Meteorology: The Science of the Atmosphere

by Charles Fitzhugh Talman

An immense amount of zeal and energy has been devoted to the study of supposed changes of climate. Evidence of such changes is sought, on the one hand, in a painstaking examination of weather records (a process often involving the tabulation of hundreds of thousands of figures), and, on the other, in the collection of geographical and historical data bearing on the question. There have been numerous reports of the gradual drying up of African and Asiatic lakes, of the discovery of ancient ruins indicating that prosperous agricultural communities once flourished in regions that are now deserts, and of various other tokens that marked vicissitudes of climate have occurred within historic times. A recent ingenious method of studying climatic variations is to measure the successive annual rings seen in cross sections of old trees. Thick rings are supposed to have been formed during periods of abundant rainfall, and thin rings when the rainfall was deficient. This method has been applied to the giant Sequoias of California, some of which are more than 3,000 years old.

The net result of a wide range of investigations appears to be that, on the whole, climate has everywhere been remarkably constant since the dawn of human history. There is much evidence that, in certain regions, there have been alternate increases and decreases—recurrent oscillations—of temperature, rainfall, etc., but there is little evidence of progressive changes in one direction.

In contrast to the uncertainty that still prevails in the scientific world on the subject of climatic changes is the confidence with which the average layman may be heard to assert that such changes have taken place within his own recollection. The popular idea that climate has changed perceptibly within a single human lifetime is a world-wide delusion, and one that has, apparently, always flourished. In the United States we hear of the “old-fashioned winter,” with its unlimited sleighing, and also of a marked increase or falling off in the rainfall in certain districts. It is an interesting fact that a century and more ago Americans were indulging in the same sort of retrospections.

In the year 1770, when Benjamin Franklin was president of the American Philosophical Society of Philadelphia, a paper was read before that society entitled: “An Attempt to account for the Change of Climate which has been Observed in the Middle Colonies of North America.” It is published in the first volume of the society’s Transactions. Barring the long s’s and the use of the word “colonies,” the greater part of it might have been addressed to the owners of automobiles and Liberty bonds. We are told of a “very observable change of climate,” remarked by everybody who has resided long in Pennsylvania and the neighboring colonies. “Our winters,” says the author, “are not so intensely cold, nor are our summers so disagreeably warm as they have been.” These changes he ascribes to the clearing and cultivation of the country.

Another firm believer in old-fashioned winters and old-fashioned summers was Thomas Jefferson. In his “Notes on Virginia,” written in 1781, he says:

“A change in our climate is taking place very sensibly. Both heats and colds are become much more moderate, within the memory even of the middle-aged. Snows are less frequent and less deep. They do not often lie, below the mountains, more than one, two or three days, and very rarely a week. They are remembered to have been formerly frequent, deep, and of long continuance. The elderly inform me, the earth used to be covered with snow about three months in every winter.”

Samuel Williams, who published a “History of Vermont” in 1794, uses almost identical language in reference to the climate of that State. “Snows,” he says, “are neither so frequent, deep, or of so long continuance as they were formerly; and they are yet declining very fast in their number, quantity, and duration.” That these changes, he adds, “are much connected with and greatly accelerated by the cultivation of the country cannot be doubted.”

What are the facts? When the statements above quoted were written few regular records of the weather had been maintained for any length of time in this country. The earliest instrumental record was begun at Charleston, S. C., in 1730. Much information was, however, available concerning the dates of harvest, of the formation and breaking up of ice in rivers and harbors, and other events dependent upon the weather, which, if anybody had taken the trouble to collect and analyze it, would have dispelled the universal belief that marked changes of climate had recently taken place. Nowadays it is much easier to refute the common assertion that the climate has changed within the memory of living men. The meteorological history of our country for more than three-quarters of a century has been recorded from day to day by a host of careful observers in every State of the Union. The records show that, while the weather of one year has often differed strikingly from that of the next, there has been no real change in climate. “Old-fashioned” winters, for example, were neither more nor less common half a century ago than they are to-day.

Our memories of past weather mislead us, chiefly because we remember the exceptional weather and forget that which commonly prevailed. Other circumstances may contribute to the illusion. Thus many people who now live in cities, where modern appliances make them more or less independent of the weather, passed their childhood under the more primitive conditions of the country.

If climates were not fairly constant for long periods of years, it would be a waste of time to compile the climatic statistics that, as we have seen, are wanted by so many different kinds of people for so many different purposes. Such statistics are based upon past events, but their practical value depends upon the fact that, within certain limits, they are a safe guide to the future.