Why Our Climate Ls Afild. IL 
’ 
ologist as “insular or moderate,” as contrasted with the ‘‘conti- 
nental or excessive’ climate of the regions east of the Sierra 
Nevadas. The west coast of Europe is also insular in its cli- 
mate. The northern limit of an annual mean temperature of 
50° Fahr. is about 51° 30’ of north latitude on western coasts of 
both Europe and America. But though there is this similarity 
in mean annual temperature, there is a decided advantage per- 
taining to our climate over that of west Europe in that our 
range of temperature is less; that is, extremes of heat and cold: 
are nearer together, and changes are therefore much less ex- 
cessive. This characteristic of our local climates is due in the 
main to two great agencies, one active, bringing heat, the other 
passive, shielding us from arctic influences. 
First: Our proximity to the Pacitic Ocean. For three 
hundred days in the year the air currents from this vast body 
of warm, placid waters flow over California, moderating summer 
heat and winter cold, and, impinging on the western slope of the 
Sierra Nevada, give to the foot-hills, up to a certain elevation, 
a valley climate and a valley range of products, as will be noted 
later. 
Second: Another agency contributing to the mild climate 
of the Pacific Coast consists in the mountain barriers upon our 
northern and eastern boundaries. Redding says it was Guyot 
who first called attention to the fact that the Sierra Nevada and 
the Cascade Mountains reach the coast of Alaska and bend like 
a great arm around its western and southern shore, thus shutting 
off or deflecting the polar winds that otherwise would flow down 
over the Pacific Coast States, while California has her own addi- 
tional protection from the north in the mountain arch which has 
its keystone in Mount Shasta. 
CHIEF TOPOGRAPHICAL AND CLIMATIC DIVISIONS OF 
CALIFORNIA, 
California is usually divided into three main areas and cli- 
mates, each distinct in typical conditions and yet separated by 
regions, more or less wide, in which these conditions merge and 
influence each other. Dr. Robertson says*:— 
Isothermal lines which normally run east and west are, as they near 
the Pacific, deflected north and south, and define three distinct climatic 
belts. These may be named coast, valley, and mountain; and while they 
resemble each other in having only two seasons, they are dissimilar in other 
respects. These differences depend upon the topography of the country, 
and are of degree rather than of kind; altitude, distance from the ocean, 
and situation with reference to mountain chains, giving to each region its 
characteristic climate. 
*Report of State Agricultural Society, 1886, p. 322. 
