The Future of Weather Foretelling
IN no other part of her wide realm has Science done so little for the good of man or her own fame as in the department of meteorology. In the solid earth her prophecies have long had a high value, in the far-off heavens her empire is affirmed, but in the unstable air between these two well-possessed provinces there is a region that is not yet subjugated. Around the border of the domain of meteorology some gains to the cause of law and order have indeed been made: we control the lightning, we are able to track a clearly defined storm for days on its path, and can help the sailor to knowledge that often enables him to escape its clutches when it assails him on the deep sea; but as for foretelling the weather in any proper sense, we have not yet attained to it. Is it attainable ? Can we hope to compass the conditions of our days so that we may sow and reap, travel, feast, or make war in weather of our choice ? This is, after all, perhaps the most interesting of the questions that the future history of science must determine. But though the perfect answer is not to be given at present, there are some things in the existing conditions of our science that make us hopeful that we are but at the beginning of the work of weather forecasting.
There have been two distinct scientific efforts at weather foretelling, as distinguished from the current survival of the modes of thought of ancient ages that are introduced in our ordinary weather prophecies, that undertaken by Admiral Fitzroy, in England, and that begun in this country by the United States Signal Corps, under the control of the late General Myer. Both of these have made their basis of the simple principle that weather always has a history; that it means conditions that pass from one region to another by certain laws of movement and at a certain rate. This general fact was long ago recognized by meteorologists, but it was not until the telegraph enabled knowledge to outstrip the storms that it was possible to make any use of it in foretelliug the weather. By the admirable labors of the United States Signal Service this method of announcing the weather that is journeying towards any locality has been brought to a high point of perfection, but it has not to any extent helped us to foretell the creation of weather. When a weather area forms in the far West, it is now traced as clearly as the path of an army, until it passes away. Sometimes the state of the barometer will tell something about storms that have not yet gathered themselves for their eastward march, but beyond this there have as yet been no means of foreseeing. The weather bureau is of no more use than a ground-hog or a goose-bone for telling us whether our coming spring or summer is to be warm or cold, rainy or dry. Is this the end of our advance ? Can we hope to do no more than take the storms we find afloat, and trace them on their courses; or can we hope to look behind them to the conditions of their origin so clearly that we can foretell their time and place of working?
To take the measure of our hope we must ask ourselves some questions concerning the nature of weather. Though the most familiar thing in the world, weather is much the most complicated of all the familiar spectacles that the world affords. The phenomena of weather changes rest primarily on a few principal causes: these are, in brief, the extreme fluidity of the air, which permits slight changes in its weight to set it in motion; the irregular distribution of the sun’s heat over the earth’s surface, brought about by the curved outline of the planet; the ease with which the air takes up a part of the earth’s water, and the many accidents that tend to cast this water back to earth again; the coming and going of the annual polar nights and days, giving alternate warmth and cold to the region about either end of the earth’s axis. In these four classes of changeful conditions are locked up a variety of effects, that defy computation or statement. The particular conditions of sky and temperature on any morning are dependent on a practically infinite variety of factors. There are involved therein not only the great general causes (the supply of heat from the sun, the character of the great heat-distributing currents of air and sea, etc.), but a thousand smaller actions, that are so far beyond the reach of foresight that we must give up hope of being able to predict them. A thunder or hail storm here or there, the occurrence of any of those sudden meteoric changes that are no more predictable than the time when a leaf will fall from a bough or a sparrow’s life end, may give a momentary set to the weather that will bring cloud or rain where else would have been fair sky.
But in the idea of weather we include not only the momentary accidents of the daily changes, but the longer and more general accidents of the seasons. We know that the seasonal changes of the weather are included in the limits of the predictable things. We know that summer brings warmth and winter cold, and in a less absolute way we know that spring and autumn have their proper kinds of weather. We know that March and November are seasons of wind, and even the forms of clouds in the several seasons are the subjects of law. Moreover, this is the sort of knowledge that human society needs. It is relatively of small importance for us to know the momentary chances of the daily weather, but it would be very greatly to our advantage to be able to extend the rough predictions we now are able to make concerning the several kinds of weather. On the variations in mass of the seasons, on their average heat and rain-fall, depends in the most absolute way the first interest of men, — their supply of food from the soil. We know, for instance, that in this country a cold, snowy winter and a summer of average heat and moisture mean an abundant crop of wheat, and that an open winter, with a following summer that shall be very wet or very dry, will be unfavorable to a good crop. In India the crop depends entirely on a supply of a certain amount of water in certain months. Even in the present state of the earth’s peoples any contribution to our knowledge of what the kind of weather six months or a year hence is likely to be would be a gift to man beside which cheap electric light would be a bauble. And with the rapid increase of population that now marks the peoples of all lands this sort of knowledge becomes yearly more important. The very fact that the seasons are in a general way predictable seems to be a fair basis for hope that science may succeed in extending the grounds of affirmation, and not only enable us to say that next summer will be warm, but enable us further to predict what sort of a season it will be, in a general way, — whether the rain-fall will be large or small, etc. We observe, at the outset, that science has made its greatest successes in extending the limits of the known rather than in opening altogether new fields of knowledge. Whenever men have been able reasonably to assert anything by crude popular knowledge, scientific methods have generally been able to increase the certainty to a very wide extent. So the fact that the seasons are in a certain way predictable gives a fair basis for hope that scientific methods of inquiry may take this crude knowledge and make it more certain in its details.
A study of the nature of the seasonal differences adds to the reasons that lead us to believe that we may in time be able to forecast their character pretty accurately. The momentary accidents that make it impossible to prophesy the precise conditions of any given day or days half a year hence are swallowed up in the more general phenomena of the seasonal divisions of the weather. The conditions that are to determine the particular variety of weather for the next Fourth of July can hardly be said to exist, but the conditions which fix the fact that the month of July will be warmer than the month of March are, we may say, in existence, and the only difficulty is to find and weigh them. Speaking generally, the seasonal conditions that determine the weather of any district are not very complicated, though they are hard to compute. The first condition is that of the heat brought into the given area. This heat, though primarily all from the sun and the fixed stars, comes to each region in several different ways. In the first place, about one half of it is derived from the fixed stars, or other slightly luminous celestial bodies. This portion of heat comes to the earth in every direction, so that each square foot of its surface receives an equal share. Then we have the heat of the sun, which gives the other half of the heat that the earth receives. This, unlike the heat of the stars, falls with great inequality on the different parts of the earth. The star heat, though not far from one half of the earth’s whole share, is only enough to lift the temperature of the earth’s surface from about five hundred below zero of Fahrenheit to about two hundred below zero. So it is the sun that does the effective work of heating on the earth’s surface, the star heat only serving partly to fill the abyss of cold that wraps the world about. Now, if the sun’s heat stayed where it fell, the regions beyond the parallels of forty degrees would be deserts of cold, the intertropical regions would be uninhabitable on account of their heat, and the belt between would fare badly from the war between the fierce conditions that lie on either side. But as soon as the sun’s heat falls upon the earth it is seized by a great machinery that serves to transport it from the regions where it is in excess to other regions where it is deficient in quantity. These conditions are very simple, but singularly perfect even for this well-ordered world. They are briefly as follows : the overheated air of the surface line at the equator rises, and to replace it the winds come down from the polar regions. The upper air at the equator in turn runs off to the poles, where it settles and regains the surface. The activity of these winds depends upon the difference between the circumpolar and the intertropical temperature. The old view was that these winds bring about the distribution of heat over the earth’s surface, but the truth is that the winds are not worth much as heat carriers, for they can only do much of this work by virtue of the water they carry, and a very little cooling takes out the greater part of their moisture. They practically do their work at second hand through the oceau currents they set in motion. The trade-winds sweeping down from the pole make strong westward-running streams in the great oceans beneath the equator. These great rivers of the sea, heated to a high temperature by the rays of a vertical sun, are turned out of their westward course by the shores of the continents that lie across their paths, and flow back toward the poles whence they came, bearing with them a vast store of heat, which they give to the cooler regions in the high north. The effect of this tide of heat upon the ultra-tropical regions of Europe and America is very great. It is not too much to say that the springs of all the life of Northern Europe flow out of the Florida seas in the waters of the Gulf Stream. Were it to cease its northward journey, the life of the region north of the Alps would practically cease to be. Mr. James Croll, whose luminous contributions to the study of climatal phenomena have thrown a flood of light upon this class of questions, has clearly shown that the region within the arctic circle receives about as much heat from the waters of the Gulf Stream as comes to it in the direct rays of the sun. We do not know with equal certainty how much of the heat of Northern Europe is derived from this source, but there can be no doubt that the Gulf Stream is the most important factor in its climate. In the North Pacific there is a similar ocean stream, only grander in its dimensions, the waters of which bear their warmth to the northwestern shore of our continent, and redeem a thousand miles of it from the arctic cold that would otherwise possess it. 1880-81. Observations upon the temperature and the volume and rate of movement of this stream are not beyond the limits of inquiry. We know that about one half of the stream passes through the Straits of Florida, and there it can be measured with almost the accuracy we could give to the measurement of an ordinary river. The part that passes outside of the Caribbean to the east of the Lesser Antilles is probably also determinable by observations not too costly for possible use.
Although the winds are incompetent to carry the surplus equatorial heat from the tropics to high latitudes, on account of the ease with which they are stripped of moisture, they are able to do the more limited duty of bearing the heat from the point where the ocean currents discharge it against the shores into the interior of the neighboring lands, and as fast as these warm waters saturate the air they touch with their moisture, it flows off on to the lands to discharge its burdens of heat and water. If the sun’s heat remained absolutely steadfast in its amount, and these currents always carried equal shares of heat from the tropics toward the poles, the conditions of our climate would not be subject to variations from this source; but there is reason to believe that, from several causes, the volume of these oceanic streams varies a good deal from time to time, and that from year to year, or from series of years to series of years, their volume, or their heat, or both, is subject to changes. Now a change in any year in the heat-carrying power of the Gulf Stream by as much as five per cent, of its total effective heat would certainly have a sensible influence upon the climate of Northern Europe, and even less considerable changes might give important results. Observations made by the venerable and distinguished Sir Edward Sabine, I believe as yet unpublished, led him to the conclusion that there was a manifest relation between the winter climate of Great Britain and the temperature of the Atlantic waters; so that it might be possible to make some general forecasts of the weather in the winter season on these islands by a study of the warm temperature to the westward. Now if this effect really exists,— and all we know of the conditions leads ns to believe that it does, — then it may be possible to determine what the average temperature of the waters off the coast of Great Britain will be some months in advance. The water now flowing westward under the equator to the Central Atlantic will arrive off the west coast of Europe in from eight to twelve months from to-day. So if we knew that the equatorial current was warm and strong beyond the average of its conditions, then we could say that as far as the Gulf Stream could effect it the north of Europe would have conditions favorable for a warm and humid winter in
In the present state of our means of observation of marine movements there is no way of ascertaining the facts except by vessels cruising in the waters which it is proposed to examine; but there is no reason to doubt the possibility of making a buoy-shaped float, which should be anchored in the ocean currents, and which should, by telegraphic connections with the land, give us the means of determining the speed and temperature of the water that passes by the place where it is fixed. There is no doubt that the placing of such a buoy in the far seas, with telegraphic land connection, would be a matter of large expense, and it is conceivable that it would be better to accomplish the result at remote points by relays of government ships, which might as well be employed in this work as in any of the duties that are now assigned to them in time of peace. But most of the points where observations need be made are near the land, and could probably be observed by a system of buoys such as suggested above. For the Gulf Stream a set of observations in the straits between the Windward Islands and another in the Straits of Florida would be sufficient to afford a test for the value of such observations. A small steamer, with a reserve of a second vessel in case of accidents, would answer for each of these points. The simple observation could be made with great accuracy practically, with but little addition to the expense of the governments which undertook the work. All modern navies abound in dispatch boats and other hardy steam craft fitted for such duty. They likewise abound in scientific men capable of such work and willing to do it. So that it cannot be said that the expense would be a startling feature of the plan.
It is desirable that the work should be supplemented by a set of studies of the extra Gulf Stream, — that little-known division of it that passes outside of the West Indian Archipelago. This could only be accomplished by an untried system of buoys, as before suggested, or by steamers cruising in those waters. This system of observations should occupy as many vessels as could be afforded for a few years ; in a decade it should be possible to learn the laws of flow of the Gulf Stream in the Antillan and Floridian region so well that thenceforth three cruising steamers would probably accomplish all the result sought for. It might be found useful to extend the observations by a system of studies on the course of the Gulf Stream north of the Straits of Florida; but while these inquiries would have a general scientific interest, and would serve to supplement the excellent observations made by the United States Coast Survey, it is not likely that they would throw much additional light upon the climatal problem we are now considering. It is probable that the rate of flow and volume of the Gulf Stream when it passes the Straits of Florida, with the observations on the varying force and direction of the winds of the North Atlantic, — which latter point could be determined by the logs of the transatlantic steamers, — would suffice for determining the volume and heat-carrying power of this current.
The effects of the Gulf Stream are greatly intermingled with that of the Japan current, its twin stream in the Pacific Ocean. It is certain that the Japan current has much less influence on the temperature of the lands about the boreal pole than the Gulf Stream has, yet the effects it has cannot be neglected if we would get an adequate idea of the possibilities of predicting the seasons in the northern parts of Europe and America. The study of this stream would be far more perplexing than that of the Gulf Stream. We know as yet much less of its general structure than we do of its Atlantic equivalent, and the acquisition of this knowledge will be a more difficult task. At no point does the Japan stream pass through such a gate-like channel as the Gulf Stream when it traverses the Straits of Florida. Its history must be sought in the open regions of the western part of the Pacific Ocean, where it finds its devious way among the coral islands of the great archipelagoes that strew that sea. It would probably require at least four times as many observers to trace the movements of the Pacific stream as we should need for the Atlantic current, and it would be necessary to have a careful system of weather reports from Oregon and the coast to the northward as far as Behring’s Straits. We should also need current observations on Behring’s Straits, to determine the amount of Pacific water that enters the Polar Sea through that gate-way, if any part whatever passes that gate.
It is likely that next after the action of these ocean currents the most powerful agentof climatal change is to be found in the relative amount of solar heat received on the earth during different years. It now seems probable that the sun’s beat does vary in its power from one series of years to another. The actual value of this element of solar radiation would have been much better known were it not for the fact that our meteorological stations have been very badly placed for observations on this matter. Almost all our statious where observations on the radiant power of the sun are made are accumulated in the regions where frequent clouds and a great variation in the heat-transmitting power of the atmosphere have made it impossible to obtain very accurate results. We need a number of statious chosen solely for measurement of the sun’s radiant energy, and placed in those regions where the most perfectly cloudless skies could be found. There are several regions where the skies are practically without clouds for from three to six months each year, and by comparing the observations of several station, together we could probably get a close reckoning of the value of the sun’s heat for each day in the year.
With such a system of observation we could hope to have the basis for approximately predicting the heat and rain-fall of the lands around the North Atlantic Ocean. It would doubtless require some years of careful study before the relations between the facts observed and the subsequent climatal conditions could be clearly discerned, but as soon as the matter was well in hand we could hope for forecasts of a very valuable nature concerning the economic weather that the growing season would be likely to bring to the several lands. Predictions of this sort, even if fulfilled only in general terms, would have a very great value. In all our husbandry there is more or less choice between several crops which suit different sorts of weather. A farmer may make sure of a crop of oats in just such weather as that in which he would lose his crop of maize, and forage plants do well in conditions that are much against wheat. There can be no doubt that as a whole such predictions would be more generally profitable than any extension of the present system of brief forecasts of weather can be.
To carry out such a scheme would require great continuity of labor, and probably a degree of patience under failure that is hardly to be expected from any one government. It seems to me that the risk could be better taken and the work better done by a commission that should be appointed by several maritime states of the Atlantic. The United States, England, France, and Germany could divide the cost of such a work without feeling the burden, and a board of experts could be easily chosen from among their scientific men, who would direct the researches. Supposing that the half dozen or so steamers could be loaned and maintained by the several governments from their naval forces, the total cost of the inquiry, including a sufficiency of stations to observe the Gulf Stream, the Pacific currents, and the solar radiation, should not exceed half a million of dollars, —less, indeed, than is required to maintain a regiment in the field or a war ship on the seas.
Even if the results of this inquiry should be to show that the unobserved and at present unobservable forces that enter into the making of our several climates so far perturb the action of these great factors which it is proposed to study that we could not use them for forecasts, still the inquiry would not be in vain. We should have gained in a few years, and with a completeness we could secure in no other way, a knowledge of the facts concerning some of the most momentous phenomena of climate, and would have a better chance for making effective our further inquiries into its problems. It is not reasonable to suppose, however, that the inquiry would meet with a complete check ; there can be no tenable doubt of a certain measure of success ; and, as in all great inquiries, the elements of failure will themselves be the germs of successes by pointing the way to supplementary inquiries which will narrow the limits of the unknown. In connection with this scheme an international commission could doubtless do very much to extend our general knowledge of thalassography, or the physical geography of the sea, by recommending to their several governments a system of observations at sea, to be made by their merchant marines.
The United States have already won an enviable prominence for their surveys of the wild countries that fall to their lot. They are, moreover’, peculiarly well placed for this inquiry, as they constitute the only state that lies upon the two great climate-making seas of the earth. There seems a certain fitness in their undertaking to lead in this inquiry. The work could best be done as a joint work, but if the other states which should feel a peculiar interest in this task should neglect it, it would be fit that our own government should itself take up the burden. It is surely many times more promising of results to science and to tire more immediate interests of humanity than all the schemes for attaining the north and south poles that now vex the spirit of adventurous peoples. Our government made the first adequate beginnings in the work of forecasting the weather, and it did the first good work that was done in the study of the marine currents. It can well afford to follow up these lines of inquiry, which are clearly adapted to the genius of its people.
N. S. Shaler.