The use of membrane gas absorption for carbon dioxide production from flue gases is discussed with special reference to the combined supply of heat and carbon dioxide to greenhouses. Novel absorption liquids are introduced which show an improved performance in terms of system stability and mass transfer compared to monoethanolamine when used in combination with commercially available, inexpensive polyolefin membranes. It is shown that the combined supply of heat and carbon dioxide from cogeneration plants to greenhouses will lead to significant primary energy savings. Carbon dioxide can be produced by the membrane gas absorption process and delivered to greenhouses at lower cost than current supply methods.