The Night Time Radiative Transport between the Earth's Surface, its Atmosphere, and Free Space

Abstract

Estimates are made for the exchange of radiative fluxes between the Earth's surface, its atmosphere, and free space on the basis of their average thermal structure and estimated values for the emissivity and absorptivity of those individual entities. The radiative fluxes obtained reflect nighttime conditions but also indicate the components of those fluxes that must be subtracted from the input solar flux for daytime conditions. The estimates show that infrared radiant energy is lost to free space from both the Earth's surface and its atmosphere. Under the normal atmospheric temperature structure there is no net radiation from the atmosphere that reaches the Earth's surface to be absorbed by it, and thus the so-called “greenhouse effect”, as it is traditionally depicted, is devoid of physical reality. The only exception occurs during atmospheric inversion conditions, but even in the presence of such rare inversions, the radiant power lost to free space from the atmosphere as a whole overwhelms the radiant power absorbed by the Earth's surface from the warmer inversion layer above it. Inversion conditions are thus the only ones in which the so-called “greenhouse effect” can possibly have any form of physical reality. But such inversion conditions, however, are present over only a small fraction of the Earth's surface for limited periods of time. In addition, since the recent increases in atmospheric CO2 concentrations have a trivial effect on the atmosphere's total emissivity, the effect of those recent CO2 increases on the overall infrared radiative flux balance is insignificant. The analysis also suggests a cloud cooling mechanism for the Earth's surface and its atmosphere that is significantly different from the one traditionally cited. Cloud blockage such as that reflected in the Earth's albedo acts symmetrically with respect to both the input heating by solar radiation and the output cooling by infrared radiation to free space. On the other hand, it is shown that the increasing infrared emissivity of the atmosphere caused by the presence of clouds provides an effective cooling mechanism that is asymmetric.