I foreshadowed last time a post on a paper that purports to explain the ‘hiatus’ in global warming through the action of trade winds. The paper is by Matthew England as lead author, and others, and it was published a few days ago in Nature Climate Change. You can view a three-minute talk about it by Professor England at the UNSW website, here. A good summary might be this: Heat stored in the western Pacific Ocean caused by an unprecedented strengthening of the equatorial trade winds appears to be largely responsible for the hiatus in surface warming observed over the past 13 years … a dramatic acceleration in winds has invigorated the circulation of the Pacific Ocean, causing more heat to be taken out of the atmosphere and transferred into the subsurface ocean, while bringing cooler waters to the surface.
The authors warn that when the winds slow down the warming will return. One of the newspaper reports called it a ‘landmark study’, and it has certainly gone global, with newspapers and websites everywhere commenting on it. And the ordinary reader is tempted to say, well, it may be the case. And it may be. But a curious reader might want to ask what caused the winds to accelerate. He or she might also wonder whether, if these winds can temper warming due to carbon dioxide accumulation over the past decade or so, might it have done so in the past as well, and might the winds rather than carbon dioxide have the predominant role in temperature change.
In short, Professor England seems to have accepted the fact of the ‘hiatus’, but his explanation for it rather brings into question the whole AGW hypothesis: that carbon dioxide is the control knob. Plainly, it isn’t, while these winds blow, if that really is the explanation. And what about this ‘dramatic acceleration’ in the winds? That puzzled me for two reasons. One is that we don’t actually have good data about winds in the past, and it turns out that Professor England accepts that is so: a lot of his paper is based on models and reanalysis, not on good hard data.
The other reason is that people were saying rather opposite things about the winds a few years ago. Here is one account, from Nature in 2006: The vast loop of winds that drives climate and ocean behavior across the tropical Pacific has weakened by 3.5% since the mid-1800s, and it may weaken another 10% by 2100, according to a study led by University Corporation for Atmospheric Research (UCAR) scientist Gabriel Vecchi. Unsurprisingly, the author said that the only plausible explanation for the slowdown is human-induced climate change. The ABC Science Unit apparently reported both stories, much as they are summarised here, but apparently without noticing in these last few days that they went in opposite directions.
All in all, this is a paper that cries out for good data and better argument. Because the oceans are vastly larger than the atmosphere, one would normally expect the oceans to have a major effect on the atmosphere and thus on the winds, rather than the winds having a profound effect on the ocean. And if all this heat is being pushed into the oceans, two questions arise. The first is why we can’t actually find much evidence of the warming in the Argo buoy data. There is a bit of extra heat, on some measures, but there is also a good of uncertainty about the accuracy of the data. There’s not much evidence of sea-level rising because of the extra heat, which you would expect to be the case because of thermal expansion. And when there really was a lot of extra heat, in the 1980s and 1990s, there was no obvious increase in the sea-levels in consequence.
The second question is where the heat goes and how it is to come out again. The notion that the missing heat has somehow passed through the first 2,000 metres of ocean depth, and is hidden in the ocean depths, has always seemed to me a highly implausible hypothesis. The England hypothesis doesn’t seem any more powerful to me. The oceans are so vast that the small amount of warming that is involved would hardly be noticed there. Oh, and when and how and why does it emerge, to bring on ‘the return of warming’?
If you want to read a tough-minded and highly skilled assessment of the England paper, go to Jo Nova, where you will also find a thoughtful contextual account of the issue by William Kinninmonth, who used to be in charge of the National Climte Centre in our Bureau of Meteorology. So far, I have seen no defence by the authors or their supporters of these analyses. Skeptical Science will tell you that the England paper is ‘consistent’ with climate research, but it doesn’t attempt at all to deal with the quite sceptical analyses that I have mentioned.