Stan Solomon and others have performed the first whole-atmosphere simulations of global change that include the lower atmosphere (0-15 km), middle atmosphere (15-90 km), thermosphere-ionosphere (90-500 km), and all relevant physics and chemistry.

Model calculations of the zonal mean annual mean changes in temperature under low solar activity conditions, as a function of latitude and pressure, for the 29-year simulation period between five-year ensembes (1972–1976 to 2001–2005). Negative contours, ranging from -9 to -1 K, with a 1 K interval, are shown in white; positive contours, at +1 and +2 K, are shown in red. The zero-change line is shown in black.

All significant known changes caused by human activity were included in a new version of the Whole Atmosphere Community Climate Model—eXtended. The basic result is that even as the lower atmosphere gradually warms, the upper atmosphere rapidly cools. Simulations were conducted for two five-year periods, 1972–1976 and 2001–2005, but using constant low solar activity conditions, in order to remove the effects of the solar cycle on the upper atmosphere. Global mean annual average temperature increased at a rate of +0.2 K/decade at the surface and +0.4 K/decade about 10 km above the surface, but decreased throughout the upper atmosphere, from about 20 km to 500 km, reaching -2.8 K/decade above 200 km. Near 90 km, very small temperature decreases were calculated, but the year-to-year variation was large, so temperature trends in that altitude region are uncertain. These results are similar to those obtained from previous work using numerical models that were confined to specific atmospheric levels, and compare favorably with available long-term measurements. These simulations demonstrate the ability of a single comprehensive numerical model to characterize global change throughout the atmosphere.

Publication Name: Geophysical Research Letters