-85- 



(Weiss, 1981). The concentration of methane was assumed to 

 increase annually by 1.0, 1.5, and 2.0 percent for the three 

 scenarios from the 1980 level of 1.6 ppm (Rasmussen, 1981). 



SEA LEVEL RISE MODEL AND THE GISS ATMOSPHERIC TEMPERATURE 



The GISS model used in this study was based on a one-dimen- 

 sional rad iat ive-convect ive (RC) model for estimating temperature 

 increases associated with atmospheric CO2 rises. _' A routine for 

 estimating sea level rises in response to temperature fluxes 

 generated by atmospheric forcings was added for this study. 



The RC model computes vertical temperature profiles over 

 time from net radiative and convective energy fluxes. Radiative 

 fluxes, in turn, depend on changes in atmospheric gases, especially 

 CO2 , and on the associated feedback effects. The GISS equation 

 used here is based on an empirical fit to the RC model. 



The fitted equation, described in Hansen et al . , was modified 

 by Lacis for this study to incorporate trace greenhouse gases. 

 Heat Flux Computations 



The heat flux into the earth's surface is estimated by an 



equation that contains all key temperature-related terms: 



F(t) = 2.6xl0~ 5 ( A C02) - 5.88xl0~ 3 ( A T) + 3.685xl0~ 4 ( A T) 2 

 [1 +.0022( A C02) ] ' 6 T e ~Y^ 



- 4.172xl0~ 7 ( A C02) ( A T) + 1.197xl0" 3 ( A CH4) - 5 



T e 



+ 5.88xl0 -3 ( A N20) - 6 + 3.15xl0 -4 ( A CC3) + 3.78xl0 -4 ( A CC2) 



- 1.197xl0 -4 ( A CH4)( N20) - 2.40xl0" 2 ( A V) - 2.10xl0" 3 ( A V) 2 



- 1.17x10-3 ( A T)( A V) + 3. 184x10-! ( A S) 



T„ 



