1022 
fossil plants and animals that occur between the layers 
of drift. In certain cases it has been possible to show 
that comparative ecologic assemblages are now living 
in climates milder than those prevailing at the fossil 
localities. From such relations it is inferred that inter- 
glacial climates, in some regions at least, were milder 
than those of today. 
Accurate quantitative data on the fluctuation of 
mean annual temperature between glacial and inter- 
glacial times do not exist. Using altitudes of cirques, 
Penck [17] calculated the differences between glacial- 
age temperature and present temperature as being of 
the order of 7C to 8C on the Atlantic coast of Europe. 
From scanty organic evidence a difference of 2C be- 
tween an interglacial maximum and the present time 
has been calculated. On this basis we have a total range 
of the order of 9C or 10C. 
Owing to the presence of variables, however, these 
figures are more suggestive than accurate. Both apply 
to glaciated regions, and it may well be, as Willett 
[23, p. 43] suggested, that the differences would dimin- 
ish in lower latitudes. 
It seems probable that minor climatic variations, 
similar to those which have taken place during recent 
millenia, occurred also during earlier times, as irregu- 
larities superposed on the major glacial and inter- 
glacial fluctuations. For the most part, however, the 
geologic record is too meager to enable us to state 
definitely that such is the case. 
Nonperiodic Character of Climatic Changes 
Neither the facts of glaciology, evidencing recent 
climatic changes, nor the facts of glacial geology, evi- 
dencing more ancient ones, afford a basis for inferring a 
periodic recurrence of any particular climatic condition. 
Briickner [5] assembled a mass of data covering a mod- 
ern 200-year period, from which he derived the concept 
of a climatic cycle with a period of about 35 years. Al- 
though widely quoted, this concept was later refuted by 
Willett (23, p. 36] and today has dubious standing. 
Paschinger [16] assembled data on regional snowlines, 
from which he concluded that climatic cycles occur in 
opposite phase in the north and south polar hemi- 
spheres. This conclusion was refuted by Matthes [15, p. 
232), 
Present Research Needs 
The usefulness of glaciers as climatic indicators has 
been established. In view of this fact it is apparent that 
research on changes in glaciers should be pursued both 
more intensively and more extensively than hitherto. 
The research needed falls into two distinct fields, glaci- 
ology and glacial geology. 
In the glaciologic field there is required a more nearly 
complete record of contemporary fluctuations of gla- 
ciers, so that after several decades curves prepared 
from annual observations will become available for 
comparison. The glaciers used for such observations 
should be carefully selected so as to include both polar 
hemispheres, both high and low latitudes, both mari- 
time and continental glaciers, and both valley glaciers 
CLIMATOLOGY 
and ice sheets. If possible, one of the observed glaciers 
should be situated very close to the equator—in East 
Africa, the Andes, or New Guinea. Such a system of 
observations would require the existence of a vigorous 
international organization with centralized mainte- 
nance of records. 
In the geologic field the greatest need is for a better 
knowledge of the areas of glaciers at various times dur- 
ing the last 10,000 years. In general, less is known about 
these comparatively recent variations than about varia- 
tions of more ancient date. Specifically, what is required 
is the mapping and study of the abandoned younger end 
moraines of valley glaciers in selected mountain dis- 
tricts, and moraines and other deposits of the former 
ice sheet in northeastern North America, a region still 
little known. 
Fulfillment of these two general needs would place 
our knowledge of climatic changes, as determined from 
past and present glaciers, on a firm basis. 
Summary 
In summary, an examination of the bearing of glacier 
research on the reconstruction of former climates leads 
to these conclusions: 
1. A close relationship between changes in glaciers 
and changes in climate, particularly temperature, seems 
established. 
2. Observations on glaciers themselves afford some 
climatic data for the last 1000 years. 
3. Geologic features related to former glaciers afford 
much cruder climatic data for the last 1,000,000 years 
or more. 
4. The climatic changes inferred from (2) and (8) 
are supported also by a variety of nonglacial evidence, 
much of it organic. 
5. The climatic variations included four major cold 
ages, with extensive glaciers, three major warm ages, 
with greatly reduced glaciers, and lesser variations 
within the last few tens of thousands of years. The lat- 
est fluctuation consists of a general rise of temperature 
within the last 100 years. 
6. As far as the existing evidence goes, the changes 
in climate seem to have been similar in character 
(though not of course in amount) throughout the world. 
There is no evidence that the changes recur in a peri- 
odic manner. 
7. Rough calculation has suggested that in districts 
near the large ice sheets the amplitude of mean tempera- 
ture fluctuation between cold ages and warm ages may 
have been of the order of 10C. 
8. Present research needs include (a) a greatly ex- 
panded, coordinated system of observations on con- 
temporary glacier fluctuations, and (0) a study of very 
late Wisconsin end moraines in order to throw more 
light on climatic changes during the last 10,000 years. 
REFERENCES 
1. Agassiz, L., Btudes sur les glaciers. Neuchitel, Jent et 
Gassmann, 1840. 
2. Au~mann, H. W., Researches on Snow and Ice, 1918-40.” 
Geogr. J., 107: 11-28 (1946). 
