that below). The cool-skin is a natural phenomenon where the upper few millimetres of the ocean surface are cooler than the warm layer beneath (which is about 700mm thick in ideal conditions) because energy leaves the surface, reducing its temperature. The cool-skin is not always present — it can be overwhelmed by solar heating at noon in the tropics, for example. Cool-skin dynamics are documented in Cool-skin and warm-layer effects on sea surface temperature (Fairall, et al., 1996). There is nothing contentious about the cool-skin. Rahmstorf’s 2006 Real Climate response was as follows:
Rahmstorf 2006 — “[Response: I try a different way. To your point 3 the answer is yes - the ocean surface is on average warmer than the overlying air, because the ocean absorbs a lot of heat from the sun, part of which it passes on to the air above. Your confusion arises simply because we are now discussing how the bulk of the ocean below the skin layer gets heated. Thus we are talking not about the gradient between sea surface and overlying air, but we are talking about the gradient through the skin — i.e., the water temperature difference between the top and bottom of the skin layer, which controls how heat flows across this layer, from the bulk of ocean water below to the surface. Obviously, if you heat the top of the skin layer, this reduces the heat flow across this layer from below. Clear? Or still confusing? -stefan]”
Stefan is referring to the idea of heat accumulating via an enhanced insulation effect rather than the actual solar source of ocean heat but even so, if that was his thinking in 2006 he has revised his view by 2013, as will be shown in Part 2. For now just note that Stefan describes thermodynamically conventional and observed (by Fairall, et al.) energy egress from the ocean surface to the atmosphere (sea => air energy transfer). He neglects the egress of radiation direct to space, but no matter. It becomes clear in a 2013 statement made by Rahmstorf that he now subscribes to a fundamentally different mechanism and mainstream view. More on that in Part 2.
Rob Painting (on behalf of Skeptical Science) is stretching the bounds of credibility by describing a single Real Climate blog post as “the established research”. There is work to be done for the Minnett theory to even enter the literature let alone for it to be verified and quantified. And from the Rahmstorf quote, the excerpt “if you heat the top of the skin layer” is highly questionable as will be demonstrated after the following aside. There can only be negligible, if any, heating effect on the cool-skin by downwelling infrared radiation (DLR in the IR-C range) but the very effective seawater heating by noontime solar SW radiation can actually eliminate the cool-skin in the tropics by heating it to warm-layer temperature, i.e., solar energy ingress overwhelms egress in that situation.
An aside
Among other things, my pointing out inconsistencies between what Skeptical Science were asserting and what climate scientists and the IPCC were actually stating must have been embarrassing for Skeptical Science because my last comment (76) on a thread dealing with these issues was retroactively removed and replaced by another as evidenced by the comment sequence:
76. scaddenp at 13:32 PM on 7 February, 2013
77. Composer99 at 17:47 PM on 7 February, 2013
Richard:
Further to your comment #76
Skeptical Science has a track record of this type of revision when the going gets tough; such is the fragility of their case and conviction apparently (also see Part 3 Rahmstorf).
Professor Peter Minnett’s anthropogenically enhanced insulation effect
In the 2006 quote Stefan Rahmstorf expands on the notion that increasing DLR as a result of rising aGHG emissions (which are unproven) heats the top of the skin layer to such an extent that the thermal gradient over a few millimetres of cool-skin from warm layer to surface is modified, creating an enhanced insulation effect so strong that energy egress from the ocean is significantly inhibited. This enhanced insulation, according to the blog theory, accounts for measured late 20th century ocean heat accumulation. Rahmstorf lent credence to this theory in 2006 but as we will see in Part 2 he is certainly not as wedded to it in 2013 as Skeptical Science is.
There are a number of problems with Peter Minnett’s blog theory that need to be addressed. DLR is emitted by all GHG including natural emissions and water vapour (gas). Clouds (liquid water) also contribute, so extracting the anthropogenic component of DLR presents considerable difficulties. The theory is also dependent upon DLR increasing over time (the last 40 years, say) in concert with rising aGHG levels. There is no study that I am aware of over that time frame to provide evidence of that happening. Recent studies that have been done do not return any correlation with CO2, for example, and even the sign of the DLR trend can be opposite the aGHG trend, or when the DLR trend is positive the magnitude can be far greater than can be attributed to aGHG.
What counts most against Peter’s theory is the significance of the insulation effect and this issue was raised in the 2006 Real Climate comments thread by Steven Sadlow but not responded to by either Stefan Rahmstorf or Gavin Schmidt. Stefan Rahmstorf describes the enhanced insulation process as “if you heat the top of the skin layer” but spectroscopic studies (e.g. this plot from Hale and Querry, 1973) show that DLR only impinges on the top 10 microns of the water surface and because of that, DLR is an ineffective water heating agent, DLR having very low energy per photon as compared to solar SW radiation. Fairall et al. state the 10 micron figure explicitly, so no dispute there either. There can only be negligible surface heating (if any) in a non-enhanced situation, because DLR energy will be used up by evaporation in calm conditions which actually aids energy egress. The intensity of DLR is not increased enough by aGHG increase to exacerbate the situation to any level of significance if the insulation effect is already insignificant and there has been no measured increase in DLR intensity. If it was, evaporation and therefore energy egress is actually enhanced. This is a key (but unproven) plank of AGW theory and contrary to Minnett’s theory.
Skeptical Science runs for cover (deletes and replaces comment 76) when asked if the Minnett effect has been quantified, the significance of it established and if so where is the documentation? The most important point regarding the cool-skin phenomenon is that if any of the Skeptical Science associates attempt to claim it in entirety for AGW, don’t believe it. They can claim only a thermally significant modification of the dynamics of it by aGHGs — but only if they can prove the significance of any such modification. Anthropogenic forcing (a tiny fraction of total DLR) would only cause a minuscule change to the warm-layer => surface thermal gradient and that brought about only by a negligible theoretical increment in DLR intensity, the trend of which in reality is wildly inconsistent globally, including decrements.
In any event, Skeptical Science, or anyone asserting that an anthropogenically enhanced insulation effect explains ocean heat accumulation, will have to provide significant and thermodynamically quantified evidence in order to eliminate an explanation involving only solar accumulation. Dr David Stockwell points out in his accumulation theory that only a very small solar forcing is required for ocean heat to accumulate and flow through to the atmosphere.
Stockwell: “…the 20th century temperature rise can be explained by the accumulation of an above-average solar forcing of 0.1 W/m2 in the ocean over the period.”
This concludes Part 1 and Skeptical Science views
Parts 2 and 3 The Improbable IPCC Mechanism and Rahmstorf, Schmittner and Nuccitelli will look at what the IPCC, Stefan Rahmstorf, Andreas Schmittner and Dana Nuccitelli are saying in 2013. It will be demonstrated that — contrary to claims by Skeptical Science — the mainstream view of those named (Nuccitelli’s view being ambiguous) is that the AGW mechanism expected to explain ocean heat accumulation is a heat transfer process operating in the opposite direction to the energy transfer processes described here in Part 1, i.e., an air => sea heat transfer process as opposed to sea => air energy transfer processes. The differentiation of energy forms is deliberate. In the process to be described in Part 2, heat is conventional sensible heat only by inference (much is required from the IPCC if they are to point to DLR as a heating agent) but in these Part 1 processes energy is radiation, evaporation and sensible heat, the respective terms and standard abbreviations being defined in Fairall, et al.
It will also be demonstrated in Part 2 that after 25 years and five assessment reports, the IPCC has yet to firm up a credible anthropogenic ocean heating mechanism (and therefore anthropogenic thermosteric sea level rise). Despite this, the AR5 WGI Chapter 10 SOD authors are “extremely certain” that the increase in global ocean heat content observed in the upper 700 m in the latter half of the 20th century can be attributed to anthropogenic forcing. This is the major issue — the Skeptical Science aspect is only really a sideshow to that.
