For 190 years the atmosphere has been thought to warm Earth by absorbing a portion of the outgoing LW infrared radiation and reemitting it back toward the surface, thus augmenting the incident solar flux. This conceptualized continuous absorption and downward reemission of thermal radiation enabled by certain trace gases known to be transparent to solar rays while opaque to electromagnetic long-wavelengths has been likened to the trapping of heat by glass greenhouses, hence the term ‘atmospheric greenhouse effect’. Of course, we now know that real greenhouses preserve warmth not by trapping infrared radiation but by physically obstructing the convective heat exchange between a greenhouse interior and the exterior environment. Nevertheless, the term ‘greenhouse effect’ stuck in science.
The hypothesis that a freely convective atmosphere could retain (trap) radiant heat due its opacity has remained undisputed since its introduction in the early 1800s even though it was based on a theoretical conjecture that has never been proven experimentally. It is important to note in this regard that the well-documented enhanced absorption of thermal radiation by certain gases does not imply an ability of such gases to trap heat in an open atmospheric environment. This is because, in gaseous systems, heat is primarily transferred (dissipated) by convection (i.e. through fluid motion) rather than radiative exchange. If gases of high LW absorptivity/emissivity such as CO , methane and water vapor were indeed capable of trapping radiant heat, they could be used as insulators. However, practical experience has taught us that thermal radiation losses can only be reduced by using materials of very low LW absorptivity/emissivity and correspondingly high thermal reflectivity such as aluminum foil. These materials are known among engineers at NASA and in the construction industry as radiant barriers [129]. It is also known that high-emissivity materials promote radiative cooling. Yet, all climate models proposed since 1800s are built on the premise that the atmosphere warms Earth by limiting radiant heat losses of the surface through the action of infrared absorbing gases aloft.
