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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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The Pacific Decadal Oscillation (PDO) is not causing global warming

What the science says...

Select a level... Basic Intermediate Advanced
The PDO shows no trend, and therefore the PDO is not responsible for the trend of global warming.

Climate Myth...

It's Pacific Decadal Oscillation

"The Pacific Decadal Oscillation (PDO) is a temperature pattern in the Pacific Ocean that spends roughly 20-30 years in the cool phase or the warm phase. In 1905, PDO switched to a warm phase. In 1946, PDO switched to a cool phase. In 1977, PDO switched to a warm phase. In 1998, PDO showed a few cool years. Note that the cool phases seem to coincide with the periods of cooling (1946-1977) and the warm phases seem to coincide with periods of warming (1905-1946, 1977-1998)." (The Reference Frame)

The Pacific Decadal Oscillation (PDO) is a climate phenomenon that occurs primarily in the North Pacific Ocean.  The “oscillation” happens between warm phases (positive values) and cool phases (negative values) that last anywhere from 10 to 40 years.  The phases are associated with changes in sea surface temperatures (SST).  While the causes of the PDO are still unknown, the primary effects seem to be changes in northeast Pacific marine ecosystems and a changing jet stream path.

Important to note, however, is that the phases are not set in stone; there are frequently short sets of 1-5 warm years during a cool phase and vice-versa.  Secondly, the “warm” and “cool” phases are less descriptive than they would appear.  The cool period, for instance, is actually associated with extremely high sea surface temperatures in the Northern Pacific (see image below).

Figure 1: PDO warm phase (left) and cool phase (right). Image courtesy of JISAO.

One way to test this skeptic theory is to plot the Global Temperature Anomaly alongside the PDO Index (shown below).  What we find is that although the PDO index appears to influence short-term temperature changes, global temperatures have a distinct upward trend, while the PDO Index does not. 

Figure 2: Pacific Decadal Oscillation index (blue, University of Washington) versus Global Temperature Anomaly (Red - GISS Temp). Smoothed data (thicker blue and red lines) and trend lines (thick straight line) are added.

Natural oscillations like PDO simply move heat around from oceans to air and vice-versa.  They don't have the ability to either create or retain heat, therefore they're not capable of causing a long-term warming trend, just short-term temperature variations.  Basically they're an example of internal variability, not an external radiative forcing.  If PDO were responsible for warming the surface, the oceans would be cooling, which is not the case.

These results are expected.  The long term warming trend is a result of an energy imbalance caused primarily by an increase of greenhouse gases in the atmosphere.  In contrast, the PDO is an internal process and does not increase or decrease the total energy in the climate system.

Last updated on 16 September 2010 by Nicholas Berini.

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Many thanks to John Cross who co-authored this post. Thanks also to Josh Willis for his advice on this topic.


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Comments 76 to 100 out of 136:

  1. thepoodlebites at 07:40 AM, just to add, whilst most people seem to focus on the magnitude of El-Nino/La-Nina events, the frequency of their occurrences is more relevant when it comes to discussing ocean based cycles.
  2. johnd at 10:26 AM, it should be clear to most readers, but in case it is not, the observations about the El-Nino/La-Nina data from NR&M are mine and not part of the JAMSTEC forecast.
  3. #74 Response: Thanks for the link Daniel. [OT] The title kinda reminds me of the that character on Big Bang Theory, Eric Kripke, the university bully with a lisp and Sheldon's arch nemesis. [end OT] I'm open to the idea that the 0.5 C warming in the last 30 years is both natural and anthropogenic. My argument continues to be more from natural variability than man-made CO2 induced. If the UAH annual trend continues upward this decade, >0.8 C, then I think the AGW proponents have a stronger case. If the trend is flat to cooler, <0.3 C, then the AGW case will be weaker. Sorry to hear about the failed Glory launch. We need better satellite-based measurements.
  4. Revisiting this topic after discussion in a recent thread: I think it's clear that the PDO has a negligible impact on centennial trends (if at all), but the skeptical focus is on decadal trends, and the argument is that the global temperature trend of the last 30 years or so is partly a result of the upswing (to about 1998). A question i've had in mind is about the difference between ENSO and PDO, where the former is linked to short-term fluctuations in the global temperature record, but the PDO is not. the language most often used is something like 'PDO shifts heat around within the system, but doesn't influence global temps.' I do not understand why one ocean/atmosphere system with fluctuating temperature indices should impact global temps (ENSO) and another shouldn't. In the other thread, I asked about this and was directed here with the comment, "PDO is basically an index whereas ENSO is a physical system." PDO and ENSOS are both expressed as indices - temperature indices. I don't see how one is a 'physical system' and one isn't. Nor does it matter what causes PDO or ENSO for the purposes of my enquiry. If PDO has a decadal influence on global temps, then it can be said that the thirty year global temp trend to 1998 may partly be a result of the PDO warm phase. Solar variability and cosmic rays show no trend for this period, but if PDO can be linked to decadal fluctuations in global temps, then the notion that natural factors have had a negligible effect on the trend for this period is undermined. Consequently, the trend rate for the last 30-40 years is only partly to do with CO2. I think skepticism has largely moved on from claiming the PDO is responsible for global warming on centennial scales, but I don't think we yet have a satisfactory response to argument about PDO effect on shorter time-scales.
  5. Fair enough about index - the "SO" about ENSO was an index and there is the MEI for expressing ENSO strength. However, ENSO is now reasonably well understood as a coupled ocean/atmosphere phenomena where the physical system can be expressed if not predicted very well. PDO remains just an index. It's an indicator of what is happening the oceans, it is not yet linked to any causitive physical system. And that index may be no more than another expression of the ENSO physical system. The interest with temperatures is not to link them to any index, but to link them to underlying physical system. This would happen if it was discovered there was an underlying ocean phenomena beyond ENSO.
  6. barry, thanks for explaining the distinction between the centenial (mostly secular) and decadal (mostly oscillatory) trends. I believe most of the fluctuation in the secular AGW trend can be explained with natural oscillations. There do not seem to be very strong long term natural trends at the moment. Specifically warming accelerated in the 80's and 90's and decelerated in the 00's. I can also answer my question from January, the La Nina was strong, especially in its effects on the continental US stemming from abnormally cold Pacific temperatures. Those effects still linger, but the La Nina has ended. However it is predicted to return, not good news for drought-stricken Texas and rain-soaked Montana.
  7. Barry, I have done some work looking at the linear vs. oscillatory trends. Two cylces have been observed with a period of just under 61 years and an amplitudes of 0.3C. When this is subtracted from the temperature data (CRU), a linear increase of 0.6C / century remains. Should these two trends continue, global temperatures would bottom out again at around 2033 at ~0.1C below current levels, before rising again. The strong La Nina has definitely been an influence as temperatures for 2011 have been below the combined trendline for five of the first six months of 2011. Scaddenp may be correct in that the PDO is just a long term index related to ENSO.
  8. Here is a link to some recent work about the contribution of decadal oscillations to the observe global temperature rise.
  9. Scaddenp may be correct in that the PDO is just a long term index related to ENSO
    Yes, it's been conjectured in the literature, but I'm not sure how that would undermine the proposition of a long-term temperature oscillation that adds its influence to global temperature fluctuations on decadal time-scales. Nor do I understand why causes matter. If we did not know the cause of the 11-year sun cycle, still we could still estimate its impact on global temperatures. Mid-centennial aerosol cooling is a strong contender for the phase shift for that period, but AFAIK, there is enough uncertainty to allow a non-anthropogenic source to be considered. I figure the consequence of a PDO-like signal (60-65yr oscillation, peaking around 1998) would be that the period of modern warming (from 1975) is not so indicative of an acceleration. What I'm now curious about is the confidence with which that can be ruled out. I'm reading some other papers on in, as well as the suggestions (thanks).
  10. barry @84, 1) If the the PDO is just "a long term index related to ENSO", then its effect is completely included by including the effects of ENSO. 2) Further, evidence suggests that the ENSO pattern is changing, both in that neutral conditions are starting to resemble an unusual El Nino like state; and there is some evidence that with warmer conditions true El Nino like states become more frequent and stronger. Given that, if the PDO is related to ENSO, past fluctuations are not a guide to future behaviour, which can be expected to change. 3) Further, if the PDO is related to ENSO, and given the response of ENSO to a warming world, the correlation between the PDO and global temperatures is more likely a causal response of ENSO (and hence the PDO) to global temperature fluctuations than a causal response of global temperatures to fluctuations in the PDO. 4) This leaves aside the issue that evidence for an actual cyclical behaviour by the PDO and AMO are weak. Using the AMO as an example, Tamino tested the case for true periodicity and found it very weak. Often tests of statistical significance for such periodicity are based mathematically on the assumption that only one period is tested, whereas in fact many periods are tested. Allowing for this, Tamino shows the only significant period in the AMO as tested using the Greenland Icecore is around 6,500 years long. Given this, and given that we have no knowledge of the causal antecedents of the PDO, predictions of it future behaviour are simply guess work.
  11. I am being mistaken for someone arguing about future climate states based on nominal multi-decadal oscillations. I assume this is a hangover from previous discussions on the PDO. Let me be clear: I am not proposing, or hoping to propose, a coming cooling period based on PDO-like indices. I was intrigued by Tamino's posts where he subtracts natural variations (solar, ENSO, volcanic) from the temp record, [Eg.], and how that impacts trends in the temp records. To restate: I am curious to know, with what confidence have the apparent decadal fluctuations of the PDO been ruled out as a low-frequency oscillation influencing global temperatures on decadal, rather than centennial, time scales.
    1)If the the PDO is just "a long term index related to ENSO", then its effect is completely included by including the effects of ENSO.
    I'm not sure that "related to" = "is purely an artifact of". I appreciate conjecture, but am curious about the degree of confidence on this. Tamino has probably had a go at quantifying a possible relationship. I read an old post of his recently on the AMO, but that was more about long-term trends. I think my interest stems from the advice that apparent oscillatory ocean/atmosphere patterns (PDO/AMO etc) simply 'shift heat around'. I had thought this was also the case with ENSO. I'm 99.9% confident it's just a hole in my understanding - and this is a good place to remedy that.
  12. barry @86, I am not one of those who says that the "oscillatory" patterns just shift heat around. Indeed, ENSO does shift heat around, but it has too large an effect relative to its proportion of the globes surface area for that to be the case. What is more, its greatest effect on global temperatures is delayed by several months from its peak. Clearly ENSO has an additional effect beyond that of the heat shifting. Personally, I consider that to be evidence of a high, and positive climate feedback. When additional surface warmth in the tropical Pacific results in a greater global warming than can be accounted for just by the change in surface temperature involved, it is difficult to interpret it any other way. However, given a high climate feedback, and given the known variations in anthropogenic SO4, it is difficult to find room for variation left for the AMO or PDO to explain. Further, contrary to denier claims, the PDO has been decreasing in average strength since around 1985. That means that even if it has an effect, it may have contributed part of the rapid rise in temperature from 1975 to 1985, but it would have been reducing the rate of temperature increase since then. That there is little difference between the rates of increase between the two periods again suggests a minor influence of the PDO on global temperatures, if any:

    [DB] Fixed linked image (system didn't like that jpg).

  13. #87 Tom Curtis Do you have a cite for variations in anthropogenic SO4? The EPA shows that U.S. trends in SO2 have been decreasing since 1981. And SO4 concentrations are linearly correlated to SO2. Here's a good website for PDO. The PDO has been more negative than positive since 1998 and could account for some of the pause in surface temperature increase in the last decade. Since global temps are tracking scenario C the best, the pause can not be related to CO2 emissions, CO2 emissions have not stopped since 2000. If the negative PDO trend continues, we should see a shift from more El Ninos (80's, 90's) to more La Ninas (00's, 10's?).
  14. #88: Surely if, given that the most likely causal relationship is that ENSO drives PDO and not vice versa, we are likely to see more 'negative' PDO state if we have more frequent La Ninas? So your last sentence is in effect backwards. As ENSO is already factored into climate attribution (most recently and most neatly by Tamino), there is no great mystery, at least in relation to PDO. I prefer PDV, with V for variation, as there is no demonstrated cyclic pattern; additionally the 'cool' part of the variation has large positive heat anomalies in the central North and south Pacific.
  15. The poodlebites...A recent paper on global SO2 emissions 1850-2005. The US and european emissions have declined since the early 80s due to cap and trade, but China and other developing areas have been increasing exponentially, making up the difference. SO2 emissions have varied between 110 and 130 Gg/year since about 1960.
  16. As mentioned, whether PDO drives ENSO variations or is just an index of ENSO changes deos not matter to its temperature influence. Yes, it would be nice to understand what causes these fluctuation, but as long as we can measure the response, we can attribute the effects on the temperature record. The PDO was positive from 1977 - 1998, and could have contributed to the obserbed warming during that period. For the next decade, it oscillated around 0 until around 2008, when it turned negative. Compare the following graph to temperature graphs. The fact that Tamino can correlate temperatures to ENSO (or PDO) should indicate that it is a factor. How great a factor is still under investigation.
  17. Eric the Red wrote: "As mentioned, whether PDO drives ENSO variations or is just an index of ENSO changes deos not matter to its temperature influence. " That is incorrect. If PDO is merely an index of ENSO, then the effects of PDO on temperature is precisely zero conditional on measurements of ENSO. Secondly if PDO is merely an index of ENSO then it is a bad idea to make projections of future climate based on PDO as it may not have any physical significance at all. There is also the point that PDO may measure the effect of changes in climate on ENSO rather than the other way round. The warming of the early 20th century is explainable by changes in solar forcing. The Pacific ocean has a large surface area and a low albedo, so it will have absorbed a fair bit of extra energy over that period. Is it inconceivable that might have had an effect on ENSO, causing the PDO? We all know that ENSO is a factor, and we have physics that can explain the magnitude of the effect, as ENSO is reproduced in modern AOGCMs. Continually pointing out correllations without a physical mechanism that can explain the strenght of the effect is not science, is fine, but it is not a good reason to doubt solid physics.
  18. Dikran, I do not think that anyone is doubting physics here. The contention was whether the PDO drives, or is simply a measure of ENSO variations. Considering that ENSO has been shown to influence temperature, then if PDO is causing the ENSO variation, then it logically, influences temperature. If PDO is simply an index of ENSO, it will indirectly influence temperature through ENSO variation. However, in this case, it would be better to use ENSO as Tamino an others have done. Pointing out correlations is indeed science, as it leads to experiments resulting in greater understanding of the correlation (or rejection thereof). To dismiss such a correlation without investigation, is not science.
  19. Eric, you're still making suggestions of PDO driving ENSO without any physical mechanism, or other evidence. There is a proposed mechanism the other way round (ENSO driving PDO), which also makes sense in terms of energy flows and ocean currents. A general question for anyone who knows, what is the sum of all ocean temperature anomalies, both positive and negative, associated with the PDO region? Or how much energy is released/absorbed by the warm/cool segments of the PDO region. As there are large warm anomalies at the same time as cool anomalies, the net influence on global temperature from the PDO region is perhaps less than thought? It would be interesting to see those numbers in relation to the same data for the ENSO region too.
  20. Sky, We know that ENSO is driven by atmospheric pressure variations in the higher latitudes, which determine the strength of the trade winds. The atmospheric pressure changes occur over long time frames, for which an adequate explanation has not been found yet. It is entirely possible that the Pacific Ocean is driving the changes in atmospheric pressure. Therefore, we cannot say whether PDO is driving ENSO (via changes in atmospheric pressure) or is just an index of ENSO.
  21. 95, Eric the Red, No, you misunderstand. We don't entirely care what drives ENSO (we do, but it's not relevant here) as far as what causes it to happen and to change cycles. What we do care to understand is how the changes in circulation during an El Niño/La Niña event of the ocean expose more or less warm/cold water on the surface, thus raising/cooling global temperatures. We further know that this doesn't actually change the temperature of the planet (except in so far as the planet radiates less heat away during a La Niña and more heat away during an El Niño, so while the planet appears cooler it is losing less heat, and while it appears warmer is is losing more heat). But while ENSO does affect temperature observations, it does not actually affect climate. It can't, and neither can PDO with out some dramatically magical (and understandable and measurable) mechanism. What you are failing to do is to explain how PDO works in any way, let alone how it can possibly (over longer time scales) warm or cool the planet. The bottom line is that only factors which noticeably cause a radiation imbalance (albedo, GHGs, aerosols, clouds) can actually warm or cool the planet. Magical, ill-defined "but what if" oscillations are not science, they're voodoo-magic-superstition.
  22. Actually Sphaerica, The El Nino / La Nina cycle does change temperatures by the exact process you describe. When the trade winds are strong, the ocean tropical ocean turnover is greater, exposing more water to evaporation. When the trade winds are weak, the ocean calms, allowing more heat to remain in the ocean. Hence the changing ocean temperature. It has nothing to do with appearance, it is real. ENSO does affect climate, everywhere on this planet. Witness the last few strong El Ninos and La Ninas. You can deny it if you wish, but that will not make it go away. I actually respected your scientific knowledge until your last line. Now it appears you are only interested in your own agenda, and are trying to shout done those who oppose you. So sad.

    [DB] It has become transparently clear as to which parties use scientific, peer-reviewed sources based on physics to support their positions versus the hand-waving of those dissemblers who continue to publish their narrative of "It's not Happening/It's Beyond our Understanding/We Must Wait for more Information" without actual understandings or explanations given as to why what we know about the climate system don't actually work the way we observe them to. 

    That, as my child says, is a "tapestry".

  23. Spaerica's comment may not have been worded in the best fashion but it is correct. Whatever "cycles" are out there (ENSO, while being an oscillation, does not show clear cyclical bheavior) can only shuffle energy around, they can not create an energy imbalance. ENSO is part of the climate, not a driver of it. It drives weather patterns and affects temperatures on a year to year basis but it is not a forcing.
  24. 97, Eric the Red, You need to distinguish between a few very different things: 1) The measured mean global temperature of the ocean surface and the atmosphere (this is not the temperature of the system, but merely what is easy to measure and observe). 2) The amount of energy in the entire "earth" system (which, by proxy, can also represent the total temperature of the entire system) 3) Short term fluctuations in the first item (which represent weather, or, at a stretch, short lived and almost certainly regional climate changes) 4) Long term fluctuations in the actual climate of the earth (meaning changes that represent an actual new equilibrium state) Obviously the difference between 3 and 4 involves some degree of subjectivity, just like the difference between warm and hot is not a precise boundary. But with those four points in mind... ENSO changes number 1, but not number 2, and so is of little interest in anything other than year to year variations. As a result, ENSO also changes only number 3, but not number 4, and so is of no interest in climate changes. PDO is the same. You need to understand the differences here to understand where you are going wrong in focusing any energy at all on something like the PDO. The only things that are actually going to affect the amount of energy in the system are things that cause heat to leave the planet. There are only two ways to get heat off the planet. The first is to heat something up (say, a vat of molten lead) and shoot it into space on a rocket. Obviously, this doesn't happen very often. The second is through radiation. Some mechanism must use radiation to direct energy out of the system and into space. PDO doesn't do that. ENSO doesn't do that (except, as already explained, through slightly increased/decreased radiation, but in the opposite direction of the observed temperature increases). The only things that do affect radiation are albedo (clouds, ice, aerosols) which reflect radiation out before it even heats the planet, or greenhouse gases (which trap radiation in the system) or changes in solar insolation (which increase or decrease the input into the system). PDO can never, ever change climate, and nor can any other fantastical oscillation.
  25. Eric the Red @97, Sphaerica's clarification of his claim should be clear enough, so this is probably redundant, but... You need to distinguish between the popular definition of climate provided by Mark Twain, ie, that climate is what you expect, and weather is what you get; and the formal definition as used by the IPCC:
    "Climate in a narrow sense is usually defined as the average weather, or more rigorously, as the statistical description in terms of the mean and variability of relevant quantities over a period of time ranging from months to thousands or millions of years. The classical period for averaging these variables is 30 years, as defined by the World Meteorological Organization. The relevant quantities are most often surface variables such as temperature, precipitation and wind. Climate in a wider sense is the state, including a statistical description, of the climate system. In various chapters in this report different averaging periods, such as a period of 20 years, are also used."
    Fairly clearly, individual ENSO oscillations do not result in statistically significant changes to the thirty year averages of temperature, precipitation, etc, and hence do not change climate in terms of the formal definition. That is what Sphaerica was claiming. Equally obviously, and for those with the relevant knowledge, an ENSO oscillation does change what we expect to get, and so does change climate for that first, popular definition. However, that change is only due to the advance of our knowledge, and it is dubious to what extent that knowledge has penetrated to the general public. That is why it is just a popular definition, it needs to be indexed to a particular time and population to deliver unambiguous results. Finally, something which changes the frequency of El Ninos to La Ninas, or changes the neutral state to more resemble an El Nino or La Nina state over a multidecadal period would result in a change in climate under the technical definition. On that basis I disagree with Sphaerica's comment about the PDO not effecting climate "without some dramatically magical mechanism", although that sentence is entirely accurate if you substitute "physical" for "magical".

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