Canadian territory extends 42° to 83° N. latitude, almost half way from the equator to the North Pole, and a slightly greater distance from east to west. Consequently the climate of Canada is one of great variation. While this variation will be treated in considerable detail in subsequent regional studies it will be necessary in this introduction to show the relationship to the general world pattern and to draw in some regional outlines.
All differences in climate from place to place on the earth's surface are due to the unequal distribution of the radiant energy of the sun and its resultant redistribution and loss. Other factors being equal, we expect temperature to decrease from the equator to the pole because of the difference in the angle with which the sun's rays strike the surface of the earth. The angle changes with the seasons since in June the overhead sun is 23° north of the equator while in December it is 23° south.
Coincident with the shift of the overhead sun there is a change in the length of day. In low latitude countries this change is of little significance but in a northern country such as Canada its effect is great. Thus while the longest day (June 21) on Pelee Island, the most southerly part of Canada, is approximately 15 hours, it is 16 hours at the 49th parallel and 24 hours at Great Bear Lake which is on the Arctic Circle (66° N. Latitude). Northward the period of daylight lengthens rapidly and at Canada's most northerly point of land the midnight sun is visible for approximately five months. This extra length of day in some measure compensates the lower intensity of the sun's rays in northern latitudes and permits the growth of some crop plants even within the Arctic circle. The corresponding lack of daylight makes the northern winter indescribably bitter.
Another important factor in temperature distribution is the difference between land and water. Land heats up more quickly and cools off more rapidly than water. In the summer the interior of a large land mass such as North America gets much warmer than its coastal areas. In winter the opposite is the case and interiors are colder than the coasts. Large water surfaces act as great equalizers Of temperature and coastal places have narrow ranges of temperature. Because of the prevailing winds and the pattern of ocean currents this effect is greater on the west coast of Canada than it is on the east. This can readily be seen in a comparison of the temperature records of Victoria, B.C. and St. John's, Newfoundland.
The effect of a continental position is shown by the record for Winnipeg, Manitoba.
Still another factor affecting the temperature pattern is the elevation of the land, but because of the complexity of mountainous regions its effect cannot be shown accurately upon small scale maps. It is often stated that a difference of 1,000 feet in elevation makes a differences of 3° F.