Space-based measurements of the temperature of the Earth's lower stratosphere - a layer of the atmosphere from about 17 km to 22 km (approx 10 to 14 miles) - indicate that December 1997 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 6 km, or about 4 miles up) show that December's value is the warmest seasonally adjusted temperature since August 1995. Indeed the troposphere was very warm in tropics, and scientists theorize that the warm tropical Pacific waters of El Nino measureably affected the bulk of the global atmosphere.
Thermometer measurements indicate that the temperature of Earth's surface is warming, while the satellite data above show a recent cooling trend in the stratosphere, and virtually no trend in the lower atmospheric layer over the past 19 years. The proven high-reliability of these space-based temperature data obtained by NASA and University scientists will continue to play an important role in the investigation of the global warming issue.