Working Group 6: Space Climate Radiation, Particles, and Responses

Global mean annual average temperature profile image
Global mean annual average temperature profile for the entire atmosphere, simulated by WACCM-X. Black line: 1972–1973. Red line: 2001–2002. Temperature change is about +0.5 in the troposphere, -1 to -3 K in the stratosphere and mesosphere, and about -9 K in the upper thermosphere, or about -3 K per decade.

The NCAR Whole Atmosphere Community Climate Model–eXtended (WACCM-X) was used to study global temperature change throughout the atmosphere during the last several decades. WACCM-X is the thermosphere-ionosphere extension of WACCM, which in turn is the whole atmosphere version of the Community Atmosphere Model (CAM), a major component of the Community Earth System Model (CESM). Thus, WACCM-X not only couples the entire atmosphere-ionosphere system, but can be coupled to ocean, ice, and land models as well. Recent additions and improvements include completion of ion-neutral chemical processes, updated heating and cooling rates, adjustments to atmospheric dynamics to account for variations in mean molecular mass, equatorial and auroral electrodynamics, and fully 3D ionospheric transport.

Two-year runs during 1972–1973 and during 2001–2002, were compared. These simulations were driven by surface emissions including carbon dioxide, methane, and chlorofluorocarbons, and by measured sea surface temperatures. Low solar ultraviolet and geomagnetic activity conditions were assumed throughout, in order to focus on the anthropogenic effects. The model produces a small but significant warming, about +0.5 K, in the troposphere, but a cooling of -1 to -3 K in the stratosphere and mesosphere. In the thermosphere-ionosphere, the cooling increases to about -9 K over the study interval, or about -3 K per decade. These results are similar to previous model and observational work studying limited atmospheric regions, but represent the first global simulation of the entire atmosphere from the surface to 500 km altitude.