Misunderstandings about the Pacific Decadal Oscillation

Misunderstandings about the Pacific Decadal Oscillation

Guest post by Bob Tisdale


The first version of this post (The Common Misunderstanding About The PDO dated June 26, 2008) incorrectly described the method for calculating the Atlantic Multidecadal Oscillation. I originally intended to do a quick correction in agreement with my post The Atlantic Multidecadal Oscillation – Correcting My Mistake, but then I decided to expand this post.


Many climate change bloggers often note that global temperatures rise when the Pacific Decadal Oscillation (PDO) is positive and drop when the PDO is negative. They then make the assumption that it’s the PDO that causes global temperature to vary. To dispel this, let’s first examine what the PDO is.


The Pacific Decadal Oscillation (PDO), Figure 1, is “derived as the leading PC of monthly SST anomalies in the North Pacific Ocean, poleward of 20N. The monthly mean global average SST anomalies are removed to separate this pattern of variability from any ‘global warming’ signal that may be present in the data.” The quote is from the JISAO website: http://jisao.washington.edu/pdo/PDO.latest

The main JISAO PDO webpage is here:



Figure 1

The semi-periodic variation in the PDO can be better seen when the data is smoothed with a 121-month running-average filter, Figure 2.


Figure 2


Nathan Mantua of the University of Washington and JISAO, in an email, described the process used to calculate the PDO. And it is a process:

“The full method for computing the PDO index came from Zhang, Y., J.M. Wallace, D.S. Battisti, 1997: ENSO-like interdecadal variability: 1900-93. J. Climate, 10, 1004-1020.

“They labeled this same time series “the NP index” (see their figs 5 and 6). The steps are listed below, and files described below can be found at: ftp://ftp.atmos.washington.edu/mantua/pdofiles/

“Data used:

* monthly 5×5 Hadley Center SST 1900-93


1. create monthly anomaly fields for all grid points

2. create a monthly mean global SST anomaly time series for all months, 1900-93, using gridpoints specified in file grid.temp.glob_ocean.977

3. create a “residual SST anomaly” field for the North Pacific by subtracting out the global mean anomaly from each North Pacific grid point in file grid.N_Pac_SST.resi.172 (20N-65N, only in Pacific Basin) for all months and locations

np_resi(mo,loc)= np_ssta(mo,loc) – global_mean(mo)

4. compute the EOFs of the North Pacific residual SST anomaly fields, and ignore all missing data point (set them to zeros)

5. the PDO index is the leading PC from the above analysis

6. for PDO index values post 1993, project observed ‘North Pacific residual SST anomalies’ onto the leading eigenvector (what we call the ‘PDO pattern’ of ssts) from the EOF analysis done in step 4. We now do this with the Reynold’s and Smith Optimally Interpolated SST (version 2) data.”


A link to the referenced Zhang et al (1997) paper is here:


The point of listing that multistep process was to show that the PDO is a statistically created dataset. Let’s look at what the PDO does not represent.


SST anomalies for the North Pacific Ocean (20N-65N) and scaled PDO data are illustrated in Figure 3. The PDO does not represent SST anomalies for the North Pacific.


Figure 3


The PDO is not calculated in the same fashion as the Atlantic Multidecadal Oscillation (AMO). NOAA ESRL calculates the AMO by detrending SST anomalies for the North Atlantic. Refer to The ESRL AMO webpage:


In Figure 4, the PDO (scaled) is compared to detrended North Pacific (North of 20N) SST anomalies (calculated the same as the AMO). While there are semi-periodic variations in detrended North Pacific SST anomalies, the PDO does not represent them.


Figure 4


Let’s subtract Global temperature anomalies (LST & SST) from North Pacific SST anomalies to see what that curve looks like. Refer to Figure 5. The PDO does not represent the difference between global temperature anomalies and North Pacific SST anomalies.


Figure 5


The PDO represents a pattern of SST anomalies in the North Pacific. The operative word in that sentence is PATTERN. Figure 6 (from the JISAO PDO webpage) illustrates the warm and cool phases of the PDO. When the PDO is positive, SSTs in the eastern North Pacific are warmer than in the central and western North Pacific, and when the PDO is negative, the reverse is true.


Figure 6

Keep in mind, though, that the PDO data itself represents only the North Pacific, north of 20N, which I’ve blocked off in Figure 7. Figure 7 is a map of SST anomalies from April 14-21, 2008 that shows a negative PDO pattern. It’s from the NASA Earth Observatory webpage here:


Specifically, this linked page:



Figure 7


There is also a popular belief that the sign of the PDO dictates whether El Nino or La Nina events dominate. There is, however, an analysis that contradicts that belief. Refer to:


And for those who enjoy PowerPoint presentations for the visuals:


In “ENSO-Forced Variability of the Pacific Decadal Oscillation”, Newman et al state in the conclusions, “The PDO is dependent upon ENSO on all timescales. To first order, the PDO can be considered the reddened response to both atmospheric noise and ENSO, resulting in more decadal variability than either. This null hypothesis needs to be considered when diagnosing and modeling ‘internal’ decadal variability in the North Pacific. For example, the observed spatial pattern of Pacific SST decadal variability, with relatively higher amplitude in the extratropics than in the Tropics, should be at least partly a consequence of a reddened ENSO response.”

In the introduction, Newman et al explain, “Anomalous tropical convection induced by ENSO influences global atmospheric circulation and hence alters surface fluxes over the North Pacific, forcing SST anomalies that peak a few months after the ENSO maximum in tropical east Pacific SSTs (Trenberth and Hurrell 1994; Alexander et al. 2002). This ‘atmospheric bridge’ explains as much as half of the variance of January-March seasonal mean anomalies of SST in the central North Pacific (Alexander et al. 2002). Furthermore, North Pacific SSTs have a multiyear memory during the cold season. Deep oceanic mixed layer temperature anomalies from one winter become decoupled from the surface during summer and then ‘reemerge’ through entrainment into the mixed layer as it deepens the following winter (Alexander et al. 1999). Thus, over the course of years, at least during winter and spring, the North Pacific integrates the effects of ENSO.” [Emphasis added]

They continue, “The prevailing null hypothesis of mid latitude SST variability posits that the ocean integrates forcing by unpredictable and unrelated weather, approximated as white noise, resulting in ‘reddened’ noise with increased power at low frequencies and decreased power at high frequencies (e.g., Frankignoul and Hasselmann 1977). In this paper, we propose an expanded null hypothesis for the PDO: variability in North Pacific SST on seasonal to decadal timescales results not only from red noise but also from reddening of the ENSO signal.”

Figures 8 and 9 are comparative graphs of the PDO and NINO3.4 SST anomalies, smoothed with 12-month and 121-month filters.


Figure 8



Figure 9


As discussed and illustrated, the PDO cannot directly explain global temperature variations because it represents a pattern of SST variability, not SST. And the Newman et al paper explains why the low frequency variations of the PDO are greater than ENSO. They write in their abstract, “Variability of the Pacific decadal oscillation (PDO), on both interannual and decadal timescales, is well modeled as the sum of direct forcing by El Nino-Southern Oscillation (ENSO), the ‘reemergence’ of North Pacific sea surface temperature anomalies in subsequent winters, and white noise atmospheric forcing.” [Emphasis added]

Do other areas of the Global oceans integrate the effects of ENSO like the North Pacific?


The links for the PDO data are included in the text of the post. HADISST NINO 3.4 SST anomaly data, HADISST North Pacific SST anomaly data, and the combined CRUTEM3+HadSST2 global temperature anomaly data are available through the KNMI Climate Explorer website:



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Bill Illis

Good post Bob,
Having worked with these ocean indices, I can say the PDO does not provide very good correlations and the ENSO, by itself, provides a much better reflection of the impacts this region of the planet has on global temperatures.
It would be relatively straight-forward to create a PDO index similar to the method used for the AMO. But one problem is, it would be covering a very large part of the globe and, hence, would already be a large part of the global temperature anomaly itself – ie. not a sufficiently independent variable.


Can you address whether the PDO is a short term, or long term phenomenon? You seem to be saying that it is simply a particular manifestation of ENSO. But ENSO varies on much shorter time scales than has traditionally been attributed to the PDO. Can you clarify, or elaborate, on that?

Harold Ambler

Don Easterbrook is an expert on the PDO.
He seems to have a completely different understanding of the phenomenon, as he:
1. Sees the PDO signal in the climate record (glacial advance and retreat, specifically) going back for (at least) centuries
2. Does regard the PDO as a driver
3. Predicts 20-30 years of mild cooling as we move forward, specifically due to the changeover of the PDO to its negative phase

George E. Smith

One thing that puzzles me in all of this. So-called “global temperature” as represented by GISStemp and the like; being just some sort of average of something (not knowing the details of Hansen’s AlGorythm) cannot explain any sort of global patterns or circulations, since it requires temperature differences to cause energy flows in any direction (other than radiation of course; which however is not in any particulaqr direction).
So I don’t see how “global warming” effects as predicted by green house gas theories of the MMGWCC kind, can cause any sort of oscillation such as the PDO or ENSO or anything else; after all they are global effects not local and it requires local temperature variations to create a drive for energy flows around the world; simply jackling all temperatures up by 0.2 deg C is not going to cause thermal energy to flow anywhere it wasn’t already going.
So for me, I can’t see any human influence appearing in PDOs or ENSOs, which presumably are perfectly normal occasional natural climate changes.
So how much is known about just what physical processes cause PDO/ENSO/La Nina events ?

I am clearly one of the bloggers who are being contradicted by the author above. Sorry, after having read the text, I am entirely unconvinced by any of the “negative” statements in this article.
As far as I can see, all widely read climate bloggers realize that PDO is about a pattern – let’s say that the PDO index is the difference of temperature anomalies between the U.S. West Coast and (minus) the central Northern Pacific. Also, most of us are convinced that the pattern helps to drive global temperatures, probably via the influence on ENSO.
I don’t see any rational counter-evidence to this statement written in the article. The observed correlation between the time-derivative of the global mean temperature and the PDO index seems to be powerful.
Also, the correlation between the relative frequency of El Nino and La Nina episodes on one side, and the PDO index on the other side, seems to be strong, and seems to be eplainable by a natural mechanism. During negative PDO phases, the warmer central Northern Pacific Ocean is able to “suck” potential El Nino conditions, bringing La Nina to the equatorial Pacific Ocean instead.
The statement that “PDO is influenced by ENSO” contradicts very basic physical principles. PDO is the slower process among the two, so it can’t possibly be measurably influenced by faster processes such as ENSO.
ENSO is faster which means that the PDO index acts as one of the external parameters determinining ENSO dynamics – at least this influence is much more important and logical to organize the events than the opposite influence. Everyone who knows what Renormalization Group or Born-Oppenheimer approximation mean will surely know where I am coming from.

Basil: You asked, “Can you address whether the PDO is a short term, or long term phenomenon?”
If we look at the last two graphs, the PDO appears to have a long term “cycle” that’s better defined than ENSO. If Newman is correct (and if I’m interpreting that paper correctly), then it’s the reemergence of anomalies (created by ENSO) that causes the PDO to persist longer and at greater amplitudes than ENSO.


Lubos Motl : ‘The statement that “PDO is influenced by ENSO” contradicts very basic physical principles. PDO is the slower process among the two, so it can’t possibly be measurably influenced by faster processes such as ENSO. ‘
That is a very good point there! unless there is any evidence of long term cycles of ENSO which could act as drivers?
PDO driving ENSO makes sense because as can be seen in the diagrams, anomalies are overall negative at the equator during cold phase, which would surely indicate a tendency towards La Nina? just an observation, I am no expert but generally all blogs/articles I have read through do put forward the idea of PDO driving ENSO, this article was quite a surprise but interesting nevertheless. However PDO graphs that are commonly used never go further back than 1900 and this is suspicious, especially since there is less oscillation in the visible data at +-1900

David L. Hagen

‘During negative PDO phases, the warmer central Northern Pacific Ocean is able to “suck” potential El Nino conditions, bringing La Nina to the equatorial Pacific Ocean instead.’
It appears in the diagrams according to the arrows that during cool phase PDO, warmer waters shift away from the equator towards the central Northern and Southern Pacific Oceans and cold waters upwell at the equator from beneath hence La Nina domination.
And during warm phase, warm water ‘accumulates’ at the equator hence El Nino, whilst cold upwelling occurs at north and south.
Seems obvious, but it appears that PDO could logically be the driving force behind ENSO events, or at least it decides what type of events will occur.

Pearland Aggie

Thanks, Bob.
By the way, here is another timely PDO article, although some of the statements in it may not agree with what you have posted.
The Pacific Ocean’s Influence on Climate Change: How Low Will the PDO Go?
The PDO is also found to be a global driver of temperature, partly because of its intimate link to the El Niño Southern Oscillation cycle. La Niña is more likely during periods of negative PDO, while periods of positive PDO yield more frequent and intense El Niño’s. Thus the tropical temperature anomalies are highly correlated with the PDO phase and in turn help produce quantifiable fluctuations in global average temperatures. From the warm to the cool PDO phase, global temperatures drop by around 0.3-0.35°F. Some may contend that these observed global temperature differences are explained by the global warming trend, as the PDO cool phase was centered in the 1950s and the PDO warm phase in the 1990s. However, it remains plausible and perhaps likely that the PDO may be an important cause of the global change and observed temperature trends during the latter half of the 20th century. Scientifically, an improved understanding of global climate change may be on the horizon, as another cool PDO phase has begun and its impacts on climate will be studied closely. If global warming ceases or cooling occurs during the next 20 years, the scientific community may come to realize that decadal fluctuations within the oceans may play a larger role in climate than is presently acknowledged. The first signs of the PDO’s impacts may already be occurring as satellite measurements of lower tropospheric temperatures derived by the University of Alabama in Huntsville (UAH) and Remote Sensing System (RSS) show no temperature increases since 2002, and in fact show a slight cooling trend. With solar activity at a 100 year minimum and the PDO expected to remain negative for several decades, the cooling trend may persist. If it does, an inconvenient truth about climate change may emerge.

John F. Hultquist

Very interesting information. Your comment “And it is a process” summed up my reaction when I first looked at the JISAO material. As all this is supposed to produce a “pattern”, and it seems to, they must have stayed up nights to think this through. It violates the “keep it simple stupid” (KISS) rule.
One of the problems of visualizing these things is the issue of map projections. We get a false impression of the areas on many of these maps. Those used here, Figure 7, for example, exaggerate the area in the far north and south. Most apparent here if one looks at Antarctic – on a globe Australia looks to be much the same size, not so here. Likewise, Greenland and Mexico are similar in size. Again, not so here.
I make an issue of this projection problem because people forget that there is substantially more of Earth’s surface area and more ocean between the Tropics and more insolation. Thus, it should not be a surprise that ENSO exerts the sorts of influences it does.
We also tend to forget that Earth is rotating and most have not looked closely at the many ocean currents. There is a country song all should listen to a few times and get this idea in their heads:
cause and effect, chain of events all of the chaos makes perfect sense
when your spinning round, things come undone
welcome to earth third rock from the sun
Joe Diffe, “Third Rock From the Sun”.

Lubos Motl: You wrote, “The statement that ‘PDO is influenced by ENSO’ contradicts very basic physical principles. PDO is the slower process among the two, so it can’t possibly be measurably influenced by faster processes such as ENSO. ”
Lubos, have a look at the monthly PDO versus NINO3.4 SST anomalies. There’s nothing slow about the PDO. Both signals are so noisy, I had to divide the data into four graphs.
NINO3.4 vs PDO from 1900 to 1925:
NINO3.4 vs PDO from 1925 to 1950:
NINO3.4 vs PDO from 1950 to 1975:
NINO3.4 vs PDO from 1975 to 2008:
They’re from my post “The Chicken or Egg: PDO or ENSO?”

There isn’t really any generation or removal of heat from “the system” with any of these processes, is there? If not, then there’s no “global mean temperature” involved, it’s just a moving around of heat to different areas. Unless new heat is being added to the system, the totally meaningless “global mean temperature” should not change. Of course that assumes complete global coverage and no garbage temperature monitoring.


Mr. Tisdale,
From reading what you have written, it is unclear: are you saying you misunderstand the PDO, or that those who see a massive long term shift in the Pacific as a strong influence on climate fail to understand the PDO?
Your clarification is appreciated.

John F. Hultquist

George E. Smith (09:52:27)
“…simply jackling all temperatures up by 0.2 deg C is not going to cause thermal energy to flow anywhere it wasn’t already going.”
The idea is that a generally warmer temperature will push the big weather makers poleward a little so that, say the boundary between summer high pressure along North America’s west coast and the Westerlies, slides northward X miles. Precipitation would decline in W. Washington and S. British Columbia. Energy would also be redistributed in these situations. There are probably better examples.
jackling? He typed that, not me. John


“As discussed and illustrated, the PDO cannot directly explain global temperature variations because it represents a pattern of SST variability, not SST.”
That looks like a non sequitur. Can the author explain further?
A pattern in SST can explain changes in total SST. It could do this by representing changed transport of heat towards the poles, or transport of heat to areas where loss by radiation was more or less efficient, or due to heat having different effects on wind, cloudiness, or precipitation depending on where it is. It’s like the way blood circulation changes make your skin go white when it’s cold and red when it’s hot. It’s a change in the pattern of where the hot blood is, but it affects temperature and heat flow too.
The correlation is saying that a large part of the change in temperature may be related to non-linear effects of the distribution of heat around the globe. For example, it could be that without any change in input, something has pushed the heat into places from where it doesn’t convect and radiate to space so easily, and so warmed the Earth. The atmosphere is not one-dimensional, as a lot of the simplistic explanations would have it, and a change in output does not necessarily imply a change in input.
Is there anything in the above analysis to show that nothing like this is happening?

Lubos: Your quote, “PDO is influenced by ENSO”, which everyone is repeating, is curious. It appears nowhere in my post. The only place the word influence was used was in the quote from Newman et al. They wrote, “Anomalous tropical convection induced by ENSO influences global atmospheric circulation and hence alters surface fluxes over the North Pacific, forcing SST anomalies that peak a few months after the ENSO maximum in tropical east Pacific SSTs (Trenberth and Hurrell 1994; Alexander et al. 2002).”
Newman et al go to great detail to explain their conclusion. If you disagree with the specifics of the paper, please detail them.

hunter: You wrote. “From reading what you have written, it is unclear: are you saying you misunderstand the PDO, or that those who see a massive long term shift in the Pacific as a strong influence on climate fail to understand the PDO?
Your clarification is appreciated.”
I don’t misunderstand the PDO. I’ve illustrated how it’s calculated, what it is, what it is not, and I’ve quoted from a paper that appears to be controversial.
Regarding long-term shifts, note that the major shifts in NINO3.4 and PDO occur at the same time in Figure 9.
Please read the Newman at al paper. Thanks.

Dear Alex, exactly! The general principle is that slower processes effectively behave as “constants” that determine the external conditions for faster processes.
Whenever we focus on a typical time scale (over which we average things etc.), the processes with the same typical duration or periodicity (in the case of periodic processes) are the most important ones. The slower processes act as external parameters (which can skew the balance of positive/negative events, like La Nina vs El Nino) while the faster processes tend to be averaged out.
Dear Bob, we must be looking at the same graphs and numbers in a very different way.
PDO is significantly slower than ENSO. This statement is obvious even from the very graphs that you have included. With the 121-month filter, it is very clear that the warm and/or cool phases of PDO last 30+ years or so, agreeing with the general “binary” classification of the warm and cool stages, see e.g.
You wouldn’t get any similar 30-year long eras out of ENSO. Of course that there is noise over there. Noise is everywhere. The difference is that also 30-year or 50-year signals can be isolated from PDO indices but they can’t be isolated from ENSO/ONI indices.
The most extreme PDO variations are very slow – multidecadal, therefore the name (!). On the other hand, La Ninas and El Ninos demonstrably take 1-3 years in average, so they’re about 10 times faster than PDO phases. This statement can also be derived theoretically because ENSO primarily depends on some atmospheric/ocean coupled behavior in a smaller region – the near-equatorial Pacific – than PDO (PDO influences 1/3 of the world’s greatest ocean) which also means that it takes a shorter time for it to switch from the negative to the positive phase.
I don’t believe that you actually disagree with any of these things because they’re completely manifest.
The statement by Newman et al. you ended up with is just a postmodern cliche of the type “everything influences everything else”. Well, yes, no, what of it? Of course that at some vague level, it’s right that anything related to ENSO influences anything else, and so on. But these things surely can’t be used to “debunk” the influence of PDO on ENSO.
What is more important than “everything impacts everything” philosophy is that one must choose a specific time scale or otherwise defined realm of phenomena and the slower processes can be approximated by constants while the faster processes may be assumed to average out.
PDO is slower than ENSO. If Mr or Ms Newman disagrees with that, and I don’t think that you have shown any evidence even for this modest statement, it simply means that Mr or Ms Newman has no idea about the ocean cycles.


I’m curious what people think about this presentation I was recently required to attend for a class: http://oregonstate.edu/groups/hydro/Seminars/spring09/docs/042209_Mote.pdf
There is video of the presentation on the same website.

Bill Illis

I just wanted to note that the actual PDO index has much more variability than the smoothed graphics you might have seen on the Internet.
Here is what the PDO Index looks like with thinner lines so you can see the additional variability. In my mind, this chart looks very, very different than the charts usually shown on the Internet.
[This is why I also do not favour using smoothing unless absolutely necessary and why I keep my line thickness down to the bare minimum so that this kind of additional detail shows up.]

Curious: You wrote, “That looks like a non sequitur. Can the author explain further?”
The PDO is independent of global temperature. It is independent of the temperature difference between the North Pacific SST anomalies and global temperature. It explains whether the anomalies in the eastern part of the North Pacific are warmer or cooler than the western and central parts. It has been correlated to other effects, such as western North American temperature, precipitation, and snowpack.

L Bowser

Can someone explain how the following is true:
The statement that “PDO is influenced by ENSO” contradicts very basic physical principles. PDO is the slower process among the two, so it can’t possibly be measurably influenced by faster processes such as ENSO.
To me this seems counterintuitive. What does the speed of a process have to do with what sort of force or affect it can exert on another process?


The question is, how much heat do the oceans exhaust or absorb over time? ENSO is important because a great deal of heat energy is exhausted into the atmosphere. The PDO is important because there appears to be a correlation between PDO phases and ENSO.
One could use the classic biological phases of North Pacific fish migration to chart the PDO. For it was fishermen who first noted that every 2-3 decades there was an obvious migration.

Lubos: “You wouldn’t get any similar 30-year long eras out of ENSO.”
Figure 9 illustrates that there are 30-year-long eras of ENSO. It’s the frequency and magnitude of El Nino events versus La Nina events that dictate whether the 121-month smoothed curve of ENSO is positive or negative. During the periods when El Ninos dominate, global temperatures rise, and when La Ninas are dominant, temperatures drop.

So, accordimg to picture 6, typhoons are to be expected in Japan, while just a few showers in the tropics..(if any). That will be a big deception for Him ( the bearer of all future distress), provided that red spot in the gulf does not mean hot waters..:), because la Nina affects that region also:

matt v.

You and I have blogged on this topic before. If
“The PDO represents a pattern of SST anomalies in the North Pacific” and if this pattern of anomalies are indicators of certain weather and climate conditions or patterns especially in the Northern hemisphere including land temperatures in North America which repeat over a period of time , then various levels of PDO can be used as predicters or indicators of past and future of climate patterns .It may not be a direct indicator of Pacific Ocean SST but it does reflect a multiple of things which originate from SST, does it not.?
You explain well, Bob, what PDO is not, but do not explain well what it is, what it can be used for and why it was developed in the first place. The definition in the CLOSING is far too confusing for any blogger

gary gulrud

I think it would help me to see, patternwise, further discussion of any ocean circulation and jet stream changes rolled into the presentation.
I admit to a provincial interest in NA weather in particular as determined by PDO and don’t care so much about the chimera, average global temp.
At any rate, ENSO as climate master doesn’t particularly alarm.

Stephen Wilde

I am conscious that ENSO in the form of El Nino and La Nina events seems to be wind driven to some extent but I am nevertheless unclear as to whether the associated changes in SSTs cause further changes in the air as a positive feedback or whether changes in the air are actually the drivers of the ENSO phenomenon.
I am also conscious that the PDO phase shifts are much larger events over longer multidecadal time scales.
Importantly there is no need for the two processes to be linked. It is quite possible that the underlying ocean cycles such as PDO, AMO et. al. could have a different causation from more temporary shifts in surface SSTs.
What matters for global air temperatures is the netted out energy characteristics of ALL the ocean cycles and various SSTs at any one time and as I have said elsewhere there are times when they work together and times when they offset one another and then one also has to add in solar variability over as many as 6 11year solar cycles or 3 22 year solar cycles.
Given that a positive PDO enhances El Nino and suppresses La Nina (or appears to) and that a negative PDO suppresses El Nino and enhances La Nina it is quite likely both that ocean cycles are seperately caused by influences other than those that cause shorter term SST variations and that those deeper longer cycles are driven more by solar variations affecting the thermohaline crculation than by changes in the air.
I don’t see the point of asserting a null effect from PDO variations by simply asserting that they represent merely a changed distribution of SSTs.
The fact is that global air changes are seen to occur after SST changes and given the basic physical differences between water than air that must be expected.
As another poster said the change in position of warm and cool areas of SST is itself quite sufficient to change the air circulation patterns and therefore the rate of energy transmission from surface to space.
Furthermore it must be perverse to suggest that changes in the SSTs such as those observed can have a zero effect on the temperature of the air globally.
This seems to be an attempt to deny the possible influence of ocean multidecadal cycles just as they are beginning to be seen to be highly significant out in the real world.
I’m not sure whether Bob supports the Newman analysis or is just putting it up as a discussion point.


Thanks. But that doesn’t clear things up much.
You say “The PDO is independent of global temperature.” Are you saying that the PDO is not statistically correlated with the rate of change of global temperature anomaly? Or are you saying that the mechanisms causing them both are such that the PDO cannot cause or influence the changes in global temperature’s rise and fall? i.e. a physical independence? If the latter, what is the argument for this?
People have looked at graphs and thought there was a correlation – that global mean temperature anomaly rose in periods of positive PDO. How has this happened, if they are independent? Eyeball failure? Or smoothing/processing errors?
If you’re saying that because PDO is not temperature, so it isn’t directly contributing to temperature in the sort of arithmetical way that both sea temperature and land temperature contribute to global temperature, then I’d agree. But I wasn’t aware that anyone had suggested such a thing. I thought the popular theory was that unknown circulation and heatflow relationships caused the low frequency component of PDO to oscillate, and that the changed patterns in heat and heat flow distribution changed the efficiency with which the Earth absorbed or radiated heat by unknown mechanisms, and that when integrated over time this caused long-term rises and falls in temperature. You wouldn’t expect PDO to equal temperature on this basis.
Are you simply correcting misunderstandings in somebody else’s theory?

Frank Lansner

Its true that Don Easterbrook foresees just a mild cooling due to the PDO.
As far as i know, he is using a GISS trend to foresee the future. (!!)
So the mild GISS cooling from 1940-77 is what he expects.
Any GISS based anything, i will not have too much faith in:

Dear Bob,
Figure 9, the very Figure 9 that you included, shows very clearly that the typical timescale over which PDO changes the sign is comparable to 30 years while the typical timescale at which ENSO changes the sign is 1-4 years.
The former is shown on the figure because the blue line has huge variations that change per 30 years. The latter is shown by seeing that there are almost no variations left after the averaging over 100+ months. If you averaged over 1-2 years, the ENSO index would give you an equally pronounced sin-like signal like PDO gives at the multidecadal scale.
The ENSO index almost certainly influences the temperature but the ENSO index itself – the relative frequency of El Ninos vs La Ninas during a decade or two – is influenced by PDO. The data clearly show this much and there are good theoretical reasons to be sure that this influence exists, too.
Best wishes

Stephen Wilde

Ah, think I see the problem.
Newman’s analysis and by implication that of Bob is that the PDO has no independent existence because it is merely comprised of data derived from the varying SST conditions involved in the ENSO phenomenon.
My comment on that, if true, is that some unrecognised underlying ocean cycle is causing that variable data to change at approximately 30 year intervals and we may as well call it the PDO.
Bob says this above:
“Figure 9 illustrates that there are 30-year-long eras of ENSO. It’s the frequency and magnitude of El Nino events versus La Nina events that dictate whether the 121-month smoothed curve of ENSO is positive or negative. During the periods when El Ninos dominate, global temperatures rise, and when La Ninas are dominant, temperatures drop.”
i.e. The 30 year variability is a function of ENSO not any underlying cycle so PDO does not exist independently.
Well in my opinion something external to ENSO is causing those phase shifts and imposing them onto the ENSO cycle. That is what I have always meant by the PDO. Perhaps we should rename it ?
Why, otherwise would the relative dominance of El Nino and La Nina change at all ?
And the same thing is going on in every ocean it seems.

I recently wrote a research article on the PDO that quantifies the impacts on climate. While we can debate as to whether the PDO and global temperatures connections are cause or effect, the raw numbers from each phase indicate that during cool phases global temperatures decrease slightly. IMO this is mostly caused by cooling in tropical Pacific, presumably from more frequent La Nina events during negative PDO.
I strongly believe that our understanding of the negative PDO’s impacts on climate will be better understood as we seek to quantify them over the next decade or so. Please check out the PDO research note here:

matt v.

I also found this helpful.
The Pacific Decadal Oscillation, or PDO, is often described as a long-lived El Niño-like pattern of Pacific climate variability (Zhang et al. 1997). As seen with the better-known El Niño/Southern Oscillation (ENSO), extremes in the PDO pattern are marked by widespread variations in Pacific Basin and North American climate. In parallel with the ENSO phenomenon, the extreme phases of the PDO have been classified as being either warm or cool, as defined by ocean temperature anomalies in the northeast and tropical Pacific Ocean.

Juraj V.

PDO cycle and US temperature record are in excellent agreement. Global temperature datasets play with PDO quite well as well – warming 1907-1940, cooling 1940-1977, warming 1977-2005. Europe is also affected by AMO, which has switched to cold recently.
Variating Solar baseline with PDO/AMO variations on the top can describe whole 20th century record very well.
@Lubos, pozdrav z Bratislavy.

Bobby Lane

All I get from this is that the PDO is not the be-all and the end-all of temperature changes globally, which makes sense to me. It does influence, however, North American temperatures – and ENSO does so especially, which with our 24 hour media coverage gets overemphasized. Weather is not climate, but it seems neither side can resist stories that illustrate their particular point of view. This is, I suppose, understandable. There are a lot more factors to global temperature than just the PDO and/or ENSO, certainly, but the world’s largest major body of water has to have at least some influence on global temperatures. If it influences cloud cover or airflow in its various temperature variations (and in NA at least this is shown to be true) then it has global reach by effect though that effect may be weak at best and overridden by stronger regional or local influences. The Earth is a closed system, therefore finite, and therefore (like your bank account) when something is spent in one place it is lacking in another. How large the effect is and how tight the correlation from place to place seems to be the key question regarding PDO and/or ENSO. That is at least my amateurish take.

First I would like to thank Bob Tisdale for his article and input. It is good in general to challenge conventional thoughts and views. Science cannot advance unless it is challenged and debated.
For now, I must remain critical of the concept however. Long term events like the PDO would be expected to have embedded short term oscillations. Likewise, the NINO cycle would as illustrated have some long term trend constructions possible. That is true of any variable data.
1998 was a very warm El Nino event. I don’t think anyone would argue that. However, I submit that the event could not have occurred without the PDO also being very warm at the time. What I make note of is figure 9. The amplitude of change in the PDO is far greater than that of the NINO.
To me it seems that the state of the ENSO can augment or mitigate the effects from the PDO but the PDO has to be the greater driver of overall temps. Along that line; referring to figure 8 and specifically the period from 1960 – 1980 it appears that the NINO was, for the most part, divergent from observed global temperature conditions while the PDO was consistent with those same conditions. Thus it would appear again that the PDO was the greater factor.

Paul Vaughan

Re: Stephen Wilde (13:10:46)
After I read the Newman et al. (2003) paper awhile back I had some similar thoughts – chicken-egg thing – is it a deck? or is it 52 cards? (Some say ENSO drives LOD; some say vice versa…) Research funding, semantics, & politics….
The Newman et al. (2003) paper was a valuable contribution.

Rhys Jaggar

I read a paper that the PDO had significant impact on US 20th century temperatures.
Given that the anomaly is close to the US west coast, this would make some sort of sense.
Is that correlation also disputed?

Tony Hansen

Thanks for the article Bob. A couple of questions if you have the time.
From fig. 7 they only use north of 20N. What percentage of the whole Pacific would this be?
From fig. 6 the max is +0.8 and the min is-.06. Why would the scale not be symmetrical? Thanks.
(Should it really be called the Far North PDO?)

matt v.

Don’t underestimate the impact of the pattern of SST anomalies that the PDO reflects as shown below. There is a correlation.
[Per HADCRUT3vgl]
1900-1926 0.048 COOL [AMO –VE, PDO –VE &+VE]
1926-1944 0.187 WARM [AMO & PDO POSITIVE]
1964-1976 0.108 COOL [AMO& PDO NEGATIVE]
1994 -2008 0.187 WARM [AMO & PDO POSITIVE]
1900 -2009 0.073 PAST CENTURY [equivalent of 0.73/century]
2002 -2009 -0.195 LATEST COOL [PDO –VE SEPT/07, AMO –VE JAN/09]
1976 -1994 0.138 C [ PRIOR TO 1994]
1994 – 2008 0.187 C [ KEY GLOBAL WARMING]
1976 – 2008 0.178 C
Notice that the period 1926-1944 had the same rate of warming as 1994-2008. Periods of global warming existed well before 1976-2008.
What made the most recent warming period [1994-2008] more significant was that some of the AMO and PDO levels were higher than usual [ AMO levels were third[1998],fourth[2003] and fifth[2005] highest ever after 1878 and 1937]
Another observation is that most of the recent warming period was really in the period 1994- 2008 and not 1976-2008. So the real warming was a decade plus three to four years only, a very short period indeed and not a climate trend or long term trend at all. It is amazing how 13-14 years got blown out of all proportions by the AGW science and misrepresented as an alarming and an unprecedented climate trend when it was really another warm hiccup of this planet where regular alternating cool and warm hiccups are par for the planet.
The AGW supporters have commented that the recent seven years of global cooling[since 2002] is too short a period to be considered a climate trend, yet the last global warming period lasted only 13-14 years, equally not a climate trend.

John F. Hultquist

Rabidkangaroo (11:46:12) About the presentation
This is standard material based on a false premise. Thus, like all the others of its ilk, each of the points can be refuted. I suggest you look at a few of the State reports and see what was done. Which was: a consulting group sold this batch of stuff to many states, controlled the process, and thus the outcomes. They are all pretty much alike.
Go to this site: http://scienceandpublicpolicy.org/scarewatch/
On the right side, under Reports, click on SPPI State Climate Profiles.
Pick a couple of the states and see what they say. When you are only allowed to consider a warming based on GHGs – and nothing else – the reports and their critiques are repetitive.

Bill Illis

People seem to like the concept of the PDO so I hesitate to write this.
But it seems to me that the PDO is just a reflection of the accumulated impact of the last few El Ninos or La Ninas over the last year or two.
It is the ENSO which drives the PDO, not the other way around, or it might be better to think of them as part of the same system.
The ENSO migrates across the Pacific at the equator from the Nina 1,2 region to Nina 3 to the Nina 4 region, from the South American coast to the Gilbert Islands/New Guinea driven by the Trade Winds.
At this point, the surface ocean currents turn to the North to form part of the Kurushio Current (the Gulf Stream of the Pacific) and the North Equatorial Counter-Current. The currents are mostly blocked to the South by shallow ocean and islands and the southery flow is weak.
The Kurushio Current then flows across the Pacific in a gyre and the ocean temperatures in the North Equatorial Counter-Current filter off further northward and, eventually, these two currents influence ocean temperatures across the entire North Pacific.
As well, at the end of the Nino 4 region at the Gilbert Islands/New Guinea, the prevailing winds shift to the NorthEast toward Alaska and California.
If the ocean surface temperatures conditions are cool at this location, the prevailing winds migrate those cooler conditions NorthEast across the Pacific (fairly rapidly) in conjunction with the ocean currents and this where we see the common wedge pattern of the PDO anomaly.
It is evident in this animation. Let it load and then speed it up as fast as your computer will allow and notice how the cool surface spreads across the Pacific from the end of the Nino 4 region.
Through these two impacts, ocean currents and prevailing winds/poleward transport of temperatures, the ENSO drives the North Pacific PDO. It also explains why the ENSO has very limited effect on southern hemisphere temperatures beyond those directly in the Tropics. Most of its energy is filtered northward.
The PDO can flow back into the ENSO region through the California Current although this current is not strong. The majority of the ocean current flowing into the ENSO region is through the Southern Pacific Peruvian/Humbolt Current and through upwelling from the deep ocean immediately below the Nina 1 and 3 regions.
Right now, despite the very negative PDO conditions, it appears that an El Nino is building. The Southern Oscillation Index has suddenly shifted to signal El Nino, the Trade Winds have slowed, Atmospheric Angular Momentum is now signaling El Nino and the Upper Ocean Heat Content is showing much warmer ocean temperature water ready to surface.

Ian Holton

One only needs to llok at a current SST anomoly map
and see why the PDO has an effect on Global Temps as the strong
cold current that flows equatorward off the western USA coast ends up in the Tropical Pacific Ocean making the current attempt by the western South American current to form an El Nino with warm water broken down by the PDO cold current mixing into and overriding it…That is why we have less El-Ninos and weaker ones generally during a cold PDO phase and of course cooler Tropical Pacific Ocean area is strongly linked to Global Temperatures…My research suggests strong links between AMO and PDO phases and Global temperatures, and in the PDO case it is not so much the measuring area of the PDO, but the effect it has on the large Tropical Pacific Ocean Area, and the El-Nino-La Nina phenomenon, which then in turn effects global temperature strongly. I cannot see how this does not make good common science sense.

Stephen Garland

My understanding, after reading this article, is that the PDO represents the SST anomaly for the North Pacific after subtraction of the global SST anomalies (please correct me if I am wrong). A positive anomaly therefore indicates the North Pacific is warmer than expected given the ‘current’ global SSTs. Does this then imply that a ‘local’ (i.e. Pacific ocean) input of energy has produced the relative increase in SSTs (e.g. volcanic, see surge tectonic theory), or can it be explained by a re-distribution of energy?
It also appears to me (due to the way the PDO is calculated) that the relationship between the phase of the PDO index and specific patterns in SST anomalies (relative difference in anomalies between east and west) are only associations (not necessarily stable).
That leads me to another aspect of the SST patterns associated with the PDO phase. I would like to know how closely the PDO anomalies correspond to SST anomalies for the Eastern Pacific. Are the PDO anomalies in the East simply an artifact of the analysis, due to the dominance of the Western and Central pacific on the calculation of the PDO index, and the influence of the Western Pacific on world climate (which influences Global SST anomalies and the PDO index) ? Or in another way, do the actual SST anomalies vary as much in the East as they do in the West?

Carl Wolk

In the past, I have removed the *immediate* ENSO signal from the PDO. Is this curve of any use in showing the underlying variation of the PDO and a possible link to ENSO?

Mike Bryant

OT… couldn’t find a place to put this comment about pan evaporation rates.
Changes in Australian pan evaporation from 1970 to 2002
Michael L. Roderick, Graham D. Farquhar *
Cooperative Research Centre for Greenhouse Accounting, Research School of Biological Sciences, Institute of Advanced Studies, The Australian National University, Canberra, ACT 0200, Australia
email: Graham D. Farquhar (farquhar@rsbs.anu.edu.au)
*Correspondence to Graham D. Farquhar, Cooperative Research Centre for Greenhouse Accounting, Research School of Biological Sciences, Institute of Advanced Studies, The Australian National University, Canberra, ACT 0200, Australia
Contrary to expectations, measurements of pan evaporation show decreases in many parts of the Northern Hemisphere over the last 50 years. When combined with rainfall measurements, these data show that much of the Northern Hemisphere’s terrestrial surface has become less arid over the last 50 years. However, whether the decrease in pan evaporation is a phenomenon limited to the Northern Hemisphere has until now been unknown because there have been no reports from the Southern Hemisphere. Here, we report a decrease in pan evaporation rate over the last 30 years across Australia of the same magnitude as the Northern Hemisphere trends (approximately -4 mm a-2). The results show that the terrestrial surface in Australia has, on average, become less arid over the recent past, just like much of the Northern Hemisphere. Copyright © 2004 Royal Meteorological Society.
It seems as though Australia has actually been getting wetter along with the Northern Hemisphere… Another inconvenient truth. Some are blaming it on Solar Dimming…

The PDO governs the temperatures in western North America – especially in the western U.S. — A graph in this document: http://www.appinsys.com/GlobalWarming/PDO_AMO.htm shows a very strong correlation between PDO and Washington/Oregon temperatures.
The shift between warm/cold phases may be related to the 22-year solar Hale cycle – see figure at the end of the PDO section in the above link.