Energy transport, polar amplification, and ITCZ shifts in the GeoMIP G1 ensemble
The polar amplification of warming and the ability of the Intertropical Convergence Zone (ITCZ) to shift to the north or south are two very important problems in climate science. Examining these behaviors in global climate models (GCMs) running solar geoengineering experiments is helpful not only...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-02-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/18/2287/2018/acp-18-2287-2018.pdf |
| Summary: | The polar amplification of warming and the ability of the Intertropical
Convergence Zone (ITCZ) to shift to the north or south are two very important
problems in climate science. Examining these behaviors in global climate
models (GCMs) running solar geoengineering experiments is helpful not only
for predicting the effects of solar geoengineering but also for
understanding how these processes work under increased carbon dioxide
(CO<sub>2</sub>). Both polar amplification and ITCZ shifts are closely related to the
meridional transport of moist static energy (MSE) by the atmosphere. This
study examines changes in MSE transport in 10 fully coupled GCMs in
experiment G1 of the Geoengineering Model Intercomparison Project (GeoMIP), in which
the solar constant is reduced to compensate for the radiative forcing from
abruptly quadrupled CO<sub>2</sub> concentrations. In G1, poleward MSE transport
decreases relative to preindustrial conditions in all models, in contrast to
the Coupled Model Intercomparison Project phase 5 (CMIP5) abrupt4xCO2
experiment, in which poleward MSE transport increases.
We show that since poleward energy transport decreases rather than
increases, and local feedbacks cannot change the sign of an initial
temperature change, the residual polar amplification in the G1 experiment
must be due to the net positive forcing in the polar regions and net negative
forcing in the tropics, which arise from the different spatial patterns of
the simultaneously imposed solar and CO<sub>2</sub> forcings. However, the reduction
in poleward energy transport likely plays a role in limiting the polar
warming in G1. An attribution study with a moist energy balance model shows
that cloud feedbacks are the largest source of uncertainty regarding changes
in poleward energy transport in midlatitudes in G1, as well as for changes
in cross-equatorial energy transport, which are anticorrelated with ITCZ
shifts. |
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| ISSN: | 1680-7316 1680-7324 |