Trends in 20 years of AIRS data: indications of climate change?

The Atmospheric Infrared Sounder (AIRS) on the EOS Aqua Spacecraft was launched on May 4, 2002, with a 95% confidence design lifetime of 5 years. Since 2002 AIRS has performed exceptionally well. We now have 20 years of AIRS data. We show that AIRS data are an order of magnitude more accurate and more stable than the 100 mK absolute and 10 mK/yr required to measure climate trends. However, the real limitation on the usable absolute accuracy and stability are time varying residual cloud contamination at all wavelength, and surface contamination effects, particularly in the SW channels. The change in contamination and large interannual variabilities due to ENSO type effects complicate the interpretation of trends for climate. The 20 years of AIRS data contain at least two changes of potential climate significance: The change of the DCC count, but it is opposite in sign to the expected trend, and decrease in the count of SCT clear cases. Both indicate unexpected changes in the cloud structure.