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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.

Printable Version  |  Offline PDF Version  |  Link to this page

Acknowledgements

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

Comments

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Comments 101 to 136 out of 136:

  1. Eric the Red You are missing the point (i) you have provided no evidence that the PDO is anything more than an index of ENSO and (ii) the direction of the causal relationship could equally be in the opposite direction and the changes in surface temperature (or more correctly the changes in forcings) may cause the PDO rather than the other way around. Noticing a correllation is where science starts, not where it finishes. If you notice a correllation, but can find no causal mechanism with sufficient power to explain the strength of effect, then the hypothesis based on that correllation has only very weak support. It would be unscientific to view such an hypothesis as reason to seriously doubt an alternative hypothesis, for which there is a causal mechanism with sufficient power to explain the results. Another important part of science is responding to criticisms of your position, in this case that you may have the direction of the cuasal relationship the wrong way round.
  2. Tom, That is probably the closest we have come to agreeing on anything. Sphaerica doesn't understanding, or possibly does not want to understand, the effects of ocean currents and winds. This is exemplified by his statement that although ENSO can change temperature it cannot change the heat content. The ENSO effects are indeed short term. Last year's El Nino generated higher temperatures, while this year's La Nina resulted in lower temperatures. Over time, they tend to balance out. However, as you mentioned, any change in the system towards a greater occurrance or strength of EL Ninos or La Ninas will affect the overall climate. The error in Sphaerica and Phillipe's arguments is thinking that radiation in the only means of transfering energy. This is narrow thinking. Convection through wind and waves can transfer significant amounts of energy. The energy is not merely "shuffled around," but can be moved, transferred, and ultimately lost into space. Not to mention the heat loss associated with evaporation. As I stated previouisly, we know that the EL Nino / La Nina patterns are driven by the strength of the trade winds, which in turn are cause by changes in atmospheric pressure. Just because we cannot explain why these changes are occurring, does not mean that they are not happening. That is the fools approach. It is not a magical system either, but very real. The moderator appears to be echoing this sentiment about ignoring what we do not understand. Not exactly a good scientific approach. It should be obvious to the moderator who is using scientific, peer-reviewed literature in this argument, as opposed to those who are trying to hand-wave away any connection as if it did not exist. The PDO may not be the best measurement of what is affecting the observed changes. Other prefer to use the SOI or other permutations thereof. Readily dismissing these parameters because the cause and effect relationship is not fully known does not lead to scientific advances. Science will tell us to investigate these relationships to see if they occur by more than chance. Two complete cycles of the PDO corresponding to the cylces observed in the temperature records seem to have a higher likelihood than solar heating and aerosol cooling just happening to occur at 60-year intervals. As to whether the PDO drives ENSO or is simply an index of ENSO-related events, we do not know yet. However, that does not mean that there is nothing driving the changes observed recently, nor does it mean that a "physical" mechanism does not exist which affects climate. Finally, Dikran, there is the possibility that changing temperatures are causing changes in the oceans, and I have said repeatedly that science starts with these types of relationships.
    Response:

    [DB] As Dikran and Sphaerica have already aptly shown, you are arguing from both an incompleteness of understanding and ignorance.  Your refusal to come to grips with that is an illustration of confirmation bias and the Dunning-Kruger Effect.  When your errors are pointed out to you, you then resort to the childish "I'm not wrong, you are".  Your position is unsupportable by the physics of the natural world which, contrary to the hand-waving and dismissive airs displayed, we actually have a pretty good understanding of (it ain't exactly rocket science or brain surgery).

    How about getting a better grounding in the science itself before wasting everyone's time?  Or is that your entire aim here at SkS?

  3. Eric the Red Sphaerica is absolutely correct. The only way the Planet can lose enegry is by radiation. There is no condiction or convection becuase the Earth exists in a hard vacuum. This means that while ENSO may cause changes in convection within the atmosphere, that is still only a redistribution of energy within the planet. It can't change the heat content of the planet. Your argument that e.g. atmospheric pressure affects ENSO is a pretty good argument that PDO is a measure of the effect of the Earth's temperature on ENSO, rather than the other way round. Thus it is an argument against attributing changes in temperature to the PDO. "Two complete cycles of the PDO corresponding to the cylces observed in the temperature records seem to have a higher likelihood than solar heating and aerosol cooling just happening to occur at 60-year intervals." Nonsense, if the temperature change were the response to PDO, you would need to explain why the physics of solar forcing and albedo from aerosol scattering is wrong. Again you are putting statistics ahead of physics; as a statistician I can tell you that is a mistake. It might be reasonable to assume some underlying cyclic process after seeing two cycles in a time series if that were all the information you had. However in this case, it isn't all the knowledge we have, if we receive more TSI from the Sun, temperatures will increase and the physics to work out by how much is not exactly rocket science.
  4. 102, Eric the Red, Please explain to everyone how "convection through winds and waves transfers energy out of the planet into space" (your exact words). There is a basic concept here the you are ignoring, and that is the fact that the earth is a mostly closed system. The only way to get energy into or out of the system is through radiation. Period (well, that and shooting rockets full of molten lead out into space). If you want to propose a mechanism by which either ENSO or PDO can affect global temperatures over long time frames, please by all means do so, but you can't go with merely "wind, currents, waves, energy... presto!" Please point to the ocean waves that travel from here to the moon, or the trade winds that blow from Japan to Mars.
  5. 102, Eric the Red, You show a constant desire, topic after topic, to cling to what "we do not understand" as a reason to put existing theory on hold until we know more. From your most recent comment (102) alone: Just because we cannot explain why... ...ignoring what we do not understand. ...the cause and effect relationship is not fully known... ...we do not know yet. Look at your comments on other threads. Every single topic always dissolves into a "what if" (and usually one that contradicts known and tested theories) followed by "we just don't know," which is inevitably followed by the proposal to wait a few decades, just to be sure. In this case, we actually know a lot. We know how ENSO works, we know how greenhouse gases work, we know how radation works. We know a lot about ocean currents, air masses, and a million other things. Given all that we do very firmly know, it is very hard for a rational person to look at an ill-defined, un-bounded and completely unexplained event (PDO) and to focus on it as an explanation for events that are already properly well explained by existing knowledge and theory. I'm not saying that we know everything. I am saying that you are exaggerating what we don't know and then using that position to cling to something that at the moment has no substance whatsoever.
  6. Sphaerica, How do you expect to explain something that is not my exact quote? You have merged two different quotes (which are not even exact) into one in an attempt to corner me. Energy is radiated from the atmosphere into space. Energy is transfered within the atmosphere through several methods. Your ridiculous analogies only point to your repeated attempts to dispute arguements through inane logic. Dikran at least understands that much. Now if he can only understrand that if more heat is transfered from the surface to the atmosphere, that more heat can be radiated out to space, then we have made progress. Saying that Sphaerica is correct, and then contradicting him in the next breath, seems illogical. Sphaerica, your last post seems to be a collection of snipits similar to a political candidate who takes bits of highlights reels of his opponent and attempts to piece them together to make him sound like he is saying something which he did not. I never said anything about a proposal to wait a few decades. Probably the only accurate statement in your last post is that you thing we know more, while I think we do not. If we know so much, why is the uncertainty so great? (i.e. more than 100% for climate sensitivity to atmospheric CO2) Or why are Trenberth and Hansen arguing about whether the missing heat is lost in the oceans or radiated out to space? I will refer you a quote. "The more we learn, the less we know for sure." - Sheridan
  7. Eric the Red Your rather arrogant tone does you no favours. If your hypothesis is correct, it is easily verifiable. Can you show that ENSO has an effect on high-trophospheric and stratospheric temperatures? If so, you ought to be able to work out the difference in outbound IR radiation that would result. Pointing out a correllation between PDO and surface temperatures is the start of some science, the next step is to look at other datasources to see if your hypothesis is feasible. It is ironic that you complain that Spherica has misquoted you and then say that I contradict Sphaerica. I didn't and if you think I did, then maybe you didn't understand the point being made. I have found over the years that generally when I think someone is contradicting themselves it is my understanding that is faulty, and asking questions that explore the contradiction is generally a better way of resolving the issue.
  8. 106, Eric the Red, You seem to understand that if an El Niño (or the PDO in a warm phase) heats the atmosphere, that this would result in a loss in energy, cooling the planet. So the short term effect is to raise observed global temperatures, while at the same time reducing the actual temperature of the planet. What now remains is to quantify this effect, and to establish some mechanism whereby this effect could account for the continual accumulation of heat over time frames that exceed one half of the cycle (30 years), thus raising global temperatures by a whopping 0.8˚C using an anomaly that encompasses less than 1/6th of the earth's surface.
  9. Eric the Red @102, I think you and the other participants on this thread are talking past each other, or at least I hope you are. To see what I mean, let's start with basics on ENSO. Fundamentally, the ENSO involves a 'sloshing' of water across the equatorial Pacific. During neutral conditions a large body of warm water lies below the surface in the Western Pacific, while during El Nino's some of that water spread across the surface of the central and Eastern equatorial Pacific. So far this is just moving heat around. However, because the warm water is at the surface, it is now able to effect the climate in a way it was not previously able to do. At a minimum it will result in greater surface radiation at the equatorial Pacific in that there is a greater surface area of warm water able to radiate. All else being equal, this will result in greater radiation to space both in that part of the IR spectrum outside the CO2 and H2O absorption frequencies, and in those frequencies because the upper atmosphere will also be warmed. Further, it is very probable that there will be climate feed-backs to the warm water. That is because physics does not care whether warmer surface waters are a consequence of radiative forcing, or simple 'sloshing' of oceanic waters. The evaporation rates will increase, the convection increase, and the radiation increase will be the same for 1 degree increase in middle tropical Pacific waters due to radiative forcing or due to an El Nino. What is more, we need those climate feed-backs to explain the strong effect of ENSO on global temperatures. So far I'm sure you will agree. However, there is one crucial difference between an ENSO oscillation and warming due to radiative forcing. The ENSO oscillation is short term. You can model a feedback by successive summing of a multiple of the initial signal. Suppose you introduce a temporary signal, when the initial feedback response is 0.6 * the initial signal. Then at T0, the output will be the initial signal. At T1 the output will be the response to the initial signal. At T2 the output will be the response to the response to the initial feedback, and so on. For any response greater than 0 and less than 1, the result will be a self damping feedback response, and will quickly fall towards zero. However, if we leave the initial signal on permanently, then at T0 the output will be 1 (the initial signal). At T1 the output will be 1 + the response to the initial signal. At T2, the output will be 1 plus the response to the signal at T1, plus the response to the response to the signal at T0, and so on. Unlike the the case where the initial signal is removed after T0, in this case we will get a positive feedback that will multiply the signal. If the feedback factor is 0.6, the final output after a while will be 2.5 times the initial signal. Again the system is stable for feedback factors greater than 0 but less than 1. The crucial point is that feedback responses initiated by ENSO oscillations will follow the first model because the initial signal is temporary. In contrast the feedback response to radiative forcing from increased GHG will follow the second. And because the response for ENSO oscillations follow the first pattern, their long term effect on climate is zero. This is the point the other participants in this thread appreciate but that you do not seem to get. Even if you have multiple El Nino events in succession, so long as there is a short interval between them they will introduce no trend to global temperatures. They will slightly raise average global temperatures for a short time, but only because the average will be the mean of a number of warm years. To be clear on this point, the difference between such a succession of ENSO's is that it will not effect the expected temperature of cool years because the cool years will be largely unaffected by El Nino feedbacks. In contrast, the genuine trend introduced by GHG radiative forcing will increase the expected temperature of both cool and warm years (which, as an aside, is what we have seen in the temperature record). I think a number of important points follow on from this analysis, but I won't go into them until we are sure we are on the same page.
  10. 106, Eric the Red,
    I never said anything about a proposal to wait a few decades.
    Would you care to clarify exactly how long we should wait to evaluate the impact of a 60 year oscillation, just to make sure that we're not missing anything, and that maybe climate change isn't really happening and it's all just part of the natural ebb and flow of the climate? [Hint: I've been here before with you. It starts with "we don't know" and moves on to "we should wait to be sure" and ends with "oh, a few decades should do it."] After all, we know so little (according to you). So, we're supposedly at the end of the warm phase of the PDO. How long will temperatures need to continue to rise for you to abandon the idea that there is anything of interest (as far as long term, substantive climate impacts) in the PDO?
  11. 106, Eric the Red, If you have not already done so, I very, very, very strongly suggest that you go read: Blaiming the Pacific Decadal Oscillation post here on Skeptical Science (from March 5, 2011). It contains a lot of information that you'll find useful, including, most importantly, a (failed) effort by Dr. Roy Spencer to attribute current warming to the PDO. Please read it thoroughly. I also suggest following the links to actually read the source papers, in particular Schneider et Al (2005).
  12. Dikran, Maybe I did misunderstand you. Looking closer at your comment, that appears to be the case. We seem to agree that ENSO can cause convectional changes. Therefore, what is preventing the additional heat in the atmosphere from radiating out to space? Sphaerica seems to think that energy can only be radiated, and dismisses convection through nonsensical analogies, which is where I perceived your contradiction. Here is just one paper on then ENSO effect on stratospheric temperatures. http://www.atmos.washington.edu/~cig4/tropprecursorsrevisedv3.pdf
  13. Eric the Red I think you have also misunderstood Sphaerica. He is is clearly talking about the Earth's energy budget, which is purely determined by radiation (convention only causes differences in the distribution of heat energy within the Earth). Hence Sphaerica is absolutely correct. I guessed that you might be arguing that PDO has an indirect effect on radiation (even though you did not actually say that) as that is the only way in which your position seemed to have any logical consistency (see my previous comment about how to deal with perceived inconcistencies). However, as I said, in order for your hypothesis to be worth considering you need to take the next step and show that PDO is actually linked to outbound IR radiation. You have not done so. Pointing out a paper that mentions PDO and stratospheric temperatures is not evidence, especially as the paper seems to be about the polar stratospheric vortex, which is not the same thing as global stratospheric temperatures or outbound IR radiation. Again your posting style comes across as unhelpfully arrogant; there was nothing non-sensical about spaerica's analogies, and rhetorical dismissal of someones scientific argument does not encourage further discussion.
  14. Tom, Thank you for that in depth response. I agree that the long term climatic effects of ENSO variations is 0. Over time, warm El Nino years (2010) are balanced by cold La Nina years (2011). Over the past century, we have had periods of stronger and more abundant El Ninos, which were characterized by higher temperatures, followed by periods of stronger and more abundant La Ninas, resulting in cooler temperatures. These cycles can be overlain atop the warming trend of the 20th century. This is not unlike what Tamino has done with his recent analysis with aerosols and ENSO. The ENSO index was largely positive, with an abundance of EL Ninos from 1977 - 1998. Prior to that, it was largely negative, with an abundance of La Ninas. Since then, we have fluctuated between the two without a strong signal until this year's strong La Nina. In answer to Sphaerica's question, it would take a period of rising temperatures in the face of repeated La Ninas for me to abandon the idea that ENSO (or PDO) has a climate impact. I am not arguing the this is responsible for the 20th century warming. My point is that during the short term, this oscillation can affect temperatures, and should not be confused with other factors. There are some on this thread that seem to think that just because I acknowledge these effect that I believe that the entire post-industrial warming was due to PDO. That is simply not the case. That would be like saying that Hansen believes the entire observed warming was due to the changes in aerosols, because he claims the recent emissions by China have cooled temperatures.
  15. Eric the Red wrote: "I am not arguing the this [judging from context ENSO] is responsible for the 20th century warming." If you are arguing that PDO has an effect on climate then yes you are, becuase the correlation we have been discussing is between PDO and the surface temperature record, which is pretty much the 20th century (with a few decades hanging off the ends). "My point is that during the short term, this oscillation can affect temperatures," In that case it is a pointless point as pretty much everybody with an interest in climate know perfectly well that ENSO has an effect on surface temperatures. It is perhaps not surprising you are being misunderstood. If your point was about the short term effects of ENSO, then it was probably a bad idea to talk about PDO which is the long term behaviour of ENSO.
  16. 114, Eric the Red,
    In answer to Sphaerica's question, it would take a period of rising temperatures in the face of repeated La Ninas for me to abandon the idea that ENSO (or PDO) has a climate impact.
    Good. It's settled, then. See 2000-2011. 4 strong La Nina's (boxed in orange): Rising temperatures: I should point out that we're currently on a path to the second warmest summer ever, despite the recent end to a moderate La Nina, and without El Nino conditions... and during the cool phase of PDO (which supposedly started in 2008). Current Temps
  17. Sphaerica... That chart gets even more interesting if you plot it with a 12 month mean. [Here.]
  18. Dikran, It is not a matter of either CO2 or PDO is causing warming. During the past 130 years, the CRU temperature record has shown an increase of ~0.6C / century. Overlain on this increase are two 60 year cycles with an amplitude of ~0.3C. The oscillation is not affecting the underlying trend. Some people are preferring to ignore the oscillating effect and claim that the temperature rise has accelerated during the upward cycle. This has led to some added explaining during the recent period. Sphaerica, notice how the temperature responds to the ENSO index? La Nina conditinos from 1999-2001, El Nino for the next 5 years, La Nina in 2008-9, El Nino in 2010, La Nina in 2011. The composite ENSO index for your entire boxed area is just slightly below 0 (in fact it was positive until March, 2011), so it does not constitute a period of predominately La Ninas. If we see repeated conditions such as existed from the end of 2007 forward continuing, then I would agree. We need a warm summer, since the first 5 months of 2011 were the second coldest during your orange box (2008 being colder).
  19. Eric the Red There appears to be a contradiction here, perhaps you can explain. If PDO does not cause warming, then there is no reason to think that there is a genuine oscillation in temperatures due to the PDO (and instead it is either a coincidence or the causal relationship is in the other direction). In that case there is no reason to think that the current upward swing of PDO is causing the acceleration (what acceleration?) in the upward rise of temperatures. I should point out that there have been several regression alanyses performed (and discussed at SkS) where the effects of ENSO are removed from the temperature time series and you get a pretty steady approximately linear rise in temperatures. A linear rise in temperatures is exactly what you would expect from an exponential rise in atmospheric CO2.
  20. Eric claims "The composite ENSO index for your entire boxed area is just slightly below 0 (in fact it was positive until March, 2011)" It is not clear exactly which period we are referring to, Tom seems to have plotted those UAH data from January 1999 onwards. The mean MEI for 1999 (Jan/Feb)- present (May/June) 2011 is -0.085. The mean MEI until Feb/March was -0.24. The ONI also give negative mean values between January 1999 and March 2011, and until June 2011. Yet, the planet has warmed. Eric, you are arguing/debating in circles, and it would really help if you backed up your assertions with data and citations-- like the extreme thread, you are again talking though your hat here. Note how the global temperatures associated with the 2007-2008 La Nina were warmer than those in 1999-2000, and how global temperatures during and shortly after the 2010-2011 La Nina were warmer than both previous events. It will happen relatively soon (within a decade or so) that even a year with a moderate of strong La Nina will be warmer [Global temperature anomaly, GTA] than 1998, a year with a the second-strongest El Nino on record. In fact, the planet was warmer in 2008 (La Nina, GTA = +0.44 C), 1999 (La Nina, GTA = +0.32 c) and 2000 (La, Nina GTA = +0.33 C)were all warmer than 1983 (El Nino, GTA = +0.25 C), and 1983 was the year of the strongest El Nino on record. ENSO etc. are oscillations superimposed on a long-term underlying warming trend because of the radiative forcing from anthro GHGs. They can modulate the trend, and that is it.
  21. Dikran, Yes! When the PDO or ENSO signal is removed from the temperature records, the oscillation disappears, and a fairly linear increase results. There has been no acceleration nor deceleration, and no reason to expect any.
  22. Eric @ 121... Well, I wonder if you removed changes in solar forcing if you'd start to see that accelerating trend. You'd also have to remove Asian aerosol effects as well. I think there are probably a lot of reasons to think the underlying CO2 induced warming trend is, indeed, accelerating.
  23. Albatross, I was using Sphaerica's orange box which appears to encompass the timeframe 1998-2011. He conveniently changes to 1999 for his temperature plot, thereby removing the highest values from 1998, and arriving at his cherry-picked trend. This is one of the fallacies of using short-term data. Had he chosen a similar start date for his temperature plot, he would have a negative trend.
  24. Eric, Thanks for dragging this discussion down. I can assure you that Tom is not in the habit of cherry-picking. You asked for a period satisfying certain conditions, and he found one (starting in 1999) and then presented the UAH data for that period. I then checked the MEI data for Tom's window and the mean MEI was in fact negative, so was the ONI. So you are making ridiculous accusation-- the very nature of your request made it necessary to identify a time window when the ENSO was predominantly negative (La Nina) but during which the planet warmed. So instead of accepting the evidence as a true skeptic would do, you start making fallacious accusations. IMHO you owe Tom a sincere apology.
  25. 118, Eric the Red, So the goal post moves from "in the face of repeated La Ninas" to "a period of predominately La Nina." Which means what? We have to wait until the roll of the dice generates a period with 8 out of 10 years being in a La Nina phase in order to prove to you what all of the evidence, logic, numbers and statistics already show? This is equivalent to my recent question to you about what it would take for you to accept AGW, and your answer was a temperature increase over the next 26 years equal to that of the past 26 years (meaning you will admit to nothing until 2037).
  26. Sorry, please replace "Tom" with "Sphaerica" in #124 above. Sorry Sphaerica!
  27. 123, Eric the Red, Gee, how very nefarious of me. Okay, lets start at 1995, which was during an El Nino, and includes the world temperature record 1998 El Nino at the start of the period. We'll end in 2009 (during a La Nina). or, if you prefer, we can end in 2010, again in the midst of a moderate La Nina. Any other cherries you'd like unpicked?
    Response:

    [DB] Perhaps this is relevant?

  28. Sphaerica, You still have a time frame when the ENSO index is essentially zero. The goal posts have not moved. As I stated previously, the period starting in 2007 may suffice, if it persists. Something similar to 1950 - 1977.
  29. Eric the Red @114, again to just make sure we are on the same page, unless the climate system is very close to a tipping point (within 0.2 degrees c), ENSO fluctuations cannot result in a "step change" in global mean temperatures. Another way to look at it is this, if you have a period of predominantly La Ninas and follow with a period of predominantly El Ninos, in a period of no underlying trend, in the immediate period of the transition that will introduce a spurious trend to global mean temperatures. But outside of any interval that ranges across the point of transition, that change will introduce no trend to the series. Do you agree? I believe that this is a straightforward conclusion from the fact that there are no long term consequences from an ENSO fluctuation. I am seeking this clarification because you qualify your response by mentioning La Ninas, whereas the lack of long term effect of an El Nino is independent of any follow on La Ninas.
  30. Tom, In essence we agree. There are no long term consequences from an ENSO fluctuation, but the effects are evident in the short term. The fluctuations do not produce a "step change," but rather a relatively smooth transition.
  31. Eric the Red So after all this, it seems your position is that ENSO causes short terms fluctuations in surface temperatures and we need to consider this in attributing climate changes to the various forcings? That has been known for a very long time and news to nobody. It is the "skeptics" you need to be telling that to, as it is them that use the fluctuations of ENSO to cherry pick arguments such as "did global warming stop in 1998". The effects of ENSO are fairly straightforward to remove via regression, giving results like this It seems to me you have just been backing away from your original point about PDO as people have refuted your argument and ended up arguing for a completely bland position that we all argee with anyway, and which has virtually nothing to do with PDO!
  32. Eric the Red @130, you will note that I said, and that you have now agreed that:
    " if you have a period of predominantly La Ninas and follow with a period of predominantly El Ninos, in a period of no underlying trend, in the immediate period of the transition that will introduce a spurious trend to global mean temperatures. But outside of any interval that ranges across the point of transition, that change will introduce no trend to the series."
    (Emphasis added) The interval from 1977 (chosen because it was a high value for the period) to 2001 (chosen because Trenberth claims 25 years is the minimal period for a significant effect) follows after the end of the period of frequent La Ninas that occurred during the 60's and early 70's. It includes no transition from frequent La Ninas to frequent El Ninos, and included no transition from negative to positive PDO phase. Therefore on the principle quoted above, neither ENSO nor PDO have introduced a trend to that period. Never-the-less the trend over that interval (HadCRUT3) is 0.156 degrees C per decade. Further, the period 1951-1975 does not include a transition from frequent El Ninos to frequent La Ninas, and has a Negative PDO phase throughout. Therefore on the quoted principle, these ocean fluctuations have introduced no trends to that period, and hence the negative trend over that interval (see graph in 131) is not explained by ENSO states or the PDO. Finally, even if we are undergoing a transition between frequent El Ninos to frequent La Ninas, and/or from positive to negative phase PDO, on the quoted principle that would at most introduce a spurious reduction of the trend in the immediate decade of the transition. Over the following decades, and until the next transition (which would introduce a temporary spurious increase to the trend), they cannot be expected to effect the trend at all. Consequently we would predict a resumption of the preceding trend, and hence have no reason to expect ENSO or the PDO to result in a reduce trend for a sustained period into the future. I think these three points follow straight forwardly from the quoted principle, which as I have said follows straight forwardly from the discussion in 109, and to which you have agreed. Given that, why would we not be predicting an increase in temperature by at least 1.56 degrees by the end of this century, and far probably more because of the increasing GHG forcing?
  33. Tom, You seem to be arguing for a step-like shift, whereas I was claiming a more gradual change. Instead of a jump around 1977, the change would slowly increase to a maximum around the trasition year, and slowly subside. If you plot the 5-year moving average for ENSO, the value rises steeply from 1975-1983, crossing zero in 1979. Hence, I would expect the greatest change over that interval. Currently, the moving average is falling, and crossed zero in 2009. We have yet to see if a repeat of the 1940s will occur. Once again, long term, the effects will cancel. As I stated previously, the 130-year near-linear trend is 0.6C / century, with early 2011 CRU data falling slightly below the trend line. I see no reason to deviate from this trend. Remember, an exponential rise in CO2 leads to a linear increase in temperature. Atmospheric CO2 concentrations have not kept pace with the expponential rise recently, so I see no reason for an increase in the temperature trend. Using a shorter time frame to determine a long-term trend may not be the best. Therefore, I think you estimate of 1.56 C by the century is high.
  34. Recommended supplemental reading:

    Going out for ice cream: a first date with the Pacific Decadal Oscillation by Tom Di Liberto, NOAA Climate.gov, Aug 25, 2016

  35. "the 130-year near-linear trend is 0.6C / century"

    The trend is certainly not near-linear since 1887.

    Warming since 1880

    As for why global warming is predicted to accelerate, see here.

    Response:

    [RH] Fixed image width. Please limit images to 500px.

  36. Recommended supplemental reading...

    Following three record years for global surface mean temperature in 2014-2016, the observed recent slowdown in average global temperature has ended.

    A Pacific flip triggers the end of the recent slowdown, News Release, Met Office, Sep 18, 2017 

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