Guest Post by Willis Eschenbach
I previously discussed the question of error bars in oceanic heat content measurements in “Decimals of Precision“. There’s a new study of changes in oceanic heat content, by Levitus et al., called “World Ocean Heat Content And Thermosteric Sea Level Change (0-2000), 1955-2010” (paywalled here). [UPDATE: Available here, h/t Leif Svalgaard] It’s highlighted over at Roger Pielke Senior’s excellent blog , where he shows this graph of the results:
Figure 1. From Levitus 2012. Upper graphs show changes in ocean heat content, in units of 1022 joules. Lower graphs show data coverage.
Now, there’s some oddities in this graph. For one, the data starts at year 1957.5, presumably because each year’s value is actually a centered five-year average … which makes me nervous already, very nervous. Why not show the actual annual data? What are the averages hiding?
But what was of most interest to me are the error bars. To get the heat content figures, they are actually measuring the ocean temperature. Then they are converting that change in temperature into a change in heat content. So to understand the underlying measurements, I’ve converted the graph of the 0-2000 metre ocean heat content shown in Figure 1 back into units of temperature. Figure 2 shows that result.
Figure 2. Graph of ocean heat anomaly 0.-2000 metres from Figure 1, with the units converted to degrees Celsius. Note that the total change over the entire period is 0.09°C, which agrees with the total change reported in their paper.
Here’s the problem I have with this graph. It claims that we know the temperature of the top two kilometres (1.2 miles) of the ocean in 1955-60 with an error of plus or minus one and a half hundredths of a degree C …
It also claims that we currently know the temperature of the top 2 kilometers of the global ocean, which is some 673,423,330,000,000,000 tonnes (673 quadrillion tonnes) of water, with an error of plus or minus two thousandths of a degree C …
I’m sorry, but I’m not buying that. I don’t know how they are calculating their error bars, but that is just not possible. Ask any industrial process engineer. If you want to measure something as small as an Olympic-size swimming pool full of water to the nearest two thousandths of a degree C, you need a fistful of thermometers, one or two would be wildly inadequate for the job. And the top two kilometres of the global ocean is unimaginably huge, with as much volume as 260,700,000,000,000 Olympic-size swimming pools …
So I don’t know where they got their error numbers … but I’m going on record to say that they have greatly underestimated the errors in their calculations.
w.
PS—One final oddity. If the ocean heating is driven by increasing CO2 and increasing surface temperatures as the authors claim, why didn’t the oceans warm in the slightest from about 1978 to 1990, while CO2 was rising and the surface temperature was increasing?
PPS—Bonus question. Suppose we have an Olympic-sized swimming pool, and one perfectly accurate thermometer mounted in one location in the pool. Suppose we take one measurement per day. How long will we have to take daily measurements before we know the temperature of the entire pool full of water to the nearest two thousandths of a degree C?
Smokey says: @ur momisugly April 24, 2012 at 7:06 am
America is a “can-do” country that can out compete anyone. But we are being sold out by anti-American traitors. There is no better term for what is being done.
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Bill Tuttle says:
April 24, 2012 at 1:16 pm
Actually, there are several — but there are ladies present…
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Don’t think us ladies haven’t thought those terms too but I prefer traitor because it is so accurate.
Willis,
I have been traveling, and was not able to respond earlier. You said:
“No, it wouldn’t lead to a rise in OHC, they’d occur simultaneously. Change in temperature is a measure of change in heat content.”
That is not really correct. If the surface temperature of the ocean were to increase and then stay the same, there would be continuous accumulation of heat over at least hundred of years, and probably over ~1,000 years. The rate of down-mixing through the thermocline is extremely slow, especially past the first few hundred meters. The shape of the thermocline itself (near exponential temperature drop off below the surface layer) is exactly the expected shape for slow down-mixing combined with slow up-welling of abyssal water.
ARGO seems to me to be the best hope for constraining climate sensitivity; I honestly do not understand your many objections to ARGO data. The issue of “inadequate coverage” which you raise in multiple posts is not so strong an argument as you seem to suggest. The surface temperature does indeed vary quite a lot, both spatially and temporally, but below the surface at constant depth the temporal and spacial variability both decline a lot.
Consider the ARGO float cycle:
“A typical Argo float mission is to profile from 2000 m depth to the sea surface every 10 days. On deployment, the float sinks to a depth of 1000 m and drifts with the ocean currents for 9 days. Then the float sinks deeper to its profile depth (usually 2000 m) before starting to ascend through the water column measuring temperature, salinity and pressure as it rises. Once at the surface it transmits location and profile data via satellite to land-based Argo data centres. After transmission the float sinks again and repeats the cycle.”
The floats migrate over quite large distances, not at the surface, but at a depth of 1000 meters, which shows that there is considerable horizontal (more accurately, isopycnal) velocity even at considerable depth. The point of which is that this horizontal motion makes the ocean remarkably more uniform in temperature profile with depth than might be indicated by examining variation in near-surface temperature. The requirement of sampling frequency and spacial coverage to generate a very reasonable estimate of total heat content at depth is less that at first meets the eye.
A lot of people (including some who are quite skeptical of the likelihood of extreme future warming) appear to agree on the relatively good quality of the ARGO data. According to Craig Loehle last year: “The quality of the Argo data is evident in that the annual cycle with a period exactly 365 days (see my paper cited) is evident in this data”.
The key thing is that ARGO was specifically designed to generate a credible estimate of changes in ocean heat content over annual and longer time scales. The fact that many climate scientists have publicly questioned the accuracy of ARGO data (or at least ignored the ARGO data) when that data conflicted with projections of rapid heat accumulation suggests to me that the system is probably reasonably close to correct, and probably a lot more accurate that you give it credit for. The story ARGO is trying to tell us is that climate sensitivity is far lower than CGCM’s suggest. It is a story I am inclinded to believe.
stevefitzpatrick says:
April 25, 2012 at 2:19 pm (Edit)
Steve, that’s exactly my point. Wherever the temperature is increasing, whether at the surface or at depth, the heat content is commensurately increasing. They are interchangeable measurements of the same thing, and are directly convertible from one unit (°C) to the other (J).
If you think that is true, you’ll have to demonstrate it with numbers, because I have demonstrated the opposite numerically in Decimals of Precision. You can’t just say you don’t think it’s true. If you don’t, you’ll have to come up with the math to show me where my numbers are wrong.
Look, I love the Argo data, it’s among the best we have, and I have lauded it repeatedly. My problem is not the data, it’s the claims that some scientists have made using the data, claims that don’t match reality.
w.
Willis,
You said earlier: “Setting that aside, you ask if a rising ocean surface temperature would “lead to” a rise in oceanic heat content? No, it wouldn’t lead to a rise in OHC, they’d occur simultaneously”
It seems to me you are arguing about semantics. I am quite aware of how temperature change and heat content are related. OK, but the substantive point remains; changes in surface temperature do not directly reflect the change in heat content below the surface, and a change in surface temperature takes centuries to fully influence the total ocean heat content. The measured surface temperature could be constant for a very long time, and the total ocean heat content could be changing significantly, either up or down. Do you not agree this is true?
With regard to showing that there is much less spacial and temporal variation below the surface layer: I will need to do some digging. I remember seeing convincing data, but I will be traveling for a few more days so can’t search now.
stevefitzpatrick says:
April 25, 2012 at 4:19 pm
I don’t see anyone who is claiming that we can tell the OHC from the surface temperature, that’s why the temperature is sampled at 24 different depths from the surface down to 1500 metres … so I’m not clear who you are arguing against.
Nor do I see anyone saying that the time constant of the ocean is other than long, centuries long.
So I’m not sure who you think you are arguing against … but it ain’t me, and I don’t think it’s anyone here …
w.
Willis writes “each year’s value is actually a centered five-year average … which makes me nervous already, very nervous. Why not show the actual annual data? What are the averages hiding?”
It would be nice to know their precise algorithm for calculating the result. Then one can ask how much data must one drop for the result to fall outside their error bars? The answer to that would, I feel, be telling of the robustness of the result.
stevefitzpatrick says:
April 25, 2012 at 4:19 pm
Thanks, Steve. If you look at the standard error of the mean you can see which areas have variations and which are more smooth. Certainly things are smoother at say 500 metres than at the surface … but they are far from even.
SOURCE
Note that even in a single month we have variations greater than half a degree at a depth of 500 metres … sure, it’s less than at the surface as you’d expect, but it is hardly smooth. Not only that, but it occurs in some parts of the ocean and not others, which is not what I had expected …
w.
Gail Combes sez “Once you are talking about a non-uniform material (the ocean) measured by different instruments at different times at different depths at different locations then you are talking about huge error bars because you adding up all the errors inherent in each measurement and not increasing the accuracy by repeating the measurement under the same conditions.”
Indeed. At the ‘precision’ of .001°, there is no such thing as a right answer, as the hypothetical point which is being ‘measured’ is changing too fast.
BTW, Gail, though you are a possibly hairy primate, I suspect it was guerrilla war you were waging.
Willis,
Thanks for finding that data. The areas were the variability at depth is the greatest are the eastern coast of Japan and the Gulf Stream, both regions are subject to strong horizontal shear due to the velocity of the surface current. No doubt that does cause locally exaggerated eddy mixing and higher variability. I had not seen that data before.
I would bet they are doing things like averaging measurements and assuming they are uncorrelated, so that they can scale the uncertainties by the inverse square root of the number of measurements. And, that assumption is, of course, bollocks. Inappropriate statistical manipulations have driven the CO2 bandwagon from the very start.