Changes in the width of the tropical belt due to simple radiative forcing changes in the GeoMIP simulations
Model simulations of future climates predict a poleward expansion of subtropical arid climates at the edges of Earth's tropical belt, which would have significant environmental and societal impacts. This expansion may be related to the poleward shift of the Hadley cell edges, where subsidenc...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-08-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/16/10083/2016/acp-16-10083-2016.pdf |
| Summary: | Model simulations of future climates predict a poleward expansion of
subtropical arid climates at the edges of Earth's tropical belt, which would
have significant environmental and societal impacts. This expansion may be
related to the poleward shift of the Hadley cell edges, where subsidence
stabilizes the atmosphere and suppresses precipitation. Understanding the
primary drivers of tropical expansion is hampered by the myriad forcing
agents in most model projections of future climate. While many previous
studies have examined the response of idealized models to simplified climate
forcings and the response of comprehensive climate models to more complex
climate forcings, few have examined how comprehensive climate models respond
to simplified climate forcings. To shed light on robust processes associated
with tropical expansion, here we examine how the tropical belt width, as
measured by the Hadley cell edges, responds to simplified forcings in the
Geoengineering Model Intercomparison Project (GeoMIP). The tropical belt
expands in response to a quadrupling of atmospheric carbon dioxide
concentrations and contracts in response to a reduction in the solar
constant, with a range of a factor of 3 in the response among nine
models. Models with more surface warming and an overall stronger temperature
response to quadrupled carbon dioxide exhibit greater tropical expansion, a
robust result in spite of inter-model differences in the mean Hadley cell
width, parameterizations, and numerical schemes. Under a scenario where the
solar constant is reduced to offset an instantaneous quadrupling of carbon
dioxide, the Hadley cells remain at their preindustrial width, despite the
residual stratospheric cooling associated with elevated carbon dioxide
levels. Quadrupled carbon dioxide produces greater tropical belt expansion in
the Southern Hemisphere than in the Northern Hemisphere. This expansion is
strongest in austral summer and autumn. Ozone depletion has been argued to
cause this pattern of changes in observations and model experiments, but the
results here indicate that seasonally and hemispherically asymmetric
tropical expansion can be a basic response of the general circulation to
climate forcings. |
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| ISSN: | 1680-7316 1680-7324 |