Montag, 13. Januar 2014

Feedback systems

Today I heard something bout feedbacks: the Prof said the three most important feedback loops are

Water feedback, a positive feedback, wich means
-more temperature causes more water vapour
-more water vapour - being a greenhous gas - causes more back radiation
-more back radiation causes more heat in the water - more evaporation and so on.

Note: This example is often used to show how the water vapour will heat up the earth to a tipping point where the heating is inrcerasing in a short time, causing overheating an a climatic catartophe.

But what is not mentioned: More water vapour means more clouds, which will keep the sunrays from the earth, causing a cooling, which everybody know.(Only at night clouds helps the earth surface to stay warmer.) So there seem to be two feedback systems linked together - water vapour is heating up, clouds are cooling down. Somehow like a thermostatic system.

Ice albedo feedback, a positive feedback, which means
more heat causes some sea ice to melt, which leaves more open sea surface, wich collects mor heat from ingoing radiation, wich heats the water, wich causes more sea ice to melt, wich create mor open water, more heating up though sun radiation, etc.

What is not said: 
- Sea ice is on the poles where the sunrays ar hitting the surface of the sea in an angle od 0-10 degree, getting reflected to a big amount. Best absorption is when the rays are hitting in a vertical axis.
- Sea ice is mostly pack ice with a rough surface, giving the sunrays lots of opportunity to hit it vertically, which means more heating up of the ice is possible, as ice is not reflecting every sunray, but absorb a certain amount. Possibly there is not so much difference in heat absorption between flat sea water and pack ice with many steep angle surfaces.
- Ice in the water is causing the water to have a temperature of about 0 degree, so no big warming up and melting is happening.
- in the winter time, when the sun is not hitting the urface at all, the ice cover in the arctic grows up to six time as much as in summer time, thus resetting any melting, which happened in the summer.

So the positve feedback loop stops at the end of each summer.


Plank feedback, a negative feedback, wich says:

A hotter matter gives away more heat, but the outgoing radiation cools it down. Which means: If the earth's surface is heated up by several factors, the surface is giving more radiation, cooling it more. Even this seems to be kind of thermostatic feed back.

One more very important feedback is not yet mentioned: 

Convection: A surface warmer than the air is heating it up. The warm air rises, allowing cold air from above commong down getting heated up as well. The circulation will go on until air and the surface have the same temperature or until next day, when sunrays again will heat up the surface.

It should be also mentioned that convection can even override the greenhouse effect:
Heat is also transported by contact:: cold air is touching the hot surface. Any molecules of the air (not only green house gases) can collect heat through contact. Hot air with all the greenhous gases in it are transportet to higher, colder altitudes with less molecules. As they have even the ability to radiate heat, they are giving it mostly out to the space, thus cooling the atmosphere. 

So it seems there are positve feedback, negative feedbacks and feedbacks which interact in a way of thermostatic response system, leading to a somehow constant temperature level. The question is if mankind is able to disturb this automatic naturl controled level.



Keine Kommentare:

Kommentar veröffentlichen