Originally Posted by Destiny's Soldier
You should take away a key learning from this .... two charts that have different y-axes and x-axes may be the same and look completely different.
Spencer's chart has stretched the x-axis and compressed the y-axis to make the change look small. The GISS chart starts in 1880 and the UAH chart starts in 1980, so the GISS chart takes in a much larger change. These charts also have different average period for calculating departures (anomalies).
You should have gone to the Wood for Trees sites, where the two charts start at 1979, the y-axis is standardised, and the offsets are aligned. The chart shows two surface-based measurements, and two satellite-based.
You say the "platinum resistance thermometers" are accurate. Of course, but a satellite cannot use the thermometers you use in a lab
. For one thing, it may be 1,000 miles or more away from the object whose temperature it is measuring. So please explain how it can work without picking up some form of electromagnetic radiation?
Ok, ok, here is the answer:
Satellite temperature measurements - Wikipedia, the free encyclopedia
Satellites do not measure temperature. They measure radiances in various wavelength bands, which must then be mathematically inverted to obtain indirect inferences of temperature. The resulting temperature profiles depend on details of the methods that are used to obtain temperatures from radiances.
As a result, different groups that have analyzed the satellite data have produced differing temperature datasets. Among these are the UAH dataset prepared at the University of Alabama in Huntsville and the RSS dataset prepared by Remote Sensing Systems. The satellite series is not fully homogeneous - it is constructed from a series of satellites with similar but not identical instrumentation. The sensors deteriorate over time, and corrections are necessary for orbital drift and decay. Particularly large differences between reconstructed temperature series occur at the few times when there is little temporal overlap between successive satellites, making intercalibration difficult
As you can see, this is not an easy process and plenty of adjustments are required, more so than for surface-based measurements. For many years, Spencer's data was completely wrong!!
BTW, temperature has a fairly precise physical definition. The temperature of a piece of matter can be taken as proportional to the average kinetic energy of its constituent particles. The scales may be arbitrary, but all physical calculations must use a scale (usually the Kelvin) that starts at an absolute 0 point.