Scientists Reconcile Global Warming Discrepancies
January 13, 2000
Despite differences between satellite and ground-based temperature data, strong evidence exists that warming of the Earth's surface is "undoubtedly real," and that surface temperatures in the past two decades have risen at a rate substantially greater than average for the past 100 years, says a new report by the National Research Council, research arm of the National Academy of Science.
"But the rapid increase in the Earth's surface temperature over the past 20 years is not necessarily representative of how the atmosphere is responding to long-term, human-induced changes, such as increasing amounts of carbon dioxide and other 'greenhouse' gases," says the report. "The nations of the world should develop an improved climate monitoring system to resolve uncertainties in the data and provide policy-makers with the best available information."
The report examines the apparent conflict between surface temperature and upper-air temperature, which has led to the controversy over whether global warming is actually occurring.
- The Earth's surface temperature has risen about 0.4 to 0.8 degrees Celsius - or 0.7 to 1.4 degrees Fahrenheit -- in the last century, the report says.
- But data from satellites and balloon-borne instruments since 1979 indicate little if any warming of the low- to mid-troposphere -- the atmospheric layer extending up to about 5 miles.
- Climate models generally predict temperatures should increase in the upper air as well as at the surface if increased concentrations of greenhouse gases are causing the warming.
A combination of human activities and natural causes has contributed to rising surface temperatures, and other human and natural forces may actually have cooled the upper atmosphere, says the report. When these variables are accounted for in atmospheric models, satellite and balloon data more closely align with surface-temperature observations.
Source: John M. Wallace, et al., "Reconciling Observations of Global Temperature Change," National Research Council, National Academy of Science, January 2000.
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