Response of the Middle Atmosphere to CO₂ Doubling Results from the Canadian Middle Atmosphere Model

• Published in: Journal of climate Vol. 20; no. 7; pp. 1121 - 1144
• Main Authors: Fomichev, V. I., Jonsson, A. I., De Grandpré, J., Beagley, S. R., Mclandress, C., Semeniuk, K., Shepherd, T. G.
• Format: Journal Article
• Language: English
• Published: Boston, MA American Meteorological Society 01.04.2007
• Subjects: Additives; Atmosfärs- och hydrosfärsvetenskap; Atmosphere; Atmosphere and hydrosphere sciences; atmospheric; Atmospheric models; Carbon dioxide; Chemistry; Climate change; Climate models; Climatology; Cooling; Earth sciences; Earth, ocean, space; Exact sciences and technology; Experiments; External geophysics; General circulation models; General properties of the high atmosphere; Geovetenskap; Heating; Heating and cooling; Klimatologi; Latitude; Lower mantle; Mesopause; Mesosphere; Meteorology; Middle atmosphere; NATURAL SCIENCES; NATURVETENSKAP; Ocean circulation; Ozone; Photochemicals; Photochemistry; Physics of the high neutral atmosphere; Planetary waves; Polar winter; Sea surface; Sea surface temperature; Simulation; Solar heating; Spring; Spring (season); Statistical analysis; Stratosphere; Summer; Temperature; Tropical regions; Tropopause; Troposphere; Upwelling; Water vapor; Water vapour; Wave propagation; Winter; Arctic region; Atmosphere model; Carbon dioxide; digital simulation; Mesosphere; Sea surface temperature; greenhouse gas; Dynamical climatology; Rossby wave; climate modification; global change; Tropopause; cooling; Air pollution; Planetary wave; Forcing; stratosphere; Anthropogenic factor
• ISSN: 0894-8755; 1520-0442; 1520-0442
• DOI: 10.1175/jcli4030.1

The Canadian Middle Atmosphere Model (CMAM) has been used to examine the middle atmosphere response to CO₂ doubling. The radiative-photochemical response induced by doubling CO₂ alone and the response produced by changes in prescribed SSTs are found to be approximately additive, with the former effect dominating throughout the middle atmosphere. The paper discusses the overall response, with emphasis on the effects of SST changes, which allow a tropospheric response to the CO₂ forcing. The overall response is a cooling of the middle atmosphere accompanied by significant increases in the ozone and water vapor abundances. The ozone radiative feedback occurs through both an increase in solar heating and a decrease in infrared cooling,with the latter accounting for up to 15% of the total effect. Changes in global mean water vapor cooling are negligible above ~30 hPa. Near the polar summer mesopause, the temperature response is weak and not statistically significant. The main effects of SST changes are a warmer troposphere, a warmer and higher tropopause, cell-like structures of heating and cooling at low and middle-latitudes in the middle atmosphere, warming in the summer mesosphere, water vapor increase throughout the domain, and O3decrease in the lower tropical stratosphere. No noticeable change in upwardpropagating planetary wave activity in the extratropical winter–spring stratosphere and no significant temperature response in the polar winter–spring stratosphere have been detected. Increased upwelling in the tropical stratosphere has been found to be linked to changed wave driving at low latitudes.