A method for removal of at least a portion of carbon dioxide from an aqueous fluid such as a blood fluid includes placing a first surface of at least one membrane through which carbon dioxide and at least one acid gas other than carbon dioxide can pass in fluid in contact with the fluid. The membrane limits or prevent passage of the fluid therethrough. A carrier or sweep gas including the acid gas other than carbon dioxide is passed over a second surface (which is typically opposite the first surface) of the membrane so that the acid gas other than carbon dioxide can pass through the membrane into the fluid, and carbon dioxide from the fluid can pass from the liquid, through the membrane, and into the sweep gas.