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If there were no mountains or oceans, and if the winds circled the earth with perfect regularity, then the amount of heat and the length of the farmer\'s growing season would progress uniformly from north to south. Instead there are all kinds of unexpected differences in climate. For instance, all along the western coast, the temperature changes little between winter and summer. In some places, the average difference between July and January is as little as 10 degrees centigrade. The climate along the northern part of this coast is similar to that of England. But in the north central part of the country, summer and winter are worlds apart. There the average difference between July and January is 36 degrees centigrade and more violent extremes are common. The coldest days of a typical January may be -40 degrees centigrade, and the hottest July day may be 45 degrees. This is the sort of climate that is found far from the moderating influence of the oceans. In the eastern part of the United States, the differ¬ence between summer and winter is also very distinct, but not nearly so extreme. Near the southwestern corner of the country, the climate is mild and springlike in winter, but in summer the temperature may reach equatorial intensity. In Alaska, almost continuous daylight in summer makes the short growing season an intense one.
The variations in temperature within the United States have had a marked effect on the country\'s economy and living standards. As the Growing Season Map on page 13 shows, there is a long crop-growing season along the south¬east coast where cotton is a principal product. This 18 also true in several small strips and pockets to the west where crops like grapes grow well during a large part of the year. In some of the cooler climates or in climates which combine coolness and humidity, animals and produce such as apples, wheat and corn thrive, thus giving the United States a large range of agricultural products.
These variations, combined with a fast transportation sys¬tem, have meant that there can be a rapid interchange of agricultural products from one part of the country to another. Thus, not only is there a greater market for what otherwise would have been strictly regional products, but this expansion of markets has meant great employment op¬portunities in all areas.
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