Stratospheric Water Vapor Increases Over the Past Half-Century

Ten data sets covering the period 1954-2000 are analyzed to show a 1% per year increase in stratospheric water vapor. The trend has persisted for at least 45 years, hence is unlikely the result of a single event but rather indicative of long-term climate change. A long-term change in the transport of water vapor into the stratosphere is the most probable cause.