The first principle is that you must not fool yourself - R. Feynman

Some time ago, Eli put up a comment about Number 6 of the Cohenite 10 in which Ferenc Miskolczi visits the haunted house of bad assumptions and math manglement to reach the promised land of never mind about climate change. It's enough to drive a bunny to drink (picture from kansaspraire.net). You could, if you were a masochist, follow the tracks at Niche Modeling or at Climate Audit, and a very long trail it is, but the current state of play was pretty well put by Alex Harvey

Alright, you’ve been absent from this debate because, as you stated publicly months ago, you lost interest in it. That’s fine, welcome back. But since then, it has been made quite clear that Miskolczi’s theory was, in the first instance, an empirical discovery. The mathematical theory of M2007 that you are objecting to here was adduced “after the fact” to explain a series of well-documented empirical observations, as Ferenc has made quite clear earlier in this thread.

All praise to Nick Stokes and Pat Classen who put considerable work into tearing the Miskolczi hocus mathepocus apart (look into their comments on the various threads). So now this waste of electrons is reduced to the claim that the optical depth of the atmosphere is held constant at 1.87 by compensating variations in the water vapor column density in the atmosphere. Well, at least for the Earth's atmosphere right now that is the value, but is it fixed and if it is what is the mechanism?

We know that the atmospheric concentration of CO2 is rising which would increase the optical depth. The only way that the optical depth could then decrease is for the water vapor column density to decrease. Measurements show that the surface is warming. Since warmer temperatures will result in higher water vapor pressure, the only way that total water vapor would decrease would be for the excess water to rain out quickly. Although there is some data on water vapor column density from way back when, it is not of the highest quality, and the further back you go, the worse it gets. Is there another way to get at this?

Why yes young fella, if you had the right satellite instruments you could look at the water vapor concentration as a function of temperature on the surface over a relatively small area. And guess what we have the right satellite instrument, the Atmospheric Infrared Sounder (AIRS) and Andrew Dessler and friends have used data from this instrument in a paper currently appearing in the Journal of Geophysical Research, and as you would expect if you were not Ferenc Miskolczi, the column density of water vapor increases as the surface temperature below increases.
The numbers refer to the water vapor content of the air at different levels in g water/kg air. Ts is the sea surface temperature below the satellite. As a sweetner, Dessler, et al., show that the compositional observations of AIRS can be used to calculate the outgoing longwave radiation (OLR) from the earth and that those results match observations of OLR from another satellite instrument (CERES). Another study is described below


A complimentary paper published by Soden, Jackson, Ramaswamy, Schwarzkopf, and Huang in 2005 (sorry, it's behind a paywall) covers the same ground, showing that the column water vapor has been increasing and, as importantly showing that a GCM can match the observations. That alone is enough to cocked hat Miskolczi but as importantly Soden, et al., provide a concise and clear explanation of what the actual issues involved in studying water vapor concentrations are. In particular, while the increase of vapor pressure with temperature drives the water vapor pressure low in the atmosphere, and this dominates, the middle and upper troposphere are different cases

When forced with observed SSTs, this model successfully reproduces the observed column-integrated moistening changes over this period (Fig. 1). However, because the mass of water vapor decreases rapidly with height, the column integral is primarily weighted by the lower troposphere, and its largely thermodynamic behavior is unsurprising (21). Consequently, there is not much debate about the projected increase of column-integrated water vapor in response to global warming, and its agreement with models provides only limited reassurance in their simulation of water vapor feedback (9).

In contrast, water vapor in the free troposphere is not so directly constrained by thermodynamic arguments (21), and its response to global warming has been the subject of long-standing controversy (9, 15–17). Given the radiative importance of moisture changes in the upper troposphere (9, 10), it is important that humidity changes there are demonstrably consistent between models and observations. Although an international network of weather balloons has carried water vapor sensors for more than half a century, changes in instrumentation and poor calibration make such sensors unsuitable for detecting trends in upper tropospheric water vapor (27). Similarly, global reanalysis products also suffer from spurious variability and trends related to changes in data quality and data coverage (24).

which tells you to be wary of the global reanalysis product and if you follow the reference it will tell you why to be wary. The study shows that not only is relative humidity in the upper troposphere remaining roughly constant and the actual humidity increasing as the air warms, but the change is captured by GCMs

Climate models predict that the concentration of water vapor in the upper troposphere could double by the end of the century as a result of increases in greenhouse gases. Such moistening plays a key role in amplifying the rate at which the climate warms in response to anthropogenic activities, but has been difficult to detect because of deficiencies in conventional observing systems. We use satellite measurements to highlight a distinct radiative signature of upper tropospheric moistening over the period 1982 to 2004. The observed moistening is accurately captured by climate model simulations and lends further credence to model projections of future global warming.