The impact of uncertainty in the rate of heat and carbon uptake by the deep ocean on climate response to increases in greenhouse gas concentrations is studied by means of simulations with a two-dimensional climate-chemistry model. We assume that mixing of both heat perturbations and carbon into the deep ocean can be parameterized by effective diffusion. Comparison of two-dimensional model and coupled atmosphere-ocean GCM simulations justifies such an approach for projections 100--150 years ahead. Rates of vertical mixing for temperature perturbations and carbon are assumed to be positively correlated. We consider the uncertainty range of transient projections of climate change when the above correlation is taken into account. Compared to taking into account changes just in the rate of heat uptake, we find that the range of projections of global surface warming is increased, but the range of projections of sea level rise due to thermal expansion is decreased. ¿ 1998 American Geophysical Union