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Proven Negative Water Feedback Means CO2 Climate Impact Irrelevant

Written by Carl Brehmer

There is an ongoing scientific debate over whether or not carbon dioxide causes atmospheric warming or atmospheric cooling. The reason that this debate continues is because no scientific study has yet been devised to directly measure the affect of carbon dioxide on the temperature of the atmosphere.

The current real world experiment being tested is this: “What effect will doubling the carbon dioxide concentration in the atmosphere from pre-industrial times have on the mean global temperature?” Nobody knows because it hasn’t happened yet and won’t for another 70 years or so when carbon dioxide is expected to reach ~560 ppm or 0.00056th or 56/100,000th of the atmosphere.

At that time the global mean temperature will be compared to the pre-industrial global mean temperature and we will have one data point. Of course no competent scientist would ever draw a definitive conclusion from just one data point. Beyond that, not only will those who are currently debating this scientific question be long dead by then, the scientists of that day will still not know because the global mean temperature fluctuates naturally. A second data point would be helpful but a redoubling of atmospheric carbon dioxide to 1120 ppm will take centuries to occur if it occurs at all.

The same is not true for water vapor–the “most potent greenhouse gas”.  The amount of humidity that is present in various climates around the world and even within the same climate from one day to the next is variable enough to measure its effect on the temperature of that climate, which I have done in a number of studies using real world, open air data.  I have observed that in climates where there is ample ground moisture present the absolute humidity in g/kg goes up and down with the temperature, but when there is not ample ground moisture, like in a desert or during a drought, the mean temperature is higher in the drier climate contrary to the “greenhouse effect” hypothesis.

Affect of Humidity on City Temperatures

Here is a sample.  I downloaded a month’s worth of temperature and humidity reading from these four cities, which are typically fairly dry, from the National Weather Service and separated the more humid days from less humid days and averaged the temperature readings.  In each case the mean temperature of the drier days was higher than it was during the wetter days; in this study by 2-4 °C.


Phoenix v Dallas humidity and temperature

This is a study of a wet vs. a dry climate and these are yearly averages.  I chose to compare Phoenix with Dallas because they are close to the same latitude and receive similar amounts of sunlight.  As you can see even though Phoenix had a lower mean absolute humidity throughout the year its mean yearly temperaturewas 6 °C higher than the more humid Dallas.

Arid v Humid Temp profille Giles Australia

This is a graph of weather balloon temperature readings that were gathered above Giles, Australia.  The difference between the red (arid) readings and the blue (humid) readings was a thunderstorm that increased the ground level humidity from 1.7 g/kg to 11.5 g/kg this jump in humidity caused a 7 °C drop in ground level temperatures.


1) As seen in these graphs the presence of water vapor in a climate system has a measurable cooling affect on the lower 4km of the troposphere, but has little affect on the temperature of the troposphere above that altitude.  This should not be a surprise to anyone since water vapor is known to decrease the atmospheric temperature lapse rate as is seen in the third chart—the radiosonde date taken above Giles, Australia.

2) Those who hold that there is a universal positive correlation between temperature and water vapor focus on areas of the globe that have ample ground or standing water to be evaporated when the temperature goes up or on the “global average”.  Since 70% of the globe is covered with standing water naturally the “global average” correlation between temperature and water vapor will be positive.  A good example is this paper: Dessler, A.E., Zhang, Z, and Yang, P. The water-vapor climate feedback inferred from climate fluctuations, 2003-2008, Geophys. Res. Lett., 35, L20704, DOI: 10.1029/2008GL035333, 2008.  The paper states the following: “Over most of the troposphere, [absolute humidity] increased with increasing global-average surface temperature, although some regions showed the opposite response.” 

This is consistent with the results that are shown in the graphs above because the “regions that showed the opposite response” are the arid areas of the globe, which if the “greenhouse effect” hypothesis where true would be cooler rather than warmer because there is less water vapor in the air to “trap heat”.  This paper, which has since been cited in 90 other publications as proof that water vapor feedback is positive, glosses over the fact that water vapor actually has a cooling affect on the lower 4 km of the atmosphere by simply focusing on humidity’s “global average” relative to a “global mean temperature”, which again is 70% covered by oceans, i.e., standing water.  This may seem to be a subtle point but it is vital.  

Positive water vapor feedback is a two-step process. Step 1: higher temperatures cause more water to be evaporated into water vapor when water is available to be evaporated. Step 2: this extra water vapor causes even more warming.  The Dessler 2008 paper observed that as a global average the first step occurs but just “inferred” that the second step occurs as well as the title of his paper states: “water-vapor climate feedback inferred“.  That is, since these scientists believe that water vapor traps heat in the atmosphere they therefore infer that more water vapor will cause additional warming.  

So, even though the data gathered in Dessler 2008 actually falsifies the hypothesis that water vapor feedback is positive (“some regions showed the opposite response”, i.e., arid regions of the earth become warmer when the regional humidity drops), he arrived at a conclusion opposite the truth through inference.  It is well known that when investigators carry out a study armed with a preconceived notion, they only see the data that affirms that notion.  This is a mental phenomenon called “selective attention” and is vividly exemplified in this video.

In summary, there is ample evidence that when ground or standing water is available an increase in temperature will cause an increase in humidity, but there is no evidence that the additional humidity causes even more warming—causes “positive feedback.”  Rather there is clear evidence in the graphs above that when nature takes the humidity out of a climate system either in a desert or in a drought the temperature goes up rather than down contrary to the “greenhouse effect” hypothesis.  This is why “heat waves” only occur during droughts when nature takes water vapor—the “most potent greenhouse gas”—out of the air.

Unfortunately, those who believe in the “greenhouse effect” hypothesis and have a vested interest in it being true cannot afford to acknowledge the truth of the above observations since it not only means that water vapor feedback is negative; it also means that water vapor causes absolutely no atmospheric warming what so ever.  Instead it has a cooling affect on those climates where it is present. Even though those debating this issue agree on little else there is general agreement that absent positive water vapor feedback the affect of carbon dioxide on the global mean temperature is irrelevant.


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Comments (7)

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    Jan Zeman


    There seems to be fallacy in the argument.
    In the “humid areas” above ocean there’s quasi-infinite amount of water available to evaporate, while in arid areas -with only limited or virtually no water available, the eavaporation can’t much cool the surface (at least not on continuous base). Then there are humid areas on the land, especially at windward shores, where is limited amount of water available for evaporation.
    When we compare, we immediately find two things:
    1. there is much more of the ocean, moreover at lower well insolated latitudes (more than half of the world ocean – 52,16% – equivalent to more than 1.25 times the total world land area is at latitudes below 30° -which is the latitude cuting the Earth surface area exactly to half) and much less land at high, less insolated latitudes, moreover unevenly distributed – there’s much more land at NH than SH). Also it can be well estimated ~90% of total amount of water evaporated yearly is evaporated from ocean.
    2. when it comes to the distribution of humid and arid regions on the land it seems to preferentially occur around tropic at the edge of Hadley and Ferrel cell (they are caused by qualitatively different insolation pattern in the tropical region than mid-latitudes region – resulting in different circulation pattern and at the edge the drier air circulates down to the surface making the arid climate) – although it seems much less visible with tropical South America and its rainforest area (which most probably is caused by geographic factors as windwardness at the east, microclima caused by compactness of the forest and barrier of Andes on the west forcing the easterlies dominated atmosphere and carrying water content from Atlantic to release it there) it anyway seems by far not outweight Sahara, Middle-East, North American West and South and Australia combined by area.
    So in my opinion if somebody finds something about oceanic climate (and I don’t necessarily infer Dressler et al are right – I could find other fallacies in their argument), it in my opinion hardly can be disproved by comparison of Phoenix with Dallas and couple of other localities when it comes to global scale.

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    Reinder van Til


    This is what I also notice as amateur meteorologist. During heatwaves the air is much more dry. When the heatwave ends humidity increases, thunderstorms are formed and then the heatwave is over in my region of the world (Europe)

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    First of all, there is no debate “over whether or not CO2 causes atmospheric warming or atmospheric cooling” because all legitimate scientists already understand that temperature change drives CO2 levels, not vice versa.

    Secondly, a doubling of CO2 levels will be beneficial, as it will increase the growth rates of all plants / crops. More abundant food at lower prices for all. There is no risk in this, as 560ppm is still a relatively low level of CO2. The typical CO2 level in a crowded night club is 3,000 to 4,000ppm. In a submerged submarine it’s 5,000 to 6,000ppm.

    Warming is good!

    Throughout history, mankind has always thrived during the earth’s warm periods, & suffered & starved during the cold ones. This entire global warming thing is a hoax. 35 years ago the same propaganda artists were screaming about the coming ice age. This crap has been going on since the first shamans & witch doctors told their people that if they didn’t do what he told them to do, that God would continue the drought, or the floods, or the hurricanes, or the earthquakes, or the volcanic eruptions that they were suffering from. Things have not improved much since then… well a little I guess. We no longer have to sacrifice our first born.. all we have to do now is give money to Al Gore…


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    Please read your last paragraph as I think you have inadvertantly made an important error.At a minimum it needs a tidy up. Otherwise very easy to follow and logical presentation.Many thanks from Oz.

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    Lonny Eachus


    Pardon me. I missed the sentence that says “In each case the [b]mean[/b] temperature of the drier days was higher than it was during the wetter days; in this study by 2-4 °C.” (emphasis added)

    Still, I think a bit more effort could have been made to make the methodology clear.

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    Al Shelton


    So logical; so simple to understand; the water cycle we learned in grade 8 or 9 Science.
    How can anyone with half a brain believe the GHE?

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    Lonny Eachus


    I would be interested to know more about the methodology used to make the measurements.

    The article mentions “days”. What about nights? Pardon me for bringing up something that many people would consider to be too obvious to even ask… but no mention is made of how and when the temperature measurements were actually made.

    In the interest of completeness, can you at least tell us more detail about your measurements? At what times of the day/night were they taken? Since only a single figure is given per “day”, is this a mean of temperatures taken at regular intervals over a 24 hr. period? Something else? If so, what?

    I’m not trying to nitpick but if I were to try to refute these findings, that would be a rather glaring and obvious point of attack.

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