All climate models predict that the atmosphere will moisten in response to increasing greenhouse gases. The concentrations of water vapor in the upper troposphere are projected to double by the end of the century. This amplified moistening aloft not only represents a key feedback mechanism, but also provides an important fingerprint for the detection and attribution of climate change. In this talk we will present results from recent efforts to utilize the growing archive of satellite microwave measurements from SSM/T-2 (1994-present), AMSU-B (1998-present), MHS (2003-present) to construct a long-term homogenized data set of upper tropospheric water vapor. Because microwave measurements are less affected by clouds compared to infrared measurements, the water vapor data set derived from these measurements has improved space/time coverage and is less prone to clear-sky sampling biases. The microwave radiances have been reprocessed to correct for viewing angle, orbital drift, and satellite intercalibration. The resulting radiance products will then be compared to climate model simulations from the CMIP5 archive in an attempt to ascertain the relative contributions of natural and anthropogenic forcings to recent changes in upper tropospheric water vapor.