Over the past century, global measurements of the temperature at the Earth's surface have indicated a warming trend of between 0.3 and 0.6 degrees C. But many - especially the early - computer-based global climate models (GCM's) predict that the rate should be even higher if it is due to the man-made "Greenhouse Effect". Furthermore, these computer models also predict that the Earth's lower atmosphere should behave in lock-step with the surface, but with temperature increases that are even more pronounced.
However, global temperature measurements obtained from
satellites of the Earth's lower atmosphere reveal no definitive warming
trend over the past two decades. The slight trend that is in the
data actually appears to be downward. These satellite data are verified
by in-situ measurements of the lower atmosphere made by balloon-borne
observations around the world.
Some scientists now believe that this apparent "disagreement" between the predictions by computer models and the measurements may be due to a less-than-accurate modeling of the role of water-vapor in the atmosphere of the GCM's.
In the June 1997 edition of the Bulletin of the
American Meteorological Society, Dr.
Roy Spencer of NASA/Marshall Space
Flight Center and the Global
Hydrology and Climate Center, and Dr. William Braswell of Nichols Research
Corporation. have shown that the low humidity of the tropical free troposphere
is playing a previously-overlooked central role in the dynamics of the atmosphere.
The very low humidity in this region allows a larger portion of the infrared
radiation to escape from the Earth, thereby cooling the atmosphere. Current
computer models do not accurately handle the processes which control the
humidity in this region, which are related to how much cloud material falls
out of rai
Contact: Dr. Roy Spencer
205 922 5960
NASA/Marshall Space Flight Center--Space Sciences Laboratory