Watt’s Up with the Greenhouse Effect?
Recently an article was posted on the WUWT web site that contained this statement:
“CO2 and other GHG’s impede the transfer of LWIR energy to the top of the atmosphere where it is finally re-radiated into space. Without GHG’s, the lower atmosphere would be very cold . . . For those who doubt this, see” Roy Spencer’s post What If There Was No Greenhouse Effect?
I do; so I did. Unfortunately Spencer’s article is just a restatement of the same hypothetical but in the form of a “thought experiment” in which he describes what he imagines the temperature profile of the atmosphere would be if there were no “greenhouse gases” in the atmosphere and no standing water on Earth that could evaporate into water vapor. He then attributes to the “greenhouse effect” the difference between what the temperature profile of the atmosphere actually is and what he imagines it would be if there were no “greenhouse gases” in the atmosphere or standing water on the planet.
The problem with such “thought experiments” is that they exist purely in one’s mind and produce no empirical evidence. In short, they are not testable. We cannot, for example, remove all of the “greenhouse gases” from the atmosphere and rid the planet of standing water in order to test the veracity of Roy Spencer’s imaginary world. An axiom in science is that you cannot use a hypothetical to prove a hypothetical because an actual, physical, empirical experiment is needed to sort out the difference between what actually exists in the physical world and what only exists in the minds of men.
Karl Popper (1902–1994) stressed this point. “Popper stresses the problem of demarcation—sorting the scientific from the unscientific—and lays the demarcation criterion falsifibility, such that the unfalsifiable are unscientific, and the practice of declaring an unfalsifiable theory proved true by scientific method is pseudoscience.”
But all is not lost. Even though Spencer’s “thought experiment” is untestable and therefore unscientific it does contain two postulates that can be tested empirically:
1) Without “greenhouse gases” in the atmosphere it would be non-emissive.
2) There is a direct relationship between the emissivity of the atmosphere and its temperature, i.e., as its emissivity goes up its equilibrium temperature will go up and as its emissivity goes down its equilibrium temperature will go down.
Let’s begin by testing the first postulate: 1) without “greenhouse gases” in the atmosphere it would be non-emissive.
For those unfamiliar with what “emissivity” means here is a common definition:
Emissivity (ε) “is the ratio of energy emitted by a material to the energy emitted by a black body at the same temperature.”
Both Watt’s statement and Spencer’s “thought experiment” presume that without “greenhouse gases” in the atmosphere it would emit 0.00 (no) IR radiation.
An observation that contradicts the accuracy of this assertion comes from two surface radiation-monitoring sites maintained by NOAA. One is in Desert Rock, Nevada and the other is in Goodwin Creek, Mississippi. In order to study the radiative thermodynamic affect of humidity on the atmosphere in the absence of clouds (since clouds are not “greenhouse gases”) I picked a period during the year that typically has both little rainfall and a number of cloud free days to study. That turned out to be 20 days on either side of the summer solstice, 2012.
I then downloaded both the temperature readings and the down-going longwave radiation (DLWR) readings for all of the cloud free days over that period then averaged them in order to calculate the mean ground-looking-up atmospheric emissivity at each location. Here are the numbers:
Notice that a reduction in humidity from 60% to 10% only caused the emissivity of the atmosphere to drop from 0.837 to 0.703. That is about a 0.03 drop in emissivity for every 10% drop in relative humidity. Were we to take all of the water out of the air we could expect its emissivity to drop to ~0.673. In a paper Effective Atmospheric Emissivity under Clear Skies, , March 1972, Staley, et al, calculated the ground level emissivity of carbon dioxide to be ~0.20. Removing this from the atmosphere as well would drop its emissivity ~0.20 further down to ~0.473. Therefore without any water vapor or carbon dioxide in the atmosphere its emissivity would still be close to that of red clay tiles, which is a long way from 0.00. So, what then is making the atmosphere so emissive in the absence of the bulk of its “greenhouse gases”? The answer can be found in the conclusion of the quoted paper. It says: “The accuracy of the effective atmospheric emissivity is limited by the absence of a computation of the flux density contributed by aerosols . . .”
So, based on this ballpark study, up to 50% of the atmosphere’s emissivity may be due to aerosols (those small particulates that are suspended in the air that create the “haze” that one sees when looking at distant mountains) and not “greenhouse gases.” Therefore any statement, paper, article or “thought experiment” that asserts that in the absence of “greenhouse gases” the atmosphere would be non-emissive is demonstrably false.
Let’s now look at the second postulate 2) There is a direct relationship between the emissivity of the atmosphere and its temperature, i.e., as its emissivity goes up its equilibrium temperature will go up and as its emissivity goes down its equilibrium temperature will go down.
To study this hypothetical we can use the same data downloaded above and you will notice that even though Goodwin Creek is about 900 meters lower in altitude and a little further south than Desert Rock and should therefore have been warmer, its temperature was never the less 2 °C cooler. Stated another way, during the same cloud free days when the DLWR was 53 W/m2 higher in Goodwin Creek than it was in Desert Rock its temperature was 2 °C cooler. This is opposite from what the “greenhouse effect” hypothesis predicts and you don’t have to take my word for it since these readings are free to the public for download.
The “greenhouse effect” hypothesis predicts that as the humidity rises, this will increase the emissivity of the atmosphere, which will, in turn, increase the amount of DLWR and this will either cause a warming of the lower atmosphere and/or a delay in cooling of the lower atmosphere resulting in higher temperatures. The first part of that statement is true. As the humidity rises, this increases the emissivity of the atmosphere, which increases the amount of DLWR, but the second half of the statement is false; an increase in the DLWR does not universally result in an increase in surface temperatures, since increasing the emissivity of the atmosphere simultaneously enhances the atmosphere’s ability to cool via the emission of IR radiation out into space.
I did a number of similar comparisons between the temperatures of humid vs. arid climates that lie along the same latitude using mean temperature and humidity readings freely available online.
In each of these comparisons the more humid climate was the cooler climate, which is opposite from what the “greenhouse effect” hypothesis predicts. Therefore the statement, “without GHG’s, the lower atmosphere would be very cold,” is out of sync with empirical observation, because as the humidity (and therefore the concentration of “greenhouse gases” in the air) decreases more often than not the temperature goes up rather than down. Just remember that droughts bring on “heat waves” and not “cold snaps.” Death Valley is so hot because the concentration of “greenhouse gases” in its air is lower than anywhere else in the USA i.e., it is the driest. “Death Valley is the hottest and driest place in North America because of its lack of surface water . . .”
Is it not scientifically inappropriate to assert the existence of causation where correlation doesn’t even exist? That is, if humidity is more often than not seen to accompany cooler surface temperatures how can one seriously believe in a hypothetical that asserts the opposite—that an increase in humidity, i.e., an increase in the concentration of “greenhouse gases,” will cause surface temperatures to rise? Or, in the words of Roy Spencer, “When you pile all of the layers of greenhouse gases in the atmosphere on top of one another, they form a sort of radiative blanket, heating the lower layers and cooling the upper layers.” Real world data (as opposed to pseudo-scientific “thought experiments”) would suggest otherwise.