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New study improves measurements of the warming oceans

Posted on 23 June 2014 by John Abraham

Heating of the oceans is, pardon the pun, a hot subject. There is a broad recognition that the oceans, which absorb approximately 90% of excess greenhouse gas energy, are key not only to how fast the planet will warm, but also how hot it will get in the end. Many recent studies have tried to measure deeper ocean regions or previously uncharted areas in the search for heat. A new study by Lijing Cheng and Jiang Zhu takes a different approach. They ask how large are biases in the estimates of ocean heating from the finite resolution of the devices themselves. Their findings are exciting, but first, let’s talk about the details of the study.

Lijing Cheng, relaxing with Kangaroos Lijing Cheng, relaxing with Kangaroos

Measuring the oceans is difficult; they are vast and deep. In order to measure the total energy in the ocean, you have to obtain temperatures at many locations and at many depths. Not only that, you need to make measurements over many years if you want to identify long-term trends.

Oceanographers have been making such measurements for decades. But the density of measurements is not spread uniformly over the oceans. There are more in coastal regions or major shipping lanes than in other locations. To further complicate the problem, the measurement methods have changed over the years.

Decades ago, insulated buckets, then, bathythermograph devices, and now ARGO floats have been used. While these devices all go down into the ocean depths, they have different depth resolutions. Over the years, we have a large number of measurements near ocean’s surfaces but as we measure deeper and deeper, fewer and fewer data points are available. As a result, we cannot construct exact temperature-depth curves. Consequently, our discrete data points give us some error, some bias compared to real ocean temperatures.

In their paper, Lijing Cheng and Jiang Zhu quantify our ocean errors. They started with a “real” ocean temperature and then they extracted discrete data and asked themselves how their discrete data matched the original temperatures. By discrete data, I mean that they extracted temperatures every 10 meters, 20 meters, 30 meters, and so forth. Somewhat like the science of calculus where smooth curves are approximated by a series of straight-lined segments.

What they found was very interesting. In the upper regions of the oceans, the discrete data was colder than the real ocean temperatures. However, deeper in the waters, the trend reversed and the discrete data was warmer. But to make things more complicated, the errors differed depending on location in the oceans. Near the equator (tropics), the discrete data exhibited a warm bias but further from the equator, the bias was cold. Furthermore, the extent of the error changed throughout the year.

The authors use their findings to calculate how close together measurements would have to be to obtain accurate ocean temperature measurements. The authors also propose a method to correct past temperature data to account for these biases. It is important for readers to recognize that the biases themselves do not make us think climate change will be worse or milder. What really matter are the changes to biases over time.

Dr. Cheng, who recently graduated with his PhD, told me,

Click here to read the rest

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Comments 1 to 8:

  1. This study is attempting to improve measurements of the "temperature of the oceans". Your headline is misleading from what their study says. Their title alone states their position: "Uncertainties of the Ocean Heat Content Estimation Induced by Insufficient Vertical Resolution of Historical Ocean Subsurface Observations".

    The authors do not state the oceans are warming as your title does. In fact, the study shows the uncertainty in temperature measurements in either direction and at different depths and different latitudes. They offer ideas on how to improve the accuracy of measurements, but do not infer that they have improved them, or that the oceans are warming.

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  2. Terranova...  What you're doing, though, is avoiding all the other relevant research that shows that the planet is accumulating heat. Of course the authors don't state that the oceans are warming, since that is a fact that is conclusively shown through other research. 

    You can't take any given piece of research in a void. You have to think of it as just another piece of the puzzle, where there are many hundreds of other pieces already in place.

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  3. Terranova@1,

    The authors do not state the oceans are warming

    If you click on to read the rest of JA's article on the Guardian, you find out what Lijing said in private communication with JA:

    "We assessed this problem in our paper and we are now working on improving ocean warming estimates.”

    That's the direct contradiction of your assertion. Assuming your intergrity, your assertion indicates you did not read the full article before posting your comment.

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  4. First, I know the oceans are warming.  I am not a denier, or a skeptic on that point.  

    Second, the scientific community knows their is a lack of long-term measurements of the global ocean.  And, that the changes in the measurement systems over the years makes documenting and understanding change in the oceans a difficult task.

    Third, this referenced paper is an attempt to improve those measurement systems.

    Rob @ 2,

    I agree with your statement "another piece of the puzzle".  My original comment was only about what the paper said versus the article headline. But, I see your point.

    chriskoz @ 3,

    I did read the entire article, but again was only talking about the paper. I am not sure what you mean with your statement about integrity. 

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  5. terranova:

    "The authors do not state the oceans are warming as your title does."

    Nor does the title state that the authors' study states that the oceans are warming.

    "New study improves measurements of the warming ocean".

    That's very clear.  The study improves measurements of the ocean, which, as it happens, is warming.  The adjective "warming" modifies "ocean", and does not in any way reference "study".

    Nor does the title suggest that the ocean is "new" ... which is an equally silly misreading of the sentence.

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  6. dhogaza@5,

    Thanks for pointing it out. I usually do not nitpick on someone's words. In this case, I can happily concede that I misunderstood Terranova's comment, although I'm not the only one who could have done so, as your case indicating Terranova's imprecise language suggests. Imprecise language is far lesser issue rather than the lack of intelectual integrity we would have to conclude if we assumed Terranova meant precisely what s/he has written.

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  7. Terranova @1&4.

    Further to the previous commenters, if you read the paper's abstract and understand its implications, you would note the error in OHC measurement being discussed amounts to "a global average of ~0.01°–0.025°C, ~1–2.5 × 1022 J," values which are large but a factor of 10 smaller than the rise in OHC that has been recorded in recent years.

    Thus you are wrong when you say @1 "In fact, the study shows the uncertainty in temperature measurements in either direction and at different depths and different latitudes. They ... do not infer ...  that the oceans are warming." Or do you consider that the authors of the paper are ignorant of the size of increase in OHC?

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  8. Perhaps this study is relevant to the issue as to when the heat in the oceans will have a significant impact on land temperatures.  Billions of brain cells may have been wasted debating whether or not temperatures have increased the last 16 to 18 years.  I say waste because if most of the heat is going in the oceans won't it eventually come back to bite us in an extreme matter.   Of course, warming oceans have many of their own negative impacts on sea life.  Not to mention ocean acidification.  

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