FERTILIZED TREES

An interesting example of the biased mindset of scientists working with complicated biological systems and anxious to relate their work to the latest politically correct fad is provided by "Mongolian Tree Rings and 20th-Century Warming'' by G.C. Jacoby, R. D. D'Arrigo, and T. Davaajamts in Science 273, pp 771-773 (1996). Choosing pine trees growing very near the tree line of mountains in central Mongolia, the authors observe a sharp increase of growth during the 20th century (see Figure 1), which they attribute entirely to 20th century temperature increases. They conclude that these increases were solely of solar origin until recently. Lacking direct temperature data before 1820, they assume that all increases in tree growth are the result of temperature increases and derive earlier temperatures from growth of similar trees, thereby constructing a correlation between growth and temperature.

No doubt tree growth, especially at these altitudes, is strongly temperature dependent, but what about carbon dioxide fertilization? Idso and coworkers have shown in their studies of Bristlecone Pine (see Figure 2 and AtE 21, No. 4, p3 (1993) for references and discussion)

that this enhanced growth correlates well with their extensive experiments on tree growth and carbon dioxide fertilization - a factor completely ignored by Jacoby, et al. The Mongolian increases are probably caused by temperature increases and carbon dioxide fertilization, but fad and fashion have hidden this from the minds of these investigators.