Claim: Each of the last three decades has been successively warmer at the Earth’s surface than any preceding decade since 1850.
I will be using GISTemp, which is available from 1880.
Decadal temperatures (GISTemp land stations)
As a starting observation, 78.6% of ALL decades are ranked number one. This ranking is taken since the beginning of the series, so a ranking of one means that the previous first rank was exceeded. Here is the chart:
Now to the question at hand… Is it unusual for the last 3 decades to successively warmer, and warmer than any other decade since 1850? We can answer the question since 1880 with this dataset. We can’t test the claim before 1900 since we need 3 successively warmer decades AND warmer than anything previous.
Answer: No, since 54% of ALL decades will make the claim true. Notice also that the claim is not unusual before CO2 emissions became “important” by IPCC standards, at around 1945. The decades before and since all have similar probabilities for making the claim true.