Overview of the various models for ice ages in the recent past (3 MYBP to present) - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 233

to produce any significant variation in solar intensity reaching the Earth, so
changes in solar intensity due to variable dust cannot directly account for glacial-
interglacial cycles.
There is a theory that smoke particles affect stratospheric conductivity and, by
means of processes somewhat obscure to this writer, affect cloud formation above
the Earth. This, in turn, affects the Earth's climate. M&M seem to be enthusiastic
about this model. Variability of the inclination of the Earth's orbital plane
modulates the accretion of interplanetary dust. The dust, in turn, is claimed to
affect climate through its effect on cloud cover and ozone.
8.7.2 Clouds induced by cosmic rays
Benestad (2005) provides an extended discussion of a theory that cosmic rays,
controlled by the Sun's magnetic field, produce changes in cloud formation which
affect the Earth's climate. He provides many references. Only a brief report is
given here.
The theory postulates that, as variations in solar activity take place, the solar
wind changes, and the solar wind controls the number of galactic cosmic rays
from deep space that enter our solar system and penetrate the Earth's atmosphere.
The solar wind thus acts like the control grid on an old-fashioned triode vacuum
tube where cosmic rays provide the ''current to the anode''. The theory then
claims that cosmic rays enhance cloud formation by producing charged
atmospheric aerosols that act as nuclei for cloud formation. Thus, according to
this model, an increased flux of cosmic rays due to lower solar activity produces a
cooling effect on the Earth. So, it is claimed that the putative correlation of solar
activity with climate is an indicator of solar wind effects that in turn affect cosmic
ray penetration, which affects cloud formation, which in turn produces cooling.
Several versions of this concept have been proposed.
Patterson (2007) asserted all of this as if it were self-evident and a proven fact.
Svensmark and Friis-Christensen (1997) compared the variation in low- to
mid-latitude total cloudiness between 1984 and 1990 with cosmic ray flux (which
is inversely dependent on solar activity). During the period of minimum solar
activity in 1986 total cloudiness was 3-4% higher than near solar maximum in
1990. From this they suggested that cosmic rays might enhance cloudiness possibly
through a mechanism involving an increase in atmospheric ionization and
formation of cloud condensation nuclei. Such an increase in cloudiness would
produce a cooling effect. Over a sunspot cycle, the authors found cosmic rays
varied by 15-20% and this correlated strongly with a 3% (absolute) variation in
cloud cover over that same period. Since total cloud cover is about 63% (see
Table 8.1 ), this is about a 5% relative change in cloud cover. A 5% relative
change in cloud cover would result in a variation in the radiation budget equiva-
lent to about 1W/m 2 (M&M).
Kernthaler et al. (1999) disputed the results of Svensmark and Friis-
Christensen (1997) on the grounds that the correlation between cosmic rays and
cloudiness is weakened if higher latitude data are included. A greater concern,