SOLAR ENERGY VARIATIONS AND ANOMALOUS WEATHER CHANGES 
amount of radiation received in either hemisphere in 
a year, and scarcely affects the total annual insolation 
at a given latitude. 
d. The effects are extremely small according to re- 
cent calculations by Simpson [22]. 
2. The theory of mountain or continent building is 
based on the idea that glaciation is caused by periods 
of continental uplift and mountain building. Conti- 
nentality presumably leads to cold winters, and moun- 
tains focus the precipitation orographically and give 
cool summers. Even today, evidence is abundant that 
these factors are favorable for glaciation. However, 
it seems likely that these factors, while they probably 
determine the patterns of glaciation and perhaps are 
necessary conditions for glaciation, are not in themselves 
sufficient. Simpson [22] has very neatly poimted out 
that the Southern Hemisphere, with only about one- 
half as much land as the Northern Hemisphere, actu- 
ally averages 2C colder in its annual mean, a maximum 
effect of 3C being reached at latitude 60° where the 
Northern Hemisphere is 60 per cent land, the Southern 
0 per cent. Moreover, geological evidence indicates that 
periods of continental uplift have occurred in some 
cases without subsequent glaciation, and that m other 
cases the associated glaciation has followed only after 
millions of years. Furthermore, the glacial and inter- 
glacial stages and substages of the Pleistocene ice age 
have no associated geological changes. 
Climatic Weather Changes. Climatic changes, with 
their smaller amplitudes, have received less attention 
than geological changes. Of the theories discussed above 
for the geological changes, only the theory of solar 
variability could carry over to explain climatic changes. 
For example, C. KE. P. Brooks, a proponent of the theory 
of continental uplift as a cause of geological variations, 
has turned to solar variability as a cause of climatic 
changes [4]. As was pointed out above, climatic oscilla- 
tions have been similar in character and intermediate 
in degree to geological variations, on the one hand, and 
to secular or week-to-week changes on the other. The 
inability of a given theory to explain all the changes is 
therefore a weakness in that theory. 
Secular Weather Changes. No cause of the secular 
weather changes, other than possible solar effects, has 
been seriously offered. Some of the statistical studies 
attempting to relate secular weather changes to the 
sunspot cycle are reviewed below (see pp. 386-387). 
Week-to-Week Weather Changes. In recent years 
week-to-week changes in the general circulation have 
been studied extensively by many meteorologists. In 
particular the Weather Bureau-M.1.T. Extended Fore- 
casting Project under Willett’s direction has conducted 
an exhaustive statistical study of the week-to-week 
pressure changes. Using a linear-correlational technique, 
Willett [26] has compared the zonal index with param- 
eters that describe other segments of the general cir- 
culation, such as the zonal easterlies, the subtropical 
easterlies, and the intensity of meridional interchange. 
These studies yield a number of consistent and statisti- 
cally significant contemporaneous correlations between 
the various parts of the general circulation. However, 
385 
they fail to yield any consistently significant lag correla- 
tions. 
The implication of this result is that the causes of 
large-scale weather changes are not to be found in the 
pre-existing state of the general circulation. Possible 
explanations are that: 
1. The changes are purely chance fluctuations. 
2. The crudeness of the statistical techniques has 
masked some real relationships. 
3. The control mechanism is in the earth’s atmos- 
phere, but is outside the region thus far studied—the 
Northern Hemisphere between the surface and 3 km. 
4. The control mechanism is outside the earth’s 
atmosphere, presumably in solar variability. 
The first explanation, that of chance fluctuations, 
is not only unlikely in view of the world-wide and per- 
sistent character of the fluctuations, but also represents 
an extremely undesirable conclusion which could not be 
accepted until all other possibilities were definitely 
ruled out. With regard to (2), the statistical methods, 
while undoubtedly crude, have served to show up cer- 
tain contemporaneous relationships and could hardly 
fail at least to indicate the existence of significant lag 
relationships. Explanation (3) cannot be investigated 
further at the present time because of lack of data. 
The external control mechanism, here, as in the cases 
of other types of irregular fluctuations, remains as a 
distinct possibility, in that adequate causes of any 
other nature have not been established. 
THE SOLAR HYPOTHESIS AS THE PRIMARY 
FACTOR CONTROLLING THE ENTIRE SPEC- 
TRUM OF ANOMALOUS WEATHER CHANGES 
The discussion of the preceding pages indicates in 
certain respects the general over-all aptness of the 
solar explanation for the entire range of irregular 
weather fluctuations, and certain objections to possible 
alternative explanations of the individual categories 
of climatic change. It remains only to present any 
available evidence favoring the solar explanation of the 
specific categories of the fluctuation of world weather 
or climate. 
Geological (Glacial-Interglacial) Fluctuations. As in- 
dicated above, the work of Simpson and others renders 
relatively untenable both continentality (terrestrial to- 
pography) and the long-period geometrical variation 
of the distribution of insolation as the primary cause 
of the fluctuations of climate during geological time. 
Of the current widely accepted hypotheses by which 
to account for the glacial-interglacial climatic cycles, 
only the variable output of solar energy remains. 
There are two schools of thought as to the probable 
solar energy change required to produce an ice age, 
that of most geologists, as formulated by Flint [7], 
which calls for a substantial decrease of the solar con- 
stant, and that of Simpson [20, 21, 22], which requires 
a substantial increase of the solar constant. Neither 
hypothesis visualizes any important selective varia- 
tion of the energy distribution in the solar spectrum. 
It is inevitable that a sufficient decrease of the solar 
constant would lead to a corresponding lowering of the 
