Contrary to general impression, the fact that the earth is a sphere was accepted by Greek geographers more than two thousand years ago.
Their writings and theories, however, were denounced as heresy and contrary to biblical interpretation by the Christian Church of the fourth century A.D., and thus remained sealed books for more than a thousand years.
An earlier Greek belief, before the spherical shape was advanced, was that the earth sloped from the equator to the north. The Greeks knew nothing of the southern hemisphere. The slope at the equator, they thought, was slight, but it became steadily steeper toward the north.
Thus, for geographical purposes, they conceived the earth to consist of seven equal broad belts, parallel with the equator, each belt having its own degree of slope. The Greek word for “slope” being klima, the successive belts were referred to as first klima, second klima, and so on northward.
Cities and other places were thus said to be in such and such a klima. With increased learning and the discovery that the earth was a globe, other methods of geographical location became essential. It had long been known that the farther one went toward the north, the longer the summer daylight lasted. So a new method was worked out on that basis.
Daring navigators were sent out into the Atlantic Ocean, and expeditions were made southward along the coast of Africa probably to the Gulf of Guinea, and northward probably to the northern tip of the British Isles.
These navigators were to determine, among other things, the length of the longest day of the year. From these data Greek mathematicians worked out a new series of klima, as they continued to call the belts, based on half-hourly differences in the longest day of the year.
Thus the first belt or klima or climate (to give the term its English form, derived through Latin) ranged from the equator, where the longest day was twelve hours, to a line parallel with it where the longest day was twelve hours and thirty minutes.
This first climate was eight degrees and twenty-five minutes in width. Each belt or climate became progressively narrower. Thus the tenth climate, along the British coast,’ ranging from a longest day of 16 hours to 16 hours, 30 minutes, embraced a belt less than three degrees wide. The half-hourly climates, as worked out by the Greeks, extended to the Arctic Circle, and were 24 in number.
In those days, thm, “a change of climate,” had the expression been used, would have meant nothing more than a change of latitude, that is, to a place nearer to or farther from the equator. But observations began to reveal that there was a direct relationship between distance from the equator and average atmospheric conditions, such as temperature, humidity, etc.
These differences then began to be embraced in the term climate.
Hence, when time belts gave place to more accurate means for determining location, climate was retained in the language with the extended meaning in which we now use it.