Warm Water, Hot Air

The oceans are heating up 40% faster than scientists realized screamed Business Insider last Saturday (January 12). Two days earlier The New York Times broke the story with “the oceans are heating up 40 percent faster on average than a United Nations panel estimated five years ago.” It’s all from a January 10 article in Science by Lijing Cheng, of the Chinese  Academy of Sciences in Bejing, along with three American coauthors, titled “How Fast are the Oceans Warming?”

Scary. Not. “40 percent” is a straw man.

The subject of all this attention is the change in the heat content of the world’s oceans. This is obviously related to their temperature—something that has proven rather difficult to measure precisely on the centennial scale because of changes in measurement techniques and data sources. (Quants: heat (in joules) divided by the heat capacity (joules required to warm the ocean a degree) gives temperature change).

At the outset, it’s important to note that this is not an original research article. It’s a “Perspectives” piece, kind of like a sciency op-ed that cites a collection of refereed publications (in this case, with a large number of self-citations) that determine the “perspective” of the writers. Quoting from Dr. Roy Spencer’s blog on January 16:

For those who read the paper, let me warn you: The paper itself does not have enough information to figure out what the authors did…

Further, Spencer notes:

One of the conclusions of the paper is that Ocean Heat Content (OHC) has been rising more rapidly in the last couple decades than in previous decades, but this is not a new finding, and I will not discuss it further here.

Of more concern is the implication that this paper introduces some new OHC dataset that significantly increases our previous estimates of how much the oceans have been warming.

As far as I can tell, this is not the case.

The “United Nations panel” in the first paragraph is, of course, its Intergovernmental Panel on Climate Change (IPCC), and in their most recent (2013) science compendium they most certainly did not estimate that the heat content of the ocean is 40% less than what it is from Cheng et al’s “perspective.” In that report, they noted five different publications, but found problems with four of them and only conferred credibility upon the highest figure, published by Dominguez et al. in 2008. The Cheng et al. study is only 11% higher than that, not 40%. To repeat, the average of the five studies mentioned in the 2013 IPCC report is 40% below the new Cheng et al. figure, but the one that the IPCC found most credible in fact differs from Cheng et al. by only 11%.

The 40% figure is therefore a straw man. 

It’s also noteworthy that the “40 percent” claim is nowhere in the Science Perspective. It’s from a guest post by Cheng et al. in “Carbon Brief,”  principally funded by the European Climate Foundation, which describes itself as “a major philanthropic initiative to help Europe foster the development of a low-carbon society and play an even stronger international leadership role to mitigate climate change.”

Another Perspective

It is obviously very important to understand historical changes in ocean heat content.  Another way to do this would be with the new “reanalysis” data sets, which combine heretofore separate atmospheric observations in the past via a dynamic model. Obviously as one goes further back in time, important data, such as vertical weather balloon soundings drop out, as they did in the 1930s. One important note:  the model is modulated with the changes in atmospheric radiation consistent with human emissions of greenhouse gases, ozone, and aerosols, as well as changes in solar radiation.

(The relevant paper is by Patrick Layloyaux of the European Center for Medium-Range Weather Forecasts, the same people who produce the daily “Euro” model that mid-Atlantic forecasters love so much in snow situations. He has 14 co-authors, with the majority being from the ECMWF.)

Here’s what the ECMWF simulates for the historical heat content (in Joules/square meter) of the upper 300 meters (984 feet) of the globe’s oceans:

Oceanic heat content (joules/square meter) or the upper 300 meters of the ocean.  From Layloyaux et al., 2018.

Somehow “ocean heat content as high as it was 75 years ago” isn’t quite so alarming.