December 8, 1996: Space-based measurements of
the temperature of the Earth's lower stratosphere - a layer of the atmosphere
from about 14 km to 22 km (approx 9 to 14 miles) - indicate that September
1996 was the coldest month on record since measurements of this type were
begun in 1979.
Dr. Roy Spencer (NASA) and Dr. John Christy (University of Alabama at Huntsville),
scientists from the Global Hydrology
and Climate Center, a cooperative laboratory involving NASA, the Alabama
Space Science and Technology Alliance, and private industry, obtain temperature
measurements of layers within the entire atmosphere of the Earth from space,
using microwave sensors aboard the TIROS-N
series of polar-orbiting weather satellites.
Despite significant warming of the stratosphere seen following the eruptions
of El
Chichon in Mexico in 1982 and Mt.
Pinatubo in the Phillipines in 1991, the entire stratospheric dataset
indicates a cooling trend over the past 15 years. This is thought to be
consistent with the depletion of ozone in the lower stratosphere.
Space-derived temperature data from a different region of the Earth's atmosphere,
the lower troposphere (a region of the atmosphere from the surface to 8
km, or about 5 miles up), also show a cooling trend of about 0.06 degrees
C per decade, although for these data September 1996 was a bit warmer than
average.
Surface thermometer measurements indicate that the temperature of the Earth
is warming, while the satellite data above show long-term cooling trends.
These differences are the basis for discussions over the existence and magnitude
of any global warming the Earth may be experiencing as a result of human
activity. The space-based temperature data obtained by GHCC scientists will
continue to play an important role in the investigation of the global warming
issue.