Absolutely impossible to know what the temperature of the earth should be at any given point in time. Think of the earth's temperature constantly self-correcting...winds, moisture, sunshine.
Why would anyone in the universe think that the temperatures in 1600, or 1700 or 1800 or 1000 BC were the temperature that the earth be now. Cant's have it both ways.
But that is specifically why the best “average global temperature “ is from the University of Alabama Huntsville satellite readings. They get the world temperature readings across oceans, deserts, plains, savannah, and the cities. NOAA reads cities.