Guest Post by Willis Eschenbach
It has been known for some time that the “Pacific Warm Pool”, the area just northeast of Australia, has a maximum temperature. It never gets much warmer than around 30 – 31°C. This has been borne out by the Argo floats. I discussed this in passing in “Jason and the Argo Notes“, and “Argo Notes Part 2“. I’d like to expand on this a bit. Let me be clear that I am by no means the originator of the claim that there is a thermostat regulating the maximum ocean temperature. See among many others the Central Equatorial Pacific Experiment. I am merely looking at the Argo data with this thermostat in mind.
First, Figure 1 shows the distribution of all of the ~ 700,000 surface temperature measurements taken by Argo floats to date.
Figure 1. A “histogram” shows how many data points fall in each of the 1°C intervals shown along the bottom axis. The maximum is in the interval 28°-29°C.
The number of temperature records peaks around 29°C, and drops quickly for temperatures above 30°C. This clearly establishes the existence of the mechanism limiting the oceanic temperatures.
What else can the Argo data tell us about this phenomenon? Quite a bit, as it turns out.
First, a look at the year by year evolution of the limit, and how it affects the temperatures at different latitudes.
Figure 2. Annual temperature variations measured by all northern hemisphere argo floats that exceeded 30°C. Temperature observations are colored by latitude. Click on image for full-sized graphic.
A couple points of interest. First, the cap clearly affects only the warm parts of the year. Close to the equator, that is most of the year. The further from the equator, the less of the annual cycle is affected.
Second, the majority of the breakthroughs through the ~30° ceiling that do occur are from areas further from the equator, and are short-lived. By and large, nobody exceeds the speed limit, especially those along the equator.
Figure 3 is a closeup of the years since 2005. I chose this starting point because prior to that the numbers are still changing due to limited coverage. To show how the mechanism is cropping the tops of the warmer parts of the year, I have added a Gaussian average (129 point width) in dark gray for each two-degree latitudinal band from 0°-2°N up to 10°-12°N.
Figure 3. Annual temperature variations measured by all northern hemisphere argo floats that exceeded 30°C. Dark lines have been added to highlight the average annual swings of the data by latitude band. Click on image for full-sized graphic.
As you can see, the warm parts of the yearly cycle have their high points cropped off flat, with the amount cropped increasing with increasing average temperatures.
Finally, here is the corresponding plot for the southern hemisphere:
Figure 4. Annual temperature variations measured by all southern hemisphere argo floats that exceeded 30°C. Click on image for full-sized graphic.
Note that there is less of the southern ocean that reaches 30°C, and it is restricted to areas closer to the equator.
Next, where are these areas that are affected by the temperature cap? I had always thought from the descriptions I’d read that the limitation on ocean temperature was only visible in the “Pacific Warm Pool” to the northeast of Australia. Figure 5 shows the areas which have at some point been over 30°C.
Figure 5. Locations in the ocean which are recorded at some time as having reached or exceeded 30°C.
Figure 5a. A commenter requested a Pacific-centered view of the data. We are nothing if not a full-service website.
Clearly this mechanism operates in a wider variety of oceans and seas than I had realized, not just in the Pacific Warm Pool.
Finally, here is another way to consider the effect of the temperature maximum. Here are the average annual temperature changes by latitude band. I have chosen to look at the northern hemisphere area from 160 to 180 East and from the Equator to 45°N (upper right of Figure 5, outlined in cyan), as it has areas that do and do not reach the ~ 30° maximum.
Figure 6. Average annual temperature swings by latitude band. Two years (the average year , shown twice) are shown for clarity.
Note that at say 40°N, we see the kind of peaked summer high temperatures that we would expect from a T^4 radiation loss plus a T^2 or more evaporative loss. It’s hard to get something warm, and when the heat is turned down it cools off fast. This is why the summer high temperature comes to a point, while the winter low is rounded.
But as the temperature starts to rise towards the ocean maximum, you can see how that sharp peak visible at 40°N starts first to round over, then to flatten out at the top. Curiously, the effect is visible even when the temperatures are well below the maximum ocean temperature.
Speculations on the mechanism
I want to highlight something very important that is often overlooked in discussions of this thermostatic mechanism. It is regulated by temperature, and not by forcing. It is insensitive to excess incoming radiation, whether from CO2 or from the sun. During the part of the year when the incoming radiation would be enough to increase the temperature over ~ 30°, the temperature simply stops rising at 30°. It is no longer a function of the forcing.
This is very important because of the oft-repeated AGW claim that surface temperature is a linear function of forcing, and that when forcing increases (say from CO2) the temperature also has to increase. The ocean proves that this is not true. There is a hard limit on ocean temperature that just doesn’t get exceeded no matter how much the sun shines.
As to the mechanism, to me that is a simple question of the crossing lines. As temperature rises, clouds and thunderstorms increase. This cuts down the incoming energy, as well as cooling the surface in a variety of ways. Next, this same process moves an increasing amount of excess energy polewards. In addition, as temperature rises, parasitic losses (latent and sensible energy transfers from the surface to the atmosphere) also go up.
So … as the amount of total radiation (solar + greenhouse) that is warming any location rises, more and more of the incoming solar radiation is reflected, there are more and more parasitic losses, more cold water and air move from aloft to the surface as cold wind and rain, and a greater and greater percentage of the incoming energy is simply exported out of the area. At some point, those curves have to cross. At some point, losses have to match gains.
When they do cross, all extra incoming energy above that point is simply transferred to the upper atmosphere and thence to the poles. About 30°C is where the curves cross, it is as hot as this particular natural system can get, given the physics of wind, water, and wave.
I make no overarching claims for this mechanism. It is just one more part of the many interlocking threshold-based thermostatic mechanisms that operate at all temporal and spatial scales, from minutes to millennia and kilometres to planet-wide. The mechanisms include things like the decadal oscillations (PDO, AMO, etc), the several-year Nino/Nina swings, the seasonally opposing effects of clouds (warming the winters and cooling the summers), and the hourly changes in clouds and thunderstorms.
All of these work together to maintain the earth within a fairly narrow temperature band, with a temperature drift on the order of ± 0.2% per century. It is the stability of the earth’s climate system which is impressive, not the slight rise over the last century. Until we understand the reasons for the amazing planetary temperature stability, we have no hope of understanding the slight variations in that stability.
My regards to you all,
w.
UPDATE (by Anthony):
Dr. Roger Pielke Sr. has some praise for this essay here:
TimTheToolMan: February 15, 2012 at 12:45 am
“… this means about 1/3 of the energy absorbed in the top few microns is used in evaporation and about 2/3 of the energy is radiated. None goes into the ocean bulk though. …”
Tim, where does that conclusion come from?
If some amount of DWLWIR is absorbed in the first few microns, then perhaps some of that is re-radiated, some energy is lost as evaporation, some is passed on by conduction, some is moved by water currents and convection.
So, if the DWLWIR can heat the first few microns of the ocean, it can heat the ocean.
So, if the DWLWIR can heat the first few microns of the ocean, it can heat the ocean.
Unless, according to Steven, below, the amount of evaporation ensures a matching amount of energy is immediately lost to evaporation.
Stephen Wilde: February 15, 2012 at 1:45 am
“…. the latent heat taken up by the evaporative event is five times the energy required to provoke that evaporation so evaporation is well able to mop up all DWLWIR that is available…..”
But, how do we quantify such a thing? If (on the above figures) 20 % of the incoming DWLWIR energy is then lost as evaporation, the system remains at eualibirium.
As it must be on that logic eh? Because if it were more than that, we would be stuck with rapidly cooling oceans.
But, if it were less than that, we again have DWLWIR warming the oceans.
Really, much of this discussion is around the mechanism itself, but really without explaining the stability of the system, or Willis’ observed ‘ceiling’ sea temperature.
“But, how do we quantify such a thing? If (on the above figures) 20 % of the incoming DWLWIR energy is then lost as evaporation, the system remains at eualibirium.”
Evaporation takes up whatever is left over after all other processes have taken their slice of the available extra energy so there is no effect on equilibrium temperature, or rather total system energy CONTENT.
One does however see a change in energy distribution which itself has a climate consequence but too small to measure compared to natural variations from sun and oceans.
It is part of the mechanism that explains the stability of the system and therefore the observation of a cap on temperature which Willis has correctly brought to our attention.
The negative system response to ANY influence other than changes in atmospheric mass, the planetary gravitational field or the level of solar input is fast, powerful and variable in three dimensions with the efficiency of evaporation as a net cooling process a primary component.
And the energy cost of a given amount of evaporation is set by atmospheric pressure.
Willis Eschenbach says:
February 15, 2012 at 12:22 am
“OK, so he is claiming that in addition to the losses he mentions from latent (70 W/m2) and sensible heat (30 W/m2) loss from the surface, that there is also some 282 W/m2 going upwards as evaporation.”
No! Please get past that stupid Trenberth cartoon showing 380W/m2 of downwelling IR. That is a result of 440W/m2 of upwelling IR. It’s like you writing a check to yourself for $10,000 each month drawn out of your own funds then you cash the check and put the proceeds back into the account from which the check was drawn. Then yoyu claim the $10,000/mo. as income. That’s the same voodoo accounting that Trenberth foisted on you with that cartoon and you bought it hook, line, and sinker. It doesn’t work that way in financial metrics and it sure as hell doesn’t work in physics where every last joule is meticulously tracked and accounted for by reality. The NET upwelling IR is all that matters and the net over the ocean is a rather consistent 60W/m2 while evaporative loss is about 100W/m2. This can be found in innumerable studies in far greater detail and in every first year college textbook on oceanography. Calculate the rainfall from 100W/m2 which is the actual mean annual evaporative energy loss. The numbers will work out perfectly with average measured rainfall.
The first thing to do when you’ve dug yourself into a hole is stop digging. Trenberth messed up your thinking rather badly. Don’t feel bad about it. He confused a helluva large crowd. NASA no longer puts that original cartoon in their propaganda. Even they finally got too embarrassed by it to continue promoting the sham.
“Is there a physical law which makes it necessary that every single water molecule heated by DWLWIR is evaporated off the surface?”
No. In fact most of them immediately emit an upwelling LWIR photon. The NET transfer is what matters.
Ultimately the surface cannot radiate more energy than it receives from the sun plus a negligible amount of internal heat leaking out of the molten core of the planet. Over the tropical ocean the mean annual solar energy absorbed is about 180W/m2. The mean annual energy loss broken down by type is 100W/m2 latent (evaporation), 70W/m2 radiative (LWIR), and 10W/m2 conductive (dry air convection).
Over land the evaporative loss percentage diminishes and radiative loss increases to make up for it. Over a desert it’s almost entirely radiative loss because there’s no water vapor to retard it.
It works this way because the energy can escape through a number of routes and it takes the easiest one first and foremost even though no path is entirely neglected. Greenhouse gases alter which path is the easiest and force the loss to take a different path.
Over land where the evaporation path is limited by available surface water the greenhouse gases that make the radiative path more difficult have only the conductive path as the main alternative. Conduction is misearbly slow so what happens is the surface temperature rises which then accelerates the rate at which both radiation and conduction can proceed. Balance is thus restored through a higher surface temperature.
It doesn’t work that way over the ocean where there is an infinite supply of water at the surface to provide a third path for energy to escape – evaporation. Evaporation is so efficient that it’s the preferred, easiest path to begin with. Thus heat loss from the ocean is dominated by evaporation almost 2:1 over radiation (about 100W/m2 vs. 70W/m2). Additional greenhouse gases that further restrict energy escape via radiation simply funnel more the energy loss over to evaporation which, because of the infinite supply of surface water, is always there.
This isn’t rationally disputable by anyone familiar with the facts and applicable laws of physics. This is how it works. In point of fact study after study of ocean heat budgets shows that even when evaporation is retarded in the warmer months (it’s actually fastest in the cooler months when RH is reduced) the energy from the warm months is stored at depth and released in the cooler months. This is why there is little seasonal variation in ocean temperature compared to seasonal variation in land temperature at the same latitude. Dirt only stores heat down to about a meter in depth while the ocean stores it to a depth of 100 meters. Thus dirt can’t store enough summer heat to raise air temperature significantly in the winter but the ocean can and does store enough heat to do that.
But more pointedly to the question posed by this article as to why there’s a nominal cap at 30C in ocean temperature with rarer departures up to 35C that’s simply, as I’ve shown earlier in this thread with references to a black body temperature calculator and reference to the highest observed land-based mean annual temperature 35C is the gray body limit for maximum mean annual surface temperature at the equator. The highest mean annual surface temperature ever rrecorded is a salt desert in Ethiopia and its mean annual temperature was 34.4C which is just about exactly the highest ocean temperature that ARGO ever records. The ocean is just a lot better at closely tracking the annual mean than land is so observations tend to be much closer to the mean most of the time.
Interestingly the highest recorded annual mean surface temperature is in one of the driest places on the earth – a salt desert on the equator. The most powerful greenhouse gas, water vapor, evidently and obviously isn’t needed to produce the highest annual mean surface temperature. Isn’t that just precious?
I got an idea to maybe help move the debate about atmospheric pressure alone raising surface temperature. The mean annual temperature at Carlsbad National Park is 63F. The mean annual temperature in the deepest part of the cave (>1000 feet) is 68F. The air pressure in the cave is quite a bit higher than at the surface and we can calculate by the saturated adiabatic lapse rate (humidity in the cave is near 100%) what its temperature should be if the lapse rate keeps going. The saturated adiabatic lapse rate is 2.7F/1000ft so we should expect the cave temperature to be about 65.7F. Dry adiabatic lapse rate is 5.4F so that would be 68.4F for the deep cave which is an almost perfect fit.
That’s interesting. It’s made more interesting by the geothermal lapse rate which is 1F per 70 feet of depth away from tectonic plate boundaries. That would predict our cave temperature at 1000′ should be about 77F and it’s much colder than that!
I don’t have an explanation offhand but I’m curious. Maybe someone else can work out why it’s the temperature it is in the deepest part of Carlsbad cave. Cold air tends to sink and higher parts of the cave like the main room at 750′ open to the public is 58F year round because cold winter air sinks into it and doesn’t tend to escape because it’s denser so there’s a stratification effect not unlike bodies of water. The deeper parts of the cave, because the openings are much smaller, are not thought to trap cold winter air. But they aren’t the temperature the geothermal lapse rate predicts nor the saturated adiabatic lapse rate. That bugs me.
Willis
[snip . . this is just way out of line. Get your people to talk to his people if you are serious otherwise don’t troll . . kbmod]
TimTheToolMan says:
February 15, 2012 at 12:45 am
Tim, now you’re picking up on richard versey’s BS that I have not proposed a mechanism. I’ve laid out the plausible mechanism in my previous thread on the subject. I’ve repeated it in this thread. Do try to keep up. Since it seems you didn’t like my explanation, here’s Stephen Mosher’s (emphasis mine):
Here’s the thing, Tim. Suppose we have a black stone sitting out in the sun. It gets hot. We paint it white. It cools down.
My point is that the paint is only affecting the very skin of the object, yet it changes the rate at which the object heats and cools. And as a result of that change just at the skin, the bulk temperature of the stone is different.
This is the part that seems to mystify people, that something occurring just at the skin can affect the whole. But as I have explained, there’s no mystery. The IR is absorbed in first couple dozen microns of the skin layer. As a result, the absorbed IR makes up part of the total energy radiated by the ocean.
And because part of the energy is provided by the IR, this in turn means the ocean itself is losing less energy, and thus the entire mixed layer ends up warmer than it would be without the DLR.
Try to wrap your head around the fact that anything that affects the rate at which the ocean loses energy will affect the entire mixed layer. Doesn’t matter what it is or where it is. If it reduces energy loss from the surface, the whole mixed layer will be warmer than it would be without it. And DLR definitely affects that rate, so it affects the temperature of the whole upper ocean.
w.
PS—And folks, don’t buy the kind of ‘it’s going off as evaporation’ nonsense that richard and others are trying to sell. Unless you think there’s an average of 16 feet of rain per year around the world, that amount of evaporation is a joke. RUN THE NUMBERS FIRST, or you will look as foolish as richard for making the ‘it’s going up as evaporation’ claim
Just The Facts Please says:
February 15, 2012 at 7:10 am
Interesting question. I think the problem is in the interplay between the geothermal lapse rate and the atmospheric lapse rate. Try these references:
Clouds in Caves
as well as Underground drainage systems and geothermal flux
Turns out, unknown to me, that the geothermal flux as well as the air lapse rate in caves are quite complex and not at all what one might expect. They are affected by a variety of things including the air flow, bottlenecks in the cave, where the air enters and leaves the caves, and of course by our old friend, water, which messes with everything it touches.
So I suspect the answer is, there is no simple answer.
Most fascinating question, though.
w.
Just The Facts Please says:
February 15, 2012 at 7:10 am
Dry adiabatic lapse rate is 5.4F so that would be 68.4F for the deep cave which is an almost perfect fit.
;———————————————————————————————————————–
This is a temperature model not a pressure model.
Although a temperature model is need to compute the pressure, there were no annual pressure measurements or calculations in your post.
Whatever the debate was regarding pressure, you’ve side stepped the issue.
“Reducing the size of the temperature gradient through the skin layer reduces the flux.”
Given that evaporation requires 5 times as much energy as is required to provoke it then it is highly unlikely that more evaporation will result in a REDUCTION of the gradient which is what would be required tor a warming effect on the bulk ocean. To achieve that outcome there would need to be surplus energy left over after the increase in evaporation but with the 5:1 ratio it couldn’t happen.
I’ve seen no evidence that the size (or slope) of that gradient actually changes. One has to measure that average slope across the entire global oceans to a depth of only 1 to 3 mm (there is some disagreement as to the actual depth of that region).
In fact, some time ago I proposed that slope as a possible diagnostic indicator.
Last time I reviewed the matter there was no such evidence but proposals were in hand to try to find ways of measuring it. Has there been some progress ?
I examined the issue in some detail back in October 2009 here:
http://climaterealists.com/index.php?id=4245
I would like to know if it is even correct to say that down-welling radiation ‘heats the ocean’, or anything else for that matter. Here’s why…..
My understanding is that heat is defined as the transfer of thermal energy. It is a flow or flux. Now with radiative heat transfer you are not flowing heat, you are flowing energy in the form of photons. Isn’t it true that I can direct a stream of photons from a cold atmosphere into a warmer planet and not heat anything at all?
It seems to me that as long as there is a larger flow of photons leaving the surface than what is coming in, the surface is cooling despite the incoming stream of energy. The only thing that matters is that the outgoing stream is larger than the incoming one and the surface is cooling.
What is really happening is that the incoming down-welling radiation reduces the net out flow of photons from the surface which means the surface will be hotter than it would otherwise be (in the absence of down-welling IR). Nothing is being ‘heated’. The entire discussion about back radiation ‘heating’ things up at the surface is, it seems to me, a fundamental misunderstanding about this flow based on our language biases about heat and heating.
It simply does not matter in the least how far the down-welling radiation is absorbed, or if it is turned into latent heat through evaporation, or even how much is absorbed at all. The only thing that matters is the net energy out-flow. If it’s high the surface cools faster than it does when it is low. Some can be from evaporation. Some can be from radiation, Some can be from conduction. As long as the total out is bigger than the total in the surface cools. Incoming back energy only affects the exit rate.
This is not to say that back radiation can’t result in a warmer planet in the presence of the sun’s incoming energy. It reduces the net out-flow yes. But it is the sun that is doing the additional heating as the primary energy source. I liken it to filing a leaky swimming pool with a fire hose (the sun) with a bit of the leaking stuff being put back in by little guys with buckets (back radiation). The little guys aren’t (heating) filling the pool. They are changing the rate of leaking. It doesn’t matter what part of the leak they fill their buckets from and it doesn’t matter where they pour it back in. The effect is the same. As long as they do their work the water level will be higher, more leaks will start and a new equilibrium level will be reached.
BTW I fell into the same semantic trap I was railing against in my second paragraph…..
“Isn’t it true that I can direct a stream of photons from a cold atmosphere into a warmer planet and not heat anything at all?”
I should have said something like, “Isn’t it true that I can direct a stream of photons from a cold atmosphere into a warmer planet and not raise the energy level or temperature of anything at all?”
Willis Eschenbach says:
February 15, 2012 at 9:58 am
PS—And folks, don’t buy the kind of ‘it’s going off as evaporation’ nonsense that richard and others are trying to sell. Unless you think there’s an average of 16 feet of rain per year around the world, that amount of evaporation is a joke. RUN THE NUMBERS FIRST, or you will look as foolish as richard for making the ‘it’s going up as evaporation’ claim
Indeed, and don’t forget that evaporation is a self inhibiting process once the atmosphere above the ocean surface reaches the appropriate vapor pressure for the surface temperature then evaporation ceases. See Clausius-Clapeyron equation.
“Indeed, and don’t forget that evaporation is a self inhibiting process once the atmosphere above the ocean surface reaches the appropriate vapor pressure for the surface temperature then evaporation ceases. See Clausius-Clapeyron equation.”
Water vapour being lighter than air the more humid stuff goes straight up or is blown along by wind so it hardly ever actually ceases.
Paul Bahlin says:
February 15, 2012 at 11:08 am
As far as I am concerned, Paul, that is a meaningless semantic quibble. However, to avoid it, I try to be very careful with my wording. For example, here’s how I worded it above:
Now, you want to say that the DLR does not “heat” anything … but the reality is that the ocean (and the planet for that matter) end up warmer when there is DLR than when there is not.
Since the planet ends up warmer, “heats the planet” makes perfect sense to me. But to you and others, somehow that’s unacceptable, so I use the wording above.
Either way you cut it … the world ends up warmer because of DLR, and to myself I call that “heating the planet” even though it may not be 100% scientifically accurate.
But to avoid this exact discussion, I didn’t say that the DLR heated the ocean, instead I said just what I said—that the ocean ends up warmer when there is DLR than when there is not, whether you call that “heating the ocean” or not.
w
My post is now up:
[snip. See sidebar. Unreliable blog. ~dbs, mod.]
huh? I specifically wrote a response to this article, and you’re censoring it? And the irony of unreliable…
REPLY: Chis, apolgies not my doing but another moderator, send the link again and I’ll publsh it. Probably got confused with the other story today…been a madhouse.
Anthony
My post is now up:
http://www.skepticalscience.com/tropical_thermostat.html
Chris, I sent you an email, and it bounced:
Your message did not reach some or all of the intended recipients.
colose@xxx.xxx
Error Type: SMTP
Remote server (144.92.197.138) issued an error.
hMailServer sent: RCPT TO:
Remote server replied: 550 5.1.1 unknown or illegal alias :
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Willis:
Agreed! I was just pushing against the argument people make about the cold[er] atmosphere not being able to ‘heat’ the planet. The reality is that, technically, it doesn’t but that doesn’t mean that you don’t end up with a higher temperature in spite of that.
Lots and lots of people conflate heat, temperature, and energy and it starts with common usage in language, IMO.
Sorry, that one was saved in the form and is now deactivated. Try again.
Just to throw a monkey into the wrench, do these Argo’s need occasional calibration ever ?
Has 1-10% been pulled out and checked for accuracy ?
Would be cool to see how they are constructed.
Would be even cooler to see what organisms may have found a new home ?
Has anyone realised that if the extra energy in the air does reduce the flow of energy from ocean to air then the air would be no warmer because less would be coming out of the ocean ?
Furthermore that due to the huge thermal capacity of the oceans it would be millennia before any warming of the oceans became apparent ?
Can’t have it both ways. Either it warms the air but not the oceans or it warms the oceans and won’t be a problem for so long that we will have solved our energy problems or be gone for other reasons.
If it warms the air but not the oceans then the sea/air interaction will ensure that the extra energy in the air is removed to space sooner by a faster water cycle via more evaporation.
“Chris Colose says:
February 15, 2012 at 3:25 pm
My post is now up:
http://www.skepticalscience.com/tropical_thermostat.html”
Why no mention of the Lapse Rate ?
It is the slope of that which governs convection between surface and tropopause not the factors which you discuss.