Guest Post by Willis Eschenbach

Today I ran across an interesting presentation from 2013 regarding the Argo floats. These are a large number of independent floats spread all across the world oceans. They spend most of their time sleeping at a depth of 1,000 metres (3,300 feet) below the surface of the ocean. Then they drop down to 2,000 metres, which is followed by a slow ascent to the surface taking measurements of temperature and salinity. Once on the surface they call home like ET, and then drop down to the deeps and go to sleep again.

Figure 1. Argo float operation. There are about 3,500 floats in the ocean, and a total of ~10,000 floats have been used over the period of operation.

Now, there were several interesting things in the presentation. The first was a total surprise to me. We hear a lot about how the heat is “hiding” in the ocean. But what I didn’t know was that according to the Argo floats, every bit of the warming is happening in the southern extratropical ocean, while the oceans of both the tropics and the northern hemisphere are actually cooling … color me puzzled.

Figure 2. Change in ocean heat content by zone. Units are 10^22 joules. Graph from the presentation linked to above.

What does that indicate? I’m sure I don’t know … but I doubt very greatly if any of the climate models reproduce that curious combination of warming and cooling.

What I found most interesting, however, was a graph of the global change in ocean heat content over the period. Here is that graph:

Figure 3. Global change in ocean heat content (OHC) since the time of the full deployment of the Argo floats. Data from the surface down to 2000 decibars (dbar), which is approximately 2000 metres.

I was sad to see a couple of things. First, this is the data with the monthly averages (the “climatology”) removed. I prefer to see the raw data so I can look at seasonal patterns. Second, the presentation lacks error bars … but needs must when the devil drives, so I use the data I have. I digitized the data so I could analyze it myself.

The first thing that I wanted to do was to look at the data using more familiar units. I mean, nobody knows what 10^22 joules means in the top two kilometres of the ocean. So I converted the data from joules to degrees C. The conversion is that it takes 4 joules to heat a gram of seawater by 1°C (or 4 megajoules per tonne per degree). The other information needed is that there are 0.65 billion cubic kilometres of ocean above 2,000 metres of depth, and that seawater weighs about 1.033 tonnes per cubic metre.

Figure 4. Ocean volume by depth. Little of the ocean is deeper than about 5 km.

Using that information, I calculated what the change in heat content means in terms of temperature change. Here is that graph:

Figure 5. Change in ocean temperature from the surface down to 2,000 dbar (~ 2,000 metres).

A change of two hundredths of a degree per decade … be still, my beating heart. Unfortunately, I can’t give you any error estimate on the trend because there are no error bars on the data in the presentation.

Let me take a detour here whose purpose will be clear in a moment. I want to look at the CERES data, which is satellite based data on the radiation budget of the earth. Here is the month-by-month change in the “Net TOA Radiation”. The net TOA radiation is the incoming radiation at the Top Of the Atmosphere (TOA) that hits the earth (sunlight) minus the outgoing radiation at the TOA leaving the earth (reflected sunlight plus thermal infrared [longwave] radiation). Figure 6 shows those changes:

Figure 6. Decomposition of the CERES net TOA radiation into a seasonal and a residual component. Units are watts per square metre (W/m2). The residual component (bottom panel) is the raw data (top panel), with the monthly averages (seasonal component or “climatology”, middle panel) removed.

Now, this is an interesting graph in its own right. In the net radiation you can see the ~ 20 watts per square metre (W/m2) effect of the annual swing of the earth towards and away from the sun. The earth is closest to the sun in January, so the earth gains energy around that time, and loses it in the other half of the year. In addition, you can see the amazing stability of the system. Once we remove the monthly averages (the “climatology’), the net TOA imbalance generally only varies by something on the order of ± half a watt per square metre over the thirteen years of the record, with no statistically significant trend at all … astounding.

But I digress. The reason I’m looking at this is that the excess energy that comes in to the Earth (positive values), peaking in January, is stored almost entirely in the ocean, and then it comes back out of the ocean with a peak in outgoing radiation (negative values) in July. We know this because the temperature doesn’t swing from the radiation imbalance, and there’s nowhere else large enough and responsive enough for that amount of energy to be stored and released.

In other words, the net TOA radiation is another way that we can measure the monthly change in the ocean heat content, and thus we can perform a cross-check on the OHC figures. It won’t be exact, because some of the energy is stored and released in both ice and land … but the main storage is in the ocean. So the CERES net TOA data will give us a maximum value for the changes in ocean storage, the value we get if we assume it’s all stored stored in the ocean.

So all we need to do is to compare the monthly change in the OHC content minus the climatology, as shown in Figure 1, with the monthly change in downwelling radiation minus the climatology as shown in the bottom panel of Figure 6 … except that they are in different units.

However, that just means that we have to convert the net TOA radiation data in watts per square metre into joules per month. The conversion is

1 watt-month/m2 (which is one watt per square metre applied for one month) =

1 joule-month/sec-m2 * 5.11e+14 m2 (area of surface) * 365.2425/12 * 24 * 3600 seconds / month =

1.35e+21 joules

So I converted the net TOA radiation into joules per month, and I compared that to the Argo data for the same thing, the change in ocean heat content in joules/month. Figure 7 shows that comparison:

Figure 7. A comparison of the monthly changes in ocean heat content (OHC) as measured by the CERES data and by the Argo floats.

Now, this is a most strange outcome. The Argo data says that there is a huge, stupendous amount of energy going into and out of the ocean … but on the other hand the CERES data says that there’s only a comparatively very small amount of energy going into and out of the ocean. Oh, even per CERES it’s still a whole lot of energy, but nothing like what the Argo data claims.

How are we to understand this perplexitude? The true answer to that question is … I don’t know. It’s possible I’ve got an arithmetical error, although I’ve been over and over the calculations listed above. I know that the CERES data is of the right size, because it shows the ~20 watt swing from the ellipticity of the earth’s orbit. And I know my Argo data is correct by comparing Figure 7 to Figure 2.

My best guess is that the error bars on the Argo data are much larger than is generally believed. I say this because the CERES data are not all that accurate … but they are very precise. I also say it because of my previous analysis of the claimed errors given by Levitus et al in my post “Decimals of Precision”.

In any case, it’s a most curious result. At a minimum, it raises serious questions about our ability to measure the heat content of the ocean to the precision claimed by the Argo folks. Remember they claim they can measure the monthly average temperature of 0.65 BILLION cubic kilometres of ocean water to a precision of one hundredth of a degree Celsius … which seems very doubtful to me. I suspect that the true error bars on their data would go from floor to ceiling.

But that’s just my thoughts. All suggestions gladly accepted.

Best of everything to all,

w.

My Standard Request: If you disagree with someone, please QUOTE THE EXACT WORDS YOU DISAGREE WITH. That way everyone can understand the exact nature of your objections.

Data and Code: The Argo data (as a .csv file) and R code is online in a small folder called Argo and CERES Folder. The CERES TOA data is here in R format, and the CERES surface data in R format is here. WARNING: The CERES data is 220 Mb, and the CERES surface data is 110 Mb.

Further Data:

Main Argo Data Page

Main CERES Page

List of Argo “gray” floats

Share this: Print

Email

Twitter

Facebook

Pinterest

LinkedIn

Reddit



Like this: Like Loading...