Physical aspects of the greenhouse effect and global warming

According to the simplest model of the earth's radiative balance, global warming will occur with certainty as humankind increases its production and consumption of nonsolar energy. This prediction is revisited, using a broader model that allows the greenhouse effect to be considered. The new model predicts a global warming of Delta T-E =(114 K)epsilon, where epsilon is the rate of surface energy release in units of the average incident solar radiation, 342 W m(-2), and Delta T-E is the average temperature rise at the earth's surface. Present values of these quantities, excluding geothermal sources, are epsilon = 0.69 x 10(-4) and Delta T-E = 7.9 mK. The model assigns a small number of optical parameters to the atmosphere and surface and qualifies the simple warming prediction: It is rigorous only if parameters other than epsilon are unchanged. The model is not complex and should serve as an aid to an elementary understanding of global warming. (C) 1999 American Association of Physics Teachers.