1016 
pleted by the formation of limestones (carbonates) and 
coal measures, and replenished by volcanic action. Or- 
dinarily the variation was slow, because a great reserve 
of CO, is dissolved in the oceans. Arrhenius and Cham- 
berlin saw in this a cause of climatic changes, but the 
theory was never widely accepted and was abandoned 
when it was found that all the long-wave radiation ab- 
sorbed by CO; is also absorbed by water vapour. 
In the past hundred years the burning of coal has 
increased the amount of CO, by a measurable amount 
(from 0.028 to 0.030 per cent), and Callendar [7] sees 
in this an explanation of the recent rise of world tem- 
perature. But during the past 7000 years there have 
been greater fluctuations of temperature without the 
intervention of man, and there seems no reason to 
regard the recent rise as more than a coincidence. 
This theory is not considered further. 
The Topographic Theory of Climatic Change. The 
theory that climatic changes are due to a combination 
of terrestrial factors—elevation, continentality, ocean 
currents, and vulcanicity—may be termed the ‘“‘topo- 
graphic theory.” Palaeogeographers have given us a 
fairly complete history of the topographic changes 
since the Cambrian; palaeontologists and palaeobo- 
tanists have reconstructed the variations of tempera- 
ture. From these data Brooks [4] made a statistical 
comparison of the topographic and climatic variations. 
The data used were: 
1. Estimates of the mean temperature of middle and 
high latitudes (from 40° to 90°N) im each of thirty 
geological periods from Upper Proterozoic to Recent. 
For this purpose a curve given by Dacqué [9] for the 
zonal differentiation of climate was converted to mean 
temperatures using the present mean temperature of 
33F and the assumed means of 53F im the Middle 
Jurassic and 28F in the Pleistocene. The assumption 
was made that the temperature of equatorial regions 
has varied little. 
2. Estimates of the mean height of the continents 
based on a curve of mountain-building activity given 
by Dacqué, assuming a mean height of 3500 ft in 
the early Quaternary, 2500 ft at present, and 500 ft 
in the warm periods. 
3. Hstimates of ‘‘continentality,” based on the areas 
of the continents in different latitudes from 80° to 
40°N. 
4. Wstimates of the volume of the warm currents 
reaching the Arctic, as a percentage of that given by 
the most favourable conditions. Both these were based 
on the geographic reconstructions by Arldt [2]. 
5. Estimates of the vulcanicity on a scale of 0-10, 
from the amount of voleanic material in the different 
formations. 
The mean temperature was compared with the four 
geographic variables by correlation, and the effect of 
one “unit” of each factor evaluated, separately for the 
Palaeozoic and for the Mesozoic and Tertiary together. 
The effect of one “unit” of each factor was also found 
from present-day conditions by independent, more or 
less theoretical calculations. The results are given in 
Table IV. 
CLIMATOLOGY 
In spite of the roughness of the data and the approxi- 
mations which had to be made in calculating the 
“theoretical”’ values, the three sets of figures agree 
well, except for Palaeozoic vuleanicity which was very 
difficult to estimate. The agreement strongly supports 
the theory that changes of orography and land distri- 
bution are a nearly complete explanation of the long- 
period changes of climate. 
Taste IV. Tur Temperature Errect or TiRRESTRIAL 
Factors In Ciimatic CHANGE 
Effect (°F) of one “unit”’ 
Factor “Unit” 7 
Palaeozoic | Mesozoic Hines 
Height of continents....} 100 ft —0.388 | —0.47 | —0.4 
Continentality......... q% 0.31 0.32 0.35 
Ocean currents......... % +0.28 | +0.28 | +0.3 
Wiwllenion@ntiiyasscsccsdocas 2 present | —1.68 | —0.42 | —0.5 
Adopting the figures for Mesozoic and Tertiary as 
a basis, a partial regression equation was formed for 
temperature on the various geographic factors, and 
the “theoretical” temperature of each geological period 
was calculated. The result, compared with the “esti- 
mated” temperature from Dacqué’s curve, is shown in 
Fig. 4. Here again the agreement is reasonably good, 
except for the earlier Palaeozoic, but there are some 
discrepancies. The three great glacial periods of the 
Upper Proterozoic, Late Palaeozoic, and Quaternary 
stand out clearly, but the “estimated” curve lags be- 
hind the “calculated” by five to ten million years, as if 
the earth took a long time both to cool and to warm 
up again in mountain-buildmg periods. There is a 
steep drop in the “calculated” curve for the Lower 
Jurassic (Lias) which is barely represented in the ‘‘es- 
timated” curve, either because the distribution of moun- 
tain ranges in relation to moisture-bearing winds was 
unfavourable for glaciation or because the cooling was 
not sufficient to freeze the polar seas. Finally, during 
the Palaeozoic the “calculated” curve 1s mostly above 
the “estimated,” probably because the reconstructions 
showed too little land in high latitudes. Our knowledge 
of Palaeozoic geography is still rather fragmentary. 
This statistical method of treatment automatically 
includes the secondary effects of freezing and thawing 
of the polar seas and changes in the atmospheric circu- 
lation, which would be difficult to handle quantitatively 
in any other way. 
Shorter Climatic Oscillations—the ‘‘Solar-Topo- 
graphic Hypothesis.” The curves of temperature in 
Fig. 4 are generalised and do not show the fluctuations 
of relatively short period. For example, crowded into 
the narrow dip of the Quaternary were at least four 
oscillations with a range of more than 5F, and similar 
fluctuations undoubtedly occurred in the other Ice 
Ages. Even in the warm periods there must have been 
short-period oscillations, though the range was prob- 
ably much less. The geographic factors (except vul- 
canicity) change slowly, and cannot account for these 
short-period changes. 
We have seen that there are two causes which could 
have produced these shorter oscillations. Changes in 
