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Satellite stories - what do new findings on tropospheric warming mean for climate change?

If you’ve followed climate contrarian talking points over the years, you’ll be familiar with the argument over satellite observations of global warming. In 1990 it was reported that the satellite record…

Data from satellites have fuelled debate over climate science. NASA via Wikimedia Commons

If you’ve followed climate contrarian talking points over the years, you’ll be familiar with the argument over satellite observations of global warming.

In 1990 it was reported that the satellite record of temperatures in the troposphere (the part of the atmosphere that should warm more or less with the surface) did not show any warming since 1979, the year satellites began measuring temperature.

Since the satellites were not calibrated accurately enough to measure climate change without delicate efforts to correct for biases, mainstream scientists were sceptical. Indeed the contrarians retreated in 2005, when revisions of their data began to show atmospheric warming consistent with that measured by surface thermometers.

Focus on the tropical upper troposphere

Most considered the debate over at that point.

However, a few sceptics established a fallback position: that the particularly rapid warming expected at high altitudes in the tropics (called either the “hot spot” or the tropical upper troposphere or TUT) is not happening. They still point to a set of warming estimates derived from weather balloons by the UK Hadley Centre, shown in the 2001 IPCC report.

But tropical observations are sparse, and these data have since been found by their own developers to be too inaccurate in the TUT region to say whether warming occurred there or not. Several other estimates of the warming have appeared, at least one clearly contradicting sceptics’ favoured satellite record outside the tropics.

But no record is definitive, and answers for the TUT region range from no warming to even more than predicted. A few sceptics have stubbornly maintained that the only observational reconstructions they trust are those which happen to disagree with models.

New studies find models are missing something

Two new studies suggest the sceptics have not been completely wrong in this. A research team from the University of Washington, well known for its previous work on satellite climate records, reports (in an article to appear in Geophysical Research Letters¹) a careful combination of information from different channels on the satellites to distinguish temperature in the upper and lower parts of the troposphere.

What they find is that the TUT has warmed since 1979, but at a rate hardly exceeding that at lower altitudes. Basic theory predicts a significant excess, and according to detailed models the odds of so little excess are about the same as the odds of rolling 12 on a pair of dice. Not impossible, but unlikely enough to suggest that the models are missing something.

Before speculating on what this means, there are two important caveats to consider. First, this new finding still suffers from the same calibration issues as other attempts to get warming trends out of satellites. Second, the period since 1979 captures only a fraction of the era of man-made global warming.

That brings us to a second study, one based on weather balloons by a team of authors led out of the UK Hadley Centre, including the developers of the 2001 data, appearing in this month’s Journal of Geophysical Research².

This one also finds that TUT warming appears weak since 1979 (though again cautioning that the data are not quite accurate enough to be sure about this). Significantly, however, the same data show much stronger warming prior to 1979.

If you look at change over the longest period available (since 1958), everything matches up pretty well, a finding on which several studies now agree. This means we must be careful not to over-generalise observations during the shorter, satellite era.

So is global warming exaggerated?

Is the “missing,” or more accurately, “inconsistent hot spot” aloft an indicator that models exaggerate global warming? This conclusion, leapt to by many climate deniers, makes no sense.

First, we care about warming near the surface, and there is no reason why less warming aloft would mean a more or less sensitive climate (an argument you may hear relating to the water-vapour feedback rests on a misunderstanding of climate physics).

Second, the different trends before and after 1979 suggest either a natural oscillation, or some influence on climate that has not been put into the models correctly, superimposed on global warming.

Strong candidates for missing influences are particulate air pollutants or changes in ozone amounts, neither of which were adequately represented in the last round of climate model simulations. This should improve somewhat in the simulations going on now for the next IPCC report in 2013, although air pollutants in particular are very tough to handle.

If upper tropospheric temperatures are indeed flopping around unexpectedly, this would challenge our current understanding about how energy is transported within the atmosphere.

That would have no direct repercussions for global warming, which is instead fundamentally about energy exchanges between the planet and space. But it would be very interesting to those of us who study how the atmosphere shifts heat around and, when sorted out, might indeed revise our estimates of future warming up or downward.

The ongoing debate is a reminder that Earth’s atmosphere may still have some secrets up its sleeve.

Footnotes:
  1. Fu, Q., S. Manabe, and C. Johanson (2011), On the warming in the tropical upper troposphere: Models versus observations, Geophys. Res. Lett., doi:10.1029/2011GL048101, in press. (accepted 24 June 2011)
  2. Thorne, P. W., et al. (2011), A quantification of uncertainties in historical tropical tropospheric temperature trends from radiosondes, J. Geophys. Res., 116, D12116, doi:10.1029/2010JD015487.

Join the conversation

31 Comments sorted by

  1. Anthony Cox

    logged in via email @optusnet.com.au

    Stupendous article Steve; really fabulous: Fu confirms McKitrick; there is no THS; and isn't it ironic that radiosonde data is back in vogue! Poor old Garth Paltridge, who took so much flack for his use of such inferior data compared with Dessler's superior satellite data, will feel so much better!

    Incidentally,I will be including Fu et al in my next article on recent papers which disprove AGW; keep an eye out for it.

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  2. Marc Hendrickx

    Geologist

    It seems the more we look, the more the observations are showing the climate is not as sensitive to human interference as the IPCC has been claiming. The implications for policy are quite clear. This might be the critical decade afterall, critical for a renewed emphasis on the value of empiricism in climate change science.

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  3. David Stockwell

    logged in via email @gmail.com

    You state a good reason for skeptics to bring attention to the hotspot inconsistency when you acknowledge that ... "[it] might indeed revise our estimates of future warming up or downward." Surely that is sufficient reason.

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  4. Steve Sherwood

    Director, Climate Change Research Centre at UNSW Australia

    The above comments are hopelessly naive. As I said in the article, temperature changes at these altitudes tell us nothing about climate sensitivity. Ask the authors of the cited studies will agree if you ask them. In fact, failure to warm at high altitudes would mean that greenhouse gases would exert an even stronger greenhouse effect, which is determined by the difference between the atmospheric and surface temperature.

    Moreover, these comments reflect tunnel vision. What about all the model…

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    1. Anthony Cox

      logged in via email @optusnet.com.au

      In reply to Steve Sherwood

      Temperature changes or lack of them where the THS was predicted to be tell us everything about CS because the THS is a function of water vapor feedback, not a first order forcing such as allegedly caused by CO2 increase. If there isn't a THS either atmosphere SH levels are not increasing, as predicted by AGW, or if SH is increasing then the increased SH is not acting as a positive feedback, as AGW predicted.

      Either way CS will be less, much less than AGW has predicted.

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    2. James Szabadics

      BSc

      In reply to Steve Sherwood

      The model ensemble from IPCC AR4 2007 appear to overestimate global warming in the recent decade. Doesn't that indicate less climate sensitivity per CO2 doubling than the models suggest? By climate sensitivity I assume we are talking about global average lower tropospheric temperature. I hope the models do improve in the next IPCC report and show less warming more in line with the real world.

      Surely arctic warming would have a great deal to do with artic sea ice decline which in turn has a great…

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    3. David Stockwell

      logged in via email @gmail.com

      In reply to Steve Sherwood

      Huh? Because we comment on your chosen topic of the THS we are hopelessly naive and have tunnel vision? You take the discussion off-topic with a list of other limitation of models with the question "Why are all these ignored by so-called "skeptics?"" They are, and these limitations are not properly acknowledged. As two examples, models get drought trend in Australia last century completely wrong (http://landshape.org/enm/files/2010/10/Critique-of-DECR-EE.pdf); and that local projections are virtually useless (http://tandfprod.literatumonline.com/doi/abs/10.1080/02626667.2010.513518). Despite these and other studies it is claimed that GCMs provide credible quantitative estimates of future climate change and are commonly used without accepted validation practises (http://kestencgreen.com/naiveclimate.pdf).

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  5. Marc Hendrickx

    Geologist

    Another paper that if correct, shows climate sensitivity to increased CO2 is less than IPCC models suggest just out in the Journal Climate Dynamics. Its not just the THS.

    On the time-varying trend in global-mean surface temperature
    Zhaohua Wu • Norden E. Huang • John M. Wallace • Brian V. Smoliak • Xianyao Chen
    For the 1980s and 1990s:
    "Depending upon the assumed importance of the contributions of ocean dynamics and the time-varying aerosol emissions to the observed trends in global-mean surface temperature, we estimate that up to one third of the late twentieth century warming could have been a consequence of natural variability."

    Currently being discussed at Judy Curry's site Climate Etc...see
    http://judithcurry.com/2011/07/14/time-varying-trend-in-global-mean-surface-temperature/#more-4080

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    1. Marc Hendrickx

      Geologist

      In reply to Marc Hendrickx

      Judy Curry's summary of the paper of interest (link above)...
      JC comments: I think this paper is an important contribution to our understanding of the climate variability of the 20th century. The paper highlights significant inadequacies in the IPCC AR4 analysis. IMO this paper provides the clearest and most robust analysis to date of a substantial contribution of natural internal variability to the observed warming in the latter half of the 20th century. This paper argues that up to a third of…

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  6. Chris Colose

    Graduate Student- Atmospheric Sciences

    There is a lot of confusion here, and part of what this post has tried to do, is provide a broader context behind the findings of individual studies. Unfortunately, people are not listening to Steve Sherwood, or similar scientists who actually study this.

    There is still a debate as to whether models and observations of the enhanced upper tropical troposphere warming robustly diverge, and the (in)consistency depends on the timescale of interest, and the ability at which useful extraction of a…

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    1. Anthony Cox

      logged in via email @optusnet.com.au

      In reply to Chris Colose

      I'm not confused Chris; the models predicted a tropical hot; McKitrick and Fu have seperately shown there is not one. The THS is a crucial fingerprint of AGW; it is not there.

      Your comment that the greenhouse effect "depends on the temperature contrast between lower and upper levels (which determines global energy flow)" is egregiously wrong; the greenhouse effect depends on an energy imbalance between radiation coming in and leaving at the top of the atmosphere.

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    2. Chris Colose

      Graduate Student- Atmospheric Sciences

      In reply to Anthony Cox

      You are living up to your description as a lawyer and arguing by attempting to create reasonable doubt, rather than outlying an objective synthesis of the evidence or paying attention to the accuracy of your statements. For example,

      //"the models predicted a tropical hot; McKitrick and Fu have seperately shown there is not one"//

      There are a lot of papers on this subject and very few come to the conclusions with the confidence that you seem to think we can justify. See e.g., Thorne et al (2011…

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    3. Anthony Cox

      logged in via email @optusnet.com.au

      In reply to Chris Colose

      Chris, you say this:

      "Is completely untrue, since we expect the tropical atmosphere to roughly maintain a moist adiabat regardless of what causes the planet to warm. As I said in my previous post, it is not obvious what this "hotspot" is "crucial" for, so simply saying it is "crucial" is not very meaningful. But it is certainly not a "fingerprint." You get the same behavior if you turn up the knob on the incoming solar irradiance, for example."

      There is no equivalence between solar warming of the troposphere and the THS predicted by the GCMs; this is evident from Figure 9.1 from AR4:

      http://www.ipcc.ch/publications_and_data/ar4/wg1/en/figure-9-1.html

      AGW theory has distinguished the form of solar heating and AGW heating of the troposphere. Attempts to obfuscate about that in the face of model failures is one of the primary reasons why the general public are losing trust in science generally and in climate science specifically.

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    4. Chris Colose

      Graduate Student- Atmospheric Sciences

      In reply to Anthony Cox

      You're not understanding the figure. The reason the solar pattern doesn't look like the GHG pattern here is because the sun has not changed much; this simulation shows zonal (east-west) average atmospheric temperature change from 1890 to 1999. You just need to read the caption; incidentally, the paper which is cited in the caption came to the conclusion that anthropogenic forcing has dominated late 20th century warming. You should read that one too.

      If the sun were to brighten considerably, the…

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    5. David Stockwell

      logged in via email @gmail.com

      In reply to Chris Colose

      Adding to Anthony's reference to Fig 9.1 from AR4, its my impression from this figure that the GHG effect peaks at around 200mbar in the upper troposphere, while the Solar effect peaks around 800mbar in the mid-troposphere with a generally more uniform distribution. I too have found it a somewhat undiscriminating to argue that both effects are equal. That is not what the figure shows.

      On Steve's article, my impression is that the issue to date has revolved around the attribution implied by the T. hotspot and not so much on the processes, though the process issue is worthwhile to raise, though apparently not so robust a stick to beat skeptics with. The issue of how much natural variability vs GHG and net anthropogenic effects have contributed to recent warming is very alive, and the role of the tropical profile as indicative of this mix seems to me to have been more prominent around the blogs than process questions.

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    6. Anthony Cox

      logged in via email @optusnet.com.au

      In reply to David Stockwell

      Hi David; I hope Chris sticks around so we can get to the bottom of this. In respect of the asserted equivalence between a GHG caused THS based on 2XCO2, the AGW benchmark, and a solar heating created THS I have elsewhere referred to a Real Climate discussion which does this:

      http://www.realclimate.org/index.php/archives/2007/12/tropical-troposphere-trends/

      As can be seen RC equates an equivalent THS between 2XCO2 and a 2% increase in solar forcing. This is obviously astounding since increases…

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    7. David Stockwell

      logged in via email @gmail.com

      In reply to Anthony Cox

      Anthony, looking at the Fig 9.1 again I see the caption could be read that the GHG forcing is much greater than Solar, and that could explain the difference (except for the stratosphere), so thanks to Chris for that clarification (I haven't read Santers paper). Of course it does mean the models are equally inconsistent for both solar and GHG forcing.

      I have to read your calculations in more detail but as you know I think the data and physics support a much greater sensitivity to solar forcing than is generally assumed - RC calcs probably are probably based on an instantaneous (<1yr) solar effect and not a long response time effect. A gain of x4 may be within the data, but I think a gain of x10 for solar forcing is plausible.

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    8. David Stockwell

      logged in via email @gmail.com

      In reply to Anthony Cox

      Yes Scafetta. "A comprehensive interpretation of multiple scientific findings indicates that the contribution of solar variability to climate change is significant and that the temperature trend since1980 can be large and upward." His framework is the define climate sensitivity (lambda) not as a constant but as a function of temperature h(T). I am not too sure about that, but it seems to be not far removed from the range of sensitivities up to almost infinite at long time scales is what is proposed by Hansen (2011). Anyway, the longer the time scale the higher the sensitivity whatever the mechanism.

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    9. Anthony Cox

      logged in via email @optusnet.com.au

      In reply to David Stockwell

      "the longer the time scale the higher the sensitivity whatever the mechanism." Do you mean the longer the forcing the bigger the response?

      Just returning to the 2XCO2 = 2% solar forcing as per RC and Hansen; if for instance the solar forcing is sustained it would not be subject to a logarithmic decline like CO2 forcing and, based on that, would be capable of putting heat into the ocean in a way that CO2 is incapable of; is that how you see it?

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  7. Chris Colose

    Graduate Student- Atmospheric Sciences

    The approximate radiative forcing equivalence between a doubling of CO2 and 2% increase in solar already includes the logarithmic relationship that GHG's are generally subject to.

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    1. Anthony Cox

      logged in via email @optusnet.com.au

      In reply to Chris Colose

      Yeah, well Chris this is a key point and David may care to comment on it; does the IPCC's formula for GHG forcing have such a boundary condition? The IPCC attributes ACO2 [CO2 from human emissions] as being the forcing agent, F, for the 2XCO2 = 3C scenario, with water vapor the feedback, f, and temperature, t, the parameter for the change; the interaction of these variables is measured by the state vector, S, which would itself change if F has the effect the IPCC alleges. IPCC represents this dynamic…

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    2. Chris Colose

      Graduate Student- Atmospheric Sciences

      In reply to Anthony Cox

      I really don't know what you mean by a boundary condition to a forcing. The forcing from CO2 is just a measure of how the outgoing radiation flux is reduced (for a given temperature) when you add a certain amount of CO2 to the atmosphere; this is basically spectroscopy.

      On Feedbacks, the sum of all feedbacks has to be negative to equilibriate at a stable climate, which is well known. No one is saying otherwise. Usually when people say feedbacks are net positive, they are implicitly ignoring the Planck radiative "feedback", but this is a matter of convention. The issue of people like Lindzen and Spencer, versus, well almost everyone else, is that that they think it is *more* negative. Unfortunately, they have not convinced virtually anyone in the scientific community, and there are a lot of papers showing why the history of their ideas are not robust.

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    3. Anthony Cox

      logged in via email @optusnet.com.au

      In reply to Chris Colose

      A boundary condition to forcing is a limit to it Chris; hence my mutt-fisted calculations to show AGW forcing has no limits.

      You say that "the sum of all feedbacks has to be negative to equilibriate at a stable climate, which is well known. No one is saying otherwise."

      That is 1/2 right, the bit about the sum total of all feedbacks, which is what I thought Lindzen and Spencer, and Knox and Douglass and many others were saying but Dr Hansen is saying otherwise;

      http://climatechangepsychology.blogspot.com/2008/12/james-hansens-agu-presentation-venus.html

      Go to the section on the Venus Syndrome at slide 22; this could only come about if either the forcing from CO2 is exponential or the feedback effects are; Hansen is saying that will happen here on Earth if all the coal is used.

      Is that your understanding?

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    4. Chris Colose

      Graduate Student- Atmospheric Sciences

      In reply to Anthony Cox

      There's several issues here, which might be worth clarifying for interested readers, because I notice confusion in concept or terminology.

      The radiative forcing involves *changes in* the energy output of the sun or greenhouse gas concentrations, volcanic eruptions, or possibly other factors. They are thought of as small, sustained changes that are externally imposed and which modify the solar and/or infrared part of the Earth's energy balance; they can also be large (such as a volcanic eruption…

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    5. David Stockwell

      logged in via email @gmail.com

      In reply to Anthony Cox

      For example, the Hansen statement: "Our model blows up before the oceans boil, but it suggests that perhaps runaway conditions could occur with added forcing as small as 10-20 W/m2."?

      This would need sensitivity to be infinite, with a trajectory as you say that is exponentially increasing. All indications are that feedback is not this high, and elsewhere he talks about finite sensitivity. He provides no basis for his estimate of 10-20W/m2. It looks to me like more gratuitous fear-mongering.

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    6. Chris Colose

      Graduate Student- Atmospheric Sciences

      In reply to Chris Colose

      Correction in my post:

      //"We define positive feedbacks to be those that would tend to make the temperature rise greater than 0.25 C per doubling, and negative feedbacks between 0 and 0.25 C per doubling. "//

      Should be per W/m2 forcing, not per doubling...

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    7. Anthony Cox

      logged in via email @optusnet.com.au

      In reply to Chris Colose

      Chris, my understanding is that AGW supposes there will be a 3.7W/m2 radiative imbalance/forcing from 2XCO2, producing a change in GAT of +3C; see:

      http://folk.uio.no/gunnarmy/paper/myhre_grl98.pdf

      2 issues with that; firstly, CO2 from humans, ACO2, has increased about 40% which should have translated to a temperature increase of about 1.3C; however GAT has only increased by about 0.7C. That should be evidence of negative feedbacks, even if you assume that AGW 3.7W/m2 forcing is correct.

      Secondly…

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    8. David Stockwell

      logged in via email @gmail.com

      In reply to Anthony Cox

      Anthony, the first issue is usually answered with the transient/equilibrium argument, that the full effect has not been felt yet.

      The second, that gain of x4, is usually applied to both CO2 and solar, on the principle that all forcing are equal, and equally amplified by water vapor.

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    9. Anthony Cox

      logged in via email @optusnet.com.au

      In reply to David Stockwell

      "the principle that all forcing are equal,"

      That's a principle which needs to be looked at; do you have time?

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    10. David Stockwell

      logged in via email @gmail.com

      In reply to Anthony Cox

      "the first issue is usually answered with the transient/equilibrium argument, that the full effect has not been felt yet."

      I forgot, there is also the 'heat hidden in the ocean' argument and the 'aerosols from China' argument.

      "do you have the time?" hmm... have to think about that.

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