Richard Lindzen, PhD
MIT Professor
of Meteorology, emeritus,
has studied this subject.
High level cirrus clouds
have a greenhouse effect
comparable to water vapor.
"Spissatus clouds"
are the highest clouds
in the atmosphere.
They form in the higher tropopause,
where most of the water vapor
freezes out, or even in the
lower stratosphere.
The tropopause separates
the troposphere from
the stratosphere.
Unlike typical wispy cirrus clouds,
Spissatus clouds are dense
and opaque, blocking sunlight.
They are formed at the tropopause
because that's where a thermal
inversion occurs
( the air starts being
warmer with increasing altitude,
rather than cooler ).
( Warming of the even higher
stratosphere, with increasing altitude,
is from ozone created from
oxygen by ultraviolet sunlight.
Ozone is not an important
greenhouse gas
below the stratosphere. )
Lindzen has written about
the “iris hypothesis.”:
Increasing temperatures
in the tropics, particularly
increasing sea surface
temperatures
( seas are 75% of the tropics ),
reduce cirrus clouds,
reducing the
greenhouse effect
of those clouds.
But the UN Intergovernmental Panel
on Climate Change (IPCC)
ignores the influence of cirrus clouds.
The IPCC's Technical Summary of the
Fifth Assessment Report (AR5, 2013)
gives the “Components of Radiative
Forcing.”
Aerosol – Cloud is given as
having a cooling effect.
There is no mention of the
greenhouse influence from clouds.
But campers in the desert at night
are sometimes surprised to find
out it gets much colder at night than
a non-desert place with the same
altitude and latitude.
That's because of the water vapor
in clouds, and general humidity,
outside of desert areas, has a
greenhouse effect, slowing
Earth's cooling at night.