Middle Atmosphere Temperature Trends in the Twentieth and Twenty-First Centuries Simulated With the Whole Atmosphere Community Climate Model (WACCM)

We use Whole Atmosphere Community Climate Model simulations made under various climate change scenarios to study the evolution of the global-mean temperature trend in the late twentieth century and the twenty-first century. Results are compared with available satellite observations, including new trend estimates derived from the Sounding of the Atmosphere using Broadband Emission Radiometry instrument on NASA's TIMED spacecraft. Modeled and observed trends are shown to be consistent throughout the entire middle atmosphere, from near the tropopause (~16 km) to the lower thermosphere (~95 km) in the period covered by the satellite data. Simulations are extended into the twenty-first century to document the evolution of the global-mean temperature trend profile. We find, consistent with previous studies, a marked change in the trend profile at the turn of the twenty-first century, which is driven by the recovery of stratospheric ozone following the adoption of the Montreal Protocol. In the twenty-first century, the trend profile becomes more uniform with altitude, but its overall shape and magnitude are conditioned by the scenario adopted for future emissions of greenhouse gases. Our results suggest that the vertical profile of temperature trends in the middle atmosphere will remain an important signature of global climate change, and they underscore the importance of global, continuous monitoring of this region of the atmosphere.