Okay, let me take this in a different direction, since I think the details of temperature measurement are a necessary, but not sufficient issue. Let’s go back to first principles, and address the most basic assumption that comes with these global average temperatures.
Are global average temperatures important?
What can you predict from a global average temperature?
You can’t decide whether or not to plant a crop.
You can’t decide whether or not to wear a sweater.
You can’t decide whether or not to buy a product.
You can’t decide whether or not to move to a certain area.
While it may be useful for a local newscast to inform you that the temperature in Los Angeles is 64 degrees F if you lived in Los Angeles, it would mean almost nothing at all to someone who lived in Vicenza, Italy. Global average temperature means even less than this, to everyone on the planet, because at least it’s theoretically possible that someone in Vicenza has some interest in Los Angeles (say, they owned stake in an avocado farm). On the other hand, there is nobody on this planet who ever experiences the average global temperature.
So what does this mean to the argument, if global average temperature is a useless metric?
For example, say global average temperature had increased by 12 degrees F over the past 100 years, because of one particularly hot plume of air on the north pole, and one particularly hot plume of air on the south pole. All other regions of the globe experienced no average temperature change — would it matter at all, to anyone, that the artificial metric of global average temperature reached an all time high?
Now, taking it back to something more realistic, we still end up with something similar — as per every IPCC report ever presented, the poles warm faster than the equator, and the averages are driven higher by higher minimums, rather than higher maximums.
Even taking that very real and agreed impact of an increase to global average temperature (polar warming, higher minimums), extrapolating that to any useful regional level, with any sort of predictive quality, has simply been impossible — and indeed, given the stochastic nature of the problem may be intractable.
So, before I can even care about whether or not someone is accurate about global average temperature and global average CO2 levels, can we explain why we even care about those two quantities?