CLIMATE—THE SYNTHESIS OF WEATHER 
By C. S. DURST 
Meteorological Office, Air Ministry, London 
Introduction 
Looking back over the last half century, one sees how 
greatly the approach of scientists to the meteorological 
problem has changed. The nineteenth-century mete- 
orologist was in most cases an amateur; even the pro- 
fessional forecasters were not educated in a scientific 
approach and learnt their trade by experience and ob- 
servation. 
It was Shaw who first saw the possibilities of a pro- 
fessional meteorological service and it was Shaw’s re- 
searches reported in the Life History of Surface Air 
Currents which started the great wave of scientific’ 
meteorological thought on synoptic matters which has 
transformed meteorology into a science. If, however, 
one looks at our progress dispassionately, it is apparent 
that the greatest advance in this scientific attitude has 
been in those branches which deal with the forecasting 
of weather and the physical problems which are as- 
sociated with it; one can trace the stimulus in that 
direction back to the illumination of the problem by V. 
and J. Bjerknes in the second decade of this century. 
The emphasis which has been placed, in the scientific 
mind, on forecasting has been reinforced by the in- 
sistent demands which have arisen from aviators for 
help in their day-to-day flights, in much the same way 
that the necessity of knowledge of the climate of the 
oceans stimulated Maury and FitzRoy in the nine- 
teenth century to the organisation of the charting of 
the winds of the sea areas in the very earliest days of 
organised meteorology. One must admit that the scien- 
tific approach has not permeated so deeply into some 
other branches of meteorology as into forecasting. In 
spite of the great work of systematisation done by 
K6ppen and Hann and their persistent groping for the 
physical causes,, there has not generally been an in- 
sistence on knowledge of the physical reasoning which 
must underlie climatology. In its application to hy- 
drology, in its use in agriculture, particularly in clima- 
tological application of rainfall data to the needs of 
man, there has been a woeful tendency to the use of 
the bones of bare statistics and mean values without 
the flesh of physical understanding. But it is not hy- 
drology and rainfall that are to be discussed in this 
article. A more general proposition is put forward: 
that climatology, as at present practised, is primarily 
a statistical study without the basis of physical under- 
standing which is essential to progress. As I see them, 
the essential needs of climatology are in the first place 
a reorientation of the expression of climate and of the 
teaching of climate, and secondly, the explanation of 
climate as a physical and dynamical phenomenon. The 
latter needs to show the process by which one season 
succeeds another. 
967 
The Expression of the Climate of the World 
Twenty years ago, climatology was assumed to con- 
sist of the meticulous amassing of the monthly means 
and extremes of elements, the mapping of normals, 
and the description of climate in terms of those normals 
and extremes. Yearbooks were published and the mass 
of data increased, but the meanings of those data were 
not examined. Of the attempts made to summarise 
and systematise them the best, at any rate in English, 
was that due to Kendrew [17] whose Climate of the 
Continents, after more than a quarter of a century, is still 
the most lucid description of the normal distribution 
of the elements over the land masses of the world. In 
reading it, however, one has a certain feeling of sus- 
pended animation, of unreality because everything is 
static; monsoonal wind arrows, indicating speeds of 10 
or 20 mph on the average, change the pattern of flow 
not a whit from month to month. Of this Kendrew 
was himself well aware and in the preface to a later 
work entitled Climate [18] he says: 
... between the Tropics and the Poles the weather is so var- 
iable... that it is difficult to form a conception of the climate 
unless it be the idea of something very changeable. Certainly 
no picture of climate is at all true unless it is painted in all 
the colours of the constant variation of weather and the changes 
of season which are the really prominent features, and it is in- 
adequate to express merely the mean condition of any ele- 
ment of climate. 
The treatment that Kendrew then gave is by elements 
in contrast to the Climate of the Continents, which as its 
name implies discusses climatology on a regional basis. 
Very recently Kendrew has revised his Climate and 
renamed it Climatology [19]. In this revision he has 
taken the various elements and discussed the physical 
causes which lead to their changes and then has en- 
deavoured to synthesise the picture into the descrip- 
tion of the climate of mountain and plateau and the 
climate of typical regions—the Sudan, the Mediter- 
ranean, and the Westerlies. Here, one is aware that the 
elements obey physical laws and some of the tools are 
provided with which to work out for oneself the picture 
of the climate of any locality in which one may be 
interested; however the completeness which the perfect 
climatology should express is still lacking. 
Mention must also be made of Miller’s Climatology 
[25], which originally treated the subject in the con- 
ventional manner, but into which, in the most recent 
edition, is inserted a chapter on the more modern 
ideas of air masses, though the more statistical approach 
is retained in the rest of the volume. More recently 
Haurwitz and Austin [14] have combined in one volume 
what Kendrew did in two. They logically treat first 
