Eruptions and Ocean Heat Content

Guest Post by Willis Eschenbach

I was out trolling for science the other day at the AGW Observer site. It’s a great place, they list lots and lots of science including the good, the bad, and the ugly, like for example all the references from the UN IPCC AR5. The beauty part is that the ones which are publicly available are marked “FULL TEXT”, so you can just search for that and step from study to study knowing that they’re not paywalled. So as I said, I was trolling through the full text links and I ran across an interesting study entitled Global Decadal Upper-Ocean Heat Content as Viewed in Nine Analyses by Carton and Santorelli, hereinafter C&S2008. Here’s their money graph, Figure 1:

Figure 1. Nine different estimates of the change on oceanic heat content, including one model and eight observational estimates. When comparing to other analyses, note that this analysis has oceanic heat content (OHC) expressed in units of 10^8 joules per square metre, and not the more usual global total OHC which typically is measured in units of 10^22 joules. The conversion is described in the last sentence of the caption. (Actually, I think that the caption to Figure 1 in their paper was from another context and wasn’t updated … but the meaning is clear).

I was hooked when I read the abstract, with its mention of the volcanic analysis, viz:

ABSTRACT

This paper examines nine analyses of global ocean 0-/700-m temperature and heat content during the 43-yr period of warming, 1960–2002. Among the analyses are two that are independent of any numerical model, six that rely on sequential data assimilation, including an ocean general circulation model, and one that uses four-dimensional variational data assimilation (4DVAR), including an ocean general circulation model and its adjoint. Most analyses show gradual warming of the global ocean with an ensemble trend of 0.77 x 10^8 J m-2 (10 yr)-1 (=0.24 W m-2) as the result of rapid warming in the early 1970s and again beginning around 1990. One proposed explanation for these variations is the effect of volcanic eruptions in 1963 and 1982. Examination of this hypothesis suggests that while there is an oceanic signal, it is insufficient to explain the observed heat content variations.

So what did I learn from this paper? To start with, I was totally unaware that there were nine different estimates of the changes in ocean heat content, so I learned that. And quite a bit more … including being reminded that this kind of “spaghetti  graph” without error estimates is useless.

So the first thing that I did was to go get the error estimates on the Levitus data shown in Figure 1 (dashed purple line) and add it to the graph so I could see what was going on:

Figure 2. Same as Figure 1, but I have highlighted the Levitus data and added the vertical red lines showing the error of the Levitus data.

Now, I have long held that the error estimates in Levitus were underestimated … I would say that this graph agrees.

I also have to note in passing that I was unable to replicate their Figure 1 regarding the Levitus results. Using the data downloaded from the above link, here is what the Levitus analysis currently shows:

Figure 3. Figure 1 from C&S2008, overlaid with current Levitus results shown in red.

As you can see, there is good overall agreement with their data with the exception of the period from 1969 to 1984 … I have no explanation for this.

However, that’s not what I was interested in. I wanted to know about the volcanoes. For some time, I have argued in a variety of posts that the effects of volcanoes on the planet’s temperature were overestimated, and sometimes greatly so. So I was surprised to see their results for the eruption of El Chichón in Mexico. They took an interesting tack in their analysis. For each area of the ocean, they compared the average ocean heat content during the four years before the eruption, with the average heat content in the four years following the eruption. That seemed like a reasonable metric to me, and a good way to go about it. Figure 4 shows their results of the 9 analyses regarding the eruption of the El Chichón volcano in 1982:

Figure 4. Ocean heat content (OHC) net change from the four years before the eruption of El Chichón, Mexico, to the four years after the eruption. Upper 8 panels show the 8 observational datasets, and bottom panel shows the model. Note the different scales … presumably used because the changes in the model results are only about 2/3 the size of the observations. ORIGINAL CAPTION: FIG. 3. Change in 4-yr average heat content spanning the eruption of Mount Agung (1963). Prior to computing the heat content change a regression analysis is used to remove the effects of ENSO and a linear warming trend (see Fig. 2). … Changes exceeding ± 5 x 10^8 J m-2 are shaded. Lowest panels show the change in heat content from a five-member ensemble of the GFDL coupled simulation CM2.1 with complete aerosol forcing. Changes exceeding ± 3 x 10^8 J m-32 are shaded.

Now at first sight, all of that looks like confirmation that the volcano caused actual cooling and that my hypothesis of minimal volcanic cooling was wrong.

However, if the cooling is from the eruption, then why are there areas of warming? Why is the cooling localized in the region just below the equator in the Pacific, when the volcanic aerosols are initially from above the equator and then spread widely around the planet? And why is there not increased cooling in the region around the eruption site in Mexico?

The answer, as usual, lies in more observations. Figure 5 shows the corresponding 4-year averages for Pinatubo …

Figure 5. As in Figure 4, but for the eruption of Mt. Pinatubo in the Philippines.

As the paper itself says …

For Mount Pinatubo most analyses show general warming except in the western equatorial [South] Pacific.

General warming of the ocean after the largest volcanic eruption in modern times? Sure seems like that supports my claims … to me, the only conclusion that we can draw from these observations of the two volcanic eruptions is that we’re looking at normal variations in OHC, and that whatever the effects are, they are pretty dang small.

Close inspection reveals a final and very strong indication that the changes shown in Figures 4 and 5 are NOT from the two eruptions, but are natural variations of unknown origin.

The indication is that the shape of the cooling does not have the form that the modelers predicted. As the models show, if forcing ruled temperature the largest effect would be expected to be immediately downwind of the eruption site.  Note in Figure 5 that of all of the nine results (8 from observations, 1 from the model), the only one showing North Pacific cooling downwind from Pinatubo was the model. You can see it in the model results, the blue area like an arrow pointing at the northern Philippines, with the tail streaming straight downwind in the north Pacific … but none of the observational datasets show that pattern of cooling downwind from Pinatubo.

Not only that, but look back at Figure 4. Care to guess which of the nine analyses claimed that there would be cooling downwind from the eruption in Mexico, in the area of the Caribbean and across the top of South America? Yeah … the model was the only one … and it didn’t happen. So even in the areas right downwind from the eruptions, we don’t find the expected heat content changes from the change in solar forcing.

The volcanoes pose a huge problem for the commonly held view that the changes in global average temperature are a linear function of the changes in forcing. The climate models are nothing but a mechanistic implementation of that circumscribed and simplistic hypothesis.

Now, we know for a fact that the solar forcing after Pinatubo underwent a large and fairly lengthy drop … but we don’t find either the amount or the pattern of cooling predicted by the models. Heck, not only that, but the predominate pattern after Pinatubo was warming, not cooling … once again, the only tenable conclusions are:

1) Whatever the volcanoes might be doing, they’re not doing what the model says or what conventional climate theory predicts, and

2) Whatever the volcanoes might be doing, they are not doing enough of it to even rise above the noise.

To me, this is simply more evidence that the underlying climate paradigm, the idea that changes in temperatures are a linear function of changes in forcing, is simply not correct. If it were correct, the eruptions would show it … but they simply don’t.

That’s why I describe myself as a climate heretic rather than a skeptic—I think that the most fundamental paradigm of how the climate works is wrong. The temperature changes are NOT a linear function of forcing changes as conventional climate theory holds.

As usual, my best wishes to you all,

w.

PS—Also as usual, please quote whatever you disagree with when you comment on it. That way we can all be clear just what you are referring to.

DATA:  Global Decadal Upper-Ocean Heat Content as Viewed in Nine Analyses, James Carton and Anthony Santorelli