The western seaboard of Europe has a maritime climate, the sea tempering the winter, but diminishing the summer heat. The prevailing winds are westerly, and the rainfall is typically abundant and distributed throughout the year. On passing inwards this type of climate changes into the continental type, with cold winters and hot summers, and diminishing rainfall. Though precipitation occurs at all seasons of the year, it tends to be greatest in summer, giving, e. g. in parts of the Balkan States, a type eminently suited to the cereal maize, which needs more summer rain than wheat.
If we bear in mind that North America is a large continent, and Europe a very small one, and that while Europe has no eastern seaboard, it is the eastern seaboard of America which faces Europe, we may realise that the climates of North America show a remarkable analogy to the European. On the western side we have in British Columbia and California respectively the same two types of maritime climate which occur in Europe, that is, British Columbia has a mild equable climate with abundant and equally distributed rainfall, and California has a Mediterranean climate.
At the eastern side the conditions are a little different, and show us that the mere presence of the sea is not sufficient to produce a “maritime” climate. The prevailing winds in eastern North America are off the shore; they cannot therefore carry oceanic influences landwards. To the north the winds tend to have a northerly component, and cold currents of water also stream out of the Arctic and chill eastern North America. The result is that we find that Labrador, though lying in the latitude of Great Britain, has a very severe climate. Further south the conditions are of the “continental” character even on the seaboard, the winters being very cold and the summers hot. Rainfall is equally distributed throughout the year, but on passing inland it diminishes in amount and tends to be limited to the warm season. The diminution would be much more obvious than it actually is were it not that the existence of the large Gulf of Mexico, and also the size of the North American continent, give rise in the south to a monsoon effect, which greatly increases the rainfall of the south-eastern corner of the States. Further to the west, in the lee of the great barrier of the Rocky Mountains, the rainfall is slight.
Incidentally, we may notice that the eastern seaboard of the great Eurasian continent also has a more extreme climate than the western, offering in this respect an analogy to the conditions which prevail on the eastern and western halves of temperate North America. The cause in both cases is the same—the direction of the prevailing winds.
We cannot close this chapter without some reference to weather, a subject of more geographical importance than is generally realised. In speaking of climate we have used figures which were invariably means, i. e. have been obtained by averaging a great number of observations. But where a great number of mean figures are used in a discussion, it is always found that the different averages are based upon varying numbers of observations, and are therefore not strictly comparable with one another. There is always a risk that such figures may mask facts of real geographical importance. No doubt some of the difficulties will disappear with the progress of meteorological science, which will enable the geographer only to select figures which are strictly comparable. Meantime, however, observations for long periods are rare, and the meteorologist must be content to take the figures which are available. For this reason as well as for others, it is advisable to add to the somewhat abstract study of means, that is, of climate, some note upon the actual conditions, that is, upon weather.
Fig. 10.—Diagram to illustrate a cyclone travelling towards the east. The two concentric circles represent isobars, that is, they are lines drawn through points where the barometer registers the same (low) pressure. Into the area of low pressure so formed the winds blow strongly in the direction known as counterclockwise, and are represented by the arrows whose double barbs signify their strength. It will be noted that in the rear of the cyclone the winds are northerly. They thus chill the air here, and by chilling it raise the pressure. The winds to the front of the cyclone are warm because southerly, they therefore tend to lower the pressure here by warming the air, and the result is that the isobars tend to be displaced towards the east, and at the same time become deformed. In other words, the cyclone moves to the east.
We may take British weather, which has become a proverb on account of its variableness, as a text for a brief discussion of the subject.