Five Reasons Why Water Vapor Feedback Might Not Be Positive
By Dr. Roy Spencer
Since it has been a while since I have addressed water vapor feedback, and I am now getting more questions about it, I thought this would be a good time to revisit the issue and my opinions on the subject.
Positive water vapor feedback is probably the most “certain” and important of the feedbacks in the climate system in the minds of mainstream climate researchers. Weak warming caused by more carbon dioxide will lead to more water vapor in the atmosphere, which will then amplify the weak warming through water vapor’s role as the atmosphere’s primary greenhouse gas.
Positive water vapor feedback makes sense intuitively. Warmer air masses, on average, contain more water vapor. Warmer air is associated with greater surface evaporation rates, which is the ultimate source of almost all atmospheric water vapor.
And since water vapor is the atmosphere’s main greenhouse gas, most scientists have reasonably inferred that climate warming will be enhanced by increasing water vapor amounts. After all, water vapor feedback is positive in all of the IPCC climate models, too.
But when one looks at the details objectively, it is not so obvious that water vapor feedback in the context of long-term climate change is positive. Remember, it’s not the difference between warmer tropical air masses and cooler high-latitude air masses that will determine water vapor feedback…its how those air masses will each change over time in response to more carbon dioxide. Anything that alters precipitation processes during that process can cause either positive or negative water vapor feedback.
Here are some of those details.
1) Evaporation versus Precipitation
The average amount of water vapor in the atmosphere represents a balance between two competing processes: (1) surface evaporation (the source), and (2) precipitation (the sink). While we know that evaporation increases with temperature, we don’t know very much about how the efficiency of precipitation systems changes with temperature.
The latter process is much more complex than surface evaporation (see Renno et al., 1994), and it is not at all clear that climate models behave realistically in this regard. In fact, the models just “punt” on this issue because our understanding of precipitation systems is just not good enough to put something explicit into the models.
Even cloud resolving models, which can grow individual clouds, have gross approximations and assumptions regarding the precipitation formation process.
2) Negative Water vapor Feedback Can Occur Even with a Water Vapor Increase
Most atmospheric water vapor resides in the lowest levels, in the ‘turbulent boundary layer’, while the water vapor content of the free troposphere is more closely tied to precipitation processes. But because the outgoing longwave radiation is so much more sensitive to small changes in upper-layer humidity especially at low humidities (e.g. see Spencer & Braswell, 1997), it is possible to have a net increase in total integrated water vapor, but negative water vapor feedback from a small decrease in free-tropospheric humidity. See #4 (below) for observational support for this possibility.
3) Cause Versus Effect
Just because we find that unusually warm years have more water vapor in both the boundary layer and free troposphere does not mean that the warming caused the moistening.
There are a variety of processes (e.g. tropospheric wind shear causing changes in precipitation efficiency) which can in turn alter the balance between evaporation and precipitation, which will then cause warming or cooling as a RESULT OF the humidity change – rather than the other way around.
This cause-versus-effect issue has been almost totally ignored in feedback studies, and is analogous to the situation when estimating cloud feedbacks, the subject of our most recent paper.
Similar to our cloud feedback paper, evidence of causation in the opposite direction is the de-correlation between temperature and humidity in the real world versus in climate models (e.g. Sun et al., 2001).
4) Evidence from Radiosondes
There is some evidence that free tropospheric vapor has decreased in recent decades (e.g. the Paltridge et al., 2009 analysis of the NCEP Reanalysis dataset) despite this being a period of surface warming and humidifying in the boundary layer. Miskolczi (2010) used the radiosonde data which provide the main input to the NCEP reanalysis to show that the resulting cooling effect of a decrease in vapor has approximately counterbalanced the warming influence of increasing CO2 over the same period of time, leading to a fairly constant infrared opacity (greenhouse effect).
Of course, water vapor measurements from radiosondes are notoriously unreliable, but one would think that if there was a spurious drying from a humidity sensor problem that it would show up at all altitudes, not just in the free troposphere. The fact that it switches sign right where the turbulent boundary layer pushes up against the free troposphere (around 850 mb, or 5,000 ft.) seems like too much of a coincidence.
5) The Missing “Hot Spot”
Most people don’t realize that the missing tropospheric “hot spot” in satellite temperature trends is potentially related to water vapor feedback. One of the most robust feedback relationships across the IPCC climate models is that those models with the strongest positive water vapor feedback have the strongest negative lapse rate feedback (which is what the “hot spot” would represent). So, the lack of this negative lapse rate feedback signature in the satellite temperature trends could be an indirect indication of little (or even negative) water vapor feedback in nature.
Conclusion
While it seems rather obvious intuitively that a warmer world will have more atmospheric water vapor, and thus positive water vapor feedback, I’ve just listed the first 5 reasons that come to my mind why this might not be the case.
I am not saying that’s what I necessarily believe. I will admit to having waffled on this issue over the years, but that’s because there is evidence on both sides of the debate.
At a minimum, I believe the water vapor feedback issue is more complicated than most mainstream researchers think it is.
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Be sure to check out Dr. Spencer’s book:
The Great Global Warming Blunder: How Mother Nature Fooled the World’s Top Climate Scientists
Highly recommended – Anthony
“”” Five Reasons Why Water Vapor Feedback Might Not Be Positive
By Dr. Roy Spencer
Since it has been a while since I have addressed water vapor feedback, and I am now getting more questions about it, I thought this would be a good time to revisit the issue and my opinions on the subject.
Positive water vapor feedback is probably the most “certain” and important of the feedbacks in the climate system in the minds of mainstream climate researchers. Weak warming caused by more carbon dioxide will lead to more water vapor in the atmosphere, which will then amplify the weak warming through water vapor’s role as the atmosphere’s primary greenhouse gas. “””
Well I don’t disagree with your point Dr Roy, but I do have a nit to pick.
What on earth does CO2 have to do with it ? Is it not true that atmospheric warming due to H2O vapor; will lead to further evaporation (largely due to surface absorbed LWIR). So WHO needs CO2.
Also is it not also true that atmospheric warming caused by CO2 will also lead to LWIR warming of the top ocean waters; which will result in outgassing of more CO2 into the atmosphere.
In other words; increased atmospheric Temperature whether caused by H2O or CO2 via the “greenhouse effect”; will result ins surface (ocean) warming which will yield more H2O AND more CO2 to the atmosphere.
So it is positive feedback for both CO2 and for H2O regardless of; or irregardless, as the case may be; which species or any other cause the initial warming of the atmosphere.
It is simply dishonest to say that CO2 is a GHG but H2O is a feedback; they are both quite indistinguishable in their behavior in that regard.
But thanks for coming to WUWT to talk to us about your thinking on it Professor.
And I agree with your reasoning. I also think that H2O (vapor) exhibits a NEGATIVE feedback effect as well; which is important because to some extent H2O does; but CO2 doesn’t.
H2O vapor in the atmosphere absorbs a very significant fraction (maybe 20% or more) of the INCOMING solar spectrum energy; and that too heats the atmosphere, BUT that absorbed energy is thus denied the opportunity to reach the surface; and in particular to reach the oceans where it can be deposited deep (to several hundred metre).
The atmospheric solar absorption due to H2O (vapor) then of course reradiates; but only half of that heads towards the surface; the rest eventually escapes to space. So the H2O absorption of incoming solar spectrum in the 760 nm to 2-3 micron range is a NET LOSS of solar energy, that otherwise would have reached the surface; and mostly get stored in the ocean.
So that is a water (vapor) NEGATIVE feedback effect that CO2 doesn’t match. Well to be pedantic; the CO2 does have some absorption in the 2 and 4 micron regions; but it is peanuts compared to H2O.
And the downward part of the LWIR that is converted water vapor absorbed solar energy causes increased evaporation so more water vapor, and enhanced reduction of solar spectrum energy reaching the surface. So definitely a negative feedback.
But in the end the clouds win anyway .
In the past, various posts here at WUWT have hit on the issue of water vapor needing microscopic “particles” to latch on to in order to form precipatation. From what I’ve seen, there’s more than enough microscopic particles in the atmosphere (man-made and not) to rain and snow on everyone for 400 days and nights. Has the “dramatic” (my opinion) increase in smog+ in the last 50 years, at various levels of altitude, been studied vis-a-vis humidity and rainfall? Do they plug this info into climate models at NOAA and The Met Office?
scienceofdoom says:
September 15, 2010 at 3:45 am
However, in the case of the climate there are also some non-linear negative feedbacks – surface radiation increases in proportion to the forth power of (absolute) temperature. If you analyze the system mathematically, a higher range of potential positive feedback leads to a thermal runaway. The lower range of positive feedback leads to amplified warming (compared with no feedback), and of course, negative feedback leads to reduced warming.
This doesn’t mean that water feedback is a positive feedback. But the idea isn’t mathematical or scientific madness.
Would it not be better to ask what we do know,rather then try to project uncertainties beyond their physical constraints ie are there physical (energetic constraints ) for a 3k doubling on RH?.
What constraints emerge in the annular cycle for the hydrological cycle eg evaporation and surface RH ?
Is there are robust (core) understanding of atmospheric circulation eg Makarieva et al 2010b
Phase transitions of water are among the major physical processes that shape the Earth’s climate. But such processes have not been well characterized. This shortfall is recognized both as a challenge and a prospect for advancing our understanding of atmospheric circulation (e.g., Lorenz, 1983; Schneider, 2006). In A History of Prevailing Ideas about the General Circulation of the Atmosphere Lorenz (1983) wrote: ”We may therefore pause and ask ourselves whether this step will be completed in the manner of the last three. Will the next decade see new observational data that will disprove our present ideas? It would be difficult to show that this cannot happen. Our current knowledge of the role of the various phases of water in the atmosphere is somewhat incomplete: eventually it must encompass both thermodynamic and radiational effects. We do not fully understand the interconnections between the tropics, which contain the bulk of water, and the remaining latitudes. . . . Perhaps near the end of the 20th century we shall suddenly discover that we are beginning the fifth step.”
One could conclude that we missed the 5th step and have stumbled into the 21st century ie running before we can walk.
Pascvaks says:
September 15, 2010 at 12:34 pm
The visible part of smog is made up of sub-micron sulfuric acid aerosols. Their size is a function of relative humidity and are usually at their smallest during the hottest time of day. Like clouds, they reflect, absorb, and radiate different levels of energy. Some have proposed injecting this harmful pollutant into the upper atmosphere to reflect incoming energy from the sun back to space. To me that is poison pie in the sky.
Dr. Roy Spencer reviews the conventional wisdom:
“Positive water vapor feedback is probably the most “certain” and important of the feedbacks in the climate system in the minds of mainstream climate researchers.”
But it’s worth condering this possibility:
As a quiet Sun changes the energy level coming into the water vapor environment causing a decline over time, water vapor evaporates heat energy to space acting to cool the sea surface temperature (SST) much like sweat acts to cool the skin temperature.
Leeding to a negative feedback in a condition of lower solar energy input.
This dissipation of heat energy from the sea surface may possibly be expressed by short term energy dynamics that many wrongfully have attributed to heating effects.
Now, it could also be possible that a positive change in solar energy level resulting in an incline over time would reverse this physical process; certainly that possibility is worth investigating, but in a solar energy level such as is now persisting, the possibility of energy dissipation through evaporation & convection processes needs to be fully explored & investigated.
Dr. Spencer raises a series of physical dynamics that might not behave as the conventional wisdom would have it.
This aspect or possibility needs to be fully investigated.
Hi Roy. Reading this something twigged in my memory and the following thought occurred:
You know those atmospheric heat distribution graphs that show a general heating over the past 3 decades near the surface of the earth but fail to show the tropical hot spot predicted by the GCMs? The same graphs show high altitude cooling during the same period.
Taking the graphs at face value, what we’ve got is an atmosphere that is, on the whole, warmer than it used to be near the surface, and COLDER than it used to be up in the stratosphere.
Combine an increasingly steeper temperature gradient with the proposed increasing H2O vapour and you get … ice crystals at higher altitudes (do you not?). And high-altitude ice constitutes a strong negative feedback by its effect on albedo (does it not?).
It would seem this consideration is easy to model, intuitively pretty obvious, and the corresponding physics is well enough known to lend itself to back-of-the-envelope calculations concerning feedback. What would these suggest?
Dr. Spencer,
This is rarely accepted well even at WUWT, but a fundamental tenent of engineering is that unstable systems do not long survive. Systems dominated by positive feedbacks are not stable by definition. That the earth’s climate is bounded within a narrow range over long geologic time demonstrates beyond doubt that it is a system dominated by negative feedback.
And yet the earth’s climate as dominated by positive feedbacks is routinely debated within the climate community as if it can be a possibility.
All of engineering await the climate scientist who can re-write this basic control theory component.
Gerry
It’s rather strange that almost nobody in this discussion notices that the process of evaporation TRANSFERS tons of thermal energy (OK, it’s actually 589 calories per gram of water at 288K, or 77.8W/M^2 for every meter-thick layer evaporated per year) from the ocean surface to the atmosphere–WITHOUT any temperature change accompanying the phase change. How anybody can impute a positive feedback into this is beyond all analytic reason. Evaporation is Earth’s stealth weapon against overheating!
tallbloke says:
September 15, 2010 at 12:25 am
I wonder if Roy Spencer might be interested in the rather good correlation I found between specific humidity at the tropopause and solar activity….
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There is also the Earthshine project showing decadal swings in albedo which is interesting since sunspot cycles average about 10 1/2 years.
Research Article: Automated Observations of the Earthshine
http://www.hindawi.com/journals/aa/2010/963650.html
“…..The earthshine observations reveal a large decadal variability in the Earth’s reflectance [7], which is yet not fully understood, but which is in line with other satellite and ground-based global radiation data (see [8, 9] and references therein). In order to continue to contribute to a better understanding of the Earth’s radiation budget continuous observations from a global network of robotic telescopes are necessary.”
Inter-annual variations in Earth’s reflectance 1999-2007.
http://bbso.njit.edu/Research/EarthShine/literature/Palle_etal_2008_JGR.pdf
Abstract.
The overall reflectance of sunlight from Earth is a fundamental parameter for climate studies. Recently, measurements of earthshine were used to find large decadal variability in Earth’s reflectance of sunlight. However, the results did not seem consistent with contemporaneous independent albedo measurements from the low Earth orbit satellite, CERES, which showed a weak, opposing trend. Now, more data for both are available, all sets have been either re-analyzed (earthshine) or re-calibrated (CERES), and present consistent results. Albedo data are also available from the recently released ISCCP FD product. Earthshine and FD analyses show contemporaneous and climatologically significant increases in the Earth’s reflectance from the outset of our earthshine measurements beginning in late 1998 roughly until mid- 2000. After that and to-date, all three show a roughly constant terrestrial albedo, except for the FD data in the most recent years. Using satellite cloud data and Earth reflectance models, we also show that the decadal scale changes in Earth’s reflectance measured by earthshine are reliable, and caused by changes in the properties of clouds rather than any spurious signal, such as changes in the Sun-Earth-Moon geometry.
Gerry says on September 15, 2010 at 4:48 pm
Gerry, is it even possible to be a little bit pregnant?
That is, is it even possible to be stable over the long term with a small amount of positive feedback?
Yes, the “heat pipe” of latent heat transport is so much more potent and responsive that it readily counteracts the trivial “fingerprint” resonance effects of any and all GHGs.
As for the tropopause: consider that its cold, uniform temperature gradient is necessarily maintained only by very active processes, which necessarily means responsive, rapid, and very efficient “dumping” of heat into the stratosphere and beyond from the troposphere, 24/7.
Richard;
Try getting just a little speaker howl feedback by positioning the mic just so. Can’t be done. The rise time to the howl is almost entirely a function of the speed of transmission between the two points.
Gerry says:
It is not a re-write of control theory. It is, however, a different usage of the term when climate scientists talk about a “net positive feedback”. There is in fact a large negative feedback in the climate system, expressed by the Stefan-Boltzmann Equation: as the earth heats up, it emits more radiation back into space. Climate scientists have tended to think of the predicted temperature change due a rise in greenhouse gases (or any other radiative forcing) predicted by the S-B Equation as the zeroth-order effect and thus often talk about net positive feedback when what they mean (in control theory lingo) is that the total feedbacks including that implied by the S-B equation are less negative than that implied by the S-B Equation feedback alone, so that the temperature change is magnified relative to what the S-B Equation predicts given the original radiative forcing.
There are some climate scientists who have tried to stay closer to the terminology usage of control theory and emphasize the relation implied by the S-B Equation as a negative feedback. See, for example, the book “Global Physical Climatology” by Dennis L. Hartmann.
At any rate, while one can fault the climate scientists for playing a bit fast-and-loose with this terminology from the engineering community, the issue is just one of terminology.
Ceri Phipps says:
You might want to look up Xeno’s Paradox. An infinite sum does not have to diverge to infinity. For example, if each 1 deg rise in temperature causes additional water vapor to go into the atmosphere that results in 1/2 deg rise in temperature then this 1/2 deg rise in temperature will cause additional water vapor to go into the atmosphere to produce an additional 1/4 deg rise. What you get is a sum like 1 + 1/2 + 1/4 + 1/8 + 1/16 + …, which converges to the value of 2, thus doubling the original temperature change in the absence of the water vapor feedback.
Reply: Xeno’s paradox also applies to roommates who don’t want to appear to finish off the food in the refrigerator thus converging to zero food in the container while never quite reaching it. ~ ctm
The simple argument against runaway positive feedbacks, based on the anthropic principle…
The climate system must be dominated by negative feedbacks otherwise it would have run out of control many billions of years ago and we wouldn’t be here to argue about it 🙂
Joel Shore says:
September 15, 2010 at 6:21 pm
“Climate scientists have tended to think of the predicted temperature change due a rise in greenhouse gases (or any other radiative forcing) predicted by the S-B Equation as the zeroth-order effect and thus often talk about net positive feedback when what they mean (in control theory lingo) is that the total feedbacks including that implied by the S-B equation are less negative than that implied by the S-B Equation feedback alone, so that the temperature change is magnified relative to what the S-B Equation predicts given the original radiative forcing.”
To anyone with any rigorous understanding of what constitutes feedback, the foregoing sentence is just analytically inept mumbo-jumbo. There is no “feedback” whatsover in the S-B equation, which is purely a nonlinear RESPONSE characteristic. And the claim that it’s just a matter of “terminology” is laughable in the face of fear-mongering about “runaway” effects, which are possible only with true feedback.
Climate science is awash in such pretensions to knowledge of system behavior, when in fact there is not even a grasp of basics. Further discussion of this painfully obvious fact is a waste of time that I will not participate in.
Here are a few numbers that we can use to assess whether the water vapour assumptions of global warming theory is accurate (and is occuring):
– The Clausius-Clapeyron equation says that specific humidity water vapour levels should rise 7% per 1.0C increase in temperatures.
– Global warming theory says that precipitation should increase by 2.0% per 1.0C increase in temperatures (although some areas may get dryer); and,
– there should be something like an increase in Cloudiness of over 2.0% per 1.0C increase.
Well, what is actually happening:
– Total specific humidity water vapour levels (are completely FLAT according to the NCEP reanalysis since 1948) (or, according to Willet et al 2008 at the highest estimate, there is an increase of about 0.0085 g/kg per year from 1973 to 2003 (on a base of 8.6 g/kg which they never tell you about – you are just supposed to accept an anomaly line going up) or about 7.3% per 1.0C in HadCruh which is close to what is expected in the C-C equation).
http://hadobs.metoffice.com/hadcruh/data/Willettetal2008.pdf
http://hadobs.metoffice.com/hadcruh/
– Global Precipitation Levels are essentially FLAT since 1979.
http://img684.imageshack.us/img684/8974/trenberthprecipitation.png
http://www.cgd.ucar.edu/cas/Trenberth/trenberth.papers/ClimateChangeWaterCycle-rev.pdf
– And there has been a general decline in the level of cloudiness according to the ISCCP project.
http://isccp.giss.nasa.gov/climanal7.html
So no, it doesn’t add up according to the theory.
“”” Joel Shore says:
September 15, 2010 at 6:21 pm
Gerry says:
This is rarely accepted well even at WUWT, but a fundamental tenent of engineering is that unstable systems do not long survive. Systems dominated by positive feedbacks are not stable by definition.
…
All of engineering await the climate scientist who can re-write this basic control theory component.
It is not a re-write of control theory. It is, however, a different usage of the term when climate scientists talk about a “net positive feedback”. “””
Well Gerry is not really correct either. Positive feedback is NOT automatically unstable. And positive feedback is used quite routinely in lots of engineereing situations.
For a start; positive feedback was very popular in a lot of early radio receivers; where it was used to increase the circuit gain of many radiao receivers. But the use of positive feedback does increase the noisiness of systems and since early radio receivers were quite noisy anyway; if you got too close to the edge with your positive feedback, then the general noisiness could throw you into an oscillatory state.
Positive feedback was very common in automobile drum brakes; where a “Two leading shoe” architecture was used to reduce brake pedal pressures. In a two leading shoe design, the brake shoes are pivoted at the “front end” in terms of the normal direction of rotation, and (of course) at a smaller radius than the brake surface. When the brakes are applied, the friction drags the brake shoe in the forward direction and that causes the shoe to try and pivot outwards in radius; thus increasing the force against the brake drum; which further increased the friction; and the pivoting moment. Although this reduced the brake pedal force it also increased brake fade. Whent eh shoes get too hot; boning materials in the brake linings tend to melt and flow out onto the shoe surface making it kind of glassy, and dropping the coefficient of friction. When the coefficient of friction dropped thus causing the brakes to fade, it also dropped the positive shoe wrtapping feedback so the fade got even worse.
The simplest drum brakes; had a single fixed pivot point for both shoes and a single brake cyclinder pushing the opposite ends apart; which was cheaper; one cylinder (and less unsprung weight). So this system has one leading show and one trailing shoe. The leading shoe self wraps giving positive feedback; while the trailing shoe tends to unwrap; which is negative feedback. This is more stable against fade; but needs more pedal pressure. Also the leading shoe does more work than the trailing shoe so you need either thicker brake lining on the leading shoe or they will wear out at different times.
Once air and hydraulic assist came along; the fancier automobiles went to two traing shoe brakes which had only negative feedback; but needed the pedal boost. If the shoes got hot and the coefficient of friction dropped, the unwrapping effect also dropped raising the force on the shoe; so they were much more stable against brake fade.
Of course disk brakes got rid of all of those problems.
Positive feedback is only unstable if the loop gain exceeds unity; well the exact definition of unstable based on a pole zero plot and the like; is a bit more pedantically correct; but the end result becomes a greater than unity loop gain.
As to your S-B negative feedback Joel, it is also highly non-linear feedback; whcih makes it all the more powerful a controlling effect. Of course the control (in terms of increasing Temperature and radiation) is rather what we don’t want too much of.
But there are more negative feedbacks besides the S-B, such as the H2O interception of signigficant amounts of incoming solar energy; by H2O vapor which is then down converted to LWIR but half of that escapes, and only half reaches the surface; so there is anet loss of solar energy to the surface; so it is a negative feedback (but the H2O vapor is also having posivie feedback by direct interception of LWIR fromt eh surface; same as CO2 does.
But then there is the overflow clamp of cloud formation which simply stops any positive feedback loops in their tracks; and only H2O does that.
“”” Bill Illis says:
September 15, 2010 at 7:02 pm
Here are a few numbers that we can use to assess whether the water vapour assumptions of global warming theory is accurate (and is occuring):
– The Clausius-Clapeyron equation says that specific humidity water vapour levels should rise 7% per 1.0C increase in temperatures. “””
Say Bill; does the C-C equation actually give that value; because that is also the exact value that Wentz et al observed in their July 7 2007 SCIENCE paper: “How much more rain will Global Warming Bring ?”
They reported 7% per Deg C, increase in total Global Evaporation; Total atmospheric water content; and (of course) total globalPrecipitation. What they didn’t add was thqat a 7% increase in precipitation might reasonably be expected to result in about a 7% increase in total global precipitable cloud cover (in area/Optical density/duration or combinations thereof).
According to wentz, the GCMs agree with the 7% increase in total atmospehric water content; but claim on a 1-3% increase in the total global Evaporation/Precipitation. So the GCMs (he claims) are off by as much as a factor of 7 compared to observations.
But that is interesting that C_C would give that exact value they found.
Roy Spencer, real scientist. Thankyou for that posting. I agree with Gerry , stability, with a tendency to iciness, is apparent in the geological record, apparently volcanic eruptions have increased atmospheric co2 abruptly in the past, but no run away warming. No control technology will remain operational under the assumptions of AWG theory but its still considered a valid theory? It takes a genuine scientist to attempt to explain what we know we do not know and why climate science is still very young and maybe not yet a science. Recently I have been wondering what of the sweeping claims of global warming science remain? Most of the alarming ,worse than ever ,claims were DOA and I’ve lost track. I read the IPCC 4th report and it did not support the claims made in its name.
Xeno’s paradox is defeated by quantum thresholds; once the arrow, room mate or CO2 molecule passes the threshold the journey has to begin again. In the real world space and time occur similtaneously but Xeno’s ghost still rules because CO2, like carbon trading, is subject to the law of diminishing returns, probably of the marginal variety.
I sort of get it:
The more you heat or cool the Earth, the more or less precipitation will carry the warmer water vapor aloft, where the rain will fall and the blackbody sheds it’s excess back to space.
I believe that is what is meant by ‘beyond the greenhouse’.
What is missing is the ratio of extra heat input vs how much the blackbody actually warms.
You might have 7 w/m^2 in, and only retain 1 w/m^2 as a higher equilibrium.
Surely everyone has heard of evaporative cooling?
* Why is it said that a healthy dog has a cold (moist) nose?
* Why did the young Jacqueline Bisset become famous for her wet T shirt scenes in the movie “The Deep”, of 1997?
http://www.mademan.com/chickipedia/jacqueline-bisset/
SORRY, but to be more serious:
The K & T “Earth’s Energy Budget” diagram, (in some quarters referred to as the “Trenberth Cartoon), in the IPCC’s AR4 report of 2007, claims that by far the greatest proportion of energy leaving the Earth’s surface is via evapo-transpiration. (~46% of all the four basic processes).
So, if there is warming, particularly of the ocean surfaces, should there not be a nominal increase in evaporation? (cooling). Given that the greatest proportion of cooling is suggested to be evapo-transpiration? Surely a small increase in this would be significant.
Yes; I agree, it is complicated, but why is there not more attention paid to this basic point in Physics?
BTW, there is an elegantly simple explanation for evaporative cooling in quantum theory: Any fluid has a mix of molecules of varying energy levels. (speeds). Thus the hotter molecules are more able to escape and leave a higher proportion of lower energy (colder-slower) molecules behind.
Harold Pierce Jr says:
September 15, 2010 at 4:02 am ,
It gets even more interesting to me. While averages aren’t the end-all in solutions, sometimes they tell the tale. I ran the numbers on a 1 dimensional model by increasing h2o content according to absolute humidity increase if one holds relative humidity constant. A 5 deg C rise assumption in the atmospheric column resulted in a mere 30% increase in the amount of water vapor. Remember that one must talk doublings (100%) for significant changes in the IR radiation effects. A 30% increase of h2o has a slightly lower effect than a doubling of co2 – thought to be around 3.7w/m^2. Combined, they provide less than 40% of the forcing required for a 5 deg C rise – enough for almost a 2 deg C rise, since co2 by itself is expected to be able to increase temperatures by around 1 deg C. Going with 2 deg C, the absolute humidity increase for a constant RH (assumption accepted by many climatologists as being true on average) is closer to 13% and drops down to under half the w/m^2 effect of the co2 – leaving us with a need to have more forcing to achieve 2 deg C rise for the co2 doubling and h2o vapor increase.
Apparently now that added forcing is supposed to occur by having fewer clouds along with the increase in water vapor. That too has a problem in that clouds provide both positive and negative effects with the negative effects outweighing the positive by a small portion of the total.
Since it is claimed that the h2o vapor is the primary ‘feedback’ mechanism, it would seem that either the claim is falsified or the claim of high sensitivity is falsified.
I recall, (vaguely,) a science fiction story about GW!
The upshot was that cloud cover dispelled the warming, end of catastrophe!
DaveE.