Researchers at Lawrence Livermore Laboratory have found evidence linking cooling earth temperatures between A.D. 1000 and 1900 to widespread deforestation. The discovery adds layers of complexity to the already difficult endeavor of predicting climate change and casts doubt on a commonly held belief that planting trees will slow "global warming."
Though scientists have known ground cover affects temperature, the new findings indicate drastic climate temperatures attributable to land-use. "The main way humans influence climate is by burning fossil fuels, which make greenhouse gasses," Philip Duffy, leader of the lab's climate and carbon cycle modeling group, said recently. "But we also suspected large-scale changes in land-use contributed to climate changes."
From a bird's-eye view, forests appear darker than agricultural land, for example, fields of grain or corn. Dark colours tend to absorb sunlight, trapping the heat that warms the planet. By contrast, lighter colors reflect solar rays back into space, resulting in cooler temperatures as the sunlight bounces away from the earth.
Using data collected from geological observations, including studies of old tree ring widths and densities, scientists long had recognized the earth's climate cooled by as much as 2 degrees Fahrenheit between A.D. 1000 and 1900. Researchers at the lab's Atmospheric Science Division theorized replacement of forests by agriculture and other land-use changes might have contributed to that change. To test their theory, scientists used supercomputers to simulate two possible scenarios: one modeling climate development accounting for agriculture, another modeling the same conditions but without deforestation. The tests showed significant differences: The regions that cooled more were the same regions where there was deforestation and dense human activity. "It complicates life for people like me who are trying to predict climate change," Duffy said. Some scientists have theorized that planting trees would thwart global warming, because trees absorb carbon dioxide. The new findings, however, quantify the extent to which trees capture heat, and suggest planting trees might not be the way to cool the planet.
Article based on information from: "Global Warming, Trees Linked?; Cleared Land Cools Earth, Study Says", The Arizona Republic May 7, 2001
