It is suggested that the postulated interstellar cloud should encounter the solar system at some unspecified time in the 'near' future and might have a drastic influence on terrestrial climate in the next 10,000 years.
Abstract

Observations indicating a hydrogen density gradient in the vicinity of the solar system are reviewed, particularly observations of an anisotropy in the far-UV flux around 950 A from the brightest and closest O and B stars as well as a variation in the local D/H ratio along the lines of sight to Alpha Cen and Alpha Aur. Possible mechanisms that may strongly affect the observed D/H ratio on a very small scale are considered, selected radiation pressure is proposed as the most likely mechanism for deuterium separation, and it is shown that this mechanism would be effective only if the density gradient of the nearby interstellar medium has remained stable for at least about 10 million years. This time scale is taken to imply the existence of a nearby (less than 2 pc distant) interstellar cloud. Observational arguments in favor of such a cloud are presented, and implications of the presence of a nearby cloud are discussed, including possible changes in terrestrial climate. It is suggested that the postulated interstellar cloud should encounter the solar system at some unspecified time in the 'near' future and might have a drastic influence on terrestrial climate in the next 10,000 years.