Global SSTa has really been ratcheting up now for a while. At the moment, the strong ongoing El Niño is doing most of the work, but there is no question that even this has been provided with a significantly elevated baseline from which to soar, a raised mean level seemingly establishing itself already years before the current El Niño started moving.
Well, it just so happens that this new level is higher than the old one by quite exactly 0.1 K. How can one tell?
Like this …
We noted and discussed already a year ago how the global lower troposphere has yet to respond to the conspicuous and mostly extratropical accumulation of surface heat in the NE Pacific basin starting in mid 2013.
Under the working hypothesis that this abnormal and persistent NE Pacific surface heat phenomenon (often simply nicknamed “The Blob”) is responsible for the entire 0.1K lift in the mean level of global SSTa since 2013, and positing that the lower troposphere has not yet responded to it, hence giving rise to the distinct divergence seen over the last couple of years between the “gl SSTa” and “tlt” curves, we lower the former en bloc by 0.1K from July 2013 onwards (yellow vertical line in Fig.1) and superimpose it on the latter:
As you can see, a pretty decent fit. The sea surface (red) is always ahead, the lower troposphere (blue) always has the greater amplitudes.
Also, since the tlt curve clearly follows a flat line from 1997/98 to 2014/15 (a stretch of time commonly dubbed “The Pause”), then since the down-adjusted global SSTa-curve in Fig.1 evidently does the same, we can be pretty sure that our estimate of a 0.1K rise in mean level since mid 2013 is accurate.
Another temperature anomaly dataset that naturally does not capture “The Blob” is the NINO3.4 SSTa one of the equatorial central-eastern Pacific. Since we know how global temps normally track the NINO3.4, how extremely influential it is on global climate, it is always instructive to compare the global with the NINO SST anomaly to see just where the two separate. The question is: If we adjust the former down by 0.1K from July 2013 (light green vertical line in Fig.2) down to the last data point, will it depart at all from (that is, run any higher than) the latter post 2012/13?
As you can see, it obviously doesn’t.
So, following this, we can be pretty confident that the rise in global mean level SSTa from mid 2013 till today really is pretty close to 0.1 K.
Having settled that, the question then becomes: Can we explain this rise entirely through the development of the NE Pacific anomaly?
Well, here’s the region in question:
The fascinating thing about this is the fact that the area of ocean surface inside the borders of this sector (I call it the “Blob-NE Pacific Sector”) covers only about 8.3% of the World Ocean as a whole. Or about one twelfth of it.
Which is to say that, if this region alone were to lift the global SST anomaly by 0.1 degree Celsius, as is claimed (by my working hypothesis), its own anomaly would have to increase by 1.2 degrees Celsius! And this feat it would have to accomplish over a period of only about two, two-and-a-half years! Which would be impressive by almost any measure, and certainly for one single, continuous expanse of water encompassing 30 million square kilometres, the same area as the entire continent of Africa!
Something really unusual would have to occur.
And apparently something did …
Here’s how the SST anomaly of the “Blob-NE Pacific Sector” has evolved since late 1981:
Notice anything in particular?
First of all, look at the general trend of the data from 1981/82 to 2013 (31-32 years). What do you see? A lot of ups and downs, especially after about 1996. But the general tendency, seeing beyond the ‘noise’, is rather non-directional, rather flattish. You could pretty much draw a thick straight line along the zero level (just slightly below it) and represent quite well the mean about which the anomalies fluctuate.
But then something truly remarkable starts happening in 2013. It’s hard to tell exactly, but the anomaly seems to rise somewhere between 1 and 1.5 degrees Celsius between 2013 and September 2015, depending on at what time during 2013 you start counting.
However, the rise is of course not immediate. It takes a full two, two-and-a-half years to get there. We’re there today, but weren’t along the way here.
So what we need to do is subtract the “Blob-NE Pacific Sector” SSTa (as depicted in Fig.4) – after having scaled it down properly for surface area – from the “global” SSTa and see what we’re left with.
Here’s the result of that operation:
Most interesting. From simply eyeballing this graph, there appears to be some extra heat remaining on the far side of the 2009/10 El Niño even after the “Blob-NE Pacific Sector” has been subtracted from the global mean.
Before we draw any rushed conclusions, though, let’s conduct this with just a tad more rigour. What we’ll do is simply compare our graph in Fig.5 above with the full global curve, only adjusted down 0.1K from July 2013 onwards. Since we’ve already established that our assumption of a 0.1K elevation of the mean global SSTa level apparently occurring some time before the rise of the current El Niño in fact seems to be a pretty accurate description of reality, then this comparison enables us to determine directly to what extent this global rise came as the result simply of the prodigious growth spurt of the NE Pacific SST anomaly starting around mid 2013.
Let’s have a look:
What do we see?
In order to fully grasp what’s going on here and understand the subtle deviations between these two curves from start to finish, one needs to relate this graph (Fig.6) to the one in Fig.4 above, of the “Blob-NE Pacific Sector” SSTa itself. (Bear in mind, the Fig.4 graph runs from 1981, this one from 1997 only).
The yellow vertical line intersects the two SSTa curves at their July 2013 data points, after which the red global curve is adjusted down by 0.1K en bloc. Before (to the left of) this line there appears to be nothing out of the ordinary going on. Up until June 2013 everything is seemingly going ‘according to plan’. What happens beyond this point (to the right of it) is what we focus our interest on. And note: While the black “global minus blob” curve drops below the red “full global” curve from 2002 onwards (to the 2006/07 transition), the former lifts above the latter starting July 2013. Which is the opposite pattern occurring at the same spot in an equivalent ENSO/SSTa sequence. (I discuss these recurring sequences since 1970 e.g. here.)
This very much suggests that at this point in time there is extra heat accumulated at the surface somewhere in the global ocean even outside the NE Pacific sector.
And it turns out there is … (As will be revealed towards the end of this post.)
However, the “Blob-NE Pacific Sector” SST anomaly grows ever stronger as time passes (as can be readily observed in Fig.4), while the ‘extra-blob’ surface heat rather seems to fall gradually back to normal. You can see in Fig.6 how the red curve is far behind the black one in 2013-14, but how it very nearly touches it come 2014 proper, before it finally runs past it in 2015. It is now pretty much where it should be. The “Blob-NE Pacific Sector” can now (as of 2015) effectively be said to be responsible for the entire extra rise of 0.1K in the global SST anomaly. But only in 2015. Not so in 2013 and 2014. You can see why in Fig.4. The NE Pacific anomaly increases abruptly, but not abruptly enough. It still takes time for it to reach the 1.2 degrees of required rise. It wasn’t there all at once …
OK. So does that mean we can now claim to have this issue finally resolved? “The Blob” does it all, at least since entering 2015?
No. Not quite. For there is one notable aspect yet to be considered, one that our final analysis needs to include.
And that is the NE Pacific ENSO effect. El Niños (and La Niñas) playing out in the equatorial zone of the East and Central Pacific Ocean influence, through so-called atmospheric bridges, the NE Pacific basin, just as they do to other major ocean basins of the world, notably the Atlantic and the Indian Ocean. Have a look once again at the NE Pacific curve in Fig.4 and you will easily spot the ENSO signal along the way, especially post 1996/97.
So part of the reason why the “Blob-NE Pacific Sector” SST anomaly has soared to unknown heights during the last year is definitely the teleconnected influence of the strong equatorial El Niño reinforcing the NE Pacific surface heat.
Which means that the NE Pacific cannot independently account for the entire rise in its own SST anomaly through 2014-15.
And so, the actual ‘extra-blob’ residual heat turns out to be larger than first assumed even in the last year, year-and-a-half …
Our original working hypothesis, that the NE Pacific “Blob” phenomenon alone has given rise to the entire apparent 0.1K upward shift in the mean global SSTa level say post La Niña 2011/12, is shown to be incorrect.
It’s hard to give an exact estimate, of course, but were I to venture a guess, I would say that about 70% of the apparent pre-2015 0.1K mean level elevation of the global SSTa are derived directly from the abnormal heat accumulated at the surface of the “Blob-NE Pacific Sector” since mid 2013, but the last 30% still somehow originate from extra surface heat elsewhere in the global ocean.
Two questions would then naturally pose themselves: Where in the global ocean? And at what time did it arise?
Answers to both are provided by the observational data. And what it seems to suggest is going on is indeed quite intriguing …
Which leads us to the final resolution …
The ‘extra-blob’ heat post 2010:
I’ve divided the World Ocean outside the NE Pacific into seven sectors or basins: The north and south polar oceans (the Arctic and the Southern Oceans), the North and South Atlantic, the Southeast Pacific, the West Pacific and the Indian Ocean:
How did the SST anomaly evolve within these seven separate parts of the ocean since 1999? (I’ve chosen this year specifically to avoid the great El Niño of 1997/98 and its direct aftermath.) I’ve set the 2009/2010 transition as the dividing line between mean levels, and use the mean of the ‘Before Period’ of 1999-2009 as the ‘climatological normal’, to see whether one can discern a lift or not during the ‘After Period’ of 2010-2015.
Let’s first have a look at the polar oceans:
The sea surface temperature anomalies around the poles of the northern and the southern hemispheres respectively move rather conspicuously in opposite directions. One could of course say, from the first diagram (upper left), that the Arctic Ocean adds to the post-2010 global rise. But at the same time it is clearly offset by the drop in the Southern Ocean anomalies (upper right diagram). Seeing how the two polar basins even in combination (though with regions of permanent sea ice excluded) make up less than 8% of our planet’s total ocean area, their separate impact on the final SSTa is rather miniscule. And so claiming that the Arctic Ocean, making up about 3% of the total ice-free area, is somehow a significant – even detectable – contributor to the post-2010 global rise in SSTa would be an overstatement, to put it mildly. Also, the polar anomalies – at least in the relative short term – seem to live their own lives to some extent, set somewhat apart from the rest of the world, the processes influencing them being largely region-specific, like – importantly – sea ice conditions.
In the final diagram of Fig.8 (the lower one) I’ve summed the SSTa of the two polar oceans (after having area weighted them against each other; the Southern Ocean is, after all, much larger than the Arctic) into one ‘Net Polar Anomaly’ stretching back to 1997. And as can be seen, there is no ‘Net Polar’ rise at all in the mean SSTa level after 2010 (yellow section) relative to the period before (light blue section).
Next up, three large sectors of the global ocean that also as a whole do not exhibit a lift in their mean anomaly post 2010: The North and South Atlantic plus the Southeast Pacific:
The orange segments wedged in between the light blue ‘Before’ and yellow ‘After’ periods mark the 2009/10 El Niño response and/or associated accumulations of surface heat. The South Atlantic one spanning from 2009 to 2011 is particularly prominent.
Finally, the ocean basins where relevant things actually do appear to happen: The Indian Ocean and the West Pacific:
There’s an obvious upward shift in the Indian Ocean mean level SST anomaly after the 2009/10 El Niño (left diagram). It is actually the same kind of shift that we saw also in the West Pacific and the North Atlantic following the great El Niños of 1987/88 and 1997/98. But this time around the net (basinwide) step up only really materialised in the Indian Ocean. (We see this phenomenon also very clearly in the OHC record.) The Atlantic Ocean responded quite remarkably to the 2009/10 El Niño, exhibiting a rather towering and persistent signal from north to south (Fig.9), but even so, it never resulted in any subsequent upward shift in its mean SST anomaly; rather, it soon after fell back to its previous level.
There certainly is no clear upward shift to be observed in the West Pacific SSTa this time around (right diagram above). Not anything like what happened in 1988 and 1998. However, there is still a certain ‘up-bulging’ to be discerned from 2010 to 2015, especially during the last couple of years. The lofty peaks of late 2013 and 2014 are mainly the result of unusual heat anomalies in the northern tropics, but also – perhaps a bit unexpectedly – in the extensive extratropical region stretching between the south coast of Australia and the Southern Ocean, and connected hydrographically rather to the Indian Ocean than to the rest of the West Pacific.
If we were to consider these two adjoining basins as one, we have almost 37% of the global ocean surface covered. The SSTa since 1999 of our ‘new’ composite Indian-West Pacific (or “Indo-Pacific”) basin would then be seen to advance through time like this:
Which would easily account for the remaining 0.03K elevation (out of the total 0.1) of the global mean SSTa over the last few years.
But would this give us the final answer to our original question ‘Where’? (Where exactly in the global ocean is the ‘extra-blob’ surface heat to be found?)
What we find if we move from anomaly time series to anomaly maps is the following:
Figure 12. Global SSTa, annual averages 2010-2014. (Maps originally created using the GISS map-generating tool; the NE Pacific basin (65N-0, 80-180W) subsequently blotted out by me.)
What quasi-consistent pattern, then, emerges from the five maps above?
To an approximation, this:
What we see is a general concentration of surface heat post 2009 in wide bands stretching west-east inside the temperate zones (the Ferrel Cells), between the 30th and 50th parallels, in all of the major ocean basins of the world; in the Atlantic, the Indian and the Pacific Ocean alike, both north and south of the equator.
And this is a familiar pattern. The same has been seen before. Both post 1987 and 1997.
What happens is that certain distinct, great (solitary) El Niños, aided by the strong La Niñas directly on their heels, will push a great deal of an accumulated excess of surface (or near-surface) heat out of the tropics and into the extratropics, from where it will have a harder time escaping before new heat enters the system through the tropical oceans. This process will generally lead to overall ‘global’ warming.
What is new this time around is that there is no upward step in the overall SSTa in either the West Pacific or the North Atlantic, only in the Indian Ocean, and the excess surface heat in the latter is now spread out mainly across the eastern and central part of its SH sector, seemingly ‘anchored’ to the southwest coast of Australia. This is something rather new.
The oceanic processes playing out globally following the great El Niños of 1987/88 and 1997/98 repeated themselves – not unexpectedly – during the equivalent aftermath of the 2009/10 El Niño. However, this time they did not manage to pull off a similar global rise in the mean global SSTa. What we see today (map in Fig.13) are the remains of an attempt that didn’t fully come to fruition, but that still made an impact, especially – for some, as of yet unknown, reason – in the Indian Ocean. It did raise the mean level of global SSTa, by cirka 0.03K, which is hardly detectable in itself, but which ended up contributing to the larger base level rise of 0.1K seen since mid 2013, caused mainly (but not entirely) by “The Blob” phenomenon of the NE Pacific.