If You Don't Spare the Tree, You May Spoil More Than the Jungle

Article excerpt

Earth scientist Gifford Miller has a warning for destroyers of tropical jungles and other natural-plant communities: Spare that tree and safeguard your climate.

His research in Australia suggests that, if it weren't for human depredation, the dry outback might be a wetter, more hospitable place today. Widespread burning starting about 45,000 years ago may have replaced vegetation that favors rainfall with vegetation that discourages it.

A careful scientist and chairman of the University of Colorado's geological-sciences department at Boulder, Dr. Miller was restrained in his presentation of this ongoing research at a meeting of the American Geophysical Union in San Francisco last month. He noted that he and his colleagues do not yet have definitive proof of the human-climate-change connection. In a recent telephone interview, however, he explained that their research has already made two important points. First, human occupation coincided with significant change of vegetation. Second, lake sediments show it also coincided with a significant increase in annual monsoon rainfall over a wide region, including Africa and India. Yet Australia's monsoon rains faltered. Miller added that "the only thing {operational} on a large-enough scale" to account for this anomaly is vegetation change. Computer-based simulations that Miller and his colleagues have run indicate that a vegetated interior Australia would enjoy twice as much rain as it now receives in monsoon season. The climate change that strengthened monsoons elsewhere probably was linked to known periodic changes in solar energy that are due to periodic changes in Earth's orbit around the sun. The computer studies indicate that the effect of vegetative change "is even stronger than" these well-known orbital effects. A smoking gun Miller concludes that "we've got a smoking gun" pointing to vegetation change as the factor that made interior Australia dry. It remains to be proved conclusively that the "smoke" came from humanly set fires. Meanwhile, Miller says the findings so far "should be a warning" against wholesale forest destruction. Changes in vegetation cover can change the way land absorbs and reflects sunshine and radiates heat. They can change precipitation patterns. Plants recycle moisture locally by absorbing rain water through their roots and transpiring it back into the air through their leaves. Half of the Amazon jungle precipitation is recycled in this way during the rainy season. Such vegetation effects are part of a complex climate system involving land, sea, and air. …