(Note that radiative
forcing is not necessarily proportional to reduction in atmospheric
transparency, because relatively opaque layers in the lower warmer troposphere (water vapor, and for the fractional area they occupy, low
level clouds) can reduce atmospheric
transparency a lot on their own while only reducing the net upward LW flux above them by a small amount; colder,
higher -
level clouds will have a bigger effect on the net upward LW flux above them (per fraction
of areal coverage), though they will have a smaller effect on the net upward LW flux below them.