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Sunday, January 10, 2016

Some more Basic Thermo stuff

I have been on break and loving it.  Progress in climate change is about like watching paint dry anyway, but there is a bit of an interesting debate over the usefulness of simple one and two dimension models versus the big honking coupled climate models.

One of the biggest mistakes made is the oceans are the heat sink concept.  The minimum temperature of the oceans is about -2 C or the freezing point of average salt ice and the rough maximum temperature of the oceans is 30 C degrees.  There are fluctuations up to around 32 C but 30 C is a bit more common.  If the oceans are a heat sink the maximum Carnot efficiency is about 9% meaning 91% of heat would be lost to space somewhere along the line.  If you tried "average" temperature of the Earth, the efficiency drops a little bit to about 6% and average ocean to average surface reduces that a bit more.  If the rate of ocean heat uptake is 0.6 Wm-2 and the uptake efficiency is 9%, that would put forcing in the 6.67 Wm-2 range.

Since this is super simple model there are a lot of questions, but it implies approximately 1/3 of ocean heat uptake isn't related to atmospheric forcing of about 4 Wm-2.  Since nearly all of the ocean heat uptake is in the southern hemisphere, this indicates to me that about 1/3 of warming of the oceans is related to long term recovery and the current solar precessional orbit position.

Along with that, most of the warming in the atmosphere is in the northern hemisphere which happens to have the warmest ocean surface temperatures.  Having the warmest SST and the least ocean heat uptake rate indicates that a simple Carnot efficient model is very limited.  However, since the northern hemisphere lacks a circumpolar current to increase heat uptake efficiency and Carnot is a maximum, nearly zero efficiency as opposed to a low 9% efficiency isn't inconsistent with the model. Anything over 9% would be obviously wrong.

I have used Carnot efficiency models about as much as they can be useful and they indicate lower climate sensitivity and larger uncertainty than most estimates I have seen.  Even with the uncertainty, the different uptake rates of the two hemispheres relative to the actual surface temperatures isn't consistent with northern hemisphere aerosols limiting surface temperature rise by very much.  "Globally" it could explain the 1/3 difference, but not by hemispherical.

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