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Abstract Transient climate sensitivity is strongly shaped by geographical patterns of ocean heat uptake (OHU). To isolate the effects of uncertainties associated with OHU, a single slab ocean model is forced with doubled CO2and an ensemble of OHU patterns diagnosed from transient warming scenarios in 12 fully coupled models. The single-model ensemble produces a wide range of Southern Ocean (SO) sea surface temperature (SST) and Antarctic sea ice responses, which are in turn associated with a 1.1–2.0-K range of transient climate response (TCR). Feedback analysis attributes the TCR spread primarily to shortwave effects of low clouds in the Southern Hemisphere (SH) midlatitudes. These cloud changes are strongly positively correlated with storm-track eddy kinetic energy. It is argued that midlatitude clouds (and thus planetary albedo) are remotely driven by SO SST and Antarctic sea ice, mediated by large-scale changes in SH baroclinicity and lower-tropospheric stability. The robustness of this atmospheric teleconnection between SO SST, Antarctic sea ice, and global feedback through midlatitude clouds is supported through additional simulations that explore more extreme SST and sea ice perturbations. These results highlight the importance of understanding physical relationships between SST, sea ice, circulation, and cloud changes in the SH as a pathway to better constraining transient climate sensitivity. Significance StatementAlthough it is well known that Earth’s global-mean surface temperature increases with increasing atmospheric CO2, there are still significant uncertainties in the temperature and sea ice trends over the Southern Ocean region. Using a climate model, we find that Southern Ocean temperature and Antarctic sea ice changes can result in substantial cloud cover changes over the Southern Hemisphere, which play a primary role in determining the amount of warming in our experiments. We suggest that, in order to reduce uncertainty in future climate change, more work is needed to understand how the climate of the southern polar region can affect the circulation and clouds of the midlatitudes.
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Global Radiative Convective Equilibrium With a Slab Ocean: SST Contrast, Sensitivity and Circulation
Abstract Warming experiments with a uniformly insolated, non‐rotating climate model with a slab ocean are conducted by increasing the solar irradiance. As the global mean surface temperature is varied across the range from 289 to 319K, the sea surface temperature (SST) contrast at first declines, then increases then declines again. Increasing SST contrast with global warming is associated with reduced climate sensitivity, while decreasing SST contrast is associated with enhanced climate sensitivity. The changing SST contrast and climate sensitivity are both related fundamentally to the effect of water vapor on clear‐sky radiative cooling. The clouds in the convective region are always more reflective than those in the subsiding region and so always act to reduce the SST contrast. At lower temperatures between 289 and 297 K the shortwave suppression of SST contrast increases faster than the longwave enhancement of SST contrast. At warmer temperatures between 297 and 309 K the longwave enhancement of SST contrast with warming is stronger than the shortwave suppression of SST contrast, so that the SST contrast increases. Above 309 K the greenhouse effect in the subsiding region begins to grow, the SST contrast declines and the climate sensitivity increases. The transitions at 297 and 309 K can be related to the increasing vapor pressure path with warming. The mass circulation rate between warm and cool regions consists of shallow and deep cells. Both cells increase in strength with SST contrast. The lower cell remains connected to the surface, while the upper cell rises to maintain a roughly constant temperature.
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- Award ID(s):
- 2124496
- PAR ID:
- 10446013
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Atmospheres
- Volume:
- 127
- Issue:
- 12
- ISSN:
- 2169-897X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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