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Dispelling two myths about the tropospheric hot spot

Posted on 24 February 2011 by thingsbreak

Things Break has kindly allowed us to repost his blog post where he debunks two common myths about the tropospheric hot spot from a few days ago. This post has also been used as the Advanced Rebuttal to "There's no tropospheric hot spot" (also found at http://sks.to/hotspot).

Part 1: The “Hotspot” as an Alleged Fingerprint of Anthropogenic Warming

A great deal of the confusion surrounding the issue of temperature trends in the upper troposphere comes from the mistaken belief that the presence or lack of amplification of surface warming in the upper troposphere has some bearing on the attribution of global warming to man-made causes.

It does not.

Attribution of anthropogenic origins of the current climatic changes can be tested from many different directions. One of the most clear examples for those with some familiarity with the Earth’s atmosphere is the issue of stratospheric cooling. If the sun were to suddenly increase its output by 2%, we would rightfully expect the atmosphere as well as the surface to warm up in response. This can be examined, for instance, by looking at the response in a GCM like GISS ModelE:

2% increase in solar forcing (via RealClimate)

Likewise, if we were to double preindustrial levels of CO2, we would expect the surface and the lower atmosphere to warm. However, unlike the case of increasing solar influence, we would not expect the lower atmosphere to warm through at all levels. Increasing the greenhouse effect should warm the surface and troposphere, but cool the lower stratosphere.

Doubling of CO2 (via RealClimate)

In the doubled CO2 scenario, there is a pronounced cooling of higher altitudes, i.e. the stratosphere, and this feature is entirely absent in the +2% solar scenario.

This stratospheric cooling is a fingerprint of increased greenhouse (as opposed to solar) warming. For a more in depth discussion of why the stratosphere cools under enhanced greenhouse warming, see discussions at Skeptical Science and The Science of Doom. In other words, the difference in the two simulations is not the presence of a "hot spot" in one and its absence in the other, it's the stratospheric cooling apparent in the increased CO2 simulation.

In the IPCC Fourth Assessment Report (AR4), historical forcings were simulated in the Parallel Climate Model, and and the zonal mean temperature responses to each were broken out in separate panels. There was some increase in solar irradiance during the period, which shows up as a modest amount of warming throughout the atmosphere, with some amplification in the upper troposphere (the sort of greenish-yellow and yellow patterns respectively in panel a). As we all know, there was a significant change in GHG forcing during that time, which manifests as surface warming, amplified upper troposphere warming, and stratospheric cooling  (panel c), and the net effect of all forcings was shown (panel f).

Fig 9.1: Zonal mean atmospheric temperature change from 1890 to 1999 (°C per century) as simulated by the PCM model from (a) solar forcing, (b) volcanoes, (c) well-mixed greenhouse gases, (d) tropospheric and stratospheric ozone changes, (e) direct sulphate aerosol forcing and (f) the sum of all forcings. Plot is from 1,000 hPa to 10 hPa (shown on left scale) and from 0 km to 30 km. (IPCC AR4 WG1)

So far so good. Right? Well, this is actually where things went off the rails.

Climate “skeptics” apparently became convinced that the “hot spot” in Figure 9.1c was the fingerprint of anthropogenic warming the IPCC was referring to, rather than stratospheric cooling coupled with tropospheric warming.

As he so often does, Monckton serves as a useful example of getting things wrong, claiming

the models predict that if and only if Man is the cause of warming, the tropical upper air, six miles above the ground, should warm up to thrice as fast as the surface, but this tropical upper-troposphere “hot-spot” has not been observed...

This unequivocally incorrect claim was also made in the NIPCC "skeptic" report (Section 3.4), which was signed off on by such supposedly "serious" contrarians as Craig Idso and S. Fred Singer

The mistaken belief in “skeptic” circles is that the existence of anthropogenic warming somehow hinges on the existence of the tropospheric “hot spot”- it does not. Period. Tropospheric amplification of warming with altitude is the predicted response to increasing radiative forcing from natural sources, such as an increase in solar irradiance, as well. Stratospheric cooling is the real "fingerprint" of enhanced greenhouse vs. natural (e.g. increased solar) warming

Part 2: The Existence of Amplified Warming in the Upper Tropical Troposphere

So, does the “hot spot” actually exist? That is to say, is the tropsosphere actually warming as expected? Unfortunately, the answer to this is much less cut and dry.

There is a good theoretical basis for this expectation of amplification in the upper troposphere relative to the surface. We expect that an increase in radiative forcing would result in a moist adiabatic amplification of warming with altitude, i.e. that the troposphere would warm faster with height. This also appears as an emergent property in climate models, which show a similar vertical profile of warming to that expected under the moist adiabatic lapse rate.

Unfortunately, actually determining what is happening in the real tropical troposphere has proven to be quite difficult. Perhaps the largest reason for this is the quality of data from the main source of our information from this region for long time periods- radiosonde networks.

Although on seasonal and annual scales, some radiosonde records are in relatively good agreement with theoretical and modeling expectations, on decadal timescales, they show less warming or even cooling of the upper troposphere. However, the tropics, especially at higher altitudes, are a notorious problem area for most if not all of the older radiosonde networks. And attempts to stitch together longer records from multiple networks (and integrate them with newer satellite records) have introduced problems as well. There have been many attempts to quantify and remove these biases (e.g. Randel 2006, Sherwood 2008). Although these attempts have managed to reconcile the observational data with theoretical and model expectations within overlapping uncertainty intervals, the real world behavior of the troposphere is still unclear (Bengtsson 2009, Thorne 2010).

Allen and Sherwood sought to side step the problems associated with the radiosonde data entirely, and examined the “dynamical relationship known as the thermal-wind equation, which relates horizontal temperature gradients to wind shear”. Thermal wind speed data, in contrast to the temperature data, lacked many of the systematic adjustment issues and other errors, and were used as a proxy for temperature. Allen and Sherwood found that the troposphere appeared to be warming in reasonable agreement to theoretical and modeling expectations.

Vertical profile of tropical mean temperature trends. Trends reflect the mean change in temperature (in K per decade) between 20° N and 20° S for the period 1979–2005, obtained from radiosonde temperature measurements5 (blue and green colours), climate models8 (dashed orange, with grey shading indicating 2-sigma range) and the new reconstructions from radiosonde winds4 (pink, with error bars indicating 2-sigma range). The surface temperature change11 from 1979–2005 (grey asterisk) and the vertical profile inferred from the moist adiabatic lapse rate (dashed yellow) are also shown. The model range was derived by scaling the model vertical trend behaviour (which has been shown to be tightly constrained8) and its uncertainties8 by the surface trend. Prior to 2007, only the HadAT and RATPAC estimates existed, and a case could be made for a fundamental discrepancy between modelled and radiosonde observed behaviour. (Thorne 2008)

Recently, Johnson and Xie have approached the question from a different but similarly indirect angle. They examined trends in tropical sea surface temperatures (SSTs) and precipitation, which have direct implications for the behavior of the vertical tropical tropospheric temperature profile:

 

As the SST threshold for convection is tied to convective instability, this threshold must be strongly related to the tropical upper-tropospheric temperature. Observations show that tropospheric temperatures in the tropics approximately follow a moist-adiabatic temperature profile, which suggests an adjustment of upper-tropospheric temperatures in response to surface temperatures in the tropics. This hypothesis of moist-adiabatic lapse rate (MALR) adjustment predicts a close covariability between the SST threshold and tropical mean SST. If true, the variability and long-term trend of the SST threshold may reveal important information about the variability and trends in the tropical troposphere.

 

Climate warming over the tropical oceans [exaggerated]: a) In a climate before warming, convection and heavy tropical rain is restricted to a region where SSTs exceed a threshold value (dotted line), and temperatures decrease with altitude. b) Johnson and Xie show that this SST threshold has risen in tandem with mean SSTs over past decades, and that the area of surface ocean where convection occurs has remained constant. As a result of warming at the sea surface, air temperatures rise most at high altitudes. (Sobel 2010)

Tropical convection and thus precipitation is heavily dependent on sea surface temperatures (SSTs). Thus the absence of increased precipitation is indicative of stability upwards through the troposphere, which suggests that the upper tropical troposphere is indeed warming faster than surface temperatures.

 

[T]he similarity between the trends of SST and the SST threshold for convection in [the following figure] is consistent with approximate MALR adjustment in observations and inconsistent with reduced upper tropospheric warming relative to the surface, as indicated in some observational data sets. Although the statistical uncertainty of 30-year trends is rather high, the clean relationship between the SST threshold and tropical mean SST at all timescales in both observations and models increases confidence that the tropical atmosphere is warming in a manner that is broadly consistent with theoretical MALR expectations.

 

Time series of tropical mean SST and the SST threshold for convection. Thirty-year time series of annual tropical mean (20° S to 20° N) SST (black diamonds) and two estimates of the SST threshold for convection (blue squares and red stars). Linear trend lines are also shown. The linear trends with 95% confidence intervals for the tropical mean SST, the PD2mmd^-1 SST threshold estimate and the linear P fit SST threshold estimate are 0:088±0:057;0:083±0:076 and 0:080±0:113 °C per decade, respectively. The effective degrees of freedom in the 95% confidence interval calculations account for the lag-1 autocorrelation in the residual time series. (Johnson 2010)

Is this the “final word” on amplified tropospheric warming? Of course not. Ideally, instrumental biases and gaps in the satellite and radiosonde records can be sorted out, longer records from newer networks will provide more confident results, and we can get an even clearer picture of what’s going on in the tropical troposphere. In the meantime, however, this is further evidence that things are behaving more or less as we’d expect.

But moreover, these papers illustrate some key aspects of science (and particularly climate science), that could use some emphasizing. Science is iterative, not dictative or supernaturally revelatory. There’s no single, infallible decree. Science is the process by which we strive to best approximate reality. The first results are not necessarily the “best” results, and they certainly are not written in stone. Our monitoring systems, particularly (ironically?) the ones with multidecadal records, were not designed for the kind of questions we may be trying to investigate with them. Or, to paraphrase a certain former Secretary of Defense, you study the world with the instruments you have, not the instruments you might want or wish to have at a later time. Would life be a lot easier if we had designed and implemented global climatic monitoring systems in the 60s and 70s with an eye for explicitly addressing the questions we have now? Of course! But we have to make do with what we’ve got, and that means working with problematic data and finding creative ways to work around them. To that end, it’s worth pointing out, proxies aren’t just used to study the past. Through comments here and at other blogs, I get the impression that people think using proxies is restricted to paleo questions. The presumption seems to be that in our digital, high-speed, satellite-monitored age, direct observations are the only game in town. As this case shows, however, this is decidedly not true. Indirect methods of assessing an issue are sometimes the only (or only alternate in the case of suspect data) methods available. And that’s not necessarily a bad thing! Sometimes looking at a question from a different angle can avoid some potential complications altogether. And finally, there is a pernicious lie that can be heard in climate denialist circles, typified by remarks like these from Dick Lindzen:

[I]t has become standard in climate science that data in contradiction to alarmism is inevitably ‘corrected’ to bring it closer to alarming models.  None of us would argue that this data is perfect, and the corrections are often plausible.  What is implausible is that the ‘corrections’ should always bring the data closer to models.

Lindzen’s implication is clear- observational data that don’t support “models” are fraudulently adjusted until they do, ergo climate change is at least partially an artifact of data manipulation. This is, in a word, absurd. First, due to the ludicrous nature of the claim and its inherent absolutism, it’s easily debunked by a single contrary example. Take, for instance, the notorious problem of climate models producing double ITCZs (e.g. Zhang 2006). This is a case in which models produced a result at odds with both theoretical expectations and observations. No one attempted to claim that the models were right about this and theory and observations were wrong.

This does illustrate a germ of truth buried in Lindzen’s conspiratorial falsehood, however. Climate models and theoretical climate dynamics/meteorology are constrained by physics, and for the most part, models tend to agree with physics-based, theoretical underpinnings of meteorology/climate dynamics. When there is an apparent discrepancy between “models” and observations, that often (but not always) means there is a discrepancy between general, theoretical meteorological expectations and the observational data. It’s not a case of trying to reconcile the observations with climate models, but rather trying to reconcile observational data (which often have well known biases) with our physics-based understanding of the climate system.

When people are quick to point out some alleged contradiction between climate models and a data set, they don’t realize that often as not they are pointing out a contradiction between the observations and our fundamental explanations of the climate system irrespective of the question of anthropogenic influence. And far from justifying a position of “nothing to worry about”, significant flaws in our understanding of the climate system would greatly strengthen the case for mitigation from a risk management perspective, as uncertainty and ignorance of consequences increase the relative value of insurance. But that’s a topic for a different day…

References:

  • Allen, R.J. and S.C. Sherwood (2008): Warming maximum in the tropical upper troposphere deduced from thermal winds. Nature Geoscience, 1, 399-403, doi:10.1038/ngeo208.
  • Bengtsson, L. and K.I. Hodges (2009): On the evaluation of temperature trends in the tropical troposphere. Climate Dynamics, “Online First”, doi:10.1007/s00382-009-0680-y.
  • Johnson, N.C. and S.-P. Xie (2010): Changes in the sea surface temperature threshold for tropical convection. Nature Geoscience, 3, 842–845, doi:10.1038/ngeo1008.
  • Randel, W.J. and F. Wu (2006): Biases in Stratospheric and Tropospheric Temperature Trends Derived from Historical Radiosonde Data. Journal of Climate, 19, 10, 2094-2104, doi:10.1175/JCLI3717.1.
  • Sherwood, S.C., et al. (2008): Robust Tropospheric Warming Revealed by Iteratively Homogenized Radiosonde Data. Journal of Climate, 21, 20, 5336-5352, doi:10.1175/2008JCLI2320.1 .
  • Sobel, A. (2010): Raised bar for rain. Nature Geoscience, 3, 821–822, doi:10.1038/ngeo1025.
  • Thorne, P.W., et al. (2007): Tropical vertical temperature trends: A real discrepancy? Geophysical Research Letters, 34, L16702, doi:10.1029/2007GL029875.
  • Thorne, P.W. (2008): The answer is blowing in the wind. Nature Geoscience, 1, 347-348, doi:10.1038/ngeo209.
  • Thorne, P.W., et al. (2010) Tropospheric temperature trends: history of an ongoing controversy. WIRES: Climate Change, in press, doi:10.1002/wcc.80.
  • Zhang, G.J., and H. Wang (2006): Toward mitigating the double ITCZ problem in NCAR CCSM3. Geophysical Research Letters, 33, L06709, doi:10.1029/2005GL025229.

This rebuttal is a repost of a blog post from The Way Things Break.

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Comments

Comments 1 to 26:

  1. Glad to see a discussion of SST effect on GW.
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  2. Maybe the best debunking to the Lindzen smear is to remind him of the 'observational data' from his buddies Spencer and Christy (which insisted they were right and models and thermometers were wrong) - for instance discussed here!
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  3. Spencer and Christy made a genuine mistake and found out how to fix it, then fixed it.

    Nothing inherently wrong in that. That's proper science and a good thing.

    It should be a cautionary tale for everyone though. Going through the 'hot spot' controversy a bit and the physics (latent heat transfer & change in the moist adiabat) looks a lot more solid than the direct temperature measurements, which we know have serious problems at that altitude.

    I'm convinced that the most reasonable explanation is measurement error, in some combination of surface overestimate and upper atmosphere underestimate. Most probably dominated by upper atmosphere underestimate.
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  4. I realize this is the advanced version, but please put some axis labels on the first four images. I assume the horizontal axis is latitude and the vertical axis is pressure in millibars, and that the word "Temperature (°C)" at the top refers to the color scale at the bottom.

    Thanks.
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  5. MarkR: Just FYI, Spencer and Christy aren't the ones who fixed it.
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  6. This is a very nice post. I agree with Johnny Vector that axis labels are needed. If possible, convert the y-axes of the first four figures to logarithmic coordinates to match the later figures (although it looks as if these plots came from RC).
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  7. Lindzen mentions corrections to data in this essay at GWPF. In the third paragraph, he discusses the tropospheric warm spot and concludes that ground-level temperature measurements must be erroneously high. After calling for corrections to those data, he goes on in the same paragraph to accuse the "climate science community" of corruption for correcting data. Did he realize that he was accusing himself of corruption?
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  8. MarkR: Just FYI, Spencer and Christy aren't the ones who fixed it.


    If you remember the beginning of W's first administration, one of the administration's storylines was the need for more research to determine whether or not global warming was true blah blah blah.

    Much of that was based on the claims of Christy and Spencer.

    There was a conference fairly early in the administration attended by Christy (and maybe Spencer) and the RSS guys and others, that pretty much led to the conclusion that the UAH people were wrong and the RSS people mostly right (there were a series of errors that had been found, and corrections made, by UAH over a period of a couple or three or so years).

    It seemed apparent that the administration had held out hope that sponsoring the event would lead to UAH being shown right, but no such luck.
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  9. MarkR -Spencer and Christy made a genuine mistake and found out how to fix it, then fixed it.

    No. For 10 years or so Spencer & Christy claimed that the surface temperature record was wrong. Rather than go over their data to check it's accuracy, they chose to do diddly. Their errors were identified by others.
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  10. "Their errors were identified by others."

    Not only that, but they continued letting the old erroneous data being used for political purposes by non scientists.
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  11. "So, does the hot spot actually exist?"

    No.

    I did this check four years ago:



    Upper Left: NASA GISS Model through 2006
    Lower Left: RATPAC Raob data through 2006
    Upper Right: UAH MSU (LT, MT, LS) through 2006
    Lower Right: RSS MSU (LT, MT, LS) through 2006
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    Moderator Response: [Daniel Bailey] Fixed image HTML tag.
  12. ClimateWatcher @12,

    Are those the trends from 1979 through 2006? It would be nice to have data up until and including 2010.

    One can see the polar amplification (a predicted consequence of a warming planet) over the Arctic nicely in most datasets.

    IMHO, one of the problems in identifying the elusive tropical "hot spot" is that it is expected to be close to the tropopause, and that is especially problematic for the coarse satellite data.
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  13. And why are M&M 2010 and Christy et al 2010 not being cited? Both are discussing the hot spot issue and analyzing the observations. I hear also Klotzbach et al 2009, which provide some explanations for the missing hot spot (a.k.a less warming in the upper troposphere than predicted), for not being discussed either.
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    Moderator Response: [Dikran Marsupial]Rather than asking rhetorical questions, you would be better off making a case for discussing them, e.g. by briefly summarising the arguments made in those papers and explaining their relevance to the article to which you are responding. Usually there are plenty of contributors here who are more than happy to discuss any scientific paper, but if you want a paper discussed, then the discussion has to start somewhere.
  14. "It would be nice to have data up until and including 2010."

    Will generate these this weekend.

    "One can see the polar amplification (a predicted consequence of a warming planet) over the Arctic nicely in most datasets."

    Yes.

    And the stratospheric cooling, and even the shape of the stratospheric cooling seems to verify.

    But the hot spot, not so much.
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  15. "Stratospheric cooling is the real "fingerprint" of enhanced greenhouse vs. natural (e.g. increased solar) warming."

    From "An influence of solar spectral variations on radiative forcing of climate - Haigh et al" we have...

    "...since April 2004, have revealed4 that over this declining phase of the solar cycle there was a four to six times larger decline in ultraviolet than would have been predicted on the basis of our previous understanding. This reduction was partially compensated in the total solar output by an increase in radiation at visible wavelengths..."

    And so compared to the the "previous misunderstanding/simplification of TSI" I'd expect there to be more than expected surface warming and more than expected stratospheric cooling. This is from a natural change in the sun's output that mimicks the CO2 fingerprint.
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    Moderator Response: [Daniel Bailey] "This is from a natural change in the sun's output that mimicks the CO2 fingerprint." You are simply incorrect on this matter. Use the search function to find several threads addressing this meme, as it is the topic of those threads. Muoncounter: I win! (Gané, Gané!)
  16. Dan, how did you know?.
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    Moderator Response: [Daniel Bailey] Just a feeling.
  17. I'm not actually sure you understand the argument Dan. This is a relatively new paper (Oct 2010) and looks at the spectral components of the TSI.

    I did a search for "Stratospheric cooling" and came up with the usual references to TSI increases resulting in a different warming profile to CO2 warming. For example

    "8.If the warming is due to solar activity, then the upper atmosphere (the stratosphere) should warm along with the rest of the atmosphere. But if the warming is due to the greenhouse effect, the stratosphere should cool because of the heat being trapped in the lower atmosphere (the troposphere). Satellite measurements show that the stratosphere is cooling."

    But this is an incorrect statement on TSI changes and assumes that all spectra change together. It turns out that this is not correct and so the observed changes since the satellite was put up there indicate a change that ought to mimick the CO2 profile.

    I'm happy to hear any arguments you have against this, but pointing to "its not the sun" links are irrelevent.
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    Moderator Response: [muoncounter] The Haigh 2010 paper was discussed in The sun upside down and on It's the sun. Search function finds prior threads. Jedi Master DB was right (again).
  18. "The Haigh 2010 paper was discussed in The sun upside down"

    OK, you have a discussion of the paper but dont relate the result to the possible impacts on the Stratospheric cooling at all. Hence my inability to find it in the context of "Stratospheric cooling"

    So why does your article indicate that stratospheric cooling cant in part be due to the sun's changes?
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    Moderator Response: [muoncounter] See the quote from the article here and discussion here here. Even the author says these results are preliminary -- and small.
  19. "Even the author says these results are preliminary -- and small."

    The author appears to say "In other words, whereas the new satellite measurements call into question computer models of solar output, it does not change the fundamental physics of human-induced global warming."

    And thats an important result. None of your discussion that you've quoted acknowledges the associated stratospheric cooling and you've all focussed on the surface warming.

    I'm pointing out that the AGW fingerprint of stratospheric cooling is also effected by this result. I'm not saying AGW is wrong and the sun did it. I'm saying the magnitude of the effect is reduced by this result. The strength of the argument that CO2 is the cause of the observed warming because of stratospheric cooling is lessened because its not the only effect now known to do so.
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  20. TimTheToolMan:

    1) It is very probable that Haig et al's result is either due to instrument error or to a atypical circumstances. We know this both because ground base observations of visible light show the opposite effect, and because the detected climate response to the solar cycle is opposite in sign to that predicted from Haigh et al's results.

    2) However taking Haigh et al's results at face value, they would predice a cooling stratosphere and a warming troposphere when the sun approaches a solar minimum, and the reverse as it approaches a solar maximum. As the cooling stratosphere and warming troposphere have been a feature of our atmosphere for at least 3 solar cycles now, it is unlikely that a forcing tied to that cycle is the cause. To the extent that it is idiosyncratic, it faces the further problem that the decline in stratospheric temperatures has been weakest when it was observed:


    (Channels ordered in terms of decreasing altitude. Still higher channels show greater trends, but I could not find any graphs of their trends up later than about 2007.)

    3) Even ignoring the temporal signature, the Haigh et al hypothesis faces a problem in the spatial signature. Based on the fact that it predicts a peak of ozone at 45 km, and declining ozone and UV below that level, it predicts a cooling lower stratosphere, and a warming or constant temperature mid to upper stratosphere. In fact, the opposite is observed, with very low cooling trends in the lower stratosphere, and a very strong cooling trend in the upper stratosphere.

    The low trend in the lower stratosphere is because decline in O3 concentrations results in more UV penetrating to that level, which tends to warm that level, and effect counterbalanced by the cooling effect of increased CO2. In the upper stratosphere, both increased CO2 and decreased O3 have a cooling effect, the reinforcement resulting in the strong cooling trend.

    In fact, the observed spatial patern of cooling and warming in the stratosphere, coupled with the observed changes in radiation at different frequencies is only consistent with cooling brought about by increased CO2 levels,and decreased O3 levels. Any other effects must be minor in comparison.



    4) Finally, a decreasing aerosol optical thickness will also warm the troposphere, and cool the stratosphere; and due to volcanism or its lack, this can be a natural effect. However, aerosol optical thickness has been observed by satellites to be increasing rather than decreasing over the last decade, in large part due to the industrialization of India and China with limited pollution controls. Increassing optical thickness, of course, warms the stratosphere and cools the troposphere, which may be part of the reason for the reduced trends in both regions since 2000.
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  21. Tom @20,

    Thanks for your thoughtful post. I think you raise a potentially critical point above (your #4). If aerosol loading has been increasing substantively in recent decades over the tropic (probably b/c India and southern China have been increasing the aerosol loading, in addition to the increased loading from forest fires), could it at least partly explained the slower rate of warming in the upper tropical troposphere?

    Research has shown that areas over and downwind of forest fires associated with deforestation over the Amazon lead to reduced deep, moist convection (i.e., thunderstorms), which means a reduced vertical transport of latent heat into the upper troposphere (see e.g., Altaratz et al. (2010). This work by Rosenfeld et al. (2008) seem to support that.

    But, this research by Koren et al. (2005) suggests the opposite effect of aerosols on the depth of convective clouds, at least over the N. Atlantic.

    I would be keen to know whether or not this hypothesis has been considered/explored in the literature than I have touched on here.

    Personally, I am inclined to think that the "missing" hot pot" is attributable to several factors, none of which refute, or are inconsistent with, the expected warming from higher GHGs.

    More at NASA's Earth Observatory.
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  22. Albatross, I'm happy to give you my thoughts as a layman, but I have exactly zero expertise in this area, so I don't know how much help that will be. I was interested, however, to note that the articles you linked to tended to confirm my initial thinking on the topic. Here goes:

    The key aspect of a thunderstorm is the updraft driven by the latent heat of condensation. Clearly, the warmer the air below, and the cooler the air above, the easier it is to generate and sustain the updraft.

    The key difference between aerosols from wood fires (and coal fires without scrubbers) is that its major component is black soot. Because it is black, it absorbs solar radiation warming the air around it, but cooling the air beneath it. In this it contrasts with sulfates, dust and salt which reflect sunlight, cooling both the air around it and below (but warming the air above it). This means that absorbing aerosols will tend to warm the air immediately above the cumulus layer, and cool the air in the cumulus layer, thus forming a barrier against the formation of updrafts. In contrast, reflecting aerosols will cool both layers equally with no resulting consequence for the ability to form updrafts.

    Both types of aerosols will act as cloud condensation nuclei, thus causing water to precipitate out slower. Your second reference says this will encourage thunderstorms at low concentrations, and your third says it will encourage it at low concentrations, but cause the clouds to evaporate too soon at high concentrations (because of increased surface area of the smaller drops). That makes sense to me, but carries me further than I can be sure logic won't lead us astray.

    So, based on that, I would say the key difference is the type (absorbing or reflecting) or aerosols that dominate in forest fire smoke or over the North Atlantic. In that respect, India's aerosols have a very high black carbon content for anthropogenic aerosols (about 25%) because so much of it is caused by cooking fires. China does not, because of the use of high sulfate fuels (like Australian coal).

    Would this effect the hot spot? I don't know. Most sulfates precipitate out within few weeks or origin, particularly black carbon. Because of that, most of the impact of sulfates is regional. But, about 1% of sulfates enter the stratosphere where they can take years to precipitate out and have global effect. That means neither Indian nor Chinese aerosols would be particularly prevalent in the tropics. On the other hand, forest fires in the Amazon, Indonesia and equatorial Africa have become prevalent and may have the effect you describe.

    As to the Hot Spot itself, evidence at the moment favours its not existing, but theory strongly favours its existance. Whether observations come to the rescue of theory or not, who knows?

    I don't think it is that important anyway. After all, solar forcings (and reduced cloud or aerosol albedo forings) predict a stronger hot spot than do green house forcings because they have a stronger effect in the tropics. So, to the extent that a missing hot spot is a problem for AGW, it is more of a problem for its competitors. Further, a missing hot spot may mean a weaker water vapour feedback, but it certainly means a weaker lapse rate feedback (it is after all, just the consequence of the lapse rate feedback). That means a missing hot spot is not likely to result in significant changes in estimates of climate sensitivity, and certainly won't change those based on paleoclimatology. Consequently, my feeling is that the issue is technically interesting, but almost irrelevant in terms of policy considerations.

    Finally, the missing hot pot is probably down to a hungry thief. (Sorry, couldn't resist.)
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  23. "1) It is very probable that Haig et al's result is either due to instrument error or to a atypical circumstances."

    The satellite used to measure the UV component of the TSI was purpose built for the task and doesn't have to deal with atmosphere or "winter night".

    The SIM data regarding UV level variability as seen above the TOA is what it is and is very probably correct. If you have an argument here it is how that data has been used in the Haigh paper.

    The problem is that the Frederick and Hodge paper you cited made its calculations based on the ground view of UV which is absorbed at varying rates in the atmosphere over time. And UV has also now been shown to itself vary over time.

    But most of all, "The goal is to define the variability in solar irradiance reaching the polar surface, with emphasis on the influence of cloudiness and on identifying systematic trends and possible links to the solar cycle."

    And then on top of all that, its goal isn't even to look at variation in the stratospheric temperature ranges.

    " taking Haigh et al's results at face value, they would predice a cooling stratosphere and a warming troposphere when the sun approaches a solar minimum"

    Taken at face value, Haigh et al shows that when TSI is thought to be low, its not because all components of the spectrum are uniformly low, rather they vary and so "Low TSI" doesn't necessarily mean low visible.

    By implication when TSI is high, we shouldn't assume that UV is also high or that visible is high, rather the combination (whatever that turns out to be when measured) is high.

    Regarding aerosols, that appears to be wishful thinking on your part. The effect of aerosols in our atmosphere is unknown. Every model has its own interpretation made on the dubious data we have and they cant all be right.

    Your point 3 is your real argument. Paraphrased (and correct me if I'm wrong) you're saying that CO2 has a particular fingerprint in atmospheric warming and reduction in UV has a different fingerprint.

    The problem with this argument is that the CO2 fingerprint has been deduced with the assumption (in the models) of how the atmosphere behaves and with "greater than expected" variance within TSI, this has turned out to be wrong. Before the CO2 fingerprint can be re-established, the models have to be corrected for the new knowledge about how solar radiation varies.
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  24. The studies I see not being cited are, Christy et al 2010 (a review article of the science and the debate), McKitrick et al 2010, Douglass et al 2007.

    Why?
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  25. Well the Douglass et al paper ignored radiosonde biases despite the authors apparently being aware them. See Santer et al to see why that paper disappeared. The other two I am unaware of. Got a link to them? Cant find either in easily in google scholar.
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  26. jonicol from here, you question the relevance of the 2007 IPCC AR4 because it, apparently post dated the controversy. Will you also question Santer et al, 1996. Santer et al identify the tropospheric hotspot along with the cooling stratosphere as a signature of enhanced warming found in the models. However, Santer et al conclude by saying:

    "Although we have identified a component of the observational record that shows a statistically significant similarity with model predictions, we have not quantified the relative magnitude of natural and human-induced climate effects. This will require improved histories of radiative forcing due to natural and anthropogenic factors, and numerical experiments that better define an anthropogenic climate-change signal and the variability due to purely natural causes."


    So, although Santer et al identify the hotspot as a feature of the model, they explicitly refuse to identify it as a unique feature of greenhouse warming. Indeed, the IPCC AR4. As near as I can identify, then, the difference between Santer et al 1996 and the IPCC AR4 (2007) is not that the IPCC conceals mention of the hotspot because of empirical failure. On the contrary they give it due prominence. Rather, the difference is that in 1996 (and in the 2001 TAR) it was not known whether the hotspot would be an effect of solar warming; whereas in 2007 it was known that it would be - at least according to the models. But neither in 1996 nor in 2007 was the hotspot claimed as a unique feature of greenhouse warming.

    You claim in Quadrant that:

    "The one modern, definitive experiment, the search for the signature of the green house effect has failed totally. Projected confidently by the models, this “signature” was expected to be represented by an exceptional warming in the upper troposphere above the tropics. The experiments, carried out during twenty years of research supported by The Australian Green House Office as well as by many other well funded Atmospheric Science groups around the world, show that this signature does not exist. Where is the Enhanced Green House Effect? No one knows."


    That claim is now seen to be wrong on several counts. First and most importantly, the hot spot was never the "one modern definitive experiment" to establish that the greenhouse effect was responsible for most of the enhanced warming of the twentieth century. There were a variety of such "experiments". If you where ignorant of these "fingerprints", you had no basis to pretend to expertise by publishing the article, and if you where not ignorant of them, ... well, moderation policy forbids.

    But not only was the hotspot not just the one signature, it was not even a signature of greenhouse warming. On the contrary, it is a signature of the lapse rate feedback, and expected negative feedback on warming. Modifying the models so that they no longer predict the hotspot would have little consequence on their predictions of greenhouse warming, but it would certainly reduce their prediction of one of the ameliorating factors.

    Now, you may be able to find a scientific paper in which the hotspot is claimed to be a unique feature of a greenhouse warming - but I do not know of it. Nor has that been at any time the general view of the climate science community. Therefore, if you where an honourable man you would withdraw your Quadrant article because of a substantial, and fundamental factual error; and would post a retraction specifying that you has made an error and the nature of that error. I would certainly like to believe of you that you where honourable in that old fashioned way that thought truth was more important than reputation. We shall see.

    Finally, I draw your attention to Part 2 of the article above. As you can see, the existence of the tropospheric hotspot remains an open question, and has certainly not been decided one way or the other.
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