Nic Lewis skewers that “oceans are warming at unprecedented rates” paper
A major problem with the Resplandy et al. ocean heat uptake paper
by Nic Lewis
Obviously doubtful claims about new research regarding ocean content reveal how unquestioning Nature, climate scientists and the MSM are.
On November 1st there was extensive coverage in the mainstream media[i] and online[ii] of a paper just published in the prestigious journal Nature. The article,[iii] by Laure Resplandy of Princeton University, Ralph Keeling of the Scripps Institute of Oceanography and eight other authors, used a novel method to estimate heat uptake by the ocean over the period 1991–2016 and came up with an atypically high value.[iv] The press release [v] accompanying the Resplandy et al. paper was entitled “Earth’s oceans have absorbed 60 percent more heat per year than previously thought”,[vi] and said that this suggested that Earth is more sensitive to fossil-fuel emissions than previously thought.
I was asked for my thoughts on the Resplandy paper as soon as it obtained media coverage. Most commentators appear to have been content to rely on what was said in the press release. However, being a scientist, I thought it appropriate to read the paper itself, and if possible look at its data, before forming a view.
The method used by Resplandy et al. was novel, and certainly worthy of publication. The authors start with observed changes in ‘atmospheric potential oxygen’ (ΔAPOOBS).[vii] In their model, one component of this change (ΔAPOClimate) is due to warming of the oceans, and they derived an estimate of its value by calculating values for the other components.[viii] A simple conversion factor then allows them to convert the trend in ΔAPOClimate into an estimate of ocean heat uptake (the trend in ocean heat content).
On page 1 they say:
From equation (1), we thereby find that ΔAPOClimate = 23.20 ± 12.20 per meg, corresponding to a least squares linear trend of +1.16 ± 0.15 per meg per year[ix]
A quick bit of mental arithmetic indicated that a change of 23.2 between 1991 and 2016 represented an annual rate of approximately 0.9, well below their 1.16 value. As that seemed surprising, I extracted the annual ΔAPO best-estimate values and uncertainties from the paper’s Extended Data Table 4[x] and computed the 1991–2016 least squares linear fit trend in the ΔAPOClimate values. The trend was 0.88, not 1.16, per meg per year, implying an ocean heat uptake estimate of 10.1 ZJ per year,[xi] well below the estimate in the paper of 13.3 ZJ per year.[xii]
Resplandy et al. derive ΔAPOClimate from estimates of ΔAPOOBS and of its other components, ΔAPOFF, ΔAPOCant, and ΔAPOAtmD, using – rearranging their equation (1):
ΔAPOClimate = ΔAPOOBS − ΔAPOFF − ΔAPOCant − ΔAPOAtmD
I derived the same best estimate trend when I allowed for uncertainty in each of the components of ΔAPOOBS, in the way that Resplandy et al.’s Methods description appears to indicate,[xiii] so my simple initial method of trend estimation does not explain the discrepancy.
Figure 1 shows how my 0.88 per meg per year linear fit trend (blue line) and Resplandy et al.’s 1.16 per meg per year trend (red line) compare with the underlying ΔAPOClimate data values.
Figure 1. ΔAPOClimate data values (black), the least squares linear fit (blue line) to them, and the linear trend per Resplandy et al. (red line)
Assuming I am right that Resplandy et al. have miscalculated the trend in ΔAPOClimate, and hence the trend in ocean heat content (OHC), implied by their data, the corrected OHC trend estimate for 1991–2016 (Figure 2: lower horizontal red line) is about average compared with the other estimates they showed, and below the average for 1993–2016.
Figure 2. An adaptation of Figure 1b from Resplandy et al. with the
corrected estimate for the APOClimate derived ΔOHC trend added
(lower horizontal red line; no error bar is shown)
I wanted to make sure that I had not overlooked something in my calculations, so later on November 1st I emailed Laure Resplandy querying the ΔAPOClimatetrend figure in her paper and asking for her to look into the difference in our trend estimates as a matter of urgency, explaining that in view of the media coverage of the paper I was contemplating web-publishing a comment on it within a matter of days. To date I have had no substantive response from her, despite subsequently sending a further email containing the key analysis sections from a draft of this article.
Full post here
So much for “peer review” catching mistakes. Nature surely didn’t.
Dr. Roger Pielke did his own analysis and found the trend is wrong, just like Nic:
Lewis is correct that the linear trends reported by Resplandy et al are not matched by what the data indicate. See figure below which I just created based on data provided by Resplandy et al.
Mistakes happen in science, that's no crime.
What matters more is what you do next. /END pic.twitter.com/ylFqZngbmm
— Roger Pielke Jr. (@RogerPielkeJr) November 6, 2018
Follow up: More Qs
There reported linear trends are not replicable based on data accompanying paper. I can get very close, in some cases, but not exact.
I see nothing in the methods explaining why this might be so.
— Roger Pielke Jr. (@RogerPielkeJr) November 7, 2018