The stochastic dynamic model describing the air-sea interaction is transformed into a Fokker-Planck equation that is then solved by the matrix continuous fraction method. As an example of the solution, the warming by CO₂ increase is calculated and its increment is 1.2℃ while CO₂ concentration in the atmosphere increases from 330 to 660 ppm. In the model the dominant period is 3～4 years and it is revealed that the periods tend to get longer when CO₂ doubling occurs.