14-20 p. 361

14. Atmospheric CO2 and water vapor help maintain moderate temperatures at Earth's surface because of the hydrologic cycle and the carbon cycle maintain stable concentrations of water and carbon dioxide in their respective reservoirs, including the atmosphere.

15. a. respiration, fossil fuels, decay, combustion

      b. decomposition product of plant and animal wastes, refining fossil fuels, raising livestock

16. a. The runaway greenhouse effect: as a greenhouse gas, increased water vapor may cause an even greater increase in global temperatures due to adsorption and the real ease of infrared radiation, which cause another upward spiral.
     b. clouds

17. This is because more CO2  is added than can be removed by natural process.

18. a.

b.