Intriguing New Paper “Climate Sensitivity To Changes In Ocean Heat Transport” By Barreiro Et Al 2011

We have been alerted to an intriguing new paper that further illustrates the complexity of the climate system (h/t to Geoff Smith). It is

Marcelo Barreiro, Annalisa Cherchi and Simona Masina, 2011: Climate sensitivity to changes in ocean heat transport. J of Climate. doi: 10.1175/JCLI-D-10-05029.1 [in press]

The abstract reads [highlight added]

Using an atmospheric general circulation model coupled to a slab ocean we  study the effect of ocean heat transport (OHT) on climate prescribing OHT from zero to two times the present-day values. In agreement with previous studies an increase in OHT from zero to present-day conditions warms the climate by decreasing the albedo due to reduced sea-ice extent and marine stratus cloud cover and by increasing the greenhouse effect through a moistening of the atmosphere. However, when the OHT is further increased the solution becomes highly dependent on a positive radiative feedback between tropical low clouds and sea surface temperature. We found that the strength of the low clouds-SST feedback combined with the model design may produce solutions that are globally colder than the Control mainly due to an unrealistically strong equatorial cooling. Excluding those cases, results indicate that the climate warms only if the OHT increase does not exceed more than 10% of the present-day value in the case of a strong cloud-SST feedback and more than 25% when this feedback is weak. Larger OHT increases lead to a cold state where low clouds cover most of the deep tropics increasing the tropical albedo and drying the atmosphere. This suggests that the present-day climate is close to a state where the OHT maximizes its warming effect on climate and pose doubts about the possibility that greater OHT in the past may have induced significantly warmer climates than that of today.”

The paper starts with the informative text

“The oceans absorb heat mainly in the tropical regions where cold water upwells to the surface and lose it in high latitudes where cold and dry winds blow over warm currents during winter time. This implies a net heat transport by the oceanic circulation from the equator to the polar regions that contributes to remove the surplus of heat received in the tropics. Averaged over long times the ocean must gain and lose equal amounts of heat in order to maintain a steady state. The oceanic heat transport is largest in the tropical region and becomes very small poleward of 45° (Trenberth and Caron 2001).”

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