Latest Global Average Tropospheric Temperatures
Since 1979, NOAA
satellites have been carrying instruments which measure the natural
microwave thermal emissions from oxygen in the atmosphere. The
intensity of the signals these microwave radiometers measure at
different microwave frequencies is directly proportional to the
temperature of different, deep layers of the atmosphere. Every month,
John Christy and I update global temperature datasets (see here
that represent the piecing together of the temperature data from a
total of fourteen instruments flying on different satellites over the
years.
As of June 2013, the Advanced Microwave Sounding Unit (AMSU-A) flying on NASA’s Aqua satellite has been removed from the processing due to spurious warming and replaced by the average of the NOAA-15, NOAA-18, NOAA-19, and Metop-A AMSUs. The graph above represents the latest update; updates are usually made within the first week of every month. Contrary to some reports, the satellite measurements are not calibrated in any way with the global surface-based thermometer records of temperature. They instead use their own on-board precision redundant platinum resistance thermometers (PRTs) calibrated to a laboratory reference standard before launch.
