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Warming, interrupted: Much ado about natural variability

Filed under: — raypierre @ 12 July 2009

A guest commentary by Kyle Swanson – University of Wisconsin-Milwaukee

I am quite humbled by the interest that has been generated by our paper “Has the climate recently shifted?” (Swanson and Tsonis, 2009), and would like the thank the RealClimate editors for the opportunity to give my perspective on this piece.

Before delving into the paper itself, a few words about the place of our work in the global warming “debate” are in order. A quote from the early 20th century Viennese polymath Egon Friedell (which I ran across in the wonderful book Cultural Amnesia by Clive James) captures the situation better than any words I could ever weave;

Electricity and magnetism are those forces of nature by which people who know nothing about electricity and magnetism can explain everything.

Substitute the words “modes of natural climate variability” for “electricity and magnetism,” and well…, hopefully the point is made.

It first needs to be emphasized that natural variability and radiatively forced warming are not competing in some no-holds barred scientific smack down as explanations for the behavior of the global mean temperature over the past century. Both certainly played a role in the evolution of the temperature trajectory over the 20th century, and significant issues remain to be resolved about their relative importance. However, the salient point, one that is oftentimes not clear in arguments about variability in the climate system, is that all else being equal, climate variability and climate sensitivity are flip sides of the same coin. (see also the post Natural Variability and Climate Sensitivity)

A climate that is highly sensitive to radiative forcing (i.e., responds very strongly to increasing greenhouse gas forcing) by definition will be unable to quickly dissipate global mean temperature anomalies arising from either purely natural dynamical processes or stochastic radiative forcing, and hence will have significant internal variability. The opposite also holds. It’s painfully easy to paint oneself logically into a corner by arguing that either (i) vigorous natural variability caused 20th century climate change, but the climate is insensitive to radiative forcing by greenhouse gases; or (ii) the climate is very sensitive to greenhouse gases, but we still are able to attribute details of inter-decadal wiggles in the global mean temperature to a specific forcing cause. Of course, both could be wrong if the climate is not behaving as a linear forced (stochastic + GHG) system.

With that in mind, our paper is fundamentally about inter-decadal variability in the climate system and its role in the evolution of the 20th century climate trajectory, as well as in near-future climate change. The climate system has well known modes of variability, such as the El Niño/Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO), that are active on inter-annual time scales. We are interested in how this short time-scale (from the climate perspective!) variability impacts climate anomalies over multi-decadal time periods.

What we find is that when interannual modes of variability in the climate system have what I’ll refer to as an “episode,” shifts in the multi-decadal global mean temperature trend appear to occur. I’ll leave the details of these episodes to interested readers (here and here), as things get pretty technical. It’s sufficient to note that we have an objective criteria for what defines an episode; we aren’t just eyeballing curves. The climate system appears to have had three distinct “episodes” during the 20th century (during the 1910′s, 1940′s, and 1970′s), and all three marked shifts in the trend of the global mean temperature, along with changes in the qualitative character of ENSO variability. We have also found similar types of shifts in a number of model simulations (both forced and unforced) that were run in support of the IPCC AR4 report.

The contentious part of our paper is that the climate system appears to have had another “episode” around the turn of the 21st century, coinciding with the much discussed “halt” in global warming. Whether or not such a halt has really occurred is of course controversial (it appears quite marked in the HadCRUT3 data, less so in GISTEMP); only time will tell if it’s real. Regardless, it’s important to note that we are not talking about global cooling, just a pause in warming.

What’s our perspective on how the climate will behave in the near future? The HadCRUT3 global mean temperature to the right shows the post-1980 warming, along with the “plateau” in global mean temperature post-1998. Also shown is a linear trend using temperatures over the period 1979-1997 (no cherry picking here; pick any trend that doesn’t include the period 1998-2008). We hypothesize that the established pre-1998 trend is the true forced warming signal, and that the climate system effectively overshot this signal in response to the 1997/98 El Niño. This overshoot is in the process of radiatively dissipating, and the climate will return to its earlier defined, greenhouse gas-forced warming signal. If this hypothesis is correct, the era of consistent record-breaking global mean temperatures will not resume until roughly 2020. Of course, this contrasts sharply with other forecasts of the climate system; the purple line roughly indicates the model-based forecast of Smith et al. (2007) , suggesting with a warming of roughly 0.3 deg C over the 2005-2015 period.

Why would anyone in their right mind believe what I’ve just outlined? Everything hinges on the idea that something extraordinary happened to the climate system in response to the 1997/98 super-El Niño event (an idea that has its roots in the wavelet analysis by Park and Mann (2000)). The figure to the left shows the spatial mean temperature over all grid boxes in the HadCRUT3 data set that have continuous monthly coverage over the 1901-2008 period. While this provides a skewed view of the global mean, as it is heavily weighted toward North America, Europe and coastal areas, unlike the global mean temperature it has the cardinal virtue of being a consistent record with respect to time. The sole exclusion in the figure is the line connecting the 1997 and 1998 temperatures.

Now, anomalous behavior is always in the eye of the beholder. However, the jump in temperature between 1997 and 1998 in this record certainly appears to pass the “smell test” (better than 3 standard deviations of interannual variability) for something out of the ordinary. Nor is this behavior dependent on the underlying time interval chosen, as the same basic picture emerges for any starting time up until the 1980′s, provided you look at locations that have continuous coverage over your interval. Again, as the temperature anomaly associated with this jump dissipates, we hypothesize that the climate system will return to its signal as defined by its pre-1998 behavior in roughly 2020 and resume warming.

What do our results have to do with Global Warming, i.e., the century-scale response to greenhouse gas emissions? VERY LITTLE, contrary to claims that others have made on our behalf. Nature (with hopefully some constructive input from humans) will decide the global warming question based upon climate sensitivity, net radiative forcing, and oceanic storage of heat, not on the type of multi-decadal time scale variability we are discussing here. However, this apparent impulsive behavior explicitly highlights the fact that humanity is poking a complex, nonlinear system with GHG forcing – and that there are no guarantees to how the climate may respond.


References:

Park, J. and M.E. Mann, 2000: Interannual Temperature Events and Shifts in Global Temperature: A Multiple Wavelet Correlation Approach. Earth Interactions, 4-001, 1-36.

Swanson, K.L. and A.A. Tsonis, 2009: Has the climate recently shifted? Geophysical Research Letters, 36, doi:10.1029/2008GL037022.


388 Responses to “Warming, interrupted: Much ado about natural variability”

  1. 51
    save gaia says:

    Related to linear and non linear systems
    http://en.wikipedia.org/wiki/memristor

  2. 52
    Mark says:

    “It seems to me that the rise is marked by a real physical event, El Nino, rather than its statistical rank in a larger record,”

    I think the idea is that an extreme event if included in a graph skews the graph analysis for much longer.

    Therefore without 1998 you can (barely) get away with 10 year trends.

    With it, you have stuffed up your ability to say anything about the underlying trend for ~10 years either side.

    A bit like a ringer in a company football game. That one player will dominate and the team will win. But the team isn’t really all that much better. That one player makes the efforts of the others virtually worthless BECAUSE they are so good.

  3. 53
    Eric Hansen says:

    “The contentious part of our paper is that the climate system appears to have had another “episode” around the turn of the 21st century, coinciding with the much discussed “halt” in global warming. Whether or not such a halt has really occurred is of course controversial (it appears quite marked in the HadCRUT3 data, less so in GISTEMP); only time will tell if it’s real. Regardless, it’s important to note that we are not talking about global cooling, just a pause in warming. ”

    You make many important points but I want to point out a contradiction in the para above that leaps off the page at this skeptic (yes – I am a skeptic).

    You state “only time will tell if global warming has stopped”

    then you state, unqualified, that “we are not talking about global cooling, just a pause in warming”

    It is critical that everybody understand (as this paper asserts) that global warming does not equate to monotonic increase in temperature. Global climatic variable will always be a fact of life and in this lite recent lack of warming does not prove or disprove anything. A climate that oscillates over a positive anomaly slope is most definitely still warming. But only time will tell.

    However, it does indicate to this skeptic that climate is subject to many forces not all of which are fully understood. While we humans certainly do need to clean up our act we also need to approach this issue, especially the policy aspects, with clear heads and eyes wide open.

    thank you

    [Response: And decadal fluctuations in ocean-atmosphere heat exchange are one of those things we don't fully understand. But, we do understand the physics of energy balance well enough to say that they cannot possibly delay warming indefinitely. The energy balance piper must eventually be paid. --raypierre]

  4. 54
    Jim Galasyn says:

    Great post, thank you Kyle.

  5. 55
    MIke says:

    Are there exact years for these climate shifts? 1910, 1940, 1970, 2000 is every 30 years.

  6. 56
    Mark says:

    “then you state, unqualified, that “we are not talking about global cooling, just a pause in warming””

    Yup, because it will take another 10-20 years to find out if it’s actually cooling.

    There have been many pauses in the upward trend of global temperatures.

  7. 57
    Mark says:

    “However, it does indicate to this skeptic that climate is subject to many forces not all of which are fully understood.”

    Uh, subject to many forces: check.

    Not all of which are fully understood: check.

    Implication that conclusions cannot be drawn: false.

  8. 58
    dhogaza says:

    You make many important points but I want to point out a contradiction in the para above that leaps off the page at this skeptic (yes – I am a skeptic).

    That’s because you’re wearing your skeptic-colored glasses.

    There’s no contradiction at all. His point is that if warming has “halted” (note his use of quotes), it is only temporary – a pause. The authors of this paper in no way suggest that AGW isn’t happening.

    It is critical that everybody understand (as this paper asserts) that global warming does not equate to monotonic increase in temperature.

    Well, duh. Climate science has never suggested it would be monotonic, this isn’t what’s new about this paper. Skeptics are the only people who insist that there should be a monotonic increase in temperature, and then use the fact that (duh) there isn’t to scream “AGW is false!”

    So go tell those folks over at WUWT that one shouldn’t expect monotonic increases, please!

    However, it does indicate to this skeptic that climate is subject to many forces not all of which are fully understood.

    This paper doesn’t discuss any “new force which isn’t fully understood”.

  9. 59
    Carl Wolk says:

    I give Swanson credit for recognizing the 1997/8 step change. However, there are better ways to show it, and a similar step change took place during the 86/7 El Nino as well. The background trend that Swanson argues is the true trend (independent of the 1997/8 step change) is actually caused by step-changes related to the 76-8 and 86/7 El Nino events.
    I’ve written a short response to his post, here:
    http://climatechange1.wordpress.com/2009/07/13/swansons-not-so-novel-post-at-realclimate/

  10. 60

    #58, dhogaza, there is nothing out there suggesting this pause. It is good to remind that Hadley
    Arctic ice sheet model failed by 40 years! I would reconsider if present El-Nino peaks same as 1997-1998 and world averages would show a cooling. So far no such thing. Temperature variability has a lot to do with planetary wave positions and the weather they give. Planetary waves seem adjusted for a strong El-Nino episode at present.

    #41 Lynn, Up here in most parts of Canada its incredibly cloudy, you should see many Canadians on holidays chasing your heat wave :(. Variability and cloud extent are joined at the hip, temperature projections fail when clouds play havoc as they do now. This is why world wide averages are key. You seem to be in a heat spot, if El-Nino grows even more, as BTO song goes:
    “you ain’t seen nothing yet” , come up here in the cloud shade for a cooling!

  11. 61
    dhogaza says:

    Carl Volk; I stopped reading when you described RC as being an “alarmist site”. Tells one all one needs to know, really.

  12. 62
    dhogaza says:

    dhogaza, there is nothing out there suggesting this pause

    I tend to agree, but … I was commenting on Eric Hansen’s misinterpretation of Kyle Swenson’s words, nothing more than that.

  13. 63
    Greg says:

    As best I can tell from reading the article, the authors have nothing to contribute to our understanding of climate change. What they seem to be suggesting is that the fit of the models to the data can be improved if the models include feedback among the recognized macro climate states (the ENSO, the Pacific Decadal Oscillation, the North Atlantic Oscillation, and the North Pacific Index). But all the independent drivers of climate are still the same.

    I have a problem with this on a conceptual (model construction) level. The real dependent variable we are interested in is the change in the heat content of the biosphere on Earth. Atmospheric temperature is only one component and a minor one at that. (The others are the oceans, cyrosphere and the top inch or 4 of the surface of the Earth.)

    By only presenting a statistical analysis of a minor part of the total system, the results are vulnerable to false signals in the dataset.

    Physical models of a single aspect of the climate system have a physics based explanation and help us understand the system by looking at a single component in isolation. Such a model is not complete, but is is well grounded in physical principals and demonstrates the first order effects of a single component.

    But the author’s math is not grounded in a single physical principal. It is an analysis of a single dependent variable at an intermediate level of the total system and is not isolated from influences from the other components. The entire set of results could just be artifacts of other, un-named, processes.

    I fail to see what predictive value there is in this approach.

  14. 64
    Marcus says:

    I would have 2 critiques of this post, both to do with the first figure and interpretations thereof:

    1st: The implication that our best guess as to the underlying signal is a linear trend of about 0.1 degree per decade. We have some knowledge about underlying forcing trends, and about the theoretical response to such trends. Indeed, the IPCC AR4 report has predictions out to 2030, with closer to 0.2 degrees per decade rise on average.

    2nd: The inclusion of the Smith et al. (2007) projection as linear. The Smith paper has a graph showing a detailed projection,with uncertainty bounds, and it would be appropriate to include the more detailed projection.

    In general, while papers such as this – or, for that matter, Smith (2007) or Keenlyside (2008) – are always interesting and welcome additions to the literature, I feel that they are too quickly leapt upon as better mousetraps because they explain the last couple of years better than the standard model. And yet, the 3 approaches yield 3 different answers. I would prefer many more caveats about the _preliminary_ nature of such a new study until and unless it is either supported by replication by a number of other groups or it makes a bold, new, unlikely prediction which then comes true.

    See the earlier post about “Science at the bleeding edge”.

  15. 65
    Mark says:

    “Arctic ice sheet model failed by 40 years! ”

    Failed in what way?

    Underestimated the speed of reduction, most likely.

    This hardly makes a good example of how we’re A-OK because models get things wrong…

  16. 66

    Mark quotes Wayne Davidson (60):

    Arctic ice sheet model failed by 40 years!

    … then responds in 65:

    Failed in what way?

    Underestimated the speed of reduction, most likely.

    This hardly makes a good example of how we’re A-OK because models get things wrong…

    “A-OK”? Mark, Wayne has undoubtedly been accused of a number of things in the past, but complacency is definitely a new one on me…

  17. 67
    dhogaza says:

    This hardly makes a good example of how we’re A-OK because models get things wrong…

    If you’d pay attention you’d understand that Wayne’s not saying any such think, he’s saying that things are WORSE, not A-OK. That yes, failed by *underestimation*, just as you say.

    If you read more carefully maybe you’d quit subjecting so many people to unappreciated friendly fire.

  18. 68
    Mark says:

    “That yes, failed by *underestimation*, just as you say.”

    Would’ve been nice if he’d said.

    “If you read more carefully maybe you’d quit subjecting so many people to unappreciated friendly fire.”

    Sorry Wayne, but dhog, where’s the bleeding fun in that?

  19. 69
    Joel Shore says:

    Rob J (#32) says: “Unless you’re cherry picking a linear trend ?!”

    I don’t think you can call fitting a linear trend line to data a “cherry pick”. It is just the simplest thing that you can do…i.e., it is the first (non-constant) term in a higher order expansion. And, alas, with global temperature data over the sort of times that we have and because of the noisiness of this data, it is really as high in the expansion as one can justify going.

    Attempts by people like Roy Spencer to fit a 5th-order(?) polynomial to the data are completely ludicrous and even Spencer himself put on the caveat that he did not mean that polynomial to have any predictive power for the future; But, it would have been better if he hadn’t shown it at all!

  20. 70
    Ike Solem says:

    If we replace the phrase “the climate system” with a more specific name, we can at least agree on what we are talking about. For the purposes of decade-scale variability, the main components of interest would be:

    1) Atmosphere

    2) Oceans

    3) Glaciers and sea ice

    3) Biosphere and soil

    4) Volcanic events

    Volcanic events are a good place to start, because they are almost truly random events which are insensitive to the state of the ‘the climate system’. There are no plausible “modes of variability”.

    Now, consider the atmosphere. Are there modes of variability in the atmosphere, “synoptic temporal periodic structures”? Despite many such claims over the years, the answer is generally not – the stratospheric equatorial jets being one exception. For a good discussion of that, see Ed Lorenz’s book, “Essence of Chaos”:

    In the following pages I shall introduce the atmosphere as an example of an intricate dynamical system, and present the case for believing that its irregularities are manifestations of chaos. After a brief overview I shall enumerate various procedures through which the presence of chaos might be confirmed. Finally, I shall examine some of the consequences of the atmosphere’s chaotic behavior.

    The oceans seem to behave in a similar manner, just slower – and the oceans are the most likely place to find any decade-scale periodic modes.

    First of all, the synoptic oceanic structures are poorly defined and studied due to lack of good data coverage. This is unlike the atmosphere, where decades of radiosonde and satellite data have given synoptic meteorologists a lot of experience with synoptic atmospheric structures. (The dynamical approach involves understanding why synoptic structures form in the first place, rather than just a statistical analysis of observed structures – before computers, all weather forecasters were strictly synoptic in method).

    The dynamic models of the oceans are hard to test because of such lack of data, which has led some people to treat the output of dynamic models as a source of synoptic data, much as if a model of atmospheric circulation was used as a reliable indicator of how cold fronts, etc. behaved, in the absence of radiosonde and satellite data.

    Then, the frequency with which such modeled synoptic structure change over time is given as evidence of a natural periodic cycle, or is correlated to some distant piece of data – sea surface temperatures, for example, or fishing records, which is supposed to be a reliable indicator of the underlying periodic synoptic structure. This procedure is not really that reliable when applied to fluid dynamic systems – works great for orbital phenomenon, however, where underlying periodicity is expected. For example, if you wanted to calculate the orbit of Saturn’s moons from a small amount of observational data, you could probably get away with this approach – but it doesn’t work for ENSO.

    With El Nino and La Nina, you have high sensitivity to initial conditions, which means that ‘mode projection’ is not useful for predicting the future. This is why people haven’t been able to reliably predict ENSO events more than 6-9 months in advance – just as major atmospheric weather events cannot be predicted more than 1-2 weeks in advance, tops. That’s related to the different mixing times of the atmosphere and ocean, and is a manifestation of the chaotic behavior – which doesn’t mean random behavior.

    For the longer-period modes, evidence is even slimmer – and what does an AMO or PDO ‘event’ look like, anyway? What is the physical basis of ‘mode coupling’, as well? On such time scales, other plausible periodic modes involve soil, vegetation and ice sheets. With the ice sheets, there is evidence that the millenial variation is timed by orbital variations, as long as conditions are such that ice sheets can be present – but for the rest? How about claimed periodic modes of desert expansion and ‘megadrought’, for example?

    Desertification is a complicated picture, as it involves soil moisture, atmospheric circulation, regional variations in geology and soils, and biosphere responses. There are regions that have suffered from extended droughts, but the evidence for a periodic driver (rather than just random drift) is also slim. Notice also, that during these past megadroughts global sea levels remained constant. Thus, regional factors probably played the major role in such climate shifts, not global atmospheric forcing (which is what is driving today’s climate change).

    All in all, it seems that the correct way to view unforced natural variability in the atmosphere and oceans is as a manifestation of chaotic phenomenon on an attractor, not as the result of a combination of periodic modes of behavior. Practically, this means that better ocean data coverage is needed, plus decadal modeling approaches similar to those used for weekly weather forecasts, i.e. initialization of the ocean state.

    Regardless of what you think about that, no one can honestly use either point of view to claim that fossil fuel-sourced CO2 isn’t warming the planet at an unprecedented rate, well beyond anything seen in the past four million years or so (current CO2 increase rates being 20-30 times greater than anything seen in the paleoclimate record.) This hasn’t kept people from trying to claim that a) the system is chaotic, so nothing can be predicted, or b) the system is periodic, so the warming is just due to overlapping cycles.

    Hopefully, that illustrates the difference between a legitimate scientific debate over how natural systems like this behave, and the abuse of a legitimate scientific debate to push various kinds of opinions, propaganda, etc.

    It is fairly important that both scientists and the general public understand how the PR industry attempts to manipulate science to serve other interests – it is not really a new phenomenon, just look at the history of eugenics, creationism and Lysenkoism for more examples.

  21. 71
    Alex says:

    #58 dhogaza says “Well, duh. Climate science has never suggested it would be monotonic, this isn’t what’s new about this paper. Skeptics are the only people who insist that there should be a monotonic increase in temperature, and then use the fact that (duh) there isn’t to scream “AGW is false!”“.

    Well, to this simple observer of the AGW scene, all of the AGW predictions, viewed as monotonically climbing graphs, show exactly the opposite of what dhogaza claims. And skeptic friends tell me that the inability of the models to predict anything other than monotonically climbing temperatures is why there’s been a rebranding of AGW as “climate change”. It seems a pity that the models seem unable to take into account significant ocean cycles, solar cycles, etc. To the simple observer it seems either that the models are inadequate or that there’s been a failure to communicate the realities of AGW (leading to articles like the above which will only ever be read by the already convinced.)

    There’s a real dilemma here that AGW proponents need to confront if they’re to win the hearts and minds of the vast mass of people who can’t appreciate the sophistries of AGW justifications and qualifications. And in these tough times, a lot of hearts and minds remain to be won.

    [Response: Models do take into account solar cycles. The long term solar variability is in the IPCC "natural forcing" runs, and many IPCC runs also contain the 11 year cycle. K.K. Tung has shown that many of the models have the correct temperature response amplitude at 11 years, so they seem to be able to take into account that. And you are completely wrong that the models can only show a monotonic increase. If you have that impression, it's only because certain people love to draw a misleading comparison between test runs with CO2 increase alone and the real world, which has other forcings in addition. Models can simulate a temperature decrease in response to volcanic eruption, strong increase in aerosol forcing, and many other things. The Keenlyside et al paper shows that the ocean dynamics can temporarily offset cooling; it may well be true that coupled models underestimate decadal variability, but that is where we are still on the learning curve. Where that shakes out has zero chance of being able to significantly affect climate sensitivity, though. It just affects how long you have to wait to see the full warming. --raypierre]

  22. 72
    Deep Climate says:

    #69 Joel Shore:
    “Attempts by people like Roy Spencer to fit a 5th-order(?) polynomial to the data are completely ludicrous and even Spencer himself put on the caveat that he did not mean that polynomial to have any predictive power for the future.”

    Actually it was “only” a 4th-order polynomial. He’s stopped that now, BTW.

    For a short history of polynomial fitting of global temperature record, see:

    http://deepclimate.org/2009/04/09/the-alberta-oil-boys-network-spins-global-warming-into-cooling/

  23. 73
    dhogaza says:

    Well, to this simple observer of the AGW scene, all of the AGW predictions, viewed as monotonically climbing graphs, show exactly the opposite of what dhogaza claims

    That’s because you’re looking at the average of many runs. Each individual shows wiggly-wiggles, not a monotonic linear change in global temperature. Climate in the real world is expected to respond like the wiggly-wiggle output of a single run. If you had 100 planet earths and could average the wiggly-wiggle response to forcing of each, that AVERAGE would look monotonically increasing. But you wouldn’t see each individual planet responding monotonically.

    If you read a little bit you could learn this yourself.

    And skeptic friends tell me that the inability of the models to predict anything other than monotonically climbing temperatures is why there’s been a rebranding of AGW as “climate change”.

    Wrong on both points. They don’t suffer from the stated inability, and it’s not why the term “climate change” was adopted.

    Again, if you were willing to invest some personal time into researching this you’d realize you were wrong.

    It seems a pity that the models seem unable to take into account significant ocean cycles, solar cycles, etc.

    Well, seeing as you’re wrong about this, too, I think something else is a pity and it has nothing to do with the work of climate modelers …

    There’s a real dilemma here that AGW proponents need to confront if they’re to win the hearts and minds of the vast mass of people who can’t appreciate the sophistries of AGW justifications and qualifications.

    Well, when people lie to you (intentional or not, your friend may also be simply ignorant rather than dishonest), and you accept those lies uncritically, whose fault is it? Scientists.

    Step back and think about the claims you’ve made … do you really think that thousands of climate scientists are SO STUPID that they’d build models that don’t include basic physical features, don’t demonstrate the kind of natural variability seen in the real world, etc, as you claim?

    [edit]

  24. 74
    Doug Bostrom says:

    Alex 13 Jul 2009 at 2:44 pm

    “sophistries”

    “Arguments that seems plausible, but are fallacious or misleading, especially one devised deliberately to be so.”

    You just can’t help yourself, can you?

  25. 75
    Todd Albert says:

    Re #6: Yvan Dutil beat me to the punch — I guess I am slow to read posts over the Boreal Summer.

    In a very simple sense, if you allow greenhouse forcing or global warming to be a linear trend over the past century of +0.7°C/100 yrs and you allow for a AMO-style 60-year cycle of ±0.1°C, and add these curves together, you can recreate much of the temperature trends of last century (minus all of the shorter-term wiggles). Follow this until about 1997 when there appears to be a distinct departure from this upward-trend and natural cycle (see http://www.toddalbert.com/files/images/temps.gif for a cartoon sketch). Could this suugest that we’ve passed a tipping point and the climate system is now settling into a new regime? As we approach new warming thresholds (i.e. 2°C) will we see more jumps? We understand that because of all of the feedbacks involved, the system is not linear. So why should we be surprised to see jumps and plateaus in the temperature record.

    Additionally, I still hold that global average temperature is not a great measure of temperature and invite my colleagues to help think up some alternatives.

  26. 76
    jkga says:

    #71 Alex

    Are you saying that science education has left the public with difficulty grasping the idea of some unpredictable natural variability superimposed on more predictable underlying trends? I do see that difficulty with many of my students. The analogy I like to use (and which is probably stated more eloquently elsewhere on this site) is that two or three warm days in the middle of Winter don’t mean that Spring is right around the corner.

    As far as the original post is concerned, the notion that the natural variability of climate provides clues to the sensitivity and response time of climate to unnatural forcings was very familiar to me as a physical chemist, where the “fluctuation-dissipation theorem” is a statement of the very same reasoning to molecular systems.

    [Response: Indeed, there is a great deal of interest currently in using fluctuation-dissipation theorems for nonequilibrium systems like climate. There were several interesting presentations on this at the Princeton Theory Center climate school in which I recently participated. --raypierre]

  27. 77

    Its swell to read Raypierre again on this site….

    [Response:It's nice to be appreciated. I've been taking a self-enforced sabbatical from RealClimate while trying to finish off writing two books plus a major review on Neoproterozoic climate. I hope to be back on a more regular basis in the Fall. --raypierre]

    #66, Timothy, the model animation in question use to be on this page:

    http://www.metoffice.com/research/hadleycentre/models/modeldata.html

    It showed 2007 similar ice minima in the year 2040 or so. My question remains, why they got it wrong?? Its a shame that they don’t display this animation again for a means of finding out just why they underestimated the melting so radically. If they do such a mistake, then not knowing why triggers doubt, in all their models, albeit ice is more complicated. But as written, 2007 the warmest year in the Northern Hemisphere, coincided with the greatest ice minima in history, this is definitely a different but obvious type of coupling, its hotter ….. there is less ice… Same thing is happening right as I write, 2009 ice extent is equal to 2008. Despite a hugely cloudy Arctic since about mid April. For anyone to claim a pause in warming would mean a stop in disappearing Multi year ice, that is not happening. The pause needs some evidence, if the current El-Nino becomes as strong as 97-98 lets see what Global temperatures say….

  28. 78
    Deep Climate says:

    “It [supposed halt in global warming] appears quite marked in the HadCRUT3 data, less so in GISTEMP.”

    Echoing several others above (e.g. Chis C., Timothy C and so on), I don’t really see the evidence for a “halt” at all in GISTemp, although there is perhaps some in HadCRUT.

    For one thing, according to GISTemp, 2000s on average are 0.19 deg above the 1990s.

    For another, the linear trend in GISTemp from 1979 onward has been rising and peaked as recently as 2007. It is down in 2008, of course, but that year seems to be an outlier affected by the confluence of La Nina and long inter-cycle solar trough. And the trend is still well above those based on any end year between 1997 and 2000 (even 1998).

    See:
    http://deepclimate.files.wordpress.com/2009/05/global-surface-trends.gif

    I’m looking forward to the pending Tamino post on this topic.

  29. 79
    Joel Shore says:

    Deep Climate (#72) says: “For a short history of polynomial fitting of global temperature record, see:
    http://deepclimate.org/2009/04/09/the-alberta-oil-boys-network-spins-global-warming-into-cooling/

    Thanks, DC! Very interesting! I appreciate all the research you do in ferreting out all the goings on in the climate contrarian world!

  30. 80
    Andy says:

    Re: response to 8. This is a question I’ve been meaning to ask Real Climate. Is the rate of heat exchange between the surface and deep waters of the ocean so robust that we can rule out changes in circulation that would cause global warming to cease, reverse or slow down for decades or centuries? Or conversely, could a change in heat exchange suddenly cook us all? I’ve thought the answer to this would be “probably not but we don’t know enough to say for sure”, or “impossible”. But the answer Raypierre gives to Hank Roberts makes it sound like “perhaps”.

  31. 81
    Susan says:

    I am a science enthusiast with limited training, but an expert drawing instructor, which makes it hard for me to ignore the obvious; telling the truth about what you see without fear or preconception is the basis of learning how to draw:

    1. On 1998, how can anyone look at the any graph and not see that it is out of the overall trend? Why does this need to be repeated, how is it not obvious?

    2. On weather, how come we get all the factoids about cool weather but nothing about heat? There’s lots of it going around; in addition to that pointed out above, how about Brazil which seems to be missing winter altogether this year? Some people might be a bit surprised if they took a good look at what is going on currently in the Arctic, let alone Greenland. So we have a lot of melt and some cooler wetter weather in the northern reaches are the area south of this melting. How is that not likely? Ice in a pan of water, anyone, doesn’t it cool the water as it melts, but overall warms more as it diminishes?
    (some background on various melting events, I love the one about the melting witch!):
    http://climatechangepsychology.blogspot.com/

    3. On climate change vs. global warming, those using words to describe events know that climate change is one way to describes some effects of global warming which loosely describes the effects of heat-trapping greenhouse gases. There’s no legerdemain here except those who created the talking point for the sake of argument.

    Ike Solem, thanks. I’ve missed you over at DotEarth.

    dhogaza, thanks for this neat summary of the problem:
    -
    “Well, when people lie to you (intentional or not, your friend may also be simply ignorant rather than dishonest), and you accept those lies uncritically, whose fault is it? Scientists.

    “Step back and think about the claims you’ve made … do you really think that thousands of climate scientists are SO STUPID that they’d build models that don’t include basic physical features, don’t demonstrate the kind of natural variability seen in the real world, etc, as you claim?”

  32. 82
    Chris Colose says:

    Alex (# 71);

    The key issue here is to understand the nature of the “noise” inherent in some climatic time-series record, in this case the global mean temperature anomaly. As demonstrated by a number of recent papers including the discussed Keenlyside paper, as well as Easterling and Wehner 2009 it is entirely possible to have some time interval (which is relatively short compared to the timescale in which radiative forcing from CO2 is important) in which a flatline or even negative trend is present. For instance if you can upwell cold water from the deep oceans and bring it to the surface then this will temporarily do the trick. This, among other reasons, is why you see a lot of wiggles in the blue line in Fig. 1 which may be entirely unrelated to the longer term trend from human activities.

    The other key issue is whether or not these wiggles have implications for what is known as climate sensitivity (i.e., the amplitude of the temperature response you get from some change in the global energy balance, a doubling of CO2 usually as an arbitrary standard). It is much more likely that it affects the nature in how we get there rather than the end result. There is no example of a simulation of internal variability through the coupled atmosphere-ocean system that abruptly produces “wiggles” on the scale of a doubling of carbon dioxide, so it is a very robust result that the warming influence of much higher CO2 levels will be realized eventually (the extra energy has to go somewhere). Note however that a doubling of CO2 is a type of forcing that far exceeds what we’ve seen over the Holocene, and in contrast the current signal is not that large (at least not overwhelmingly so) and so scientists are working on detecting a trend which has only begun over the last few decades to exceed the noise of natural variability.

  33. 83
    Jim Cross says:

    Thanks to RC for posting this even though in so many ways it seems in opposition to many of the views posted here.

    A while back, there was a threads with numerous posts debating whether we were cooling or not since 1998, 1999, 2000 – pick the year. And anyone that argued that we were cooling was declared to be a denier and were told the lower temperatures were natural variability and that any year now temperatures would be right back up to the 1998 level. Then there was the Keelyside post with, I believe, even a bet that we couldn’t be cooling.

    Now comes this article declaring that, indeed, perhaps we are in for 20-30 years of cooling or flat temperature, even with rising CO2. Twenty or thirty years – that is almost “climate”. Or, do we now need to redefine climate to something longer and these 20-30 year excursions can be called “climeather”?

  34. 84

    wayne davidson wrote in 77:

    Its swell to read Raypierre again on this site….

    #66, Timothy, the model animation in question use to be on this page:

    http://www.metoffice.com/research/hadleycentre/models/modeldata.html

    It showed 2007 similar ice minima in the year 2040 or so. My question remains, why they got it wrong?? Its a shame that they don’t display this animation again for a means of finding out just why they underestimated the melting so radically…

    Ask and Ye shall receive

  35. 85
    Hank Roberts says:

    Jim, those time spans refer to how much variability there is in the data and how many data points are needed to do the statistical tests to detect a trend.

    Remember “angry beast” — if the variability is increasing, the length of time needed to detect a trend also increases.

    Look at this, for example:
    http://scholar.google.com/scholar?sourceid=Mozilla-search&q=permanent+el+nino

  36. 86
    Chris Colose says:

    # 81 (Susan),

    1) 1998 was a significant El Nino year which is why it shows up as such a spike. 1998 was one of the biggest, so its net effect (0.1-0.2 K) was among the largest and is easily identifiable visually on a plot of global Temperature vs. time, but it is also superimposed on the much larger (0.7-0.8 K) long-term trend. But the interest is not just *that year* but the impacts on the climate system *after* that year, perhaps even into present day.

    2) There are lots of news stories about anomalous cold and warm events (or even things like drought which may have more to do with precipitation/evaporation than temperature), hurricanes, floods, or what have you. The problem with climate change is that, when discussed correctly, it is not very news worthy. I say that because in the media there is a lot of focus on the “latest” and “up-to-the-minute” stories, whereas climate change is about longer-term statistics, which require a lot of stories being grouped together over extended periods of time to paint a certain picture. This is not really how the media communicates. You need to look past the stories about cold and warm events to see the direction the whole system is headed in on timescales of decades to centuries. This also requires abandoning the notion that a super hot day in January is global warming, and a cold day in July cancelled out global warming, as neither of those things are valid.

  37. 87
    Hank Roberts says:

    Thanks to Ray, for the inline response way back at Comment #1 and for filling in for Kyle.

    So, Ray, I guess one question that’s bound to come up — I linked a few responses back to a search on “permanent El Nino” (a typical journal article title from that search is:
    “A permanent El Niño-like state during the Pliocene” )

    Can you tie the observations in this paper to that paleo work and suggest how the course of events might go if that’s where we’re going this time around, only much faster?

    I asked earlier if a significant prolonged El Nino would cause detectable increased infrared energy radiated away from the plane, not just a rearrangement of heat within the climate system? (Does El Nino pump heat mostly into the atmosphere to be rearranged, or does it pump heat significantly out into space?)

    I suppose someone is bound to suggest that El Nino is the mechanism Gaia uses, glaring heat rays from wide-irised eyes to cool off — do the models include a permanent El Nino condition for a long while, and what difference does it make in radiation going out?

    [Response: On a short time scale, the El Nino is a good example of how ocean circulation can cause a temporary change in ocean-atmosphere heat transfer by exposing more warm water to the air. One problem I have with "permanent el nino" as a mechanism for climate change is that the way the el nino warms the atmosphere is not sustainable. You eventually run out of energy. I had an interesting conversation on this subject with Ros Rickaby during my recent visit to Oxford, and another problem with "permanent el nino" is that it's hard to satisfy angular momentum balance if you permanently get rid of equatorial easterlies. Not impossible, but it's a hard state to make sense of. An interesting idea she has is that "permanent el nino" is not the disappearance of ENSO cycles, but rather a deepening of the thermocline so that ENSO has less expression in sea surface temperature. Makes a lot of sense to me. --raypierre]

  38. 88
    Icarus says:

    “Now comes this article declaring that, indeed, perhaps we are in for 20-30 years of cooling or flat temperature, even with rising CO2. Twenty or thirty years – that is almost “climate”. Or, do we now need to redefine climate to something longer and these 20-30 year excursions can be called “climeather”?”

    I have a – probably naive – question that relates to this:

    Let’s suppose that there has been no significant increase in global cloud cover or any other natural factor which could reduce the total amount of solar heating in the last decade or so. In that case, all the additional CO2 in the atmosphere surely must have caused the Earth to warm up, so if we’re not seeing the warming in the global average temperature measurements for the last decade, that must just mean that we’re not measuring it correctly. It can’t mean that the Earth is actually staying the same temperature, because simple physics tells us that that additional heat must be going somewhere. Is that right?

    If we were just able to measure things more completely, would we ‘find’ that heat (maybe in warming of the deep ocean or somewhere else) and would the apparent pause in global warming then just disappear, with being able to see the complete picture? I’m not suggesting that Kyle’s paper is wrong, at all – if I understand it correctly, there is no contradiction between saying that: (a) the way heat is redistributed between ocean and atmosphere has had a genuine shift every few decades, and; (b) the Earth as a whole is warming constantly with no significant deviation from a long-term trend. It seems to me that without a substantial change in cloud cover or some other very obvious factor, (b) just has to be true, because of simple physics (a radiative imbalance in the Earth’s total energy budget, or whatever the correct terminology is).

    What do you think?

    If this is right then it seems to be a mistake to say or imply that we have had, or expect to have, a period of falling or constant global average temperatures – we should rather say that the heat is there in the climate system somewhere (like a pan on a stove that is slowly and steadily warming up) and that this heat will sooner or later manifest itself in any series of measurements in which we’re currently seeing an apparent cooling or levelling off. Presumably we would expect to see a corresponding rapid warming in due course as that series of measurements ‘catches up’ again to the long-term trend.

  39. 89
    Carl Wolk says:

    Chris Colose #86,
    “But the interest is not just *that year* but the impacts on the climate system *after* that year, perhaps even into present day.”

    I have made this same argument on your blog, though you rejected it, saying,
    “Response– The 1998 El Nino is a spike. The long-term trend is due to radiative forcing, and there is very low probability of having the number of warmest years we’ve had in the last decade in a system characterized by just noise, but that changes when you introduce the trend– chris”

    I guess once the idea is presented in such a way that does not challenge your understanding of climate, it is acceptable.

  40. 90

    #84 Thanks Timothy, is it possible that “A1B” scenario is way off?? As opposed to the animation model itself? The questions remain, finding out model or scenario failure reasons are important. In other words, do you have other animation scenarios out of your magic computer?

  41. 91
    Alex says:

    My thanks to raypierre for his reply (#71) and also jkga, dhogaza, chris colose, as I write, and even the gentleman who thinks I’m a troll (which assuredly I’m not.) I’m interested in all of your responses but, in a way, they make my point for me. I’m sorry if I didn’t make myself clear enough, but the problem that I see is the mismatch between the message that is perceived by the wider public, and the reality of the climate science position, as so well presented in the replies that I mentioned.

    How many people do you think have the time or the inclination to go and find then read the Keenlyside paper, for instance? Or even understand it? I have a degree in physics, so I’m not completely unqualified to understand the issues in climate science, but I have friends – engineers, scientists, technologists – who mostly (not all) exhibit a high degree of skepticism about the “alarmism” (as they describe it) about global warming.

    These are intelligent people with a science background, but if even they (and sometimes me too, I’m afraid) are struggling to match up the story from the climate science with the way that the world is actually behaving around them, then that’s not actually their problem, it’s a climate science problem, because its message is confused or diluted or corrupted.

    I’ve actually found the article in this post very helpful, but I get the feeling that it’s preaching to the converted. It’s a receptive audience here at RC! … one that understands the science. But the common perception out in my community is that the world is certainly not warming, hasn’t been for some time, and that’s at variance with the models. I understand why averaging many models can mask the variance, but for most people the simple appeal of the averaged graphs trumps any explanations like the ones here. I could mention other objections that I hear, all of which you’d be able to dismiss with a scornful laugh, but the point is that dismissing them takes a level of comprehension that virtually none of the population have (who aren’t in the trade.)

    People (or at least the people that I know) need a message that fits their understanding. Not the simplistic “the earth is going up in flames” that we see in some of our press, nor highly technical discussions at the other end of the spectrum. They want a story that matches their intelligence and capability to absorb without having to go and search the scientific press.

    Most importantly, it has to match their understanding of what’s going on, climate-wise. And the ideas in Kyle Swanson’s article above could help a lot, but it needs to reach a much wider audience than the readers of RC who obviously understand it all already.

    As I re-read what I’ve written above, I see that I’ve probably tried your patience. Maybe RC isn’t the right place to raise the issue, but I’m sure that there is an issue, and it’s an issue that climate science in general will need to address if it’s to win the argument in the long term. If, as seems likely, there is a pause in global warming, then climate science will need to find a way to communicate that in a way that gently and authoritatively corrects the over-simplistic perceptions out there. Gently, because many people have become inured to the shrill voices of some commentators, and the resetting of expectations for a longer-term scenario will take some intelligent marketing.

  42. 92

    So we seem to have climatus interruptus.Not surprising since most phenomena in nature don’t obey a constant relationship for very long. Kyle Swanson ends his post on an ominous note. “……the fact that humanity is poking a complex,non-linear system with GHG forcing-and that there are no guarantees to how the climate may respond.” We are indeed playing with fire.

  43. 93
    Chris Colose says:

    Carl (# 89),

    I don’t quite recall the context of our discussion, so just responding to your comment.

    It is very unlikely that in a stationary climate we would observe the recent cluster of warm years, most of which being the warmest in the instrumental time period (see Zorita, Stocker, and von Storch 2008). The “long-term trend” I don’t indicate to mean the last decade (even if there is a residual component from El Nino to a new cliamtic state, an idea that I don’t really take to, but I’m also not an expert here), but rather the much longer influence (say over the last 50 years) which is clearly due mostly to greenhouse gases and not El Nino.

  44. 94
    Jim Cross says:

    Hank 85 and 87

    Surely you are not suggesting that a permanent El Nino is lurking behind what may be a temporary downturn in temperature?

    Is there an official RC viewpoint on this post?

    See this post:

    http://www.realclimate.org/index.php/archives/2008/05/global-cooling-wanna-bet/

    Here is the bet proposed by RC:

    “The bet we propose is very simple and concerns the specific global prediction in their Nature article. If the average temperature 2000-2010 (their first forecast) really turns out to be lower or equal to the average temperature 1994-2004 (*), we will pay them € 2500. If it turns out to be warmer, they pay us € 2500. This bet will be decided by the end of 2010. We offer the same for their second forecast: If 2005-2015 (*) turns out to be colder or equal compared to 1994-2004 (*), we will pay them € 2500 – if it turns out to be warmer, they pay us the same. The basis for the temperature comparison will be the HadCRUT3 global mean surface temperature data set used by the authors in their paper.”

    Would RC still make that bet?

    [Response: Almost certainly yes. As an exercise for the reader calculate what the mean temperature anomaly would need to be for RC to lose the first part of the bet... - gavin]

  45. 95
    Jim Cross says:

    What about the second part of the bet?

  46. 96
    Jim Galasyn says:

    Hank, isn’t it the case that the various oscillations (ENSO, PDO, etc.) are simply re-arranging the energy fluxes within the climate system? Put another way, these oscillations have no effect on the long-term global energy budget. Or put yet another way, the final equilibrium temperature will be exactly the same with or without these transient oscillatory modes. Am I right?

  47. 97
    Gareth says:

    Seems to me that the new El Nino event will provide a nice test of the “pause” hypothesis outlined in the post above. GISTEMP noted in its review of 2008:

    Given our expectation of the next El Niño beginning in 2009 or 2010, it still seems likely that a new global temperature record will be set within the next 1-2 years, despite the moderate negative effect of the reduced solar irradiance.

    The El Nino is here, and while it’s not impossible that it might fizzle, the current expectation is that it will last into 2010. There are some intriguing possibilities: strong El Nino, new global temp record in 2010 (ie above 2005 GISS, 1998 HadCrut); moderate El Nino, new global temp record; moderate El Nino, no new record, etc etc. If we had a strong El Nino and no new record, that might suggest something along the lines of the “pause” hypothesis – and no doubt the usual suspects would make hay… Forgive me a shudder at the thought.

  48. 98
    tamino says:

    Re: #91 (Alex)

    I agree that there’s tremendous room for improvement in how climate science is communicated to the public. RealClimate is top-notch, but doesn’t reach enough people to counter the very effective propaganda campaign attempting to deny the reality, human origin, and danger of global warming.

    I’m especially vexed by the perception by so many that there’s “proof” that “global warming has stopped.” This is based on faulty statistics (often by those who should know better, hence are not just mistaken but dishonest) and the truly silly, but pervasive, idea that global warming means every year should be hotter than the one before it. Anyone who reads my blog knows I work very hard to dispel these myths, but a lot remains to be done to communicate these sometimes not-so-simple truths to the voting public.

    In fact, perhaps Al Gore did a better job of it than the scientific community. But much of his efforts are negated by the mean-spiritied, dishonest, but effective character assassination aimed at him. Despicable, yes — but also effective propaganda.

    On topic: I’ve posted a comment on this post:

    http://tamino.wordpress.com/2009/07/14/warming-interrupted/

  49. 99
    GlenFergus says:

    #70:

    Thanks Ike; excellent summary. I too am inclined to wonder about the current fad for ocean quasi-cycles. ENSO sure; but PDO/IPO, AMO, IOD etc etc? Seems the favoured “explanation” for this or that phenomenon correlates most closely with the domicility of the observer. Eg the way we’ve all got the hots for IOD in Australian hydrology at the moment (yeah, ugly pun, sorry).

    G.

  50. 100
    Jim Bouldin says:

    Raypierre (22):

    Thank you and I fully agree. I thought the Easterling paper, and Gavin’s similar analysis here earlier, regarding expected plateau periods within a longer term warming, were not only quite useful in providing rational justifications, but also quite interesting.

    Doug (29):

    I fully agree but that won’t stop the deniers from screaming anyway.


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