Climate models predict that the concentration of water vapor in the upper troposphere could double by the end of the century as a result of increases in greenhouse gases. Such moistening plays a key role in amplifying the rate at which the climate warms in response to anthropogenic activities, but has been difficult to detect because of deficiencies in conventional observing systems. We use satellite measurements to highlight a distinct radiative signature of upper tropospheric moistening over the period 1982 to 2004. The observed moistening is accurately captured by climate model simulations and lends further credence to model projections of future global warming.

A method for the intercalibration of the high-resolution infrared sounder (HIRS) upper-tropospheric water vapor band brightness temperature data is developed and applied to data from 1981 to 1993. Analysis of the adjusted anomaly time series show the location and strength of both the large-scale ascending and descending circulations in the Tropics as well as water vapor anomalies. Comparison of these HIRS data with outgoing longwave radiation and sea surface temperature anomalies reveals that both convection and increased upper-tropospheric moisture occur over anomalously warm water in the deep Tropics. The development and movement of deep convection and increased upper-tropospheric moisture can clearly he traced during the El Niño/Southern Oscillation warm events. These HIRS data are particularly useful in monitoring upper-tropospheric water vapor variability between the Tropics and subtropics. Abstract A method for the intercalibration of the high-resolution infrared sounder (HIRS) upper-tropospheric water vapor band brightness temperature data is developed and applied to data from 1981 to 1993. Analysis of the adjusted anomaly time series show the location and strength of both the large-scale ascending and descending circulations in the Tropics as well as water vapor anomalies. Comparison of these HIRS data with outgoing longwave radiation and sea surface temperature anomalies reveals that both convection and increased upper-tropospheric moisture occur over anomalously warm water in the deep Tropics. The development and movement of deep convection and increased upper-tropospheric moisture can clearly he traced during the El Niño/Southern Oscillation warm events. These HIRS data are particularly useful in monitoring upper-tropospheric water vapor variability between the Tropics and subtropics.