Oceanic Heat Transport and Climate Sensitivity

[Snow_Miser]

My knowledge of how Oceanic Heat Transport changes in relation to climate change is somewhat limited, though I was reading a few interesting papers on this subject that suggest that if OHT was to increase further with possible future warming, this would create a cooling effect in the Tropics, since heat is being transported from the Tropics to the mid latitudes. This in turn leads to a higher albedo in the Tropics associated with an increase in low lying cloud cover, and therefore would strongly reduce warming in the Tropics, which would have large implications to Earth's Energy Budget.

http://www.fisica.ed...iMasina2011.pdf

Using an atmospheric general circulation model coupled to a slab ocean, the effects of ocean heat transport (OHT) on climate are studied by prescribing OHT from 0 to 2 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. The strength of the low cloud–SST feedback combined with the model design may produce solutions that are globally colder than in the control run, 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 effects on climate and raises doubts about the possibility that greater OHT in the past may have induced significantly warmer climates than that of today.

Keep in mind that the authors are refering to the Tropical Climate System and not the entire Global Climate System, so an increase in OHT would lead to cooling in the Tropics and low level cloud cover increases would accentuate that cooling in the Tropics, thus making low cloud cover increase in response to OHT changes a positive feedback. However, when looking at the Global Climate System as a whole, this is a strong negative feedback in response to possible future warming.

Discuss.

[WeatherRusty]

This seems to argue that our current climate is in generally a fairly steady state, within bounds experienced during the Holocene. However we know that climates of the past have been very much warmer than today, and very much colder too.

Climates seem to exist in relatively steady states until sufficiently perturbed to cause a sudden shift to a new, different equilibrium state. Thus the concept of tipping points enters the picture. It is thought that we are dangerously close to initiating a tipping point which will flip the climate into a new, different equilibrium state from which it will not easily return.

[Snow_Miser]

There is an interesting commentary by an atmospheric scientist with a doctorate on this paper. Yes, this link is to a blog, but the commentary is very interesting nonetheless.

http://tnrtb.wordpress.com/2012/02/27/climate-change-the-oceanic-thermostat/