Do you think it is possible to forecast the weather a thousand years in advance -or even five thousand? You don’t? Then read of this new positive way to prophecy the future, and to read the dim past.
September 1949
By Philip Ferry
The original graphic that appeared with the September 1949 article on tree rings.
In a busy laboratory overlooking the limitless Arizona desert, a kindly looking, bespectacled old gentleman pores over a batch of charts crisscrossed with a maze of whirligigs serve only to confound the layman. Andrew Ellicott Douglass, Doctor of Sciences, and director of the Stewart Observatory, a unit of the University of Arizona at Tucson, is pursuing his favorite hobby of tree-ring research. As the world’s leading authority on the subject, Doctor Douglass is eminently qualified to discuss the value of tree-ring research in modern weather forecasting.
Tree-ring chronology is a minor science so simple any eighteenyear-old with a smattering of high school botany can grasp its principles and appreciate its importance in the realm of research. Its chief value to science lies in its use as a long range weather chart- a sort of self-perpetuating calendar which has yielded a continuous record of the weather in the Southwest for nearly two thousand years, enabling scientists to carry the calendar back to the year 175 A.D. in that area.
“Tree-ring chronology is so simple,” explains Doctor Douglass, “that today anyone can walk into an ancient pueblo ruin, pick up a prehistoric timber and by comparing its annular rings with our skeleton plot, determine for himself the year when that tree had been cut.”
Yet such are the whims of fate, it was almost by chance that Doctor Douglass became interested in the study of tree rings. The Doctor is essentially an astronomer and it was his researches into the effects of sunspots on weather that led him into the study of tree rings. It was long known there was a rhythm in the occurrence of sunspots, that these solar phenomena were most prominent at eleven-year intervals. As an aid in his investigations of the influence of sunspots
on the weather, Doctor Douglass studied trees, knowing that solar changes affect the weather which in turn affects the growth of trees and other vegetation. Every year most trees add a new layer of wood over their entire surface. A tree is a living, growing organism whose food supply, fortunes and misfortunes are reflected in its structure. Through long periods of time and with
unfailing regularity, trees jot down a record of their adventures through life. Rainfall, drought, a bolt of lightning, a forest fire, insect attack, a falling neighbor-all may leave their mark on the tree.
In the and regions of the Southwest, where trees are few and other vegetation scarce, rainfall is of vital importance to all growing things. The dependence of Arizona’s trees, particularly the conifers, on rainfall, makes them unfailing rain-gauges. Hence in the rings of the pines we find lean years and fat recorded. The recurring successions of drought and plenty that have swept over the forests of the plateau country are here indelibly recorded. By learning how to
interpret these records-specifically those of the pines and other conebearers whose rings are easy to read-Doctor Douglass was able to correlate sunspot occurrences and weather changes. Before he finished, he was to discover a magic key that would enable him to unlock the historical secrets of the past.
Evidence of the eleven-year sunspot cycle, together with its influence on the weather and consequent effect on trees, was easily observable in Arizona’s pines. Corroboration of Doctor Douglass’ findings came about in a dramatic way. The pines of Arizona had recorded the regularly recurring wet and dry periods for five hundred years, except for the years from 1650 to 1725. During this 75-year interval the rings gave no evidence of periodical changes in the weather such as had been found in other seasons.
Sometime after encountering this phenomenon, Doctor Douglass received a letter from Doctor Walter Maunde, eminent English astronomer who, unaware of Doctor Douglass’ findings, wrote that his studies of solar phenomena had revealed a total absence of sunspots between the years 1647 and 1715. Did the pines of Arizona reflect this omission? As Doctor Douglass remarks:
“The amazing coincidence between the failure of Arizona’s trees to record weather changes during a particular period of time and establishment of the fact by entirely independent study that the customary sunspot cycle had not occurred during approximately those same years, helped confirm the relationship between solar changes and the growth of trees.”
With this discovery came a sudden realization that in the process of cutting and codifying tree sections-in correlating sunspots and tree growth-Doctor Douglass had hit upon a possible method of dating the historical occurrences of North America’s past. If the rings in a tree indicated the wet and dry years, then perhaps with proper correlation they could be made to indicate the date when those weather changes had occurred as well as the year when a particular
tree had been cut. Obviously, the cutting date would be the year of -or the one next following- that of the outermost growth ring. With proper arrangement, an integrated succession of rings would be formed which could be fitted together into a natural calendar. It was a fascinating prospect to contemplate. Its solution was to take nearly ten years.
Doctor Douglass discovered that no living growing tree in the semiand Southwest carries the record back more than a few hundred years. When he had reached the earliest date recorded by any observed tree, he hit upon the idea of studying timbers that had been cut before the living trees took up the story. By arranging these in their proper chronological order, so that the rings of a dead timber matched those of a living tree, he would have an unbroken succession of timbers and trees whose chronology would be indisputable. The problem now remaining was to date these occurrences. This difficulty was solved by the simple process of matching the rings of dead timbers with those of living trees growing around Flagstaff whose age was easily established and working backward in time.
Having established this theoretical course of action, Doctor Douglass devoted his attention for several years to the new tree-ring science. The first chronology was made possible in 1913 with the introduction of crossdating-trees being said to crossdate when similar ring patterns are found in many trees. By this process of crosschecking, a climatic ring record is formed which is based not on a single finding but on a crossdated group of readings from many trees. In a few years crossdating was found to be general throughout the forests of the Southwest. This
first chronology was 500 years long and consisted of pine tree records of the Flagstaff area.
In the summer of 1922 a well organized expedition took the field. In the desert regions of the Southwest began the series of investigations which culminated in the establishment of what has since become known as dendrochronology, or tree-ring chronology. The drama unfolded slowly. For severalyears Doctor Douglass and his associates at the newly established Laboratory of Tree-
ring Research at the University of Arizona collected and studied the cultural remains of old pueblo villages and cliff dwellings. Here and there timbers were found whose later years were contemporaneous with the early life of living trees growing around Flagstaff. By matching these up, a sort of skeleton framework was formed and a basis established for setting up a permanent table of tree-ring’ occurrences. When in 1926 a beam was found whose earliest ring could be
definitely identified as having been formed in 1260 A.D., archeologists knew that a new science was being born.
But there were annoying gaps in the record of succession. While the age of some of the pieces was readily established by comparison with modern trees around
Flagstaff, others leaped the centuries and their period of growth remained a mystery. Some of the beams obviously had been cut as much as a thousand years before but still could not be fitted into their proper places in the puzzle. Eventually enough material was collected to form a second chronology, one which partly filled the uncharted interval between prehistoric timbers
collected at Chaco Canyon Ruin and modern trees near Flagstaff. There remained only two or three short gaps of undetermined length.
By February of 1928, the gap between the Chaco Canyon period and that of Wupatki Ruin had been bridged and Doctor Douglass and his colleagues were in possession of a continuous historic sequence of 580 years. The scientists now began to scour the Hopi mesa villages, knowing from old records that these hilltop villages had been occupied continuously since at least 1540, when
the Spaniards first visited them. By bribing the superstition-ridden Hopis, they were permitted to work at Old Oraibi, the oldest continuously occupied community in the United States (their researches subsequently revealed that Oraibi had been occupied for at least 700 years). Here they cut portions from ceiling beams, sawed cross-sections from the projecting ends of logs and bored out cores from roof timbers. One beam yielded a superb series of rings
covering the years 1344 to 1260 and appeared to have been in use for well over five hundred years.
Having exhausted the possibilities of the Hopi mesa villages and still with unfilled gaps in the chronology, the scientists looked about for some locality whose founding antedated that of Oraibi.
In 1929 a third expedition went into the field. Of the areas contemplated, the Showlow and Pinedale ruins, because of their proximity to growing pines, made the stronger appeal. Among the specimens uncovered at this prehistoric pueblo site were several charcoal logs whose rings showed dates in both the prehistoric and historic series. Some of the fragments had, in their charred condition, survived the centuries but still showed the marks of a sandstone rasp that
had been plied by some now longdead craftsman.
Among the specimens unearthed at Showlow was one log Which stood out as the greatest single find made in all their years of collecting. This was a beam whose end had been burnt off in the form of a cone, as is common with burnt logs. Its outer parts were recognized at once as belonging to the 14th century, rings being traceable to 1380 A.D. Sensing that here was a link of great potential importance, the scientists gave it the field number of HH39 and bound it carefully with twine. Even so, the specimen fell to pieces, upon which it was discovered that the supposedly solid log was a mere shell of charcoal from which the unburned interior had decayed.
By the use of their skeleton plots of prehistoric tree-rings, they traced the timber’s record slowly inward. Here were the thin rings that told of the hard years of 1299, 1278 and 1275, the ring for each year corroborating the diary entries given by other logs. As they followed the record inward toward the core the years 1283, 1280 and 1260 told the same sad story of lean years and hard living. When the beam enabled them to extend their chronology back to 1237, their hopes soared and they began to wonder if perhaps here might not be the keystone that would bind together all the unintegrated parts of their laboriously erected structure.
When the ring for the year 1251 matched perfectly with that of the ring representing the 551st year of their old chronology, one and all knew that the final gap between the old and the new chronologies had been closed. At last they had an integrated series of rings that went back uninterrupted to 700 A.D., giving the record of drought and plenty in the plateau country for twelve hundred years. So accurately did Beam HH39 fit into the picture that Doctor Douglass’ associates were able to say that seven beams from Pueblo Bonita ruin had been cut in 919 A.D. They could point back through the centuries to certain years, such as 1067 and 840 and say with certainty that these had been years of excessive drought in the Southwest.
Once he had learned how to decode the message they held, these talkative pines conversed freely with Doctor Douglass. They told a mutely eloquent story of human endeavor in the Southwest over the centuries and revealed the social history of that region for a thousand years. Since the prosperity of the Southwest has always been dependent on the crops, which in turn are utterly dependent on the rainfall-by reverse reasoning the state of the weather told the yield of the
crops which in turn divulged the welfare of the people.
The years of abundant rain would be the years when the corn and beans, the melons and cotton flourished; the years of excessive cold would be the years when the sheep shearing was heaviest but when the people shivered nonetheless in their high plateau shelters. The periods of depressing drought would be the years when hard pressed nomads ravaged the Southwest, killing and plundering in their desperation. All this the talkative pines told Doctor Douglass and his associates. The message of the tree rings plus man’s ability to translate them, had given the world a new medium of historical interpretation; a measuring stick that could be applied to practically all ruins in which datable timbers existed.
In the spring of 1931, the scientists began work on the chronology preceding 700 A.D. In that year a ring-pattern was found which carried the chronology back to 475 A.D. Since 1935, specimens found near Durango, Colorado, have extended the records back through the 200′s to the year 175 A.D. Thus today the identified ring patterns extend nearly eighteen hundred years into the past.
Doctor Douglass’ interest in dendrochronology did not end with his mastery of the language of tree rings. Today the University of Arizona has a Department of Treering Research whose ultimate goal is the establishment of cyclic phenomena in tree growth which will enable scientists better to understand world-wide fluctuations in climate and their use in long-range forecasting.
“Accurate forecasting,” says Doctor Douglass, “would be of inestimable value to mankind. The history of the water supply of the last several centuries would give an idea of the amount of precipitation that may be expected in the future. This would indicate the amount of heavy construction necessary to meet future needs. During 1934 and 1935, my colleague, Doctor Edmund Schulman, subjected to cycle analysis all of the important tree-ring series developed in the past, as well as much geophysical data. Doctor Schulman has made tree-ring studies of the
history of the water supply of the drainage of the Colorado River to develop five-hundred-year indices of the runoff of that river, which supplies Boulder Dam and Mead Lake. Already it is possible to arrive at a general index of the annual runoff of the Colorado River in central Arizona for the last seven hundred years.
“At the present time efforts are being concentrated on what appears to be the groundwork of then problem of cycles and tree growth: the development of enough long-period tree-ring indices sensitive to fluctuation in seasonal weather so that a reasonably comprehensive worldwide network is available. In this work, Doctor Schulman offers the hydrologist something of unique value. The growth curves derived from tree-ring series supplement the observed meteorological data by providing a length of record many times that of the longest meteorological series.”
To this, Doctor Schulman adds: “The extension of this work is destined to be world wide. Because of the increasing use of hydroelectric power and the construction of reclamation projects in semi-arid countries throughout the world, deficiency of water becomes a serious factor in a nation’s welfare. If the engineer in charge of a reservoir wishes to know what the situation will be in the next three years, the tree-ring statistician can tell him how many three- year droughts per century have occurred in the last five hundred years and, based on the
records of the past, can make predictions for the future.
“The great potential and actual developments of hydroelectric and irrigation projects, together with the problem of soil conservation and the need for research in longrange climatic forecasting, make it increasingly desirable to assemble centuries-long histories of the year to year changes in rainfall and in river runoff. The ultimate value of this research in long climatic records rests in the possibility of using such records in the precise forecasting of climate for years or even decades in advance.
“However,” Doctor Schulman warns, “full understanding of the information contained in these ring indices must await the compiling of similar series for the other dry lands of the earth. Until comparable series are developed and completely analyzed for the many other drought-sensitive areas over the globe, cycle studies in tree growth must remain necessarily limited.”
Doctor Douglass and his staff of scientific nature sleuths have high hopes that this
autobiography of the climate will eventually form the basis of a continuous weather chart which when coordinated with the unfolding record of the present, will enable man to predict with some degree of accuracy not only drought and flood, but even the type of weather of the future. The implications of this possibility-the hope of one day accurately forecasting the weather-is a goal
of almost incalculable value to mankind.
When and if a real theory of climate has been developed, to Doctor Douglass, the man who first talked with trees, will go the credit for having forged the master key that enabled scientists to interpret the hidden language of tree ringsa key that unlocked the historical secrets of the past and which bids fair to anticipate the weather of the future.
THE PIONEERS
The charlatan is always a pioneer. From the astrologer came the astronomer, from the alchemist the chemist, from the mesmerist the experimental psychologist. The quack of yesterday is the professor of tomorrow. Even such subtle and elusive things as dreams will in time be reduced to law and order.
-author unknown
