Tree-Rings & Weather

Such a babble of speculation, such a jumble of conflicting theory has arisen in recent years about long-range weather forecasting that the rich, inquisitive Carnegie Institution of Washington lately decided that it must have more information on this stormy subject. Last week it seemed eminently proper that the Institution should turn to a man who knows how much rain has fallen every year, wet or dry, in various corners of the world, for hundreds and even thousands of years.

Though Andrew Ellicott Douglass is a capable astronomer and director of the University of Arizona's Steward Observatory, he is most widely renowned for his pioneer work on the growth of tree rings. More than three decades ago Dr. Douglass had a great hunch and started examining the rings on yellow pines. By the time he had made 10,000 meticulous measurements and compared them with weather records he had verified what he suspected from the first--that the thickness of each year's growth ring is proportional to the amount of rainfall that year. It was clear then that before man-made records were dreamed of, the trees were faithfully inscribing rainfall records in their hearts. To patch together a continuous rainfall calendar it remained for Douglass to match thickness & thinness sequences from innumerable pieces of wood, new, middle-aged and ancient. Later work with the Carnegie Institution's help took the record back to pre-Christian dates.

Dr. Douglass was now able to settle controversies about the age of Indian dwellings, by matching their timbers against his charts. There were some pueblos about whose age archeologists disagreed by centuries. Dr. Douglass examined the logs of one, reported: "The wood for this dwelling was cut in the year 1260 A. D." But what interested the Carnegie Institution most was his finding evidence of periodicity in his charts which led him to believe that weather might repeat itself in cycles, and his invention of a way to detect and analyze such cycles.

Last week University of Arizona officials announced that, by arrangement with the Carnegie Institution which will pay his salary and provide him with three assistants, Dr. Douglass will be detached from his astronomical duties to devote all his time to an intensive two-year program of cycle analysis looking toward long-range weather forecasting.

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