The Wunsch/Lloyd controversy and the ocean deeps

A month ago, "The Australian" published a summary by Graham Lloyd of a forthcoming paper by Carl Wunsch which found cooling, not the warming predicted by Warmists, in the ocean deeps.  This embarrassed Wunsch, who wrote a "corrective" letter which was published in "The Australian" shortly thereafter.  A warmist blog then piled onto the action in an attempt to rubbish the Lloyd article but added little to what Wunsch had said.  I have now had time to read all three documents and can see nothing wrong with the Lloyd article.  I reproduce below both the original article and Wunsch's reply so that people can judge for themselves.

The only substantial point Wunsch makes in his short reply was that he believes that the ocean is warming overall, though he does not say by how much.  That may have saved Wunsch's reputation among Warmists but it was not the point of the Lloyd article.  The point is that all the warming allegedly hidden in the ocean deeps was not found. There was in fact on average a tiny degree of cooling.  Even in his reply Wunsch admits that.  So the Lloyd article is indeed fatal to the last-ditch defence of their theory currently being mounted by Warmists

Perhaps the most interesting part of the Lloyd article, however, was a comment obtained from a Prof. Hogg at the very end of the article.  He pointed out that change comes very slowly to the ocean deeps:  “So if cooling has occurred over large parts of the abyssal ocean, it is unrelated to global warming of the atmosphere over the last century.”  Equally, then, if warming has occurred over large parts of the abyssal ocean, it is unrelated to global warming of the atmosphere over the last century.  The implication of that would seem clearly to be that there is NO CHANCE of current warming being found in the ocean deeps.

Puzzle of deep ocean cooling

THE deep oceans have been cooling for the past two decades and it is not possible to say whether changes in ocean heat adequately explain the “pause” in global warming, two of the world’s leading ocean scientists have said.

Warmer oceans have been a key explanation for the “missing” heat. Global average surface temperatures have not increased dramatically for more than a decade despite steadily rising carbon dioxide levels in the ­atmosphere.

A paper by Carl Wunsch from Harvard University and Patrick Heimbach from MIT, accepted for publication with the Journal of Physical Oceanography, says more work is needed.

“Direct determination of changes in ocean heat content over the past 20 years are not in conflict with estimates of the radiative forcing, but the uncertainties remain too large to rationalise, e.g. the apparent ‘pause’ in warming,” Professor Wunsch and Dr Heimbach say.

They conclude that much less heat is being added to the oceans than has been claimed in previous studies.

Professor Wunsch and Dr Heimbach say trends showed a warming in the upper ocean and a net cooling below 2000m. Below 3600m, the cooling is about 0.01C over 19 years.

“As with many climate-­related records, the unanswerable question here is whether these changes are truly secular, and/or a response to anthropogenic forcing, or whether they are fragments of a general red noise behaviour,’’ the paper says.

Some climate scientists claim the deep oceans are not significant because of the long time­frames over which temperature changes occur.

Professor Wunsch and Dr Heimbach say shifts in deep ocean properties “may indeed be so slight that their neglect in discussions of heat uptake and sea level change is justified”.

“The history of exploration suggests, however, that blank places on the map have either been assumed to be without any interesting features and dropped from further discussion, or at the other extreme filled with ‘dragons’ invoked to explain strange reports,” they say.

The paper says that, given the combination of the high stakes for society in the accurate ­estimation of global heating rates and sea level rise, and the fundamental science questions of understanding of oceanic variability, direct confirmation or refutation of the existing hypothesis was essential.

Andy Hogg from ANU said while there was uncertainty about temperatures in the deep ocean, shallower regions were well understood, and the findings of the Wunsch paper were “consistent” with warming oceans. He said cooling of the deep ocean was not necessarily significant. “Most parts of the abyssal ocean take a very long time (centuries to millennia) to come into equilibrium with surface forcing,” he said. “So if cooling has occurred over large parts of the abyssal ocean, it is unrelated to global warming of the atmosphere over the last century.”

He said there were key parts of the abyss, which had a closer connection with the surface. “The paper indicates that these regions have indeed been consistent with the expected heat uptake of the ocean in a warmer world,” Dr Hogg said.

A recent paper by Matthew England, executive director of the climate change research centre at the University of NSW, said the global surface temperature “hiatus” could be explained by increased winds in the Pacific Ocean. The paper claims the strong trade winds, which pushed heat deeper into the ocean, explained why climate models had not matched physical observations on global temperatures, a key area of dispute between climate scientists and sceptics.

Understanding the ocean

THE article by Graham Lloyd will likely leave a mis-impression with many of your readers concerning the substance of our paper that will appear in the Journal of Physical Oceanography (“Puzzle of deep ocean cooling”, 25/7).

We never assert that global warming and warming of the oceans are not occurring — we do find an ocean warming, particularly in the upper regions.

Contrary to the implications of Lloyd’s article, parts of the deep ocean are warming, parts are cooling, and although the global abyssal average is negative, the value is tiny in a global warming context.

Those parts of the abyss that are warming are most directly linked to the surface (as pointed out by Andy Hogg from the ANU).

Scientifically, we need to better understand what is going on everywhere, and that is an issue oceanographers must address over the next few years — a challenging observational problem that our paper is intended to raise.

Carl Wunsch, Harvard University and Massachusetts, Institute of Technology

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