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Over the past 130 years human activities have contributed to the
earth's rising surface temperatures, according to a new analysis
by Robert
Kaufmann, a College of Arts and Sciences associate
professor of geography and core faculty member of the Center
for Energy and Environmental Studies. Kaufmann and an associate,
David Stern of the Australian National University's Centre for
Resource and Environmental Study, analyzed historical data for
greenhouse gas concentrations, sulfur emissions from human activities,
and variations in solar activity between 1865 and 1990.
They found that eliminating any one variable -- whether greenhouse gases, sulfur emissions, or solar activity -- caused significant errors to appear in their statistical estimates for recorded temperatures. This means that all the factors taken together are needed to explain the observed changes in the earth's surface temperature, including the products of human activity.
Additionally, they found differences in the two hemispheres. In the north the cooling effect of sulfur emissions, produced primarily by coal-burning power plants, almost exactly offsets the warming effect of greenhouse gases. In the south, where sulfur emissions are lower, the rise in temperature is more evident.
"Since sulfur emissions have slowed, due to laws aimed at reducing acid rain, the warming effects of greenhouse gases have become more apparent," says Kaufmann.
The scientists report that doubling the atmospheric concentration of carbon dioxide from its preindustrial level -- which is expected to occur within the next century -- will increase temperatures in the northern hemisphere by 2.3 to 3.5 degrees Celsius (4.1 to 6.3 degrees Fahrenheit). While this may seem like a minor change, Kaufmann observes that during the last ice age (15,000 years ago) the global temperature was only three to five degrees Celsius cooler than it is today.
Kaufmann's and Stern's research appears in the January 2002 issue of the Journal of Geophysical Research (Atmospheres).
Graphs: Temperature variation in the Northern and Southern Hemispheres from 1860-1990. The black line traces actual temperature changes, red line indicates trend predicted by Kaufmann's model. |
