It is something that most climate scientists don't much investigate, but CO2 is not the most significant factor in heat conservation and may not be the primary factor in global warming.
Everybody noticed (or used to before they started living inside when the ambient temperature outside drops to uncomfortable levels), clear and starry nights are cold and dry whilst cloudy nights are relatively warm since clouds block terrestrial heat radiation. Likewise cloudy days are relatively cold because the warm sunshine cannot penetrate the cloud layer too well.
Yes, water in the form of cloud cover is acknowledged (even by scientists) to have a greater effect on ambient temperature than CO2.
So how do the climate scientists factor in the possible variation in cloud cover over the last century?
I'm sure it's an idea worth exploring.