From ice samples, we know how much CO2 has been in the atmostphere for millions of years, so that's a pretty solid baseline. And the CO2 levels we have over the past century have been rising dramatically.
No offense, Kevin, because we've all been bombarded by the same storyline, but this is the kind of shallow analysis by people who have very little scientific education (i.e., most reporters and politicians) that the "climate science" community counts on to keep the grant money flowing.
Most quotes of CO2 concentrations kind of hope you'll ignore the units, PPM or parts per million, so let's get a handle on that. Imagine a building a thousand meters high, taller that any yet built (and about 2.5 times as high as the twin towers, to give some perspective.) That building would be one million millimeters high. So, measured against this imaginary giant skyscraper, one part per million would be a millimeter.
Over the earth's history, the concentration of CO2 in the atmosphere has varied from near zero to almost 10,000 PPM. The widely accepted value for the post-Ice Age, pre-industrial concentration is about 290 PPM. The value currently stands at about 395 PPM. Again, measuring against the side of our imaginary thousand meter building, we're talking about a column of CO2 that started out reaching about up to your shin, and now reaches up to, well, a little higher on your shin. In the totality of the atmosphere, these are infinitesimal percentages.
So, how do "climate scientists" get around this inconvenient truth? Why, they lop off the top 99.9% of the graph, and only show you the bottom four feet of that giant skyscraper. To a layperson who slept through statistics class (like Al Gore), these graphs look alarming indeed.
If Global Warming were real, someone would be making money from it. Think about it...when you say you believe that the earth is getting warmer, you're saying that you know the future, and who among us wouldn't love to know the future when we choose our investments? And yet, the "sure thing" of Global Warming hasn't caused so much as a ripple in the financial community. Farm land in northern Canada ought to be skyrocketing in price; it isn't. You can still buy beachfront property that (the finger-waggers tell us) is sure to be underwater in the near future, and easily find an insurance company that will cover it for you.
Just as in the past when "scientists" made alarming predictions (remember when AIDS was about to "break out" into the heterosexual community, and the Y2K bug meant that our computers would all revert to smoldering chunks of plastic and silicon?), the only ones who are getting rich over Global Warming are the academics. The spigots of grant money are wide open, and for a while the alarmists and Chicken Littles will prosper handsomely. Eventually, however, just as in the past, the hubbub will die down, calmer heads will prevail, and we will all look back and realize how silly it all was.