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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)

At a glance

Oscillate. To move repeatedly from side to side or up and down between two points, or to vary between two states or amounts. To vary above and below a mean value. To move or travel back and forth between two points. To swing backward and forward like a pendulum.

These and similar definitions are to be found if you look up the meaning of 'oscillate' online. Yet global warming is wobbling its way up a one-way course. We've just witnessed the hottest year since temperature records began (2023). Every few years that record goes again. Conclusion: global warming is not an oscillation.

The Pacific Decadal Oscillation or PDO is one of a number of phenomena that affect the world's major oceanic basins. It is a good example of heat being moved around within the ocean and atmosphere. Like all climatic oscillations it has warm, neutral and cool modes and these may endure for years or decades. Oscillations like this do not correspond to a timetable, but are irregular in nature.

The PDO is directly driven by conditions in the northern Pacific but has considerable reach in its effects. Prevailing winds and atmospheric pressure-patterns over that ocean dictate the mode. When winds are predominantly from the southwest, warmer conditions occur along the western USA seaboard. That is due to the onshore transport of warm, subtropical waters. Conversely, when winds are mainly from the north, upwelling of cool and nutrient-rich waters occurs in the open ocean, with cooler conditions prevailing.

Notable long, warm modes of the PDO include 1925-1946 and 1977-1998. 1947-1976 was a lengthy cool phase. More recently, the flip-flopping has been of a much shorter duration with cold and warm phases lasting just a few years. The reason for this switch is incompletely understood.

Like the El Nino Southern Oscillation or ENSO, which flips around over annual timescales, the PDO affects weather patterns, particularly in Asia and North America. It also has considerable impacts on fisheries and if there was one good reason to understand the PDO, it's right there. However, despite the loose coincidence with global temperatures in the early and mid-20th Century, that apparent relationship is no more. For example, a negative PDO mode commenced at the end of 2019 and was still ongoing in mid-2023, the latter having been the warmest year globally since records began.

Like all oscillations, there is no net gain or loss of heat involved in the PDO. It is merely a pattern involving how the heat in the system is being moved around within it. Global warming is different because it involves impeding the loss of heat, originally reaching the planet as sunshine, back out to space. That makes it a climate forcing agent. Big difference.

Oscillate. It's all in the name.

Please use this form to provide feedback about this new "At a glance" section. Read a more technical version below or dig deeper via the tabs above!

Further details

The Pacific Decadal Oscillation (PDO) is a climate phenomenon that occurs primarily in the North Pacific Ocean. It has wide ranging effects on weather patterns, especially over North America and Asia. Like other ocean-basin oscillations, it has a warm mode, expressed as positive values in the PDO index, and a cool mode, with negative values. These modes last anywhere from a few years to multiple decades and feature changes in sea surface temperatures.

While the causes of the PDO are still poorly understood, the primary effects seem to be changes in northeast Pacific marine ecosystems and therefore fisheries. Also they affect the position of the jet stream's path, that may in turn impact agriculture.

During the PDO positive mode, winters in the southern and eastern US states tend to have above average temperatures and higher rainfall. In the western and north-western states, the opposite is the case. Asian winters tend to be cooler and dryer, although above normal temperatures and higher rainfall tend to occur over India.

In the negative PDO mode, warmer and drier winters occur through much of the contiguous USA, with cool conditions confined to the north-west, although parts of the central USA may see notably wet conditions. Over in Asia, India and China see relatively cool and wet winters, whilst Japan has both the warmth and the rainfall. Clearly, a key impact of the PDO is on agriculture, hence its extensive study and the substantial scientific literature surrounding it.

It is important to note, however, that the PDO modes are not set in stone. Frequently, especially in recent years, short sets of 1-5 warm years have occurred during a cool phase and vice-versa. In addition, the warm and cool modes are less descriptive than they would appear. The cool mode, for instance, is in fact associated with high sea surface temperatures in the Northern Pacific (Fig. 1). Another important point is that the hottest year in the global temperature record, 2023, has occurred within a negative PDO mode.

Example of the PDO warm mode.Example of the PDO cool mode.

Figure 1: Examples of the PDO warm mode (above) and cool mode (below). During the positive PDO mode, sea surface temperature anomalies over the North Pacific Ocean form a vast cool area north of Hawaii. At the same time, warmer than normal waters are present near the North American coast. During negative PDO conditions, warm waters are found north of Hawaii and cooler than normal waters are encountered near the North American coast. Images courtesy of World Climate Service.

Because the PDO is an oscillation, it does not present a clear trend. If you compare the Global Temperature Anomaly alongside the PDO Index (fig. 2), you will see that although the PDO index appears to influence short-term temperature changes, global temperatures have had a distinct upward trend, especially since the late 1970s.

 Global temperature anomaly 1850-2023.

PDO time series.

Figure 2: Top-panel: global temperature anomaly 1850-2023. Graphic: Realclimate. Bottom-panel: Pacific Decadal Oscillation index, 1870-2023. Smoothed data (thicker black line) included. Graphic: NOAA.

Natural oscillations like the PDO simply move heat around from oceans to air and vice-versa. They don't have the ability to either add or remove heat to or from the overall system. Therefore, they're not capable of causing a long-term warming trend like that of the last 50+ years. Instead they are another example of a process causing short- to medium-term temperature variations. Basically they're good examples of internal climate variability. If the PDO was responsible for warming the surface, the oceans would be cooling, which is not the case.

The long term warming trend on Earth is due to increasing greenhouse gas levels. These constitute an external radiative forcing, creating an energy imbalance. In contrast, the PDO is an internal process and does not increase or decrease the total energy in the climate system. Essentially, like other such oscillations, it cancels itself out. The fact that its name defines it as an oscillation should communicate that fact.

Last updated on 31 March 2024 by John Mason. View Archives

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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 1 to 25 out of 137:

  1. John and John and Josh Nice job.
  2. Roy Spencer's view on how the PDO fits the equation:, a brief part of a new paper being submitted.
  3. "Obviously the PDO as an oscillation between positive and negative values shows no long term trend. In contrast, temperature displays a long term warming trend." This PDO index shows no trend because the globally averaged SST is subtracted out. The globally averaged SST is subtracted out because it is assumed that the PDO is not effecting global SSTs but is rather a mode of variability on top of global SSTs. As far as I know this is not a robust conclusion and therefor I feel that it is misleading to compare the "trendless" PDO to globally averaged surface temperature the way that it is done in the above graph.
  4. ptbrown31, your contention is not quite correct. The actual definition is "the Pacific Decadal Oscillation (PDO) Index is defined as the leading principal component of North Pacific monthly sea surface temperature variability (poleward of 20N for the 1900-93 period)."
  5. Tom Dayton - Here is the WHOLE actual definition: "Updated standardized values for the PDO index, 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." If the "global warming" signal wasn't subtracted out of the index there would be an upward trend.
  6. ptbrown31, you have missed the point. You wrote that "it is assumed that the PDO is not effecting (sic) global SSTs," and "this is not a robust conclusion." The Pacific Decadal Oscillation does what, by definition? It oscillates! That means it goes back and forth--reverses course, then repeats. Its lack of a non-oscillating component is neither an assumption nor a conclusion, but part of its very definition. You have misunderstood the skeptic argument that blames the PDO for the "apparent" global warming long trend. That skeptic argument is not that the PDO has a long-term warming trend. Rather, the skeptic argument is that no long-term warming trend exists. At all. The skeptic argument is that the PDO's warm phases have been long and frequent enough that climatologists have mistaken them for long-term warming. The skeptic argument is that if we simply wait a bit longer, we will see PDO cooling phases long enough to wipe out all the warming we've seen since the 1850s. The counterargument is captured in the figure that you objected to. PDO warm phases are much too short to be responsible for the warming we've observed since the 1850s. There already have been counteracting cool phases.
  7. Tom Dayton - "You have misunderstood the skeptic argument that blames the PDO for the "apparent" global warming long trend. That skeptic argument is not that the PDO has a long-term warming trend. Rather, the skeptic argument is that no long-term warming trend exists. At all." Perhaps I have misunderstood the skeptical argument that this post is directly addressing but nevertheless I have indeed heard it argued that the PDO has caused the long term upward warming trend. My problem with this post is that it seems to use the fact that there is no upward trend in the PDO as evidence that the PDO could not have caused an upward trend in temperature. My problem is that this PDO index is trendless for artificial reasons. Like you said, someone defined the PDO such that it would not have a long term trend. This does not seem to be good evidence to dismiss it as a contributor to warming.
  8. If in the cool phase of the PDO, the northeast pacific is cool and the central north pacific is warm, and in the warm phase of the PDO its vice versa, how does the PDO affect global surface temperatures? According to figure 2, the PDO seems to be exerting short-term influences on global surface temperatures superimposed on a long-term warming trend. Because of the correlation between the PDO index and global surface temperatures, it seems like the negative PDO contributed to mid-century cooling, was the PDO alikely a culprit in mid-century cooling? And, since it went back to a cool phase a few years ago, could this cause global temperatures to rise less quickly over the next few decades? Could the PDO be a factor in determining who fast global surface temperatures rise on a decadal a timescale even though the long-term is obviously up? Please explain this to me.
    Response: Your question is exactly what is addressed in the post at the top of this page. Your question, and other questions you have asked on other pages, seem as if you have not actually read the posts, but only the posts' titles. Or maybe that you have read only the Basic version when there is also an Intermediate version and sometimes an Advanced version. I sincerely apologize if I am incorrect; I most definitely do not want to discourage you from asking questions or raising points for discussion. But it is difficult to answer your questions without simply repeating the contents of the posts at the tops of the pages.
  9. The post does not address the physical mechanism of how the cooling in the northeast pacific that is compensated for by a warming in north-central pacific affects global temperatures, it just states and displays the correlation. What I'm curious about is what is the exact mechanism of how cyclical changes in the distribution of sea surface temperatures in the north pacific affects global temperatures. As stated in the intermediate post, "Consequently it would appear that there is nothing fundamental about a PDO that would cause significant changes to global temperatures." But then in figure 2, there is good correlation between the PDO index and global temperatures if the linear warming trend is removed. Please describe link between the two concepts I stated in the previous two sentences. And I repeat my original questions asked in my first comment on this post. Finally, I apologize for any misunderstandings of the other questions a posted on this website. To be honest I read the posts so many times that I have memorized them. Thank you.
  10. Karamanski #9: "But then in figure 2, there is good correlation between the PDO index and global temperatures if the linear warming trend is removed." I'm not sure how good this 'correlation' actually is (for instance a PDO peak corresponds to a temperature drop ~1994), but in any case correlation does not equal causation. Isn't it equally likely that fluctuations in global temperature drive the PDO? Or that a third factor (e.g. the solar irradiance cycle) is influencing both and producing the partial correlation you think you see?
  11. The causation is what I'm curious about. Is it the PDO index that resulted in the short-term correlation or is like you suggested global temperatures that are driving the PDO index? If the PDO index is responsible for the short-term correlation what is the physical mechanism by which the PDO would affect global temperatures?
  12. Roy Spencer classifies the PDO index as a radiative forcing, because he claims that changes in the phase of the PDO are significant enough to cause a change in global cloud cover which alters the absorption of sunlight and escape of heat. Does this hold up to scrutiny?
  13. It is well known that the PDO cycle is directly related to the sun's torque cycle. (there is no correlation in this case, only a relation: the sun doesn't respond to the Earth's ocean or atmosphere; that be ridiculous. Hence, since there's only one way to relate; it's a relationship and not a correlation.) Since the solar torque cycle is thus also and of course independent of the Earth's atmospheric CO2 levels, the strongest causation is that the Earth's atmosphere (temperatures) respond to the ocean temperatures and not the other way around. Need additional proof? Look at the global atmospheric temperatures and how they responded to the strongest el nino in 1997/1998 (ENSO cycle, that in turn is dependent on the PDO and solar cycle too). That El Nino lasted from march 1997 to march 1998, peaking nov-dec 1997 through jan 1998. In addition, a la nina was already official in may 1998. However the global temperatures lag 6 months: peaking jun-aug 1998 ... Hence global atmospheric temperatures respond to global oceans temperatures. Now that causality has been established we can dig some more: I've been looking at the NOI data (SST for EL nino region 3.4) from NOAA available since 1950 and what is striking is that since the el nino from 1958, each peaking el nino has been stronger than the previous one, until the 1997/1998 el nino: 1958: 1.7, 1973:2.1, 1983: 2.3, 1998: 2.5, (2010: 1.8, trend reversal! more about that later) Doing simple linear regression; the peaks increase by 0.0017/month with an R-square of 0.97. That said, looking at la ninas since the 1950s; these increased in strength until the one in 1974 1950: -1.7, 1956: -2.0, 1974: -2.1 and have since then decreased (the peak la ninas that is) until the most recent one in 2008: 1989: -1.9, 2000: -1.6, 2008: -1.4 Interestingly, the decrease in la nina peaks is also 0.0017/month with an R-square of 0.97. The fact that both the el nino and la nina peaks increased and decreased, respectively, with the exact same slope is due to an underlying causation: the PDO. Adding PDO events (warm to cold reversals, vice versa, phase shifts, etc) to the NOI data we instantly see the following: The 2008 la nina coincides exactly with the PDO GPTC The 1998 el nino coincides exactly with the PDO phase shift from warm to cold The 1988 la nina coincides exactly with the highest PDO (LPTC) since 1934 The 1977/78 el nino coincides exactly with PDO phase shift cold to warm The 68/69 la nina coincides exactly with PDO's phase reversal The 55/56 la nina coincides exactly with the lowest PDO value since 1900 In addition, between 1950 and 1977 there were 126 la nina seasons (months) and 75 el nino seasons: PDO was cold Between 1977 and 1998 there were 53 el nino seasons and 27 la nina seasons: PDO was warm Hence, it is obvious that the enso cycle is highly correlated with the PDO which in turn is highly correlated to the sun's torque cycle. In addition, we've entered a trend reversal in ENSO strength; the 2009/2010 El Nino was less strong than the 1997/1998 one. Although it's only one data point to confirm this, it makes all sense using the above. Hence, the ocean and atmosphere is going from an el nino dominated 40 yr period that ended in 1998 to a la nina period of several decades that started in 2008. Now back to the global warming issue. 1998 was the year with the highest recorded temperature: +0.57 and global atmospheric temperatures have dropped since... See a pattern? Follows the PDO exactly. Now 2010 is on track to at least equal 1998, and is currently at +0.54. However, for October the global temperature anomaly is +0.42 deg, which is the lowest monthly temperature anomaly seen in what has been a very warm year: the atmosphere is starting to respond to the developing La Nina and is still in "El Nino mode". Just like I illustrated with the year 1998! In addition, I am sure if we subtract the el nino effect of the warming for 2010 we'll be left with little net warming if any at all.
  14. Re: WHATDOWEKNOW (13) Taking theories from some "skeptical" website run by an ex-British merchant marine dude vs Climatologists who have spent a lifetime studying and advancing the science itself? Gee, hmm, tough choice... Sorry, man. Checked my incredulity at the door. BTW, you should really double check your sources some. 1998 was perhaps the hottest year in the HadCRUT3 dataset, but the GISS and the NCDC have 2006 as hotter (see here). Smart money's on the professionals. That's what we've come to know. The Yooper
  15. I stand corrected on the two other data-sets with 2006 as the warmest year on record. On the other hand, why aren't these 3 data-sets pinpointing the same year? Nevertheless, the solar torque cycle and PDO coincide beyond a shadow of a doubt, as well as the ENSO cycle. The "dude" (calling researches that present other valid arguments "dudes" and not climatologists: those that suite your thinking... is nothing but self-justification: now go and look that up!) forecast every single la nina and el nino event correct to the month when each peaked. Using his work, this can be done years in advance. The developing la nina was already in the books... sorry but just a hard fact! It is also beyond a shadow of a doubt that the sun influences the oceans and atmosphere and not the other way around. It is also beyond a shadow of a doubt that peak el ninos and la ninas have increased and decreased respectively with the exact same and absolutely linear rate; as I have shown, paralleling the PDO cycle. It is also beyond a shadow of a doubt that ENSO events influence global temperatures. Considering that the ENSO cylce and PDO cycle's events coincide, as I clearly pointed out in my earlier comments, PDO therefore also influences global atmospheric temperatures. It is also beyond a shadow of a doubt that global (atmospheric) temperatures have increased since the 1970s but that since (1998 or 2006 as you may will) this increase has at least halted. The most important question is thus: what has caused this increase and what has caused the stabilizing to declining trend in the last several years? Given the above, PDO, ENSO and solar (torque) cycles need to be taken into account when trying to answer these questions. Once taken into account, the impact of ever increasing CO2 levels may maybe not be as dramatic as some make/may believe, which in it self is nothing wrong with. Finally, what makes you believe I am not a professional? Are you? And in science it is absolutely normal to have utterly different opinions about the same research topic! That's what drives science and our understanding forward. If everybody in the room agrees and all nod there heads; now that's when I, as a scientist, get scared, really scared. But then again self-justification is all about: don't confuse me with the facts, I've already made up my mind. Or as Lord Molson said it best: I will look at any additional evidence to confirm the opinion to which I have already come. Better yet, Richard Feyman puts it like this: "It doesn't matter how beautiful the guess is, or how smart the guesser is, or how famous the guesser is; if the experiment disagrees with the guess, then the guess is wrong. That's all there is." And that of course goes for the skeptics as well as the non-skeptics!
  16. Whatdoweknow, Different datasets provide different results due to having different base reference periods. The global temperature rise has not halted. The 2000s were the warmest decade on record, and all indicators show that the Earth is still accumulating heat. Is global warming still happening? (argument #4) Would you be scared of an entire room of scientists nodding in agreement that the Earth is a distorted spheroid?
  17. WHATDOWEKNOW wrote : "If everybody in the room agrees and all nod there heads; now that's when I, as a scientist, get scared, really scared." A room full of people agree with the theory of evolution and nod their heads when someone states that the theory is correct. WHATDOWEKNOW gets scared, really scared...
  18. I am pretty sure you know what I mean, so don't take things word for word, I am talking about scientific objectivity; scientific discussions drive science forward, not (forced) agreement. Of course those matters you point out are absolute facts that cannot be argued with (though some still like to debate evolution...). Nevertheless if somebody PERCEIVES a circle as a square, and is absolutely convinced about that; you can bring any fact to the table proofing the circle is indeed a circle, but that person will only become more steadfast in the opinion that it's a square! That's called reducing dissonance: our human mind has a very hard time agreeing with the fact we actually might be wrong and will do almost anything to stay in consonance. And by the way, it's not about being wrong; it's about not always having to be right... Not until the person actually accepts he/she is not right; then her/his mind opens up for arguments. But only then. Hence, bringing different facts to the table need to be embraced 100% objectively, open-minded and scientifically. Not instantly dismissed or ridiculed due to opinion. Continuing, since Biblio and Murphy can only comment on my phrasing and word choice; I assume they agree ENSO and PDO affect to a large extend global atmospheric temperatures. Jeee, the oceans cover >2/3 of our planet... if anything is important to understand climate change it are the oceans. So the fact thus stays that the global atmosphere responds to PDO and ENSO cycles. More proof needed? Looking at the GISS data: PEAK monthly index temps since 1990 shows that January 2007 had the highest temperature index (0.89) since 1880, again I apologize for making the mistake of claiming 1998. Almost each and every peak coincides with pre-occuring el ninos. The GISS temperature peaks between 1990 and 2007 actually increase with 0.0159C/month; exactly the same increase for el nino peaks between 1973 and 1998 (0.0159C/month) when the PDO was in it's warm phase ('77-'98). The last el nino of 1.8 already shows the trend reversal and with a PDO having shifted from warm to cold in 1998, and the peak 2010 temp is (therefore) also lower than that in 07. Why isn't it much lower? Well, since the 09/10 el nino was 2nd to last in strength since NOI records began in 1950 and since PDO has shifted to cold. Simply because we've been in an el nino dominated phase for the last 40yrs: more net-release of heat than there was heat adsorption (la ninas). Given the latent response properties of the GLOBAL atmosphere this makes perfect sense. Now this theory will be challenged rather soon with the current developing la nina (still not official since 5 consecutive seasons haven't been below an SST of -0.5C yet).
  19. WHATDOWEKNOW, are you looking at the Intermediate version of this thread ? Have you also read this thread ? Do you see the figure which shows "the contrast in trends between PDO and global temperature. Obviously the PDO as an oscillation between positive and negative values shows no long term trend. In contrast, temperature displays a long term warming trend." And, despite what you may believe, the warming is continuing.
  20. WDWK #18 The PDO merely redistributes heat. It is not a heat input into the earth's atmosphere. It's action is complex and/or chaotic. With the state of our current knowledge of the PDO it's very difficult to say what it's behaviour will be as a consequence of climate change, but it does seem to help create temperature extremes (high and low), so is an important noise component in the system. When I looked at the statistical behaviour of the PDO compared to temperature anomaly, I could not draw any conclusions from the simple methodology I employed.
  21. Warming only since 1970... You can't simply draw a straight regression line through any data that has a trend... you need to detrend it first! 1) First of all you need to de-trend the global temp since it has a has an annual cycle. 2) you then need to de-trend it based on the PDO and ENSO long term cycles (which are multiple cycles in it self and by it self) 3) after that you need to do a trend-reversal analsys to make sure that your data isn't experiencing different signs of slope for certain periods of time. 4) Finally, you can then do simple linerar regression through all the data with the same slopes (so if global temperatures have changes of sign-of-slope, then you can't run linear regression through the entire data set. That's just plain wrong, but done so frequently it's amazing. 5) Now please go and do that and please then come back and tell me how much of the increase in temp since ~1970 can be explained by any and each of the variables: PDO, ENSO, CO2 etc. ps: even the oceanic heat content has a cycle. Can you calculate it? All the data is freely available and all these statistics are relatively easy to perform for an expert. It will take some data transformation, blood, sweat and tears, but only by doing it yourself can you trust your own analysis. Please note that I've never said that there is no global warming/climate change (due to excess anthropogenic CO2 emissions). I am only conveying the importance of oceanic long term cycles on the little over a hundred year of direct observations. These cycles should not be dismissed and in fact can only help in explaining the observations. The better we understand our observations, the better we can act if necessary. Any of the trends in ENSO, PDO and global temperatures I've presented so far are solid and a fact! Still they don't say there is no human induced global warming, that's a deducted PERCEPTION. See the difference?
  22. WDWK #21 I've done this type of regression analysis on a range of variables (solar variation, volcanic activity, ENSO and CO2 from memory. I found the only statisticaly significant predictors were CO2 and solar variation for annual mean temperature data. The effect of ENSO was miserably small, even in the context that it was not statistically significant, indicating that it's involved in the redistribution of heat, not a sink/store phenomenon. In the early 20th century, solar accounted for the majority of variance, and in the late 20th century, CO2 did. There were also some interesting non-linearities in the system indicating poorer predictive power (underestimating anomaly) with increasing CO2 concentration. Happy. Feel free to replicate it. The data and some of the R code I used for analysis is here. Disclaimer: I used the methods I'm used to as a social scientist rather than more 'correct' (or convention bound to your taste) methods that an earth scientist would use, so my results, while in good agreement with the peer reviewed literature, are only really worthwhile as an impressionistic analysis. However, given that limitation, they are in good agreement with the published literature.
  23. It might be instructive to read Atmoz' take on PDO: On the Relationship between the Pacific Decadal Oscillation (PDO) and the Global Average Mean Temperature. [Edit: After much searching, I finally was able to resurrect a cached copy of this post on PDO by Tamino: Exclamation Points !!! as well as this one: PDO: the Pacific Decadal Oscillation. End edit] The Yooper
  24. As stated in the lead post, the PDO, like other identified patterns observed in other oceans, is a measure of internal processes that provides an indication of the conditions in place at any given time during the transfer of heat between the oceans and the atmosphere. In the examination of any correlation between global temperatures and the PDO, looking for any apparent trends, in both the lead post and the subsequent discussion, all that is being considered is the magnitude of each event. Whilst that may appear the simplest means of establishing correlation, it should instead be most obvious that magnitude is not the right indicator when looking for trends if there is any understanding at all, of all the processes involved in the redistribution of heat within the system. What is relevant, and where any trends should be looked for instead is the frequency of the oscillations and the amount of time the index resides in each phase. In other words, instead of merely looking for trends in how wide the refrigerator door is being opened, it is the frequency of how often it is being opened, and how long that it is being held open, or closed, that is relevant.
  25. JMuprphy #19. In my initial post I showed Dr Landsheidt's relationship between PDO and the solar torque cycle: a 178.8-year cycle that began in 1899.9 and will last till 2078. Within this cycle is the 35.8 year cycle most often revered to when comparing PDO and solar cycles. From that it is obvious that the PDO just doesn't simply oscillate randomly around 0, and that it has long-term trends at different times scales. (Nothing in nature at [such large scales] happens randomly). That said, within a cycle are upward and downward trends; Just look at a simple sinus wave with say a wave length of one 1 yr. Between 0-3 months the sinus wave has an upward trend, between 3-6 months it has a downward trend, 6-9 downward and finally 9-12 upward again. Hence; within cycles are up and downward trends. However, on average (doing linear regression for example) over one period a sinus wave with a period of 1 shows a slope of 0... So, one has to look at the appropriate periods to compare trends within cycles. That said, take a look at the temperature record from 1900 to YTD again: apply the same trend line as what the PDO exhibits (based on the available observations) to the temperature record (yielding an r2 of 0.75... ). That temperature trend line then shows decreasing temperatures from 1900 to ~1910, increasing from ~1910 to ~1945, slightly decreasing from ~1945 to ~1968, increasing ~1968 to current. And yes an r2 <1 means not all variation is explained, thus there are other variables involved. But, again I never said the PDO explains everything. But a lot. Also, I still haven't heard any argument or discussion that can explain or dismiss other than the PDO and solar cycle why el ninos and la ninas have increased and decreased in max strength, respectively, with the exact same rate with an r-square of almost 1 (see post #13) and why the increase of max el nino strength has the exact same rate as the increase of the max temperatures (see post #18) also with an r-square of almost 1 over the last 20yrs? In addition, there is nothing wrong looking at peaks, as it essentially takes away all the noise and as long as you compare rates.

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