This paper discusses the areas contributing to uncertainty in the modeling of the effects of launchers on the atmosphere. The main areas dealt with are (i) the aerothermodynamics of rocket plumes which includes the combustion and expansion process and (ii) climate modeling including the insertion of small scale plumes into relatively large scale climate models. The complexity of modeling necessary for a proper and accurate assessment of plume effects implies the need for validation data which may require flight and ground campaigns as well as laboratory experiments.