Modelling our planet s weather is a very complicated, a near impossible task to accomplish. There are just too many interrelations and too many variables to account for. Take for example the effect of carbon dioxide on the oceans. If carbon dioxide does cause global warming, then the oceans temperatures would rise. Warmer ocean water would allow for more plants to grow.
Plants remove carbon dioxide from the atmosphere.
Thus the effect is nullified. Increased temperatures cause ice to melt, changing the amount of radiation reflected by the planet. Your book discusses many possible scenarios, and an infinite number more could be imagined. The major debate point about global warming revolves around the issue of climatic modeling - who do you believe. Some people think that temperature predictions are underestimated, other say that they are overesimated.