Microwave Sounder observes the temperature trend of the atmosphere

The global-average air temperature at the surface of the Earth is believed to be warming at about 0.17 degree Kelvin (K) per decade. The question of whether the main part of the atmosphere (the troposphere) is warming or cooling is debated in the scientific community, largely because the observed temperature from the Microwave Sounding Unit (MSU) on NOAA polar-orbiting satellites has shown a nearly zero trend in some previous studies. This debate is directly related to the debate on changes in global temperature.

Calibration errors are a major source of uncertainty in determining the temperature trends observed by the MSU instruments, especially when these are on different satellites in different orbits. To reconcile this problem, scientists in STAR have re-calibrated MSU instruments on four different NOAA satellites, using the technique of simultaneous nadir overpasses, and produced a new set of data that are well-intercalibrated for climate studies (see figure at right). The new dataset has diminished the bias of this instrument going from one satellite to another, to only 0.05 to 0.1 degree Kelvin, wherever satellite observations overlap. After re-calibrating MSU, the globally averaged temperature trend of the troposphere over the ocean is 0.20 degree K per decade, from 1987 to 2003. This trend value suggests that the troposphere is warming slightly faster than the surface of the Earth.

Learn more:

• MSU research, also here
• Satellite calibration