Global-warming warnings are more than hot air
Scientists say the surface temperature of Earth rose about 0.7 to 1.4 degrees Fahrenheit in the past century.
February 1, 2000
Web posted at: 10:37 AM EST (1537 GMT)
By Environmental News Network staff
Despite contradictory temperature readings taken from the air, surface global warming is a fact of
21st century life, a panel of atmospheric scientists concludes in a National Research Council
"The difference between surface and upper-air trends in no way invalidates the conclusion that the
Earth's temperature is rising," said John Wallace, chairman of the panel and a professor of
atmospheric sciences at the University of Washington.
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The panel did not say whether human activities such as fossil-fuel burning contribute to the
warming. "The task of establishing causality is much more difficult than reaffirming the reality of
the warming," said Wallace.
At issue is the apparent conflict between surface temperatures and upper-air temperatures, which
has fueled a controversy over whether global warming is truly occurring.
Earth's surface temperature has risen about 0.7 to 1.4 degrees Fahrenheit in the past century.
Data collected by satellites and balloon-borne instruments since 1979, however, indicates little, if
any, warming of the atmospheric layer extending about five miles above Earth's surface.
An aerial view of Mount Pinatubo after it erupted on June 15, 1991. Disparity between surface temperatures and temperatures of the atmosphere can be attributed to natural causes such volcanic eruptions.
Climate models generally predict an increase in upper-air as well as surface temperature if greater
concentrations of greenhouse gases are causing the warming.
The panel concluded that at least part of the disparity between surface temperatures and temperatures of the atmosphere can be attributed to natural causes such
volcanic eruptions and human causes such as depletion of the ozone layer.
For example, natural events such as the eruption of Mount Pinatubo in 1991 tended to decrease
atmospheric temperature for several years. The burning of fossil fuels produces tiny aerosol
particles that have a cooling effect, and chloroflourocarbons and other chemicals also reduce
"In the presence of the uncertainties in the measurements, we don't know how to assign weights
to these two factors (natural and human). It might be all one, all the other or a mix of the two,"
Nevertheless, when these variables are accounted for in atmospheric models, satellite and balloon
data more closely align with surface-temperature observations, the scientists report.
The difference between surface and upper-air temperatures can also be attributed to uncertainties
in temperature measurements. Satellite measurements go back only 20 years, and validation of the
data is limited.
To resolve all the uncertainty, the panel recommends an improved temperature monitoring
system, including more accurately calibrated satellites, a refurbished weather balloon system and
consistent surface observations.
"Our reports represents only a small step toward alleviating the public's confusion about global
warming, but at least it's a positive one," said Wallace. "Our most important achievement is
reaching a consensus among a diverse group of experts on an issue that has been hotly
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