[kkjjkgjjgg]

I don't think that explanation is correct. The average temperature of a year is just a specific way to take a measurement. Comparing it to an average of averages over several years is then the same as comparing a measurement to an average of measurements.

That the climate should never see averages changing seems obviously false. There clearly are cycles that last longer than a year, for example, as several ice ages came and went before industrialization. El Nino take phases last between two and seven years.

[beowulfey]

Yes, the averages can and do change—that is my point. A changing average suggests something about the system is changing. It doesn’t need to be compared to preindustrial temperatures, but it is a good baseline because the temperature variation (as shown in the chart) was pretty small within that timeframe compared to the changes we are seeing today.