Precision global temperatures from satellites and urban warming effects of non-satellite data

Data sets designed for operational use are now being employed to monitor the earth on decadal time scales, an application outside of their original purpose. One data set, from the Microwave Sounding Unit, measures atmospheric temperature in deep layers since late 1978. Procedures for verifying and validating these data by two tests are presented: one by comparison with an independent satellite and one by comparison with radiosonde data. The results show that data from such an instrument are precise and therefore ideal for global studies. Temperatures measured by surface thermometers have considerable error for long-term studies because of various factors. Widely varying results are shown for California stations, where the few sites chosen for global temperature trend estimation are shown not to be representative of the average trend measured by over 100 stations in the state. Such a result calls into question the ability of scattered, selected surface networks to provide a true picture of long-term trends. The global temperature trend of the lower troposphere measured by the Microwave Sounding Units from January 1979 to March 1994 is −0.06°C per decade.