Dr. Roger Pielke Senior posted this today, since he has no comments on his blog, I felt it would be good to repost it here to allow discussion – Anthony
There is an excellent collection of interviews posted by Sam Patterson on April 23 2011 on the weblog Climatequotes.com titled
I have reposted his very informative set of interviews and commentary below.
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From: Climatequotes.com
Note: I wrote this post many weeks ago and never posted it because I was waiting for some more feedback. However, Pielke Sr. has posted specifically on this issue recently and Watts ran it also, so I feel now is a good time to post it.
This post deals with the the question of whether or not climate sensitivity should be measured by global average surface temperature anomaly. I asked multiple climate scientists their opinion, and their responses are below. First, some background.
Over at The Blackboard there is an interesting guest post by Zeke. He attempts to find areas where agreement can take place by laying out his beliefs and putting a certain confidence level on them. This idea was commented upon by several blogs and scientists. Judith Curry, Anthony Watts, Jeff Id, and Pielke Sr. all contributed. I want to focus on Pielke’s response, because he challenges a core assumption of the exercise.
In Zeke’s post, he gives his position on climate sensitivity:
Climate sensitivity is somewhere between 1.5 C and 4.5 C for a doubling of carbon dioxide, due to feedbacks (primarily water vapor) in the climate system…
Here is Pielke’s response to this claim:
The use of the terminology “climate sensitivity” indicates an importance of the climate system to this temperature range that does not exist. The range of temperatures of “1.5 C and 4.5 C for a doubling of carbon dioxide” refers to a global annual average surface temperature anomaly that is not even directly measurable, and its interpretation is even unclear…
Pielke goes on to explain that he has dealt with this issue previously in the paper entitled “Unresolved issues with the assessment of multi-decadal global land surface temperature trends.” Here is the main thrust of his response:
This view of a surface temperature anomaly expressed by “climate sensitivity” is grossly misleading the public and policymakers as to what are the actual climate metrics that matter to society and the environment. A global annual average surface temperature anomaly is almost irrelevant for any climatic feature of importance.
So we know Pielke’s position. He is adamantly opposed to using surface temperature anomaly when discussing climate sensitivity, for various reasons, not the least of which is it ignores metrics which actually matter to people.
I haven’t heard this view expressed very often, so I decided to contact other climate scientists and find out their opinions on this issue. I asked the following questions and invited them to give their general impressions:
1. Do you believe that global annual average surface temperature anomaly is the best available metric to discuss climate sensitivity?
If yes to Question 1, then:
2. Could you briefly explain why you consider global annual average surface temperature anomaly the best available metric to discuss climate sensitivity?
If no to question 1, then:
2. What do you believe is the proper metric to discuss climate sensitivity, and could you briefly explain why?
John Christy
1. Do you believe that global annual average surface temperature anomaly is the best available metric to discuss climate sensitivity?
No. The surface temperature, especially the nighttime minimum, is affected by numerous factors unrelated to the global atmospheric sensitivity to enhanced greenhouse forcing (I have several papers on this.) The ultimate metric is the number of joules of energy in the system (are they increasing? at what rate?). The ocean is the main source for this repository of energy. A second source, better than the surface, but not as good as the ocean, is the bulk atmospheric temperature (as Roy Spencer uses for climate sensitivity and feedback studies.) The bulk atmosphere represents a lot of mass, and so tells us more about the number of joules that are accumulating.
Patrick Michaels
I think it is a reasonable metric in that it integrates the response of temperature where it is important–i.e. where most things on earth live. However, it needs to be measured in concert with ocean measurements at depth and with both tropospheric and stratospheric temperatures. For example, if there were no stratospheric decline in temperature, then lower tropospheric or surface rises would be hard to attribute to ghg changes. Because we don’t have any stratospheric proxy (that I know of) for the early 20th century, when surface temperature rose about as much as they rose in the late 20th, we really don’t know the ghg component of that (though I suspect it was little to none).
Having said that, I suspect that where we do have such data, it is indicative that the sensitivity is lower than generally assumed, but not as low as has been hypothesized by some.
Gavin Schmidt
Your questions are unfortunately rather ill-posed. This is probably not your fault, but it is indicative of the confusion on these points that exist.
“Climate sensitivity” is *defined* as being the equilibrium response of the global mean surface temperature to a change in radiative forcing while holding a number of things constant (aerosols, ice sheets, vegetation, ozone) (c.f. Charney 1979, Hansen et al, 1984 and thousands of publications since). There is no ambiguity here, no choice of metrics to examine, and no room for any element of belief or non-belief. It is a definition. There are of course different estimates of the surface temperature anomaly, but that isn’t relevant for your question.
There are of course many different metrics that might be sensitive to radiative forcings that one might be interested in: Rainfall patterns, sea ice extent, ocean heat content, winds, cloudiness, ice sheets, ecosystems, tropospheric temperature etc. Since they are part of the climate, they will be sensitive to climate change to some extent. But the specific terminology of “climate sensitivity” or the slightly expanded concept of “Earth System Sensitivity” (i.e Lunt et al, 2010) (that includes the impact on the surface temperature of the variations in the elements held constant in the Charney definition), are very specific and tied directly to surface temperature.
People can certainly hold opinions about which, if any, of these metrics are of interest to them or are important in some way, and I wouldn’t want to prevent anyone from making their views known on this. But people don’t get to redefine commonly-understood and widely-used terms on that basis.
I sent a response to Gavin clarifying my questions, and including Pielke Sr’s comments. Here is his response to Pielke’ comments:
I disagree. Prof. Pielke might not find the global temperature anomaly interesting, but lots of other people do, and as an indicator for other impacts, it is actually pretty good. Large-scale changes in rainfall patterns, sea ice amount, etc. all scale more or less with SAT. (They can vary independently of course, and so ‘one number’ does not provide a comprehensive description of what’s happening).
Kevin Trenberth
1. Do you believe that global annual average surface temperature anomaly is the best available metric to discuss climate sensitivity?
This is not a well posed question. This relates to definition: the sensitivity is defined that way. It is not the best metric for climate change necessarily
If yes to Question 1, then:
2. Could you briefly explain why you consider global annual average surface temperature anomaly the best available metric to discuss climate sensitivity?
I think the best metric overall is probably global sea level as it cuts down on weather and related noise. But global mean temperature can be carried back in time more reliably and it is reasonably good as long as decadal values are used.
If no to question 1, then:
2. What do you believe is the proper metric to discuss climate sensitivity, and could you briefly explain why?
However, it is all variables collectively that make a sound case
Pielke Sr.
We have already discussed Pielke’s position, but I contacted him to find out what metrics he would prefer to use. Here is his response:
1. Do you believe that global annual average surface temperature anomaly
is the best available metric to discuss climate sensitivity?
NO
If yes to Question 1, then:
2. Could you briefly explain why you consider global annual average
surface temperature anomaly the best available metric to discuss
climate sensitivity?
If no to question 1, then:
2. What do you believe is the proper metric to discuss climate
sensitivity, and could you briefly explain why?
The term “climate sensitivity” is not an accurate term to define how the climate system responds to forcing, when it is used to state a response in just the global average surface temperature. This is more than a semantic issue, as the global average surface temperature trend has been the primary metric used to communicate climate effects of human activities to policymakers. The shortcoming of this metric (the global average surface temperature trend) was discussed in depth in
“National Research Council, 2005: Radiative forcing of climate change: Expanding the concept and addressing uncertainties. Committee on Radiative Forcing Effects on Climate Change, Climate Research Committee, Board on Atmospheric Sciences and Climate, Division on Earth and Life Studies, The National Academies Press, Washington, D.C., 208 pp. http://www.nap.edu/openbook/0309095069/html/“
but has been mostly ignored in assessments such as the 2007 IPCC WG1 report.
A more appropriate metric to assess the sensitivity of the climate system heat content to forcing is the response in Joules of the oceans, particularly where most the heat changes occur. I discuss this metric in
Pielke Sr., R.A., 2008: A broader view of the role of humans in the climate system. Physics Today, 61, Vol. 11, 54-55.
http://pielkeclimatesci.files.wordpress.com/2009/10/r-334.pdf
Pielke Sr., R.A., 2003: Heat storage within the Earth system. Bull. Amer. Meteor. Soc., 84, 331-335. http://pielkeclimatesci.files.wordpress.com/2009/10/r-247.pdf
More generally, in terms of true climate sensitivity, more metrics are needed as we discussed in the 2005 NRC report. The Executive summary includes the text [http://www.nap.edu/openbook.php?record_id=11175&page=4]
“Despite all these advantages, the traditional global mean TOA radiative forcing concept has some important limitations, which have come increasingly to light over the past decade. The concept is inadequate for some forcing agents, such as absorbing aerosols and land-use changes, that may have regional climate impacts much greater than would be predicted from TOA radiative forcing. Also, it diagnoses only one measure of climate change “global mean surface temperature response” while offering little information on regional climate change or precipitation. These limitations can be addressed by expanding the radiative forcing concept and through the introduction of additional forcing metrics. In particular, the concept needs to be extended to account for (1) the vertical structure of radiative forcing, (2) regional variability in radiative forcing, and (3) nonradiative forcing. A new metric to account for the vertical structure of radiative forcing is recommended below. Understanding of regional and nonradiative forcings is too premature to recommend specific metrics at this time. Instead, the committee identifies specific research needs to improve quantification and understanding of these forcings.”
It is, therefore, time to move beyond the use of the global annual average surface temperature trend as the metric to define “climate sensitivity”.
Differing views
There are clearly differing views on this subject.
John Christy does not support the metric. He points out that the surface temperature is affected by numerous things other than greenhouse forcing, and then gives two metrics which he prefers. The first is the change in joules in the system, with particular emphasis on the oceans. The second is bulk atmospheric temperature.
Patrick Michaels supports using the metric. He points out that the metric is important because it addresses the area where people live. However, he emphasizes that the surface temperature must be taken in concert with measurements such as ocean temperature at depth, and tropospheric and stratospheric temperatures. Without these other measurements, it would be difficult to assess the impact of GHGs on surface temperature.
Gavin Schmidt supports the metric unreservedly. He and Trenberth rightly point out that climate sensitivity is defined by global average surface temperature anomaly. Of course, the point of my question is challenging whether or not this is the best definition. Gavin seems to think so, and points out that the metric is “commonly-understood and widely-used”. He states that other metrics such as rainfall patterns and sea ice amount track very well with surface air temperature.
Trenberth is very brief, but states that global average surface temperature anomaly is not necessarily the best metric to use for climate change. He considers that global sea level is a better metric because it cuts down on weather related noise. However, he also points out that global average surface temperature anomaly is useful because it can be applied to the past more reliably. He also states that all variables taken together make a sound case.
Pielke Sr. is adamantly opposed to using this metric. We’ve already discussed his reasons. He also proposes a different metric for assessing climate sensitivity, “A more appropriate metric to assess the sensitivity of the climate system heat content to forcing is the response in Joules of the oceans”. He supports these claims with several of his own papers as well as a NRC report.
Conclusion
Pielke and Christy want to stop assessing climate sensitivity by using global average surface temperature anomaly, and both recommend using a change of joules (particularly in the ocean) as a better metric.
Michaels and Trenberth support the metric while emphasizing that other metrics must also be taken into account. Schmidt does not mention any drawbacks and emphasizes that the metric is already widely used and it works well with other metrics.
It seems to me the main problem here isn’t the metric itself, but the emphasis placed on it. I don’t believe that Pielke or Christy believe the metric has no value at all, only that it is a poor choice to use as the main metric when discussing CO2′s impact on climate. In Pielke’s case, the emphasis on CO2 itself is a problem, as he believes that other human impacts are far more important.
Climate science so frequently focuses on CO2 and temperature that it seems natural climate sensitivity would be measured by global average surface temperature anomaly. A shift away from this metric seems unlikely. However, if it can be shown in the future that a change in joules in the ocean directly contradicts other metrics then I’m sure this discussion will come up again. Pielke’s paper mentions an apparent contradiction found by Joshua Willis of JPL, although the measurements are only taken over a four year period. Only time will tell which metric is most valuable.
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How can global sea level even be considered to be a good metric for CO2 sensitivity? We know sea level has been going up at about the same rate before and after increases in CO2 levels, so that alone means that it’s a poor metric. There could very well be a delayed feedback that we have not yet seen, but it’s clear that right now it cannot be used, unless the conclusion you draw is that the sensitivity is exactly zero.
I agree that the ocean heat content is the best one available.
The sniff test on that plot:
250PPM of CO2 would cause cooling?
🙂
I’m not a climate scientist, though I do play one on the blogs.
I would not use the surface temperature anamoly for two reasons.
The only globaly viable temperature anamoly available is the satellite record which only goes back 30 years and is still subject to dispute regarding adjustments. The surface station network is such a mangled hash that I do not believe a reliable global value can be recovered from it.
The second reason is that even once we do manage to agree as to what the actual surface temperature anamoly is, there is still no agreement as to how much of that anamoly is attributable to CO2 and how much is from other factors. Heck, we still don’t even know what all the other factors might be.
Gavin seems to think so, and points out that the metric is “commonly-understood and widely-used”.
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Kind of reminds me of the way they used to try and shout down skeptics by declaring that there was a consensus in favor of their position.
The answer above is, in my opinion, the kind of answer a politician gives, not a scientist. Just because a metric is widely used is not evidence that it is right.
Dr Schmidt’s definition would be like defining corn crop yield by the average height of the corn stalks. Sure you could define it that way but in actuality it means nothing.
An excellent discussion. Pielke Sr. has often advocated for a more regional approach to examining climate change as well, focusing on local to regional changes rather than the global metric of sensitivity most commonly used. Roy Spencer has advocated the use of the global average temperature (see http://www.drroyspencer.com/2010/05/in-defense-of-the-globally-averaged-temperature/ ) to aid in diagnosing climate change and sensitivity. I think the regional approach should be persued on top of the global, with the many regional effects of forcings and the various oscillations taken into account in context. Thats just me, however.
Based on Gavin’s response, I’m left to wonder if he doesn’t understand what a measurement of temperature is. What matters to people on the ground is what weather to expect on their crops in the next 6 months. There’s countless major influences on that, but probably the easiest one to point to is whatever dominant oceanic energy cycle affects your area. That is entirely dependent on where you live. Global surface temperature anomaly doesn’t tell you anything about where energy in the form of heat is going between the ocean and atmosphere, so it tells you nothing about what to expect in terms of rainfall or sunshine for the near future.
More importantly, if we’re speaking long-term, as I would expect a climate change person to be speaking of. The energy budget is *all* you should care about. The temperature measured is simply not going to give you the information you want if you’re trying to track where the temperature will be tomorrow. It is a talking point, a footnote, a blurb that has no bearing on the work of someone trying to demonstrate that the world will get warmer.
His reply frankly reads like a form of flailing created by either ignorance of thermodynamics, or an awkward political position. Here’s hoping it’s the latter.
What about climate scientist sensitivity? That is, the increase in blood pressure for each doubling in contradictions to their preferred theories.
Scientists who don’t like the term ‘climate sensitivity’ should just define a new term, ‘climate responsiveness’, in terms of joules. Or in terms of a weighted average of several factors, where the weights are determined by emprical studies.
Scientists can push their results on ‘climate responsiveness’ out to the press. They won’t know the difference.
next time replace Gavin with a real scientist and not a propagandist like Gavin clearly is …
I’ll go with temperature.
Climate is where I live, and until I get over my fear of sharks, the heat content of the ocean doesn’t do it for me. The oceans moderate the climate, certainly, and likely regulate it, but they aren’t any measure of it. Sea level is not even in the ball park.
Temperature, humidity, precipitation, and their seasonal changes are the climate.
I have checked temps. so far in Europe, Australia, southern Africa and south America.
(35 years records). Everywhere I looked (so far) I did not find the minima rising faster then maxima and mean temps. when looking at them on an annual basis. So draw your conclusions?
http://www.letterdash.com/HenryP/more-carbon-dioxide-is-ok-ok
“People can certainly hold opinions about which, if any, of these metrics are of interest to them or are important in some way, and I wouldn’t want to prevent anyone from making their views known on this.”
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Well, thank you, Gavin. Very generous of you to allow other people to have, and express, opinions on this matter.
The sheer arrogance of the man never fails to amaze me………
Excellent article. I’m in no way, shape, or form a climate scientist. My problem with surface temperature anomaly as a metric is pragmatic. The value is noisy and apparently sensitive to many things — some of which are poorly understood. As a result, otherwise intelligent people spend an awful lot of time arguing about small changes in values that are very likely some combination of measurement noise, measurement biases, and exogenous events like the movement of warm and cool ocean water masses.
Out of curiosity, how does one measure joules in a system if not through temp?
Doug says:
April 26, 2011 at 12:27 pm
How can global sea level even be considered to be a good metric for CO2 sensitivity? We know sea level has been going up at about the same rate before and after increases in CO2 levels, so that alone means that it’s a poor metric.
Or it means that CO2 sensitivity is small and/or overridden by myriad other factors.
Gavin is a mathematician, not a scientist. He doesn’t understand that temperature is an intensive variable and thus that the concept of global temperature is a nonsense.
My metric for climate sensitivity is the value of damage inflicted on humanity per year, caused by a doubling CO2, divided by Global GDP. After a 40% rise of CO2 from pre-industrial times this is 1/1000th of diddly-squat and my projection is that it will continue to be 1/1000th of diddly-squat even after 100% is passed.
As I’ve commented on a couple of occasions: If we for a moment ignore the fact that most of the heat capacity is in the oceans: Global average temperature isn’t even a valid measure of the heat content of the atmosphere, since a 1 degree air temperature increase represents a larger amount of added energy if the temperature is high to begin with than if it is low to begin with. A +0.5 C global anomaly which is mainly located in temperate or tropic zones may represent about the same “excess heat” as a +1 C (or even more) global anomaly which is mainly located in the Arctic.
I don’t see the sense of even using the term “climate sensitivity.” Climate is not a single measurable. Even if it were a single measurable quantity, it would logically be subject to several “sensitivities” – in addition to the various gaseous elements of the earth’s atmosphere. Allowing the widespread use of the concept that global “climate” (meaning temperature) is only a function of CO2 , describable by a single number is not science.
“”””” “Climate sensitivity” is *defined* as being the equilibrium response of the global mean surface temperature to a change in radiative forcing while holding a number of things constant (aerosols, ice sheets, vegetation, ozone) (c.f. Charney 1979, Hansen et al, 1984 and thousands of publications since). There is no ambiguity here, no choice of metrics to examine, and no room for any element of belief or non-belief. It is a definition. “””””
Well that is totally wonderful Gavin. Aerosols, ice sheets, vegetation, and Ozone, are ALL variables of “The Climate”.
How does one observe the response of the climate to a single variable (the radiative forcing) while at the same time insisting that other variables of the climate system shall not change ”
Reminds me of some rocket scientist British University researchers (can’t recall who), who did a study (computer modelling) of what happens, when you double the atmospheric CO2 abundance; which I presume is the same change, as a CO2 doubling; while at the same time holding the surface Temperature constant. Evidently their study was an analysis of how the laws of Physics change; how else could you double the atmospheric abundance of CO2; or cause a CO2 doubling; your choice, and at the same time have no change in the surface Temperature; which after all, we are told, is a direct consequence of the CO2 abundance.
I learn something every day. Today I learned from Dr Schmidt that the global mean surface Temperature is (or can be) in equilibrium. Well I suppose if Kevin Trenberth can have the earth conduct heat so fast as to remain an isothermal body; then the global mean surface Temperature can be in equilibrium. Gavin doesn’t seem to be sure whether he is talking about the “global mean surface Temperature” ; or the global mean surface Temperature anomaly ! Is this the sloppy way NASA does climate science; perhaps NASA needs to get back to Aeronautics, and Space.
And by the way; presuming that the actual Warming degree C as a function of the PPM CO2 actually falls somewhere in the range between the blue and the red curves; blue for cold, and red for hot; how can one be sure that the function isn’t a straight line. Can you prove it doesn’t follow a curve of the form:- y = exp(-1/x^2) ?
To determine whether there is net change happening, instead of some redistribution, we need a global measure. Global average surface temperature is surely imperfect, but it is difficult to find a better indicator. Total system (ocean at all depths, ice and atmosphere) energy content would be great, but we don’t have such a measurement yet. When we do have total system energy, we won’t have a history with which to compare it.
Sea level is attractive as a global measure, because it is sensitive to the total ocean heat content. As Trenberth says, it has a decent signal/noise ratio. However, the volume change of sea water caused by adding some quantity of heat depends on pressure and temperature. Consequently, the distribution of changes in heat content affects sea-level. Of course, glacial meltwater and the drainage of aquifers also add to sea-level. So sea-level requires careful interpretation, which some would deride as “adjustments.”
So, essentially, I’m to believe that image depicting climate sensitivity to CO2 is real, good to honest, truest of science, and not the para-climatological modeled garbage from the house of Hansen, the preamble of the IPCC church of climate.
And, of course, everything assumes the static value of 280 ppm, the only statistical value that never change the higher resolution the future brings and, apparently, a value nobody seem to know if there is any actual scientific proof for no more.
But what does it all matter we do so have the global temperature from 1750, for, apparently, because, I mean, we got it for, well, London, and like the crazed climate communist hippies always says: One (tree)ring to to rule ’em all (and one localized ancient temperature measurement for global reference.)
Mike from Canmore – Excellent question. Joules is the unit of heat and requires a mass. For example, an object at 10C has twice the heat of another object at 10C with half the mass. In the atmosphere, also, the contribution of water vapor to the heat content must be included; e.g. see:
Pielke Sr., R.A., C. Davey, and J. Morgan, 2004: Assessing “global warming” with surface heat content. Eos, 85, No. 21, 210-211. http://pielkeclimatesci.wordpress.com/files/2009/10/r-290.pdf
and Section 3 in
Pielke, R.A. Sr., K. Wolter, O. Bliss, N. Doesken, and B. McNoldy, 2006: The July 2005 Denver heat wave: How unusual was it? Nat. Wea. Dig., 31, 24-35.
http://pielkeclimatesci.wordpress.com/files/2009/10/r-313.pdf
Averaging is like the old saw about statistics. That is why I agree with Dr. Pielke.
In my household, the average height for thr foour of us is 5′ 9″. If i was to build my doorways at 6′ heights, only two of us could walk through these doorways without ducking.