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University of Alabama in Huntsville

For Additional Information:

Dr. John Christy, (256) 961-7763
Phillip Gentry, (256) 824-6420

May 1, 2003

Comparing satellite & balloon climate data corroborates slower rate
of global warming

HUNTSVILLE, Ala. -- A detailed comparison of atmospheric temperature 
data gathered by satellites with widely-used data gathered by weather 
balloons corroborates both the accuracy of the satellite data and the 
rate of global warming seen in that data.

Using NOAA satellite readings of temperatures in the lower
atmosphere, scientists at The University of Alabama in Huntsville
(UAH) produced a dataset that shows global atmospheric warming at the
rate of about 0.07 degrees C (about 0.13 degrees Fahrenheit) per
decade since November 1978. 

"That works out to a global warming trend of about one and a quarter 
degrees Fahrenheit over 100 years," said Dr. John Christy, who
compiled the comparison data. "That's a definite warming trend, which
is probably due in part to human influences. But it's substantially
less than the warming forecast by most climate models, and it isn't
entirely out of the range of climate change we might expect from
natural causes. 

The UAH team's research is published in the May 2003 edition of the 
American Meteorological Society's "Journal of Atmospheric and Oceanic 
Technology."

"We know the climate is changing," said Christy, a professor of 
atmospheric science and director of UAH's Earth System Science
Center.  "Earth's climate has never been stable. What we don't know
is the rate of natural climate change, which makes it really tough to
say how much of the warming that we see might be due to things like
adding greenhouse gases to the atmosphere."

The study published in the JAOT describes an updated global
temperature dataset using NOAA satellite measurements of the
atmosphere's microwave emissions, which change with the temperature.
In this new version, the UAH team applied a more accurate accounting
for temperature changes caused by the satellites' east-west drift.

To test the accuracy of the new dataset, Christy and his colleagues
used independent data from 28 radiosonde weather balloon sites in an
area bounded by eastern Canada, the Caribbean, Alaska and the
Marshall Islands in the Western Pacific. They also used American,
British and Russian composite datasets of hundreds of weather balloon
sites around the world.

They used balloon data to test the satellite readings because 
balloon-borne thermometers and satellites both measure temperatures
in deep layers of the atmosphere -- comparing apples to apples.

"There is a 94 to 98 percent correlation between the satellite data
and the different balloon datasets," said Christy. "The more
difficult statistic to measure, the overall trend in the lower
troposphere, agreed so well it was difficult to estimate the error
bars." 

Ultimately, the team calculated a 95 percent confidence in the 
satellite-based temperature trend within plus or minus 0.05 degrees 
Celsius per decade.

If the satellite data are reliable and accurate over the wide range
of environments and climates represented by the balloon weather
stations, Christy said, it is likely to be reliable over the rest of
the globe. 

Many climate models forecast that global warming should be happening
at a rate much faster than that seen by either the UAH satellite
dataset or the weather balloon data.

"But models don't provide scientific measurements," Christy said. 
"Climate models can be valuable for many scientific purposes, but
models and their output shouldn't be confused with data or used as a
standard for validating real data.

"If you have reliable data that disagree with a computer model, it's 
time to find out what's wrong with the model. To do anything else
might lead you to conclude that your theories are correct and the
real world is wrong."

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