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APRIL 21, 1993

NashvrIle Tennessee 1' ‘El pages F sections

Let's cool the rhetoric
about global warming
By John R. Christy
The Philippine volcano Mount Pinatubo
threw a curve to climate watchers around
the world: Just when reports of global
warming and its terrible consequences
were becoming standard fare, the global
temperature dropped by an amount equal
to a quarter-century of the predicted
warming.
Forecasts of a Midwestern desert or of
melted polar ice caps flooding coastal cities in the 21st century are more difficult
to accept these days when we've just expenenced the Blizzard of '93.
But how reliable are the data used to
support claims of warming due to the enhanced greenhouse effect'
Earth's atmosphere includes some
gases which have a distinctive trait: They
let sunlight pass through to heat Earth's
surface, but they capture energy that
leaves this sun-warmed surface. These
are called greenhouse gases.
If more of these gases were added to
the air — and nothing else changed — the
atmosphere would retain more heat. It
would get warmer If that were the case.
global warming due to an "enhanced
greenhouse effect" should occur.
The concentration of some greenhouse
gases. like carbon dioxide and methane. is
increasing. There is really no debate on
that issue. The debate arises from results
expected for the real atmosphere, the behavior of which, scientists agree, contains
great uncertainties.
What about the data? Most of the data
used to support global warming forecasts
come from temperature records collected
by a wide variety of thermometers and
stations around the world. Most arc In
easily accessible land areas. Other reports come from "ships of opportumty,which record the temperature of the water not the air) drawn in to cool the en'
In any case, most of the world is not
covered with regular thermometer readings. The "global temperature" from
these surface stations is, in reality, not
global. It neglects vast regions, including
most of the world's oceans. Antarctica
and interiors of South America, Ainca
and Greenland.
There is another problem, too. Of great
concern to scientists is the lack of consistency in the way readings are taken and to
the thermometer surroundings. Since
most thermometers for which long-term
records mast are in towns and cities, the
effects of population growth and the construction of nearby roads, parking lots,
runways and buildings will cause the temperature to rise a little due to urbanisation.
Many of these sites are easily detected
by their strong warming trends, though
they are still averaged into the "global
temperature" and give a false climate
Are we really witnessing an "...splialt
effect" instead of the "greenhouse effect"

ComiNn_Nrry VOICES
in these data? The best that can be said
for the surface temperature is that over
the last 100 years one can see about a 1
degree Fahrenheit warming for those
places that have thermometers. This is a
valuable record, but it is far from perfect.
A new method for measuring global
temperatures was developed by Dr. Roy
Spencer of NASA's Marshall Space Flight
Center and myself. We use satellites to
record the "brightness temperature" of
microwaves emitted by oxygen in the atmcephere. The key advantages of this
method are:
• The satellite observes the entire
Earth.
• Its thermometer is calibrated more
than 3.000 times a day.
• Only one thermometer per satellite
does the measuring, so there is no conflict
with incompatible instruments.
The instruments which collect these
data provide global temperature readings
to an accuracy of about 0.04 degrees
Fahrenheit per month. They have shown
that the temperature of the entire globe.
for the atmosphere from the surface up to
about 16,000 feet, has experienced warm
and cool periods, but there is no significant trend up or down since 1979. As of
March 31, 1993, the I4-year trend was
slightly downward.
In contrast, the surface record shows
an upward trend of about 0.2 degrees
Fahrenheit per decade in that same penod. Before Pinatubo, the surface data
trend since 1979 was up almost 0.4 degrees Fahrenheit.
Even then, the satellites showed no significant trend at all.
When Mount Pinatubo exploded in June
1991. it seat more dust, ash and sulfur
into the stratosphere than any volcano
this century. Those "aerosols" had a
slight shading effect on the Earth:, the
global temperature has since fallen more
than 1 degree Fahrenheit. The Northern
Hemispheres summer of 1992 and the
Southern Hemisphere's just completed
summer of 1992-93 were both the coolest
in 14 years.
There are many environmental problems — toxic waste disposal, water and
au- pollution remember, carbon dioxide
is not a pollutant), deforestation, ecological degradation and overpopulation —
that are immediate threats to our wellbeing.
Evidence that global warming is an immediate threat has not been substantiated.
Some day, after a lot of research, we
may finally know if the climate is changing. Let us hope we make the proper decisions along the way to mitigate real problems and not perceived ones.
John Christy is assistant professor of alma.phenc science. global Climate systems resat,
scientist at the University of Alabama Muni,Pile Earth Systems Scyea Laboratory and Alabama *sealant state dllmatolOglat since 19bil.

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