I think it’s pretty clear that no authoritative cite for this point exists. It’s just an alarmist meme.
Well, note that ±2% would correspond to total variations in global temperature of almost 12 K, which isn’t all that small. As for how good this estimate is, it probably isn’t too bad…although it may be on the low side, particularly if the “snowball earth” hypothesis is correct.
No. In order to determine that, you have to look both at what the temperature variations were and what the estimated forcings were. And, particularly for the more recent events where we have the best data on this, the estimates seem to give results implying that the climate sensitivity is compatible with…or perhaps higher than…current best estimates from the climate models (as the Science paper I linked to many times in this thread discusses).
Just to add one more thing: One also has to be careful about what sort of timescale one is talking about in regards to feedbacks. E.g., it is possible that there are negative feedbacks operating over very long timescales; for example, as that Wikipedia page on the faint sun paradox discusses, there can be feedbacks involving the carbon cycle:
So, the question of relevance is not whether there are significant negative feedbacks on some geological timescale but whether there are significant negative feedbacks that will come into play on the timescales that we care about. And, that is why it is best to find specific analogs in the not-to-distant past that involved changes that were on timescales that are not too different than the sort of century one we are interested in and involving forcings that we have some estimate for, rather than just making broad general statements about what has been true on geological timescales (based on the limited temperature proxy evidence that we have) in the presence of forcings that we don’t even know all that much about on a planet that may have had a very different distribution of continents, mountains, ocean currents, ice sheets, etc.
Of course it depends on how you define “small.” However, if somebody told me that for millions of years, notwithstanding super volcanos, asteriod strikes, etc., the temperature of the earth had not gotten more than 6 degrees above (or below) the average, I would infer that there are strong negative feedbacks at work.
And I don’t need a calculator to know that the Earth has been through some pretty serious forcings over the years.
It is fine to use vague, hand-waving arguments without a calculator to get some rough ideas, but it is silly to believe they have more validity than actual hard calculations. I personally don’t even know how to get any sort of decent estimate the forcings due to the various things that you describe.
Your argument boils down to saying: “Forget the changes in the relatively recent past that we can look at with some care and do some real calculations on. I’d rather think about some vague things we know almost nothing about and try to draw conclusions from that.” That sort of reasoning suffers from all the problems that I mentioned above…and frankly seems pretty desperate.
Also, don’t get too hung up on your ±6 K number. I noticed that on that Wikipedia page about the snowball earth that one hypothesis is that the equator was a cold as Antarctica is now…So, it is in fact not at all clear how good an estimate that is. There may have been considerably larger excursions.
It depends on the hard calculations. It’s possible that you have been fooled just like the IPCC fooled you with their “best estimate” of mitigation costs. Please link to the paper in question and I will take a look at it.
Here is the paper. But I have little doubt that you will find a reason to feel justified in discounting it.
Lol. That’s hardly a surprise given that the paper doesn’t say what you claimed it did.
Or did I miss the “hard calculations” you have been trumpeting? You know, the “hard calculations” that looked at climate sensitivity over time scales of 50 to 100 years? The “hard calculations” that would show that there are NOT strong negative feedbacks at work over time scales of 50 to 100 years?
Schrag is kinda short on “hard calculations”. For example, they say:
There’s a raft of assumptions in there:
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Where is the justification for assuming that the tropics was "relatively unaffected by changes in high latitude ice cover?
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Where is the citation showing that the tropics are relatively unaffected by changes in ocean circulation?
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Where is the science showing that if the cooling wasn’t from changes in ice cover and circulation, that therefore it “must be explained” by CO2?
If that’s what you call “hard calculations”, jshore, I’d hate to see what you think of as soft calculations. If it takes three very large and un-cited assumptions to get to your final resting point, there’s nothing “hard” about that except swallowing the huge assumptions.
This is just another example of the common AGW supporters’ cry, “We can’t explain it … so it must be CO2”. Why must it be CO2? The clouds changed during the ice age, the humidity changed during the ice age, the wind changed during the ice age, and all of those affect the ocean temperature … so why does the explanation “have to be” CO2?
I’m sick and tired of scientists who advance speculation as though it were scientific truth. If you don’t know why the oceans cooled as much as they did during the ice age … just say so, rather than making unsustainable claims.
w.
As always, jshore, a very interesting piece of research.
Unfortunately, while everything you say is correct, there’s a bit more to the story.
Consider a parcel of air that starts to rise. At some point, condensation starts, and a cumulus cloud forms. More rising air, and we get a thunderstorm.
Now, within the core of the thunderstorm, we have rising saturated air. As you point out, the warmer it starts, the more the condensation warms the rising air.
The missing part in your exposition, jshore, is something linking this to the temperature of the middle troposphere. A thunderstorm converts the heat given off by the condensing water into increased lift, that’s why it is able to drive all the way up through to the upper troposphere.
At the the top, the air finally reaches a zone at which the density is such that it can rise no more. It spreads out and descends to the surface again.
Now, where has the heat gone? Well, it has gone into work, the work of lifting the air parcel.
Where has the heat not gone?
Into the middle troposphere. Inside the core of the thunderstorm, it has bypassed the middle troposphere entirely, and has been converted from heat into work.
This is another example of why we can’t just use “simple physics” to predict the climate. Nature, unfortunately, is rarely simple.
w.
jshore, what I said before was incomplete.
I want to congratulate you. You say:
And indeed, you did exactly that, identified the driving mechanism (water moving between its many forms), and gave a very lucid description of the principles.
Hat tip,
w.
Thanks. I appreciate it.
intention: Of course, I agree with you that nature is always more complicated than a simple theory. However, I do have two comments on what you have said here:
(1) I am a little confused as to why you think that the parcel necessarily must be driven up in the middle and upper troposphere. Maybe you are right but I thought that if the air is sufficiently unstable (i.e., environmental lapse rate is higher than moist adiabatic lapse rate) then the buoyancy itself would cause it to continue to rise. [Eventually, as it gets toward the top of the troposphere, the environmental lapse rate will decrease and the air will no longer move up, which is why you see those anvil-like tops of thunderheads.]
(2) More importantly, I think your notion that this view of thunderstorms invalidates the simple physics of moist adiabatic lapse rates leading to amplification of temperature fluctuations as one goes up in the troposphere would prove too much. I.e., since thunderstorms have a timescale on the order of hours, it would seem that if they invalidated the effect that I described then one would not see this amplication of temperature fluctuations on timescales longer than this. However, in fact, as Santer et al. show, the observational data are in good agreement with the simple theory and the models incorporating the theory in a presumably somewhat more complicated way for fluctuations that are even on the timescales of months to a few years. It is only when you look at decadal trends that the observations (depending on which data set you believe) seem to show some deviation from this. I have a hard time understanding how the physical processes in thunderstorms could lead to such deviations on the decadal timescale but not on the monthly to yearly timescale.
Thanks, as always, for the interesting food-for-thought.
First of all, to get more details, you will clearly have to dig deeper than just that short piece summarizing the research. You can start by looking at all of that paper’s citations.
However, your basic argument seems to amount to the claim that they can’t rule out all possible speculative hypotheses that you might be able to dream up that could conceivably explain the observations in some other way. Unfortunately, I don’t think any theory can pass the test of definitively excluding all possible speculative hypotheses. At some point, you actually have to put pen to paper or computer code to computer and flesh out a speculative hypothesis and try to demonstrate that it provides an alternative explanation…and that it explains the data better and more convincingly than the prevailing theory.
In particular, you seem to be suggesting that perhaps changes in clouds can account for the cooling of the tropics during the ice ages. That is all well and good but if the changes in clouds are a feedback effect then you seem to be positing a positive cloud feedback, which of course, is going to make the climate system more unstable…not more stable. (And then you are going to have a difficult time explaining how the known change in radiative forcing due to changes in greenhouse gas concentrations coupled with this feedback didn’t produce a significant effect.) And, if you are positing that the cloud changes occurred for some other reason, what exactly is that reason; what was it in response to?
I understand the desire to know with certainty that there is no other conceivable explanation for the data. However, I really don’t see how one can expect any theory in science to ever do this. It gets back to the whole fact that science is an inductive, not a deductive, process. And again, it is a case where climate science is being singled out for special treatment because people don’t happen to like the policy implications of the scientific conclusions.
jshore, please quote and cite the “hard calculations” you have been trumpeting. (No doubt you studied them carefully and satisfied yourself of their validity before mentioning them in this thread.)
Thank you.
Actually, we have a somewhat different philosophy on science. I don’t feel the need to personally verify every single piece of science before I provisionally accept it (and all knowledge in science is provisional). That would not be realistic, as it would mean that essentially I couldn’t accept anything in the biological sciences and only a tiny fraction of the available knowledge in the physical sciences.
The point is that the scientists have studied these past events by doing some real modeling of them, not just by waving their hands and saying that they think the climate is very insensitive without even trying to estimate the forcings involved. And, they have published their results in refereed journals, not just stating their conclusions on messageboards. And, most other scientists in the field seem to have agreed with their conclusions.
jshore, thanks for the reply.
You say my claim is that “they can’t rule out all possible speculative hypotheses that you might be able to dream up that could conceivably explain the observations in some other way.”
So you are saying that the idea that tropical temperatures are affected by the wind, by the humidity, and by the clouds are “speculative hypotheses”?!? … jshore, you’ve made some interesting claims here on the boards, but this is one of your best. The idea that the wind and clouds affect tropical temperatures is somehow “speculative”? On which planet?
They are using an exclusionary argument. An exclusionary argument means that first we show the result must be from one of say four possible causes. Then we rule out three of them, and thus we show it must be the fourth cause. This is a valid (albeit quite difficult) way to scientifically establish something.
But they have not done that, other than by claiming without any citation that it can’t be ice sheets (why can’t changes in ice sheets affect the tropical temperature?) and it can’t be changes in currents (why can’t changes in currents affect the tropical temperature?). Now you are claiming that it can’t be changes in wind, or in humidity, or in cloud cover either.
I hate to be picky, but … why can’t changes in wind or humidity or cloud cover change the tropical temperature?
And once again, you seem to think that somehow I am responsible for patching the hole in their argument by providing complete compelling alternative theories for the wind, the water, the humidity, and all the rest.
Sorry, not my job. If you want to argue by exclusion, you have to rule out the alternative possibilities, not me. Not only that, but you have to show that your list of possible explanations is complete, and that you have ruled out every plausible explanation but CO2. Not me. You.
I know that’s difficult, I said that before. Arguing by exclusion is difficult, because you have to rule out all other plausible possibilities. But if you choose that path, that’s your difficulty, not mine.
Like I said before, this is just the “We don’t know what caused it … so it must be CO2” explanation so favored by the AGW crowd. I’m surprised that you, as a scientist, are unwilling to acknowledge the gaping hole in the logic.
w.
jshore, you say:
BZZZZT! Sorry, didn’t answer the question in any way, shape, or form. If you can’t quote or cite the “hard calculations” you were on about, just say so. This wriggling is unseemly.
w.
PS - In most fields of science, your statement that “I don’t feel the need to personally verify every single piece of science before I provisionally accept it …” makes perfect sense. Unfortunately, climate science is not like that. It is full of unsubstantiated claims made in perfectly respectable refereed journals.
While your statement is is a testament to your faith in the essential goodness of human beings, it ignores the reality of climate science. From Phil Jones’ refusal to reveal his data sources for the HadCRUT3 temperature dataset, to Michael Mann’s CENSORED file, to Thompson’s refusal to archive the Guliya and other data, to Nature Magazine’s refusal to make its pet scientists follow Nature’s own rules for archiving, to the IPCC’s blatant flouting of their own procedures for reporting on controversial subjects, to the modelers not submitting their models to industry standard V&V and SQA, to the NSF not following up on their own reporting and archiving requirements, the field is rampant with poor science, unverified models, “rubber stamp” peer review, execrable handling of data, and unsubstantiated claims. See my previous post for a discussion of one of far too many examples.
In the face of that, saying that you don’t “need to personally verify” the climate science studies that you read simply reveals that you haven’t been following the story. The watchword in this field is trust … but verify.
Absolutely.
I would go further than that: If the IPCC or an article makes a claim that agrees with your pre-conceived ideas, you basically swallow it uncritically, without considering the source; without any skepticism; without doing the “spade work” as intention would say.
That’s why the IPCC was able to completely fool you with the mitigation cost “estimate” which wasn’t really an estimate.
I would submit to you that your philosophy is not a good one in climate science. Just as you were fooled about the mitigation cost “estimate” issue, you are vulnerable to being fooled on other points.
Until you actually quote and cite the “hard calculations” you have been trumpeting, you are the one who is hand-waving.
I agree 100%.
jshore, re-reading your post I noticed I had missed an interesting point you had discussed. You said:
My own understanding of the climate system is that the globe has an equilibrium temperature set by physical interactions and physical constants of sun, wind, and water. Only a system based on physical constants could keep the planet at ±2% temperature change for the last half a billion years.
The tropical cloud albedo is the throttle of the planetary heat engine. The tropical thunderstorms and the ocean currents are the main heat transfer mechanisms, moving tropical heat to the poles. As Bejan shows, this system runs at a maximum of power production/dissipation.
Now, obviously over the centuries and the millennia, this equilibrium temperature, this position of maximum power throughput, has drifted slightly up and down. Why?
First thing that comes to mind is the position of the continents. The climate heat engine uses the winds and the ocean currents to transfer heat to the poles. How easily they can do this depends on the location of the continents. This, by the way, is the difference between the North and South Poles. At the South Pole, you have a chunk of eternally frozen down to the planetary bone ice and dirt, surrounded by warm currents that originate at the equator.
At the North Pole, on the other hand, you have a layer of ice with warm currents from the Equator running underneath it, with the ocean floor not frozen. But I digress …
Next would be anything affecting tropical cloud formation. This is particularly important over the land areas, because of the presence there of short-lived aerosols that can affect cloud formation. Also, the albedo change over the tropical land (both in area and strength) is much larger than over the ocean (because the land warms and cools more). Thus, changes there have a disproportionate effect.
Next would be anything affecting average wind speed. Evaporation is directly proportional to wind speed, so a small change in wind speed can reduce or increase evaporation drastically. There is a coupling and an interchange of momentum between the atmosphere and the planet, which results in slow longer term wind speed changes.
Of course, not just wind but anything affecting evaporation is an issue. There is speculation that the amount of diesel oil from destroyed ships in the North Atlantic during the peak of WWII affected the evaporation.
My point in all of this is simple. I have listed some possible reasons for longer term temperature trends. That is by no means an exhaustive list. I see no reason to assume a priori that the same processes that equilibrate the daily temperature (the temperature driven tropical cloud cover and thunderstorm number and size) would be responsible for the slower, longer term drift in that equilibrium state. I lean the other way, I would say it is more likely that they would involve different mechanisms entirely.
Now, one of those mechanisms could be increasing GHGs … but there’s a fly in the ointment. That mechanism, as presently theorised, requires that tropical temperature trends aloft be greater than at the surface. This is for reasons of radiation balance. For every additional watt per square meter of infra-red energy that the surface radiates to the troposphere, it only gets half of that back.
w.