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What percentage of the atmosphere is carbon dioxide?

Percentage is findable, but I'm currently lazy. CO2 concentration is about 370 ppm and increasing.

What percentage was it 10, 20, 30, 50 years ago?

I take it you haven't ever heard of the Keeling Mauna Loa CO2 curve?

Don't be misled by the curve shown in post 53. There are many competing processes at work. For instance, The current increase follows a 300 year warming trend. Surface and atmospheric temperatures have been recovering from an unusually cold period known as the Little Ice Age. The observed increases are of a magnitude that can be explained by oceans giving off gases naturally as temperatures rise. It has been shown that carbon dioxide rises have a tendency to follow rather than lead global temperature increases.

This is explained in the article I linked to in post 51 and it has more information which helps to put the situation in perspective.

Contrast the steadily upward trend in CO2 concentration of your post 53 with the correlation between solar activity and global temperature of Friis-Christensen, E., and K. Lassen, "Length of the solar cycle: An indicator of solar activity closely associated with climate," Science, 254, 698-700, 1991.

This correlation of the length of the solar cycle does a much better job of explaining the up and down observed global temperature than the steadily increasing CO2 concentration. (Pardon the Danish, or whatever language the chart contains.)

I've heard that the Friis-Christensen/Lassen correlation did not perform as well over the last 10 years or so as it did before 1991. The observed temperature curve went higher than the solar correlation during this recent period. On the other hand, that sort of mismatch (observed temperature > solar correlation) has happened before at the ends of pre-1860 up-cycles in global temperature (other authors have extended this solar correlation back centuries in time).

The length of the solar cycle is a good proxy for solar radiation but apparently not a perfect one.