The database is the one created by the Met Office in Great Britain. Also this:
None of these adjustments are, considering the errors of measurement, statistically significant, but they do affect the ranking of years, which is important if the associated errors are not considered, as is often the case in the media. The overall conclusion is that global temperature datasets are fluid and change from month to month, and this must be taken into account in any analysis. It would be nice to have explanations for such changes.[emphasis mine]
Because of the unexplained adjustments, 1998 is no longer the hottest year on record, a “fact” trumpeted loudly by global warming scientists for more than a decade.