In Europe and above all in Italy the abundance in historical documents, early and modern instrumental data are a unique valuable source of climate information. In the first part, documentary data and the Italian unexploited early instrumental observations carried out, at the heart of the Little Ice Age, by several Galileo Galilei’s followers after the invention of the first thermometer are presented here for the first time. These data are a unique chance to reconstruct a temperature series covering a time twice respect the results reported in the IPCC 2007 report. In the second part, satellite data are used for climatic investigation applied at site testing for astronomy. At present, the remote sensing technique is the more effective mean to perform a worldwide survey of different climate parameters over the already active but also over future astronomical sites. The use of several satellite detectors with improved spatial resolution is explored to test, over the last decades, the unchanged sky quality characteristics in four among the top world sites. Moreover, for the first time, it is studied the cloud coverage and the aerosol content over a new exploitable ELT site: Tolonchar.