With one stoke of computer code between 1999 and 2000, the continental United States, with the best temperature measurement system in the world, went from a history of cooling from the great Dust Bowl days of the 1930s to considerable warming according to the U.S. government’s Goddard Institute for Space Studies (GISS, headed at the time by notorious environmentalist radical, Dr. James Hansen): https://stevengoddard.files.wordpress.com/2010/10/1998changesannotated.gif . More details on the changes can be found here: https://stevengoddard.wordpress.com/data-tampering-at-ushcngiss/
Those are the actual graphs that were published on the GISS web site itself (with the scales made to match between the two graphs). The Global Historical Climate Network (GHCN) continues in the same vein, with temperatures adjusted higher with each succeeding “version,” further enhancing the apparent warming of the planet.
It is clear that while some adjusting is necessary to account for station location changes, time of observation bias (TOB), etc., the degree to which the various global databases have been warmed by artificial adjustments are overestimated even without taking into account methodological errors (see https://notalotofpeopleknowthat.wordpress.com/2015/02/09/how-much-do-temperature-adjustments-affect-global-temperatures/).
When looking at actual individual station adjustments from the raw data, it turns out that the GHCN produces spectacular changes in temperature history that find no basis in the real world (as opposed to the artificial world in which blunt force, computer-generated adjustments are made to temperature databases in an effort to produce a “homogenized” data set).
While the bias introduced by this massaging of the data has long been understood by many researchers, they are just now starting to do more comprehensive examination of individual station raw temperature histories (including surrounding stations) and then comparing them with the massaged data that is produced by computer algorithms.
As it turns out, it is becoming more and more clear that there is less justification (and often none at all, at least that fits into the usual explanations given by temperature data aggregators such as NASA and NOAA) for the adjustments which are made than previously assumed. Which leads to the present article where the author states the following:
When future generations look back on the global-warming scare of the past 30 years, nothing will shock them more than the extent to which the official temperature records – on which the entire [global warming] panic ultimately rested – were systematically “adjusted” to show the Earth as having warmed much more than the actual data justified.