Greenhouse Effect: Does Water Vapor Increase or Decrease the Lapse Rate?
Written by Carl Brehmer
At first glance this simple question appears to be lifted from a first year, undergraduate class in meteorology, because everyone who has even a rudimentary understanding of the thermodynamics of the atmosphere knows that water vapor decreases the lapse rate, i.e., the rate at which the air temperature changes with altitude—ascending air cools at a certain rate as it “does work” against its progressively less dense surroundings and descending air warms at a certain rate as its progressively more dense surroundings “does work” on it.
As countless weather balloon soundings have shown water vapor decreases this lapse rate and it has even been observed that this attenuation becomes more acute as both the temperature and the humidity increase. One wonders then why the country’s most prestigious universities in classes across the hall are teaching their students that water vapor increases the lapse rate via a hypothetical “greenhouse effect”.
Princeton “The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since part of this re-radiation is back towards the surface, energy is transferred to the surface and the lower atmosphere. As a result, the temperature there is higher than it would be if direct heating by solar radiation were the only warming mechanism.”
“What is the greenhouse effect?
“This refers to the retention of the sun’s warmth in the Earth’s lower atmosphere by greenhouse gases. These gases (primarily carbon dioxide, methane and nitrous oxide) act as a thermal blanket for the planet, warming the surface to a life-supporting average of 59 degrees Fahrenheit (15 degrees Celcius).”
“55% of the heat that warms the atmosphere is quickly re-radiated radiated back to the earth (324 W/m2). This warms the earth and the lower atmosphere.”
“Some of the emitted radiation [from the surface] passes through the atmosphere and travels back to space, but some is absorbed by greenhouse gas molecules and then re-emitted in all directions. The effect of this is to warm the Earth’s surface and the lower atmosphere. Water vapor (H2O) and carbon dioxide (CO2) are the two largest contributors to the greenhouse effect.”
“We have demonstrated how the ‘natural’ greenhouse effect (e.g. H2O, natural CO2) elevated surface temperature. Next time we will extend this simple model to show how the addition of greenhouse gases increases surface temperature.”
Now, you might be saying, “What are you talking about? None of these definitions mentions a ‘lapse rate’,” but notice that each one of these definitions of the “greenhouse effect” hypothesis asserts that “greenhouse gases” only warm the “surface and the lower atmosphere.” Not one of them asserts that “greenhouse gases” warm the entire troposphere or the upper troposphere. Doing so, of course, would be foolish since the upper troposphere in the mid-latitudes is commonly as cold as -60 °C and can be as cold as -80 °C! By default then, when one asserts that there exists a thermodynamic process within the atmosphere that only warms the lower troposphere and not the upper troposphere one is asserting that that process increases the lapse rate—the temperature differential between lower tropospheric air and upper tropospheric air that is quantified in °C/km. Indeed, it has even been suggested by some that if there were no “greenhouse gases” in the atmosphere there wouldn’t even be a lapse rate.
“Without the destabilization provided by the greenhouse effect, convective overturning would slow and quite possible cease altogether. The atmosphere would eventually become isothermal, as the full depth of the atmosphere would achieve the same temperature as the surface through thermal conduction; without IR emission, the middle and upper troposphere would have no way to cool itself in the face of this heating.” Roy Spencer
The mental construct that “greenhouse gases” either create or at least augment the lapse rate can also be seen in this mathematical hypothetical being taught at Boston University . . .
When one digs deeper into the “greenhouse effect” hypothesis one finds that it is not actually increasing CO2 levels that are causing concern in the minds of some people but rather it is the expected increase in humidity that atmospheric warming from any source is likely to cause. Via what is called “positive water vapor feedback” this extra humidity is said to amplify any lower atmospheric warming from any source up to 300%
“Water vapor is a greenhouse gas, even more effective at absorbing the thermal radiation from the Earth’s surface than carbon dioxide.
“As the temperature of the atmosphere rises, more water is evaporated from ground storage (rivers, oceans, reservoirs, soil). Because the air is warmer, the relative humidity can be higher (in essence, the air is able to ‘hold’ more water when its warmer), leading to more water vapor in the atmosphere. As a greenhouse gas, the higher concentration of water vapor is then able to absorb more thermal IR energy radiated from the Earth, thus further warming the atmosphere. The warmer atmosphere can then hold more water vapor and so on and so on. This is referred to as a ‘positive feedback loop’.
“ . . . CO2 provides a measurable direct addition to the atmospheric trapping of infrared radiation leaving the surface of our planet. However, a simple comparison of the relative greenhouse efficiencies of water vapor and CO2 quickly becomes problematic because water vapor enters the climate system mostly as a “feedback” gas . . . Thus, as climate warms (cools), the holding capacity of the atmospheric water vapor increases (decreases) exponentially. This is a powerful water vapor positive feedback mechanism—that is, a process that acts to amplify the original warming caused by increasing CO2 levels. With this major positive feedback, the modeled “climate sensitivity” increases by about a factor of three, to roughly 3 °C.”
The “greenhouse effect” hypothesis therefore is the belief that “greenhouse gases” 1) create or enhance the lapse rate, which 2) raises the Earth’s average ground level air temperatures some 33 °C and 3) that at least 22 °C of that enhancement is the doing of water vapor, “the most powerful greenhouse gas.”
“Water vapor is a more powerful heat-trapping greenhouse gas than carbon dioxide.” Columbia University
So, let’s test out this hypothesis by looking at what actually happens to the temperature profile of the troposphere when nature removes the water vapor from the air such as in a desert or during a drought. Here is a graph of the troposphere’s current average temperature profile with water vapor in it. It varies slightly from the Standard Atmosphere because water vapor is only present in significant amounts within the lower 5 km of the troposphere and this lowers the lapse rate of the bottom half of the troposphere compared to its top half.
At the left side of this graph you can see that the mean global air temperature at sea level is about 15 °C. From sea level to about 5km in altitude the “lapse rate” averages roughly 6 °C/km and above that altitude the “lapse rate” increases to an average of about 8 °C/km the rest of the way up to the tropopause at about 11 km whose average temperature is -60 °C on average. The reason that there is a change in the lapse rate at about 5 km in altitude is because most of the water vapor that is present in the lower troposphere has condensed out of the air by that altitude. This creates a “dog leg” in the temperature profile of the troposphere as the lapse rate changes from a moist lapse rate to a dry lapse rate.
As we saw above, the “greenhouse effect” hypothesis asserts that “greenhouse gases” either create or augment the lapse rate and that 2/3rds of that augmentation is the doing of water vapor. Therefore, according to the hypothesis if there were no water vapor in the atmosphere the lapse rate would decrease markedly causing ground level air temperatures to drop some 22 °C. Since water vapor is only present in significant amounts within the lower 5 km of the troposphere then this entire 22 °C of cooling would have to happen within that space and would require the following change in the temperature profile of the troposphere.
Ergo, if the “greenhouse effect” hypothesis were true and water vapor were causing some 22 °C of ground level warming then when nature removes the water vapor from the air, like over a desert or during a drought, then the lapse rate within the lower 5 km of the troposphere would have to drop down to about 1.6 °C/km for that much cooling to occur. As demonstrated in the above graph, this would create a much more acute bend in the “dog leg” at 5 km. (Again, remember that all of the above definitions of the “greenhouse effect” hypothesis assert that “greenhouse gases”, including water vapor, only heat “the surface and lower Atmosphere”. Therefore, if the “greenhouse effect” hypothesis were true removing water vapor from the air would only cool the surface and lower atmosphere.)
So, with that in mind let’s look at what actually happens when nature takes the water vapor out of the air in the Nevada desert.
This is a comparative study that I did of weather balloon soundings on two cloudless days in June of 2012 that compares the temperature profile above Jackson, Mississippi, which had an average ground level mixing ratio of 12.7 g/kg and Las Vegas, Nevada, which had an average ground level mixing ratio of 3.2 g/kg. I chose these two locations because they lie roughly along the same latitude and I chose cloudless days because I wanted to see what effect water vapor alone has on the temperature profile of the troposphere.
In essence nature performed an experiment for us by taking 75% of the water vapor out of the ground level air. Instead of increasing the acuteness of the bend in the “dog leg” of the temperature profile though (which would have happened if the “greenhouse effect” were true) the elimination of 75% of the water vapor from the ground level air removed the “dog leg” altogether as the lapse rate of the now drier lower 5 km of the troposphere increased to match the ~8 °C/km lapse rate of the upper troposphere. As you can see, the result of removing the water vapor from the air, rather than decreasing the temperature of the lower troposphere as the “greenhouse effect” hypothesis predicts, actually increased the temperature of the lower troposphere!
The fact that ground level air temperatures increase when nature takes the water vapor out of the air is not a new scientific discovery, since “heat waves” have always been preceded by droughts and desert climates have always been predictably warmer than humid climates along the same latitude. Here are some examples based on 2011 yearly mean temperatures and yearly mean humidity readings.
In each of these cases the mean annual temperature in the more humid climate was cooler than the mean annual temperature in the drier climate—an impossibility if the “greenhouse effect” hypothesis were true.
Again, the fact that water vapor has a cooling effect on ground level air temperatures is not hidden knowledge but instead has been observed by multiple scientists.
This was written in 2001
“ . . . water vapour steadily cools the troposphere by radiation, even where its concentration is quite low, owing to very active rotation bands and continuum effects (Doherty and Newel1 1984; Clough et al. 1992).” Mapes, Brian, Water’s Two Height Scales: The Moist Adiabat And The Radiative Troposphere, NOMCIRES Climate Diagnostics Center; USA, Q. J. R. Meteorol. SOC. (2001), 127, pp. 2353-2366
This was written in 2008:
“ . . . water vapour causes a negative feedback, not a large positive feedback . . . clouds cause a negative feedback, not a positive feedback.” Gregory, Ken, Why Climate Models Fail
These were written in 2009:
“A new 2009 paper finds that the crucial assumption in the GCM models used by the IPCC concerning strongly positive feedback from water vapor is not supported by empirical evidence and that the feedback is actually negative.” Carlin, Alan, Comments on Draft Technical Support Document for Endangerment Analysis for Greenhouse Gas Emissions Under the Clean Air Act, NCEE/OPEI, Based on TSD Draft of March 9, 2009
“Negative trends in q 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.” (Paltridge, 2009)
This was written in 2010:
“So which effect is stronger, water vapor’s cooling effect or warming effect? Interestingly, it is seldom mentioned in the global warming debate that the surface cooling effect of evaporation (which creates water vapor) is stronger than its greenhouse warming effect.” weatherquestions.com
This was written in 2011:
“This cooling effect of water vapor was proved following the 9-11 terrorist attacks. Atmospheric scientists studied the effect of water vapor on temperature in the wake of the attacks.” Ashworth, R., Nahle, N., Schreuder, Hans, Greenhouse Gases in the Atmosphere Cool the Earth!, Updated version – 10 May 2011
This was written in May of 2012 based on a study of data from 5600 weather stations:
“Direct evidence for negative water feedback is found in CRUTEM4 station data by comparing temperature anomalies for arid regions (deserts and polar regions) with those for humid regions (mainly saturated tropics).” Evidence for Negative Water Feedback Posted on May 23, 2012 by Clive Best
Is it any wonder then that the young people who are currently graduating from major universities are confused about the effect of “greenhouse gases” on the atmosphere’s temperature? Within one class at these universities students are being taught that water vapor increases the lapse rate via a “greenhouse effect”, which warms the “surface and the lower atmosphere”, while in another class across the hall they are being taught the truth—water vapor actually lowers the lapse rate, which results in a cooling of “the surface and lower atmosphere”. They are thus ill prepared to deal with the current tsunami of media propaganda that asserts that anthropogenic global warming (which in reality is hypothetically due primarily to positive water vapor feedback) will devastate the planet by the end of the 21st Century “without serious policy changes.”
“This report spells out what the world would be like if it warmed by 4 degrees Celsius, which is what scientists are nearly unanimously predicting by the end of the century, without serious policy changes. The 4 °C scenarios are devastating: the inundation of coastal cities; increasing risks for food production potentially leading to higher malnutrition rates; many dry regions becoming dryer, wet regions wetter; unprecedented heat waves in many regions, especially in the tropics; substantially exacerbated water scarcity in many regions; increased frequency of high-intensity tropical cyclones; and irreversible loss of biodiversity, including coral reef systems.” The World Bank, Turn Down the Heat, 2012
Again, the “4 °C scenarios” that this report would have you trembles in fear over are all based upon the false notion that water vapor increases the lapse rate and thus creates a positive feedback to atmospheric warming whatever the source. Perhaps that is why the World Bank itself included this disclaimer at the beginning of its own paper: “The World Bank does not guarantee the accuracy of the data included in this work.”