The choice of cartographic system on the calculation of Earth's surface parameters from maps, namely of the GMST

A previous paper of the author introduced a graphical method, allowing anyone interested to form one’s own opinion on data published in the form of computer-maps to re-compute the map data by means of a simple and efficient use of commonly available computer-graphic products. This was shown to allow a data re-analysis of sound metrological quality—there applied to a NASA video concerning the ice coverage on the Earth’s surface. In the present paper, the same procedure shows an efficient way to (re-)compute the annual value of the so-called Global Mean Surface Temperature (GMST)—a parameter normally provided by dedicated International Organizations, such as the ONU-supported IPCC—from whole-Earth maps of different types, often obtaining different results. A cartographic reason for this is given and discussed, explaining the differences found, some of which might have remained implicit in the published information.