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."
