That's an unwarranted conclusion. The primary greenhouse gas is water vapor,Yeah, in a greenhouse. Otherwise where's the global greenhouse affect?
Or is normal weather no longer weather but renamed greenhouse instead?
The calculation of what Earth's temperature would be without an atmosphere is not a difficult one. This is called the black body temperature calculation. One calculates how much energy is absorbed versus what is retransmitted as heat.
The moon undergoes this unpleasant up and down of temperature, as it shares Earth's orbit, though not its rotational speed. Accordingly, the surface of the moon grows uncomfortably hot when in sunshine, and bitterly cold in darkness. I have not seen what the temperature range would be if the moon rotated in a twenty-four hour period, (but here's a discussion of that).
It is Earth's atmosphere that helps to moderate and to boost the overall temperature. The atmosphere operates as the "glass" of our greenhouse. Different components of the atmosphere affect the temperature to different degrees. Argon, for instance, has approximately four times the effect of carbon dioxide, but it remains a constant, as it is chemically inert.
As the chart above shows, carbon dioxide has an effect that seems ridiculously small for the amount of discussion that the matter has received. What the chart does not show is that the amount of carbon dioxide has been slowly increasing as carbon that had been sequestered in fossil fuels gets released. It really needs a third or fourth column to show the effects of increasing carbon dioxide.
But primarily what we do not know is the dependability of Earth's "thermostat"; the way that cloud cover moderates temperature.
It is known that an increased global temperature will pump more heat into the tropical systems that produce atmospheric moisture. What is not known is how this varies after it begins mixing with the atmosphere. All of the water in all of the rivers of Earth began as atmospheric moisture. Along the way it formed clouds and snow that reflect sunlight, as well as damp earth that absorbs it.
The calculation of these matters is still beyond our capability.