It also makes the huge assumption that human activity is the cause, when there are many, many other possible causes. As someone else mentioned, volcanic activity and changes in solar activity/radiation, just to name two. CO2 levels are dependent on many things besides just how many cars we're driving around, or how many lumps of coal we're burning. That's the point I am trying to make: that no one can say that human activity is responsible, and to start trying to change our behavior to change CO2 levels is absurd.
The relevant period is the last 10,000 years, a period of unusual climate stability. And I've also indicated, in this thread, the CO2 range of variability over the past 640,000 years. We are 30% out of that range (on the high side) now. Otherwise, understanding paleoclimate helps scientists understand current influences on climate, but is not directly comparable.
CO2 levels are dependent on many things besides just how many cars we're driving around, or how many lumps of coal we're burning. That's the point I am trying to make: that no one can say that human activity is responsible, and to start trying to change our behavior to change CO2 levels is absurd.
There are multiple lines of evidence indicating that increasing CO2 in the atmosphere is due to human activity. Look at post 91, and you can even calculate the ppm annual change due to 656 Megatons annual CO2 emissions (but be careful because there may be unit conversions). There are other ways of proving it -- the Suess effect, stable carbon isotope dilution, is one way.
I agree with your final sentence. But... I say that changing our behavior and our energy infrastructure to reduce the economy's dependence on foreign oil is NOT absurd. I think that it's the prudent and patriotic thing to do, just as you and I would have gladly rationed a host of commodities to support the war effort during WWII.