It doesn't excuse the author's inconsistency, but the reality is that it doesn't matter - the difference between 1860 and 1960 is trivial compared to the differ

It doesn't excuse the author's inconsistency, but the reality is that it doesn't matter - the difference between 1860 and 1960 is trivial compared to the difference after that. The hottest year on record between 1860 and 2005 is probably after 1990 in most cities.