Does Global Warming increase total atmospheric water vapor (TPW)?

By Andy May

Some have speculated that the distribution of relative humidity would remain roughly constant as climate changes (Allen and Ingram 2002). Specific humidity can be thought of as “absolute” humidity or the total amount of water vapor in the atmosphere. We will call this amount “TPW” or total precipitable water with units of kg/m2. As temperatures rise, the Clausius-Clapeyron relationship states that the equilibrium vapor pressure above the oceans should increase and thus, if relative humidity stays the same, the total water vapor or specific humidity will increase. The precise relationship between specific humidity and temperature in the real world is unknown but is estimated to be between 0.6 to 18% (10-90%ile range) per degree Celsius from global climate model results (Allen and Ingram 2002).

Carl Mears and colleagues (Mears, et al. 2018) have recently published a satellite microwave brightness record of TPW from 1988 to 2017 showing TPW, over the world’s ice-free oceans, increasing in lockstep with global mean temperature. This surprised me since Benestad (Benestad 2016), (Partridge, Arking and Pook 2009), (Miskolczi 2014) and (Miskolczi 2010) have previously reported that TPW, as computed from weather balloon data, has gone down recently, although their time periods were earlier and longer than the record shown in Mears, et al.

CO2 does not have a large direct effect on temperature, Ramathan and Coakley estimated that the direct effect of doubling CO2, with no feedbacks, would cause temperatures to rise 1.2°C, which is no big deal (Ramanathan and Coakley 1978). Water vapor is a much more powerful greenhouse gas, it has twice the radiative effect (or “greenhouse” effect) of CO2 according to Pierrehumbert (Pierrehumbert 2011) and transports thermal energy around the Earth in ocean currents and as latent heat in water vapor via atmospheric convection. If adding man-made CO2 to the atmosphere somehow, directly or indirectly, causes the amount of atmospheric water vapor to increase, then this “feedback” could cause temperatures to rise more than we would see from adding CO2 alone. Water vapor is the dominant greenhouse gas, according to (Soden, et al. 2005). Likewise, if adding CO2 somehow caused water vapor to decrease or some reflective clouds to increase, the resulting negative feedback could cause temperatures to go down or stay the same. No one really knows how much water vapor feedback, or even if it is positive or negative, is occurring. For this reason, there is considerable interest in determining the current atmospheric water vapor trend.

Figure 1 shows the NCEP weather reanalysis version 1 (Kalnay, et al. 1996) total specific humidity converted to kg/m2 up to about 8 km (300 mb) as an orange line. This value is based mostly upon weather balloon, surface data and after-the-fact analysis of weather using a global weather (not climate) forecasting model. The yellow line is from the NCEP reanalysis 2 global weather model (Kanamitsu, et al. 2002), it provides a total atmosphere TPW estimate, but only goes back to 1979. The gray line is the HADCRUT version 4 global surface temperature anomaly and the blue line is the RSS ice-free ocean TPW estimate from satellite microwave measurements. The RSS estimate is much higher presumably because it only uses samples over oceans that have no sea ice. The RSS data is only available from 1988 to present. Besides the problems with sea-ice, the RSS data has missing data due to rain events and the measurements used can be affected by clouds (Vonder Harr, Bytheway and Forsythe 2012).

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Figure 1. Various estimates of total precipitable water (TPW) in the atmosphere compared to the HADCRUT4 temperature anomaly.

The two NCEP analyses are global estimates from models that are calibrated using actual measurements, thus they are “reanalyses.” Their advantage over the RSS estimate is they are truly global and have values for every map grid. The reanalysis grid for NCEP reanalysis 1 for 2017 is shown in Figure 2. The NCEP reanalysis 1 model had several problems as described in (Kanamitsu, et al. 2002), but most have been fixed as discussed in the reanalysis 1 web site. The data for all of the TPW estimates displayed here was downloaded in May or June of 2018.

The specific humidity reanalysis results are not based solely on weather balloon radiosonde data, but the NCEP reanalysis 1 is more reliant on them than the reanalysis 2 project. Both projects also use land-based weather station data, ship data, aircraft and satellite data. Some have concluded that the radiosonde humidity data prior to 1973 and north of 50°N and south of 50°S is unreliable. Paltridge, et al. excluded this data and confirmed the negative overall trends in TPW, at least in the upper troposphere.

clip_image003Figure 2. The NCEP reanalysis 1 grid of average TPW for 2017 in kg/m2. Data source: NCEP reanalysis 1.

The RSS grids are much sparser as can be seen in Figure 3. The white areas (land- and ice-covered areas) of Figure 3 have no values which, in part, explains why the average RSS TPW values are so much larger than the NCEP values. The color scales used in all the maps are the same. Besides excluding areas containing sea-ice, areas with “moderate and high rain rates” are excluded from the RSS dataset, this introduces a systemic “non-rainy” bias to the dataset (Mears, et al. 2018). However, Mear’s and colleague’s dataset is probably a fairly accurate representation of TPW over the areas sampled. The problem with it is that the land areas and most of the polar regions are excluded and it only goes back to 1988. This is very unfortunate since the AMO began to turn significantly positive in 1988, which makes the RSS comparison to global temperature look “cherry-picked.”

clip_image004Figure 3. The RSS satellite microwave measured TPW over the ice-free oceans, moderate to severe rain events are excluded. Data source: Remote Sensing Systems.

The NCEP internet retrieval program would not allow me to download the reanalysis 2 TPW data for 2017 for some reason, but I did get the 2017 “canned” dataset from their website, it is shown in Figure 4. The data retrieval was done from here.

clip_image005Figure 4. The NCEP reanalysis 2 TPW for 2016. Data source and description: NCEP Reanalysis 2.

Compare Figure 4 to Figure 2, they are similar, except around the Pakistan/Tibet/China border. This shows as a cool, dry area in reanalysis 2 and as a wet anomaly in reanalysis 1. The NCEP reanalysis 2 shows more water vapor in the tropics than the reanalysis 1, this makes the reanalysis 2 averages higher. Further the reanalysis 2 TPW is for the whole atmosphere, whereas the reanalysis 1 TPW is only to 300 mbar (~8 km).

All three estimates shown in Figure 1 show an increase in TPW from around 1990 to the present, but the RSS increase is more dramatic. The increase in global average temperature begins in 1976, 14-16 years earlier. In Figure 2, we can see that the NASA CO2 record shows a rapid increase in trend beginning even earlier in the 1950s.

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Figure 5. The NASA CO2 reconstruction from 1850 to the present. Data source NASA.

Because of the large differences in the various estimates of TPW, the relationship with global temperature is difficult to see. Figure 6 is a close up of the RSS TPW and HADCRUT4.

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Figure 6. RSS TPW plotted with HADCRUT4. Data sources: RSS and Met Office Hadley Centre.

In Figure 6, we see a close correlation between global temperatures and the RSS ocean TPW measurements from satellite microwave data. Even the details match well. In Figure 7 we see the longer NCEP reanalysis 2 record compared to HADCRUT4. Again, there is a close match in detail, but the trends from 1979 to 1992 are opposite.

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Figure 7. The NCEP reanalysis 2 TPW record compared to HADCRUT4. Data sources: NCEP Reanalysis 2 and Met Office Hadley Centre.

Finally, in Figure 8, we see the NCEP reanalysis 1 record, which goes back to 1948, compared to HADCRUT4. The records match well from the present to the early 1980s and then begin to diverge, the divergence becomes extreme in the 1950s. Roy Spencer has blamed this on the poor-quality hygrometers used in weather balloons in the early days. Perhaps, but weather balloon data is not the only data used in these reanalyses. The NCEP reanalysis 2 results are almost certainly better than the reanalysis 1 results, but they are tantalizing short, beginning in 1979. We need 20-30 years more data to see if the influence of global mean temperature can be swamped by the influence of the AMO and other ocean cycles as suggested by the reanalysis 1 results.

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Figure 8. Data sources: NCEP reanalysis 1 and Met Office Hadley Centre.

While surface temperature is clearly a large factor influencing TPW over the short term, there may be other factors influencing it. Figure 9 compares the smoothed AMO index of Atlantic Ocean temperatures to NCEP R1.

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Figure 9. Data sources: NCEP reanalysis 1 and NOAA.

So, if the TPW estimates in the 1950s are accurate enough, perhaps they reveal a strong influence of the AMO cycle on TPW? It is hard to tell since many have questioned the quality of the early hygrometer data.

Over the short term, the correlation between TPW over the oceans and temperature is good, see Figure 10A. This however, is certainly not surprising. Over the longer term, using the NCEP R1 data, it is poor. As seen in Figure 10B, the correlation deteriorates. The time period and the data selected matters.

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Figure 10. Data sources NCEP, RSS and the Met Office Hadley Centre.

The correlations between RSS TPW and NCEP R1 versus HADCRUT4 have similar slopes, which is surprising. Both show an increase of about 2.5 kg/m2 (9%-13%) per degree of global temperature increase, but the NCEP reanalysis 1 plot suggests that there are actually two slopes, thus two trends and factors other than average surface temperature influencing TPW. Compare this estimate to the earlier cited specific humidity range of 0.6% to 18% per degree Celsius (Allen and Ingram 2002). The uncertainty in the amount of increase in TPW, due to global temperature changes is large.

TPW in the Upper Troposphere

As Partridge, et al. (Partridge, Arking and Pook 2009) have noted climate models predict that specific humidity will increase in the upper troposphere as global warming continues. Yet, this is not what is seen in the NCEP reanalysis 1 data, see Figure 11. Partridge, et al. have investigated more measurement levels and report that all levels above 850 hPa (~1.4 km) have a negative trend through 2007 in the tropics and southern midlatitudes. They also found that every level above 600 hPa (~4 km) in the northern midlatitudes has a negative trend.

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Figure 11. Global average TPW (blue line) from 500 hPa to 300 hPa or roughly 5 km to 8 km altitude compared to the HADCRUT4 temperature anomaly. Data sources: NCEP reanalysis 1 and Met Office Hadley Centre.

In many ways this negative trend is counterintuitive since the world is warming and more evaporation is expected. A warming atmosphere should cause more evaporation and a higher TPW. From Paltridge, et al.:

“Negative trends in q [TPW] as found in the NCEP data would imply that long-term water vapor feedback is negative—that it would reduce rather than amplify the response of the climate system to external forcing such as that from increasing atmospheric CO2.”

This was also the conclusion reached by Ferenc Miskolczi (Miskolczi 2014). Others, such as Roy Spencer and Richard Lindzen, have suggested that warmer temperature will cause more clouds, which will increase the albedo of the Earth and lower temperatures or reduce the rate of warming (provide negative feedback) as a result.

Conclusions and Discussion

The various estimates of total atmosphere TPW available do not agree with one another very well. Even the two NCEP estimates, both global, vary by over 18% and these estimates are 33% lower than the RSS ocean-only estimate. However, since about 1990 all the total atmosphere estimates trend upwards. Prior to 1990, the story is more complex. The longer NCEP reanalysis 1 estimate trends down from 1948 to 1975 in sync with the AMO, but different from the HADCRUT4 trend. All datasets agree that short term changes (<30 years) in surface global temperature have a positive (if small) influence on total atmosphere TPW, but it is not clear that long-term changes (>30 years) in TPW are related solely to global surface temperatures, they might be impacted more by ocean surface temperature cycles, such as the AMO.

The global climate models predict that global warming will increase upper troposphere specific humidity, but the weather balloon data shows a decline in specific humidity and in TPW in the upper troposphere. The humidity data declines in quality with altitude and lower temperatures, but even in the tropics where water vapor concentration is high at high altitudes, this trend persists. This also contradicts satellite data, but the ability of satellites to separate the signal of the upper troposphere water vapor from the lower is unclear. The accuracy of the specific humidity calculations in the upper troposphere is also unclear. However, both the NCEP reanalysis and the European reanalysis show a decline (Benestad 2016) and (Partridge, Arking and Pook 2009).

While there is great uncertainty in the amount of TPW in the whole atmosphere and in the upper troposphere, the importance of TPW and its trend is undeniable. In the tropics, at the lower levels of the atmosphere, the large amount of water vapor already traps nearly all the IR (infra-red radiation), so adding CO2 to this atmosphere has little effect (Pierrehumbert 2011). But, in the upper troposphere, where IR is emitted to space and additional CO2 or water vapor may make a difference, water vapor may be decreasing, at least according to NCEP reanalysis 1. Uncertainty abounds in this critical area of research and most important, what data we have is over too short a time period. Consider this quote from Pierrehumbert (Pierrehumbert 2011):

“For present Earth conditions, CO2 accounts for about a third of the clear-sky greenhouse effect in the tropics and for a somewhat greater portion in the drier, colder extratropics; the remainder is mostly due to water vapor. The contribution of CO2 to the greenhouse effect, considerable though it is, understates the central role of the gas as a controller of climate. The atmosphere, if CO2 were removed from it, would cool enough that much of the water vapor would rain out. That precipitation, in turn, would cause further cooling and ultimately spiral Earth into a globally glaciated state. It is only the presence of CO2 that keeps Earth’s atmosphere warm enough to contain much water vapor. Conversely, increasing CO2 would warm the atmosphere and ultimately result in greater water-vapor content – a now well understood situation known as water vapor feedback.”

So, we see the crucial role assumed for water vapor in the entire man-made climate change hypothesis. CO2 has only a minor role to play in warming the Earth by itself. It is only the assumed, but unmeasured, feedback from water vapor that allows a large impact on our climate to be predicted. Yet, as shown above, this assumed feedback cannot be measured with any accuracy with the data we have available. In fact, over climate time scales (>30 years) we cannot even be sure the feedback is positive. There is a strong correlation between temperature and total atmospheric water vapor concentration over short time periods, especially over the oceans from 1988 to 2017, when the AMO index was rising. But, it falls apart over longer periods of time and it is negative in the crucial upper troposphere. I can offer no solutions or great insights here, only questions and problems.

Andy May is a writer and author of “Climate Catastrophe! Science or Science-Fiction?” He retired in 2016 after 42 years in the oil and gas industry as a petrophysicist.

The R code and other information, including links to the original data, used to make the figures in the post can be downloaded here.

Works Cited

Allen, Myles, and William Ingram. 2002. “Constraints on future changes in climate and the hydrologic cycle.” Nature 419. https://www.climateprediction.net/wp-content/publications/nature_insight_120902.pdf.

Benestad, Rasmus. 2016. “A Mental Picture of the Greenhouse Effect.” Theoretical and Applied Climatology 128 (3-4): 679-688. https://link.springer.com/article/10.1007/s00704-016-1732-y.

Kalnay, E., M. Kanamitsu, R. Kistler, W. Collins, D. Deaven, L. Gandin, M. Iredell, et al. 1996. “The NCEP/NCAR 40-year reanalysis project.” Bulletin of the American Meteorological Society. https://journals.ametsoc.org/doi/abs/10.1175/1520-0477(1996)077%3C0437:TNYRP%3E2.0.CO;2.

Kanamitsu, Masao, Wesley Ebisuzaki, Jack Woollen, Shi-Keng Yang, J. Hnilo, M. Fiorino, and G. Potter. 2002. “NCEP-DOE AMIP-II Reanalysis (R-2).” BAMS. https://journals.ametsoc.org/doi/abs/10.1175/BAMS-83-11-1631.

Mears, Carl, Deborah Smith, Lucrezia Ricciardulli, Junhong Wang, Hannah Huelsing, and Frank Wentz. 2018. “Construction and Uncertainty Estimation of a Satellite-Derived Total Precipitable Water Data Record Over the World’s Oceans.” Earth and Space Science. https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2018EA000363.

Miskolczi, Ferenc. 2014. “The Greenhouse Effect and the Infrared Radiative Structure of the Earth’s Atmosphere.” Development in Earth Science. http://www.seipub.org/des/paperInfo.aspx?ID=21810.

Miskolczi, Ferenc. 2010. “The Stable Stationary Value of the Earth’s Global Average Atmospheric Planck-Weighted Greenhouse-Gas Optical Thickness.” Energy and Environment. http://journals.sagepub.com/doi/abs/10.1260/0958-305X.21.4.243.

Partridge, G., A. Arking, and M. Pook. 2009. “Trends in middle- and upper-level tropospheric humidity from NCEP reanalysis data.” Theory of Applied Climatology. https://link.springer.com/article/10.1007/s00704-009-0117-x.

Pierrehumbert, Raymond. 2011. “Infrared radiation and planetary temperature.” Physics Today, January: 33-38. http://faculty.washington.edu/dcatling/555_PlanetaryAtmos/Pierrehumbert2011_RadiationPhysToday.pdf.

Ramanathan, V., and J. Coakley. 1978. “Climate Modeling Through Radiative-Convective Models.” Reviews of Geophysics and Space Physics 16 (4). https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/RG016i004p00465.

Soden, Brian, Darren Jackson, V. Ramaswamy, M. Schwarzkopf, and Xianglei Huang. 2005. “The Radiative Signature of Upper Tropospheric Moistening.” Science. https://www.researchgate.net/profile/Xianglei_Huang2/publication/7554296_The_Radiative_Signature_of_Upper_Tropospheric_Moistening/links/00b4953c458b4cc3c7000000.pdf.

Vonder Harr, Thomas, Janice Bytheway, and John Forsythe. 2012. “Weather and climate analyses using improved global water.” Geophysical Research Letters 39. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2012GL052094.

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157 thoughts on “Does Global Warming increase total atmospheric water vapor (TPW)?

  1. An issue is that HADCRUT has been “adjusted”, so the cooling trend many were worried about from 1945 to 1975 is mostly gone.

    • Exactly, Hadcrut4 is radically different from the sat record of temperature from 1980 to the present. It is probably comparing apples and aardvarks.

      Too bad they did not keep the output from SCAMS and NEMS so you could push the record back to close to 1970.

      • shrnfr

        “…Hadcrut4 is radically different from the sat record of temperature from 1980 to the present.”

        Here are the satellite TLT and HadCRUT4 temperature records from Jan 1980, all set to UAH’s preferred 1981-2010 anomaly base period:

        https://s33.postimg.cc/gi4ff3gan/Had_CRUT_vrs_RSS-_UAH.png

        Hard to see how the satellite sets can be described as ‘radically different’ from HadCRUT4. All show statistically significant warming. The warming trend in UAH is slower than that in HadCRUT4, but the warming trend in RSS is faster than that in HadCRUT4.

        The biggest disagreement is between the UAH and RSS satellite estimates, not between the various satellite estimates and HadCRUT4.

        • Yes ironically , it used to be alarmist RSS was warming slightly slower than skeptical UAH. That seemed healthy and gave hope that they were both doing their best to be objective.

          Then Mears gave in to pressure and “corrected” his dataset.

          • Actually, I just don’t understand why there is all the blending of SST and land air temps. They are very different media with their own climates and weather. ( Plus the fundamental problem that you can not ADD temperatures across different media. )

            They should study land and sea separately and the results would look very different and may actually tell us something.

          • The satellite and surface temperature data producers all provide separate data for ocean and land temperatures. For instance, CRUTEM4 is the latest HadCRU land-only component of HadCRUT4, and HadSST3 is its current ocean component. The ocean is warming less quickly than the land, as would be expected due to thermal lag, but both still show warming over the long term.

            https://s33.postimg.cc/yqp78iwdr/Crutem_vrs_Had_CRUT.png

    • How can there be any sea surface records prior to the deployment of buoys? The oceans were 98% not sampled. All charts of global temperatures need a warning “do not use for setting policy”.

  2. Uncertainty is a monster, and ignorance is an even bigger monster. Science by PR is also a monster, which is how we got to this point. Unsettling science.

  3. Perhaps a qualified meteorologist can confirm or dispel this question. Does a tiny amount of water vapor in the Arctic and Antarctic regions affect winter temperatures?

      • The thing about the Arctic Ocean is that it is mostly frozen in the winter. The atmosphere is very cold and very dry. It takes relatively little energy to heat the air. The swings in temperature can be pretty dramatic.

        In the summer there’s a phenomenon where any open water is covered by a mile high (+/- a lot) column of fog. That has to have some effect on solar radiation.

        The other (perhaps main) thing is that, in the summer the ice is melting. That goes a long way to regulating the temperature. Here’s a link to graphs showing the temperature north of 80 since 1958. You will notice that the summer temperature never differs much from the average.

        • Summer Arctic temperatures are subject to a strong non-linearity. The use of anomalies in calculating average temperatures relies on temperatures being linear so that correct comparisons can be done. I assume that very secret adjustments are done to correct the data.
          A simple experiment to demonstrate this is taking a glass of water and microwaving it for a minute and measuring the temperature anomaly. Then take a second glass containing the same amount of water in the form of ice and microwaving it for a minute. According to climate science, the same number of degrees have gone into both glasses so the anomalies should be the same, but the actual results are different. I guess this is some kind of quantum climate spookiness.

          • There is a simple explanation that even elementary students know the answer to that one. It is called latent heat of fusion.

  4. There is a limit to how much solar energy strikes the surface of the planet. That energy can do a few things, one of which is evaporate water.

    There are two delimiting cases:

    First, if the atmosphere above the ocean is saturated (ie. 100% RH) the only way it will accept more water is if its temperature rises. We should also remember that it takes a lot more energy to evaporate water than to raise the air temperature.

    On the other hand, if the atmosphere above the ocean is completely dry, the limit on how much water evaporates is determined entirely by the available energy. Solar energy isn’t increasing. That puts a hard limit on how much water can be evaporated.

    The assumption of a constant RH, it seems to me, isn’t based on a calculation of what the available energy is doing.

    • After reading many justifications for the assumption of a constant distribution of RH, it’s unclear to me that there is any reasonable justification for the assumption. Maybe someone else can describe the logic behind it in a way I can understand, if you write them, I will read them.

      • Maybe someone else can describe the logic behind it in a way I can understand …

        Here’s a link in which WUWT commenter aveollila explains that the assumption is a feature of climate models.

        Here’s a link to a NOAA blog post that explicitly deals with the energy constraint.

        It’s pretty clear that nobody has a really solid understanding of exactly what’s going on. It’s a complicated mess. Any simplifying assumptions are probably unjustifiable.

        • This talk from a NASA GISS scientists provides great insight into why it is such a complicated mess:
          https://www.youtube.com/watch?v=hjKJyn_uoIE
          He shreds the basis of climate models and in the question/answer portion at the end he states climate models have thousands of tunable parameters so can produce whatever you want from them (I knew that before but to see a GISS scientist state it is refreshing honesty). The models are fundamentally flawed because they are based on simplistic radiation transfer principles that cannot be applied to the atmosphere.

          This is, without a doubt, the soundest scientific discussion I have seen on climate science.

          Mishchenko must wince when he reads the technical portion of the IPCC reports – if he bothers to put himself through such agony.

    • To kick this off, here is the justification given in Allen and Ingram, cited in the post:

      “The distribution of moisture in the troposphere (the part of the atmosphere that is strongly coupled to the surface) is complex, but there is one clear and strong control: moisture condenses out of supersaturated air. This constraint broadly accounts for the humidity
      of tropospheric air parcels above the boundary layer, because almost all such parcels will have reached saturation at some point in their recent history. Physically, therefore, it has long seemed plausible that the distribution of relative humidity would remain roughly constant under climate change, in which case the Clausius–Clapeyron relation implies that specific humidity would increase roughly exponentially with temperature. This reasoning is strongest at higher latitudes where air is usually closer to saturation, and where relative
      humidity is indeed roughly constant through the substantial temperature changes of the seasonal cycle.”

      This chain of logic has numerous flaws, but I will mention only one now: How does he know that that “almost all such parcels have reached saturation” recently? I can think of dozens of reasons why a high altitude parcel might not have been saturated recently.

      • Even IF you assume that distribution of RH stays roughly the same, you still have a lot of other factors to account for. At temperatures approaching freezing, a temperature increase doesn’t change the amount of water vapour the air can hold by very much, regardless of humidity. Engineer’s Tool Box:

        https://www.engineeringtoolbox.com/water-vapor-air-d_854.html

        So it seems to me that in addition to understanding distribution of RH, you also have to layer over top of that the temperature for any given area. Cold regions (high altitude, high latitude) are most sensitive to a change in forcing, but these are the area in which a change in temperature has the least effect on the amount of water vapour that can be in the air (and hence minimizes any feedback from water vapour). In warmer climes, a change of a few degrees can in fact increase the holding capacity of the air considerably (again, see link above) but since by definition these are the warmest parts of the planet, due to Stefan-Boltzmann Law, these are the areas that require much higher changes in forcing to achiev a change in temperature, so again the effect of water vapour increase is minimized by the physics.

        So while the correlation between temperature and water vapour is interesting, I think looking at it from a global perspective hides some important nuances. The forcing from water vapour in cold regions is minimized by the small change in water vapour for a given change in temperature, and the forcing in warm regions is minimized by the much larger forcing you need to change the temperature in the first place.

        My two cents for the day. Still on coffee 1 so perhaps it is only 1 cent.

      • Hi Andy. You said- This chain of logic has numerous flaws, but I will mention only one now: How does he know that that “almost all such parcels have reached saturation” recently?
        .
        .
        Suppose it’s 11 a.m. in the Western Pacific 100 miles east of the Philippines. There is a column of moist still air that is one kilometer on edge and 1 km High, mabe 90% RH. As it rises up it gets to an altitude where the RH at that temp is 100%, then say 30% of the moisture makes a cloud 1 km on edge containing the other 70% of the moisture. It in travels towards Manila and runs into the heat island Rising column and goes even higher and cooler and precipitates all of the rain in a 1 p.m. rain shower.
        .
        .
        Could this happen, it would explain how the parcel got saturated before dumping on Manila?
        .
        .
        Sandy,
        Minister of Future

        • Your hypothetical is fine and high altitude air over the equatorial Pacific is expected to have reached saturation recently. Perhaps not over Canada or Siberia or the central Sahara. I take issue with the “almost all” part of his statement. Areally, especially in the Northern Hemisphere, there is a lot of room to redistribute Relative Humidity if something changes climatically. I don’t think the assumption has any support in the real world.

          • Worse than that, cloud formation requires super-saturation. But supersaturation does not guarantee cloud formation, at least at temperatures typically above circa -30 Celsius, if I recall correctly. But there is no general way of predicting when water will condense over the whole likely ranges of temperature, pressure, water content, availability of condensation nuclei, etc. This is partly why cloud formation is so poorly understood.
            Yet there is much atmospheric moisture in radiatively-important parts of the atmosphere in a thermodynamically unstable state, just waiting for an appropriate trigger to condense.

            I have not yet seen any credible description of how climate models treat this. I think they probably can’t, even if they wanted to. What do you do if you have embarked upon a career to write computer models to calculate something that you know probably cannot ever be calculated with useful precision or accuracy?

            It’s not a recipe for long term mental stability because you have to lie to yourself first. Edward Lorenz warned meteorologists and climate scientists to only tackle tractable tasks, but hubris and money has persuaded too many to ignore his advice.

          • Thank you for stating this more clearly than I have ever managed to do.

            “What do you do if you have embarked upon a career to write computer models to calculate something that you know probably cannot ever be calculated with useful precision or accuracy?”

          • I’m glad you think so, Charles.
            Back in the 1980’s it came as something of an intellectual body-blow to me to learn about some of the implications of chaos theory, as explained in popular science books about Mandelbrot and Lorenz.

            I suspect many researchers in the hard sciences sub-consciously tell themselves that if they can’t actually prove they might be working on an intractable problem, then it is OK to carry on if they think they might still demonstrate some utility that might arise serendipitously.

            In all seriousness, I think it should at least be mandatory that engineers and hard-scientists take a course emphasizing the existence of such limits before they embark on a higher Degree/Qualification in their subject after undergraduate studies.

          • I think it’s similar to hydraulics, where you can’t calculate specifics, but you can calculate generality. Something that is generally true for the purposes at hand. Which for engineering is culvert size, bridge height, flood plane inundation levels. Good enough to be useful, but can never be called “accurate”.

            Doing this for atmospheric models could only ever be called “generally true”, but not “specifically true”.

          • I’ve thought about the engineering angle. The way I imagined it, engineers would value precision and accuracy in measurements, and also know how much “uncertainty” is allowed; beyond that, and the design is no good. But I wasn’t thinking about hydraulics! You’re right, makes sense. And that, too, could have a climate component that is informed by climate models.

            I have a very limited idea of what engineers do. Aren’t they the ones who wear denim overalls and hats, and a red bandana around the neck? And when they come to a town, they blow the whistle. Choo choo!

          • “What do you do if you have embarked upon a career to write computer models to calculate something that you know probably cannot ever be calculated with useful precision or accuracy?”

            This depends entirely on what you call “useful.”

            My background is in ecology. There are all kinds of stochastic factors in ecology – climate being one of them. Models can be very complex – not as complex as climate, but somewhat similar in quality. I’m comfortable with probabilities and uncertainty. I recognize that the uncertainties within each model are sometimes high, but that it’s significant when many models agree. There is very high overlap among models in the range of climate sensitivity, for instance.

            I believe the climate models are indeed useful. They help people understand patterns they are seeing, and that enables them to prepare for the future.

            Look at just one prediction that is already observable: increased precipitation intensity. There’s a lot of hulabaloo about coastal cities and sea level rise, but snowstorms and flooding are both costly and fatal. Crops and homes can be destroyed, people swept away, increased car accidents, power outages, evacuations. In 1998 75% of Bangladesh was flooded. In 2017 flooding there and in Nepal and India killed 1200 people (and that doesn’t count all the people who died from disease and undernourishment as a result of the floods). Then imagine it much worse in the future, affecting not only South Asia, but the developed world.

            The models are also useful in looking at different scenarios. A lot can be learned by changing the parameters. How about we slow down the AMO, for instance, what happens then? Of course, one always has to keep in mind models’ weaknesses, which are both shared and variable.

            “It’s not a recipe for long term mental stability because you have to lie to yourself first. Edward Lorenz warned meteorologists and climate scientists to only tackle tractable tasks, but hubris and money has persuaded too many to ignore his advice.”

            Why do so many comments begin with interesting science and end by insulting scientists, alarmists or the Left? Is that necessary to show you are part of the club, the ones who love to despise and demean others? Like a secret handshake or something? I’d forgotten you’d written that, or I wouldn’t have spent so much time on my reply.

          • Kristi Silber says:
            “Why do so many comments begin with interesting science and end by insulting scientists, alarmists or the Left?”

            Answer:
            Because the “coming climate change catastrophe”
            is a fantasy based on almost no science,
            and heavily supported by left-wing politicians!
            .
            It’s one assumption on top of another,
            leading to wild guesses of the future
            average temperature, using computer games
            — predictions that have been grossly inaccurate
            for the past 30 years.

            If that’s not junk science, I don’t know what it.

            There is almost no real science behind the global warming
            scaremongering — just because people with science degrees
            are involved does not mean what they are doing is real
            science that can be falsified — I don’t expect you to know that,
            but I’ve described reality.

            Government bureaucrat “climate scientists”
            DESERVE to be insulted … and fired — they have
            been wasting the taxpayers’ money for decades,
            accomplishing nothing of value … while tearing down
            the reputation of science in general.

            Real science, I mean — where experiments can be
            replicated, and theories can be falsified.

      • The key to this puzzle is the atomic weight of water vapor. It is very light compared to the average air weight. If you get more water evaporation at the surface this air becomes less dense. Less dense air rises.

        Essentially, more warming at the surface enhances convection. The air columns rise faster. This added speed lifts the air column higher into the troposphere which must cause stronger condensation because it is colder. More water vapor is extracted and the resulting air has a lower amount of water vapor. Also more clouds are formed.

        So, you might see an increase in TPW but the specific humidity at altitude goes down. This is exactly where the greenhouse effect is most important since it is already saturated near the surface.

        I believe this is why Gero/Turner 2012 found no increase in downwelling IR for 14 years even as CO2 increased. This water vapor feedback directly canceled any warming effect from CO2.

        • The key to this puzzle is the atomic weight of water vapor. It is very light compared to the average air weight. If you get more water evaporation at the surface this air becomes less dense. Less dense air rises.

          That depends on several things. If the water is cooler than the overlying air then you could get a relatively cool boundary layer which, because of its temperature, does not rise in spite of its greater humidity. Of course, when the wind blows all that goes out the window. 🙂

          • My comment was speaking to averages, but the fact is it will vary considerably. In colder climates you won’t get a lot of convection period but you also won’t get a lot of evaporation. Hence, the feedback computation will necessarily change. Same is true at night when you have less convection.

            As a result cold climates and nights should warm. Days and hot climates may actually cool.

        • If that is a correct picture, this is also a mechanism the the GCMs predict, then they also predict a hotspot in the tropical mid-upper troposphere due to the increased conversion/release of latent heat to sensible heat due to phase change of water at this altitude. The CMIP3 ensemble mean predicted about a 1.3 ratio of 8km temperature increase relative to the surface T increases under this CO2 GHG effect.
          The actual balloon data and satellite data provides an observation of about a 0.8 ratio.

          Paraphrasing Dr. Feynman, if the observation doesn’t support the theory, the theory is wrong. It is that simple.
          CO2 increase as causal to recorded surface warming is acquitted.

          The fact that the surface temps are warming faster than the mid-upper troposphere clearly indicates other explanations are needed.
          Other explanations include solar EUV/stratospheric ozone changes, cloud albedo uncertainties in the models, UHI E contamination of surface records, too much infilling from the loss of rural stations, modern maximum solar UV heating of the oceans, unaccounted for ocean cycles/internal variability, and so on.

      • Specific humidity is not mass of water vapor per unit volume, it’s per unit mass of air- it’s dimensionless. I’m not sure how you’d get TPW from that; it would be pretty tough to calculate, I’d think. In the troposphere the mass of air would be very small compared to that from which the water vapor arose, and therefore easily saturated. That’s my, guess, anyway. Does that make any sense?

    • Exactly Bob..
      In GHG theory, energy is analogous to Other People’s Money – there is an infinite amount to do with as you wish. Then, via randomly chosen bits of cherry science, both are conflated with temperature. Always rising of course. Gotta keep things on-the-up.
      Cause & Effect go through the liquidiser yet again.

      Sorry Warmists, but what goes on with the copious hot water, condensations and clouds of steam in your shower/bathroom bears ZERO relation to what happens in the Mid Pacific during a thunderstorm. Or any other time for that matter.

    • CommieBob

      Per your comment: “There is a limit to how much solar energy strikes the surface of the planet. That energy can do a few things, one of which is evaporate water.”

      Thanks, you beat me to it and got to the heart of the problem.

      From an chemical engineering perspective, an increased temperature in the air column would only increases the possibility of increase humidity in the column. But an increase in humidity in the column will occur if and only if there was addition energy at the surface to cause additional evaporation.

      Without additional solar energy hitting the surface; it is seems unlikely their would be much, if any, additional evaporation occurring at the surface… unless the time delay in transferring radiant heat from the surface to the atmosphere cause by GHGs was long enough to allow additional energy transfer by mass & fluid transfer mechanisms (i.e. evaporation, sublimation, conduction, and convection).

      Taking you point a bit further, any increased evaporation would simply decrease the amount of energy available to radiant transfer and hence decrease the impacts of GHG warming by radiant transfer. (Keeping in mind that the primary reason GHG warming occurs, as a product of radiant transfer theory, is because these gases delay heat transfer by the radiant transfer mechanism – in simplistic terms the energy being transferred by a radiant mechanisms is repeatedly being “stored” in green house gases and then re-emitted as the energy moves up the air column. Its the “stored” energy that causes the increased air temperature.)

      I’ve always been skeptical that increase evaporation is likely to occur; because, radiant transfer is exceptional fast (occurring literally at the speed of light) where as the mass transfer mechanisms associated with evaporation take much longer. The more likely out come, in my view, is that the gas column above the surface would warm due to radiant transfer coming quickly to equilibrium with little to no additional evaporation occurring … since there is little to no additional energy available at the surface to produced increased evaporation.

      From this view, one would expect CO2 to create only modest temperature increases and a related expansion of volume of the air column… and hence the sized of troposphere… per the ideal gas law. I suspect this is why were seeing fewer serious hurricanes as CO2 concentrations rise. Specifically, because roughly the same amount of energy is being dispersed in a troposphere with greater volume.

      One of my pet peeves, as a chemical engineer, it that weather and climate models are produced with detailed radiant & fluid transfer considerations in mind… and with an near complete lack to understanding of, or inclusion of, the relationships between radiant transfer, heat transfer and mass transfer. They simply combine radiant transfer with fluid transfer and call it a day. This approach may be “good enough” for weather predication; but, is isn’t “good enough” to predict changes in the climate.

      In this respect, I don’t think AGW advocates have made a science-based case. The absence of creatable explanation why we should expect increased evaporation is a glaring defect in their logic that could have and should have been “filled” long ago.

    • “First, if the atmosphere above the ocean is saturated (ie. 100% RH) the only way it will accept more water is if its temperature rises. We should also remember that it takes a lot more energy to evaporate water than to raise the air temperature.” Sort of but if the
      saturated atmosphere Is force to move allowing dryer air to move over the ocean area then “temperature” has little to do with it.
      “On the other hand, if the atmosphere above the ocean is completely dry, the limit on how much water evaporates is determined entirely by the available energy. Solar energy isn’t increasing. That puts a hard limit on how much water can be evaporated.” That puts a hard limit on how much water can be evaporated? Not really you are leaving out friction – air movement – wind – wind at different speeds. Think about it. example: you come home and find you have a water leak and your carpet is soaked to the sub floor. What do you do? You could turn up the thermostat to 90 or open the windows and doors and tour on a bunch of fans. which method would dry out the carpet the fastest?

      • … which method would dry out the carpet the fastest?

        It depends on the relative humidity. 🙂

        If I had a rug that was sopping wet I wouldn’t rely on evaporation. I would haul out the shop vac and suck the water out of the carpet the same way I would remove a pile of sawdust.

        The energy to evaporate water has to come from somewhere. It could be the heat of the sun or it could come by cooling the atmosphere, like a swamp cooler.

        • “If I had a rug that was sopping wet I wouldn’t rely on evaporation. I would haul out the shop vac…..” That is true. But you still open the windows and doors and use fans to move the water vapor to a less humid area. Again which method would dry out the carpet the fastest?

  5. This is wrong in so many ways. Consider most especially that temperature can be calculated to a great accuracy by simple invocation of routine psychrometry. It is done so every day. There is no need to invoke CO2 concentration to calculate our temperature or moisture content now or later.

    • You reference psychrometry, and then declare “…There is no need…to calculate our…moisture content…” Ummmmmm… if you don’t know the moisture content, you don’t know psychrometrics. There is a much more elaborate post percolating in my head. Perhaps I’ll lay it out soon.

    • I suspect the fact that the conjunction of very dry areas with very wet areas near the Himalayas is what caused the differences between the R1 and R2 grids.

      • Obviously modelling the wettest place on earth as one of the driest makes the R2 model wanting. Who dares to publish a lousy reanalysis like this, does nobody look at the calibration with the real world? And why are the absolute values of the three darasets mutually contradicting?

  6. Evaporation is an endothermic process so the temperature at the surface of evaporating water will always tend to approach the atmospheric dew point. Equilibrium at ice/ air interface will also be near the measured atmospheric frost point. These surfaces will radiate at these temperatures. Thus, water cycles are controlling surface temperatures not CO2 back radiation. The cold tops of thunder clouds are radiating at their frost point. Dew point is a function of specific humidity. Water vapor is not a feedback for CO2.

    • Nicely put. Add to that the physical transportation of heat energy in the form of ‘enthalpy’ and the ‘sequestration’ of Water Vapour in ground water and as ice/ snow, and we come closer to understanding the dual role of Water Vapour as GHG that both warms and cools!

      • I find it odd that AGW physicists claim that without CO2 in the atmosphere there would be no water vapour. I have seen it written several times. The idea is used to market the meme ‘water vapour is only a feedback’. On snowball Earth, there was sublimation of ice and there was always water vapour. WV can drive itself without any CO2 at all. Adding CO2 does add a feedback in certain circumstances but it is tiny compared with the dominating gas.

        The two comments above are succinct and helpful. I will not be surprised to find that the WV feedback from CO2 is nearly zero under present conditions. CO2 adds cooling capacity to the upper atmosphere because it is a radiative gas. This lowers it’s capacity to hold WV, as witnessed in radiosonde readings. I don’t see why anyone is surprised by the falling humidity above 600 mb.

  7. I have to put my ignorance on full display here now:

    I never really got how water vapor, already evaporated into the air because of some quantity of heat, could do anything to add heat back to the quantity of heat that got it into the atmosphere in the first place.

    It seems that water vapor would heat, yes, and hold heat (I guess you could say) a bit longer than air, … and distribute heat, … in other words, REGULATE how warm or cold we humans feel, but this seems like a far cry from what alarmists are saying or trying to say.

    If I put a water bath around something that is at a higher temperature than the water, then the hotter thing cools because of the water, and the water heats up to a higher temperature than it was, but not to a higher temperature to add heat back to the thing it cools.

    I wonder whether CO2 has any consequences whatsoever for what water vapor does or does not do.

    • Robert Kernodle, water vapor is a very strong greenhouse gas, at least twice as strong as CO2. This means it absorbs infrared radiation and re-radiates it, this slows cooling of the surface of the Earth. When the amount of water vapor increases, the slowing increases and the temperature goes up slightly until the atmosphere reaches a new equilibrium. This is fairly straightforward, what the warmists (and everyone else) don’t know is what happens then in the complex climate system. Is there more rain? How will the water vapor be distributed? Same as today or differently? The system is very complex.

      Further, water vapor carries latent heat with it, this thermal energy is released when the water vapor condenses and joins a cloud or rains out. Do clouds increase? Where? Upper level clouds that reflect solar energy, but don’t help trap thermal energy at night? Or low level clouds? The devil is in the details.

      • The phrase, “slows cooling”, has no meaning to me. “Slow” with respect to what time frame?
        Why the hurry? How do you time that? — when do you hit the stopwatch button to begin, and when do you hit the stopwatch button again to end? — what’s the correct time for cooling — in minutes?, … hours?, … days?

        • An analog would be the way a resistor decreases the flow of electric current. For heat the equivalent of ohms is r-value.

          You could express the flow of heat in BTU per hour.

          In practical terms atmospheric heating and cooling is easily observable over an hour. For instance, in a desert the temperature changes drastically at sundown.

          • But when we say “slow cooling”, the consideration being focused on is the time it takes for cooling to happen. Okay, cooling slows, but cooling EVENTUALLY happens, right? — It just took a little longer. How does taking a little longer to cool add any more heat to anything? Again, what schedule are we on to cool? Who decided on this schedule? Cool by 6AM?, … 7AM?, … 6PM?, … 7PM? And by how much per minute?, … per hour? … per day? And how does this add any heat? Cooling STILL takes place. When do we start the timer?

            I get the feeling that people use the phrase, “slow cooling”, to mean that cooling never really gets to the end, and so heat somehow stays built up or “trapped”, because it NEVER has time to dissipate through the cooling at its slow rate, which is really not slow, but infinitely decelerating to trap heat or prevent it from EVER getting out, and this is absurd.

          • Think about it like this:
            If you want your pot of water to boil faster you can either:

            1. turn up the heat, or
            2. put on the lid.

            The second one slows down the cooling of the water, trapping more heat. The energy being added to the system is not changed, but is used more efficiently because less is lost, raising the water temperature and the water boils faster. That’s what’s happening with a greenhouse gas in the atmosphere, it’s like a lid on the energy being added to the system from the sun.

          • No, the lid does not slow the cooling due to a ‘greenhouse effect’, it slows the cooling because the lid stops convection from removing the saturated water vapor above the water, thereby preventing more evaporation from taking place. The lid stops/reduces the evaporation heat loss. This is a phase change effect .. nothing to do with a greenhouse effect.

          • I’m reconsidering the resistor analogy now, and I think it’s not quite right. I thought that a resistor REMOVED energy from a circuit to control the amount of energy coming out the other side of it, which means that the resistor builds up heat, while the energy is reduced on one side ofit. The energy on the entering side is unchanged, while the energy on the exit side is decreased, and the heat in the resistor does not add to or take away from either — it dissipates.

            H2O or CO2 can absorb infrared and re-emit, which is sort of like a resistor removing energy, but I don’t see H2O or CO2 holding back any energy to control how much goes out the other side — they just vibrate a little more and translate these vibrations to other atmospheric molecules, which revs up convection, which sweeps the air into ascending currents that cool.

            The H2O is adding to a cooling effect on the day side of Earth, and because of its heat capacity, maintains a warming effect on the night side of Earth.

    • I agree and dont forget that when ocean water evaporates the newly created latent heat inside the water vapour molecules ; comes from both the ocean water itself AND the atmosphere. When that water vapour finally condenses as it eventually must (because the air at a certain temperature can hold only a limited amount of water vapour) the key question is where are those clouds that are condensing? If they are high because of convection; then doesnt the newly released latent heat (which is now real sensible heat) get radiated out to space? If it got radiated back to the surface of the oceans the oceans would never lose their heat and they would boil over because of the constantly added new solar energy hitting them. It seems that convection is a far more important player than any back radiation caused by CO2. Are we sure that NASA is even measuring back radiation properly because isnt NASA treating the sky and CO2 molecules as a black body with an emissivity of 1 when the real emissivity should be around 0.002 which would make the measured back radiation 500 times larger than it really is?

  8. Thanks for this Andy. Has anybody shown how latent heat moves via semi steady state streams of air around the equator ( or xtra tropical)?
    .
    . From article …
    As Partridge, et al. (Partridge, Arking and Pook 2009) have noted climate models predict that specific humidity will increase in the upper troposphere as global warming continues. Yet, this is not what is seen in the NCEP reanalysis 1 data,
    .
    .
    Can govt climate models even be forced to predict cooling? Otherwise the upper tropo anomaly must indicate … Global Cooling! Mini ice age 2023.
    .
    .
    Sandy,
    Minister of Future

    • Sandy, I’m not sure I understand the question. About 50% of the thermal energy transported from the equator to the higher latitudes is transported by water vapor as latent heat. This is done via winds.

      • Hi Andy. Sorry, its a fuzzy idea, heh.
        The NE trade winds carry these heat parcels west around the equator while the Hadley circulation carries them north (south) to about 30 dgr. Do they dump the heat by raining on a cold patch?
        .
        .
        Sandy,
        Minister of Future

    • Sandy, Too many unknowns. Does precipitation go up? What happens to the quantity and altitude of clouds. The classic explanation used by the warmists is way to simple and has too many holes.

  9. In “modern climate science”
    when different sources of data,
    such as water vapor levels,
    do not agree, then you select the
    source that best supports
    your pre-determined conclusion,
    present it with great confidence,
    and of course never mention
    likely margins of error,
    or the contradictory data.
    .
    Otherwise people (laymen)
    are likely to get confused.
    .
    Of course I don’t believe in
    modern climate science,
    because it is just junk science
    backing wild guess predictions
    of the future average temperature,
    and if that wasn’t bad enough,
    the predictions have been wrong for
    the past 30 years !

    My climate change blog:
    http://www.elOnionBloggle.Blogspot.com

  10. Very interesting and educational article! However, “(9%-13%) per degree of global temperature increase” seems too high. My understanding is that, between 0°C and 35°C, the water-vapor capacity of air only increases by about 6-7% per degree Celsius.

    • Dave Burton, I’ve seen those values as well as 5% in the literature. These values come from analyzing the output from various climate models. Allen and Ingram (see post for reference and link) provide a spectrum of values taken from a large number of models, some constrained by observations. It is nice when actual data is included. As stated in the post, no one really knows what the relationship is currently. Those that want to stick to model calculated percent SpHum/degree values poo-poo the measurements from radiosondes, but these are actual measurements and not contrived values using thousands of assumptions and parameters. I agree with Paltridge, et al. (reference in the post) that the radiosonde data needs to be considered. I don’t like replacing real data with model results.

  11. Andy, a confounding factor is that when you match TPW to a jiggered temperature record, the relationship is meaningless. Re-analysis may be a fudging exercise because of this destruction of the temperature record out of expediency to blame human CO2 emmissions, get rid of the dreaded Pause and to show accelerating affects for policy purposes. They apparently didnt think of the consequences of changing one metric of the complex system that is climate.

    Almost all the 0.8C warming took place by 1940. This couldnt be tolerated if selling the CO2 meme.

  12. Andy
    A wonderful piece.
    During periods of accelerated heat water vapour release from tropical latitude’s, there is a corresponding increase of pressured displacement toward the poles. Days not weeks in some cases.

    Equator to pole temperature gradient is secondary to the pressure gradient. If I understand correctly, Antarctic ice sheet volume has increased as the Greenland sheet etc, and glaciers. These are destinations for transportable water. The more water transferred into the atmosphere the faster the conveyer belt.

    These must be included into the equation along with other forms of precipitation.

    I raise these issues for your consideration.
    Regards

  13. I have opined natural cyclical warming of oceans releases more water vapor in the air, which would have a bigger effect on temps where its coldest and driest, hence the disproportionate warming of polar areas in their coldest seasons and the skewing of the planets temperatures, Fact is where its warmest, the temperature rise has been much less, which is in line with WV attribution ( and that from the warmer oceans which is a long cycle process involving many things, co2 likely the least of them) , Look at saturation mixing ratios, Minute increases in WV correlate to large increases in temperatures where temperatures are very low , which would make sense given more cloud cover would develop inhibiting cold. But its the WV driving temp, and more so where its coldest and driest

  14. Bottom line, as my professor Dr John Cahir at PSU opined many years ago, quantification of Saturation Mixing ratios would be a better climate indicator than temperatures and likely take away much of the hysteria due to implied limits of how warm it can get ( the warmer it is, the harder it is to get warmer)

    • Joe Bastardi, Both of your opinions make perfect sense to me and are areas that deserve more investigation. We call the AMO and PDO sea surface temperature indexes, but I doubt the impact of the sea surface temperature change has as much impact on weather trends as the change in total evaporation, that is the change in atmospheric water vapor content. Can’t prove it, of course.

  15. The effect of water on the atmosphere and climate is very complex and much of this complexity is ignored or ”parameterized” in the GCM:s

    A few points:

    Water exists as a gas, a liquid and a solid in the atmosphere. Only the gas is a GHG, water and ice are (nearly) black body radiators. Water is constantly changing between these three phases in the atmosphere. Indeed the vaporization of water at the surface and re-condensation at high altitude is the most important mechanism for transporting heat to the TOA. An accurate GCM must be able to calculate these transitions accurately in three dimensions from basic physics. None comes even close.

    The amount of water vapor in the atmosphere strongly affects the lapse rate. More water means a lower lapse rate which works as a negative feedback on the surface temperature.

    The relative humidity is usually considered to stay constant with increased temperatures. This is contrary to actual data. TPW increases with temperature, but not fast enough to keep the RH constant.

  16. Here is all you need to see that the pattern of the US weather over the past century +, in which mid 1930s-40s highs were not surpassed by the 1998 El Nino until jiggered by Hansen. The earlier record was the strongest hockey stick of all. We have hardly warmed since 1937-45. All the state records and longest heatwaves are still to be found in the State temp records. They pushed this central high down mercilessly or the AGW CO2 meme was dead in the water. The 0.8C increase since 1880 is still the same but pushed off until the 1980s-90s and the 30-40 year decline in temperatures from 40s to late 70s was tilted up.

    The argument that it was only US and it is 3% of the globe (9% of the landmass). Lets add on Canada, Greenland, Europe and Siberia – it is the same. Let’s add on South Africa (Capetown):

    https://wattsupwiththat.files.wordpress.com/2017/01/clip_image0022.gif

    Lets add on Paraguay and Ecuador, even Australia (although they’ve trashed the record even worse). One day we will have to use these unadjusted, strongly corroborative records along with TWP, and a host of otherr metrics to repair the global temperature record in the post global gov putsch.

    • HadCRU and the other governmental gatekeepers have thoroughly cooked the books to a crisp, and now are putting their fat thumbs even on the “raw data”.

      Yes, the world heated up more during the early 20th century warming cycle than during the late 20 the century. Then it got really cold from the late ’40s to about 1977, when the PDO flipped dramatically, as I well remember. Yet during those decades, CO2 rose.

      QED that CACA was DOA.

    • “They pushed this central high down mercilessly or the AGW CO2 meme was dead in the water.”

      Yes, the Climate Charlatans erased the warmth of the 1930’s/40’s because it would definitely blow up the “Hottest Year Evah!” meme.

      Just about all unmodified temperature charts show the same temperature profile as the United States, i.e., the 1930’s/40’s are warmer than subsequent years.

      That is the temperature profile to which we should be comparing the CO2 chart. Comparing a bogus Hockey Stick chart to the CO2 chart is a worthless exercise.

  17. I am puzzled by this apparent puzzle as my understanding of how water behaves indicates that there will be no increase in TPW due to global warming. There are two constants in this behaviour: namely gravity and the temperature at which water evaporates at a particular pressure., which is determined by gravity. It is this that generates the lapse rate alongside the gas laws. I cite here my observation of the kettle in my kitchen which not only boils at a constant temperature (100C) ; but also increases the rate of boiling as the heat is turned up. This observation is but one datum point on the trace of temperatures in the rise in altitude where exactly the same parameters prevail.

    Secondly and similarly a steam generator varies it’s output at constant temperature but additionally recycles the same water through the Rankine Cycle which is what the atmosphere does thus with no increase in the water being required, albeit all at an increased rate. It all basic steam engineering.

    So where is the puzzle?

    Perhaps if global precipitation rates were measured then some confirmation on a global scale could be established; as this should marginally increase with additional energy input. Not an easy task.

    As an aside and perhaps off thread I am equally puzzled by the debate on whether water produces a positive or negative feedback to the purported CO2 effect; as it seems equally obvious to me that water provides the basic global thermostat although not very good at keeping the Earth warm. In trite terms the Earth sweats to keep cool- just like you and I.

    • Gravity indeed. Water vapour is lighter than air and is rapidly buoyed upwards to release its heat at altitude so that it is radiated readily into outer space, complicated by formation of clouds which reflect incoming solar. Not your average steam engine.

      • Dead right Gary. Indeed water is lighter than air until it condenses back to liquid , becomes heavier and it starts raining. Similarly, up in the Cirrus clouds nudging the Tropopause when the ice forms it again gets heavier than air and once more gravity takes a hold. In the steam engine we use a condenser so we can pump the water back into the boiler. The atmosphere just does it by raining. All done by gravity. Basic Rankine Cycle.

    • So here’s the question. As the average temperature of the planetary atmosphere increases does the average atmospheric pressure also increase? If it does increase in pressure then that means that the atmospheric mass has increased. How come? Well the atmosphere is carrying more water vapour, because all the other gases are none condensing, so question answered. But has the average pressure increased?
      Something else to measure and to calculate.

      • The atmosphere expands and contracts depending upon its average temperature. When the sun puts out more power, the atmosphere expands enough to endanger satellites in low orbit.

        More H2O in the air does increase the mass of the atmosphere a bit, but, as you know, increasing volume, following Boyle’s Law, means that pressure should decrease, all other things being held constant.

        PV = k, where P means pressure, V means volume and k is a constant.

        • Felix.
          Planetary atmospheres are gravitationally bound to their parent body. So as the total global atmosphere increases in mass the average surface pressure for the whole planet does not increase? You are kidding right?

          • Not at all.

            The greater mass of water is tiny compared to the effect of expansion from heating.

            The increase in H2O in the air is so slight as to be scarcely measurable on a global basis, as the uncertainties in this post show.

            Anyway, the increase will be greatest in regions where the H2O content is at its very lowest, ie polar deserts. The moist tropics won’t get much wetter, if at all, since temperature there isn’t increasing.

            The increased volume of the air however, thanks to more solar power at the peak of its cycles, is noticeable.

          • “The increase in H2O in the air is so slight as to be scarcely measurable on a global basis, as the uncertainties in this post show.”

            So this discussion is about weather and not about climate. Right

        • Fexlix

          Not to be a kill joy but strictly speaking Boyle’s Law only applies to ideal gas systems with constant mass and temperature. The air the body of a descending deep-sea diver being a classic example.

          Moreover, your conflating the ideal gas law, which assumes a gas body is operating in a system subject to a constant gravitation field, with the Newton’s laws describing the relationship between gravity, force, distance, and acceleration.

          The full Ideal gas law is PV = nRT where n is the number of moles (number of molecules in the gas), R is a constant, and T is absolute temperature.

          In the context of Philip Mulholland’s question use of the ideal gas law translates to:

          PV/nT = the constant R. Not PV = a constant k

          Anyway you look at it increasing the mass (or moles) in the atmosphere above you is going to increase pressure. Keeping in mind Pressure = Force/Area and the gravitational force of the atmosphere on the earths surface is, in simplistic Newtonian terms, Force = G * M * m / r2 where G is the gravitational constant, M is the mass of one body, m is the mass a second body, and r is the average distance between their centers of gravity.

          In this case M would be the earth, m the atmosphere, and r the average distance between these two “bodies”. (I’m not going to complicate this response by touching Newtonian shell theory).

          Boyle’s law can be roughly applied to the deep-sea diver example I used above because: 1) the diver change in depth is relatively negligible and the change in the gravitational field is relatively small, and 2) the air in the divers system has constant mass. The same can’t be said for the earth’s atmosphere where distance and significant changes in mass matter.

          In fairness I understand your later explanation that the changes in water mass you expect is small and your assumption the that any changes in absolute temperature is small. So, form those assumptions, your assuming Boyle’s law applies… I’m just not taking your assumptions at face value.

          For example, It does not follow in that later explanation that “The greater mass of water is tiny compared to the effect of expansion from heating.” If the effect of heating is significant then the temperature changes are significant and, strictly speaking, Boyles law cannot be applied.

          If you had said that the your expected the changes in additional mass was small and thus the change in the resulting pressure small I could have bought that generalized argument. But, introducing Boyle’s Law as an explanation is a bit much.

          • (I’m not going to complicate this response by touching Newtonian shell theory).
            Dave, I am glad that you dodged that one. The surface pressure reduction due to spherical geometry is about 5 mbar for planet Earth. The total average atmospheric pressure is 1013.25 mbar (that gas pressure equates to a fresh water layer with a thickness of 10.333m). So if the TPW at the equator is 60 kg/m2 that equates to a layer of water 6mm thick and a partial gas (vapour) pressure of 0.588 mbar. This is where it gets tricky TPW is a total column measure and we have an assumption of 100% precipitation efficiency (the total column becomes dry). How much increase in TPW does the radiative theory demand? As I said earlier; time for some more measurements and calculations.

          • Correction: I am getting my hundreds (cm) and thousands (grams) mixed up. Apologies. 60 kg/m2 of TPW is 6cm of water and that equates to a vapour pressure of 5.88 mbar. Looks like these numbers are ones that we can measure after all. It saddens me beyond belief that a world class physicist could not notice that in order to boil the oceans off the surface of the planet the atmospheric pressure must inevitably rise. Maybe its because my grandfather drove steam engines that I know that steam and pressure are linked.

          • All these references to kg/m2 don’t sound right to me. How can a 3D measurement (kg) be compared to a 2D one (m2)? How can a planar slice of atmosphere contain a weight (volume?) of TPW?

  18. When the Earth transitions to a hothouse climate mode, the polar regions are no longer “arctic”, they become “temperate (cool)”, possibly even “temperate”. Ice caps are replaced by open ocean, and humidity (and cloud cover) goes up.

  19. * more TPW may means more GHG effect from water…provided this isn’t already close to saturation. And it is. As dry as Sahara is, I am pretty sure adding water in its atmosphere would not result in it getting more warm.

    * however, TPW obviously correlates with clouds and rain. They are not the same thing, of course, but “all that goes up, must go down” applies to water, and even if there are some delays, rain is a pretty good proxy. Meaning,
    1) it shouldn’t be that difficult to know if there is, or not, more TPW. You just need rain statistics.
    2) more TPW means more clouds, sooner in the day, more albedo/less solar energy at day time. It would also means less loss at night, if I am not wrong (not sure about this one).

    Bottom line: climate studies should focus on clouds, which ARE the crux of the whole system, both under command and commanding, instead of focussing on GHG and CO2

    water vapor is a very strong greenhouse gas, at least twice as strong as CO2.

    • ” As dry as Sahara is, I am pretty sure adding water in its atmosphere would not result in it getting more warm.”

      It would increase the energy content of the air but probably not the temperature.

    • ‘What goes up must come down’, that is not quite what is meant with the water feedback (water vapour up > more warming) the point there is that not all water vapour precipitates out or forms clouds. I.e. on average it just stays in the atmosphere thereby increasing the greenhouse effect. Rain statistics are not going to Help in establishing if the water vapour content is increasing or not.

      I’m not convinced that all this is actually hapening but that is the argument needed for the water feedback.

  20. Bottom line is, they cannot predict local water concentrations in the atmosphere any better than they can predict clouds, or absence thereof. Obviously the two are intimately related, but total global atmospheric water content is no more helpful than a global average temperature. It is local water that counts. When the IPCC refer to non-condensible greenhouse gases, what they really mean is “please don’t ask me about water, or I shall start to whimper.”

    Even Science-of-Doom had a reasonable post about “The Strange Case of Stratospheric Water Vapor” back in 2010. https://scienceofdoom.com/2010/04/28/the-strange-case-of-stratospheric-water-vapor-non-linearities-and-groceries/
    Water transport across the tropopause, stratospheric methane oxidation to produce water in the most radiatively-sensitive part of the troposphere, and more….so many unknowns before one even starts on clouds.

    …And so many opportunities for climate modelers to make unjustified assumptions about the molecule (H2O) that really governs the Earth’s climate. It is axiomatic in Chemistry that you can collectively formulate credible postulates about chemical reactions and their mechanisms in a whole host of different solvents, except one. When it comes to water you need a whole new book, not just an additional chapter.

  21. With so much of the Data adjusted out of shape to fit the political requirements, studies like this face a lot of complications in forming a reliable result. In any case, they do show that the Science is not settled by a long shot.

  22. Perhaps a ckarification would be appropriate:
    – the temp Hockey Stick is not a credible comparison
    – the “world” is not warming. parts of the world may be warming, but not very much and not in lockstep.
    -since the upper atmosphere hotspot is not existing as predicted, what does any of this do except to further falsify the AGW hypothesis?

  23. Imagine that the atmosphere consisted of only CO2 and Water vapour. If more CO2 was added then the surface would warm and more water would evaporate and cool the surface to the point where evaporation is reduced. The water vapour would rise to the point where it forms clouds or precipitates and at a higher level as warming occurs. I predict more clouds and more precipitation so more upward transport of latent heat and more reflection of solar energy, both being negative forcings. Precipitation would increase so creating more evaporatable water at the land surface so more precipitation, more cloud and more negative feedback. CO2 would clearly have a job on its hands to raise surface temperature very much as the cooling of extra rain would be severely limiting.

    Who can do the maths?

    • And of course more rain and CO2 means more plant growth, transpiration and conversion of insolation into vegetable matter.

    • “Who can do the maths?”

      Nobody. Convection is a mesoscale (or smaller) process which is vastly beyond the capacity of existing computers to model. To go from 100 km cells to 1 km cells (still on the large side) requires 100^4 = 100,000,000 times larger computation capacity. The exponent 4 is because in addition to the 3 spatial dimension you also need to shorten the time-steps in the same proportion.

      Not gonna happen soon.

  24. Thanks Andy!

    More evidence that the strong positive water vapor feedback necessary for CAGW is not being observed in the real world! Alarmist’s have no answer for that one…

  25. Hi, should not that be kilograms per cubic meter? Square meter is a unit of an area. How on Earth can you have kilograms of water wapour on a flat surface!? It is embarrassing, how many people, including those claiming to be scientists, are grappling with the difference between length, area and volume.

    • No, it is a square meter on the ground, but it’s also a square meter all the way up from there, so it is measuring what’s in a volume, but it is not a volume.

      Specific humidity can be thought of as “absolute” humidity or the total amount of water vapor in the atmosphere. We will call this amount “TPW” or total precipitable water with units of kg/m2.

      • Specific humidity is actually the mass of water vapor per unit total mass of air. It’s dimensionless.

  26. This dissertation on TPW is exhibit A on why the AGW theory has never been scientifically validated.
    Without the water vapor feedback loop there can not be AGW as is claimed by the IPCC et al.
    Because all involved are fully aware of this major shortcoming the pretence of scientific certainty has been nothing short of fraud.

  27. Square root of TPW is a function of temperature multiplied by relative humidity. In nature relative humidity is not static but it is dynamic with changing winds. So, also TPW is not static but it is dynamic, this is more particularly when we talk of global TPW.

    Dr. S. Jeevananda Reddy

  28. Andy
    The removal of heat from the oceans is a self
    compounding issue that is resolved with time. Heat can enter the oceans faster than it can be dissapated. Why, because it is the heat of the surface of the ocean that controls the atmospheric temperature and therefore the solubility value.

    In the current so called modern warming phase the anomalies are recording ocean heat removal by atmospheric transport. Atmospheric circulation around the tropical latitude’s changes, but always within bounds. Therefore the heat removal is limited to those variables.

    The atmosphere flowing from African deserts onto the east Atlantic will remove more ocean heat because it is proportional warmer and dryer, but soon reaches equilibrium. Thermal upwelling and sidewelling at tropical latitude’s due to evaporation is enormous, replaced at sea level by a continuous fresh charge of atmosphere. If that fresh charge is near equilibrium ocean cooling is significantly reduced, heat remains. As many observers find incoming and outgoing heat never aligns. Part of the delay is circulation related, part is atmospheric heat removal effectiveness.

    From my own observations the heat removal process by way of water vapour takes mass into the atmosphere ultimately to the poles. Some condenses on route. This mass has flow on effects in that it can create blocking mechanisms that influence the hemispherical direction of the flow. These vary seasonally, but also serve to provide another measurement of heat release volume. As no one is analysing the reason for locational anomalies, the anomalies tell us very little.

    Close successive El Ninos compound heat loss issues, and give the appearance of run away warming therefore it must be something that has changed in the atmosphere and out come the calculators. Humans are impatient, earth has it’s own timetable.

    Try and dry your hair with ambient air, you need increased volumes flowing across the surface to accelerate the process, and if it’s a humid day?
    Regards

    • Andy
      Water has three states, solid, liquid and vapour.
      Solid has high albedo and reflects most heat, but still warms. Liquid has low albedo and and responds well to warming. Water vapour in the atmosphere it acts as a relector and blanket, but does water vapour increase in temperature in the atmosphere by either incoming our outgoing ?.

      I can’t recall that being discussed. If it does humidity will change.

  29. The water has to come from someplace. By what amount would this offset any ocean level rise?

  30. The question still remains: why is the desert hotter where there is very little water vapor and at the same latitude where there is much higher water vapor it is cooler? In fact, there seems to be a thermostat controlling how warm the surface can get. Convection rules the day, not radiation.

    The idea that water vapor can be the cause of a runaway “greenhouse” effect is laughable. There is zero evidence to support such a hypothesis. It’s a pipe dream.

    • no question here. Water evaporation is a huge cooler, absorbing 2265 kJ per kg (that is, 1mm spread on 1m²). Do do this in ~3 hours (10 ks) require over 200W. The world yearly average is 87W according to NASA, but obviously this will range from zero in dry condition to 500W or more were sun and wind soak 1mm/hour.
      Yes, water rules

    • Yeah, if water can absorb more energy and hold more energy before its temperature increases and then radiate more energy at a given rate, then water is COOLING and CONTROLLING temperature, NOT raising temperature.

    • Sunny days are warmer than cloudy ones, generally, right? Well, think about cloudy vs clear winter nights in the temperate zone (if you’ve experienced them). Clouds reflect the sun, but hold the heat in at night.

      Deserts are the same principle; they get hot in the day and cool down very quickly at night because there is little humidity to either block the sun or hold the heat in. The paucity of (actively photosynthesizing) plants in the winter and in deserts means less of the sun’s energy is absorbed and released later.

  31. P.S. Carl Mears has morphed into just another AGW lackey. His latest “adjustments” to RSS is a disgrace to Metrology.

  32. It occurs to me that cosmic rays may have something to do with upper tropospheric TPW. This would depend on whether water vapor or ice crystals are better radiators. If the water vapor is a better radiator, then desaturating the atmosphere by cosmic rays would produce ice crystals and lower the effective emissions height, producing cooling at the surface. This cooling would take place at solar minimum, when cosmic rays are most intense. Just a thought.

  33. Aqua/MODIS global satellite data shows TPW has declined from 2.26cm in 2002 to 2.17cm in 2010 then to 2.15cm in 2017.
    https://neo.sci.gsfc.nasa.gov/view.php?datasetId=MYDAL2_M_SKY_WV

    No idea about its absolute accuracy but I suspect it has the trend nailed.

    Measurements contradicts climate models but then what do you expect when they are based on fantasy about radiation transmission through atmosphere:
    https://www.youtube.com/watch?v=hjKJyn_uoIE

    For the earth surface temperature to rise the atmosphere needs to increase in mass and/or its specific heat increase in value. With no increase in TPW there is no increase in surface temperature. The stable condition of the sea ice supports that conclusion.

    • Oops. 10 hPa about 30 km, mabe QBO? Hadley abt 9 km, 300 hPa.
      .
      .
      Sandy,
      Minister of Future

  34. Lets face it, we just don’t know what mechanism is behind this, but we do know TPW is not increasing lock step in line with temperature globally. Over the oceans perhaps, but not over land, and not then not consistently with altitude.

    So the fundamental mechanism at the heart of every climate model, WV feedback, is shown to be bunkum. And with it all their predictions are equally junked.

  35. “Does Global Warming increase total atmospheric water vapor (TPW)?
    By Andy May : ” I can offer no solutions or great insights here, only questions and problems.”
    Andy May is a writer and author of “Climate Catastrophe! Science or Science-Fiction?”
    xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
    Anyone want to BUY YET ANOTHER BOOK ???????????????????????????????????????
    xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
    This ARTICLE………………..like MY ANSWER……………………….is UNHELPFUL !

  36. Anybody have an idea about the 200 kph antartic circulation in the QBO nullschool link?
    .
    .
    Sandy,
    Minister of Future

    • On the nullschool link, can change to 500 hPa for 5.6 km wind, or 700 hPa for 3 km wind. Got ‘no data’ when tried 300 hPa.
      .
      .
      Sandy,
      Minister of Future

  37. I thought I had read sometime ago on this site that NASA had found no appreciable increase in atmospheric water vapour

    • I’ve seen announcements like that as well as announcements that it has increased and decreased. They don’t know any more than we do. What is discouraging is that the uncertainty in the water vapor trend is so rarely mentioned. This is a key element of CAGW, and we don’t have a friggin’ clue.

  38. Andy,

    The biggest surprise to me in your figures 2 and 4 is that the total highest TPW in the tropics seems to be over land???(amazon and west africa)
    Any thoughts on why that would be the case?

    I can’t think of any reason other then that plants are more effective ‘evaporators’ then the ocean surface.
    That could turn things around a little…

    Great article, thanks for posting!
    Best,
    Willem

    • You got it – it’s the plants. They are constantly drawing water out of the ground and moving it into the atmosphere. Rainforest is a huge water vapor and O2 source.

  39. As I have said from the beginning of the AGW farce, the incompetent Hansen has been using the WRONG units of measure for the amount of HEAT in the air. It is not C or F, it is Total Heat per weight per degree. (BTU/#/F) Air temperature is not a measure of Heat, it is only a partial measurement indicating Sensible Heat, it excludes Latent Heat. This entire fraud is built on gullible rubes being hornswaggled with a bait and switch.

    The presence of humidity dampens temperature swings because it’s latent energy must also flow either in or out as well. The fact that global humidity tracks the AMO only continues to underline the driver of climate being the sun, the main supplier of energy to power the climate system.

    Either Hansen is grossly incompetent as a scientist OR he is a con artist. In My Opinion, he is a con man who has sought to enhance his public image and wealth through this deception. The fact that others jumped on the bandwagon to enrich themselves like Al Gore and Tom Steyer via subsidized and mandated products just gave Hansen cover.

  40. When looking at trends in the data using linear regression, I propose that we include the uncertainties in the intercept and slope. It is unclear whether the small upward trend in some of these graphs are significant in the statistical sense. Reporting the std uncertainty of the slope would either verify that the slope is significant or show that it is not (at the specified 1-sigma, 2-sigma, or 3-sigma level).

  41. “So, if the TPW estimates in the 1950s are accurate enough, perhaps they reveal a strong influence of the AMO cycle on TPW?”

    And as the AMO is warmer during low solar periods, it would be a huge negative feedback, along with changes in the vertical distribution of water vapour, declines in cloud cover, and higher atmospheric CO2 levels because of the warm North Atlantic and drier continental interior regions.

    • And I do not mean TSI or sunspot number. Cold AMO periods in the early to mid 1970’s, the mid 1980’s, and the early 1990’s, all occurred during periods of higher solar wind temperature/pressure. AMO warming since 1995 occurred from when the solar wind strength declined.
      https://snag.gy/d2v3aJ.jpg

  42. In Dr. Richard Alley’s book, “The Two Mile Time Machine,” he states that there is a clear linear relationship in the ice core data between precipitation and temperature… the warmer it gets, the more precipitation there is. More precip. comes from more clouds. Clouds increase earth’s albedo, reflecting sunlight back into space. This is a negative feedback.

  43. As Andy May himself remarks, this research seems to incite more questions than it answers, and there seems to be some contradiction in the correlation of “Total Precipitable Water” with temperatures since 1975 and the lack of correlation in the 1945 – 1975 period.

    The article starts with the premise that “Some have speculated that the distribution of relative humidity would remain roughly constant as climate changes”, but the remainder of the article deals with “specific humidity”, or mass of water vapor per volume of air.

    Relative humidity is defined as the ratio of the specific humidity to the saturation humidity, with the latter being defined by the Clauseus-Clapeyron equation as the maximum amount of water vapor in the air in equilibrium with liquid water at a given temperature. The data presented in this article do not answer the question of whether relative humidity remains constant as temperature rises.

    If we consider a volume of air, initially at a given temperature, flowing over a body of water, if the air temperature rises by one degree, attempting to maintain the same relative humidity would require evaporation of enough liquid water to increase the specific humidity to the higher value at the higher temperature, which requires input of heat. The amount of heat required increases with the temperature and relative humidity of the air, but at typical ocean temperatures of 10 to 30 C, and relative humidities over the oceans of 70% or more, a heat and mass balance shows that the heat absorbed by evaporating water would range from 50 to 80% of the heat used to warm the air by one degree.

    The assumption of constant relative humidity by some climate modelers therefore introduces a negative feedback of -0.50 to -0.80 on the “warming of the atmosphere”, since that fraction of the heat absorbed (by excess CO2) is consumed by evaporating enough water vapor to maintain constant relative humidity.

    It would be interesting to compare the “Total Precipitable Water” data in each grid cell to the saturation humidity as a function of temperature, to determine whether the relative humidity has decreased with warming temperatures over the 1975 – 2000 period.

  44. This is an excellent post by Andy May as well as the comment thread.

    My comment is slightly OT but related to TPW. There seems to some less than fully understood (by me) in the discussions of ‘water vapor’. Is water vapor a ‘catch all’ descriptor of all water content regardless of its state? If so, being used in this manner is as cloudy as a cloud.

    As I have read numerous articles and comments over time, to summarize the general consensus, water vapor at less than saturation (at less than 100% RH) would be completely transparent to LWIR. Visible clouds are opaque and grab and reflect the LWIR and reflect the visible coming in from above. Seems to be the general line of overall discussion. If that is the case and various explanations seem to say that only/primarily C02 is the cause of DWLWIR because invisible (to the eye) water vapor in the air simply absorbs and reflects LWIR but does not retain any of its energy. I have a problem with that in my mind.

    If someone can clear these issues up with me I would be thankful. Then I will follow up with a more important and relevant comment for discussion.

    If an LWIR meter were aimed at the bottom of a developing storm cloud (say 8ooo ft) on a hot and humid day and the measurements were taken as close as possible in time and were made at 1000 ft (elev) increments, would the readings be the same throughout the range of elevations? Observations requested, if modeled please state so.

    • Water vapor is a gas. Clouds, fog, and mist are liquid water. Snow and sleet are solid water.

      Water vapor–even a single molecule–absorbs and emits LWIR. It does not reflect LWIR. When a water vapor molecule absorbs LWIR, its energy states increase in one or more particular ways. Usually that molecule then transfers that energy to other molecules (of any kind, not just water vapor) that it bumps into. Much less frequently, that molecule first and instead radiates that energy, again as LWIR. Meanwhile, that same molecule gains energy by bumping into other molecules. CO2 molecules behave the same, at some of the same LWIR wavelengths as H2O molecules, but also at some different wavelengths.

      Visible clouds are not 100% opaque to visible light, nor to LWIR.

      I’ve never seen anyone claim that only or primarily CO2 is the cause of downwelling LWIR, if by “cause” you mean proximate cause. Indeed, a main feedback of CO2-direct-caused warming is an increase in water vapor due to the increased atmospheric temperature that allows more water to remain as vapor. However, that feedback mechanism is why CO2 is called the main control knob of temperature. If at a given atmospheric temperature you throw up more water vapor, the atmosphere can’t hold it and it condenses out (as a global average, in about 10 days). CO2 does not condense out, so adding more causes that additional amount (not those individual molecules) to stay there a really long time, which means the atmosphere has time to warm, which allows more water vapor to stay in the air. Here is a little more about water vapor; read the Basic tabbed pane and then the Intermediate one.

      • Tom,

        Thanks for your reply. I hurried in my initial posting/comment with regards to writing that the water vapor ‘grabbed and reflected’ the LWIR (my bad) as it absorbs and emits. There’s a bit of country boy in me. So, per your comment, water vapor in less than saturated air will increase in temperature due to LWIR. That was one of the most important things I wanted to verify. Would it be fair to say that as the relative humidity increases the temperature would also increase due to LWIR and would intensify at some scale or would it simply depend on the absolute humidity and results be the same

        • Only the absolute number of water vapor molecules matters, so only specific (absolute) humidity matters. Relative humidity is irrelevant in that regard. You’ll sometimes see relative humidity discussed. That’s because relative humidity (globally averaged) is expected to stay constant as temperature increases, based on fundamental physics and supported by more complex physics. If relative humidity stays constant while temperature increases, the consequence is that specific/absolute humidity increases.

          • Thanks Tom, in keeping OT and focused on a single point of reference of the underside of a developing storm cloud let’s disregard global averages for the time being. Too much modeling going on there. I originally arbitrarily chose 8k feet as the bottom of cloud, but 5k – 6k would be an equally good reference as long as discussion doesn’t start to forget the reference and if we use land conditions we stay with that. If a discussion is referenced to ‘apples’ we need to try and stay with apples. I’m trying to understand the interaction of water vapor, LWIR and temp within a defined point/state. That being the underside of the developing cloud base.

            So as a storm cloud begins to develop over a previously hot sunny surface the humid air is now being heated intensely from both above (bottom of the cloud at the temp of condensation, dew point?) as well as from UW LWIR from the surface. That would tend to negate standard lapse rate temperature calculations for a rising parcel of moist air in my reasoning as any water vapor is constantly being heated from the cloud above, the ground/surface below, and as well from adjoining parcels of air. Are we in agreement on this before I continue?

          • You are avoiding the conversation now? Do you agree with the above post? Too complicated to continue?

            I thought it was leading to a productive dialog.

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