We consider a simple climate model of global warming to help
understand and constrain predictions from the more comprehensive
General Circulation Models (GCMs). By using observations to
constrain the climate gain factor, which presents the greatest
uncertainty in GCMs, we discuss the atmosphere's response to a
doubling of carbon dioxide concentration in the atmosphere in both
equilibrium and time-dependent states.
Mathematics Subject Classification: 86-01, 86A15, 86A10.