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Blaming the Pacific Decadal Oscillation

Posted on 5 March 2011 by Riccardo

The Pacific Decadal Oscillation (PDO) has gained some traction as an alternative hypothesis as the cause of the last century warming or at least a good part of it. More often, this hypothesis is based on the apparent visual correlation between warming periods and the positive phase of the PDO, but others ventured in semi-quantitative analysis (e.g. Dr. Roy Spencer).

Although none of them can be called strong evidence, it's worth looking at this climate feature in more details, obviously starting from describing it. The first thing to note is that the PDO, like any other oscillation, can not be the cause any long term trend. Whatever the impact of one phase might be, the opposite phase would have the opposite effect and after a full cycle the system would be brought back to where it was at the beginning. The heat can just be moved around through different parts of the system and it may even be "hidden" for some time, but after a full cycle it will be back. In other words, an oscillation does not create nor retain heat and we cannot have both an air and ocean long term warming trend.

The Pacific Decadal Oscillation

The PDO is a pattern of climate variability of the North Pacific (north of 20°) with period around 60 years. It's characterized by a positive (warm) phase with an anomalously cold central-western Pacific sea surface temperature (SST) and a warm eastern pacific SST. The opposite applies for the negative (cold) phase. Note that the terms "warm" and "cold" are definitely USA-centric.



Fig. 1: Typical wintertime Sea Surface Temperature (colors),  Sea Level Pressure (contours) and surface windstress (arrows) anomaly patterns during warm and cool phases of PDO. Left panel: positive (warm) phase; right panel: negative (cold) phase. (from JISAO).

Although the PDO may vary from year to year, it shows a tendency to be either in the positive or in the negative phase. To summarize its behaviour with time, the PDO index is derived as

[...] the leading PC of monthly SST anomalies in the North Pacific Ocean, poleward of 20N. The monthly mean global average SST anomalies are removed to separate this pattern of variability from any "global warming" signal that may be present in the data.

In other words, given a spatial pattern, this index describes how it changes with time. It is important to note that the "monthly mean global average SST anomalies are removed"; hence this index actually describes the "anomalous anomaly" of the North Pacific with respect to the global ocean.

Fig. 2: annual PDO index from 1900 to 2010 (grey line). The red line is a 5 year smoothed version. Vertical dashed lines represent the three regime shifts (see text).

Three so-called regime shifts can be seen in the PDO index shown in fig 2, namely around 1923, 1945 and 1977. In particular, from the PDO index we see that between 1945 and 1977 the global ocean has warmed more than the North Pacific; this is the reason why some skeptics think that the PDO pushed the brakes on global warming.

The process to separate variability from the global warming signal implicitly assumes that the SST response to global warming is spatially uniform. This looks quite unlikely and we should expect the global warming signal to "leak" into the PDO index (Bonfils et al 2010). This fact alone should make the alarm bell ring before using it to explain global warming or even to remove the natural variability associated with PDO from observational datasets.

The causes of the PDO

It should be clear that in a strongly coupled system like our climate, nothing happens in isolation or by itself. Although a definitive answer to the question of what causes the PDO cannot be given, several studies have shown that the PDO depends on other climatic factors.

Some of you may have noticed that the PDO patterns shown in fig. 1 somewhat resemble the ENSO pattern (here in the positive phase); indeed, the PDO can be described as a long-lived ENSO-like pattern. Newman et al. 2003 have found that the PDO can be modelled as a first-order autoregressive process driven by ENSO. To make it simple, we may say that the PDO is atmospheric "noise" interacting with ENSO. Even more important, Shakun et al. 2009 obtained similar results regressing separately over the North and South Pacific. This means that the PDO is part of a more general pacific decadal variability driven by ENSO.

Schneider et al 2005 added to the picture the Aleutian low variability and the ocean circulation along the Kuroshio–Oyashio Extension (the Western Pacific counterpart of the Gulf Stream in the Atlantic Ocean). They conclude that the PDO is "a response to changes of the North Pacific atmosphere resulting from its intrinsic variability, remote forcing by ENSO and other processes, and oceanwave processes associated with ENSO and the adjustment of the North Pacific Ocean by Rossby waves".

Thus, the PDO is a response to something else; treating it as a forcing must be taken with caution.

The impact of PDO on global temperature

As noted before, some skeptics claim that the PDO is responsible for the 20th century temperature trend. Prominently, Roy Spencer used a simple energy balance model (EBM) forced by "cloud cover variations directly proportional to the PDO index values" to show that indeed much of the warming can be accounted for by the PDO alone. A zero-dimensional EBM relates the temperature change with the energy imbalance of the earth; mathematically, it can be written as



where C is the heat capacity, λ the climate sensitivity and F(t) the forcing; it can be shown that the response time of the system is given by τ = C λ .

In his post Spencer does not give many details on what he did. In particular he says that he "ran many thousands of combinations" with varying parameters and that his graph shows "an average of all of the simulations that came close to the observed temperature record"; a bit mysterious and hard to reproduce. Though, he gives an average value of the parameters: 800 m for the ocean mixing depth, λ = 0.33 °C/Wm-2 and a proportionality factor between the PDO index and forcing of 1.7-2.0 W/m-2. With these numbers it's possible to calculate ΔT from the equation above; the result is shown in the figure below as blue line.

Fig. 3: triangles: GISS anomaly baselined 1900-1920; the black line is a 11-years smoothed version. Blu line: ΔT calculated from the PDO index. Red line: the same as the blue line but with a shifted PDO index.

It's evident that the calculated curve does not follow the measured ΔT much nor it is anything like Spencer's curve. Indeed it couldn't, it behaves exactly as expected given that the PDO index has no trend. The question is, then, how to reproduce Spencer's result. Answering this question requires a sort of "reverse engineering", which is prone to result in the wrong answer; nevertheless, I tried. Using the same parameters as before but shifting the PDO forcing up by about 2 W/m2, i.e. assuming an initial imbalance that large, I obtained the red curve shown in fig. 3 which this time looks pretty much like Spencer's curve.
(Note: you might want to read a similar and more authoritative explanation on how to cook a graph or Barry Bickmore's take).

If true, this is equivalent to adding a background linear temperature trend. In the end, contrary to Spencer's claim we can rule out at least that the PDO alone can explain the last century warming trend.

The PDO in the past

There has been some reconstructions of the PDO in the past. Clearly, there are no measurements available and it's also hard to find reliable proxies of the sea surface temperature in the North Pacific. Typically precipitation sensitive proxies are used.

Bondi et al. 2001, for example, used tree rings for the period from 1660 to 1992 from trees collected between Southern California and northern Baja California, a region chosen for the good correlation between tree rings and PDO. They found a dominant bidecadal cycle throughout the record up do the end of 19th century and longer periodicities, similar to those found in the instrumental record, in the 1900s associated with larger PDO-ENSO variability. Although there has been periods of reduced variability and loss of periodicity, nevertheless it appears that the PDO has been a more or less permanent feature of the Pacific Ocean variability.

One of the longest reconstructions I'm aware of is reported in MacDonald at al. 2005 which extend the record back to year 993. They found again the 50-70 years cycle but it is not stable throughout the record; in particular, this cycle is lost for extended periods during the 13th century and from the 17th to the end of the 18th century. But the more evident feature is the unusually low PDO during the Medieval period, as shown in the figure below.

Fig. 4: reconstructed annual PDO index from AD 993 to 1996. The heavy line is the index smoothed using an 11 year moving average. Insert: the same reconstruction compared to instrumental data.

This anomalously cold eastern North Pacific is in agreement with a semi-permanent La Nina-type condition found by Mann et al. (2005). Both data and models agree on this somewhat paradoxical finding, warmer conditions over the tropical Pacific in the long run lead to the devleopment  of a prevalently negative PDO-ENSO. This can be explained (Cook et al. 2007) by the so-called Bjerknes feedback, where in a warmer tropical Pacific the east-west temperature gradient increases and so does the Walker circulation, creating the conditions for the development of a La Nina.

Conclusions

In this brief post I've tried to highlight some features of the PDO that I believe are important in the context of its impact on the global temperature trend. Although it is a well recognized pattern of variability with clear implications on the regional climate, it appears that it can not be invoked to explain the current warming trend; both recent and paleo data and our understanding of PDO-ENSO tell a different story.

NOTE: This post written by Riccardo is the Advanced rebuttal to "it's the Pacific Decadal Oscillation"

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Comments 51 to 82 out of 82:

  1. RickG, Yes water vapor is tied to temperature - meaning higher temperatures are associated with increased water vapor/evaporation. But the whole cycle of surface water -> water vapor -> clouds -> precipitation -> surface water is what's driving the whole water based feedback mechanism and the energy balance - not just the water vapor alone. That was my point. "As for clouds, those with small water droplets (lighter clouds) tend to reflect light while those with larger water droplets (darker clouds) tend to absorb more light. Am I wrong?" I'm not sure.
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  2. Moderator, "Moderator Response: Fixed open italics tag." Thank you!
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  3. RW1, "I don't find them convincing at all" The conclusions in Yeh et al (ref above), are from "calculations based on historical El Nin˜o indices" augmented by "the six climate models with the best representation of the twentieth-century ratio of CP-El Nin˜o to EP-El Nin˜o". Doesn't get much more more convincing than that. "All I'm saying is if natural oscillations can cause ... " Nope, you're ducking that question. What natural forces are these? Are they already accounted for in existing forcing calculations? Are they global? What physical phenomena can be measured to determine their efficacy? It is high time that the 'natural forces' gambit is held to the same level of scrutiny as GHGs. And note that the warming of concern is that rapid rise since circa 1970: 0.15C per decade, not 0.6C in a century.
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  4. RW1 at 08:20 AM, the water vapour having removed heat from the surface, rises to the point where condensation begins, resulting in a nett cooling effect on the atmosphere at that point as the water droplet receives the heat carried by the water molecule. That effect continues on upwards until all moisture in the air has been removed at the highest level where clouds form. The only way to determine the bottom line of the process would be to measure the amount of heat being liberated from the surface by evaporation against the amount of heat that is returned to the surface by rain.
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  5. Tom Curtis at 01:37 AM, re "For a start, during El Ninos, the water surrounding Australia is cooler than normal, yet Australia tends to be hotter than normal." The conditions in Australia are very much subject to what is occurring in the Indian Ocean, perhaps more so, as is evident when trying to find correlation between droughts and the conditions in the oceans surrounding Australia.
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  6. RW1 wrote in 47:
    All I'm saying is if natural oscillations (variations) can cause up to 0.5 C of temperature change in one year, why couldn't natural forces cause most of the 0.6 C of warming over the whole of 20th century?
    I believe the subject of this post is the climate oscillation known as the Pacific Decadal Oscillation. Climate oscillations like the Pacific Decadal Oscillation store energy, release it, get recharged then release it again. El Nino is a classic example of this. Just after an El Nino temperatures go up due to the energy that is released into the atmosphere. Then temperatures go down. Climate oscillations are responsible for much of the year to year natural variability in temperature. Another source is solar insolation. But we know that but for the solar cycle output has been flat to falling since at least 1962 thanks to satellite measurements. Climate oscillations can't create energy. They can only store it then release it. The sun hasn't been producing additional energy. Where is the energy for your natural variability being the "cause most of the 0.6 C of warming over the whole of 20th century" supposed to come from? We know that CO2 absorbs thermal radiation. We are able to easily demonstrate this in a lab. See the "CO2 Experiment" video at the top of this page.) We have known this since the mid 1800s. We are able to measure the absorption spectra of carbon dioxide and other greenhouse gases. We know that in terms of its greenhouse effect carbon dioxide acts primariyly in the region of the spectra centered around 15 μm (15 microns), a wavenumber of 667 cm-1 that is due to the quantized bending mode of the molecule -- which acts in accordance with the principles of quantum mechanics to result in the absorption of radiation in this part of the spectra. We know that absorption keeps going up as you raise the levels of carbon dioxide. Using satellites we are able to image atmospheric carbon dioxide. We are able to see the plumes rising up from the heavily populated East and West coasts of the United States. We can image the carbon dioxide because it reduces the rate at which infrared radiation escapes to space. If energy is escaping the climate system at a reduced rate but entering the climate system at the sate rate as before we know that the amount of energy in the system has to increase. We know that the temperatures have to increase. We know that for every degree Celsius you increase the temperature the humidity of saturation has to increase by 8%. We know that for every 10°C it roughly doubles. And we know that water vapor absorbs radiation, just like carbon dioxide, and are able to satellite image that, too. Water vapor doesn't condense to form clouds unless it exceeds the humidity of saturation -- and the humidity of saturation increases with temperature. By a factor of 2 for every 10°C. RW1 wrote in 47:
    The bottom line, for me at least, is net positive feedback is an extraordinary claim that requires extraordinary proof, especially since solar energy is not amplified to anywhere near such an extent and since net negative feedback is far, far more logical for a system stable enough to support life as the Earth is.
    "... especially since solar energy is not amplified to anywhere near such an extent." It is amplified to roughly the same extent. We can't explain the warm interglacials and ice ages without the amplification due to carbon dioxide (which is released by the oceans when they warm like a warming soda losing its fizz but absorbed when the oceans cool), ice sheets (due to their melting and growth) and water vapor feedback. "... net negative feedback is far, far more logical for a system stable enough to support life as the Earth is." Have you ever heard of the Permian/Triassic Extinction? Nearly all life as we know it was wiped out when a flood basalt supervolcano erupted, sending vast quantities of carbon dioxide into the atmosphere. We won't likely reach that level but something resembling the Paleocene-Eocence Extinction may be within our reach.
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    Moderator Response: [muoncounter] Missing link for 'absorption spectra'. [Daniel Bailey] Tim, I took a shot at what you meant to use for your absorption spectra link. If I was wrong, please let me know what the correct link is & I'll update it.
  7. Timothy Chase at 09:57 AM, regarding your comment "El Nino temperatures go up due to the energy that is released into the atmosphere. Then temperatures go down." The energy released into the atmosphere then goes where? Having come from the oceans in the first place it is unlikely to all have gone back there again otherwise conditions would be such that a repeat El-Nino would occur. With energy being released from the oceans by an El-Nino, would more CO2 be sunk as a result?
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  8. johnd (RE: 54), "The only way to determine the bottom line of the process would be to measure the amount of heat being liberated from the surface by evaporation against the amount of heat that is returned to the surface by rain." Plus the amount of incrementally reflected sunlight from clouds. According to Trenberth 2009, the total reflectivity of clouds is about 79 W/m^2, and the total reflectivity of the surface is about 23 W/m^2. Clouds reflect away over 3 times as much incoming solar energy as the surface for a loss of of about 56 W/m^2 for each additional m^2 of cloud cover. However, the clear sky has an average transmittance of 40 W/m^2 and the cloudy sky has an average transmittance of 30 W/m^2 - making the amount of incremental surface power trapped per each additional m^2 of cloud cover 10 W/m^2. Thus, according to Trenberth's numbers at least, each additional m^2 of cloud cover results in a net loss of about 46 W/m^2, which is quite a bit.
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  9. Timothy Chase (RE: 56), ""... especially since solar energy is not amplified to anywhere near such an extent." It is amplified to roughly the same extent." How do you figure? 239 W/m^2 of post albedo solar energy becomes 390 W/m^2 at the surface (390/239 = 1.6), where as 3.7 W/m^2 from 2xCO2 becomes 16.6 W/m^2 at the surface (16.6/3.7 = 4.5). If this much amplification is within the systems boundaries, why doesn't it take about 1075 W/m^2 at the surface to offset the 239 W/m^2 coming in from the Sun (1075/239 = 4.5)???
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  10. RW1 quotes RickG then writes in 51:
    "As for clouds, those with small water droplets (lighter clouds) tend to reflect light while those with larger water droplets (darker clouds) tend to absorb more light. Am I wrong?" I'm not sure.
    It's pretty obvious in the visible part of the spectrum. Rain clouds -- where the drops are coalescing to form larger drops that are eventually heavy enough to fall -- are darker than the light fluffy clouds. Dark clouds tend to produce especially downpours. However, clouds per se are close to being perfect black bodies in the infrared spectrum. This doesn't matter much if the clouds are close to the surface since they will be roughly the same temperature as the ground and emit radiation at roughly the same rate that they absorb it. But in accordance with Kirchoff's law high altitude clouds absorb radiation independently of their temperature but emit radiation proportional to their temperature taken to the fourth power. So increasing high altitude clouds will tend to warm the climate system as they reduce the rate at which energy escapes to space. As they warm they reduce the rate at which heat escapes from successively lower layers as they decrease the temperature differential until those lower layers warm like the layers above them. Given an enhanced greenhouse effect, whether it is due to higher levels of greenhouse gases or high altitude clouds, an equilibrium will eventually be reached. At some point the rate at which radiation leaves the climate system will equal the rate at which radiation enters the climate system. However the altitude that radiation escapes from will be higher. The greenhouse gases and clouds involved will have to warm in order to radiate energy to space the same rate as the greenhouse gases and clouds at the lower altitudes did before. After the equilibrium has been reestablished the lapse rate -- rate at which temperature falls with increasing altitude -- will be roughly the same. And given the warming of the higher altitudes this will imply a warmer surface.
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  11. Timothy Chase (RE: 56), "We can't explain the warm interglacials and ice ages without the amplification due to carbon dioxide (which is released by the oceans when they warm like a warming soda losing its fizz but absorbed when the oceans cool), ice sheets (due to their melting and growth) and water vapor feedback." Sure we can. The glacial and interglacial periods in between are driven by changes in the Earth's orbit around the Sun, which in turn changes the distribution of the incoming solar energy immensely. This is enough to overcome what appears to be a very strong net negative feedback operating on the system. CO2 lags or follows these cycles - it does not coincide or precede them.
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  12. johnd - Evaporated water carries heat into the upper atmosphere, where condensation releases heat to the cooler air, warming it. The resulting precipitation has less energy, or it would remain vapor. Energy thus transferred to the atmosphere is then radiated or convected away. This heat of condensation powers thunderstorms and hurricanes - heating the atmosphere, causing updrafts that drag moist air up to where it condenses, releasing more heat, and so on... The energy can then get radiated out to space (partially), or radiated back to the surface (again, partially). But the point remains - precipitation has less energy than water vapor, and the precipitation cycle is a major pathway of energy into the atmosphere. Not back to the surface. And calculating global precipitation (and the energy moved in that fashion) is how Trenberth obtains the 78 W/m^2 latent heat figure in his energy balance diagrams. --- I would suggest taking clouds to one of the cloud feedback threads.
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  13. KR, "But the point remains - precipitation has less energy than water vapor, and the precipitation cycle is a major pathway of energy into the atmosphere. Not back to the surface. And calculating global precipitation (and the energy moved in that fashion) is how Trenberth obtains the 78 W/m^2 latent heat figure in his energy balance diagrams." Yes, but precipitation is also still a considerably large pathway of energy back to the surface, and any latent heat energy removed from the surface that isn't returned to the surface in equal amount will have a cooling effect on the surface, reducing surface emitted radiation; thus equally offsetting any latent heat energy radiated into the atmosphere that ultimately escapes out to space.
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  14. RW1 - My point was that precipitation is not, repeat, not a pathway of energy back to the surface. That energy of evaporation is left in the atmosphere, representing part of the energy transfer to the atmosphere (convection, latent heat, and IR, in increasing order). Latent heat loss certainly cools the surface. Some of that energy returns to the surface as backradiation (not precipitation), some is radiated out to space.
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  15. RW1 @ 61. I don't see how your short paragraph argues against the CO2 feedback in interglacials. The adverb "immensely" used in reference to the change in insolation distribution is more rethorical than accurate. Nonetheless, the fact that CO2 changes follow the initial deglaciation induced by orbital changes does nothing to indicate CO2 does not or can not act as a positive feedback. Furthermore, the radiative properties of CO2 are such that it is physically impossible for the gas to not act as a positive feedback at some level. Paleo data show CO2 levels coinciding with interglacials and following the initial degalciation. It also shows temp increasing to a level that insolation changes alone would not explain. If you want to argue against that, make an argument that is at least logical. The fact that CO2 changes follow the deglaciation by itself is not enough to prevent it from acting as a feedback.
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  16. #47 RW1 says "The bottom line, for me at least, is net positive feedback is an extraordinary claim that requires extraordinary proof,... " Net positive feedback in climate science is not the same as net positive feedback in most other fields. The terminology in climate science are a bit messed up in that a "net positive" feedback per standard climate science convention would still be a net NEGATIVE feedback as long as the positive feedback is less than the increased blackbody radiation from the increased temperature of the earth. Or to put it another way, the increased blackbody radiation from a warming earth is not included in the feedback sums to determine whether there is postive or negative feedback.
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  17. Philippe (RE: 65), "I don't see how your short paragraph argues against the CO2 feedback in interglacials. The adverb "immensely" used in reference to the change in insolation distribution is more rethorical than accurate." How do you figure? Does the angle of insolation and subsequent distribution not change significantly? "Nonetheless, the fact that CO2 changes follow the initial deglaciation induced by orbital changes does nothing to indicate CO2 does not or can not act as a positive feedback. Furthermore, the radiative properties of CO2 are such that it is physically impossible for the gas to not act as a positive feedback at some level." Yes, the physics do suggest at least some positive feedback effect is likely, but I think the data strongly suggest it's negligible and the main forces driving the changes are the orbit combined with the ebb and flow of surface ice, especially since temperatures at the end of the interglacials continue to fall significantly even as CO2 remains relatively high. "Paleo data show CO2 levels coinciding with interglacials and following the initial degalciation. It also shows temp increasing to a level that insolation changes alone would not explain. If you want to argue against that, make an argument that is at least logical. The fact that CO2 changes follow the deglaciation by itself is not enough to prevent it from acting as a feedback. The Paleo data also shows previous interglacials, with lower CO2 levels, being warmer than the one were are in now. This is a strong indication that CO2 is not a significant driver of these cycles. If it were, temperatures would be even warmer than previous interglacials - not cooler.
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  18. I had written in 56:
    We can't explain the warm interglacials and ice ages without the amplification due to carbon dioxide (which is released by the oceans when they warm like a warming soda losing its fizz but absorbed when the oceans cool), ice sheets (due to their melting and growth) and water vapor feedback.
    RW1 responded in 61:
    Sure we can. The glacial and interglacial periods in between are driven by changes in the Earth's orbit around the Sun, which in turn changes the distribution of the incoming solar energy immensely. This is enough to overcome what appears to be a very strong net negative feedback operating on the system. CO2 lags or follows these cycles - it does not coincide or precede them.
    CO2 lags warming by no more than 1000 years, likely as the deep ocean gives up carbon. And when I stated that carbon dioxide (under these circumstances) is a feedback that implied a lag of sorts. The warming from a glacial to interglacial takes several thousand years. Therefore the carbon dioxide actually coincides with much of the warming. Which is why the curves appear to be almost on top of one-another. Looking at just the warming due to solar insolation you can't explain the saw tooth structure of the temperature and CO2 trendlines. Things warm rapidly, with the warming period appearing to be perhaps 7000 or 8000 years. But the cooling takes perhaps 100,000 years. Orbital forcings can't explain why this asymmetric pattern appears time and time again. But the rapid decay and slow growth of ice sheets as well as the rapid degassing but slow absorption of carbon dioxide by the oceans and ultimately it minearlization can. For the sawtooth structure please see Figure 1 here: CO2 lags temperature - what does it mean? http://www.skepticalscience.com/co2-lags-temperature-intermediate.htm In the review article: C. Lorius (13 Sept 1990) The ice-core record: climate sensitivity and future greenhouse warming, Nature, Vol 347 ... Hansen and coauthors state:
    The orbital forcing is, however, relatively weak when considered on an annual globally averaged basis (the total insolation received by Earth has varied by 0.7 W m-2 over the past 160 kyr). The amplification of this forcing, the observed dominant 100-kyr cycle and the synchronized termination of the main glaciations and their similar amplitude in the Northern and Southern Hemispheres cannot easily be explained despite developments including the nonlinear response to ice sheets to orbital forcing.
    Solar forcing is weak. You can't even explain the extent to which warming to place even when you include the nonlinear response of ice sheets. And you can't explain the synchronicity of the warming of both hemispheres. Both GCM studies and multivariate studies of paleoclimate data suggest that roughly 40% of the warming of the Antarctic from glacial to interglacial was due to the increase in CO2 from 200 to 300 ppmv. (See page 144.) Furthermore, while recognizing that orbital forcing was responsible for the Milankovitch cycles, they predicted that through the analysis of upcoming ice core samples it would be possible to identify the lag time between the initial warming and the rise in carbon dioxide. Please see:
    This objective is part of the GRIP (Greenland Ice Core Project) and GISP II (Greenland Ice Sheet Project) now being conducted in north central Greenland by Eurpopean and American scientists. These dirllings are expected to reach the bedrock (ice thickness is 3.2 km) in 1992 and to cover the last climate cycle and hopefully more. These cores will allow further documentation of the rapid climate changes discussed here. With a snow accumulation higher than at Vostok they should also allow a better determination of the relative timing (phase lag) of climate and greenhouse forcing. pg.145
    But just as importantly there were times when carbon dioxide rose first. The ice cores from Greenland and Antarctica have taken us back the better part of a million years now. During this time temperature always seems to rise first. However, if you look back further in the case of supervolcanoes and their flood basalt eruptions carbon dioxide rose first, then temperature. Examples of where continental and submarine supervolcanoes gave rise to Large Igneous Provinces resulting in mass extinction include: 55 Mya, Paleocene-Eocene Thermal Maximum – North Atlantic Basalts 65 Mya, end-Cretaceous event resulting from a supervolcano that gave rise to the Deccan basalts in India as it collided with Asia at the time of the formation of the Himalayas 183 Mya, Toracian Turnover (a lesser warming and extinction event in the Early Jurassic period) – Karoo Basalts (Africa) 201 Mya, End Triassic Extinction – Central Atlantic Magmatic Province 251 Mya, Permian-Triassic Extinction that resulted from a supervolcano that left behind the Siberian basalts during the breakup of Pangaea. 360-375 Mya, Late Devonian Extinction – Viluy Traps (Eastern Siberia, more tentative according to Rampino below) For a more extensive list, please see: Vincent E. Courtillot and Paul R. Renne (2003) On the ages of flood basalt events, C. R. Geoscience 335, 113–140 For a recent commentary: Michael R. Rampino (April 13, 2010) Mass extinctions of life and catastrophic flood basalt volcanism, PNAS, vol. 107, no. 15, pp. 6555-6556 Here is recent study showing that the eruption of the Central Atlantic Magmatic Province occured simultaneously with the end Triassic Extinction 201 Mya: Jessica H. Whiteside (April 13, 2010) Compound-specific carbon isotopes from Earth's largest flood basalt eruptions directly linked to the end-Triassic mass extinction, PNAS, vol. 107, no. 15, pp 6721-6725 In recent times temperature generally rose first. But if you look further back, in some cases carbon dioxide rose first, then temperature. And those times that carbon dioxide rose first are strongly associated with sudden changes in climate and the resulting major and minor extinction events.
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  19. RW1 - all sorts of wonderful explanations work if you dont worry about arithmetic. The problem with the milankovich theory from day one is that variation in solar and insolation alone are insufficient. You need the GHG feedback as well make it work. You also need a means to turn a NH effect into a global effect - which GHG feedbacks manage nicely. As to idea, that previous interglacial temperatures should depend only on CO2 - we ALREADY agree that milankovich forcing drive this and they are different for each interglacial. How about a model run with ALL the forcings and feedbacks included? To say nothing of also ignoring the physics. How does a change in DLR due to change in GHG NOT have an effect on surface temperature? This is an extraordinary claim that I want to see the evidence for from skeptics.
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  20. Timothy Chase at 09:34 AM on 6 March, 2011: Thanks for the link to Tamino's mistake. He used the wrong North Atlantic SST dataset [Kaplan] for his comparison to GISS LOTI. http://wattsupwiththat.com/2011/02/03/tisdale-tasks-tamino/ or at my blog if you'd prefer: http://bobtisdale.blogspot.com/2011/02/comments-on-taminos-amo-post_03.html And thanks for the link to DiLorenzo 2010, but I have read it.
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    Moderator Response: [Daniel Bailey] If you feel Tamino used the wrong dataset why have you not corrected him? I note, having read the entire post Tim linked to for you, you were absent from the discussion therein. By definition, Kaplan is THE dataset to use for NA SST's.
  21. scaddenp (RE: 69), "How does a change in DLR due to change in GHG NOT have an effect on surface temperature? I make no claim that it doesn't, but we are getting off topic here. Moderators - any suggestion where this discussion should go?
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  22. Inline to comment 56 the moderator wrote:
    Moderator Response: [muoncounter] Missing link for 'absorption spectra'. [Daniel Bailey] Tim, I took a shot at what you meant to use for your absorption spectra link. If I was wrong, please let me know what the correct link is & I'll update it.
    Actually that particular link was to a copy of the well-known graphic showing downwelling and upwelling radiation at Top Of Atmosphere as well as the absorption due to different greenhouse gases including nitrous oxide: http://climate-guardian.agilityhoster.com/avatar/index.php?inner_page=transmission Not a big deal, though. While I have made a number of my own graphics using web-based tools, mapping to spheres, etc. that particular graphic is from Global Warming Art. Unfortunately it seems to be having trouble today. Something involving the MySql database I believe.
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  23. Well claiming that is "minor" amplification compared to albedo is pretty close, especially when in fact albedo and GHG component are of same order. Perhaps we should takes this "CO2 lags temperature" if wish to continue to argue that GHGs are unimportant for glacial/interglacial cycle.
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  24. I wrote in #58: "Plus the amount of incrementally reflected sunlight from clouds. According to Trenberth 2009, the total reflectivity of clouds is about 79 W/m^2, and the total reflectivity of the surface is about 23 W/m^2. Clouds reflect away over 3 times as much incoming solar energy as the surface for a loss of of about 56 W/m^2 for each additional m^2 of cloud cover." Actually, I don't think this is the right way to do this. Clouds cover about 2/3rds of the surface, so 341 W/m^2*0.67 = 228 W/m^2 average incident on the clouds. 79 W/m^2 divided by 228 W/m^2 = 0.34 average reflectivity of clouds. 1/3rd of the surface is cloudless, so 341 W/m^2*0.33 = 113 W/m^2 average incident on the cloudless surface. 23 W/m^2 divided by 113 W/m^2 = 0.20 average reflectivity of the cloudless surface. 0.34-0.20 = 0.14. 341 W/m^2*0.14 = 48 W/m^2 loss for each additional m^2 of cloud cover.
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    Moderator Response: [muoncounter] Sounds like its time to go to an Albedo thread. From that thread, you can link back to originating comments here if necessary.
  25. "Does the angle of insolation and subsequent distribution not change significantly?" What do you mean by significantly? You use a lot of adverbs. If you were talking with Poptech, he would altogether dismiss you for being "subjective." Of course, that would be another sterile rethorical trick. "The Paleo data also shows previous interglacials, with lower CO2 levels, being warmer than the one were are in now. This is a strong indication that CO2 is not a significant driver of these cycles. If it were, temperatures would be even warmer than previous interglacials - not cooler." That argument would hold only if the current temp was equilibrium. It's not. In any case, that is a different argument than your original one in #61, which was that CO2 was not acting as a positive feedback. Once again, ill defined words such as "strong indication" or "significant driver" push your argument more toward the rethorical. I'm not sure what you mean by driver. If that would be initial cause, it is well accepted that the orbital changes are the driver and that CO2 is a feedback. Your argument in post 61 that the lag shows that CO2 is not a feedback is no more valid now than it was before. Perhaps it was just poorly formulated. Your assertion that CO2 levels and interglacials do not coincide is false, as shown in the graph in your post #67.
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  26. Timothy Chase said: We know that for every degree Celsius you increase the temperature the humidity of saturation has to increase by 8%. We know that for every 10°C it roughly doubles. And we know that water vapor absorbs radiation, just like carbon dioxide, and are able to satellite image that, too. Water vapor doesn't condense to form clouds unless it exceeds the humidity of saturation -- and the humidity of saturation increases with temperature. By a factor of 2 for every 10°C. --------------------------- How does this correlate with the climate4you humidity graphs? http://www.climate4you.com/GreenhouseGasses.htm
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  27. Are the graphs of global relative humidity here right? http://www.friendsofscience.org/assets/documents/The_Saturated_Greenhouse_Effect.htm
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    Moderator Response: See "Humidity is falling."
  28. RW1 @47:
    The bottom line, for me at least, is net positive feedback is an extraordinary claim that requires extraordinary proof, especially since solar energy is not amplified to anywhere near such an extent and since net negative feedback is far, far more logical for a system stable enough to support life as the Earth is.
    Given that mean global surface temperatures have fluctuated over a 4 degree range (at least) in the recent past, and that over period in which life has existed on Earth has fluctuated over a 20 degree range (at least), the notion that the climate system is dominated by negative feedbacks has been refuted. Given that the 0.1 w/m^2 variation in total solar forcing has a detectable effect on climate (although difficult to detect), the idea that negative forcings dominate under current circumstances is also shown to be false.
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  29. JohnD @55, as a Queenslander, I can tell you that ENSO absolutely dominates weather patterns in Queensland. They are also significant in NSW, Victoria, and across northern Australia. Weather patterns in WA and across the southern states are also affected by events in the Indian Ocean, with a seasonal component as to which is most dominant in the South.
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  30. Tom Curtis at 15:17 PM, whilst the IOD alone determines weather patterns across perhaps half of Australia from the north-west to the south-east during it's negative (wet) phase, during it's positive phase it's influence covers about 2/3 of Australia, hence the difficulty in correlating droughts in Australia with El-Nino alone. However, as we have seen recently, the widespread flooding has been due to a -ve IOD coinciding with a La-Nina pattern, the last such unique coincidence being 1975, that period likely the wettest time since first settlement, definitely since official records begin.
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  31. KR at 10:48 AM, re "Evaporated water carries heat into the upper atmosphere, where condensation releases heat to the cooler air, warming it. The resulting precipitation has less energy, or it would remain vapor." Lets think about this. The evaporated water, now a gas, has become an integral part of the atmosphere, thus the heat it carries then becomes accounted for as part of the total carried by the air, does it not? When the water molecule condenses into a water droplet, ie. ceases to be a gas and hence part of the air, even if it gave up all of it's carried heat, then logically there should be no change to the air. Therefore, any heat energy carried with it will mean a loss of heat energy from, and thus a lower temperature of the air it has ceased to be a part of. Does that make sense?
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  32. nofreewind wrote in 76:
    Are the graphs of global relative humidity here right? http://www.friendsofscience.org/assets/documents/The_Saturated_Greenhouse_Effect.htm
    "The Saturated Greenhouse Effect?" The greenhouse effect wouldn't be saturated if CO2 were more than 50X its current concentrations. But for the crayola colors and line thicknesses and the exaggerated scales they appear to be similar to what you found at Climate4You. However, even if one takes at face value a drop in relative humidity that absolute humidity would appear to rise. Moreover, Chris Colose has pointed out that the reanalysis products this is based off of aren't of the highest quality. He states:
    Radiosondes provide water vapor information in the atmosphere since the 1940′s, but earlier products had a lot of biases, and since then changes in instrumentation have taken place which may lead to discontinuities in the data, and problems arose especially for upper atmospheric data. Is the atmosphere drying up? June 23, 2008 http://chriscolose.wordpress.com/2008/06/23/is-the-atmosphere-drying-up
    Furthermore in the AR4 WG1 it shows that data is consistent with increasing humidity in the upper troposphere and that relative humidity has shown little change. Please see:
    In the absence of large changes in relative humidity, the observed warming of the troposphere (see Section 3.4.1) implies that the specific humidity in the upper troposphere should have increased. As the upper troposphere moistens, the emission level for T12 increases due to the increasing opacity of water vapour along the satellite line of sight. In contrast, the emission level for the MSU T2 remains constant because it depends primarily on the concentration of oxygen, which does not vary by any appreciable amount. Therefore, if the atmosphere moistens, the brightness temperature difference (T2 − T12) will increase over time due to the divergence of their emission levels (Soden et al., 2005). This radiative signature of upper-tropospheric moistening is evident in the positive trends of T2 − T12 for the period 1982 to 2004 (Figure 3.21). If the specific humidity in the upper troposphere had not increased over this period, the emission level for T12 would have remained unchanged and T2 − T12 would show little trend over this period (dashed line in Figure 3.21). 3.4.2.2 Upper-Tropospheric Water Vapour http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch3s3-4-2-2.html
    The reanalysis is using the very same sondes that have proven problematic in the past with respect to the so-called "missing tropospheric hot spot." So it should come as no surprise that "The Friends of Science" bring up the hot spot only a little further down the page:
    However, the Hadley Centre's real-world plot of radiosonde temperature observations shown below does not show the projected CO2 induced global warming hot-spot at all. The predicted hot-spot is entirely absent from the observational record.
    They would appear to be cherry-picking their unreliable datasets. In contrast others appear to be finding the "hot spot" with little problem. See for example:
    Insofar as the vertical distributions shown in Fig. 3 are very close to moist adiabatic, as for example predicted by GCMs (Fig. 6), this suggests a systematic bias in at least one MSU channel that has not been fully removed by either group. The discrepancy could in principle be explained by a surface temperature trend greater from that at 850 hPa, but this trend would have to be nearly 1.0 C decade −1 , which is far greater than indicated by surface records. Steven C. Sherwood et al. (2008) Robust tropospheric warming revealed by iteratively homogenized radiosonde data, Journal of Climate, vol. 21, issue 20, p. 5336
    ... and:
    We find that tropospheric temperature trends in the tropics are greater than the surface warming and increase with height. Our analysis indicates that the near-zero trend from Spencer and Christy's MSU channel-2 angular scanning retrieval for the tropical low-middle troposphere (T2LT) is inconsistent with tropical tropospheric warming derived from their MSU T2 and T4 data. Qiang Fu and Celeste M. Johanso (26 May 2005) Satellite-derived vertical dependence of tropical tropospheric temperature trends, Geophysical Research Letters, Vol. 32, L10703
    ... but then Friends of Science aren't exactly a science organization, are they? Please see:
    In an August 12, 2006, article The Globe and Mail revealed that the group had received significant funding via anonymous, indirect donations from the oil industry, including a major grant from the Science Education Fund, a donor-directed, flow-through charitable fund at the Calgary Foundation. The donations were funnelled through a University of Calgary trust account research set up and controlled by U of C Professor Barry Cooper. [2] [3] The revelations were based largely on the prior investigations of Desmogblog.com, which had reported on the background of FoS scientific advisors and Cooper's role in FoS funding. SourceWatch: Friends of Science http://www.sourcewatch.org/index.php?title=Friends_of_Science
    Here are some other organizations you might not want to get your science reporting from:
    For those who are interested, here is a list in alphabetical order of 32 organizations involved in both the denial campaign surrounding tobacco and that surrounding Anthropogenic Global Warming. I also researched the organizations to see which would appear to be libertarian, including a source for each. Blowing Smoke: 32 Organizations
    Anyway, to answer your original question, the graphs of trends in global averaged relative humidity at specific altitudes has little to say about whether or not the humidity of saturation increases roughly as an exponential function of temperature. But that didn't seem to be what you were really focused on so I turned to consider what you were concerned with.
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  33. This is a most interesting topic and one which I think addresses a critical point about the climate system's response to certain forcings. It's very refreshing to see such an informative discussion which is purely objective and devoid of any personal attacks or sarcastic remarks, unlike some other sites. I'm a skeptic of AGW but always enjoy reading here because the debate is civil and friendly. This site's comments section is arguably the best for a balanced and thorough examination of the science.
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  34. johnd at 16:37 PM on 7 March, 2011. You appear to be giving yourself contradictions by thinking of water droplets as not part of the air - surely what is crucial is that they are there in the atmosphere, and probably at equilibrated temperature with the air. The water vapour forming droplets releases heat into the atmosphere, which necessarily increases the atmosphere's temperature. That heat has been carried from the surface liquid water into the atmosphere by the evaporation-condensation cycle. So the bottom line is that it warms the atmosphere.
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  35. johnd - I'm not certain I can follow your logic there. Water vapor rising into the atmosphere reaches a point where the air is cool enough to condense it; cooler than the water vapor. When it cools and condenses the energy involved in that transition is given over to the air, which warms. That heat energy is not inconsiderable - the updrafts in thunderstorms and hurricanes are driven by the heat from condensing vapor. The downdrafts are considerably cooler. Thunderstorms end when there is insufficient moist air drawn in, hurricanes weaken when they get over land and lose the warm moist air over the oceans as an energy source.
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  36. When quoting (82) from the webpage that nofreewind (76) had referred us to:
    However, the Hadley Centre's real-world plot of radiosonde temperature observations shown below does not show the projected CO2 induced global warming hot-spot at all. The predicted hot-spot is entirely absent from the observational record. http://www.friendsofscience.org/assets/documents/The_Saturated_Greenhouse_Effect.htm
    ... I pointed out that the Friends of Science claim that "the predicted hot-spot is entirely absent from the observational record" is at best cherry-picking the studies, and gave two examples of studies that claim to have found the "hot-spot" where the warming trend is higher in the mid-troposphere than on the ground. However, I appear to have missed the bit where they referred to the hot-spot as being the "projected CO2 induced" global warming hot-spot. Such words are strongly suggestive of the often-repeated claim that the hot spot is a signature of CO2 induced warming -- and if the temperature profile don't fit you must acquit. Chris Colose reminds us that the hot spot is actually the signature of any global warming, whatever the forcing. Please see:
    Tropospheric warming in the tropics is a signature of greenhouse warming, but it is more accurate to say that it is not a unique signature (i.e., you get this "hotspot" with all types of forcings). The 'hotspot' arises due to the moist adiabat. In the extra-tropics you do not don't expect the lapse rate changes to be so dominated by moist convective effects. Skeptics/Denialists Part 2: Hotspots and Repetition Posted on December 20, 2008 http://chriscolose.wordpress.com/2008/12/20/skepticsdenialists-part-2-hotspots-and-repetition
    He also points out that it is part of a negative feedback, and if the "hot spot" isn't there then global warming will actually be somewhat stronger than we expect. More evidence that Friends of Science should not be regarded as a trusted source of science news... In any case my apologies for not getting this in the first time around.
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    Moderator Response: Also see the Skeptical Science Argument "There’s no tropospheric hot spot."
  37. scaddenp (RE: 73), "Perhaps we should takes this "CO2 lags temperature" if wish to continue to argue that GHGs are unimportant for glacial/interglacial cycle." Yes, I'm arguing the evidence doesn't support that GHGs (i.e. CO2 levels) are a significant factor in the glacial/interglacial cycle. Do you wish to discuss this further over there?
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    Moderator Response: Definitely not here.
  38. "The question is, then, how to reproduce Spencer's result." Did you consider e-mailling him and asking him what he did?
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  39. Riccardo, "Thus, the PDO is a response to something else; treating it as a forcing must be taken with caution." I'm not sure the point you're trying to make with this? You think that because PDO maybe a feature or related to ENSO that this undermines it's possible role in forcing climate? I can see if we knew the whole truth about PDO that would help in understanding it's role but I don't get why we should specifically treat it with caution because it is related to ENSO?
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  40. I wonder if you could go into the relationship between PDO and ENSO a little more? It appears that to a large extent PDO may just be a measurement of one of the impacts of ENSO in an appear outside of the 'tradional' ENSO region. Is this what you mean?
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  41. The Moderator replied, "[Daniel Bailey] If you feel Tamino used the wrong dataset why have you not corrected him? I note, having read the entire post Tim linked to for you, you were absent from the discussion therein." Most of my comments are deleted at Tamino's OpenMind. You continued, "By definition, Kaplan is THE dataset to use for NA SST's." Kaplan SST data is “A” Sea Surface Temperature anomaly dataset, not “THE” dataset. The ESRL uses Kaplan North Atlantic SST data (0-70N, 80W-0) to create their AMO dataset, similar to JISAO using the obsolete UKMO and obsolete Reynolds OI.v1 and the current Reynolds OI.v2 SST data for their PDO data. In some respects it’s similar to the Met Office using Hadley HADSST2 for their HADCRUT product, and similar to GISS using a combination of HADISST/Reynolds SST for their LOTI product. The ESRL selected a SST dataset to use for their AMO product. They could have used any long-term SST dataset. A question: If you wanted to determine the global sea surface temperature anomaly contribution to the global GISS LOTI data would you use Kaplan SST or the datasets GISS uses? The multidecadal variability of the Kaplan SST data is different than the SST datasets used by GISS and those differences biased Tamino's results. They gave him the result he was looking for, but they were wrong results because he used the wrong SST dataset. I illustrated that error very clearly in the post that I linked earlier. Here’s the address again: http://bobtisdale.blogspot.com/2011/02/comments-on-taminos-amo-post_03.html
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    Moderator Response: [DB] When it comes to climate-related time series data analysis I trust those who not only do it for a living, but those who's work has proven to not only withstand the tests of time and other research, but who have established gold standards for accuracy and understanding of the underlying physical processes the analysis' represents. Tamino's body of work has long been regarded as the de facto standard in climate data analysis. So a choice between Tamino or you is a non-choice. As to issues with moderation on Tamino's blog, he has come to have little tolerance for those unwilling to learn, but has demonstrated great patience with those trying, but struggling, to do so.
  42. DB: Since you believe Tamino's use of the wrong SST dataset in an analysis is "de facto standard in climate data analysis", there's no reason for me to continue to discuss this matter.
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  43. Timothy Chase: Please contact me ASAP. mandias-at-sunysuffolk.edu
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  44. When was the PDO discovered and when did it come to the attention of climatologists? Just curious because skeptics often act like something is a new discovery even when it's old news.

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    Moderator Response:

    [DB] The term was coined in 1996.  This is a good discussion of it by the originator of the term.

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