Precipitable Water

Guest Post by Willis Eschenbach

One of my great pleasures is to come across a new dataset. Turn me loose on new observations of this magical world, and there’s no telling where I’ll end up. Thanks to a recent article here on WUWT I got to thinking about water vapor. Some research found the RSS 1° gridded “total precipitable water” (TPW) dataset. Total precipitable water (TPW) is the mass (or sometimes the depth) of water in a 1 metre by 1 metre column from the surface to the top of the atmosphere, if it all fell as rain. The RSS dataset has the TPW (for the ice-free ocean areas only) since 1988. Figure 1 shows the average values, in kilograms of water per square metre. Note that the RSS dataset only covers the ice-free oceans.

map average TPW RSSFigure 1. Total Precipitable Water. 

Now, there are a few interesting things about Figure 1. First, you can see why they call it the “wet tropics”. There’s lots of water in the air.

Next, the horizontal red band just above the equator delineates the effect of the band of thunderstorms perpetually boiling along the length of the inter-tropical convergence zone (ITCZ).

You can also see why CO2 is called a “well-mixed” greenhouse gas, and water vapor is not. The amount of water in the air varies from the poles to the tropics by more than an order of magnitude.

Seeing Figure 1 made me think that I could estimate the change in the poorly-named “greenhouse effect” due to a given change in water vapor. Ramanathan proposed that the magnitude of the clear-sky atmospheric greenhouse effect could be measured as the amount of upwelling longwave radiation (ULR) from the surface that is absorbed by the atmosphere. Ramanathan also observed that the variation in the strength of the clear-sky greenhouse effect was an effect of the variations in water vapor.

To show the close relationship between variations in the atmospheric absorption of the surface radiation, and the total water vapor seen in Figure 1, Figure 2 shows the atmospheric absorption as revealed by the CERES data:

Average Clear-Sky ULR absorptionFigure 2. Average atmospheric absorption of upwelling surface longwave radiation, clear-sky CERES data. Calculated as the amount of longwave (infrared) emitted by the surface minus the amount observed at the top of the atmosphere.

Seeing those two figures gave me the idea that I could actually measure the amount of change in downwelling radiation from a given change in precipitable water vapor. So here is a scatterplot graph relating the two:

atmospheric absorption versus TPWFigure 3. Scatterplot of Total Precipitable Water (logarithmic, horizontal scale) versus Atmospheric Absorption (vertical scale). Dashed vertical line shows global average value. Dotted lines show the range of the global average value over the period.

This is quite an impressively tight result, particularly given that the two variables (absorption and TPW) are from totally different datasets. I note that this is experimental validation of the IPCC’s statement about the underlying physics, viz:

The radiative effect of absorption by water vapour is roughly proportional to the logarithm of its concentration, so it is the fractional change in water vapour concentration, not the absolute change, that governs its strength as a feedback mechanism. IPCC AR5 WGI Box 8.1

More than just validating the IPCC claim of a generalized logarithmic relationship, however, this has allowed us to actually quantify the relation between the two. It also allows us to differentiate that relationship in order to determine the slope of the atmospheric absorption as a function of water vapor. That slope turns out to be 62.8 / TPW. At the average TPW value in Figure 3 of 29 kg/m^2, this gives us a slope of 62.8 / 29.0 = 2.2 W/m2 increase in absorption per kg/m2 change in TPW.

That is to say, we get a bit over two watts per square metre of increased absorption for every additional kilo of atmospheric water per square metre.

Now, that is an interesting finding which we can combine with the following look at the change in global average total precipitable water since 1988:

plotdecomp total precipitable water tpwFigure 4. Decomposition of the total precipitable water data (upper panel) into the seasonal (middle panel) and residual (bottom panel) components.

Some things of interest. First, in the bottom panel you can see the effect on TPW of the El Nino episodes in 1997/98, 2010/11,  and 2015/16. You can also see that we haven’t quite recovered from the most recent episode.

Next, there is a clear trend in the TPW data. The total change over the period is ~ 1.5 kg/m^2, centered around the long-term mean of 28.7 kg/m^2.

And utilizing the relationship between water content and atmospheric absorption derived above, this indicates an increase in downwelling radiation of 3.3 W/m2 over the period.

Now, please note that this 3.3 W/m2 increased forcing from the long-term increase in water vapor since 1988 is in addition to the IPCC-claimed 2.3 W/m2 increase since 1750 in all other forcings (see Figure SPM-5, IPCC AR5 SPM). The IPCC counts as forcings the long-term changes in the following: CO2, CH4, Halocarbons, N2O, CO, NMVOC, NOx, mineral dust, SO2, NH3, organic carbon, black carbon, land use, and changes in solar irradiance … but not the long-term changes in water vapor.

This leads us to a curious position where we have had a larger change in forcing from water vapor since 1988 than from all the other IPCC-listed forcings since 1750 … so where is the corresponding warming?

Sunny today, I’m going for a walk …

w.

My Usual Request: We can minimize misunderstandings by being specific. If you disagree with me or anyone, please quote the exact words you disagree with, so we can all understand the exact nature of your objections. I can defend my own words. I cannot defend someone else’s interpretation of some unidentified words of mine.

My Other Request: If you believe that e.g. I’m using the wrong method or the wrong dataset, please educate me and others by demonstrating the proper use of the right method or identifying the right dataset. Simply claiming I’m wrong about methods or data doesn’t advance the discussion unless you can point us to the right way to do it.

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137 thoughts on “Precipitable Water

  1. I suspect some of our alarmist friends will point to this and say ‘there’s the positive feedback that we said would happen’.

    • But it’s not positive feedback, as it has been happening during the “pause” in warming …

      And in either case my question remains—where is the projected warming claimed to result from the 3.3 W/m2 increase in water vapor forcing?

      w.

      • “where is the projected warming claimed to result from the 3.3 W/m2 increase in water vapor forcing?”

        Willis, I suppose you yourself think that the rise in temperature is nihilized by the upwards energy transport by the extra H2O, inclusive a possible rise in the upward velocity of the rising water vapour / condensed air.

      • Got to agree with Willis on this one. There is a rise in water vapour, but that rise was not ‘forced’ by an increase in temperature driven by an increase in CO2. Quite the opposite. With no rise in temperature at all, particularly in the tropics where most of the water is, the total water mass has increased. Whodunnit?

        Whatever the mechanism, it appears that an increase in water vapour concentration has caused an increase in CO2 concentration. Mankind spews a very large mass of water vapour into the air each year – a huge amount. Is this the first identifiable fingerprint of man-made global whatever-it-is?

        It is obvious that an increase in the total water mass is going to create more clouds sooner or later. So Willis, is there a link between this water concentration data and your cloudiness data, say, in the tropical zone where it matters the most?

        If there is 3.3 W/m^2 additional forcing from water vapour perhaps there is at least a corresponding loss due to shading by the clouds formed earlier each day because of the additional water vapour. That also seems obvious. We might soon have a good understanding of the temperature governor mechanism and the reason(s) for its 8 month delay.

      • As I see the graph, I think warming and TPW are pretty well aligned. Both goes up until about 2001, then have a pause until 2014 and then goes up again.

        Why not do an analysis of this?

        You may for instance make a scatterplot of warming vs water vapor

        /Jan

      • Water vapour increases when temp increases, Temp increases when cloud decreases or during el nino.
        The lack of warming is caused by convective cooling which increases exponentially with temp.
        simple.

      • There’s another effect, where the incremental latent heat removed by increasing evaporation offsets the incremental solar input, keeping ocean temperatures from rising much above 300K. You can see this in a scatter plot of surface temperature vs. water content, where water content becomes nearly asymptotic to a temperature around 300K and which is most pronounced over the oceans.

        All this evaporation is the driver of the band of tropical thunderstorms, which like a Hurricane, leaves cooler water in their wake demonstrating that weather has a net negative feedback like influence. I say ‘feedback like’ because the IPCC’s understanding of feedback systems is horribly broken.

      • so where is the corresponding warming?

        Outside my door. It is currently 98F with a dew point of 76F.

      • There isn’t a 3.3 W/m^2 increase in WV forcing because WV is not well mixed in the atmosphere. Increasing precipitation where there had already been a lot of precipitation does almost nothing to increase the forcing, maybe it even decreases it due to the increase of latent heat transport?

      • The energy from the forcing is reflected back to space by increased clouds?
        Increased clouds would count as increased precipitatable water, right?

        Like Lindzen’s iris effect?

        A negative feedback, stabilizing our wonderful earth.

      • Cispin,
        “It is obvious that an increase in the total water mass is going to create more clouds sooner or later.”

        You would think so, but water increases monotonically with temperature, while cloud coverage increases monotonically up to about 0C and then starts to decrease with temperature until it starts to increase again near the equator. The reason is because the fraction of the surface covered by clouds is Lindzen’s iris that adapts to the needs of the system in order to achieve radiant balance. The reason for the change at 0C is because the characteristics of the system changed, where below 0C, ice reflects the same as clouds, thus the only effect of incremental clouds is to warm the surface. Above 0C, clouds now reflect more than the surface and incremental clouds decrease the average temperature. An interesting point is that while the cloud area decreases with increasing temperature, cloud volume increases linearly with water vapor which increases monotonically with temperature. There are many scatter plots showing the sensitivity of almost every climate variable to every other climate variable as measured using the ISCCP weather satellite data set.

        http://www.palisad.com/co2/sens/index.html

      • Humidification lowers air temperature. The Arizona (or other areas of the globe) monsoon is all the evidence you need. That or a psychrometric chart. Might not be the whole story, but has to be part of it…

      • Willis
        Thanks for fascinating analyses.
        With the increase in precipitable water, there appears to be a corresponding increase in precipitation.
        See: Global Dimming and Brightening Wild 2015. Inset graph ~ slide 25?

        A quick search brought up:
        Improved Historical Analysis of Oceanic Total Precipitable Water Thomas M. Smith, Phillip A. Arkin
        DOI: http://dx.doi.org/10.1175/JCLI-D-14-00601.1

        Strongest multidecadal changes in the global mode are 1910–40 and since 1980. An ENSO mode for the extended period indicates a trend since the 1980s, opposite to the tendency in the global mode. . . .Analysis of SST over the same period shows climate modes consistent with the TPW modes, and for the satellite period there are consistent variations in the satellite data, showing the strong link between SST and oceanic TPW.

        Wang, X, Zhang, K, Wu, S, Fan, S and Cheng, Y 2016, ‘Water-vapor-weighted mean temperature and its impact in the determination of precipitable water vapor and climate change analyses’, Journal of Geophysical Research, pp. 1-20. (Paywalled but looks interesting.)

        Happy hunting.

      • Willis,

        “But it’s not positive feedback, as it has been happening during the “pause” in warming …”

        I second what Jan said. It looks to me like you have two peaks associated with El Ninos and two plateaus, one before the earlier El Nino and one at a higher level between the two. I think that is a lot like the temperature record. Might be worth plotting the water vapor forcing vs. temperature and compare the slope to the IPCC feedback.

        “And in either case my question remains—where is the projected warming claimed to result from the 3.3 W/m2 increase in water vapor forcing?”

        But you can not tell the difference between warming due to water vapor and water vapor due to warming. You can only see if the slope is correct. The IPCC mean is 1.6 W/m^2/K (Table 9.5), so that would take 2K warming, which has not happened. The question then is: What are your error bars like?

      • where is the projected warming claimed to result from the 3.3 W/m2 increase in water vapor forcing?

        LWIR emmissions are ‘isotropic’, that is they act in all directions equally. In other words, the IR photons shoot off in every direction, not just down. Thus, if down-welling LWIR is increasing then so must up-welling LWIR. The latter is lost to space. The absorption and radiative properties of water vapor and CO2 are the same in that increasing either gas in the atmosphere increases the amount of LWIR lost to space which logically must cool the atmosphere. The basic premise of looking for a temperature increase from CO2 or water vapor forcing would seem to be backwards

        Water vapor is different than CO2 however in that its radiative effect is dwarfed by its phase change effect. A cloud containing water droplets and water vapor will resist temperature change – either upwards or downwards due to evaporation or condensation absorbing or releasing latent heat. To understand the temperature impact of water vapor in the atmosphere, you also have to know how much water in the form of water droplets is present. I don’t think you have that data.

      • “projected warming claimed” what do you define as warming? A rise in the energy content of air near the ground or the temperature of the air near the ground? This is my biggest issue, CAGW likes to mix two different things depending on what gives them their desired answer. I know you are not intending to do that here, but it is an important distinction, the higher humidity has more heat content but not necessarily higher temperatures as you already know. So which would one are you referring too.

      • NASA 2015:
        “Increased Rainfall in Tropics Caused by More Frequent Big Storms

        A new study based in part on NASA satellite data has shown that an increase in large, well-organized thunderstorms is behind increased rainfall in the wettest regions of the tropics.
        (….)
        “The observations showed the increase in rainfall is directly caused by the change in the character of rain events in the tropics rather than a change in the total number of rain events,” said lead author Jackson Tan, who conducted this research while at Australia’s Monash University but now works at NASA’s Wallops Flight Facility, Wallops Island, Virginia. “What we are seeing is more big and organized storms and fewer small and disorganized rain events.”
        (….)
        The study helps chip away at one of the big questions facing climate change science: To what degree will a warmer world accelerate the water cycle and patterns of rainfall and drought? In particular, this study revolves around what scientists call organized deep convection – in short, large thunderstorms. These storms make up about five percent of the weather systems in the tropics but are responsible for about 50 percent of tropical rainfall.

        While this study does not delve into what’s causing the increase in large storms, it does reveal a tight correlation between this trend and increasing rainfall.

        Analyzing rainfall and cloud data from 1983 to 2009, Tan found that these large storms are still producing similar or even less amounts of rain on average, but they are happening more often.
        (….)
        Co-author George Tselioudis, a researcher at the NASA Goddard Institute for Space Studies in New York, authored a paper in 2010 that defined trends in organized deep convection in the tropics and sparked Tan’s curiosity on what was driving those trends.

        “This work changes our perception of why tropical precipitation is increasing,” Tselioudis said. “We thought it was because the warmer atmosphere holds more moisture and, therefore, when storms occur they rain more. But that doesn’t seem to be the case. Instead, the warmer tropical atmosphere becomes better organized to produce large storms more frequently.”

        The researchers analyzed rainfall data from NASA’s Tropical Rainfall Measuring Mission (from 1998-2009) and from the Global Precipitation Climatology Project (from 1983-2009). These rainfall data were compared to cloud data from the International Satellite Cloud Climatology Project for the period from 1983 to 2009

        While climate models have long predicted that a warmer world would see an acceleration of the water cycle and changes in rainfall patterns, models have not as of yet produced this change in the frequency of organized deep convection.

        The new finding also raises an intriguing next question: Why are these weather systems organizing in the atmosphere more frequently? That’s not yet known, Tan and Tselioudis said
        (….)
        (….) There has to be more emphasis on the dynamics. If you look at the grand challenges of figuring out the water cycle – this is where the emphasis is moving to.”

        Source: http://www.nasa.gov/press/2015/goddard/march/increased-rainfall-in-tropics-caused-by-more-frequent-big-storms-0

  2. First off – thanks Willis for this. An interesting and new perspective on water vapor. That is always a good thing.

    Do US weather balloon data give us enough information to get TPW for north America? I would like to see this same analysis done there.

    Bernie

  3. You noted the correspondence to the ENSO.

    Also note that data starts from 1988 and 1988 was the biggest La Nina on record. So the starting point (more like several months into the starting point considering there is a lag) is close the lowest TPW we should see while 2015-16 was one of the biggest El Ninos on record so the ending point is close to the highest TPW we should see.

    Text versions of the data 60N-60S and 20N-20S available here.

    http://data.remss.com/vapor/monthly_1deg/tpw_v07r01_198801_201606.time_series.txt

    I compare the RSS water vapor dataset to the NCEP Renalysis dataset, and the ENSO and the IPCC AR5 climate model forecasts in this chart going back to 1948.

    • Bill Illis

      That is cool, but RPC 6.0 is not a believable scenario. Is there something more believable that you can plot? If it was 2.1 or some such, it might start to provide ‘guidance’ if not prophecy.

      • Bill, and while you are at it, could you reposition the upper left key.. It overlays the peak of the 1983 ENSO value. Thx

    • Thanks for this chart. It suggests the RSS derived upward change in TPW and so WVF is partly an artifact of the time period. So the derived forcing is overestimated.

    • Crispin in Waterloo

      3.0C per doubling is based on a 7.0% increase in water vapor per 1.0C increase. Almost every climate model uses this value (a few are at 6.0%).

      So 3.0C later, all the of the RCP scenarios have a lift of 22.0% in water vapor.

      • Bill, Judith Curry and I had quite a go on this. 7% per 1C is canonical Clausius Clapeyron. Models do use that at the surface. They don’t at altitude. But AR4 black box 8.1 was adament that they still behave as if this was so was supported by observation, when it actually isn’t. See comment below.

      • 7% is the value that Wentz et al reported measuring in their July 13 2007 SCIENCE paper: “How much more Rain will Global Warming bring ? ” They said it was the one result that the GCMs agreed with.

        I believe this value is also derived from the Clausius-Clapeyron equation.

        G

      • Thanks Bill, George and Ristvan.

        And to think that it is this week that I am helping someone with calculating condensation on plastic-wrapped heavy objects in descending aircraft. Dew you have a formula ;~) ?

        Fortunately WUWT’s Nutty Professor is backing me up.

  4. Great article Willis

    You have demonstrated and quantified the positive feedback mechanism of water vapor here.

    Some warming produce more water vapor, which produce some additional warming, and so on. Not enough to get a runaway process, but enough to give a positive feedback, which confirm one fundamental element in the IPCC models.

    /Jan

    • NO ! More water vapor equals more clouds, and less sunlight reaching the surface.

      So it is a definite negative feedback. It is the principal regulator of earth’s Temperatures.

      G

      • In fact it actually shows this.
        The bulk of the water is at the equator and the bulk of the solar radiation enters there. This is how the TPW remains in the tropical region. The difference between CO2 and TPW in the atmosphere poor mixing.

        The fact that the 3.3W has not boiled the world is in itself fantastic proof.

      • No, that is not how the thermodynamics works.

        There are no doubt that water vapor is a greenhouse gas, and warm air can hold more water vapor than cold air before it condensate.

        Clouds are liquid droplets or small ice crystals. These droplets and ice crystals forms when water vapor condensate. It takes more water vapor to condensate in warm air than in colder air.

        That means that if the temperature could increase and the water content was held constant, the clouds would disappear.

        If the temperature was constant and the water content increased, the amounts of clouds would indeed increase.

        However, what is happening is that both air temperature and water vapor are increasing, and that will not necessary give more clouds.

        /Jan

      • More clouds would indicate more radiation released at altitude – clouds can’t form unless the vapor they form from loses some energy. Less than half that energy will return to warm the lower atmosphere below the clouds. Indeed, the the formation and dissipation of virga below the clouds indicates that additional energy is being captured in the lower atmosphere and carried aloft. The system of cloud formation must be a net cooling process even with “downwelling radiation from CO2 and water vapor.

      • For clarity, my response above was to George E. Smith in his saying that

        More water vapor equals more clouds,

        This is not correct. More water vapor do not necessary mean more clouds as long as the air temperature increases. Hotter air can contain more water without forming clouds. This will increase the greenhouse effect, just as the IPCC models says it does.

        Figure 2 in Willis article, which is actually a direct measurement of the greenhouse effect, confirm this.

        /Jan

      • JKA – more water vapor does mean more clouds only at a higher elevation. (The ALR is what it is.) and more clouds leads to more cooling, eventually.
        Also, the greening of the earth could be, in part, due to slightly increased pptn not just CO2.
        Willis – yet another thought provoking article – thanks!

      • Well Jan, you can have it any way you want it.

        More water vapor means MORE EVAPORATION. That is the common name for the process that produces water vapor in the atmosphere.

        More evaporation means MORE PRECIPITATION. That is the common name for the process that removes water vapor from the atmosphere.

        In most places on earth, it is a tradition to have clouds before you can get to precipitation.

        Overall, precipitation and evaporation must balance over the globe. That is to ensure that the oceans remain below us, rather than above us.

        Ergo, more water vapor means m more clouds; which are a net cooling effect.

        But if where you live you don’t have clouds before precipitation then that would be an exception to the general rule.

        G

      • George says:

        More water vapor means MORE EVAPORATION. That is the common name for the process that produces water vapor in the atmosphere.

        Sorry George, but it is not clear what you actually mean with this.
        More water where?
        If you by “More water” mean “more humidity in the lower atmosphere”, it is clearly not correct. More humidity in the air means less evaporation.

        You cannot by pure logic deduce that a larger amount of water in the atmosphere leads to more or less flux of water to or from the atmosphere. It can be correct, but any such claim has to be based on empirical evidence. So where are the scientific articles that says that the combination of higher temperature and more water vapor in the atmosphere necessarily give more clouds?

        But if where you live you don’t have clouds before precipitation then that would be an exception to the general rule

        Ha, ha, I perceive it as just funny, let’s keep it funny not nasty.

        /Jan

    • No, that would be implying that anthropogenic CO2 is the reason for the increased water vapor, not ENSO cycles. (see Bill Illis’ post above)

    • NASA make the question of cloud forcing seem very simple in their intro to the subject for the general public ( such as me) :

      -“The study of clouds, where they occur, and their characteristics, play a key role in the understanding of climate change. Low, thick clouds primarily reflect solar radiation and cool the surface of the Earth. High, thin clouds primarily transmit incoming solar radiation; at the same time, they trap some of the outgoing infrared radiation emitted by the Earth and radiate it back downward, thereby warming the surface of the Earth. Whether a given cloud will heat or cool the surface depends on several factors, including the cloud’s altitude, its size, and the make-up of the particles that form the cloud. The balance between the cooling and warming actions of clouds is very close although, overall, averaging the effects of all the clouds around the globe, cooling predominates.”-

      http://earthobservatory.nasa.gov/Features/Clouds/

    • Jan Kjetil,

      but enough to give a positive feedback, which confirm one fundamental element in the IPCC models.

      :

      How come – when it’s already been reassured that GCM’s don’t care about clouds. How could they with grid sice 100’s mile of size.

      • Johann writes:

        Jan Kjetil,
        but enough to give a positive feedback, which confirm one fundamental element in the IPCC models.
        :
        How come – when it’s already been reassured that GCM’s don’t care about clouds

        Because this is about water vapor not about clouds.
        Clouds are water droplets, not water vapor.

        /Jan

  5. All those “forcings” are not additive like resistances in series. Think parallel resistances with water vapor and clouds being the big ones.l

    • Well Steve when was the last occasion that you got precipitated on by TPW without a cloud in the sky.

      Clouds are the part of TPW that is already on its way to precipitating, which is an essential step to precipitation.

      NO clouds = NO precipitation. (of H2O)

      G

      • Sorry if I phrased it ambiguously. TPW and condensed water are separate measured values, on different sides of the phase transition. The cloud part of the water is no longer TPW.

      • By George! Steve Fraser is right, in a very specific way…
        http://www.remss.com/measurements
        There are separate measures for TPW (vapor only) & CLWC (cloud liquid water content).& “Rain Rate” (RR) which includes liquid + solid water (snow, ice).

        Deliberately side-stepping the obvious link between high TPW & CLWC is a bit cheesy. Playing as Devli’s advocate though, seems the “best” estimate of total water in all forms is RR – CLCW + TPW.

  6. Doesn’t it also matter where in the vertical column the water vapor is found? Isn’t water vapor at higher altitudes supposed to have a larger effect and isn’t it true that water vapor has been decreasing?

    That is, if you have more evapotranspiration due to increased downwelling IR you get more low level water vapor but this leads to stronger convection, more clouds and more condensation which lowers water vapor at high altitudes.

    This could be the reason for the lack of warming and also the reason for no hot spot. I think you really need to know the changes at various altitudes to compute a true feedback.

  7. The different hemispheres’ monthly pattern can be seen (1997-2004 data) in Figure 11 of Wang, et al. (2006) ” A near-global, 2-hourly data set of atmospheric precipitable water from ground-based GPS measurements”; free full text = wiley.com/wol1/doi/10.1029/2006JD007529/full

  8. The stratosphere is cooling, the surface is warming (due to reduced clouds) the net result is an increased lapse rate and increased convective cooling that overwhelms other feedbacks. That is why OLR in increasing contrary to AGW.

  9. To the question of where is the warming, there are three partial answers which collectively might explain the whole.
    1. As Bill Illis points out, Enso versus RSS time period suggests the change in WVF is likely overstated.
    2. Your many previous posts on the thermoregulatory effect of tropical thunderstorms via albedo and humidity washout. Higher TPW suggests more such activity would occur.
    3. All specific humidity is not created equal in terms of forcing. What matters most for GHE is the upper troposphere where ULR can finally escape to space. Upper troposphere water vapor gets there via thunderstorm convection cells. Lindzen’s adaptive infrared iris suggested higher temp/humidity, bigger more violent thinderstorms, so less anvil moisture detrainment. He focused on negative consequences for cirrus cloud formation (since icy cirrus warm because ice is transparent to incoming sunlight but opaque to ULR), but cirrus is also a proxy for upper troposphere specific humidity. Higher TPW also suggests a dryer upper troposphere through these mechanisms. And indeed, there are both satellite and corrected radiosonde reading which suggest this drying over the relevant time period. See, for example, Paltridge 2009 for sondes and John 2011 for satellite, both discussed in the climate chapter of The Arts of Truth with several footnotes.

    • ristvan, my response below is much narrower. In the larger scheme of things, if there is more TPW and a higher rate of transfer from surface water to TPW to cloud condensation to precipitation, there is a good chance that the entire nominal increase in energy of DWLWIR has been used up in increasing the rate of the hydrological cycle. I think this is like your number 2.

      In a dynamic system with spatial and temporal heterogeneity, there are many possibilities.

  10. A fascinating analysis and correlation. Much more relevant than the number of pirates. Any idea if this idea has been explored in scientific literature?

  11. Why is there more TPW?

    Because there are fewer clouds.

    Why fewer clouds?

    1) Fewer plankton-sourced cloud condensation nuclei
    and/or
    2) Fewer galactic cosmic ray-source cloud condensation nuclei

    If it is the first, we could be in part to blame. Plankton get their micronutrients from airborne dust. We increase ground cover through irrigation, CO2 fertilization, and tree planting so there is less dust going into the oceans.

    If it is the second, it is a natural cycle and we have to decide if trying to control it is a good idea.

    Either way, if it is a problem, it can be fixed through ocean iron fertilization: http://russgeorge.net/

    • 2) Fewer galactic cosmic ray-source cloud condensation nuclei
      Except that the cosmic ray flux has been increasing due to lower solar activity, so it is hardly your number 2)

      • Please help me out here Leif. If the cosmic ray flux increases, wouldn´t that create more cloud condensation nuclei, or did I not understand Svensmarks theori correct ?

      • vboring said:
        2) Fewer galactic cosmic ray-source cloud condensation nuclei
        could be the reason. I pointed out that solar activity has been decreasing and therefore cosmic rays have been increasing, contrary to vboring’s ‘explanation’.

      • Willis and mulder. Suggest exploring: Wild’s presentation with links to papers:
        Global Dimming and Brightening: Decadal changes in sunlight at the Earth’s surface Martin Wild Dec 2015 AGU Press Conf.
        Wild shows trends of declining sulfur and aerosols with corresponding “brightening” since ~ 1985.

        This may affect various aspects of environmental change
        (e.g., global warming, intensity of the global water cycle,

        Note the different SOx and brightening trends between northern and southern hemispheres.
        If you find similar differences in TPW that could further evidence for that cause.

    • vboring,

      Something else to consider: http://www.hardydiagnostics.com/articles/Ice-Forming-Bacteria.pdf

      Bacteria may well be more important than salt crystals, dust, and plankton for providing condensation nuclei. Yet, most people are probably unaware of the role that they play. They can also affect the temperature at which water freezes.

      Have humans had any influence on airborne bacteria? I’d say that there is a good chance that we have because of the widespread and common use of antibiotics, not only for ourselves, but for livestock.

    • the decrease in plankton could be due to increase in uv light reaching the oceans . uv light is a plankton killer.

  12. The analysis was done to correlate TPW to change in outgoing radiation over clear sky, which doesn’t really tell us anything about the big picture does it? For instance, the increase in TPW might very likely effect how often skies are clear and how much heat latent heat transfer there is.

  13. Hello Willis. I shall presume to give you a home work assignment.
    The U.S. Climate Reference Network (USCRN) has 10 years of data that can be put into a graph. I believe that Mr. Watts has a list of a few still functioning, well sited stations that have been in operation for over 100 years. So if a graph of those 100+ years were in the last 10 years to match the USCRN graph or not match, that would be interesting.

  14. Precipitable Water? We should be able to see a large red dot over the British Isles…

  15. I offer this recent image from the world of aviation weather services. Notice the prevalence of hail at high altitude in the hot, humid summertime. This illustrates the effect of higher water vapor content on CAPE and updraft velocity. Stronger updrafts >> more hail at altitude >> stronger upward heat delivery by liquid-to-solid-to-liquid-again phase change as hail forms, falls, and re-melts. I realize this image is for land, not oceans, but still the concept applies. In the global warming alarmist movement, in my opinion, the fixation on upwelling/downwelling radiative heat transfer distracts from the obvious power of phase change and vertical movement far above the surface. By the way, anyone can see this frequently updated aviation weather product without an account by going to www[dot]duats[dot]com.

    • power of phase change and vertical movement far above the surface.

      Even just the average change in entropy is significant ~9kJ/kg every night as temps drop from max to min.

  16. I found that it was TPW that I was measuring with my IR thermometer pointed straight up, and where we live we see large swings in humidity, which also shows up with the ir thermo (they just need a calibration from one of the gov IR stations).
    Here’s the impact of dew point/humidity on my local temps.

    The 97 El Nino altered the land based surface stations daily minimum temp, like a change in TPW would, and my climate sensitivity calculation show only one extra-tropic band with an increase in CS right when temps stepped up

    It might be possible to look at global TPW prior to this step, and after this step to see if the routing of this band of Atm PW changed it’s path altering the land based stations.

    The two possible effects are an increase in water vapor, or a reduction in clouds in this band that coincided with that El Nino.

      • What it appears to me is, first the oceans drive surface weather patterns, they both influence the path of weather, they also are the source of all of the water vapor that carries a lot of energy from the tropics to the poles, warming the surface while cooling along the way.

        The “step” in temps after the 97 El Nino, was a recorded increase in min temps, but only for the stations in the 20-30 N latitude band. I’m not sure (yet) whether this was from a change in dew point (the path TPW took changed), or a change in cloud patterns. This change in min temps were then propagated into the global temperature average.

        Why doesn’t anyone tell us that all of that temperature increase came from a change in the recorded min temp at stations in one region?

        Now one question I haven’t really answered is did these changes record an actual increase in the planets temperature, or whether there really was no warming, just the land change was measured, and the reciprocal cooling where this area of increased min temps moved from was not.

    • It might be possible to look at global TPW prior to this step, and after this step to see if the routing of this band of Atm PW changed it’s path altering the land based stations.

      I found a place to look at TPW, http://images.remss.com/cdr/climate_data_record_browse.html
      it’s easy to step a month at a time and watch the generation of water vapor, 98 does have a very strong band of high TPW at the equator, but it fades, and would not be the source of a long term change in minimum temps.

    • Steve, I was wondering the same thing. Can someone provide a succinct explanation of the difference?

  17. Thanks Willis. Not sure if I should have been…but I was startled by the incredibly tight correlation between the two. I mean, I understand the theory, but to see it so…starkly…was a surprise. Thanks again.

    rip

  18. Thermalization of terrestrial radiation explains why CO2 has no significant effect on climate. See ‘EPA mistake’ at http://globalclimatedrivers.blogspot.com

    The analysis at that link in no way rules out that increased water vapor could be contributing to warming. Water vapor has increased as a result of primarily, increased irrigation, cooling towers at electricity generating facilities, and increased burning of hydrogen rich fossil fuels. More water vapor in the atmosphere means more warming and possible acceleration of the hydrologic cycle.

    Adding a water vapor factor will certainly help explain the growing separation between measured average global temperatures and the expected temperature decline accompanying other factors as shown at Figure 17 at the link.

    The remaining issue is whether or not the water vapor driven warming will be significant enough to mitigate the otherwise expected cooling.

  19. And utilizing the relationship between water content and atmospheric absorption derived above, this indicates an increase in downwelling radiation of 3.3 W/m2 over the period.

    This leads us to a curious position where we have had a larger change in forcing from water vapor since 1988 than from all the other IPCC-listed forcings since 1750 … so where is the corresponding warming?

    That increase in DWLWIR occurs at the water surface, because that is where that water vapor came from.

    This is related to a question that I have often asked here, at ClimateEtc, and at RealClimate: What would actually happen at the water surface if the DWLWIR increased a little bit: some warming, some warming with increased evaporation; increased evaporation without warming? I think that the answer is not known. However, about 550 times as much energy is required to evaporate a gram of water as to warm a gram of water by 1 C, so even if there is a tiny increase in the evaporation rate, there can only be a tiny increase in temperature from an increase in 3.3 W/m^2.

    Thank you again for your essay.

  20. What happened to the Log (TPW) as shown in your Figure 3? You used linear(TPW) in your average gradient but the linear(TPW) gradient will reduce as TPW increases. What will that do to your calculations?

  21. To Willis: Thanks for your usual great mathematical analysis. However, unless I have misread your result, you assumed linearity between water vapor concentration and absorbance. This is roughly true for small absorbances (up to about 10%), but linearity fails badly above 50% absorbance. And most of the water vapor absorption lines in the bond-bending vibration band from 1200-2200 cm^-1 are almost completely saturated (near 100% absorption), so much so that the literature doesn’t even show spectra extending above 1500 or 1600 cm^-1 (for example, the MODTRAN spectrum available at https://en.wikipedia.org/wiki/Radiative_forcing , which closely models an actual spectrum at Guam, available at http://climateaudit.org/?p=2572 ). So increasing water vapor by 7% does not increase absorbance by 7% (I estimate this is a factor of 3 too high, if we include the partially saturated water vapor lines from 200-600 cm^-1 which correspond to changes in rotational states only in the ground vibrational state). Below 200 cm^-1, the MODTRAN curve shows a match with a 220 K Planck black body emission curve, since the average translational kinetic energy at 220 K is about the same as the energy of a 200 cm^-1 photon (so constant complete absorption is followed by complete emission, producing a Planck black body emission curve). This won’t change much with a small 4% change in water vapor. From 200-600 cm^-1, the actual spectrum departs from the 220 K black body curve, indicating that absorption is not 100% complete in the entire path length from the Earth’s surface to 10 km (where T = 220 K), so the Signal measured by the satellite looking downward is due to modified Beer-Lambert absorption (modified by a small emission term, following the Schwarzschild Equation), In another Comment re water vapor, I showed that even the 7% figure is too high: climate sensitivity on doubling CO2 must include the smaller TOA emission from the 62% of the Earth’s surface that is clouded (the MODTRAN curve was calculated for a cloudless surface; you can see that the TOA emission at 300 ppmv CO2 is 260 Wm^2, fully 20 W/m^2 higher than the mean value of 240 W/m^2 needed for energy balance. The TOA emission above the clouds must therefore be 228 W/m^2 at energy balance. From this, including the extra emission from the stratosphere on doubling CO2 (which means the Earth’s surface emission doesn’t have to increase as much for energy balance), climate sensitivity on doubling CO2 (not including water vapor and cloud feedbacks) is about 0.6 degrees, not 1 degree. This decreases the Clausius-Clapeyron increase in water vapor on doubling CO2 from 7% to 4%. And as others have pointed out, increasing water vapor is likely to increase cloud cover, which produces a net negative feedback. I estimate that this negative cloud feedback is about -0.2 degrees, which cancels most of the +0.27 degree positive water vapor feedback. The net result is that the 1 + 2 = 3 degree climate sensitivity estimate is about a factor of 5 too high. It is AT LEAST a factor of 2 too high, as the logarithmic relation between CO2 and warming means that an increase in CO2 from 280 to 400 ppmv is an increase by a factor of 2^0.5146 , which means 0.5146 doublings. If one doubling really produces 3 degrees warming, then 0.5146 doublings ought to produce 0.5146(3) = 1.54 degrees, which is almost a factor of 2 higher than the 0.8 +/- 0.1 degree in the historical record from 1850 to 2015. This is way outside the error bars of 0.8 +/- 0.1 degrees. This explains why all the fancy computer models based on a climate sensitivity of 3 degrees do not match the historic record, and why they are doomed to make even worse predictions of future warming, as saturation (diminishing returns) means even less warming on increasing CO2 linearly. For example, just look at the green and blue absorption curves in the MODTRAN computed spectra (which I assume are accurate): they are almost identical, except for a slight increase in areas at absorptions due to sidebands centered at 618 and 721 cm^-1. The stated radiative forcing of 3.39 W/m^2 is only 8.9% of the total CO2 absorption ditch, which corresponds to about 38 W/m^2. This is nowhere near the 100% increase in area expected on doubling CO2, if absorbance were linear, and not severely restricted by saturation effects.
    If I have misinterpreted your calculations, I’m sorry, but I do not normally spend much time reading WUWT articles carefully (most of the Comments raise valid points of disagreement).

  22. Is “precipitable water” a misnomer? (URL:http://glossary.ametsoc.org/wiki/Precipitable_water)

    The total mass of water is what results from the calculation based on the definition, which includes all phases, solid, liquid and gaseous.

    But “precipitable” refers to water that has not yet precipitated, whereas at any moment cloud cover is about 50%. And whether the water forming the clouds is liquid or solid, that water has already precipitated.

    Some water is in process of transit, falling as rain, hail or snow, or rising in updrafts.

    Thus, water, both in clouds and in transit, is not water vapour. Such water does not have water vapour’s radiative properties.

    So the jest by “son of mulder” may be apropos, that Willis has arrived at his result by failing to adjust the data.

    http://earthobservatory.nasa.gov/Features/CarbonHydrology/

    ***
    A related thought occurs to me. When water vapor precipitates and falls or rises in updrafts, does liquid water absorb CO2 and does solid water (snow and ice) entrain CO2 as it falls?

    Ice cores indicate that precipitated water does entrain CO2. But is the percentage entrained the same as the average percentage in the atmosphere? Even if the atmosphere is well-mixed, its constituent gases differ in their solubility in liquid water and possibly in their propensity to be entrained in solid water.
    ***

    In effect, precipitated water that sinks into soil or into the oceans would tend to reduce atmospheric CO2. Plants are a carbon sink because they take up this CO2.

    Recent trends in hydrologic balance have enhanced the terrestrial carbon sink in the United States
    https://earthscience.arc.nasa.gov/sge/ecocast/publications/pubs/nemani-grl.pdf

    Lovett, Richard A., June 7, 2002: Rain Might Be Leading Carbon Sink Factor, Science
    http://geo.arc.nasa.gov/sge/ecocast/publications/press/ScienceSummaryJune7.pdf

    My interest in the relationship between precipitation and carnon sinks arises from Murry Salby’s recent lecture. Having studied his textbook, I am inclined to take Dr Salby seriously, but I remain skeptical, always skeptical, whatever the claim.

    Salby, M. Physics of the atmosphere and climate 2012, CUP.

    • Frederick,

      You asked, “A related thought occurs to me. When water vapor precipitates and falls or rises in updrafts, does liquid water absorb CO2 and does solid water (snow and ice) entrain CO2 as it falls?”

      Clearly, water falling through the atmosphere absorbs CO2. The next time it rains, run outside with a piece of litmus paper and you should get a pH reading of about 5.5 from the raindrops. Obviously, snow entrains surface CO2, because that is how the CO2 values are derived from ice cores.

  23. Willis,

    You wrote:”And utilizing the relationship between water content and atmospheric absorption derived above, this indicates an increase in downwelling radiation of 3.3 W/m2 over the period.
    Now, please note that this 3.3 W/m2 increased forcing ”

    I am concerned that you are conflating three different quantities here. Increased absorption is not necessarily the same as increased down welling radiation. More significant is that it is not the same as forcing. Most of the absorption by water vapor is in the lower troposphere. But that has relatively little effect since vertical energy transfer in the lower troposphere is controlled by convection. What matters is the absorption at the altitude above which the atmosphere is optically thin (the “emission altitude”). That is much weaker, since there is so much less water vapor at those altitudes.

    But interesting, even if not quite correct.

  24. Very interesting stuff Willis. Clearly and succinctly presented.

    That slope turns out to be 62.8 / TPW. At the average TPW value in Figure 3 of 29 kg/m^2, this gives us a slope of 62.8 / 29.0 = 2.2 W/m2 increase in absorption per kg/m2 change in TPW.

    What you are doing here is taking the tangent of the log curve at the ‘average’ TPW point. I’m sure you realise this has limited applicability. The general effect is without doubt but the numbers could be less than you are finding.

    Also, although all the data are per sqr metre, the averaging will be unduly weighted to higher latitudes because the grid points are smaller and getting over counted. Presumably an area weighted average would be higher up the curve and have a lesser slope. That’s just some caveats on the actual values, the principal is correct.

    Alternatively maybe you could take the average of log(TPW) as the base point for the calculation.

    What is interesting is that the slope ( the positive w.v. feedback ) will be at lot less in the tropics and more in the cooler higher latitudes. It would be worth showing some numbers from both ends to get an idea of the variation due to the log curve.

    .

    This leads us to a curious position where we have had a larger change in forcing from water vapor since 1988 than from all the other IPCC-listed forcings since 1750 … so where is the corresponding warming?.

    Well clearly there are negative feedbacks. That is presumably what you are pointing to.

    The first and dominant -ve feedback is the Planck feedback. The absorbed outgoing LW is calculated as the difference of what estimated to leave the surface and what is measured as leaving at top of atmosphere (TOA). That estimation of surface emissions must be based on a Planck type calculation from SST. The drift to “a warmer world” pushes the data towards the right of the graph and lower WV slope. Less +ve f/b in a warmer world. ( Hardly a recipe for runaway warming. )

    So the next step, I suppose, is to get an estimation of the ‘average’ Planck feedback over that period and compare to the w.v. number.

  25. Willis, have you seen the New Scientist article about icing at v high altitude over the ITCZ? Interesting mechanisms being proposed for a phenomenon observed by pilots and dismissed as ‘impossible’. Now ATSB begining to think it could be a contributory factor in a number of crashes, including AirFrance over S Atlantic. I can send you a scan if you PM me.
    Only relevant to this post in that it relates to water transport and phase change in the tropics, but I do think you’d find it interesting.

  26. Firstly it looks like that the TPW values have different trends depending on the data sets. Here I have two figures. :

    Secondly the absorption of the upwelling LW radiation flux according to your Figure 3 is about 150 W/m2 in the clear sky. The emission rate of the clear sky is about 396 W/m2 at the surface, which would make the upwelling flux of 246 W/m2 (=396-150) at the TOA. Actually this flux rate is about 260 W/m2 for the clear sky. I cannot explain the difference.

  27. Willis: What a delightful mess! The science appears wrong, but the evidence appears compelling. Can I shed some light on this phenomena?

    In AIT, AL Gore makes the mistake of assuming that a correlation between CO2 and temperature in ice cores implies that CO2 causes warming. We should have learned from Big Al that correlation is not conclusive evidence of causation. The correlation between CO2 and temperature could be because increased CO2 causes warming, or because warming causes increased CO2, because both are responding in parallel to a third phenomena (such as orbital mechanics) or because of some combination of these possibilities.

    Above, you show a correlation between log(TPW) and absorption of OLR by the atmosphere. However, we still have three possibilities: 1) TPW increases atmospheric absorption – which is certainly logical since water vapor absorbs LWR. 2) Atmospheric absorption causes an increase in TPW – which is certainly logical since absorption causes warming and warmer air can hold more water vapor. 3) Both TPW and atmospheric absorption change in parallel in response to a third variable such as temperature. TPW obvious varies with temperature, but it isn’t immediately clear why atmospheric absorption should change in response to temperature, but we can come back to this issue. So far we have at least three hypotheses to consider. You considered only one.

    What is “atmospheric absorption”? You say: “Ramanathan proposed that the magnitude of the clear-sky atmospheric greenhouse effect could be measured as the amount of upwelling longwave radiation (ULR) from the surface that is absorbed by the atmosphere.” This is slightly incorrect; Ramanathan said that we can quantify the “greenhouse effect” (G) – not absorption – by:

    G = oT^4 – TOA

    where TOA is the LWR flux reaching space. However, Ramanathan never claimed that G was a measure of “atmospheric absorption”, because he knew that the atmosphere both absorbs and EMITS photons. It is well-known that about 90% of the photons reaching space are emitted by the atmosphere, not the surface. The flux reaching space (240 W/m2) is about 60% of the flux leaving the surface (390 W/m2), not the 10% one would expect from simple absorption. The greenhouse effect is the net result of absorption AND emission AND the decrease in temperature with altitude in the troposphere. If temperature didn’t decrease with altitude, the GHE wouldn’t exist. In the lower stratosphere – where temperature increases with attitude, rising CO2 causes cooling, not warming.

    Therefore, everywhere in this post that you refer to “atmospheric absorption” you should substitute the term “greenhouse effect” – at least if you cite Ramanathan as an authority. Your plots are of the GHE, not absorption. So let’s restate the three hypotheses above using the correct terminology: 1) TPW increases the greenhouse effect – which is certainly logical since water vapor is a “greenhouse gas”. 2) The greenhouse effect causes an increase in TPW – which is certainly logical since the greenhouse effect causes warming and warmer air can hold more water vapor. 3) Both TPW and the greenhouse effect change in parallel in response to a third variable such as temperature. Since the GHE involves emission and emission increases with temperature, hypothesis 3) is looking more attractive.

    Since you have plotted the greenhouse effect vs. log(TPW), you can not longer say that your plot “is experimental validation of the IPCC’s statement about the underlying physics, viz: The radiative effect of absorption by water vapour is roughly proportional to the logarithm of its concentration,” The IPCC’s statement is correct, but you have not plotted absorption vs concentration. The proper place to determine the relationship between water vapor concentration and absorption is in a laboratory spectrophotometer, not the atmosphere.

    You also said: “That is to say, we get a bit over two watts per square metre of increased absorption for every additional kilo of atmospheric water per square metre.” Unfortunately, the x-axis of your plot is the log of the TPW. You could conclude that the G increases about 50 W/m2 for every doubling of TPW.

    In the next section, you confuse atmospheric absorption with “forcing”. If you use the right term – the greenhouse effect – and remember that forcing is also called the enhanced greenhouse effect – things are clearer.

    Unfortunately, none of my complaints about your science provide an explanation for the fairly linear plot you show in Figure 3. To be continued.

  28. When are you people going to get over ‘upwelliing radiation’…?
    Water Vapour physically TRANSPORTS heat from the surface to the upper atmosphere.

    • Yes, I do get rather annoyed about talk of radiation “welling” up and down. Radiation does not well, it radiates: hence the name. Moist air is less dense than moist air so the could be called upwelling, but not IR radiation.

      Upward and downward or incoming and outgoing would be better adjectives for radiation or the energy flux due to successive absorption and re-emission of LWIR

      • Upward and downward or incoming and outgoing would be better adjectives for radiation or the energy flux due to successive absorption and re-emission of LWIR

        Interestingly, while a normal IR Thermometer doesn’t measure the IR from Co2, it is suppose to do a good job measuring the TPW with a calibration, but in either case it’s cold, clear sky temps are 70 or 80 F colder than the surface on hot humid days, and can be over 100F colder on cold dry days. And it’s like this all the time under clear skies.
        Now clouds can be near air temp.

      • Greg,

        Upwelling came from the same people who gave us the gift that keeps giving, ocean acidification. What, do you expect accuracy from those working in the field of virtual reality?

    • Charles,
      The conflation of energy transported by photons (surface radiation, GHG emissions, etc.) and energy transported by matter (latent heat, thermals, etc.) into a single pool (upwelling ‘radiation’) seems to be an invention of Trenberth where he needed wiggle room in the radiant balance in order to support his preconceptions, or more precisely, to obfuscate reality. Only the energy transported by photons matters for the radiative balance. We are only concerned with the LTE response, so for non gaseous matter in the atmosphere (primarily water) to be in LTE, it must be absorbing the same amount of energy that it’s emitting, thus there can be no NET conversion of the energy transported by matter with the energy transported by matter. Otherwise, the matter in the atmosphere would warm or cool without bound.

      • CO2isnotevil wrote: “there can be no NET conversion of the energy transported by matter with the energy transported by photons”.

        Nonsense! Matter emits and absorbs photons. A CO2 molecule in the atmosphere can be excited by a collision or by absorbing a photon of LWR arriving from above or below. The CO2 molecule doesn’t remember how excitation occurred, it simply emits a photon in a random direction after an average of 1 second – UNLESS it is relaxed by a collision before emission occurs. In the troposphere and lower stratosphere, collisional excitation and relaxation occurs thousands of times more often than emission or absorption of a photon. When a photon is emitted, that photon doesn’t carry any information that will allow a molecule with which it collides to “decide” whether to absorb or reflect/scatter that particular photon

        Following the laws of QM, the net result of these processes is a flow of heat (the NET result of all transfer of energy) from hot to cold.

        If you sum up all of the fluxes in the Trenberth energy balance diagram, the net flux of energy is always from hot to cold: between sun and surface, between sun and atmosphere, between sun and space, between surface and atmosphere, between earth and space, and between atmosphere and space.

        Most of these are two-way fluxes: 1) In some cases, we can easily measure the energy fluxes in both directions – for example via radiation. 2) In other cases, we ignore the flux in one direction because it is so small – the OLR emitted by the atmosphere that is absorbed by the sun is negligible compared with the SWR traveling in the opposite direction. 3) In some cases, we often ignore the flux in one direction. When air is saturated with water vapor (100% relative humidity), water molecules still continue to escape from surface of the water at the normal rate, but water vapor is returning to liquid water at the same rate, producing no net evaporation. When relative humidity is 80% (as it is over the ocean), the rate that water molecules return from vapor to liquid is 80% of the rate at which they escape from water. The 80 W/m2 of latent heat leaving the surface in Trenberth’s diagram is really about 400 W/m2 of latent heat in water molecules evaporating and 320 W/m2 of latent heat in water vapor returning without condensing. 4) In the case of conduction, we can’t measure the amount of heat transferred by individual collisions between molecules on the surface and molecules in the atmosphere, but we know the net flux is from the [usually] hotter surface to the [usually] cooler atmosphere adjacent to the surface.

      • Frank,
        Yes, matter emits and absorbs photons, but you missed the importance of the ‘and’. For matter to be in LTE, it must be absorbing the same as its emitting, thus has no NET effect on its environment.

        The idea that energy moves from hot to cold is mostly relevant for matter in contact and not photons. A photon has no idea whether where it will be absorbed is hotter or colder than where it was emitted. This concept of energy flowing from hot to cold tends to be a non sequitur that interferes with ones ability to understand how the RADIANT balance works. For example, clouds and GHG’s, which are colder than the surface radiate photons back to the surface making it warmer than it would be otherwise.

        Consider the 2 body system where a hot radiating body and a cold radiating body are each is affected by the radiation of the other, in LTE, both will have a temperature of 0K having radiated all their energy away. Can you see the influence of the environment? Understanding the Earth’s climate is at least a 4 body problem, the Sun, the surface, the atmosphere and space (the environment) where 2 of these bodies are coupled and the other 2 are independent, one of which is the source of all input energy.

        Yes, Trenberth’s numbers add up, but it you look carefully, all the non radiant power leaving the surface (latent heat, thermals, etc) is returned back to the surface since non radiant power can not leave the planet, only photons can. Trenberth muddies the waters by calling the return of non radiant power ‘back radiation’ when there is not a single photon involved and this is the nature of his bogus conflation. Most of the latent heat is returned back to the surface as liquid water since as water condenses in the atmosphere, the latent heat of the phase change warms the water it condenses upon which then falls as rain. Whatever latent heat from evaporation that is not directly returned to the surface as liquid water supplies the power driving the heat engine producing weather ultimately still returns that energy to the surface. It should also be clear that whatever effect the non radiant power has, it’s already accounted for in the surface temperature and its required radiance per the SB LAW.

        In fact, the radiative balance excluding non radiant power balances even better with no ambiguity and no guessing required and what we find is that 1/2 of the radiant energy emitted by the surface and absorbed by the atmosphere by clouds and GHG’s is ultimately emitted to space while the remainder is returned to the surface. The data supports this and confirms the requirement of geometry which also requires the 50/50 split since energy enters the atmosphere across half the area that it can leave from.

        One final point is that on average, about 1 m of rain per m^2 per year falls, meaning 1 m of water (1E3 kg) per m^2 evaporates per year. Dividing 1E3 kg by 31.5 E6 seconds per year gives us an average evaporation rate of .0000317 kg/sec. At a latent heat of 2265 kj/kg, the average rate of latent heat from evaporation is 78 joules/sec*m^2 or about 80 W/m^2. Where does your 400 W/m^2 value come from?

      • CO2isnotevil wrote: “For matter to be in LTE, it must be absorbing the same as its emitting, thus has no NET effect on its environment.”

        This is wrong. A group of molecules in Local thermodynamic Equilibrium (LTW) means that molecules are exchanging energy via collisions with each other much faster than energy is entering or leaving the group (for example, via emission or absorption of a photon). In that case, the group has a well-defined mean kinetic energy and therefore a thermodynamic temperature. That temperature can be used in the Boltzmann distribution to predict what fraction of the molecules are in an excited state and therefore capable of emitting a photon. Where LTE exists, the rate of emission of photons depends only on the local temperature and not on the rate excited states are created by absorption of a photon. The troposphere and lower stratosphere are in LTE. The upper atmosphere is not. Infrequent collisions can relax excited states more slowly than they are created. (LED’s, fluorescent lights and lasers are not in LTE, which is what allows us to get light without much heat from them.) See Grant Petty’s book on Atmospheric Radiation.

        When radiation is in thermodynamic equilibrium with any material it is passing through, the rate of absorption and (temperature-dependent) emission are equal. The postulates used to derive Planck’s Law are quantized oscillators, radiation in equilibrium with them, and the Boltzmann distribution. Therefore radiation in equilibrium with its surroundings will always have blackbody spectral intensity at the wavelengths that are absorbing and emitting fast enough. At some altitudes and some wavelengths (not the atmospheric window), the radiation passing through is in thermodynamic equilibrium and therefore has blackbody intensity at the wavelength. As the atmosphere thins with altitude, all wavelengths eventually lose equilibrium.

        CO2isnotevil wrote: “Yes, Trenberth’s numbers add up, but it you look carefully, all the non radiant power leaving the surface (latent heat, thermals, etc) is returned back to the surface since non radiant power can not leave the planet, only photons can. Trenberth muddies the waters by calling the return of non radiant power ‘back radiation’ when there is not a single photon involved and this is the nature of his bogus conflation.”

        This is not true. If the sun emitted more SWR, the surface would receive more SWR, warm and lose more latent heat via evaporation. That latent heat will warm the atmosphere when the water condenses. We tend to confuse transfer of energy and transfer of heat. Trenberth’s diagram covers transfer of energy. Heat is the NET transfer of energy between to locations. Energy is transferred from water to air in a sealed jar half filled with water every time a water molecule escapes the surface. No heat is transferred because the reverse process is equally fast at saturation. It is easier to avoid mistakes by never using the term heat and only discussing how much energy goes where.

        80 W/m2 is the energy in the NET flux of water to an 80% saturated atmosphere. About 4 of 5 molecules that evaporate return to liquid water without condensing into rain drops. They are initially trapped in a thin layer of atmosphere adhering to the surface. That is why wind speed has a big effect on the rate of evaporation – it turbulently mixed the saturated layer with the boundary layer. Over the ocean, the boundary layer is about 80% saturated. If totally dry air where overlaying the ocean, the NET rate of evaporation would temporarily increase 5-fold. Without turbulent mixing, however, diffusion isn’t fast enough to let many molecules escape. My point was that all forms of energy are transported in two directions, even latent heat. Trenberth’s diagram shows a two-way flux only for LWR – making it appear to be the ONLY flux in both directions.

    • do NOT go to jail; collect a cigar in passing.

      The heat physically transported (convection) to the upper atmosphere, is mostly the 590 cal/gm of latent heat (of evaporation).

      As that moist air rises, it is cooled by the upper air, because of the lapse rate, until it cools to the dew point, and somewhere around there, depending on the availability of a substrate to CONDENSE ON (NOT Precipitate) it has lost all of the latent heat tpo the cooler air, and it condenses into water droplets, or else it looses another 80 calories per gram, and becomes ice crystals.

      Once in condensed form (liquid or solid) it is then quite capable of radiating LWIR , thermal radiation isotropically, about half of which escapes to space.

      G

      • Think PV=nRT (perfect gas Law). What we measure as temperature in a gas is mostly the result of collisions of molecules. When a water vapor molecule collides with an air molecule energy is transfered between them. This transfer does deviate from the perfect gas law resulting in a wet adiabat. While this transfer of energy is going on, water molecules are radiating in all directions and air molecules are not. In thunderstorms, Most of the transfer of energy is upward by convection. As to the rate of transfer, it is mostly rapidly upward by convection of air, water vapor, water, plus a tiny amount of CO2. Most radiative energy transfer in clouds is retained within the clouds Think line-of sight and fast as light..

      • GES,

        Close, but no seegar! It isn’ t cooled by the upper air, it IS the upper air. The lapse rate exists because of the ideal gas law, i.e. PV = nRT, or for this situation, more appropriately, T = PV/nR. That is, as the convecting air mass rises, it experiences less confining pressure, expands, and decreases in temperature. The lapse rate is modified from the ideal dry gas by the presence of water vapor, which changes state when it gets cold enough.

    • Charles Nelson,

      Water vapor can’t physically transfer latent heat from the surface to the upper atmosphere without an unstable lapse rate. Without an unstable lapse rate, moist air rises, expands and cools slightly, is more dense than the surrounding air, and sinks.

      The only way water vapor can physically transfer latent heat from the surface to the upper atmosphere is for the upper atmosphere to RADIATIVELY cool to space – past whatever GHGs are in the upper atmosphere. If convection transfers more latent heat to the upper atmosphere than can escape to space by radiation, convection ceases.

      FWIW – not much IMO – AOGCMs show a slowing of “overturning” of the atmosphere associated with GHG-mediated warming. One can divide total precipitable water vapor in the atmosphere (about 3 cm) by the average rainfall (about 3 mm/day) and discover that the average atmospheric lifetime of a water molecule that evaporates from the surface is about 10 days. (9 days if I look up the real numbers.) Although my intuition rebels at the thought, models show the average lifetime of a water vapor molecule in the atmosphere increasing as the surface warms, because the upper atmosphere can’t radiatively cool fast enough.

  29. Willis, you write:
    “And utilizing the relationship between water content and atmospheric absorption derived above, this indicates an increase in downwelling radiation of 3.3 W/m2 over the period.

    Now, please note that this 3.3 W/m2 increased forcing from the long-term increase in water vapor since 1988 is in addition to the IPCC-claimed 2.3 W/m2 increase since 1750 in all other forcings (see Figure SPM-5, IPCC AR5 SPM). The IPCC counts as forcings the long-term changes in the following: CO2, CH4, Halocarbons, N2O, CO, NMVOC, NOx, mineral dust, SO2, NH3, organic carbon, black carbon, land use, and changes in solar irradiance … but not the long-term changes in water vapor.

    This leads us to a curious position where we have had a larger change in forcing from water vapor since 1988 than from all the other IPCC-listed forcings since 1750 … so where is the corresponding warming?”

    Just as peculiar: Where is that increase in “downwelling longwave radiation” that everyone’s keep talking about and thus apparently assumes is there? The CERES data only goes back to March 2000, but it shows no sign of any general increase globally, until that final 2015 Niño spike, that is:

    In fact, the mean global “DWLWIR flux” actually weakened since 2000, relative to tropospheric temps:

  30. http://www.engineeringtoolbox.com/evaporation-water-surface-d_690.html

    using a swimming pool calculator, I get a quick result of 220 watts/m^2 for the evaporation of water (221.2kw/1000m^2). Surely that is a lot more energy being carried skyward, where it can radiate to space, than the piddly 2 or 3 watts/m^2 for GHG.

    Whenever I see the cartoon graph for the earth’s energy budget I’m amazed how little energy is attributed to evaporation. Try and keep a pool warm without a pool cover.

    • Take an early morning swim in a placid lake after a clear sky, no-wind night and you can actually feel the heat loss at the surface. How much energy is radiated in an eight hiur period to cool a couple of centimeters of water by between 5 and 10 degrees? I don’t think CO2 has much of a relative effect in that process. On the other hand, when the humidity is high, a thin fog layer will form just above the surface of a calm lake. Energy is being transported from that moisture near the surface, to the surface of the water, and then transported to space by radiation.

    • using a swimming pool calculator, I get a quick result of 220 watts/m^2 for the evaporation of water (221.2kw/1000m^2). Surely that is a lot more energy being carried skyward, where it can radiate to space, than the piddly 2 or 3 watts/m^2 for GHG.
      Whenever I see the cartoon graph for the earth’s energy budget I’m amazed how little energy is attributed to evaporation. Try and keep a pool warm without a pool cover.

      I calculate the average for what’s measured at surface station, between the days max temp to the following morning min temp, the average loss of entropy in the atm is 9kJ/kg, the cooling of just one cubic meter over night counteracts the entire forcing from Co2, and there are a lot of cubic meters of atm stacked up in the air column, the shear amount of energy exchanged daily at every point on this planet far exceeds the minor forcing from Co2, this is why it doesn’t show up in the temperature record.

      The regulating mechanisms that controls night time cooling rates are all triggered by air temp approaching dew point. Even if this point is reached slightly later during the night, it’s still reached, and it then still slows cooling. Up till then, I’ve seen 4 or more degrees F cooling per hour, per hour.

    • ferdberple,

      It is easy in Phoenix! When I lived there my pool was 96 degrees F in August.

    • Ferdberple: “Whenever I see the cartoon graph for the earth’s energy budget I’m amazed how little energy is attributed to evaporation.”

      Ferdberple, do you know how that evaporation (cartoon graph) is calculated? A bigger temperature gradient between warm and cold area’s – for example because the tropics would extend by warming and the temperature at the south pole remains constant – will result in stronger winds with an exponential effect on evaporation. Do you know whether we can find this back in the models?

    • ferdberple,
      “Whenever I see the cartoon graph for the earth’s energy budget I’m amazed how little energy is attributed to evaporation.”

      Evaporative heat can be calculated straight forward from the precipitation; what goes up must come down (mass balance). See this comment:
      https://wattsupwiththat.com/2014/01/17/nasa-revises-earths-radiation-budget-diminishing-some-of-trenberths-claims-in-the-process/#comment-1540077
      Based on average global precipitation of 2.6 kg/m2.day (=2.6 mm/day), average global evaporative heat should amount 68 W/m2.

      Willis finds in the main post:
      “Next, there is a clear trend in the TPW data. The total change over the period is ~ 1.5 kg/m^2, centered around the long-term mean of 28.7 kg/m^2.”

      This is an increase of ≈5% during the period 1998-2015.
      Assuming that the average residence time of water in the atmosphere has meanwhile not changed (average velocity, average distance traveled of water molecules going up and down through the atmosphere) then precipitation should have increased with the same ≈5%, i.e. 0.05 * 2.6 = 0.13 mm/day.

      This approximately coincides with the findings of Wild, as earlier referenced by David L. Hagen above:
      https://fallmeeting.agu.org/2015/files/2015/12/Wild-slides.pdf (slide 27).
      Here a precipitation increase is found of ≈35 mm/year ≈0.1 mm/day (NH land), period 1998-2010.

      As the relation between average global precipitation and average global evaporative heat is linear, the latter should have increased by the same ≈5%, i.e. 0.05 * 68 = 3.4 W/m2.
      This more or less equals the increase in downwelling radiation of 3.3 W/m2 over the reference period, which Willis has found.

  31. Willis, thanks! You say/prove, and it’s sounded reasonable to me for about 15 years:

    Next, there is a clear trend in the TPW data. The total change over the period is ~ 1.5 kg/m^2, centered around the long-term mean of 28.7 kg/m^2.

    And utilizing the relationship between water content and atmospheric absorption derived above, this indicates an increase in downwelling radiation of 3.3 W/m2 over the period.

    That is, I’ve been asking the same question for ~15 years, “Why would water vapor need CO2 to do what it could already do according to the same ‘ghg’ mechanism claimed for CO2?” – Given that there is a source for water vapor bigger than the Oceans, and that water vapor concentrations should increase with any level of the ‘right’ emitted long wave radiation, to a limit which empirically turns out to be ~logarithmic.

    I’m not even saying that the “ghg” mechanism is or isn’t warming the atmosphere. And I’m ignoring your Tropical Thunderstorm Mechanism even though it sounds like it acts to feed back from the surface up, on changes in Solar input either way.

    Likewise, why would CO2 suddenly be able to invoke “increased water vapor” to do what water vapor should have already done without CO2?

    In other words, I’m still thinking I had it hypothetically figured out ~15 years ago but still want to know what is wrong with my thinking or interpretation of what you’ve shown in this Post.

    • That is, I’ve been asking the same question for ~15 years, “Why would water vapor need CO2 to do what it could already do according to the same ‘ghg’ mechanism claimed for CO2?”

      This is what positive feedback would do, a repeating cycle of warmer air evaporating more water, warming the air.
      Obviously there is no sustained positive feedback, or we would not be here to ask this question.

      The more I dig, the more regulating effects I find.

      • “The more I dig, the more regulating effects I find.”

        All I knew about climate ~16 years ago was that the fact that it changed is already in the definition of “climate”, otherwise why even talk about it? And that there are different climates already existing on earth, and were in geologic history. But I didn’t expect many “scientists” in a big “study” studying “climate change” to totally abandon “science”!

  32. Crispin in Waterloo
    July 26, 2016 at 12:40 am

    Is the aircraft pressurized, or unpressurized? If pressurized, do you know the pressurization schedule / profile for descent?

    Many modern pressurized cabins Max at about 9 PSI differential at altitude, or approximate a 7000 foot ambient atmosphere, and gradually reduce differential pressure to achieve destination field elevation at at touchdown. Pressurization scheduling is contoured to minimize rate of cabin pressure change within the planned origin / cruise / destination elevation / altitude profile.

  33. I wonder about the reflection of light by water droplets . . light doesn’t strike clouds as if real “objects”, it strikes water droplets. I “discovered” years ago that if one looks up into the blue, on a clear dry summer day, one can see (what I assume to be) water droplets in the air . .

    And years ago I “discovered” that tiny glass beads are added to the paint used to make road lines . . the round white (en mass) beads especially reflect light back at the source, not scattering it equally in all directions . .

    So I’m wondering about the reflection of light by zillions of tiny water droplets, right back at the sun, which we would not see as we do clouds . .

    • JK,

      Clouds come close to being a Lambertian reflector, meaning that it has diffuse reflectance, reflecting nearly equally in all directions. That is to say, no matter where your viewing position is (except directly underneath a cloud) the cloud will appear of equal brightness.

      • Clyde,

        Thanks . . I’m wondering about individual water “particles” of a very small size . . in the general atmosphere, especially up high, where some might act as directional reflectors . . collectively generating a low level “sheen” that increases with increasing total water vapor . .

      • JK,

        All light impinging on a droplet will be both reflected and refracted inward. Clouds are diffuse reflectors not just because of the large number of water droplets, but because the drops can be slightly different shapes and when a light ray enters, you can get total internal reflection. Where a ray exits will be affected by the shape of the droplet and where the ray enters. Because the water is clear and the droplets very small, almost all the intensity is preserved; the intensity decays slowly. But, that means that while the droplets in the outer regions have similar sources of light (the sun), those deeper in the cloud are getting the multiple reflections and internal refractions from all possible angles.

        You would probably be more likely to get directional reflectance with ice clouds, if the platey crystals have a parallel or sub-parallel alignment.

      • Clyde,

        “but because the drops can be slightly different shapes and when a light ray enters, you can get total internal reflection.”

        Yes, that’s what I figured . . and I’m wondering about very small “particles”, in general, of which some might be close enough to spherical to act as those glass beads do. Other shaped particles would (theoretically) not cancel/nullify such a unidirectional effect, so it seems to me it might be a “negative feedback” . . peerhaps of some small significance anyway.

        “You would probably be more likely to get directional reflectance with ice clouds, if the platey crystals have a parallel or sub-parallel alignment.”

        I just so happen to have posted this comment on another post here, two weeks ago;

        ‘Settled Science: Clusters of small satellites could help estimate Earth’s reflected energy’

        “I’m a nobody who had read about these matters for about a decade, and there is this idea that has at times rattles around in my ignorant skull . .

        Water molecules at the edge of space, being “aligned” into sheet-like thin layers, sometimes, by magnetic fields, which creates a slight “sheen”, sometimes, deflecting some light in some places . .

        So, please abuse me of my affliction if it’s silly, experts ; ) “

      • JK,

        To quote Sean Connery, “Never say never!” But, other than wind, I’m personally unacquainted with anything that might align small water droplets or ice crystals. And, if you are talking about the upper reaches of the stratosphere, I wouldn’t expect much water and I would expect it to be frozen.

    • ” I “discovered” years ago that if one looks up into the blue, on a clear dry summer day, one can see (what I assume to be) water droplets in the air . . ”

      Ever since I first started using Coleman Lanterns for indoor light at night in a cabin I have without electricity, I’ve been able to see wave action coming from its light: small dark and bright rectangles lined up amidst a general “waving” emission [roughly, since I’m not using a Coleman right now]. But if I look at clouds moving against or compared to a “fixed” mountain ridge, I see the clouds start and stop, which I think is due to the “saccadic” [searching] movement done automatically by the 6 muscles which control eye movement, so I see the clouds as starting and stopping. But why would my eyes be searching for light waves in particular? Maybe it’s just the light source’s light:

      Anyway my point is that the Physics I’m seeing here at WUWT is amazing, with many teachables! I took only one Physics Course in undergrad, and it was taught by a guy nick-named “The Vector” because his head resembled one. Not that he was bad looking, but because he also acted like one. Once I saw him take ~3 steps sideways to the left and then 10 directly backward. He disappeared into the storage room and we heard a loud crash.

      [Digression: I don’t know how I managed to get as high as a “B” in his Class, because I could never figure out where these Equations came from and nobody even talked about that; when I should have just taken them as “Well, there they are, go ahead on with your bad self!”

      So I did get high marks when I realized that in answer to any question I didn’t quite get, I should simply write down everything I know and hope for the best. Once I got an “A+” in an English Class because I knew a lot about the past Authors, but never worried about placing them in an Age or time period! The Final’s question asked us to “Pick 4 from a certain time period and discuss them.” I got lucky.

      And in the one, and highest level Latin Course offered, that I took, I got another A+. Because I knew the Prof was quite a Romantic in his own right, so I was successful in guessing what the passage was from Homer’s Illiad that he would have us translate by “sight” unseen. I’d narrowed it down to two via an English translation of “The Illiad”. The test question was on “Rumors flying on winged something, etc.”

      Ah, “The Art Of The Deal”! But:

      Once I got a “C” in Microbiology, when on the Mid-Term I’d scored a “60”, and the level for an “A” was only “above 40”. I couldn’t believe my eyes then nor my Final “C”. Then I got an “Honors” in NeuroAnatomy because I lucked onto the Internal Capsule when I was dissecting my Brain. Finally when they asked us at the end of Med School to participate by voting for the 10 best Students in our Class, I voted for the 10 least likely, and 5 of them made it! I’d worked with most of the 10 so I excluded the best, most of whom also made it!. After the very first test, where I scored in the “Upper Third”, I relaxed down to a slow burn for me for the remainder and ended up “In the Middle”. But I was in the top ~3%, 13th, of my Under Grad Class with ‘only’ a 3.57 ave., when I never even thought about rankings and only learned of it ~20 yrs later when I had to get a Transcript. I’ve still got only a .357 Magnum, but it also shoots .38’s, so that must be better?]

      • I read somewhere that some some eyes (of frogs when placed into utterly darkened test chambers), can react to individual photons . .

  34. Well, water molecules are polar, so one wonders if magnetic fields might have (under the right conditions) an aligning effect . . Thing is, there would not need to be a particularly persistent or especially widespread effect along the lines of what I’ve mentioned, since it would (theoretically) be “unopposed” by other effects . . and according to JK’s first law of physicality: An unopposed force is infinite ; )

  35. WIllis: As discussed above, you have plotted Ramanathan’s measure of the greenhouse effect (G = oT^4 – TOA) vs log(TPW), not absorption vs log(TPW). I find it fascinating that you have discovered a LINEAR relationship between the greenhouse effect and log(TPW).

    Since the GHE is a complicated phenomena involving absorption (which is concentration-dependent and concentration varies with altitude) and emission (which is concentration-, temperature-, and altitude-dependent) and lapse rate, and involves two major competing GHGs, there may not be a simple explanation for the linear relationship in your Figure 3. I decided to look at results from MODTRAN, which takes all of these factors into account. Using typical tropical, US Standard, and subarctic winter atmospheric soundings with various surface temperature offsets (and constant humidity for the offsets and default GHGs including 400 ppm CO2), I calculated TOA OLR and then G for a dozen different surface temperatures. G rises from 39 W/m2 at 249 K to 186 W/m2 at 304 K. G increases an average of about 2.77 W/m2/K of surface temperature, but there is modest upward curvature. If I plot logG vs Ts, the curvature disappears and R2 rose to 0.99 for a linear fit.

    TPW obviously usually increases with surface temperature. One can calculate a saturated water vapor pressure for each surface temperature, and plot G vs the log of saturated vapor pressure. The relationship is fairly linear, but more curved than the one in your Figure 3. The relationship between TPW and saturated water vapor pressure at the surface isn’t as simple as I first imagined. MODTRAN gives values for the amount of water vapor at each altitude for various surface temperatures and atmospheric soundings, but integrating them will take some time.

    Photons absorbed by water vapor escape to space only when they are emitted from high enough in the atmosphere to avoid absorption by water vapor on the path to space. If the average photon at a given wavelength reaching space is emitted by a water molecule 4 km above the surface, it will be about 26 K colder than at the surface and the decreased spectral intensity and therefore G will reflect this temperature difference. At a less strongly absorbed wavelength, the average escaping photon could be emitted from 2 km where it is only 13 K colder than at the surface. G will be smaller at the weakly absorbed wavelength than the strongly absorbed one. Increasing TPW raises the height from which the average photon escaping to space is emitted. This is the conventional explanation for the greenhouse effect. As before, this still doesn’t explain a LINEAR relationship between G and the log of TPW.

    • Dear Mr. Eschenbach,

      I don’t have the answer to your question, “so where is the corresponding warming?” A better question might be, “With the concentration of CO2 and water vapor continuing to increase, why the global cooling?

      See – GFS UM CCI Monthly Global Temperature Anomaly Trends 2001 – 2015

      Clearly Global Cloud cover has an inverse effect on temperature.

      See – HADCrut4 Global Average Temperature Cloud Cover

      Sorry, this post would not accept copies of these 2 charts.

      If I could change the subject, with respect to the Modtran Results Regression Equation

      Forcing = 2.94 Log2(CO2) + 233.6

      Which I believe you referenced around 2006, could you please provide or refer me to the source for this expression?

      Thank You.
      Bill Van Brunt

  36. Willis: I’m still finding your observation in this post fascinating. As discussed above, you have plotted Ramanathan’s measure of the greenhouse effect (G) vs. logTPW, where

    G = oTs^4 – TOA

    where TOA is OLR at the TOA for cloudless skies. The GHE often discussed in terms of an effective emission altitude (h) from which the average photon escapes to space. If we model emission to space as blackbody radiation emitted from height h with temperature Th

    G = oTs^4 – oTh^4

    Substituting Th = Ts – 6.5h, expanding, neglecting terms with Ts^2 or lower affords:

    G = (4*6.5*o*Ts^3)*h

    I can plug the data I got on how G varies with surface temperature from Modtran and calculate how the effective emission altitude (h) varies with surface temperature: h = 4.3 km for a clear tropical atmosphere above a surface at 300K, 3.7 km for the US Standard atmosphere above a surface at 288 K and 2.0 km for a sub-arctic winter atmosphere above a surface at 257 K.

    Next we need to distinguish between:

    1) absorbance (A) or optical thickness (tau) – which is proportional to the AMOUNT of absorbing molecule present). In the atmosphere, technically A = Int[n(z) ο.dz], where this o is the absorption coefficient) and n(z) is the density of water molecules at altitude z. TPW is the integral of n(z).dz from the surface to space. A = o*TWP. Log(TWP) = log(A) – log(o)

    2) absorption – the ENERGY absorbed. G (W/m2) is energy, the net result of absorption and emission of energy.

    3) Absorptance (absorptivity) – a dimensionless ratio between 0 and 1 which is equal to 1 – transmittance or 1- I/I_0. When we say that 90% of the photons emitted by the surface are absorbed before they can reach space, we are talking about absorptance. Absorptance and transmittance are confusing concepts when emission can make transmittance formally appear to be greater than 1. T = exp(-A) in physics and 10^(-A) in chemistry. If we use the chemistry definition, A = -logT. LogA = log(-logT). There is no point in going further down this path.

    TPW is the amount of adsorbing water and therefore proportional to absorbance (A) or (tau). log(TPW) is logA + a constant. Neither TPW nor logTPW are measures of absorption (or emission), the factors important to G.

    Your fascinating Figure 3 shows that log(TPW) is proportional to G. I have shown (via an imperfect blackbody model), that G should be proportional to the effective emission altitude for photons escaping to space, but is also proportional to Ts^3. Combining:

    G = (4*6.5*o)*h*Ts^3 = log(TPW) + C = logA + C’

    where C and C’ are constants. I was hoping to show that the effective emission height (h) was proportional to the absorbance or optical thickness of the water vapor in the atmosphere (most of which lies below the effective emission altitude). This is not true. h does not depend in any simple way on TPW or log(TPW) or the optical thickness of the water in the atmosphere which is proportional to TPW. As best I can tell, you have demonstrated a purely empirical relationship which doesn’t have a simple fundamental explanation. G is the result of absorption and emission (which depends on temperature and therefore lapse rate).

    • optical thickness of the water vapor in the atmosphere

      I think you need to look at it as compared to Rel Humidity. I’m trying to figure out why cooling slows late at night when rel humidity gets in the upper 80’s and 90’s %.
      And I think it’s an optical (I ruled out enthalpy for the change in rate to my satisfaction for those keeping score).

    • Mark, Willis,
      Mark: “I can plug the data I got on how G varies with surface temperature from Modtran and calculate how the effective emission altitude (h) varies with surface temperature: h = 4.3 km for a clear tropical atmosphere”

      WR: I try to imagine what this means for a high (till 20 km) rising tropical thundercloud. Am I right, that all the condensation energy which is released at a height above 4.3 km – if not transported down by a downdraft –is prone to emitting to space?

      In that case clouds towering above local emission altitudes (h) do the work (as you always have said, Willis) They break as a rocket through the energy retaining shield and release the surface energy to space. The more thunderclouds in the tropics – and I think the more low pressure area’s in the moderate latitudes – the more energy disappears to space.

      Evaporation rises exponentially with the rise of wind speed. Wind speed is dependent on the pressure gradient and this pressure gradient is connected to the temperature gradient. The temperature gradient rises as the rising temperatures in the warmer area’s are combined with continuing low temperatures somewhere else (as in Antarctica).

      If this all is right, the quantity of [the forming of] clouds above (h) is worth to be measured. And this can be linked to any extra energy reaching the surface. Then this feedback mechanism is known.

    • Surely, if 98% of the atmosphere (Nitrogen and Oxygen) doesn’t do IR then G must be proportional to TPW*. And you see this in the relationship between wet and dry weather systems and climate zones. If CO2 is well mixed, then you are only left with H2O vapour variations (O-4%).

      If the vast bulk of the atmosphere can only warm or cool by collision with GHGs it isn’t hard to imagine which is the dog and which is the ‘tale’ in AGW story! ;-)

      “Water water everywhere…” but It’s not warm enough to be wet at the South Pole (Cold desert) and it’s not cool enough to be dry at the equator (Hot jungle). Insolation dominates where water is abundant and climate zones are dominated by water availability everywhere else.

      *I’m not sure how those TPW figures deal with the spatial distribution of clouds regarding the nongaseous states of H2O within them in relation to the surrounding air though. As to cooling or warming, positive or negative feedback, you would have to separate out the effects of the water content of clouds and cloud systems from the background atmospheric vapour content and their associated atmospheric systems.

  37. I read an article once about a method of estimating the total precipitable water concentration in an area by an analysis of gps position error.

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