The ‘Roots’ of Climate-Gate

Today, a lot goes into counting tree rings, as we can tell from the back and forth over the statistics and ‘tricks’ of Climate-gate. Rep. Ed Markey has remarked efforts to understand what happened with the important record of historical temperature at the controversy’s heart risk devolving into a ‘Siberian tree ring circus.’

However, the science at stake has relatively humble beginnings in the work of one sort of unlikely character by the name of Andrew Ellicott Douglass, an astronomer pouring over tree samples as early as the turn of the last century.

Douglass had established himself at the University of Arizona Tuscon to pursue his personal ambitions of discovering the effects of sunspots on the earth’s climate. To do this, first and foremost, he needed to establish an accurate record of historical climate to track alongside the 11 year cycles of our sun.

It was as a part of these studies that Douglass began looking more closely at the trees of the American Southwest. Others had guessed the growth patterns of trees might store information on historical weather patterns. Douglass’s work would firmly establish links between weather and tree growth across climate regions, based on the year-to-year variation he found in the moisture-stretches, sensitive trees available for study in Arizona.

At point, the history of science and the science of history—or how we learn about very old things using the scientific toolkit neatly overlap.

In Norway this month, you could pick up a journal called Viking : tidsskrift for norrøn arkeologi. In the latest issue, as Swedish archaeologist Martin Rundkvist has helpfully translated, two northern researchers Niels Bonde & Frans-Arne Stylegar, have published the dates obtained for two Viking ships buried below-ground centuries ago using the science of dendochronology—more commonly known as tree-ring dating.

For ships built and put to rest this long ago (770 and 780 AD respectively) arriving at an accurate date of origin with systematic precision is not an intuitive science. Trying to date something that’s been buried underground for over a thousand years, you’re not just counting rings to find the ages of the trees that make up your find. You need to know when the trees that make up those ships, or those ornaments, or those house beams stopped growing and producing more rings.

An extraordinary 1919 edition of Douglass’s Climactic Cycles and Tree Growth, beautifully illustrated with images of the old-growth trees that produced his data explains the next step of his methodology. Douglass called cross-identification “the most fundamental and essential feature of the method of studying tree-growth.” The patterns of ring growth within trees corresponded to weather patterns year to year—higher rainfall had allowed for greater growth—but more interestingly, he had found that the same time periods in different trees from the same regions matched up.

Dendrochronological dating draws on a comprehensive chronological map constructed from samples of living and dead tree samples.

Douglass could attempt to date his first archaeological ruins not long after he developed his theory—reviewing wood samples from ruins left by Anasazi Native Americans in the Four Corners region. In the end, after decades spent ironing out gaps in his tree-ring chronology, Douglass made more headway with this methodology than in finding any links to sunspots. In the end the world of archaeology claimed him for his inadvertent contribution.

In something of a return, besides our Norwegian ship archaeologists, the tools Douglass developed have become key to establishing records of long-term climate change. Make of ‘climate-gate’ what you will, environmental scientists continue combing through tree rings and cores of arctic ice.

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