At Junkscience.com they discuss the average temperature of our planet A. without an atmosphere, B. with an atmosphere without GHG and C with an atmosphere with GHG. One of the curiosities of averages here is the loss of important information. It turns out apparently that our planet with an atmosphere would be a little warmer than with (but without GHG) because of albedo. What gets lost in the compilation of the the data down to a single number is the breadth of temperatures that would be seen on a planet with no atmosphere.
A different point to start charts from I discovered the other day when refreshing my abilities to read a Mollier diagram. The point we describe as Zero Enthalpy, which I believe (if I read correctly) corresponds with the Triple Point of water.
In any case, the zero point should be something I can replicate without need to resorting to Harry Read Me type analysis. I can go into the lab and find the freezing point of water. I can find the Triple point of water. I can find the point at which molecules stop moving. I can find the point at which water boils. I don't have to have an advanced degree in computer science, statistics, and climate science to establish what the zero point is (a la our current system of anomalies with hidden internal dependencies).
I would happily agree to any zero point that is tied to a physical constant.
This does not mean however that I think the Gold Standard is a good thing.