Contact: Frank J. Wentz
NASA/Goddard Space Flight Center–EOS Project Science Office

Frank Wentz, a physicist at Remote Sensing Systems in Santa Rosa, Calif., has confirmed that the atmosphere has gotten warmer and wetter over the last decade. The results of his research will appear in the January 27, issue of Nature.

As part of NASA’s Pathfinder Activity, the study involved comparing the Advanced Very High-Resolution Radiometer (AVHRR), the Microwave Sounding Unit (MSU), and a Special Sensor Microwave Imager (SSMI) for their accuracy and consistency in monitoring global climate.

The instruments measure three important facets of the climate system. The AVHRR measures sea surface temperatures, the MSU measures air temperature, and the SSMI measures humidity. Wentz and his co-worker, Matthias Schabel, compared the data from the instruments to see if changes in sea surface temperature, air temperature, or humidity matched one or both of the other data sets. “Even though eleven years is a very short time to observe climate change,” says Wentz, “the combination of these three instruments can produce a much better definition of climate trends than any of the instruments could alone.”

“The three satellites combined provide some of the strongest evidence so far of a climate trend of increasing air temperature and humidity,” says Wentz. This would make sense because as air temperature increases the atmosphere is able to hold more water and as the Earth’s global temperature increases, scientists would expect the amount of water in the atmosphere to increase.

“We have found that the amount of water vapor in the atmosphere has increased by 2 percent between 1987-1998,” says Wentz, “Water vapor is really the primary greenhouse gas in the atmosphere and has a greater influence on global warming than carbon dioxide, but we’re not sure whether this increase of water in the atmosphere will lead to an increase in global warming.”

This study not only validates the accuracy of the three satellite instruments, but also provides new information on climate dynamics and should help resolve some of the past controversies concerning the accuracy of satellite data.

“There is now clear evidence that the atmosphere has significantly warmed and moistened over the last decade,” says Wentz, “Now, whether or not this is due to natural climate variability or to human-induced climate change is still uncertain.”