Using 1999 GISS Data, Global Warming Trend Since 1866 Only 0.5°C Per Century!

NoTricksZone
We are told over and over again that the globe has warmed by 0.8°C since 1880 or 1850. Lately we have seen article after paper after publication that states this number in Fahrenheit, 1.44°F, because that sounds larger. But is this number correct? What is it based on?