Very thought provoking book. Spencer does believe that global warming is happening. Has graphs that show same. He just doesn't believe that the small amount of CO2 increase is significant, compared to the enormously greater amount of water vapor (as strong a green house gas as CO2 and 100 times more plentiful) in the atmosphere. He also points out that atmospheric circulation carries heat from the surface to high altitudes where it radiates the heat into space. The magnitude of this heat transfer dwarfs the tiny amount of extra heat trapped by rising CO2 levels. He casts doubt on the reliability of computer models (very reasonable doubts that, after 40 years of computer work, I share). The effects of cloud cover are poorly understood, and the relationshp between a warmer earth, more water evaporation, forming more clouds is even less well understood. The model's handling of clouds, increasing humidity and numerous other factors is problematic.
Well worth reading.