I just happened across (part of) the original paper that Svante Arrhenius published back in 1896. And I have to say, even with my modest knowledge of climatology, it seems pretty impressive. Here are some of the things that were known over 100 years ago:
The atmosphere retains heat (light or dark) in two different ways. On the one hand, the heat suffers a select diffusion on its passage through the air; on the other hand, some of the atmospheric gasses absorb considerable quantities of heat. (“Dark heat” here refers to infrared radiation.)
At first that paragraph didn’t make sense, until I realized that the “select diffusion” referred to what we now know as the filtering of UV rays by the ozone layer:
The selective diffusion is extraordinarily great for the ultra-violet rays, and diminishes continuously with increasing wave-length of the light.
...I kind of wonder how they knew this. If they weren't detecting UV on the surface, how did they know it was being diffused? Wouldn't they think it just as likely that the sun simply did not emit UV?
Now the good stuff:
If the quantity of carbonic acid increases in geometric progression, the augmentation of the temperature will increase nearly in arithmetical progression
A simple calculation shows that the temperature in the arctic regions would rise about 8 to 9 C, if the carbonic acid increased to 2.5 or 3 times its present value
Not sure if he's implying arctic regions would have a greater warming or not, though he does touch on ice albedo feedback later:
But in both these cases [warming or cooling], I incline to think that the secondary action due to the regress or the progress of the snow-covering would play the most important role
Another bulls eye, which is of course happening:
The geographical annual and diurnal ranges of temperature would be partially smoothed away, if the quantity of carbonic acid was augmented.
He even touches on water vapor feedback:
DE MARCHI has arrived at wholly other results than myself, because he has not sufficiently considered the important quality of selective absorption which is possessed by aqueous vapor….If, then, the mean temperature sank from its actual value by 4-5C, and the aqueous vapor remained in the air, the relative humidity would increase to 101 or 105 per cent. This is, of course, impossible.
Anyway, just thought this was kinda cool. Plus, reading old-timey science papers is a good way to pretend you're smart, e.g. his belief that UV is absorbed by the majority of the air in the atmosphere.