Future prospects - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 365

measurement of climate sensitivity; however (as he admitted), none of them are
straightforward.
According to Lindzen: ''a very important consideration ought to be how dry
and how large the areal coverage is of the very dry subsiding regions.'' Getting
satellites to measure humidity over dry regions over a period of years during
which CO 2 is increasing would provide the necessary relevant data.
Lindzen (1997) suggested ''a proper observational determination of the
sensitivity to global forcing.'' In this approach, one would attempt to measure the
monthly average top-of-atmosphere (TOA) flux integrated over the whole Earth
for several years along with surface temperature over the same period. One could
then correlate TOA flux with temperature. A caveat raised by Lindzen is that
OLR may change in response to changes in circulation without accompanying
changes

in mean temperature. This could make interpretation of the data

confusing.
An indirect approach might be based on observations of the Earth's response
following a major volcanic eruption. However, past attempts to do this had very
large error bars.
Cosmic rays as the forcing function for ice age-interglacial cycles Kirkby et al.
(2004) proposed ''a new model for the glacial cycles in which the forcing mechanism
is due to galactic cosmic rays, probably through their effect on clouds'' and suggested
that ''the model makes definite predictions that can be tested by further observations
and experiments.'' They suggested the following program:

''The first area to be tested concerns the paleo record of GCR flux, its orbital
components and association with climate change. Further 10 Be measurements in
sediment cores are required, over longer time spans and with improved precision
and dating. Parallel improvements are required for paleomagnetic intensity and
direction in order to study the orbital components and to separate solar and
geomagnetic effects in the 10 Be record. Orbital influences on the geomagnetic
field should be modeled. Further satellite data on GCR/solar wind characteristics
in the heliosphere are required, both in and out of the ecliptic, and during
different periods of solar magnetic activity. GCR transport in the heliosphere
for a magnetically quiet Sun (e.g. Maunder Minimum) should be modeled to
estimate the expected magnitude of orbital variations of the GCR flux.
The second area to be tested concerns the interactions of GCRs with Earth's
clouds and climate. Improved and extended satellite observations of clouds are
needed. Investigations are required on the effects of GCRs on clouds and
thunderstorms, including ion-induced cloud condensation nuclei production,
electro-freezing of super-cooled liquid droplets and atmospheric electrical
processes. The microphysics of GCR-cloud-climate interactions should be inves-
tigated in laboratory experiments under controlled conditions, and the results
applied to models and field observations. Combined interdisciplinary efforts in
these directions may quite quickly be able to establish whether or not the GCR
model for the glacial cycles is further supported, and where more work is needed
to quantify its physical basis.''