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 numerical simulations with the two-dimensional climate-chemistry model developed in the framework of the MIT Global Change Joint Program. This model incorporates parameterizations of most physical processes, includes fully interactive atmospheric chemistry and calculates carbon uptake by the ocean and, therefore, simulates the main nonlinear interactions taking place in the climate system. At the same time, it is much more computationally efficient than coupled atmosphere-ocean general circulation models. Results of the simulations with calculated CO2 concentrations are compared with those of simulations with a prescribed CO2 increase. This comparison shows that the uncertainty in the increase in global mean surface temperature due to uncertainty in the rate of oceanic heat uptake is enhanced by taking into account the related uncertainty in oceanic carbon uptake, while the uncertainty in sea level rise is decreased.Includes bibliographical references (p. 5).Abstract in HTML and technical report in HTML and PDF available on the Massachusetts Institute of Technology Joint Program on the Science and Policy of Global Change website (http://mit.edu/globalchange/www/)