In chapter 2 of Part 1 of Climageddon, in a section called How long carbon dioxide remains in our atmosphere, the following was stated:

Carbon dioxide is currently the most important greenhouse gas related to global warming. For the longest time, our scientists believed that once in the atmosphere, carbon dioxide remains there for about 100 years. New research shows that is not true. 75% of that carbon will not disappear for thousands of years. The other 25% stays forever. We are creating a serious global warming crisis that will last far longer than we ever thought possible.

"The lifetime of fossil fuel CO2 in the atmosphere is a few centuries, plus 25 percent that lasts essentially forever. The next time you fill your tank, reflect upon this...[the climatic impacts of releasing fossil fuel CO2 to the atmosphere will last longer than Stonehenge… Longer than time capsules, longer than nuclear waste, far longer than the age of human civilization so far." —“Carbon is forever,” Mason Inman ( Mason Inman. "Carbon is forever." Nature.com. November 20, 2008. http://www.nature.com/climate/2008/0812/full/climate.2008.122.html)

It needs to be corrected in one sentence as follows:

“25% of that carbon will not disappear for thousands of years. In terms of a human lifespan the rest stays virtually forever.”

The point that was being made is that the carbon we put in the air today will be the curse of those who come behind us for a very, very long time, and we need to take our ongoing carbon pollution far more seriously.

Additionally, how long carbon stays in the atmosphere is still an ongoing scientific discussion. Several long-term climate models, though their date details differ, all agree that anthropogenic CO2 takes an enormously long time to dissipate. If all recoverable fossil fuels were burned up using today's technologies, after 1,000 years passed, the air would still hold one third to half of the CO2 emissions. "For practical purposes, 500 to 1000 years is 'forever,'" as Hansen and his colleagues put it. In this time, civilizations can rise and fall, and the Greenland and West Antarctic ice sheets could melt substantially, raising sea levels enough to transform the face of the planet. See also:  http://www.nature.com/climate/2008/0812/full/climate.2008.122.html