Munk and Forbes (1989) have proposed an acoustic technique for measuring the ocean warming caused by the buildup of greenhouse gases in the atmosphere. Travel time from a source in the South Indian Ocean will be monitored at receivers as far away as the North Atlantic and North Pacific. However, there are natural perturbations of acoustic travel time over long distances as a result of oceanic mesoscale eddies, seasonal fluctuations, and interannual variability. Results from a global eddy-resolving ocean model are used here to assess the importance of two of these noise factors. Neither mesoscale nor seasonal effects are found to be large enough to obscure the anticipated signal of global change in the ocean. Analyses of the modeled temperature trends and variability along three selected paths give insights into where mesoscale and seasonal variability affect the acoustics. ¿ American Geophysical Union 1990