The 30 years prior to 1945 showed warming, which is statistically indistinguishable from the most recent 30-year warming cycle starting in 1975 (the IPCC AR4 poster period).
This is only broadly true in a superficial sense. A closer inspection of the data reveals that the details are quite different. The main difference being that warming is almost equal over land and sea surfaces from 1915-1945, whereas sea surfaces have warmed about half as much as land over the past 40 years.
This suggests that the warming in the latter period is mostly driven by ‘external’ radiative forcing changes, whereas warming in the earlier period was to a greater extent driven by ‘unforced’ internal ocean changes.
