In order to do a data assimilation of CO2, I need a model which has a CO2 as a prognostic variable.  So, I added one prognostic variable which has only the process of advection and diffusion.  Like the equation that Dr. Inez Fung introduced, I didnÕt consider any chemical processes and there is no feedback between the integrated CO2 and radiative properties in SPEEDY.  And the source of CO2 is only from the surface.  Here, IÕll just show you the result of CO2 concentration when there is only the forcing from fossil fuel emission.