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A disparity between temperature trends on the earth¿s surface and in the troposphere, the level of the atmosphere where most weather takes place, has long fueled debate over climate change. Theoretically, if global warming is indeed happening, the troposphere should be heating up at least as fast as the earth¿s surface is. Yet temperature data obtained with devices called microwave sounding units (MSUs) over the past 25 years have consistently suggested little if any tropospheric warming. Some climate scientists have therefore argued that global warming models are flawed. New research suggests that the error lies not in the models but rather in the temperature readings themselves.
Different MSU channels measure radiation emitted in distinct frequency ranges that correspond to different levels of the earth¿s atmosphere. Researchers knew that channel 2, which provides data on the troposphere, is strongly influenced by the cooling effects of the overlying stratosphere, but they had not succeeded in developing an accurate adjustment for this interference. University of Washington atmospheric scientist Qiang Fu and his colleagues used a second channel, sensitive almost exclusively to the stratosphere, to quantify this layer¿s exact contribution to channel 2 readings. After reanalyzing data collected between 1979 and 2001, the team found that the troposphere¿s temperature has risen by about two tenths of a degree Celsius (almost one third of a degree Fahrenheit) each decade, bringing it in line with the surface trend.
Fu concludes that the results of the study, published today in the journal Nature, demonstrate that "satellite measurements cannot be used to argue that global warming is not happening." He notes: "I think this could convince not just scientists but the public as well." --Alla Katsnelson
