X-ray emission due to charge transfer collisions between heavy solar wind ions and neutrals has been predicted to exist both in the heliosphere and in the geocorona. The heliospheric X-ray emission can account for roughly half of the observed soft X-ray background intensity. It was also suggested that temporal variations in the heliospheric and geocoronal soft X-ray intensities will result from solar wind variations. In this paper, a simple model of the charge exchange X-ray emission mechanism is combined with measured solar wind parameters as a function of time and used to generate predictions of the temporal variation of the X-ray intensity observed at Earth for the time periods 1990--1993 and 1996--1998. Measured solar wind proton fluxes are also directly compared with the long-term enhancement part of the soft X-ray background measured by the R¿ntgen Satellite (ROSAT). A significant positive correlation exists, which supports the existence of X-ray emission associated with the solar wind interaction with either interstellar neutrals and/or with geocoronal neutral hydrogen. ¿ 2001 American Geophysical Union