- On an evolutionary level, there are three remarkable facts about skin. It comes in colors, of course. Compared to other mammals, our skin is relatively hairless. And it’s sweaty. In the last few million years, humans became the sweatiest of mammals.Q. Is that important? It’s often said that our large brains are what made it possible for us to evolve from ape to human. But those big brains could never have developed if we didn’t have exceptionally sweaty skin.
- It happened this way. There was a tremendous takeoff in human evolution about two million years ago when primates who could no longer be called apes appeared in the savannahs of East Africa. These early humans ran long distances in open areas. In order to survive in the equatorial sun, they needed to cool their brains. Early humans evolved an increased number of sweat glands for that purpose, which in turn permitted their brain size to expand. As soon as we developed larger brains, our planning capacity increased, and this allowed people to disperse out of Africa.
lördag 28 augusti 2010
Sauna, Sweating and Global Warming
The World Sauna Championship 2010 in Finland ended in tragedy with one finalist dead and another hospitalized after serious burns apparently caused by adding too much water to the stove giving a wet sauna.
Everybody with some sauna experience knows that it is possible to survive a higher temperature in a dry sauna than in a wet sauna saturated with water vapour. Why?
Because, in a dry sauna the sweat on your skin can vaporize and thereby consume heat energy. But in a wet sauna the sweat cannot vaporize and thus has no cooling effect. And sweating is
the main mechanism for keeping your body temperature constant at 37 C: The more you work, the hotter you tend to get, which is balanced by vaporizing sweat.
Is there a connection to global warming? IPCC climate alarmism claims that the World is turning into sauna: Doubled atmospheric CO2 is supposed to cause a "radiative forcing" of 4 W/m2, which will increase global temperature by 1 C and with additional feedbacks to a climate sensitivity of 2 - 4.5 C = Alarm!
But is this argument credible? Or is global temperature like our body temperature kept almost constant by vaporization? Yes, the oceans absorb heat energy radiated from the Sun, which is used to vaporize water, which is convected to higher levels of the atmosphere, where it condenses and releases heat energy, which is finally radiated to outer space. The Earth thus can keep surface temperature constant under varying forcing by sweating: Radiative forcing can be balanced by increased sweating under constant temperature. In principle.
Let's look at the numbers:
The Earth surface (mainly oceans) recieves about 180 W/m2 and gets rid of 60 by radiation and
120 by vaporization/convection/condensation/radiation. The lapse rate is 6 C per km connecting the Earth surface at 15 C with a Top of the Atmosphere TOA at -18 C (at 5 km height) from where 240 W/m2 are radiated to outer space (with 60 of incoming 240 absorbed by clouds).
With a fully transparent atmosphere the lapse rate could be 0 and with an atmopshere fully opaque to outgoing radiation it could be the adiabatic rate of 9.8 C/km. The corresponding
radiation would range from 180 to 0, with the observed 60 at a lapse rate of 6 C/km.
A "radiative forcing" of 4 W/m2 corresponds to a 7 percent reduction of radiation to 56, or a compensating increase of 3.5 percent to 124 of vaporization/convection/...... with a change of
lapse rate about 0.035 x 6 = 0.2 C/km and a corresponding change of surface temperature
of 1 C.
This calculus thus indicates a climate sensitivity of 1 C, including feedbacks = No Alarm!
Note that a 7 percent change of the radiation characteristics of the atmosphere is big change; It may be more reasonable to consider changes of 1-2% which would reduce climate sensitivity to
0.2 - 0.4 C, a factor of 10 smaller than the 2 - 4.5 C of IPCC: No Alarm!
Do you think that my argument is simplistic? Then bear in mind that the IPCC argument is even more simplistic.
Note that according to anthropologist Nina Jablonski:
We learn that sweating is what allowed us to survive the merciless tropical Sun and develop scientific brains for survival, and also what makes the Earth survive the exposure to the Sun.