  An old conceptual physics-based back-of-the-envelope model for greenhouse
effect is revisited and validated against state-of-the-art reanalyses.
Untraditional diagnostics show a physically consistent picture, for which the
state of earth's climate is constrained by well-known physical principles, such
as energy balance, flow and, conservation. Greenhouse gas concentrations affect
the atmospheric optical depth for infrared radiation, and increased opacity
implies higher altitude from which earth's equivalent bulk heat loss takes
place without being re-absorbed. Such increase is seen in the reanalyses. There
has also been a reduction in the correlation between the spatial structure of
outgoing long-wave radiation and surface temperature, consistent with
increasingly more processes interfering with the upwelling infrared light
before it reaches the top of the atmosphere. State-of-the-art reanalyses
further imply increases in the overturning in the troposphere, consistent with
a constant and continuous vertical energy flow. The associateion between these
aspects can be interpreted as an entanglement between greenhouse effect and the
hydrological cycle, where reduced energy transfer associated with increased
opacity is compensated by tropospheric overturning activity.
