- Climate was 'normal' only between 1936-1977
- Every year 1987-present has been warmer than any year before that
- 1976 was warmer than any year before 1926
- 1978 (next coldest year of the recent run) was warmer than any year before 1940
From this we see that every year 1977-present is above the zero line, much the same as we had in my earlier note. But, which I paid little attention to at the time, every year in the early part of the record -- everything to 1936 -- is also below the 'normal' (0 anomaly) line. A long run of negatives is as good a disproof of things being part of the 'normal' as a long run of positives. Further, 1976 is much colder than all the years which follow and 1937 is much warmer than all the preceding years. So this makes a good span, 1936-1977, to try to call 'normal'. It does still satisfy our requirement that to call temperatures climate we want at least 20-30 years, though, at 42, we can't afford to lose many off either end of the record.
This satisfies one of the traits for 'normal' -- no long runs of always above or always below normal at the start or end of the record. But another trait we often require is no trend. That is a continuation of the idea that climate is stable in some meaningful sense. The trend for 1936-1977 is indeed zero. So for this span, it is indeed reasonable to say that there's a normal climate that weather is bouncing around. Here's what the data themselves look like, using 1936-1977 for the reference:
If by normal we mean what happens most often, then (for 30 year trends) what's most common is for climate to be changing, not to be some stable reference around which weather bounces.