New talkshop visitor ‘David’ has dropped a fruitful link on Wayne Jackson’s recent thread which, after a bit of sleuthing via AstroBio.net, leads to a new paper from the Trieste Astrobiology Group led by Giovanni Vladilo. This will be of great interest to our friends Nikolov and Zeller, because it vindicates their contention that atmospheric pressure is the principle determinant of planetary surface temperatures. However, there is a twist. As well as affecting the near surface heat capacity, evaporation rates and meridional energy transport, atmospheric pressure also affects the atmospheric optical depth of atmospheres, and this explains the role of ‘greenhouse gases’ and their radiative properties in contributing to the overall distribution and magnitude of energy at planetary surfaces. Although not dscussed in the paper, I think it will also be the case that regardless of extra emissions of a greenhouse gas such as carbon dioxide, since the pressure is the primary variable, the optical depth will remain constant, as NASA Physicist Ferenc Miskolzci found. If so, the Man Made Greenhouse Panic is over.
The pressure-dependent habitable zone is shown in the left figure below. The circles indicate solutions of the climate simulations with mean global annual habitability h>0. The area of the circles is proportional to the habitability h; the colors are coded according to the mean annual global surface temperature, Tm. The size and color scales are shown in the legend. The solid lines are contours of equal mean temperature Tm=0 C (magenta), 60 C (red) and 120 C (black). (Click for larger image)
The key passage from the paper is this one:
4.2.1. Surface Pressure and Planet Temperature Variations of surface pressure affect the temperature in two ways. First, for a given atmospheric composition, the infrared optical depth of the atmosphere will increase with pressure. As a result, a rise of [pressure] will always lead to a rise of the [radiative] greenhouse effect and temperature. Second, the horizontal heat transport increases with pressure. In our model, this is reflected by the linear increase with [pressure] of the diffusion coefficient D (Equation (A5), Appendix A.2). At variance with the first effect, it is not straightforward to predict how the temperature will react to a variation of the horizontal transport. In the case of Earth, our EBM calculations predict a rise of the mean temperature with increasing D. This is due to the fact that the increased diffusion from the equator to the poles tends to reduce the polar ice covers and, as a consequence, to reduce the albedo and raise the temperature.
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