Anthropogenic (man-made) global warming is predicated on two major things. First, that the earth is abnormally warming. This was alleged to be proven true by the 'hockey stick' temperature graph. The Climategate emails have driven a stake through the heart of this fraud. Second, human activity generated CO2 is causing this alleged abnormal increase in global temperatures. That allegation is also false. The 'hockey stick' graph of CO2 concentrations has been 'fudged' too. Historical CO2 levels are determined from bubble in ice cores. Since the age of the ice is known, this data can be compared with temperature data to see if there is a relationship. The validity of the ice core CO2 can be compared to modern measurements to see if they match. Here is where the fraud mirrors what happened to the 'hockey stick' temperature graph. You may remember historical temperature records are determined from proxies. The main proxy is tree rings. Around 1940, the tree ring data and actual temperature diverged. The 'hockey stick' creators artificially adjusted the data for a few years, then, beginning in the year 1980, truncated it completely and replaced it with instrumental temperature records. That is the only way they could get the temperature 'hockey stick' graph. It turns out the CO2 ice core bubble data did not match(pdf link) the modern measurements either. Without any scientific basis, they artificially shifted the historical CO2 data exactly 83 years to match the modern data and, not coincidentally, the temperature 'hockey stick' graph. (see chart shown below) The deeper you go down the 'global warming' rabbit hole; the worse it gets.
(Click image for a larger view)
Image found here in pdf format.